Category X-15 EXTENDING THE FRONTIERS OF FLIGHT

Previous rocket planes, such as the X-1 and X-2, had been able to conduct the majority of their flight research directly over Edwards and the lakebeds immediately surrounding the base. The capabilities of the X-15, however, would need vastly more airspace. The proposed trajectories required an essentially straight flight corridor almost 500 miles long, and the need to acquire real-time data necessitated the installation of radar, telemetry, and communications sites along the entire path. There was also a need for suitable emergency landing areas all along the flight corridor. Fortunately, the high desert was an ideal location for such requirements since many of the ancient lakes had long since vanished, leaving behind dry and hard-packed contingency landing areas.-113

As early as 7 April 1955 Brigadier General Benjamin S. Kelsey wrote to Hugh Dryden (both were members of the Research Airplane Committee) suggesting a cooperative agreement on the construction and operation of a new range to support the X-15 program. A range had been included in the initial Air Force cost estimates, with $1,500,000 budgeted for its construction. At a meeting of the Research Airplane Committee on 17 May 1955, the NACA agreed to cooperate with the WADC and AFFTC in planning the range: the Air Force would build and equip it, and the NACA would operate it after its completion. It was much the same agreement that governed the X-15 itself.114

However, this decision was not favorably received by AFFTC personnel, who felt they were "being relegated to the position of procurement agent" for the XACA. On 15 June, Walt Williams met with the AFFTC commander, Brigadier General J. Stanley Holtoner, to discuss the concept for the new X-15 range. Williams began by updating Holtoner on the status of the X-15 program since the general had not heard any details since the previous October. During this discussion, Holtoner indicated his willingness to cooperate in developing the range and agreed with Williams that the AFFTC should not become actively involved until the XACA was able to discuss "detailed items of hardware" and support. Nevertheless, he felt the AFFTC "should have a somewhat stronger position in the project."113

Despite the apparent lack of enthusiasm for the arrangements within the AFFTC, on 28 July 1955 an amendment to the original X-15 development directive was issued that clearly established the AFFTC’s responsibilities for building the range. However, since neither document discussed which organization would operate the range, the AFFTC renewed its efforts to acquire this responsibility.

A conference at ARDC Headquarters in Baltimore on 15 September 1955 set in place the basic architecture of the range. Technical personnel reviewed the availability of various types of radar and decided that all of the range stations should be similar and include telemetry receivers as well as radar equipment. Although no decision was made regarding the specific radar equipment, the choices were narrowed to the AFMTC Model II used on the Atlantic Missile Range, and the Canoga Mod 3 used by North American at White Sands. On 13 October the HSFS proposed expanding the use of telemetry beyond that used on earlier X-planes. In addition to the normal engine-related information that was traditionally monitored, the HSFS wanted to obtain aircraft information (structural, flight path, temperature, etc.), research data (cosmic ray concentrations, etc.), and pilot physiological effects. This was a stretch for the available technology.-1161

Developing the final specifications for the new range was the subject of a meeting on 16 November 1955. This is when the AFFTC made its move for control, stating that the Air Force would like to operate and maintain the range on the condition that the NACA could also use it for the X-15. The NACA reminded the Air Force that the verbal agreement between Hugh Dryden and General Kelsey had already settled the issue. The NACA representatives also pointed out that the safe operation of the X-15 would depend heavily upon data acquired by the ground stations, and that a division of responsibility would not be desirable. The issue, however, would not go away, and on 2 December 1955 the AFFTC deputy chief of staff for operations at the AFFTC, Lieutenant Colonel Bentley H. Harris, Jr., wrote to the commander of ARDC formally requesting that his center "be assigned the responsibility for operating, as well as developing, the test range." The ARDC reiterated that the NACA would operate the range, but the AFFTC could use it on a non­interference basis.-171

Despite this contentious beginning, in the end the NACA and AFFTC cooperated in planning and using the range. The HSFS instrumentation staff under Gerald M. Truszynski largely determined the requirements based on experience gained during prior research programs. In November 1955, Truszynski informed the Research Airplane Committee that the range should be at least 400 miles long, with three radar stations able to furnish precise data on aircraft position, reentry prediction, geometric altitude, and ground speed. The X-15 required a launch site located near an emergency landing area, intermediate landing sites, intermediate launch sites (for less than full-power/full- duration flights), airfields near the radar sites that could be used for support, and a "reasonably straight course" for the high-speed flight profile.-1181

Besides the technical issues, many other factors determined where the range and its associated ground facilities would be located. Because of the sonic booms, it was not desirable to have the X-15 fly over major metropolitan areas, at least not routinely. Avoiding commercial airline corridors would make flight planning easier, and avoiding mountains would make the pilots happier. Ground stations needed proper "look angles" so that at least one of them could "see" the X-15 at all times. Emergency landing sites had to be spaced so that the X-15 would always be within gliding distance of one of them. The parameters seemed endless.

Truszynski and his staff concluded that the best course lay on a straight line from Wendover,

Utah, to Edwards, with tracking stations near Ely and Beatty, Nevada, and at Edwards. The range would take the X-15 over some of the most beautiful, rugged, and desolate terrain in the Western hemisphere, flying high over Death Valley before swooping down over the Searles basin to a landing on Rogers Dry Lake.-181

All of this led to construction of the High Altitude Continuous Tracking Range, which is generally known simply as the High Range. Officially, the effort was known as Project 1876. The Electronic Engineering Company (EECo) of Los Angeles accomplished the design and construction of the range under an Air Force contract awarded on 9 March 1956. The requirements noted that the "range will consist of a ground area approximately 50 miles wide and 400 miles long wherein a vehicle flying at altitudes up to 500,000 feet can be tracked continuously."-201

Despite the hopelessly optimistic original budget of $1,500,000, the three tracking stations did not come cheap-the more-sophisticated Edwards station cost $4,244,000, and the costs of the other two together were about the same. The Air Force spent another $3.3 million on initial High Range construction, and the NACA would spend a similar amount for improvements over the first few years of operations. An office at Patrick AFB, Florida, managed the procurement of the radar equipment under a modification to an existing contract for the Atlantic Missile Range (later the Eastern Range).-211

The agreement between the NASA and the AFFTC stated that the Air Force would "retain title to the land, buildings, and equipment, except those physically located within NASA facilities." In addition, "control, operation and support of High Range will revert to USAF upon the conclusion of X-15 Flight Research or earlier if the Research Airplane Committee judges that the National Situation so dictates."-221

Although Truszynski and his staff at the HSFS had developed the basic configuration of the High Range, it was up to the EECo-with the advice and consent of the government-to select the actual sites for the tracking stations. Since the HSFS staff had already made rough site selections, the next step was developing a radar coverage map. This map showed considerations such as obstructions on the horizon, the curvature of the Earth, and the range in which a target could be "seen" by radar at specified altitudes. This map narrowed down the area that the EECo needed to investigate in detail. Next came a lot of field work.[23]

Preliminary investigations by AFFTC, NACA, and EECo personnel indicated a possible site called VABM 8002 located 1.5 miles northwest of Ely, Nevada (the number referred to the site’s elevation: 8,002 feet above sea level). However, measurements and photographs from this site taken by EECo personnel indicated that it would not provide the required radar sight lines because of an extremely wide and high blockage angle almost directly downrange from the site. In addition, constructing an access road would have required a "considerable amount" of rock blasting. EECo ruled out using the site.-124

An alternate site in Ely was on Rib Hill. This 8,062-foot-high location was a considerable improvement over VABM 8002 in terms of radar sight lines and the ability to build a road and construct the site itself. The downside was that it was adjacent to the Ruth Copper Pit, and the Kennecott Copper Corporation was already planning to extend the operation into the side of Rib Hill. Even if the hill went untouched, the mining operation would have created too much earth movement for a precision radar installation, so again the EECo ruled out the site.[25]

Fortunately, while investigating the Rib Hill site, EECo personnel ventured to the south ridge of the Rib Hill range. This site was promising because the radar sight lines were excellent. The civil engineering firm of F. W. Millard and Son conducted a detailed land survey, mapping out the best location of the buildings and the access road. The EECo estimated that a 5.65-mile-long, 12- foot-wide road from U. S. Highway 50 to the site would cost approximately $72,400, which included installing culverts and drainage ditches, cutting and filling slopes, clearing and compacting the base, and finishing the gravel road.[26] The road would take advantage of southerly exposures to gain maximum natural snow removal, and arrangements with the White Pine County Road Department and the Nevada Highway Department provided additional mechanical snow removal. It was 10 miles southeast to the town of Ely from the junction of the site access road and Highway 50. The Ely Airport, which was a scheduled stop for several commercial airlines, was five miles east of the town. There were some drawbacks, however. The Kennecott Copper Company offered to supply electricity for a nominal cost, but an evaluation of the mining company’s generators showed that the current could fluctuate 10%, which was unacceptable for the sensitive electronic equipment at the site. EECo estimated that voltage regulators and power lines would cost more than procuring primary and backup generators and generating the required power on-site. In addition, there was no water available at the site, so tank trailers would have to haul water from Ely and store it in a tank at the site.-127

The site at Beatty was somewhat easier to locate. Preliminary investigations by the AFFTC and NACA resulted in the selection of a location approximately six miles northwest of Springdale, Nevada. Further investigation by EECo personnel substantiated this selection. The site was at an elevation of 4,900 feet, approximately three miles west of U. S. Highway 95. The radar sight lines were excellent, and the civil engineering firm of F. W. Millard and Son prepared a detailed survey of the area. Only 1.75 miles of new gravel road would be required to connect the site to Highway 95 at the cost of $30,500, including the installation of culverts and ditches. The site was 20 miles by road from Beatty, and an additional five miles to the Beatty airfield. No commercial power or water was available at the site, so the EECo again installed diesel generators. Water (at no cost,

initially) from the Beatty city water supply was trucked to the site.-1281

RANGE FUNCTIONAL DIAGRAM

r^n

RADAR,

TELEMETER.

VOICE

MICROWAVE AND TELEPHONE LWt INTERCONNECTING CIRCUITS

TRANSMITTED BETWEEN STATIONS

TELEMETERING DATA

TIMING

TELEMETERING DATA

The High Range consisted of three stations: one at Beatty, Nevada, one at Ely, Nevada, and the main station at the High-Speed Flight Station at Edwards. All three sites were interconnected by a sophisticated (for 1955) communications network. Each of the Nevada sites had a "local plot" that could track the course of the X-15 if needed. The general concept of the High Range formed the basis of the later manned spaceflight control networks, not surprising since the same man – Gerald Truszynski – was responsible for the High Range and the initial Mercury network. (U. S. Air Force)

The third site, an extension added to the back of the third floor of building 4800 at the HSFS, was the easiest to select. The construction would extend the building toward the airfield ramp from the existing "Flight Control" room using the exterior doorway as the entrance to the new addition. Initial estimates indicated that 1,200 square feet would be adequate for the intended purpose, but further investigation showed that structural constraints required the addition of at least 1,500 square feet. The additional 300 square feet was necessary to take advantage of the existing second-floor columns for greater support of the third-floor addition. After reviewing the plans, the Air Force and NACA requested that EECo further enlarge the addition to 2,500 square feet, which was the maximum the building could accommodate. The addition contained four rooms of roughly equal size: a monitor room with plotting boards, a radar room, a telemetry and communications room, and a utility/work area. No plumbing was required in the addition since the main building housed adequate restroom facilities and photographic dark rooms.-1291
competitive bid would perform the actual construction after the Air Force secured the land for the two remote sites. For unexplained reasons, the acquisition was not as straightforward as expected. For instance, the original schedule showed completion of the access road to the Ely site by 15 December 1956, but the Air Force ran into unexpected difficulties in withdrawing the site from the public domain, which delayed construction. In the end, it was October 1957 before the road was completed.-1301

At both remote sites, a 100-by-100-foot area was graded and hard-surfaced with asphalt paving and a sealant coat. This graded area was large enough to accommodate the radar shelter, vehicle parking area, and such items as the diesel generator, fuel tanks, etc. Because of the remote locations, officials decided to station permanently a Dodge Power Wagon four-wheel-drive truck at each site to provide transportation to the airfield. These trucks had sufficient towing capability to haul the water trailers, and the four-wheel drive allowed access to the site during inclement weather.-1311

Interestingly, the way the Air Force had written the High Range contracts, EECo was responsible for constructing 800 square feet of each shelter to house the telemetry equipment and "housekeeping" rooms, but the Reeves Instrument Company was responsible for constructing another 800 square feet at each shelter to house the radar equipment. Smartly, in order to avoid too much duplication of effort and to ensure a uniform appearance, the companies decided that one or the other should build the entire shelter. Since Reeves was not interested in facility construction, the honor fell to EECo. This was probably not the optimum solution, however, since Reeves retained the responsibility to construct the radar pedestal itself (which was an integral part of the building structure) because the exact position of the radar antenna was important to the final operation of the radar, and both contractors believed that the radar contractor should build the pedestal.-1321

EECo developed a generic 1,760-square-foot floor plan for the remote sites, although each would diverge somewhat from the ideal due to site-specific considerations. In essence, each building consisted of four large rooms: a radar room, a telemetry room, a room for data transmitting and receiving equipment, and a utility/work area. The building also included a smaller telephone- equipment room and dark room, and even smaller restrooms and closets. Oddly, the telephone room could only be accessed from outside the building. EECo calculated that each site would use approximately 155 gallons of water per day (5 gallons for personnel use, 50 for the dark room, and 100 gallons for the flush-type toilet). A 1,000-gallon tank meant that each site would need weekly water deliveries if it was manned continuously. Extreme weather conditions at Ely dictated that the water be stored inside the shelter to keep it from freezing. The shelters consisted of a metal exterior over an insulated framework and drywall interior, with a wooden false floor installed above a concrete slab to provide a location to run wires and cables.1331

The Ely, Beatty, and Edwards tracking stations had radar and telemetry tracking with oscillograph recording, magnetic-tape data collection, and console-monitoring services. Especially early in the flight program, a backup "communicator" was located at each station in case the communication links went down. Each ground station overlapped the next, and communications lines allowed voice communication, timing signals, and radar data to be available to all. Each station recorded all acquired data on tape and film, and strip charts and plotting boards displayed some of the data locally for the backup communicator.1341

Instrument Corporation modified the three Model II radars (generally called Mod II) and the Air Force supplied them to the EECo as government-furnished equipment. The radars had two selectable range settings: 768,000 yards (436 miles) and 384,000 yards (218 miles). The normal method for acquiring the initial target was to use a remote optical tracker. The antenna pedestal also had provisions for mounting an 80-inch boresight camera. Using a unique (for the period) range-phasing system, two or more Mod 2 radars could simultaneously track the same target without mutual interference.-1351

The radar used a 10-foot parabolic dish that transmitted a 2.5-degree wide beam. Peak power was 350 kilowatts with a pulse width of 0.8 microsecond and a selectable pulse-repetition frequency between 205 and 1,707 pulses per second. The maximum slewing rates were approximately 5 degrees per second in azimuth and 2.5 degrees per second in elevation. These were considered adequate for the X-15, although these limitations were considerations during the selection of launch and contingency landing lakes.-351

Precision azimuth and elevation information was obtained from two optical encoders, and range data came from one electromechanical encoder attached directly to the radar. The optical encoders were 16-digit analog-to-digital converters produced by the Baldwin Piano Company that used coded glass disks to produce a reflected binary (Gray)-371 code. The output of these units was a 16-digit parallel code produced by an internally synchronized flashlamp actuated 10 times per second by the master timing signal. This was the primary precision tracking information obtained from the radar system, and an Ampex FR-114 magnetic tape recorder recorded it in digital format. In addition, a data camera photographed the selsyn dial indications of azimuth, elevation, and range for coarse trajectory information.381

The AFFTC Project Datum system at Edwards provided automated processing for the radar and telemetry data recorded on the magnetic tapes. This was a general-purpose data-reduction computer system developed by the Air Force to accept a variety of input data tapes and generate output tapes compatible with the IBM 704 computers used for data processing. The IBM computer, in turn, provided data on factors such as the geometric altitude, plan position, trajectory position, and velocity. Project Datum was a post-test analysis tool, not a real-time system. Another IBM 704 computer was located at the FRC for processing the oscillograph data from the X-15. Operators transferred the raw data on the oscillograph and photorecorders to IBM punched cards by using manually operated film recorders, and the punched cards generated magnetic tapes.-391

Each of the three tracking sites had a "local" Electronic Associates Model 205J plotting board that showed the position of the X-15 as reported by its local radar, and the station at Edwards had a "master" board that correlated all of the results and plotted the vehicle along the entire trajectory. The local boards at each site could alternately display parallax-corrected data from another station. It is interesting to note that the technology of the day did not allow the parallax from the Ely station to be corrected digitally at Edwards because the results would cause the data receiver register to overflow (i. e., the resulting number would be too large for the available space). Since it was necessary to correct the parallax before displaying the data on the master plotting board, engineers devised a method to alter the analog voltage signals at the input to the polar-to – Cartesian coordinate converter. It was an innovative solution to a technological limitation. The coordinate converter itself was an Electronics Associates Model 484A computer.-401

The X-15 made extensive use (for that time) of telemetry data from the vehicle to the ground. As originally installed, the telemetry was a standard pulse duration modulation (PDM) system capable of receiving up to 90 channels of information in the FM frequency band. A servo-driven helical antenna was located at each range station to receive telemetry data. The antenna was slaved to

the radar to track the vehicle, although it could also be positioned manually using a hand crank. Later in the program, NASA installed auto-tracking telemetry antennas at each site. Ampex FR – 114 magnetic tape machines recorded 40 analog real-time outputs from an Applied Science Corporation Series M telemetry decommutator. Immediately after each flight, the receiving station processed the recorded information onto strip chart recorders. At the very end of the flight program, X-15-3 received a modern pulse-code modulation (PCM) telemetry system, and NASA modified the Ely and FRC sites to process the data (NASA had decommissioned Beatty by that time).[41]

Engineers and researchers on the ground needed to look at some of the telemetry data in real time to assist the X-15 pilot if necessary. They could look at this information in various forms on the data monitor consoles located at all three stations, although Edwards generally conducted the critical analyses. All parameters were presented in the form of vertical bar graphs on two center – mounted oscilloscopes, which allowed rapid assessment of a group of parameters to determine whether the operation was within predetermined limits. Of the total parameters transmitted, researchers could look at any 40 at one time, and the strip charts could display an additional 12 channels.-421

When thinking about radar operators, generally a large "radarscope" comes to mind. However, that was not the case during the 1950s, and the output from a radar was generally a small set of oscilliscopes as shown here on the Mod II unit. (It takes a computer to convert raw radar data into a plan-view for display on a radarscope, and such computers largely did not exist during the late 1950s.) For the most part, on the High Range the radar data was processed and displayed on a set of large paper charts that traced the flight progress on a pre-printed map. The position was plotted using one color of ink for position and another for altitude. (NASA)

Standard military ground-to-air AN/GRC-27 UHF equipment provided voice communications with the X-15. Originally, the Air Force indicated that it would provide the radios as government – furnished equipment; however, the long lead times caused the AFFTC to ask EECo to bid on supplying them separately. EECo found a Collins unit with 1,750 channels that it could acquire within nine months. The radio was fully compatible with the AN/ARC-34 UHF transmitter-receiver set that North American would install in the X-15.[43]

To ensure positive contact between any of the tracking sites and the X-15 regardless of its location over the High Range, EECo installed a network communications system. Each range station contained two UHF transmitters and receivers (one of each was a spare) and a specially designed communication amplifier and switching unit. When an operator keyed a transmitter at any location, all three stations transmitted the same information simultaneously. The receivers at all three stations fed their outputs onto a telephone line and, regardless of which station received the information, all stations could hear the transmission. The EECo also installed dedicated station-to-station communications links.[44]

simultaneously, the airborne receiver experienced an "audible beat or tone" interference. The solution to this heterodyne interference problem was to offset each transmitter frequency by a small amount without drifting outside the frequency bandwidth of the receiver. Experimentation led the team to adopt offsets of 0.005-0.010% of the operating frequency as nearly ideal. It was also determined that each transmitter should be offset by an unequal amount to avoid creating a noticeable "beat" in the audio. In the end, technicians tuned the Edwards transmitter 22 kilocycles below the center frequency, while the Ely site transmitted at 14 kilocycles above the center frequency. Beatty, being in the middle, used the center frequency for its transmitter.*451

Since a microphone at any one of the stations modulated all three transmitters simultaneously, the signal arrived at the aircraft at slightly different times because of differing distances from the station to the aircraft. In addition, signals originating on the aircraft took slightly different times to reach each of the ground stations. Consequently, some slightly different delays affected each signal. Given that such signals travel at the speed of light (186,000 miles per second), the time difference for an actual transmission was a maximum of approximately 4 milliseconds. A slightly longer delay was encountered in sending the keying signals between stations, resulting in a total delay of about 12 milliseconds between the two outermost sites (Edwards and Ely).*461

It was found, however, that the time delay was not totally undesirable. The human voice contains a multitude of continuously varying harmonic frequencies. The time delay canceled out a small number of these frequencies since they were 180 degrees out of phase with each other. The only effect this had was to introduce a slight flutter in the reproduced sound that did not seriously degrade speech intelligibility. The second effect the time delay brought was a slight echo effect. Due to the acuity of the human ear, there must be a spacing of approximately 30 milliseconds between signals for the ear to detect that an echo is present. Researchers discovered that a small echo effect actually increases the intelligibility of a voice because of the slight lengthening of word syllables. Analysis indicated that the maximum predicted 12-millisecond time delay would not be sufficient to cause undesirable effects, so the X-15 program elected to ignore the issue.*471

In the course of determining solutions to the various communications challenges, EECo discovered that it was not the first to confront these issues. Commercial airlines had been using similar systems (operating in VHF instead of UHF) for approximately five years after they had installed communications networks under their frequently traveled routes to allow aircraft to be in constant touch with their home offices. Each of these networks was composed of several transmitter – receiver sets that contained between two and six stations tied together by a transmission link. Several groups made up a complete network.*481

United Airlines had designed a similar communications system and contracted its operation to the Aeronautical Radio Company to make it available for other airlines. As Aeronautical Radio expanded and upgraded the original network, it contracted the work to Bell Telephone. Aeronautical Radio leased the system from Bell, and in turn leased the services to the airlines. Collins Radio worked with the service providers and airlines to create a series of radios specifically tailored to operate in the multiple-transmitter environment. Aeronautical Radio, Bell Telephone, Collins Radio, and United Airlines all provided information and assistance to EECo at no charge.*491

In order to evaluate a working communications system of this type before committing to the use of one on the High Range, EECo arranged for a demonstration using one of the airline VHF networks that ran in a line between Oceanside near San Diego to San Francisco, California. The NACA flew a Boeing B-47 Stratojet from Los Angeles to San Francisco at an altitude of 15,000 feet, returning to Los Angeles at 40,000 feet. The pilot made contact with the ground at 10- minute intervals while Air Force, NACA, and EECo representatives located at the Los Angeles

International Airport monitored the two-way communications.1501

The network spanned a distance of 400 miles, but used six stations (instead of the three planned for the High Range) to provide communications down to an altitude of 1,000 feet. Coverage for the High Range was concentrated above 7,000 feet, and one of the goals of the evaluation was to determine how the concept worked at high altitudes. On the return flight at 40,000 feet, it was likely that the B-47 received signals from all six ground stations, and that all six ground-stations received signals from the aircraft. Thus, potential interference was even greater than it would be with the three-station network planned for the High Range. The only effect noted during the evaluation was a flutter or warble at certain locations in the flight path. Researchers played tapes recorded during the flight for numerous pilots and ground personnel at Edwards, and nobody voiced any serious objections. This validated the concept for the High Range, and the EECo began procurement of the various radios, switching units, and other components.1511

The three High Range stations could share radar and telemetry data to automatically direct the next radar in line to the target, and to plot radar data from a remote station on a local plotting board if desired. It was necessary to convert the data from each station into the correct relative position using a set of fixed translation equations, which is one reason why the exact position of each radar antenna had to be precisely determined during construction.1521

The High Range stations were positioned on top of mountains to provide the best look angles for the radar and telemetry receivers. The Beatty, Nevada station was closed when the X-15 program ended and nothing remains at the site except for the concrete slabs where the buildings once stood. (NASA)

There were three likely ways to transmit data between the three sites: a leased wire facility, a scatter propagation system, or microwave transmission.1531 The contract with EECo specifically stated that "the contractor shall investigate the possibility of using a microwave service link for

radar data transmission originating at the Ely site, passing through the Beatty site, and terminating at Edwards Air Force Base." To satisfy this requirement, EECo personnel discussed possible microwave solutions with the Collins Radio, Pacific Telephone & Telegraph Company (PT&T), Philco Corporation, and Raytheon Manufacturing. EECo also discussed the possibility of a scatter propagation system with the same companies, although only Collins provided any meaningful data.[54]

A typical solution to the microwave system provided three main terminals at Ely, Beatty, and Edwards linked together by 10 repeater stations located approximately 30 miles apart. Each location had complete standby power and radio frequency (RF) equipment to ensure reliability. Engineers estimated the propagation delay from Ely to Edwards at 1.8 milliseconds. There were, however, substantial costs to build the system. For instance, each of the repeater sites needed power generators (at least primary, and probably backup). Then there was the cost to build roads to each repeater site; at an average cost of $3,000 per mile for an estimated three miles per site, this came to $90,000. The roads were to be of the same quality as a typical "pole maintenance" road not intended for regular vehicle traffic. The estimated cost of the microwave system was $396,000, and estimated operating expenses were $33,000 per year, not including amortization of the initial installation costs.-55

The propagation scatter system would have involved placing 28-foot-diameter antennas at each of the three sites and bouncing signals off the troposphere. Collins Radio recommended using a UHF system for distances up to 350 miles, and VHF for distances up to 1,200 miles. At the time, the Federal Communications Commission (FCC) had not made any licensing provisions for tropospheric scatter systems since it appeared only the government would be interested in using them. Collins pointed out that each system was custom-made, and the only way to determine whether such a system would work between any two or more locations was to try a Collins Transhorizon System in a van setup between each of the sites. Collins estimated the original system cost at $287,600, not including installation or spare parts. Collins also pointed out that the system was very susceptible to atmospheric disturbances and weather.-155

The leased wire facility would provide telephone lines from Edwards through Los Angeles and Sacramento to Reno, Nevada. From Reno the lines would branch off through Tonopah, Nevada, to the Beatty site, and through Wendover, Utah, to the Ely site. The estimated propagation delay from Edwards to Ely was 10 milliseconds. The standard telephone facilities at Ely and Beatty would be "semi public toll service stations," meaning that they would be on a party-line hookup with the towns of Ely and Beatty. All calls from these telephones would be toll calls (10 cents minimum) with a minimum charge of $5.00 per month. The transmission links were semi-permanently connected lines that would not go through an operator’s patch panel, avoiding the chance of accidental disconnections. Pacific Telephone would provide all of the maintenance.-1571

Ma Bell, being Ma Bell, had charges for everything. The initial construction charge (running the necessary land lines and terminal equipment) would be $55,000, but there was also an "installation charge" of $95 per site to have a technician actually connect the equipment. The total annual operating costs would be $113,790, not including the cost of two standard telephones at Ely and Beatty, which would run an additional $5 each per month. Pacific Telephone also informed the government that if it selected a microwave system, the telephone company would not find it profitable to provide only standard telephone service to the two remote sites-this would be economically practical only if Pacific Telephone provided the entire data transmission contract.-581

system since it did not seem to offer any great cost advantage and represented a largely unknown operational quantity. The microwave system offered low annual operating costs, assuming the system continued to be used for at least six or seven years to amortize the installation costs. Additional channels were readily available with minor expenditures, and engineers considered the link more secure since it was unlikely anybody would attempt to "tap" it. The principal disadvantages of the microwave system were its high initial costs, the possibility that the repeater sites would be inaccessible during bad weather, and that maintenance was the responsibility of the end user (the NACA).[59]

On the other hand, leased telephone facilities offered high reliability and low initial costs, and the telephone company would provide all maintenance. Its principal disadvantages were high annual operating costs and the inability to easily add more channels, particularly high-bandwidth ones.*60*

EECo conducted a cost analysis that included amortization of the initial costs over 5-, 10-, and 20-year periods. The results of this analysis for the "Cost per Channel per Mile per Year" were as follows:*611

The total annual operating costs, also based on the three possible amortization options were:*62*

The microwave cost curve dropped sharply in the early years and then leveled off to some degree after 10 years. Additional channels, however, dropped the per-channel cost considerably. This was because the basic investment in a microwave system was in the initial installation; additional channels only required more relatively low-cost multiplex equipment. This reduction, however, only extended until expansion filled the full bandwidth of the microwave system. At this point, the cost would increase greatly because additional microwave equipment would be required. This was not a major concern since the proposed system provided a bandwidth of 100 kilocycles, and the seven required channels only used 21 kilocycles.-*63*

Nevertheless, the Air Force was in the position to make the final decision, and it selected the telephone system. There were four reasons for this choice: 1) the high reliability offered by a utility-maintained system, 2) the high initial cost of the microwave system, 3) the distance and inaccessibility of the microwave repeater sites for maintenance, and 4) the fact that the telephone company maintained all telephone facilities. These reasons were unquestionably valid. However, in reality, the more likely rationale was the simple fact that although the Air Force was responsible for funding the installation of the chosen system, the NACA was responsible for maintaining the system once it was operational. The Air Force, therefore, chose the system that would cost it the least amount of up-front money, with little consideration given to future capabilities or operating costs. By March 1961, even before the Ely station came on line (in April 1961), NASA had opted to install a microwave system between the stations on the High Range. The microwave capability from Beatty was operational in June 1961, with Ely following in January 1962.[64]

A master timing system at Edwards provided a constant time reference for all the tracking stations using three separate timing signals: 1,000 parts per second (pps), 100 pps, and 10 pps. An operator at any station could record timing marks on recordings at all three stations to indicate a significant event for later reference.-65

Early in the program, a pilot staffed each of the High Range sites in addition to the engineers and technicians necessary to run the equipment. The pilot at Beatty used the call sign NASA-2, and the one at Ely used NASA-3. For later flights, pilots often did not staff the remote sites as the communications links between the sites acquired more bandwidth and all involved gained more confidence in the reliability of the systems. Normally, important information from the control room passed to the pilot through the NASA-1 controller, who was usually another X-15 pilot. However, other ground-control personnel had the capability to transmit directly to the pilot in the event of an emergency where there might be insufficient time to relay information through NASA – 1, or, as happened on several occasions, the radio at Edwards did not work properly.-66

Although they were not designed as part of the original control room, researchers added various specialized devices during the flight program. For instance, engineers programmed a small analog computer to take radar-derived altitude, velocity, and vertical velocity measurements and compute the resulting range footprint to assist ground personnel in understanding which contingency landing sites were available at every moment during the flight. A scope-type map display presented the data in the control room. The analog flight simulator generated the data to program this computer. The flight surgeons also gained a dedicated biomedical console.-671

The station at Ely was functionally identical to the one at Beatty, although the physical layout of the two sites differed somewhat due to local environmental conditions. At the end of the X-15 program, the Ely station reverted to the Air Force and continued to play a part in test operations until 1992 when it was finally closed. (NASA)

The High Range underwent a series of modifications over the years. For instance, on 10 March 1967, NASA replaced the Mod II radar at Ely with an improved Reeves Instrument Corporation MPS-19C unit that became operational on 2 May. Wallops Island shipped another MPS-19C during March 1967 for installation at the FRC. At the FRC, the original Mod II had been located on top of building 4800, but engineers deemed this unacceptable because the increased accuracy of the new radar required a firmer base to eliminate vibration and flex. As a result, the new radar was installed a mile or so west, primarily in a new facility with a stiffer base. In addition, in early 1967 NASA upgraded the microwave relay system from Ely to Edwards to handle the higher-bandwidth PCM data from X-15-3. The first successful test (at 144 Kbs) was on 29 March 1967, and the system successfully supported flight 3-58-87 on 26 April.[68]

Robert S. Houston, a historian at the Air Force Wright Air Development Center, wrote the most frequently quoted X-15 history in 1959. This narrative, unsurprisingly, centered on the early Air Force involvement in the program, and concentrated mostly—as is normal for Air Force histories— on the program management aspects rather than the technology. Dr. Richard P. Hallion, later the chief historian for the U. S. Air Force, updated Houston’s history in 1987 as part of volume II of The Hypersonic Revolution, a collection of papers published by the Aeronautical Systems Office at Wright-Patterson AFB. Hallion added coverage of the last nine years of the program, drawing mainly from his own On the Frontier: Flight Research at Dryden, 1946-1981 (Washington, DC: NASA, 1984) and "Outline of the X-15’s Contributions to Aerospace Technology," written in 1977 by Ronald G. Boston. These historians did an excellent job, but unfortunately their work received comparatively limited distribution.

I began this history by using these earlier works as a basis, checking the sources, expanding upon them as appropriate, and adding a NACA/NASA and Navy perspective. Amazingly, almost all of the original source documentation still existed in one archive or another, allowing an evaluation of the tone and inflection of some of the earliest material. Although it is largely a new work, anybody who is intimately familiar with the earlier histories will recognize some passages—the original historians did a remarkably thorough job.

Many people assisted in the preparation of this work, and all gave generously and freely, well beyond any reasonable expectation an author might have. Foremost were Betty J. Love, Tony Landis at Dryden, and Dr. Roger D. Launius at the National Air and Space Museum. The surviving X-15 pilots—Neil A. Armstrong, A. Scott Crossfield, William H. Dana, Brigadier General Joe H.

Engle (USAF, Retired), Colonel William J. "Pete" Knight (USAF, Retired), and Major General Robert M. White (USAF, Retired)—contributed immensely, and several of them read the manuscript multiple times to ensure that nothing significant was missed or misrepresented. John V. Becker and Charles H. Feltz spent many hours explaining things I probably should have already known, greatly improving the manuscript. Then there are the flight planners—Johnny G. Armstrong,^ Richard E. Day, and Robert G. Hoey. I would have missed many subtleties without the patient tutoring from these engineers, all of whom read and commented on several versions of this manuscript and continued my education well past my two engineering degrees.

There was correspondence with many individuals who had been involved with the program:

William P. Albrecht, Colonel John E. "Jack" Allavie (USAF, Retired), Colonel Clarence E. "Bud" Anderson (USAF, Retired), Bill Arnold (RMD/Thiokol, Retired), Colonel Charles C. Bock, Jr., (USAF, Retired), Jerry Brandt, Richard J. Harer, Gerald M. Truszynski, and Alvin S. White. In addition, Jack Bassick at the David Clark Company, Stephen J. Garber and Colin A. Fries at the NASA History Office, Michael J. Lombardi at the Boeing Company Archives, Air Force Chief Historian Dr. Richard P. Hallion, Dr. James H. Young and Cheryl Gumm at the AFFTC History Office, and John D. "Jack" Weber at the AFMC History Office all provided excellent support. Friends and fellow authors Gerald H. Balzer, Robert E. Bradley, Benjamin F. Guenther, Scott Lowther, Mike Machat, Michael

Moore, Terry Panopalis, and Mick Roth also assisted.

Others who contributed include Lynn Albaugh at Ames, Jack Beilman, Rodney K. Bogue at DFRC, Anita Borger at Ames, John W. Boyd at Ames, Russell Castonguay at the JPL archives, Erik M. Conway at Langley and NASM, Mark L. Evans at the Naval Historical Center, Dr. Michael H. Gorn at the DfRc History Office, Matt Graham at DFRC, Fred W. Haise, Jr., Wesley B. Henry at the Air Force Museum, T. A. Heppenheimer, James B. Hill at the John Fitzgerald Kennedy Library, Dr. J. D. "Dill" Hunley at the DFRC History Office, Kenneth W. Iliff (DFRC, Retired), Bob James (DFRC, Retired),

Jack Kittrell (DFRC, Retired), Christian Ledet, F. Robert van der Linden at the National Air and Space Museum, Marilyn Meade at the University of Wisconsin, Roger E. Moore, Claude S. Morse at the AEDC, Karen Moze at Ames, Doug Nelson at the AFFTC Museum, Anne-Laure Perret at the Federation Aeronautique Internationale (FAI), Colonel Bruce A. Peterson (USMCR, Retired), Charles E. Rogers at the AFFtC, Mary F. Shafer (DFRC, Retired), Bonita S. Smith at GRC, Colonel Donald M. Sorlie (USAF, Retired), and Henry Spencer.

It all would never have seen the light of day had it not been for Tony Springer of the Aeronautics Research Mission Directorate at NASA Headquarters.

Republic also seemed at a disadvantage in the X-15 competition, for many of the same reasons North American was. However, the company was working on a Mach 3+ interceptor, the XF-103, and had developed the first supersonic combat-type aircraft, the experimental XF-91. With the XF-91, the company had gained experience in integrating a liquid-fueled rocket engine into a manned aircraft. The XF-103 was providing a wealth of experience (most of it unhappy), including information concerning the effects of high-speed heating on aircraft structures. In addition, Republic had Alexander Kartveli, one of the most innovative aircraft designers in the world.11271

The Republic AP-76 was the heavyweight of the competitors, with a launch weight of 39,099 pounds. Nevertheless, Republic expected the design to exceed very slightly the speed specification at 6,619 feet per second, although it fell somewhat short of the altitude requirement at only 220,000 feet.11281

Like Bell, Republic opted for XLR81-BA-1 engines, although the heavyweight AP-76 used four of them. Each of the engines produced 14,500 lbf, so a total of 58,000 lbf was available at 40,000 feet. Republic justified their choice by noting that "a sacrifice in weight was made in order to use these four units in place of a single thrust chamber engine. The increased safety of numbers as well as the increased reliability of starting one or more units influenced this choice." The engines used a fuel called JP-X that consisted of 40% unsymmetrical dimethylhydrazine (UDMH) and 60% jet fuel. The oxidizer was red, fuming nitric acid. The combination was hypergolic, so no ignition system was required. The thrust line of each engine chamber passed through the center of gravity of the airplane, eliminating any directional component of single – or multiple-chamber operations.12^

A switch panel at the normal throttle location on the left console controlled the engines, based on experience gained on the XF-91 interceptor. The XF-91 had both switches and a conventional throttle quadrant, but the pilots preferred using the switches. A fixed handgrip next to the switches ensured that the pilot’s hand would be near the switches at all times. There were nine two-position switches on the panel: a "master arm" switch, four individual "arm" switches, and four "on" switches. Igniting varying numbers of the engines varied the thrust, just as it had on the X-1 and D-558. Republic did not seem to incorporate the ability to use the "half-thrust" feature of the XLR81.130

Much like the XF-103, Republic eliminated the conventional canopy enclosure and submerged the pilot inside the fuselage. Three glass panels on each side of the fuselage provided side vision from launch until the airplane had descended to approximately 25,000 feet. Once the AP-76 had slowed to Mach 0.7, a hatch on the upper surface of the cockpit raised 13 degrees at its leading edge to expose a mirror system that provided forward vision during approach and landing. The system used two mirrors—one in the front of the hatch reflected an image downward to a second mirror on top of the instrument panel. The pilot looked at the second image. This system was similar to the one that had been developed for the XF-103 and had received favorable comments from the pilots during simulations. Surprisingly, the system offered good depth perception and minimal loss of brightness. Republic chose this unique system "because the problem of protecting the pilot from the high temperatures and, if need be, from cosmic radiation in a [conventional] canopy arrangement seem almost impossible." The cockpit and forward instrument compartment used gaseous nitrogen to maintain 40-100°F at a 5-psi differential, while the aft compartment had a 2.5-psi differential.131

The Republic AP-76 was large, heavy, and although Republic indicated it could slightly exceed the velocity requirements, it fell about 15 percent short of the desired altitude capability. In reality, very few believed it could attain the performance numbers generated by Republic, especially given the weight gains that seem to occur during any development exercise. The Republic entry placed last in the evaluation. (Republic Aviation)

To assist the pilot in flying the predetermined trajectory, Republic proposed installing a "flight program indicator." This display presented the pilot with a second-by-second trace that showed the proper speed, altitude, angle of attack, and path angle during powered flight. The pilot simply guided the airplane to match the cues on the display. It would have been a useful tool.-1132!

Normal Air Force fighter standards (+7.33/-3.00 g at burnout weight, but a great deal lower at full gross weight) provided the structural requirements for the AP-76, in contrast to the other competitors that only stressed their designs for +5 g. To accomplish this, and to withstand the expected heating environment, Republic proposed a novel structure for the fuselage. The main structure consisted of longitudinal titanium "Z" stringers. The structural titanium skin attached to the inner leg of the stringers, and the outer leg held a series of 0.020-inch-thick corrugated Inconel X shingles that formed a heat shield. The corrugations were very mild, with a 0.08 depth – to-length ratio, and permitted circumferential growth resulting from high transient temperatures. In between the heat shield and inner skin were 0.5-inch-thick blocks of Marinite insulation made by the Johns Manville Company. The 2-foot-wide Inconel outer skin sections stretched over three frames and used elongated attachment holes that allowed the sheets to expand and contract without warping. With the Inconel outer skin at its full 1,200°F, the interior titanium structure would never exceed 300°F.[133]

of the propellant tanks, and storage bottles were located below the wing carry-through structure. To the rear of the second nitric acid tank was the JP-X tank. The titanium oxidizer and fuel tanks were an integral part of the fuselage, but because nitric acid reacts with titanium at elevated temperatures, the acid tanks had removable aluminum liners.[134]

The trapezoidal wing used a slightly rounded leading edge with a flat airfoil between the 20% and 80% chord lines and a blunt trailing edge. Unlike the fuselage, Republic did not attempt to insulate the wing structure, and designed it to carry the design loads at elevated temperatures without developing high thermal stresses. The wing used three main sections: 1) the main wing structure, 2) the leading edge, and 3) the trailing edge, which consisted of a conventional single-slotted landing flap and a conventional aileron. The primary load-carrying structure was a tapered multi­cell box that ran from tip to tip and attached to the fuselage at four points (two per side). Intermediate spars were located on 5.5-inch centers with 15 spars at the root and four at the tip. The Inconel X skins were on average 0.10 inch thick. The leading edges were made of kentanium (a titanium carbide alloy) castings segmented into six parts per wing.[135]

The vertical and horizontal stabilizers were "of conventional size made possible by the use of double wedge type sections with rounded leading edges." The included angles were 10 and 12 degrees, respectively. The horizontal surfaces were all moving, but the airplane used conventional ailerons instead of the differentially moving horizontals found on the North American design. The vertical surfaces consisted of a dorsal stabilizer and a jettisonable ventral stabilizer. Wind-tunnel data from the XF-103 provided data for the rudder design, although the overall shape was different. The rudder consisted of the upper 46% of the surface and the entire trailing edge aft of the 70% chord line. Spilt flaps, consisting of the trailing 30% and 35% of the vertical and horizontal stabilizers, respectively, opened through a maximum angle of 50 degrees to increase drag and reduce the speed of the aircraft during reentry. Like the ailerons, these split flaps were each divided into three sections to permit operation while under thermal stresses. The stabilizers were generally of the same construction as the wings, and, like the wing, the leading edges of the empennage were made of cast kentanium.[136]

The landing gear consisted of two main skids and one tail skid. The 48-by-5-inch main skids, installed externally on the side of the fuselage bottom just ahead of the center of gravity, extended 18.5 inches using pneumatic shock absorbers. Just before landing, the tail skid automatically extended when the pilot jettisoned the ventral stabilizer. The landing gear could accommodate descent velocities of only 6 feet per second, considerably less than the 9 fps that tactical aircraft were design to absorb. The rationale was that "highly experienced pilots only are expected to fly this airplane." In fairness to Republic, the NACA had conducted an analysis of earlier research airplane landings and found that the majority were well below the 6-fps figure.-113^

Two hydrogen peroxide auxiliary power units each drove an alternator and hydraulic pump. A 60- gallon supply of the monopropellant could drive the power units for 30 minutes and operate the reaction control system for 3 continuous minutes. The reaction control system used six 90-lbf thrusters (one on each wing tip and four at the rear of the fuselage). Republic linked the thrusters to the same control column that the aerodynamic controls used, and a switch in the cockpit activated them when necessary. At the time of the proposal, the thrusters were throttleable, but Republic noted that "studies of a ‘bang-bang’ system, that is ‘full-on’ or ‘full-off…appear very promising."[138]

AP-76. "Consideration was given to the use of a pilot’s escape capsule in the AP-76. It was found to be extremely difficult to design a capsule which would have the necessary stability characteristics in the low density air of the high altitudes attained by the AP-76." Similarly, Republic found it was almost impossible to provide drag devices that would retard the capsule’s descent to the degree necessary to prevent excessive skin temperatures. In its place was an escape seat with leg (but no arm) restraints; the pilot would rely on his partial-pressure suit for protection during ejection.-1139!

Not surprisingly, given the weight of the AP-76, Republic chose a Convair B-36 bomber as the carrier aircraft. Republic had some experience in using the B-36 since the company manufactured the RF-84K parasite fighter used in the FICON project. The AP-76 was sufficiently large that it took up the majority of all four B-36 bomb bays. The lifting frame and main attach points were mounted on the B-36 wing box and attached to the AP-76 on top of the fuselage over its wing. It was necessary to modify two main bomb bay frames on the B-36 to clear the research airplane, and to add sway braces to "suitable strong points on the lower longerons of the bomb bay truss." A fairing with a soft gasket sealed the bomb bay when the B-36 was carrying the AP-76.!140!

Unfortunately, Republic appears to have misread the intentions of NACA and the Air Force, and its proposal stated that "the achievement of the speed [6,600 fps] is paramount whereas flight at very high altitudes has a secondary role." Because of this, Republic concentrated on designing an aircraft that would be capable of meeting the velocity requirement, while ignoring the altitude requirement to some degree. Although the proposal listed 220,000 feet as the maximum altitude of the aircraft, other data submitted with the proposal indicated that the company believed the aircraft could achieve almost 300,000 feet if necessary.-141!

The typical high-speed flight profile for the AP-76 began with the airplane being carried aloft by a B-36H142 carrier from Edwards AFB. The research airplane pilot would be riding in the comparative comfort of the pressurized compartment of the bomber. The B-36 would carry the AP-76 to a predefined release point approximately 540 miles from Edwards and launch the airplane at an altitude of 40,000 feet and a true air speed of 350 knots. After the AP-76 dropped clear of the B-36, the pilot would ignite all four rocket engines and pull into a 20-degree climb before running out of propellants after 105 seconds at approximately 140,000 feet. The AP-76 would then continue a free-flight trajectory to a peak altitude of 220,000 feet about 69 seconds after burnout. During the climb through 100,000 feet, the pilot would activate the switch that armed the reaction control system; thereafter, the movement of the control column and/or rudder pedals would activate the thrusters in addition to the now-useless aerodynamic controls.

The airplane would continue on a ballistic trajectory until it reached an altitude of 150,000 feet, where the aerodynamic controls would regain effectiveness. The airplane would go through a series of pull-ups and glides while the pilot maintained the angle of attack at a constant 6 degrees. The speed brakes on the horizontal and vertical stabilizers would open as needed. When the descent reached 25,000 feet and the speed reduced to Mach 0.7, the pilot would jettison the ventral stabilizer since it was no longer required for directional stability, and raise the hatch to expose the mirror system to provide forward visibility. Finally, the airplane would glide to a landing on its skids on Rogers Dry Lake.143

The Republic approach to the required two-seat engineering study was a little different from and decidedly more useful than the other proposals. All of the other competitors had simply deleted all of the research instrumentation and installed accommodations for an observer, although North American, at least, had provided a proper canopy arrangement. Republic, however, stretched the constant-section of the fuselage just ahead of the forward propellant tank by 29 inches. On the single-seat aircraft, two compartments held the research instrumentation (550 pounds ahead of the pilot and 250 pounds behind the pilot). For the two-seat airplane the 250 pounds in the rear compartment were deleted, and, combined with the 29-inch extension, this provided a full-size cockpit for the observer. The airplane could still carry the other 550 pounds of instrumentation – in fact, it was the only proposed two-seat aircraft that could carry any. The empty weight of the airplane increased 380 pounds and the launch weight increased 610 pounds, resulting in a degradation of performance of 170 fps.-1144

Although the hypersonic research airplane concept developed at Langley had met with almost unanimous endorsement by the Air Force, the lack of a suitable powerplant was a major shortcoming in the eyes of the WADC Power Plant Laboratory. The Langley study had determined that an engine (or engines) that could produce roughly 50,000 lbf was needed for the research airplane. The flight profiles developed by John Becker and his researchers showed that the ability to vary the thrust during flight would provide much better data and allow pilots to repeat maneuvers with some precision. The laboratory thought the Hermes A1 engine used in the Becker study was not capable of evolving into a man-rated engine, and suggested several engines it believed were "more suitable" for a manned aircraft. Despite these suggestions, however, the laboratory believed further study was required before any engine could be selected.-^

By October 1954, researchers from the Air Force, Navy, and the NACA had selected four existing or proposed power plants for possible use in the X-15. These included the Aerojet XLR73, Bell XLR81, North American NA-5400, and Reaction Motors XLR10. Despite the tentative selections, the Power Plant Laboratory thought that any engine would require major modifications to meet the needs of the X-15. The laboratory also believed the Air Force needed to "accept responsibility for development of the selected engine and…provide this engine to the airplane contractor as government furnished equipment." The primary consideration, for both the laboratory and the NACA, was that the engine be able to operate safely under any condition (acceleration in any axis) the X-15 was likely to experience. Maintenance and reliability (as defined by time between overhauls) did not need to be up to production standards.-21

The 30 December 1954 invitation-to-bid letter from the Air Materiel Command included summaries of the four engines recommended by the Power Plant Laboratory. However, although the stated preference to use one of these engines did not forbid bidders from using other engines, it did require the bidder and engine manufacturer to justify the selection. The bidder needed to present the justification to the X-15 Project Office for approval.

The powerplant that was ultimately selected for the X-15 was not one of the four recommended ones, but became known during discussions with Reaction Motors concerning the XLR10 from the Viking missile. During a meeting with the Air Force, the company promoted "a larger version of the Viking engine" that was under development for the Navy as the XLR30. After these discussions, the Power Plant Laboratory estimated that Reaction Motors could develop the XLR30 into a suitable engine for less than $5,000,000 in approximately two years. It was not even close.-31

On 25 January 1955, the Air Force requested additional information from Reaction Motors. The company replied on 3 February 1955 with details on the XLR10 and XLR30, and recommended four possible combinations for the X-15 program. These included an oxygen-ethanol XLR10, an oxygen-ammonia XLR30, an oxygen-hydrocarbon XLR30, and an oxygen-ethanol engine using two XLR10 chambers fed by a single XLR30 turbopump. Each of the engines used hydrogen peroxide to drive the turbopump. After it was briefed on the Becker study, Reaction Motors doubted that a single XLR10 was "adequate to perform the objectives of this type of aircraft."-41

Although it suggested a combination of XLR10 thrust chambers and an XLR30 turbopump, Reaction Motors believed this engine would be overly complicated and predicted it would weigh 815 pounds (compared to 420 pounds for either of the XLR30 configurations). The company suggested that relatively minor modifications to the XLR30 would allow throttling between 17,000 and 57,000 lbf with a specific impulse of 278 seconds. The XLR30 installation required a

space 70 inches long and 30 inches in diameter, considerably less than that required for the larger XLR10-XLR30 combination.-51

between 1949 and 1955. (Reaction Motors Inc.)

Independently, Reaction Motors determined that the two most important safety requirements were the propellant combination and the means of achieving combustion during ignition and shutdown. The company reviewed seven propellant combinations in depth, and eventually narrowed the choices to liquid oxygen and anhydrous ammonia. Reaction Motors based this choice largely on its significant experience with this combination, which had shown that ammonia had fewer critical starting characteristics than most hydrocarbon fuels. Additionally, the propellants were ideal for the regenerative cooling of the proposed engine’s thrust chamber.

The Air Force, however, was still more interested in the XLR10, and on 4 February 1955 it asked Reaction Motors for additional information on that engine. On the same day, however, Reaction Motors and the X-15 Project Office held a meeting during which the company detailed a significant development program to man-rate the XLR-10 for the X-15. Given the development effort required for either engine, the company believed the XLR30 would ultimately be a better engine. After a meeting between the Air Materiel Command and the X-15 Project Office, the government advised Reaction Motors to "make all further estimates on the basis of the XLR30’s development." [6]

Concurrently, the Air Materiel Command had also been in discussions with the other three engine manufacturers. The fact that the other manufacturers showed a somewhat lower level of interest than Reaction Motors is understandable-after all, Reaction Motors engines had powered most of the rocket-equipped X-planes since the original XS-1. In fact, by this time North American had already requested that the Air Force withdraw the NA-5400 from consideration. On 18 March 1955, the Air Force supplied the prospective airframe contractors with the specifications on the three remaining engines. The Air Force expected that a flight engine would be available to the winning contractor within 30 months.-^

The X-15 Project Office released its analysis of the data provided by the engine manufacturers on 22 March 1955. One of the comments was that generating the necessary 50,000 lbf would require multiple Bell and Aerojet engines. The X-15 Project Office made clear that the final engine was not a production item, and that the amount of available propellants was the only limit to the operating time of the engine.[8]

After much discussion, the Air Force decided to release a request for proposal for the X-15 engine that was separate from the airframe competition. On 26 April, Headquarters ARDC requested that "the engine program be subjected to a final critical review apart from, but concurrent with the evaluation of the airframe proposals." The Power Plant Laboratory, NACA, and Navy would complete their engine evaluations by 12 July. The evaluation was to come to one of three conclusions: 1) that one engine was so superior to the others that its use would be mandated, 2) that one engine was so inferior that its use would be forbidden, or 3) that all of the engines were so nearly comparable that the choice would be left to the airframe contractor. The WADC scheduled the final engine evaluation meeting for 28 June, although this later slipped to 6­7 July.[9]

Although they had one of the most ideal test locations in the world, the Air Force and NACA could not simply go out and begin conducting X-15 operations. Several hurdles had to be overcome before the X-15 could ever do more than just conduct short flights over the Edwards reservation.

It had been recognized early during planning for the X-15 flights that suitable contingency landing locations would need to be found in the event of an abort after separation from the B-52 carrier aircraft, or if problems during the flight forced the pilot to terminate the mission before reaching Edwards. Since North American had designed the X-15 to land on dry lakebeds, the logical course of action was to identify suitable lakebeds along the flight path-in fact, these

lakebeds had been one of the factors used to determine the route followed by the High Range.

The Air Force and NACA had to identify lakebeds that would enable the X-15 to always be within gliding range of a landing site. In addition, the flight planners always selected a launch point that allowed the pilot a downwind landing pattern. Normally, the launch point was about 19 miles from the lakebed runway and the track passed the runway 14 miles abeam. To establish the proper launch point, flight planners used the fixed-base simulator to determine the gliding range of the airplane, including both forward glides and making a 180-degree turn and returning along its flight path. Another consideration was that the flight planners needed to selected lakes that would provide an overlap throughout the entire flight.[69]

The first hurdle for the Air Force was to secure permission from the individuals and several government agencies that owned or controlled the lakebeds. Next was seeking permission from the Federal Aviation Agency (FAA-it became an administration later) to conduct flight operations over public land.

Although responsibilities concerning the lakebeds continued throughout the life of the X-15 program, there were several spurts of activity (two major and one minor) concerning them. The first occurred, logically enough, just before the beginning of the flight program when efforts began to secure the rights to the lakebeds needed for the initial flight tests. The second involved securing the lakes needed for the higher-speed and higher-altitude flights made possible by the introduction of the XLR99 engine. One final push later in the program tailored the set of lakes for the improved-performance X-15A-2 and its external tanks.

Eventually, 10 different launch locations would be used, including eight dry lakes: Cuddeback supported a single launch; Delamar was the most used, with 62 launches; Hidden Hills saw 50 launches; Mud hosted 34; Railroad was used for only 2; Rosamond was used for 17, Silver hosted 14, and Smith Ranch was used for 10. In addition, the Palmdale VOR (OMNI) hosted eight launches, and a single flight originated over the outskirts of Lancaster. Hidden Hills was usually the intended site for the abortive 200th flight. The vast majority of these flights (188) would land on Rogers Dry Lake. Two would land at Cuddeback, one at Delamar, four at Mud, one at Rosamond, one at Silver, and one at Smith Ranch. The X-15-3 broke up in flight and did not land on its last flight.[70]

Rosamond Dry Lake, several miles southwest of Rogers, offered 21 square miles of smooth, flat surface that the Air Force used for routine flight test and research operations and emergency landings. This dry lakebed had served as the launch point for many of the early rocket-plane flights at Edwards. It is also the first lakebed that most visitors to Edwards see, since the road from Rosamond (and Highway 14) to Edwards crosses its northern tip on its way to the main base area. Scott Crossfield would make the X-15 glide flight over Rosamond Dry Lake, and no particular permission was necessary to use Rosamond since the lakebed was completely within the restricted area that made up the Edwards complex. Unfortunately, the lake was only 20 miles away from the base, so it did not allow much opportunity for high-speed work.

The Rogers and Rosamond lakebeds are among the lowest points in Antelope Valley, and they collect seasonal rain and snow runoff from surrounding hills and from the San Gabriel Mountains to the south and the Tehachapi Mountains to the west. At one time, the lakebeds contained water year-round, but changing geological and weather patterns now leave them wet only after infrequent rain or snow. A survey of the Rosamond lakebed surface showed its flatness, with a curvature of less than 18 inches over a distance of 30,000 feet.[71]

Beginning in early 1957, North American, AFFTC, and NACA personnel conducted numerous evaluations of various dry lakes along the High Range route to determine which were suitable for X-15 landings. The initial X-15 flights required 10 dry lakes (five as emergency landing sites near launch locations, and five as contingency landing sites downrange) spaced 30-50 miles apart.^72

The processes to obtain permission to use the various lakebeds outside the Edwards complex were as diverse as the locations themselves. For instance, permission to use approximately 2,560 acres of land at Cuddeback Lake as an emergency landing location was sought beginning in early 1957, with first use expected in January 1959. The lakebed was within the land area reserved for use by the Air Force at George AFB, California, but the Department of the Interior controlled the lakebed itself. Since the Air Force cannot acquire land directly, officials at the AFFTC contacted the Los Angeles District of the Army Corps of Engineers, only to find out that George AFB had already requested the Corps to withdraw the land from the public domain. The Bureau of Land Management controls all land in the public domain, although control may pass to other government agencies (such as the military) as stipulated in various laws (U. S. Code Title 43, for example). At the time, the Corps of Engineers acted as the land management agent for the U. S. Air Force, and John J. Shipley was the chief of the real estate division for the Los Angeles District.

This map shows the general location of the lakebeds as well as the radar coverage afforded by the three High Range stations. The two primary restricted airspace areas are shaded, although the entire flight path of the X-15 was restricted on flight day. (Dennis R. Jenkins)

Officials at George intended to use the lakebed as an emergency landing site. In turn, on 17 May 1957 the Corps wrote to the Bureau of Land Management on behalf of the Secretary of the Air Force, requesting a special land-use permit for Air Force operations at the lake. When the Los Angeles District received the request from the AFFTC, Shipley contacted Lieutenant Colonel C. E. Black, the

installations engineer at George AFB, requesting that a joint-use agreement be set up that would permit sharing the lake with the AFFTC for X-15 operations.-1731

By the end of July 1959, the Bureau of Land Management had approved the permit, and George AFB had agreed in principle to the sharing arrangement. The special-use permit gave George AFB landing rights for several years, and permitted the lakebed to be marked as needed to support flight operations. John Shipley, very intelligently, decided that the joint-use agreement between the AFFTC and George was an internal Air Force affair and bowed out of the process after the issuance of the Bureau of Land Management permit. Although there seemed to be no particular disagreement, the joint-use agreement had a long gestation period. The special-use permit was granted at the beginning of August, but at the end of September Colonel Carl A. Ousley, the chief of the Project Control Office at the AFFTC, questioned why a written joint-use agreement had not been signed. Major Resiner at George replied on 14 October that he had received verbal approval from all parties, but written approval was required from two separate Air Force commands (the ARDC and the Tactical Air Command (TAC)), the Corps of Engineers, and the Bureau of Land Management. He foresaw no difficulties in obtaining the signatures, and apparently the process worked itself out within a suitable period since there appears to have been no further correspondence on the matter. The joint-use agreement with George AFB essentially stated that the AFFTC was responsible for any unique preparations and marking of the lakebed required to support X-15 operations, although George did offer to supply emergency equipment and personnel as needed.-741

Simultaneously with the request to use Cuddeback, the AFFTC issued a similar request for Jakes Lake and Mud Lake, both in Nevada. Originally, the X-15 program had wanted to use Groom Lake, Nevada, as a launch site instead of Mud Lake. However, the security restrictions in place at Groom Lake (also known as "The Ranch") to protect the CIA-Lockheed reconnaissance programs led the AFFTC and NASA to abandon plans to use this facility. Officials at Nellis suggested Mud Lake as a compromise between the needs of the X-15 program and the highly classified CIA programs.751

The AFFTC asked for approximately 2,500 acres of land in the public domain at Jakes Lake; at Mud Lake, the request was for 3,088 acres. The indefinite-term special-use permits sought the right to install fencing to keep cattle from grazing in certain areas. Several ranchers had grazing rights on the public domain land, so this required modifying these agreements and compensating the ranchers with Air Force funds. In this case the Air Force did not want to remove the land from the public domain, but it did want to use approximately 9,262 acres of land at Mud Lake that had already been withdrawn from the public domain for use as part of the Las Vegas Bombing and Gunnery Range.761

October 1957 for approval and funding. By the end of January 1958, however, Lieutenant Colonel Donald J. Iddins at the AFFTC began to worry that the process was taking too long. The X-15 needed the lakes in July 1959, and there was no evidence of final action. Part of the problem was that land actions involving over 5,000 acres (which the two actions together did) required approval from the House Armed Services Committee. The AFFTC reminded the chief of engineers that they did not want to remove the land from the public domain, which seemingly eliminated the need for congressional approval, and brought the situation to the attention of the X-15 Project Office during a management review at Wright Field on 5 February 1958. The result was a renewed effort to ensure that all three lakes (Cuddeback, Jakes, and Mud) were available for X-15 use on schedule, including the right to build roads to the lakes, marking approach and landing areas, and fencing certain areas if necessary to ensure the safety of the X-15.-177

On 14 February 1958, the chief of engineers responded that he had initiated the process to grant special-use permits, but had terminated the effort when he noted that the AFFTC wanted to fence off the land. However, the law did not permit fencing to be erected on special-use permitted land. This meant that the land would have to be withdrawn from the public domain after all, or go unfenced. It appears that the answer to the problem was obtained by the AFFTC agreeing to a reduction in the Mud Lake acquisition to just under 2,500 acres (versus the original 3,088), bringing the total to under 5,000 and circumventing congressional approval. This allowed the land to be withdrawn from the public domain, and some of it was fenced as needed to keep stray cattle from wandering onto the marked runway.-178

Simply getting access to the lakebeds was not always sufficient. For instance, Mud Lake was in the extreme northwest corner of Restricted Area R-271, meaning that Sandia Corporation, which controlled R-271 for the Atomic Energy Commission (AEC), had to approve its use. A "Memorandum of Understanding between the Air Force Flight Test Center and Sandia Corporation" allowed AFFTC support aircraft to operate in the immediate vicinity of Mud Lake during X-15 flights. The AFFTC had to furnish flight schedules to Sandia one week before each anticipated mission, and Sandia made the point that it had no radar search capability and could not guarantee that the area was clear of traffic. Sandia also agreed not to schedule any tests within the restricted area that might conflict with X-15 flights. Once approved by Sandia, the AFFTC sought additional approval from Nellis AFB since Mud Lake was also within the Las Vegas Bombing and Gunnery Range. This approval was somewhat easier to negotiate because it was obtained from another Air Force organization.-1791

On 3 November 1958, a team from the AFFTC visited Mud Lake to conduct a preliminary study of lakebed conditions and to determine what action would be required to clear areas of the lakebed for use as a landing strip. When the group from the Flight Test Operations Division and Installations Engineer Division arrived over the lake, the pilot made several low passes to orient the group and obtain a general knowledge of the various obstructions that might conflict with landing on the lakebed. What the group saw was a general pattern of obstructions running east to west in a straight line across the center of the lakebed. The team landed at the Tonopah airport and proceeded by car to the lake, 16 miles away, for a closer inspection.-1801

They found that the obstructions observed down the center of the lake were a series of old gunnery-bombing targets dating from World War II. Practice bodies, wooden stakes, and good­sized rocks used to form bull’s-eyes for bombing practice littered the lakebed. The targets were in a narrow straight band down the center of the lake from west to east, but the debris covered a considerably wider area. As would become standard practice on all the lakes, the group dropped an 18-pound steel ball from a height of 6 feet and measured the diameter of the resulting impression. This gave a good indication of the relative hardness of the surface and its ability to support the weight of the X-15 and other aircraft and vehicles. At the edges of the lake, the ball left impressions of 3.25 inches or so, while toward the center of the lake the impressions were only 2.25-3.0 inches in diameter. At the time, the Air Force believed that impressions of 3.125 inches or less were acceptable. The general surface condition of the lakebed varied from relatively smooth and hard to cracked and soft. Although it was not ideal, the group thought the lakebed could be made useable with minor effort.-1811

More lakebed evaluations followed on 13-14 July 1959. X-15 pilot Bob White and the AFFTC chief of flight test operations, Colonel Clarence E. "Bud" Anderson, used a Helio L-28 Super Courier aircraft to visit 12 dry lakes along the High Range route. At each lake, Anderson and White dropped the "imperial ball" from six feet and measured the diameter of the resulting impression.

By this time, the Air Force had changed the criteria slightly: a diameter of 3.25 inches was acceptable, and anything above 3.5 inches was unacceptable. The survey included an evaluation of the surface hardness, surface smoothness, approximate elevation, length and direction of possible runways, and obstacles. Anderson remembers that there was "only one lake where we had to make a full power go-around as we watched the tires sink as we landed." Many future surveys would take personnel from AFFTC, NASA, and North American to most of the larger dry lakes along the High Range route.-1821

In addition, on 13 July 1959, four FAA representatives and two members of the AFFTC staff held a meeting at the FAA 4th Region Headquarters in Los Angeles to discuss using Silver Lake as a launch site for the X-15. Since some of the X-15 flight corridor would be outside existing restructured airspace, FAA approval was necessary. The FAA claimed jurisdiction under Civil Aeronautics Regulation 60.24, but was anxious to assist the Air Force within the limits of the law. The Air Force intended to use Silver Lake launches for early X-15 flights with the XLR11 engines. The proposed 100-mile flight path consisted of Silver Lake, Bicycle Lake, Cuddeback and/or Harpers Lake, and then on to landing at Edwards. The FAA had no particular problem with the concept, but since its charter was to protect the safety of all users of public airspace, it believed that certain restrictions needed to be in place before the flights could be approved. The participants spent most of the meeting discussing possible operational problems and concerns, and then developing limitations or restrictions that mitigated the concerns.1881

For Silver Lake launches, both the launch and the landing were performed in a restricted airspace called a "test area." Silver Lake was inside Flight Test Area Four, while Edwards was at the center of Flight Test Area One. However, none of the test areas surrounding Edwards were restricted 24 hours per day, or seven days per week. In fact, they were open to civilian traffic most of the time, and their closure had to be coordinated with the FAA (the airspace immediately around Edwards was always closed to civilian traffic). In addition, the flight path from Silver Lake to Edwards would take the X-15 out of restricted airspace and into civilian airspace for brief periods. Future flights using the northern portion of the High Range would also be outside normal test areas. The FAA, therefore, needed to approve the plans and procedures for using that airspace.1841

On 1 September 1959, L. N. Lightbody, the acting chief of the General Operations Branch of the Los Angeles office (4th Region) of the FAA wrote to Colonel Roger B. Phelan, deputy chief of staff for operations at the AFFTC. The letter contained a "certificate of waiver covering the release of the X-15 research vehicle over Silver Lake" subject to some special limitations. The FAA imposed the limitations to ensure "maximum safety not only to your AFFTC personnel and equipment, but also to other users of the immediate airspace. Further, the communications requirements will insure the blocked airspace may be returned to its normal use with minimum delay." The FAA approved the certificate of waiver (form ACA-400) on 1 September 1959 and listed the period of waiver as 1

October 1959 to 31 March 1961, although it was subsequently extended to 1 July 1963, and later still through the end of 1969.[85]

Given the effort that accompanied the acquisition of Cuddeback Lake in late 1957 and early 1958, it is surprising that the first serious survey of the lake does not appear to have taken place until 7 October 1959. Of course, conducting detailed surveys significantly ahead of the anticipated use was not a particularly useful exercise since the periodic rains that kept the lakebeds useable also changed their character each time, as did the effects of other vehicles (such as cars). By this time, the X-15 had already made its first two flights from over Rosamond Dry Lake, landing each time at Rogers. Since the Air Force expected the X-15 to begin rapidly to expand its flight envelope, North American sent George P. Lodge to Cuddeback in an Air Force Piasecki H-21 Shawnee helicopter.1861

Lodge conducted the standard hardness tests by dropping the same "imperial ball" used in the other surveys. He found that the ball left an impression of about 3 inches (which was considered acceptable) at the southern end of the proposed runway, but quickly degraded to 4-4.5 inches by the northern end. He noted that these measurements compared unfavorably to tests on Rogers (2 inches) and Rosamond (2 inches) conducted after the last rains. A note emphasized that there were a set of deep ruts running the length of the runway made by a vehicle when the lake was wet, and that although it was only a single set of ruts, they "wander around to some extent." The nature of the lakebeds was such that grading or other mechanical methods could not repair major damage-only nature could do that. Lodge recommended that "Cuddeback lake, in its present condition, not be considered as an alternate landing site for the X-15 airplane and should be used only as a last resort in an extreme emergency." He warned that "should a landing be attempted with the X-15 airplane on Cuddeback lake in its present condition, there would be more than a 50-50 chance of wiping out the nose gear." It was clear that the lakes had both good and bad qualities: they were largely self-repairing each time it rained, but they could also be self­destroying by the same process.-1871

Two weeks later, Lodge, who was a flight safety specialist for North American, performed a survey of Silver Lake and nine other lakes to determine their suitability as emergency landing sites. At Silver, Lodge found that the prevailing wind was out of the north, with the best landing heading estimated at 200-310 degrees magnetic. The southern portion of the lake was soft with numerous sinkholes, and not satisfactory for touchdown. Lodge also found an abandoned railroad bed, approximately 2 feet high and 10 feet wide, running north to south across the east side of the lakebed. There was also a dirt road with deep ruts running east to west across the northern part of the lake, a paved road going from Baker to Death Valley along the eastern perimeter, and another dirt road (this time with no ruts) running diagonally northwest to southeast.-1881

Despite these obstacles, there was approximately 16,000 feet of satisfactory lakebed between the soft southern portion and the northern road. There were a few sinkholes, most measuring about 7 inches across and 3-4 inches deep, but the Air Force would fill these before use. The usual imperial-ball tests resulted in impressions between 2.9 and 3.7 inches in diameter, although the main area was on the lower end of that range. In addition, Lodge pounded both 3/8-inch and 1/2-inch steel rods into the ground with 200 pounds of force to determine what the condition of the soil was under the upper crust. The 3/8-inch rod generally penetrated between 1 and 3 inches, while the 1/2-inch rod penetrated between 0.25 and 1.5 inches. The results of the tests led Lodge to recommend a location for a marked runway. Of the other nine lakebeds visited,

Lodge landed only on the east and west lakes in the Three Sisters group, and determined that both were satisfactory for emergency use despite having "a few rocks and ammo links strewn 1891

about.

As 1959 ended, George Lodge was a busy man, and at the end of November he conducted yet another lake survey, this time of approximately 50 lakes in California, Nevada, and Utah. Again, the intent was to find suitable emergency landing sites for the X-15 as it expanded its flight-test program. The test methods Lodge used on the lakes were the same as he had used the previous month at Silver Lake.-90

The Air Force and NASA continued to survey the established and previously used lakebeds periodically, particularly after it rained to determine that the lakebed was dry enough to support operations and that no sinkholes or gullies existed. Changing the direction of the available runways on a lakebed also required a revised survey. For instance, in early December 1959 Lodge conducted a new survey of Rosamond Dry Lake to determine whether the lake would support a marked runway running northeast to southwest. Marked runways already existed on headings of 10-190 degrees and 70-250 degrees. Starting from a location in the southwest corner of the lakebed, Lodge inspected a heading of approximately 30 degrees, roughly toward the telemetry station located on the edge of the lake. He found that the lakebed was hard and smooth for 2 miles, moderately smooth at 2.5 miles, smooth again at 3 miles, moderately rough at 3.5 miles, and rough from 4 miles to the edge of the lakebed. Imperial-ball drop tests yielded diameters of about 2.5 inches across the route. The conclusion was that the runway was practical, and, as viewed from above, would result in a runway approximately halfway between the two existing runways, with all three converging at the southwest edge of the lakebed.-1911

The second round of lake acquisitions began when the XLR99 engine came on line. First up was securing rights to use Hidden Hills dry lake, slightly west of the Hidden Hills Ranch airstrip. Simulator studies had confirmed that Hidden Hills would be ideal as an emergency landing site during the launches for the initial XLR99 flights that needed to be conducted further uprange than the XLR11 flights. The lakebed would continue to be used as a contingency site as the program continued to launch further uprange into Utah. At the beginning of 1960, it was expected that the program would need access to the lake by 1 October 1960.[92]

However, schedules change, and the XLR99 flight dates kept slipping. A revised plan showed that the XLR99 research buildup flights would use Silver Lake and Hidden Hills Lake in California, Mud Lake in Nevada, and Wah Wah Lake in Utah as launch sites. The program needed various intermediate lakes along the upper portion of the High Range to provide complete coverage for emergency landings along the route. The Air Force would staff the intermediate lakes with crash and emergency personnel during flights. Additional contingency lakes would have runways marked on them, but would not be staffed with support personnel. At first the AFFTC and NASA had wanted to mark "all lakes with a satisfactory 10,000 feet landing surface" to provide an additional factor of safety for the X-15 program. Although no plans existed to use these lakes, the planners believed that marking them would also allow continued X-15 operation when a primary intermediate lake was wet. However, legal personnel indicated that there was "NO possibility" (emphasis in original) of marking any lake unless a right-to-use permit was obtained. Since personnel and funds did not exist to negotiate all the required permits, this plan was abandoned and a list of essential contingency sites was drawn up.[93]

The 30 September 1960 plan included launching immediate flights from Silver Lake, with the west lake at Three Sisters and Cuddeback acting as intermediate emergency sites. By 1 February 1961, operations would move to Hidden Hills, with Cuddeback as the intermediate site. On 1 April, Mud Lake would become the primary launch lake, with Grapevine and Ballarat as the intermediate sites, and contingency sites located at Panamint Springs and Racetrack. Two months later the launches would move to Wah Wah Lake, with Groom Lake, Delamar, and Hidden Hills becoming the intermediate sites, and Dogbone and Indian Springs the contingency sites. The AFFTC sought permission from Nellis to use the last two sites because they were located on the Las Vegas range, as was Mud Lake.[94]

Planners had always considered Smith Ranch Lake as a backup site to Wah Wah Lake, using Mud Lake as the intermediate site and the same contingency sites used during Mud Lake launches. This was still true at the end of February 1961. The program expected to begin launches from Hidden Hills in March 1961, and the launch lake still needed to be surveyed and marked. NASA expected to begin using Mud Lake in April 1961 and two of the support lakes (Grapevine and Panamint) still required use permits, while Ballarat had replaced Racetrack as the second contingency site. The program still needed to survey and mark all three of the support lakes. Launches from Wah Wah would begin in June 1961, and all of the sites along that route (except for Hidden Hills) still had to be "acquired," surveyed, and marked. As the program continued, however, it abandoned plans to use Wah Wah Lake, in part because of difficulties in obtaining permission to use the Nellis contingency sites (particularly Groom Lake) and airspace rights over Nevada’s restricted areas. Instead, the government eventually acquired the alternate launch site at Smith Ranch Lake, although flights from this point did not begin until June 1963.[95]

Determining if a lakebed could support the weight of an X-15 and its support airplanes was a relatively non-technical endeavor. A large steel ball, nicknamed the "imperial ball" was dropped from a height of six feet and the resulting impression was measured. For most of the program, a diameter of 3.25 inches or less was considered acceptable to support operations. Neil Armstrong is kneeling beside the ball in this June 1958 photo at Hidden Hills. (NASA)

I owe a particular mention of Jay Miller, author of the popular The X-planes: X-1 to X-45, (Hinckley, England: Midland Publishing, 2001), among many other works. Anybody interested in reading about the other X-planes should pick up a copy of this excellent book. Jay was responsible for the first photograph I ever had published, and published my first book—a short monograph on the Space Shuttle. Somehow, I feel I have him to blame for the quagmire of aerospace history I find myself embroiled in. I truly appreciate the help and friendship from Jay and his lovely wife Susan over the past 25 years or so.

Thankfully, my mother, Mrs. Mary E. Jenkins, encouraged me to seize opportunities and taught me to write and type—such necessary attributes for this endeavor. As for so many things, I owe her a great deal of gratitude, along with my everlasting love and admiration. After listening to my trials and tribulations about this project for a decade, she passed away before publication. I hope she has found the peace and rest she so richly deserves.

A note regarding terminology: In the days before being politically correct became a prime influence on engineering and history, engineers called piloted vehicles "manned" aircraft, and the process of making them safe enough to fly was termed "man-rating." This work continues to use these terms since they are what were in use at the time.

[1] The Armstrong quote is in the foreword to Milton O. Thompson, At the Edge of Space: the X – 15 Flight Program (Washington, DC: Smithsonian Institution Press, 1992), p. xii.

[2] John V. Becker, "The X-15 Program in Retrospect," 3rd Eugen Sanger Memorial Lecture, Bonn, Germany, 5 December 1968, pp. 1-2

[3] Harrison A. Storms, "X-15 Hardware Design Challenges," a paper in the Proceedings of the X – 15 30th Anniversary Celebration, Dryden Flight Research Facility, Edwards, California, 8 June 1989, NASA CP-3105, p. 27.

[4] In the 3rd Eugen Sanger Memorial Lecture in 1968, John Becker stated that 109 flights exceeded Mach 5. A reevaluation of the flight data shows that only 108 actually did. See Becker, "The X-15 Program in Retrospect," p. 3 for Becker’s original numbers.

[5] Despite all that is written, the program held very few "official" records, mainly because it seldom invited the FAI out to witness the flights. In fact, it appears that the 314,750-foot altitude record set by Bob White is the only official record ever set by the program.

[6] Ronald G. Boston, "Outline of the X-15’s Contributions to Aerospace Technology," 21 November 1977. Unpublished preliminary version of the typescript available in the NASA Dryden History Office. For those interested in Boston’s original paper, the easiest place to find a copy is in the Hypersonic Revolution, republished by the Air Force History and Museums program. It constitutes the last section in the X-15 chapter; Letter, William H. Dana, Chief, Flight Crew Branch, DFRC, to Lee Saegesser NASA History Office, transmitting a copy of the SETP paper for the file. A slightly rewritten (more politically correct) version of the paper was later published as The X-15 Airplane-Lessons Learned (American Institute of Aeronautics and Astronautics, a paper prepared for the 31st Aerospace Sciences Meeting, Reno Nevada, AIAA-93-0309, 11-14 January 1993). Boston listed 1,300°F as the maximum temperature, but Bill Dana reported 1,350°F in his SETP and AIAA papers. Boston also listed the max-q as 2,000 psf, but in reality it was 2,202 psf on Flight 1-66-111.

[Z] Storms, "X-15 Hardware Design Challenges," pp. 32-33

[8] Becker, "The X-15 Program in Retrospect," pp. 1-2

[9] J. D. Hunley, "The Significance of the X-15," 1999, unpublished. Typescript available at the DFRC History Office.

[10] Officially, Johnny Armstrong (who is now the chief engineer in the Hypersonic Flight Test Team) maintains the AFFTC Hypersonic Flight Test Team Project Files and is, fortunately, something of a pack rat. However, to everybody at Edwards and Dryden, this wonderful collection is simply the Armstrong Memorial Library.

The airframe evaluation process lasted from mid May until late July, with the Air Force, NACA, and Navy conducting independent evaluations based on a number of preestablished criteria. The preliminary NACA evaluation of the proposals consumed the better part of three weeks before each of the laboratories forwarded preliminary results to Hartley Soule. On 3 June 1955, Ames tentatively ranked the submissions as 1) Douglas, 2) North American, 3) Bell, and 4) Republic. The Douglas ranking resulted from "the completeness and soundness of design study, awareness of factors in speed and altitude regime, and relative simplicity of approach." Ames, however, expressed skepticism over the Douglas magnesium hot-structure wing because it would preclude the study of problems associated with insulated-type structures that would potentially be used in future aircraft intended for greater flight duration. This seemed to be a major disconnect between Ames and Langley. It appears that Ames wanted to test a structure that would be representative of some future production aircraft; Langley just wanted to test a structure that would survive.

Another problem that worried the Ames evaluators was the flammability of magnesium. It seemed that "only a small area raised to the ignition temperature would be sufficient to destroy the aircraft." The researchers at Ames held that if Douglas should win the competition, the company should build two aircraft with the proposed HK31 structure, but a third aircraft "should have a wing based upon the alternative higher temperature insulated type of design approach." The Ames report continued to stress the need for a wing of greater leading-edge sweep angle (at least 53 degrees) "for the purpose of minimizing the rate of heat transfer to the leading edge."145

At Langley, on 6 June, researchers rated the North American proposal number one, followed by Douglas, Bell, and Republic. According to the Langley assessment, led by John Becker, the research utility of the North American hot-structure approach outweighed the advantages of the simplicity of the magnesium structure proposed by Douglas. Slightly rebuffing Ames, Langley noted that the 21% reduction in heat transfer gained by increasing the leading-edge sweep from the proposed 40 degrees to 53 degrees did not seem to justify the alteration of the planform. This was particularly true because the structure appeared capable of handling the heat load.-1146!

In a reminder to the evaluation teams, also on 6 June, Arthur Vogeley and Captain McCollough reiterated that the purpose of the evaluation was "to select a contractor rather than a particular design." Although certain features of the winning design could be unsatisfactory, it was the basic design approach as described in the proposal that might best be relied upon to produce an acceptable research airplane.147-

On 10 June 1955, the HSFS sent its airframe results to Soule, detailing the design approach and research utility aspects of the airframe, flight control system, propulsion unit, crew provisions, handling and launching, and miscellaneous systems. Researchers at the HSFS ranked the proposals as 1) Douglas, 2) North American, 3) Bell, and 4) Republic, although the proposals from Douglas and North American were essentially equal.148

The final evaluation by Ames, on 10 June, ranked the proposals as 1) North American, 2) Douglas, 3) Bell, and 4) Republic. This represented a change from the earlier Ames evaluation, based largely on researchers considering the North American structure superior in terms of research utility—an opinion voiced earlier by Langley. The Ames evaluators had apparently changed their minds about wanting to test a production-representative structure. The laboratory had also finally given up on advocating an insulated structure since no serious support for their earlier recommendation of equipping the third aircraft with a different wing structure had materialized (sufficient funds to construct an alternate wing were simply not available).-1149-

The final evaluation from Langley on 14 June ranked the proposals as 1) North American, 2) Douglas, 3) Republic, and 4) Bell. Although researchers at Langley thought the magnesium wing structure of Douglas was feasible, they feared that local hot spots caused by irregular aerodynamic heating could weaken or destroy the structure. The use of Inconel X by North American presented an advantage with regard to thermal limits—not only from the standpoint of margins for maneuverability within the design temperatures, but also from a safety viewpoint if the airplane ever exceeded its design temperature.

A few days after receiving all of the final evaluations, Soule sent copies of each to the WADC Project Office, along with a consolidated result. The final NACA ranking was (points based on a scale of 100) as follows:150-

Oddly, the final order representing the overall NACA evaluation was 1) North American, 2)

Douglas, 3) Bell, and 4) Republic, despite the fact that Douglas scored slightly more points in the evaluation (152 versus 150 for North American). Soule pointed out that although Ames, Langley, and the HSFS did not rank the four proposals in the same order, the final ranking did represent an overall NACA consensus. All of the laboratories involved in this portion of the evaluation considered both the Douglas and North American proposals to be much superior to those submitted by Bell and Republic. While researchers preferred the Inconel X structure of the North American proposal, the design was not without fault. For instance, the NACA thought that the landing-gear arrangement was undesirable, the differentially-operated horizontal stabilator design in lieu of ailerons was an overly complicated arrangement, and (at least at Langley) the replaceable fiberglass leading edges were unacceptable.

John Becker wrote to Hartley Soule on 16 June attempting to clarify why the North American design was superior to that of Douglas. The letter listed the thermal limits expected for the new aircraft, and showed that the Inconel X structure on the North American design was "impressively superior" to the magnesium alloy used by Douglas. The data were shown for three categories: 1) performance within the design temperature limits in terms of allowable velocity, altitude, and dependence on speed brakes; 2) reserve heat capacity (in case the design temperatures were exceeded by a moderate margin) such that the structure would still have a fair possibility of remaining intact; and 3) the possibility of melting or burning in case the design temperatures were greatly exceeded in local hot spots. There appears to be no further correspondence on this subject, so Becker’s explanation seems to have answered whatever unasked questions existed.-1151-

During the first two weeks in July, the WADC evaluation teams sent their final reports to the WADC Project Office. As with the NACA evaluations, the Air Force found little difference between the Douglas and North American designs, point-wise, with both proposals considered significantly superior to those of Bell and Republic.

George Spangenberg was in charge of the Navy evaluations, which got off to a late start and ended up being cursory. In the end, the Navy found much the same thing as the NACA and ranked the airframe proposals as 1) Douglas, 2) North American, 3) Republic, and 4) Bell. Given the Navy’s long—and successful-association with Douglas airplanes, the order was not surprising. Most Navy concerns centered on the selection of an engine. As Clotaire Wood explained, "the airframe-engine combination was to be evaluated and not the engine alone, since it had been agreed that the engine of the winning design would be the engine supported by the special development program." This was not how the Power Plant Laboratory saw the process, but it seemed to put the Navy at ease. In addition, Wood indicated that "it would be of real value to have the Bureau’s [BuAer] recommendations regarding an engine development program once the winner of the competition is determined."-152

In early July the Navy began to raise questions about the various airframe proposals. For instance, the BuAer electronics group did not believe the Bell design had a satisfactory electrical power system, and Navy researchers rated the North American design last from an equipment (e. g., life support) perspective. The Douglas and Republic designs had the best potential flying qualities, and BuAer researchers felt that North American had incorrectly assumed laminar flow over much of their design, and had therefore underestimated the heating values. It was a bit late to be raising concerns, but most of the issues were minor and did not materially affect the outcome of the competition. After conferring with his Air Force and NACA counterparts, on 15 July George Spangenberg finalized the Navy’s position as Douglas, North American, Republic, and Bell.-1153!

On 26-28 July, the Air Force, NACA, and Navy evaluation teams met at Wright Field to select an airframe contractor. George Spangenberg stated that it was unfortunate that the point system used in the evaluation "appeared to give no conclusive winner," since a contractor could score highly in one area and low in another yet still have a winning score, while another that was satisfactory in all areas would be rated lower. He also indicated that the goals of the project seem to have shifted somewhat, resulting in a "firm requirement" for 1,200°F skin temperature research instead of the previous "desire" for high temperatures.-1154!

Presaging events to come, discussions ensued concerning the amount of work recently awarded to North American and Republic, and whether additional awards would spread their engineering groups too thin. Other discussions included the possibility of selecting Douglas but directing it to redesign its aircraft using an Inconel hot structure instead of magnesium. In the end, the Air Force and the NACA concluded that the North American proposal best accommodated their requirements. The Navy did not want to cast the only dissenting vote and, after short deliberation, agreed to go along with the decision.-11551

During the week of 1-5 August 1955, the WADC Project Office prepared the final evaluation summary and oral presentation: "the evaluation of the proposals submitted in competition was made in five areas: performance, technical design, research suitability, development capability, and cost." It is interesting to note that this competition was not about the "lowest bidder," and none of the proposals were anywhere near the original $12.2 million estimate. The results of these evaluations were as follows:!156!

Performance: The performance evaluation consisted of a check of the probability of the different designs, considering present uncertainties, of meeting the specified speed and altitude requirements. The probabilities were calculated to be best for the North American proposal, equal for the Bell and Douglas proposals, and least for the Republic proposal; but because of the assumptions of the analysis, all designs were judged able to meet the requirements.

Technical Design: This factor was judged on the awareness shown by the contractor of the problems of high-speed, high-altitude flight and of the means, as indicated by the airplane designs, the contractor proposed for exploring and studying these problems. The general design competency of the contractor also was judged from the designs submitted: North American 81.5 points; Douglas 80.1 points; Bell 75.5 points; and Republic 72.2 points. No design, as submitted, was considered safe for the use intended. The Douglas design was considered best in this regard, but did not include adequate margins for ignorance factors and operational errors.

Research Suitability: In this area, the fundamental differences in the proposed structures were examined and rated because of their decisive importance in the research uses of this aircraft. North American was rated acceptable because of the Inconel X "hot-structure" heat­sink, which was most suitable for research and which was potentially the simplest to make safe for the mission. Republic and Bell were considered unsatisfactory because of the hazardous aspects associated with the insulated structures used, and Douglas was considered unsatisfactory because of the low safety margins available and because of the limited future usefulness of the "cool" magnesium heat-sink principle.

Development Capability: Ratings were based on the physical equipment and manpower the contractor had available for pursuing the project, and the resulting time proposed for development. Evaluation of this factor resulted in the following ratings: (1) Douglas was acceptable; (2) North American was acceptable; (3) Bell was less acceptable; (4) Republic was less acceptable. North American, Republic, and Douglas estimated that the first flight date would be within 30 months, but the Republic estimate was not believed to be credible, hence their lower score. Bell promised a first flight date within 40 months.

Costs: Costs for three aircraft plus static test article, engines, and spares as adjusted by AMC to a comparable basis are: Bell, $36.3 million; Douglas, $36.4 million; Republic, $47.0 million; and North American, $56.1 million.

On 9 August, Captain McCollough presented the results of the evaluation to Brigadier General Howell M. Estes, then chief of the Weapons Systems Division, under whose jurisdiction the WADC Project Office fell, and a select group of senior Air Force officers. McCollough made a second presentation in Baltimore on 11 August for Generals John W. Sessums and Marvin C. Demler, who were the commanders of the WADC and ARDC, respectively, and Hartley Soule from the NACA.-157

The final briefing to a combined meeting of Air Force, NACA, and Navy personnel was at NACA Headquarters on 12 August. The attendees included Hugh Dryden, Gus Crowley, Ira Abbott,

Richard Rhode, and Hartley Soule from the NACA; Brigadier General Kelsey, Colonel Donald H. Heaton, Lieutenant Colonels Gablecki and Maiersperger, and Major Heniesse from the Air Force; and Captain R. E. Dixon, Abraham Hyatt, and George Spangenberg from BuAer. Following this, the Research Airplane Committee met, accepted the findings of the evaluation groups, and agreed to present the recommendation to the Department of Defense.-1158!

Because the estimated costs submitted by North American were far above the amount tentatively allocated for the project, the Research Airplane Committee included a recommendation for a funding increase before signing the final contract. A further recommendation-one that would later take on greater importance-called for relaxing the proposed schedule by up to 18 months. The committee approved both recommendations and forwarded them to the Assistant Secretary of Defense for Research and Development.

Three companies-Aerojet, Bell, and Reaction Motors-submitted proposals for the X-15 engine on 9 May 1955, the same day as the airframe competitors. North American had already asked the Air Force and NACA to dismiss the NA-5400 as an alternative. A copy of the Aerojet XLR73 proposal could not be located.

Bell was conservative in its engine proposal and stated that "modifications have been limited to those necessary to permit the engine to be used in a piloted aircraft." The changes to the XLR81 were made primarily in the starting and control systems, mostly to provide additional safety margins. The modified engine would be capable of multiple starts with a safety system based on a similar device provided for use during ground testing. The modifications provided an engine that could operate at an 8,000-lbf thrust level in addition to the normal 14,500-lbf full thrust. The modifications included the addition of a propellant bypass valve just in front of the injector so that, at the reduced thrust level, approximately one-half of the propellants would return to the tanks instead of being injected into the thrust chamber. This eliminated the need to change the pump discharge pressures, and allowed the same amount of propellants to flow through the cooling system. Only one engine in each airplane would have the capability to provide the 8,000- lbf level, although this reflected the removal and capping of the bypass valve and not any major change in engine configuration. Bell also proposed changing the fuel as a safety measure. In an attempt to minimize the risk of mixed propellants accumulating and exploding, Bell wanted to exchange the jet fuel normally used in the XLR81 with a mixture of 40% unsymmetrical dimethylhydrazine (UDMH) and 60% jet fuel (Bell called this combination "JP-X"). This would make the two propellants hypergolic, eliminating the hazard. Bell also pointed out that these propellants would not need to be topped off from the carrier aircraft, since neither had an appreciable vaporization rate. Bell noted that "since tests of the major components of the XLR81-BA-1 engine have been successful, extensive development tests of these components will not be required for the X-15 engine program."10

Like the Bell proposal, the proposal from Reaction Motors was brief (Bell used 15 pages, and Reaction Motors used just 14). The XLR30 would be modified to "1) emphasize safety and minimum development time, 2) start, operate and shutdown at all altitudes and attitudes, and 3) be capable of at least five successive starts without servicing or manual attention other than cockpit controls." Instead of the thrust-stepping proposed by Bell, Reaction Motors offered an infinitely variable thrust ranging from 13,500 to 50,000 lbf at sea level. Reaction Motors believed that "the highly developed state of the major engine components, i. e., turbopump, thrust chamber and control valves allows RMI to meet the schedule…." Unlike Bell, which extensively discussed the modifications required to make its engine meet the X-15 requirements, Reaction Motors instead gave a technical overview of the XLR30, and it was not possible to determine what the modifications were. Nevertheless, the overall impression was that the state of XLR30 development was far along.-1111

As the X-15 program moved on to higher and faster flights, support became more difficult because it required more time to travel to the sites and more lakes for each flight. The minutes of the X-15 Operations Subcommittee on 9 March 1961 give some insight into the coordination required. The subcommittee membership included Richard J. Harer, Colonel Bud Anderson, Major Robert M. White, Major K. Lewis, Captain J. E. Varnadoe, Lieutenant R. L. Smith, Captain F. R. O’Clair, Joseph R. Vensel, Stanley P. Butchart, C. E. Sorensen, and Lieutenant Commander Forrest S. Petersen. White and Petersen were X-15 pilots, and several of the other members had long and distinguished flying careers (especially Anderson and Butchart), so the group was not without a certain amount of applicable expertise.-1961

The previous October Paul Bikle had written a letter to the X-15 Operations Subcommittee and the AFFTC outlining an increase in support that would be required as the X-15 program moved uprange to the more remote lakes. The letter provides insight into how complicated it really was to conduct X-15 flights. For instance, each of the uprange stations (Beatty and Ely) had an operating crew of eight people, and the Air Force had to arrange transportation for the crew "a few days prior to each X-15 flight and for their return to Edwards after the flight." Given that NASA frequently scheduled flights once per week, this required a constant movement of personnel. Beatty supported all launches, while the program only used Ely for the high-speed flights scheduled out of Wah Wah Lake beginning in June 1961.[97]

The subcommittee did not think that supporting Hidden Hills launches would place any additional burden on the AFFTC since the effort required was generally similar to that needed for Silver Lake. However, flights from Mud Lake and farther uprange would require a much greater level of support. In its letter, NASA increased the amount of support requested, largely based on the unknown factors of never having launched from uprange. The AFFTC agreed that the equipment and personnel requirements for the uprange lake sites (as listed in the NASA letter) were valid and, at least initially, appropriate. The Air Force hoped, however, that subsequent experience could reduce some of the requirements.[98]

One of the attachments to Bikle’s letter provided the details of the support he was requesting.

This example uses a launch from Wah Wah Lake because it was the most comprehensive. The X – 15 launch would take place 20 miles north of Wah Wah Lake and would require the X-15, NB-52, and two chase aircraft. An emergency team would be located at Wah Wah Lake in case the X-15 engine did not start or some other emergency required an immediate landing. This team would consist of two Air Force 500-gallon fire trucks, an H-21 helicopter, eight firemen, an Air Force pilot as lake controller, an Air Force crew chief, an Air Force doctor, an Air Force pressure-suit technician, and a NASA X-15 specialist. Delamar Lake, the next contingency landing site, was 120 miles away. One Air Force 500-gallon fire truck, four firemen, four Air Force flight crew, two Air Force paramedics, and a NASA X-15 specialist would staff it. A Jeep would carry a nitrogen purge system to safe the X-15 after landing. One hundred and fifteen miles closer to Edwards was Hidden Hills, the primary emergency site in case the pilot had to shut down the engine early. Orbiting this lake were two F-104 chase aircraft that were intended to pick up the X-15 as it slowed down at the nominal end-of-mission, but could also provide assistance in the event of emergency. An Air Force C-130 waited on the lake to evacuate the X-15 pilot in case of an emergency landing, along with an Air Force 500-gallon fire truck, four firemen, two pilots, four Air Force flight crew, two Air Force paramedics, and a NASA X-15 specialist.-1991

Back at Edwards, the NASA radio van, an H-21 helicopter, the NASA lake controller, two Air Force fire trucks, eight firemen, two Air Force flight crew, the Air Force flight surgeon, a pressure-suit technician, and a NASA X-15 specialist awaited. In addition, staged between Wah Wah Lake and Delamar were a NASA-provided Jeep and three NASA X-15 specialists in case the X-15 had to set down unexpectedly at a lake other than those manned for the flight. An F-104 also orbited between Delamar and Hidden Hills to provide chase if the X-15 had to slow down during mid­flight. It was a complex ballet.

As it turned out, however, the increase in support that NASA was requesting was not possible. For instance, NASA wanted three C-130 aircraft and four paramedics dedicated to each launch, but the AFFTC did not have these resources. The AFFTC only had four C-130s assigned, and two were normally at El Centro supporting activities at the National Parachute Range. The base flight surgeon indicated that he believed it would be acceptable to provide a capability for a flight surgeon to be on the scene of an accident "within one hour," and the AFFTC adopted this suggestion. In general, however, the level of support provided by the AFFTC was consistent with that requested by Bikle; it differed primarily in some convenience items, not in essential services. On the other hand, NASA had proposed sending crews to the uprange sites the morning of each flight (meaning in the dark, since the X-15 often flew near first light). The AFFTC believed it was easier to send the uprange crews up the day prior to each flight. In most cases the personnel stayed in hotels in the towns near the support sites and reported to the site by 0800 hours in order to be ready by 0830 to support a 0900 takeoff of the NB-52.[100]

By early 1961 the X-15 Operations Subcommittee reported that security restrictions concerning Groom Lake seemed to be easing, and everybody agreed that Groom Lake was a preferable landing site compared to Delamar Lake. The program hoped to gain permission to use Groom Lake in the future, and Captain Varnadoe agreed to contact the appropriate offices to determine the likelihood of that happening. As it ended up, although one black project (the U-2) was ending at Groom, another (the Blackbird) was getting set to begin, and the X-15 program never would obtain permission to use the lakebed.[101]

By this time the Edwards and Beatty sites of the High Range were operational and had supported 34 X-15 flights. The Ely station became operational in April 1961. One of the concerns of the X – 15 Operations Subcommittee involved directing rescue forces to a downed X-15 pilot. The H-21 rescue helicopters did not have onboard navigation equipment, and required direction to within five miles of the crash site. From that point they could use radio homing equipment to find the rescue beacon on the pilot. The beacon itself was relatively new and at that time NASA had only installed it on X-15-2; however, it would later install the beacon on the other two airplanes. North American had promised a 30-mile range for the beacon, but testing at Edwards revealed much less capability. The beacon was returned to North American and discovered to have only half­power in its battery (range is a square function, so this resulted in only one-quarter of the projected distance). The H-21 used an AN/ARA-25 direction (homing) finder to locate the beacon. The subcommittee believed it would be desirable to install an ARA-25 receiver on the NB-52s also to allow the carrier aircraft to locate the pilot and direct the H-21s to the site. In addition, the NASA budget included funds to install auto-trackers on the High Range telemetry antennas. Once installed, the antennas could be set to 2.443 MHz and automatically track the pilot rescue beacon.[102]

Jah *<вє

Each X-15 pilot was issued a typed summary of lakebed information, along with hand-drawn sketches of the lakes and the marked runways. These were the lakes available in January 1966. (North American Aviation)

handled by NASA, although an AFFTC crane would be provided to lift the airplane onto a flatbed trailer.-103-

The first 50 years of powered human flight were marked by a desire to always go faster and higher. At first, the daredevils-be they racers or barnstormers-drove this. By the end of the 1930s, however, increases in speed and altitude were largely the province of government-the cost of designing and building the ever-faster aircraft was becoming prohibitive for individuals.

As is usually the case, war increased the tempo of development, and two major conflicts within 30 years provided a tremendous impetus for advancements in aviation. By the end of World War II the next great challenge was in sight: the "sound barrier" that stood between the pilots and supersonic flight.

Contrary to general perception, the speed of sound was not a discovery of the 20th century. Over 250 years before Chuck Yeager made his now-famous flight in the X-1, it was known that sound propagated through air at some constant velocity. During the 17th century, artillerymen determined that the speed of sound was approximately 1,140 feet per second (fps) by standing a known distance away from a cannon and using simple timing devices to measure the delay between the muzzle flash and the sound of the discharge. Their conclusion was remarkably accurate. Two centuries later the National Advisory Committee for Aeronautics^1 (NACA) defined the speed of sound as 1,117 fps on an ISO standard day, although this number is for engineering convenience and does not represent a real value.-12!

The first person to recognize an aerodynamic anomaly near the speed of sound was probably Benjamin Robins, an 18th-century British scientist who invented a ballistic pendulum that measured the velocity of cannon projectiles. As described by Robins, a large wooden block was suspended in front of a cannon and the projectile was fired into it. The projectile transferred momentum to the block, and the force could be determined by measuring the amplitude of the pendulum. During these experiments, Robins observed that the drag on a projectile appeared to increase dramatically as it neared the speed of sound. It was an interesting piece of data, but there was no practical or theoretical basis for investigating it further.-13!

The concept of shock waves associated with the speed of sound also predated the 20th century. As an object moves through the atmosphere, the air molecules near the object are disturbed and move around the object. If the object passes at low speed (typically less than 200 mph), the density of the air will remain relatively constant, but at higher speeds some of the energy of the object will compress the air, locally changing its density. This compressibility effect alters the resulting force on the object and becomes more important as the speed increases. Near the speed of sound the compression waves merge into a strong shock wave that affects both the lift and drag of an object, resulting in significant challenges for aircraft designers.!41

Austrian physicist Ernst Mach took the first photographs of supersonic shock waves using a technique called shadowgraphy. In 1877 Mach presented a paper to the Academy of Sciences in Vienna, where he showed a shadowgraph of a bullet moving at supersonic speeds; the bow and trailing-edge shock waves were clearly visible. Mach was also the first to assign a numerical value to the ratio between the speed of a solid object passing through a gas and the speed of sound through the same gas. In his honor, the "Mach number" is used as the engineering unit for supersonic velocities. The concept of compressibility effects on objects moving at high speeds was established, but little actual knowledge of the phenomena existed.-131

None of these experiments had much impact on the airplanes of the early 20th century since their flight speeds were so low that compressibility effects were effectively nonexistent. However, within a few years things changed. Although the typical flight speeds during World War I were less than 125 mph, the propeller tips, because of their combined rotational and translational motion through the air, sometimes approached the compressibility phenomenon.-131

To better understand the nature of the problem, in 1918 G. H. Bryan began a theoretical analysis of subsonic and supersonic airflows for the British Advisory Committee for Aeronautics at the Royal Aeronautical Establishment. His analysis was cumbersome and provided little data of immediate value. At the same time, Frank W. Caldwell and Elisha N. Fales from the Army Air Service Engineering Division at McCook Field in Dayton, Ohio, took a purely experimental approach to the problem.171 To investigate the problems associated with propellers, in 1918 Caldwell and Fales designed the first high-speed wind tunnel built in the United States. This tunnel had a 14-inch-diameter test section that could generate velocities up to 465 mph, which was considered exceptional at the time. This was the beginning of a dichotomy between American and British research. Over the next two decades the United States—primarily the NACA—made most of the major experimental contributions to understanding compressibility effects, while the major theoretical contributions were made in Great Britain. This combination of American and British investigations of propellers constituted one of the first concerted efforts of the fledgling aeronautical community to investigate the sound barrier. 181

Within about five years, practical solutions, such as new thin-section propeller blades (made

practical by the use of metal instead of wood for their construction) that minimized the effects of compressibility, were in place. However, most of the solution was to avoid the problem. The development of reliable reduction-gearing systems and variable-pitch, constant-speed propellers eliminated the problem entirely for airplane speeds that were conceivable in 1925 because the propeller could be rotated at slower speeds. At the time, the best pursuit planes (the forerunners of what are now called fighters) could only achieve speeds of about 200 mph, and a scan of literature from the mid-1920s shows only rare suggestions of significantly higher speeds in the foreseeable future. Accordingly, most researchers moved on to other areas.-19

The public belief in the "sound barrier" apparently had its beginning in 1935 when the British aerodynamicist W. F. Hilton was explaining to a journalist about high-speed experiments he was conducting at the National Physical Laboratory. Pointing to a plot of airfoil drag, Hilton said, "See how the resistance of a wing shoots up like a barrier against higher speed as we approach the speed of sound." The next morning, the leading British newspapers were referring to the "sound barrier," and the notion that airplanes could never fly faster than the speed of sound became widespread among the public. Although most engineers refused to believe this, the considerable uncertainty about how significantly drag would increase in the transonic regime made them wonder whether engines of sufficient power to fly faster than sound would ever be available.-110!

John Stack, head of the Compressibility Research Division at NACA Langley, was one of the driving forces behind the original set of experimental airplanes, such as the Bell X-1 and Douglas D-558 series. Although he lent expertise and advice to the groups developing the X-15, he remained in the background and did not repeat the pivotal roles he had played on earlier projects. (NASA)

characteristics of the test sections. However, the beginning of the Second World War increased the urgency of the research. Therefore, on a spring morning in 1940, John V. Becker and John Stack, two researchers from the NACA Langley Memorial Aeronautical Laboratory in Hampton,

Virginia,11 drove to a remote beach to observe a Navy Brewster XF2A-2 attempting to obtain supercritical aerodynamic data in free flight over Chesapeake Bay. After it reached its terminal velocity in a steep dive—about 575 mph—the pilot made a pull-up that was near the design load factor of the airplane. This flight did not encounter any undue difficulties and provided some data, but the general feeling was that diving an operational-type airplane near its structural limits was probably not the best method of obtaining research information.-112!