Category X-15 EXTENDING THE FRONTIERS OF FLIGHT

Because the research program was the rationale for the X-15’s existence, flights to obtain basic aero-thermo data began as soon as North American and the government were sure the airplane was relatively safe for its intended purpose. Nevertheless, almost from the beginning, the airplanes carried a few minor experiments that had little to do with its basic aero-thermo research objectives; the B-70 emission coating and a radiation detector were early examples. Still, the first couple of years of the flight program were primarily dedicated to expanding the flight envelope and obtaining the basic data needed by aerodynamicists to validate the wind-tunnel predictions and theoretical models used to build the X-15.

As this goal was increasingly satisfied, more X-15 flights carried unrelated experiments, such as

tests of ablative materials and star trackers for the Apollo program. Usually these experiments required little support from the X-15 itself, other than some power and recording capacity. Later in the program, flights began to be conducted for the sole purpose of supporting the "follow-on" experiments, although even these usually gathered aero-thermo or stability and control data to support continued evaluation. In reality, the X-15 as an experiment ended sometime in 1963 (except for the advanced X-15A-2); after that, the airplane was mostly a carrier for other experiments.

With the appearance of high-performance aircraft and missiles during the mid-1950s, designers began to be concerned with the effects of a turbulent boundary layer on the performance of optical equipment. As early as 1956, wind-tunnel researchers determined that the effects of a narrow beam of light through a turbulent boundary layer were a function of the free-stream Mach number and the density of the stream. The effects of this "light spreading" on the accuracy of star trackers were studied by Autonetics in 1957 and again by North American in connection with the B-70 program. Researchers observed the first actual effects of aerodynamics on aerial photography in 1957 when pictures taken from a McDonnell RF-101 Voodoo at Mach 1.4, viewed stereoscopically, provided a false evaluation of the terrain. This led the Army Corps of Engineers to award a contract to Vidya (a division of Itek Corporation) during 1959-1960 to develop a theory that explained the phenomena. The Navy sponsored similar work at MIT during 1959 to determine the degrading effects of turbulent flow on the resolving power of cameras.1991

instrumented aerial cameras and multiple boundary-layer rakes.-1100!

Officially called the "induced turbulence experiment," this project sought "to determine the effects of aerodynamics associated with supersonic and hypersonic aircraft, typified by the X-15 research airplane, on the performance of (1) a high-acuity modern camera set, exemplified by the Fairchild KS-25, and (2) a cartographic camera, exemplified by the Fairchild KC-1." The cartographic aspects of the experiment were of interest to the U. S. Army Corps of Engineers, while the Air Force was interested in the possible effects on tactical and strategic aerial reconnaissance. This experiment also used data collected by the small two-camera package installed in X-15-2 as part of experiment #27.101

This program was very involved, and significantly funded under an Air Force contract to North American as part of Project 6220, Photographic Reconnaissance Technology. The Reconnaissance Division of the Air Force Avionics Laboratory under the direction of Donald I. Groening coordinated the experiments. Two principle subcontractors were also involved: Aeroflex Laboratories fabricated parts for the ART-15A stabilized mount, and Vidya provided theoretical and image analysis. Fairchild Camera and Instrument Corporation provided the KS-25 camera under a separate Air Force contract. The Hycon Manufacturing Company provided the camera lens and conducted resolution testing, and the Cornell Aeronautical Laboratory assisted in determining the final target design.-102!

Phase I

The Army Corps of Engineers and the ASD jointly sponsored Phase I. The initial requirement was for three separate flight profiles: high-speed, high-altitude, and one that mimicked the Mach 3 B-70 bomber. The exact profiles were important because the launch lakes had to be established well in advance of the flights so that the Air Force could erect 6 to 10 photo targets along the flight path. This involved removing yet more land from the public domain. The B-70 profile placed another constraint on the program because it required flying the XLR99 at 40% thrust, and the early engines were incapable of doing this reliably. There was also a desire to photograph the same targets during Phase II.103

The launch lakes were Delamar and Smith Ranch. The targets would be located along the flight path from Delamar to Edwards with single three-bar targets located near Pahrump and Indian Springs in Nevada, and two sets of three targets straddling the flight path at Pilot Knob and Cuddeback in California. The single target at Pahrump determined the performance of the camera primarily at the maximum altitude point on the high-altitude missions, while the single target at Indian Springs determined performance at the maximum speed point on the high-speed profile. Triple targets at Pilot Knob and Cuddeback allowed for accumulated navigation errors and measured performance at high-supersonic speeds. The Pilot Knob targets also measured the camera performance at the point of reentry from the high-altitude profile. Each target was a collection of white stripes of different widths on a black background (a standard Mil-Std-150A photo-calibration target pattern) with an additional large contract patch and two sharp edges normal to each other to determine the atmospheric attenuation and edge response. The Air Force called this the Delamar camera range.104

A photometric van from the Scripps Institute of Oceanography at the University of California was usually set up at the Pahrump site. This van had three photometers that measured the total sky radiance, solar radiance, and radiance of the surface of the target. Researchers located meteorological instrumentation near each target to provide compensation data for the analysis, and the Air Force launched standard radiosondes to support the experiment.105

The X-15 package for the cartographic program contained a KC-1 camera, an ART-15A stabilized mount, and photometric and environmental instrumentation to measure the conditions that prevailed during the time of the experiment. The KC-1 had been modified with a GEOCON I lens designed by Dr. J. Baker of Spica, Incorporated, to combine low distortion with relatively high acuity, and was adapted for operation at high altitude. The experiment package, minus the camera, weighed approximately 156 pounds. The KC-1 camera and lens added another 85-90 pounds depending on the film load, and occupied a space about 16 inches long by 18 inches wide by 21 inches high at the bottom of the instrument compartment. The GEOCON I low-distortion mapping lens had a focal length of 6 inches and a relative aperture of f/5.6, and could provide a resolution of 37 lines per millimeter on Super-XX film. North American modified X-15-1 to accept a KC-1 camera, including modification of the ART -15 mount and the addition of an 18- inch-diameter window that was 1.5 inches thick in the bottom of the instrument compartment. The film was nominally 9 by 9 inches, and 390 feet of it were stored in the magazine.-1106!

PHOTOGRAPHIC INSTALLATION

KC-1 CAMERA WITH GEOCON I LENS

PHOTOMETERS

(10° AND SCATTERED TIGHT)—i

PH CTO MEIER AN;’

SPECTROMETER

KS-25 CAMERA

PHOTO METERS

[10° AND SCATTERED LIGHT

PHOTOMETER AND

j^CTROMETER

The Photo Optical Degradation Experiment (#5) was used to determine the degradation of optical
imagery caused by supersonic and hypersonic shock waves, boundary layers, and rapid frictional heating of the photographic window. Several different experimental packages were employed using well-instrumented aerial cameras and multiple boundary-layer rakes. Two different camera systems were installed in the X-15 for the experiment. (NASA)

Bob Rushworth flew the first flight (1-33-54) with the KC-1 on 11 April 1963 and NASA shipped the exposed film to Westover AFB in Massachusetts for processing. The last of six flights (1-38­81) was made on 18 July 1963, again with Rushworth as the pilot. The majority of the detailed results are still classified, but a general overview is given in the Phase II discussion.-107

Paul F. Bikle was born on 5 June 1916 in Wilkensburg, Pennsylvania, and graduated from the University of Detroit with a bachelor of science degree in aeronautical engineering in 1939. His career with the Army Air Forces began in 1940 when he became an aeronautical engineer at Wright Field, and in 1944 he became chief of the aerodynamics branch of the Flight Test Division. While working closely with other government agencies in establishing the first flying qualities specifications for aircraft, he wrote AAF Technical Report 50693 ("Flight Test Methods"), which was used as a standard manual for conducting flight tests for more than five years. During World War II he was involved in more than 30 test projects and flew over 1,200 hours as an engineering observer.

In 1947, Bikle became chief of the performance engineering branch and directed tests of the XB – 43, XC-99, and F-86A. When the flight-test mission was transferred to the newly formed Air Force Flight Test Center (AFFTC) at Edwards, Bikle came to the desert and advanced to assistant chief of the flight-test engineering laboratory in 1951. From there, he advanced to the position of AFFTC technical director. He replaced Walt Williams as director of the NASA Flight Research Center (FRC) in September 1959. Like Williams, Bikle had little use for unnecessary paperwork, and often remarked that he would stay with NASA as long as the paperwork level remained below what he had experienced in the Air Force. He was also an avid soaring enthusiast and established two world soaring records during a flight near Lancaster on 25 February 1961 that still stands as of 2006. In July 1962, Bikle received the NASA Medal for Outstanding Leadership for directing the "successful X-15 flight operations and research activities," and he received the 1963 FAI Lilienthal Medal. Bikle retired from NASA in May 1971 and died on 20 January 1991.[6]

Al White was the second contractor pilot assigned to the X-15 project. He participated in the centrifuge program, attended the training sessions, flew the fixed-base simulator, practiced the landing-approach flights, and flew the photo chase airplane for many of the early X-15 flights. White never flew the X-15.

Alvin S. White was born in December 1918 in Berkeley, California. In 1936, he enrolled in the University of California at Davis to study electrical engineering, transferring to the Berkeley campus two years later. In 1941, he enlisted as an aviation cadet in the Army Air Corps, graduating from flight school at Williams Field, Arizona, in May 1942.[29]

After nearly two years as an advanced flight instructor at Williams Field, White joined the 355th Fighter Group in England on 4 June 1944. He flew two tours as a combat fighter pilot from D-Day until the end of the war in Europe. White returned to the University of California at the end of 1945, earning his degree in mechanical engineering with elective courses in aeronautical engineering in 1947.

In 1948, White reenlisted in the Air Force and spent nearly three years conducting parachute research at Wright-Patterson AFB and the National Parachute Range at El Centro. In 1952, White graduated from the Air Force Test Pilot School at Edwards and joined the fighter test section. In May 1954, he left the Air Force to join North American Aviation.

After four years of testing the F-86 series, the F-100 series, and the F-107, he became backup pilot to Scott Crossfield on the X-15. In 1957, White became project pilot for the XB-70, and concentrated his work on that program after the completion of the North American X-15 flights. After he retired from North American, White became a well-respected aviation consultant until his death on 29 April 2006.-130

During the development of the X-15, many wanted to expand the program beyond the three airplanes covered under the original agreements. This opinion obviously did not prevail, but the proposals are nonetheless of passing interest. Early on, North American suggested using X-15 as part of an extensive training program for astronauts and test pilots, believing that such a program could familiarize pilots with rocket-powered aircraft, the use of reaction controls, and the physiological sensations of space flight. The Air Force did not express any particular interest.-141

Early in 1958, researchers at the HSFS wanted to procure one additional X-15 for flight-control research, but NACA Headquarters did not concur. It was the first of several such proposals.142–

In mid-1958 the first serious proposal to expand the X-15 program came when Air Force Headquarters asked the ARDC if there was any merit to expanding the X-15 program. On 8 April 1958, headquarters requested recommendations for "configuration changes, estimated costs, aircraft availability, the increased performance expected, the test results to be obtained, and a brief substantiation of their value." Headquarters wanted the results of the study at an early date because it needed to make a decision before North American disbanded the engineering team.143–

The X-15 Project Office asked the AFFTC, North American, and WADC for recommendations. By 29 April, these organizations concluded that the best approach would be to improve performance using new structural materials and an improved rocket engine instead of the XLR99. The development difficulties with the XLR99 apparently influenced the call for a new engine, although the WADC suggested that any new engine should "be obtained as a result of across the board BMD [Ballistic Missile Division] and other efforts, and not as a sole X-15 effort."144-

The Navy verbally concurred with expanding the program on 19 May, and the NACA agreed a day later. On 13 June the X-15 Project Office recommended to the ARDC that three additional airplanes be constructed using higher-temperature structural materials than those used in the original design. The ARDC forwarded this recommendation to Air Force Headquarters on 16 June.145-

Apparently, the seeming urgency in the 8 April letter from headquarters had evaporated. On 18 November 1958, Major General Marvin C. Demler, director of research and development at Air Force Headquarters, finally informed the ARDC that the X-15 program would not be expanded. In the interim, the Research Airplane Committee had met on 31 October and Hugh Dryden concluded the three original airplanes were adequate for NASA’s purposes. Ultimately, the Research Airplane Committee recommended against procuring additional airplanes.146

There was, however, another fleeting prospect. After an explosion seriously damaged the X-15-3 during an XLR99 ground test, the X-15 Project Office had to solicit additional funds from the Pentagon to rebuild the aircraft. This prompted a renewed interest in the X-15 and the data it might deliver for future use in the Air Force space program. On 12 August 1960, Air Force Headquarters ordered a complete review of the X-15 program. The X-15 Project Office presented its results at the 17-18 October 1960 X-15 program review. The briefing identified original program objectives that were no longer valid, new objectives to consider, continuing objectives, and funding requirements. Surprisingly, the general officers who were briefed agreed that the X – 15 promised to be considerably more important to the Air Force space effort than had been foreseen when the program was initially conceived in 1954, or when the program expansion was rejected in late 1958. The Pentagon advised the ARDC that it would "entertain" proposals for additional X-15s to be operated exclusively by the Air Force.

As part of the ongoing discussion, the AFFTC put together its own recommendation for the program. On 26 October 1960 the AFFTC released a report that called for three additional X-15s and one more NB-52 "to carry out R&D objectives not presently covered by the present NASA-AF – Navy X-15 program." The AFFTC expected to "own and operate" these aircraft. Based on a 1 January 1961 start, the AFFTC expected the first aircraft to be delivered (along with a third NB-52) in September 1961, with the others following in March and June 1962. The flight program was to average 60 flights per year through December 1965. Some of the research objectives for the new aircraft included flight control and guidance, aero-thermo-elasticity, supersonic boundary-layer turbulence, sonic fatigue, landing-impact data, and electromagnetic propagation. The AFFTC expected that it would need an additional 330 people to support the X-15, plus 37 more to operate the High Range during AFFTC flights.147

Another proposal, originating from Brigadier General Donald R. Flickinger at ARDC Headquarters, was for a two-place biomedical research version of the airplane.-1148!

The Air Force called a meeting at Wright Field on 14 November that brought together representatives from the ARDC, the WADC,149 the command and control division of the Air Force Cambridge Research Laboratories, and the Army Corps of Engineers.-1501 It was immediately apparent to the X-15 Project Office that if all of the stated requirements for X-15-type aircraft were to be satisfied, "several additional X-15s will be required." Two weeks earlier the government had notified North American of the meeting, and Charlie Feltz prepared a briefing outlining several advanced X-15 configurations. Feltz presented his briefing on the afternoon of 14 November and provoked further interest in a comprehensive extension program.151

Although a two-seat X-15 engineering study had been required in the original proposals, the government had not taken any action on the idea. Nevertheless, it loomed in the background during much of the early X-15 program. The variant shown during the November 1960 meeting differed somewhat from the one originally proposed. North American optimized this version for "space training and biomedical research." Instead of simply deleting the research instrumentation and extending the canopy over the second cockpit, the new configuration extended the fuselage by approximately 14 inches and added a second cockpit with a separate canopy. The company deleted the aero-thermo research equipment, but the extension provided space for a variety biomedical equipment.-1152

North American environmentally separated the second cockpit from the primary cockpit so that it could study alternate atmospheres (i. e., not nitrogen-purged). A separate set of dummy controls could be installed that would allow the second pilot to react independently from the pilot flying the aircraft. His responses would be recorded and reconstructed on the ground to evaluate performance under acceleration and weightless conditions. It was expected that flight profiles could be developed that would allow five minutes under essentially weightless conditions during flights to altitudes in excess of 500,000 feet. The change added 354 pounds to the aircraft, but the use of an uprated XLR99 would have increased performance by 120 fps.[153]

The meetings resulted in NASA rearranging the existing X-15 program slightly to accommodate the Air Force research priorities, and relegating excess work to the new research extension program. The product was a revised System 605A plan released on 1 February 1961. Essentially, the X-15 Project Office requested approval for the construction of two additional aircraft, both of them slightly stretched two-seat versions similar to one proposed by Charlie Feltz in November. For the moment, the question of additional single-seat aircraft or advanced models was not considered pressing and was deferred. The two-seat aircraft would satisfy the need for biomedical research and training of future aerospace research pilots and Dyna-Soar astronauts.-1154

The idea was short-lived. On 20 March 1961, Major General Marcus F. Cooper, chief of research and engineering at ARDC Headquarters, disapproved the development plan. Cooper instructed the X-15 Project Office to revise the existing (October 1960) development plan to reflect funding changes proposed by the Pentagon. Nevertheless, in one paragraph Cooper instructed Wright Field to "give consideration to the election of the best type of vehicle to use in training future

Aerospace Research Pilots___ The possibility of using the existing X-15s for this purpose after

completion of the test program should be explored. In addition the need for additional X-15 aircraft or other vehicles, such as Dyna-Soar, for this purpose should be considered." The concept could potentially require additional X-15s.[155]

Although this kept hopes alive for an expanded X-15 program, it essentially buried the two-seat X-15. As Cooper explained, funding shortages for FY61 and FY62 would prevent "the additional heavy funding required in those years to support the proposed additional X-15 aircraft." It had also become apparent that the existing X-15s, with some additional equipment and telemetry installations, could acquire the majority of the desired biomedical data at far less cost. The X-15 Project Office had also begun to worry that stretching the X-15 fuselage might involve more engineering and development work than anticipated, although the subsequent development of X – 15A-2 proved this concern to be unfounded.-156

The ARDC Commanders Program Management Review in March 1961 tasked the X-15 Project Office to review "identified problem areas which might require investigation by X-15 type aircraft with particular attention given to the relationship between the problem areas and presently authorized advanced aerospace programs and studies." The response indicated that two additional single-place X-15s would be useful for investigating a variety of Air Force-specific areas of interest. The ARDC rejected this recommendation on 2 August 1961, and all thoughts of additional X-15s seemed to fade.-152

As near as can be determined, the three X-15s spent their entire career in and around Edwards, except for the occasional trip back to Inglewood to be repaired or modified. There was one exception, part of Project Eglin 1-62. On 2 May 1962, Jack Allavie and Bob White, along with a pressure-suit technician and a B-52 crew chief, took the NB-52A and X-15-3 to Eglin AFB in Florida for the 4-hour-long "Air Proving Ground Center Manned Weapons Fire Power Demonstration" attended by President John F. Kennedy. According to Allavie, "[W]e took off with an inert X-15 and flew all the way to Eglin AFB in Florida… that’s 1,625 miles and it was a simple flight. We landed there, put the X-15 on exhibit, and then flew it back to Edwards" on 5 May with a stop at Altus AFB, Oklahoma, for fuel. Photographic evidence shows a mission marking on the NB-52A depicting an X-15 oriented in the opposite direction of the regular launches (indicating, one guesses, a flight eastward) and the inscription "PRES. VISIT EGLIN FLA." Although it was by far the longest captive carry of the program, NASA did not assign the flight a program flight number.[185]

Back at Edwards, during the summer of 1962 Bob White made three flights in X-15-3 that demonstrated the potential problems of matching the preflight profile. On the first flight (3-5-9), White became disoriented during the exit and decided that he needed to push the nose down slightly so that he could visually acquire the horizon: "When we got up to 32 degrees, and at about 60 seconds in time, I guess it was just a small case of disorientation. I say a small case because I didn’t lose complete orientation but when I was up at this climb angle, and this is the first time that I’ve had this feeling, I looked at the ball, I had 32 degrees in pitch, but I had the darndest feeling that I was continuing to rotate. I couldn’t resist the urge just to push on back down until the light blue of the sky showed up. I never did get to the horizon, but I was satisfied that it wasn’t happening." By the time he was satisfied and began his climb again, his energy was such that he undershot his planned 206,000-foot peak altitude by 21,400 feet.[186]

White’s next flight (3-6-10) was only nine days later. This one was much better. White undershot by only 3,300 feet, about average for the program. White reported that the weather obscured most of his view of the ground: "I did look around quite a bit, and I was a little disappointed because of all the low clouds that obscured the coast line. I took a couple of definite looks because I wanted to try and scan up further north, and down along the Mexican coast, and pick out some places, but the cloud cover was so extensive that I couldn’t really do that. Then too, when you’re up there it feels like everything’s right under the nose. It was reassuring again to hear ground saying you’re right on profile and track. That eliminates any concern on the pilot’s part."^

If it seemed that White was getting better at hitting his planned altitude, the next flight would dispel any such thoughts. On 17 July 1962, White took X-15-3 on a flight that was supposed to go to 282,000 feet, which was sufficient to qualify him for an Air Force astronaut rating. The MH – 96 failed just before launch, which probably should have meant scrubbing for the day. Instead, White reached over and reset the circuit breakers. The MH-96 appeared to function correctly, so White called for a launch. White seemed to be trying to make up for the altitude he had not achieved on his last two flights. The climb angle was a bit steeper than called for, and the engine produced a bit more thrust than usual and burned a bit longer than expected. The result was a flight that was 32,750 feet higher than planned, setting a new Federation Aeronautique Internationale (FAI) record for piloted aircraft of 314,750 feet and becoming the first winged vehicle to exceed 300,000 feet, the first flight above 50 miles, and the first X-15 flight that qualified its pilot for an astronaut rating. This time, as the first astronaut from Edwards, White was suitably impressed with the view:11881

You could just see as far as you looked. I turned my head in both directions and you see nothing but the Earth. It’s just tremendous. You look off and the sky is real dark. I didn’t think the impression would be much different than it was up around 250,000 feet, but I was impressed remarkably more than I was at 250,000 feet. It amazed me. I looked up and was able to pick out San Francisco bay and it looked like it was down over there off the right wing and I could look out, way out. It was just tremendous, absolutely tremendous. You have seen pictures from high up in rockets, or these orbital pictures of what the guy sees out there. That’s exactly what it looked like. The same thing.

White reentered and arrived over the high key at Mach 3.5 and 80,000 feet. The potential for a repeat of Armstrong’s excursion to Pasadena was present, but White had learned from Armstrong’s mistake: "I was mainly concerned at this time with the possibility of overshooting the landing point. I think that was my overriding consideration at this point. I went by the lake and turned it around, and when I went around in the turn I just pushed in on the bottom rudder so I could get the nose down and stay in where I had some q. I didn’t want any bounce in altitude. If I had gotten bounce, I would never have gotten back."11891

A wide sweeping turn over Rosamond brought White back to a more normal high key at 28,000 feet and subsonic speeds. He continued around for a near-perfect landing at 191 knots. Milt Thompson in the chase plane commented, "Nice, you really hit that… Bob," and Joe Walker in the NASA-1 control room finished by saying, "This is your happy controller going off the air." Despite having overshot the altitude by more than 10%, White flew the flight nearly perfectly, and data from this flight would be used for several years to check out and calibrate the fixed-base simulator.11901

The altitude missions demanded precise piloting, and even then, several variables beyond the control of the pilot could result in significant altitude errors. On 17 July 1962, Bob White took X – 15-3 on a flight that was supposed to go to 282,000 feet. The climb angle was a bit steeper than called for, the XLR99 produced a bit more thrust than usual, and it burned a bit longer than expected. The result was a flight that was 32,750 feet higher than planned, setting a new FAI record for piloted aircraft of 314,750 and becoming the first winged vehicle to exceed 300,000 feet, the first flight above 50 miles, and the first X-15 flight that qualified its pilot for an astronaut rating. (NASA)

Interestingly, this flight will probably remain an altitude record for airplanes as long as the FAI has a category for rocket-powered aircraft. In theory, it is possible to break the record one time. According to the rules, new records must exceed the old mark by 3%, meaning that somebody will have to fly at least 324,193 feet altitude to beat White’s record. However, according the FAI, the atmosphere ends at 328,099 feet (100 kilometers). Therefore, it will be impossible to better the subsequent record without going into space, which would disqualify the attempt (as happened with Joe Walker’s 354,200-foot flight). The chances of somebody managing to get above 324,194 feet without exceeding 328,098 feet are extremely remote. It has been 40 years and nobody has tried yet.[191]

technological contributions to the advancement of flight and for great skill and courage as test pilots of the X-15." By this point Crossfield had been gone for two years, and Petersen had already left to become the commanding officer at VF-154. Nevertheless, all four pilots journeyed to Washington to accept the trophy on the South Lawn of the White House. The National Aeronautic Association annually awards the Collier Trophy, which is generally considered the most prestigious recognition for aerospace achievement in the United States. In the case of the X-15, the selection of the recipients was not arbitrary; it represented the first pilot from each organization (North American, Navy, NASA, and Air Force) to fly the airplane. The trophy itself was 7 feet tall and weighed 500 pounds, and when Kennedy presented it to Bob White (the spokesman for the group), he commented, "I don’t know what you are going to do with it."[192]

Later the same day the Air Force presented White with his astronaut wings during a small ceremony at the Pentagon, and that evening NASA feted all four pilots at a dinner where they received the NASA Distinguished Service Medal from Vice President Lyndon B. Johnson. NASA administrator James E. Webb commented at the dinner that the X-15 program was "a classic example of a most effective way to conduct research."

Since the beginning, the X-15 program had used four North American F-100 Super Sabres as Chase-1. However, the F-100 was getting old, and the AFFTC was happy to begin receiving new Northrop T-38 Talons during October 1961. Pilots reported that the T-38 "appears as good or better than the F-100F for X-15 support." The Air Force conducted several test flights, sans the X-15, to evaluate whether the T-38 could fly close chase at 45,000 feet when the NB-52 was in a right-hand turn-something the F-100 could not do. Such a capability would allow a right-hand NB-52 pattern prior to a launch, and would greatly improve ground telemetry reception during that period since the NB-52 fuselage would not block the X-15-to-ground line of sight. The previously used left-hand pattern resulted in a loss of telemetry during the turn until approximately 2 minutes prior to launch, but allowed the F-100F to remain in a suitable chase position during activation of the X-15 systems. The problem was that during a right turn the F – 100 was on the inside of the turn and had to fly at a slow indicated airspeed. In a left turn on the X-15 side, the F-100 was on the outside of the turn, flying at a higher and more acceptable indicated airspeed. The first flight (1-32-53) to use a T-38 was in July 1962 and the T-38 would be Chase-1 for almost every flight until the end of the program.-1193

On 18 July 1962, president John F. Kennedy presented the Robert J. Collier Trophy to the X-15 program. The award was accepted by Scott Cross field, Forrest Peterson, Joe Walker, and Bob White in a ceremony on the South Lawn of the White House.. The trophy is seven feet tall and weighs 500 pounds. (NASA)

Previous X-planes had recorded all of the research data onboard, mainly because telemetry systems were in a very early state of development and bandwidth was very limited. Nevertheless, several earlier programs did telemeter a small amount of data to the ground in real time. It was decided early on that all X-15 data would continue to be recorded onboard the aircraft, although much more extensive use of telemetry would also be made. The reason for recording everything onboard was "to eliminate the risk of data loss and degradation inherent in radio-frequency telemetry links." This took on more significance for the X-15 program since the airplane would frequently be out of range of the antennas at Edwards, and would have to rely on the new and untried High Range installations at Beatty and Ely.-11

Initially, the instrumentation centered on the aero-thermo environment that the researchers intended the X-15 to investigate. When the follow-on experiments began to arrive, more of the instrumentation and recording capacity shifted to support non-aero-thermo investigations. A group of researchers from the HSFS, Langley, and Lewis-with limited input from the WADC and AFFTC-came up with the initial requirement for between 1,000 and 1,100 data points. Per the original specification, instrumentation was limited to 800 pounds and 40 cubic feet, and could use up to 2.25 kilowatts of power. The approved design included 1,050 instrumented points (588 thermocouples, 64 strain gages, 28 control surface position indicators, 136 aerodynamic surface pressures, 22 basic flight parameters (angle of attack, etc.) and 212 airplane condition monitors). By contrast, the X-2 had used only 15 thermocouples and a few electrical pressure transducers, and carried only 550 pounds of research instrumentation.-12!

In mid-1957, the NACA asked the Air Force to modify the X-15 specification to double the amount of research instrumentation carried by the airplanes. Given that North American had already frozen the design by that time, this came as something of a shock. In order to keep the airplane’s weight (and hence performance) from being too seriously degraded, numerous structural and subsystem details were redesigned to save weight.-13

When the X-15 emerged from North American, it could carry 1,300 pounds of research instrumentation, the majority of which were installed in a removable elevator in the instrumentation compartment just aft of the cockpit. Engineers designed the cabling so that they could remove the entire elevator from the airplane, which allowed them to perform all pre – and postflight calibrations more easily. Originally, the engineers intended this feature to remove the instrumentation from possible ammonia contamination, but NASA seldom used it for that purpose. Within the airframe itself, all of the wiring and tubing were routed through the fuselage side tunnels.-4-

In addition to the instrumentation compartment, North American installed small amounts of equipment in the nose of the airplane, in a center-of-gravity compartment located between the oxidizer and fuel tanks, and in the rear fuselage. The main instrumentation compartment and the nose compartment were pressurized and temperature-controlled. The center-of-gravity

compartment was temperature-controlled but unpressurized, and the rear fuselage area was insulated against high temperatures but was otherwise uncontrolled. Individual instruments and equipment were shock-mounted or hard-mounted as necessary; hard mounting was preferred because it saved weight and space.[5]

In many respects, X-15 development occurred at an awkward time. Modern data-processing systems were in their infancy, but they promised to offer a substantial improvement over the largely mechanical systems that had preceded them. However, the simple fact was that they were not ready. This forced the instrumentation engineers to rely on oscillographs and precision photographic recorders for the aircraft instead of modern magnetic tape recorders. Most of the rationale was simple: these devices were available from commercial sources or from NACA stock, lessening the cost of an already over-budget program. The program could also procure and test them within the time available before the first flight.

However, they came with some handicaps. The time associated with processing data from an oscillograph system, especially when large quantities of data were involved, was long and tedious compared to that required for data from magnetic tape systems. The instrumentation community debated this problem at length, but finally decided that the 15,000 data points expected to be collected on each flight would not result in processing times that would be detrimental to the planned flight schedule. It was also a fact that during 1956-1957, a costly, time-consuming development program would have been required to obtain a fully automatic magnetic tape system that could withstand the X-15 environment.-^

Despite the "design" instrumentation list, as manufactured the first two airplanes each had 656 thermocouples, 112 strain gages, 140 pressure sensors, and 90 telemeter pickups. The thermocouples were 30-gage chromel-alumel leads that were spot-welded to the inside surface of the skin. The leads connected to 20-gage extensions that were routed to the signal­conditioning equipment and recorders. The use of 20-gage extensions was necessary to reduce circuit resistance in the thermocouple loops and to minimize measurement errors due to resistance changes caused by the large temperature variations along the wire. Since the thermocouples were inaccessible after the airplanes were constructed, North American designed the installation to function for the life of the airplane and require no maintenance. A silicone – impregnated fiberglass braid covered the leads and extensions, and those in close proximity to the skin used an outer sleeve of unimpregnated fiberglass. The silicone impregnation slowly sublimated during repeated exposure to elevated temperatures, but retained its electrical insulating properties. Its use, however, created a potential problem since tests showed that out – gassing could result in an explosion if the temperature quickly rose to 1,200°F for the first time. NASA eliminated this hazard on the X-15 by gradually building up to the maximum Mach number during the course of the envelope-expansion program.-71

The first two airplanes used Bakelite strain gages, but these lost their effectiveness as structural temperatures increased. Consequently, North American completed X-15-3 with Micro-Dot weldable-type strain gages designed for use at higher temperatures. The static pressure taps consisted of 0.3125-inch-outside-diameter tubing installed flush with the outside surface of the skin. A study was made of the lag effects of a tube-connected system, and it was determined that 0.25-inch tubing with lengths as great as 40 feet was acceptable for gradual maneuvers and steady-state data at altitudes up to 100,000 feet.-81

either side. Because of installation difficulties, no instrumentation was located near the integral propellant tanks. Similarly, North American did not initially install any pressure instrumentation in the horizontal stabilizers due to the difficulty of running tubing to this location. However, the company did install some strain gages in the horizontal, with the wiring running through the pivot point. As part of a loads study late in the program, North American manufactured a new set of horizontal stabilizers with electrical pressure transducers, loads sensors, and thermocouples. Toward the end of the flight program, researchers also installed instrumentation in the wing-tip pods and ventral stabilizer on some flights.-191

Precision NACA recorders that employed servo-repeater systems to position a light source on moving film recorded angle-of-attack and angle-of-sideslip data provided by the ball nose. Similar devices recorded the attitude-angle outputs from the stable platform. Electrical transducers sensed all other data. A central patch panel in the main instrumentation compartment collected the data, routed it to appropriate signal conditioners, and then sent it to recording oscillographs and the telemetry set. The NACA-developed photo-oscillographs were capable of recording 36 channels each. Recording speeds could be varied from 0.25 inch per second to 4.0 inches per second, resulting in recording times ranging from 56 minutes to only

3.5 minutes using 70-foot film magazines. The photo-oscillographs used a blue-sensitive polyester-based thin film with the trade name Cronar®. A variety of 16-mm motion picture cameras photographed portions of the pilot’s instrument panel, and the wings and empennage during flight.1101

This block diagram shows the basic interrelationship of the various pieces of research instrumentation carried on the X-15. The exact instrumentation varied considerably between airplanes, and flight to flight. Late in the program the X-15-3 received a much more modern PCM telemetry system. (NASA)

Recorder limitations restricted the number of installed sensors that could be recorded simultaneously. A 12-channel oscillograph recorded 40 thermocouples per channel at 1-second intervals, and four manometer-oscillographs recorded up to 96 pressure transducers. A NACA – designed aneroid-type 24-cell film-recording manometer similar to those used in previous flight programs recorded the surface pressures. Again, recorder limitations restricted the number of pressure measurements that could be recorded simultaneously. The exact data recorded often differed on each flight as researchers and engineers connected different sensors to the recorders and telemetry system. A single switch in the cockpit turned on all of the recorders, and an event switch allowed the pilot to mark the recording when something significant occurred.[11]

Two separate cockpit instrument panels were supplied with each of the first two airplanes: one for the initial low-speed flights using the XLR11 engines and the nose-mounted flight-test boom, the other for hypersonic flights using the XLR99 engine and the ball nose. NASA significantly revised the instrument panel in the first two airplanes early in the flight program based on pilots’ comments that the original panel was difficult to scan under all flight conditions, especially when they were wearing the MC-2 full-pressure suit. As initially completed, X-15-3 had an instrument panel identical to the XLR99 panels manufactured for the first two airplanes. However, when North American rebuilt the airplane following its XLR99 ground explosion, the Air Force decided to incorporate the Minneapolis-Honeywell MH-96 adaptive flight-control system, and this necessitated a unique instrument panel. NASA subsequently replaced this panel late in the flight program with a set of vertical-tape displays developed by Lear-Siegler. All of the instrument panels were in a constant state of flux as various switches and indicators were added to almost any available location in the cockpit to support the various experiments and data requirements for any given flight. Every attempt was made to keep the critical displays and switches in constant locations between the three airplanes (at least as much as possible given the radical difference in X-15-3), and twice the program created a "standard X-15" cockpit arrangement and brought the airplanes into compliance. This greatly eased the problems associated with keeping the simulator accurate, and made life much easier for the pilots and flight planners.-1121

Initially, the X-15s used a pulse-duration modulation (PDM) telemetry system that researchers considered state of the art when they selected it. However, the system was insufficient for many types of data that researchers wanted to view on the ground (particularly the biomedical parameters), and the AFFTC Human Factors Subcommittee requested the installation of a more sophisticated FM-FM telemetry system. Initially, the FRC objected to the proposed change because of the size and volume requirements of such a system. However, on 2 December 1960 Paul Bikle stated that he favored the installation of a FM-FM system if it fit into the space then used by the existing North American telemetry system. By then, the state of the art allowed the Air Force to purchase a 12-channel FM-FM system for use in the biomedical package. NASA subsequently installed this system in the X-15s as needed to support biomedical work, and the first flights took place in late 1961.-131

In May 1967, NASA installed a modern pulse-code modulation (PCM) system in X-15-3. The first flight (3-58-87) for the new system was on 26 April 1967 with Bill Dana at the controls. By all accounts, the new system worked well and provided a great deal more bandwidth than the old PDM and FM-FM telemetry systems. It appears that NASA never updated the other two aircraft to PCM.1141

The Phase II experiment involved six data-gathering flights using X-15-1 beginning with flight 1-42-67 on 5 December 1963, again with Rushworth as the pilot. As it happened, this proved to the fastest flight by a basic X-15, reaching Mach 6.06. Jack McKay flew the last flight (1-49-77) of the experiment on 30 June 1964. Three checkout flights (1-39-62 through 1-41-65) had preceded the data-gathering flights.108

The purpose of the experiment was to obtain quantitative data to determine the effects of aero – thermo distortions associated with vehicles flying at hypersonic speeds and extreme altitudes. Researchers believed the results were directly applicable to the Lockheed A-12/SR-71 and North American B-70/RS-70 programs, and to "future hypersonic reconnaissance systems." The Air Force conducted similar experiments (albeit at much lower speeds) using Martin RB-57D aircraft and high-altitude balloons.109

The high-acuity experiment package was somewhat more sophisticated than the one flown during Phase I, replacing the original KC-1 camera with a more sensitive KS-25. In addition to the new camera on the same ART-15A stabilized mount, researchers installed a small analog computer that collected signals from the X-15 stable platform to use for image-motion compensation and instrumentation to monitor the mechanical and optical performance of equipment. Seven downward-looking photometers measured the spectral changes in light with respect to altitude and provided a signal to the automatic exposure control system on the KS-25. Two additional upward-looking photometers monitored the amount of visible light remaining in the upper atmosphere. Instrumentation provided a continuous record of the temperature on the inner and outer surfaces of the photographic window. A multiple-pickup boundary-layer rake determined whether the boundary layer was laminar or turbulent and monitored its thickness for subsequent comparison with photographic quality. A display of delta cross-range using inertial system outputs in the cockpit center pedestal assisted the pilot in maintaining the correct course.119

The KS-25 and its additional electronics weighed 325 pounds in addition to the 156-pound experiment support package from the earlier tests. The KC-25 was much larger than the earlier KC-1, occupying a volume approximately 13 inches long, 10 inches wide, and 43 inches high; this camera took up the entire height of the instrument compartment. Again, Dr. J. Baker of Spica built a special lens that had a focal length of 24 inches and a relative aperture of f/4, and could provide a resolution of 70-90 lines per millimeter on Super-XX film. The film was nominally 4.5 by 4.5 inches and 250 feet of it were stored in the magazine. The camera had to undergo several modifications to adapt it to the X-15 environment. The automatic focus control was disabled since its time range was not compatible with the speed of the X-15, and the automatic exposure control was modified to fix the lens at f/4 (instead of varying it between f/4 and f/16). After it was modified, the Air Force tested the camera in a centrifuge at the Rocket Propulsion Laboratory at Edwards to determine the effects of large acceleration on its electromechanical properties.-1111!

The X-15 flew both high-speed and high-altitude flights with the experiment, and the Air Force analyzed the photographs to determine the influence of the hypersonic flight environment on the degradation of image quality. Researchers deemed the image quality from four particular flights (1-42-67, 1-45-72, 1-46-73, and 1-47-74) to be the best, and used these data for the analysis. These flights varied in altitude from 101,000 feet (three flights) to 175,000 feet (1-46­73) and in speed from Mach 5.01 (1-46-73) to Mach 6.06 (1-42-67). NASA returned the experiment to the vendor for repair after it malfunctioned prior to launch on abort 1-A-68, and reinstalled it in time for flight 1-45-72. In addition to the support used in Phase I of this experiment, Phase II also used a Boeing RB-47 Stratojet equipped to photograph the same targets just before and after the X-15 flights, providing researchers with a known reference.-112

Researchers performed a laboratory analysis on the film to determine the extent of the deleterious effects of the flight conditions on the optical performance of the camera system. They determined the resolution for those frames that contained images of the three-bar resolving power targets. They then used these readings to check the values of resolution obtained by making microdensitometer traces of edges appearing in the photographs, converting these edge traces to transfer functions, and finding the intersection of these with the film threshold to estimate system resolution and determine the degradation in optical performance. The resolution ranged from less than 11 to greater than 60 lines per millimeter for a lens-emulsion combination whose low – contrast performance was between 80 and 90 lines under laboratory conditions.-113

Regardless of the technical considerations, the photography proved to be rather spectacular. On each flight the camera exposed a frame with the X-15 still attached to the NB-52 to use as a reference. This frame almost always had a resolution of over 80 lines per millimeter. On one flight the X-15 photographed the Indian Springs target while at Mach 5.47 and 101,400 feet, when the temperatures on the camera window were -4 degrees on the inner surface and +287°F on the outer surface. The resolution of the photograph was 60 lines per millimeter.114

Other examples included a photograph of Indian Springs AFB taken at Mach 5.43 and 120,000 feet, with inner and outer window temperatures of -1°F and +321°F, respectively. Three aircraft parked on the ramp of the base were readily identifiable. Another photo taken at Mach 4.37 and 169,600 feet also had a 60-line resolution. Researchers determined from these tests that the photographic quality obtained at high speeds and altitudes was acceptable. Researchers also performed a subjective analysis of the image quality for the bulk of the photographs in an effort to find some correlation between image quality and certain data from the flight environment. However, they could not establish any direct relationship.115

In the latter part of Phase II, researchers also tested several experimental near-infrared color films for the first time in flight. Various reports indicate that the X-15 flights led directly to the use of near-infrared color film during the conflict in Southeast Asia (the heat-sensitive colored emulsions showed enemy activity under the dense jungle canopy). Researchers soon adopted similar techniques for Earth-resource photography.116

Conclusions

The experiment had its share of problems. In addition to the accumulated navigation errors experienced on most flights that often precluded directly overflying the targets, numerous equipment malfunctions plagued the experiment. For instance, both the KC-l and KS-25 incorporated a vacuum system that used a sense line routed from the experiment to ambient pressure in the aircraft’s liquid-nitrogen bay. Sporadic malfunctions occurred that resulted in loss of vacuum and, hence, loss of data. A survey of six flights showed that three of them experienced

problems with the vacuum system.-1117!

The researchers did not believe the experiment was particularly conclusive, since there were many unanswered questions. For instance, researchers found isolated instances of high-quality images being obtained at speeds between Mach 2.5 and 6 at altitudes of 55,000-100,000 feet. However, they also noted nonperiodic image smears that evidently arose from image motion that was not accounted for in the flight data by vibration, aircraft motion, or stabilizer-mount movements. This behavior limited the analysis of the experimental results. Still, researchers concluded that the distortion of the quartz window due to thermal effects had a negligible effect on resolution, and that scattering from the turbulent boundary layer was not severe and its optical effects were slight in any case.!1181

It was also determined that the mathematical model used to predict the optical performance gave good agreement with the measured performance, and that further improvements in the method could not be made using the results of these X-15 flights. Like Phase I, the detailed results of Phase II remain classified.-1119!

However, it is likely that the results of this experiment are no longer terribly applicable. Although the 3-arc-second cameras tested on the X-15 apparently showed a negligible impact from the hypersonic aero-thermo environment, the increased sensitivity of the more-modern 0.5-arc – second (or better) cameras may well be subject to significant degradation from shock waves and boundary-layer flow.

Experiment #6: Earth Atmospheric Degradation Effects

The Air Force combined experiment #6, originally known as the "environmental effects on optical measurements" experiment, with experiment #5.!120!

Experiment #7: Electric Side-Stick Controller

The ASD and FRC jointly sponsored this experiment to address pilots’ complaints about the feel of the side-stick controllers in the X-15. Side-stick controllers were of interest because of the relatively small cockpit space they required and the better support they provided for the pilot’s arm under accelerated flight conditions. Pilots criticized the side stick in the X-15 because of the adverse feel characteristics caused by connecting it mechanically to the center stick and the power actuators that moved the control surfaces. As in the much-later F-16, there was no mechanical linkage between the electric side stick and the flight-control system, and the electric side-stick would have transmitted instructions to the MH-96 adaptive control system to fly the airplane. In addition to providing a better control system for the X-15, the electric side-stick program would have provided experience applicable to the Dyna-Soar. By the end of 1962, North American had begun flight-testing a modified F-100C equipped with an electric side stick, but these tests were not completely successful. The Air Force put plans to install the electric side stick in the X-15 fixed-base simulator on hold, and then canceled the experiment at the end of 1963 when the Dyna-Soar program abruptly ended. NASA never installed the electric side stick in X-15-3.-1121!

Experiment #8: Detachable High-Temperature Leading Edge primary restraint; 2) a thin-skin, refractory-metal concept that relied on a low coefficient of expansion to minimize thermal stresses; 3) a prestressed leading edge that used a mechanically or thermally applied prestress system; and 4) a nonmetallic leading edge that contained an ablative material (much like North American’s X-15 proposal).-1122

The original X-15 wing and empennage leading edges used a round profile to minimize the effects of heating. NASA (particularly Ames) had wanted removable wing leading edges to allow different designs to be tested during the flight program, but these disappeared early in the development period. After the basic envelope expansion was completed, various researchers in the Air Force and NASA became interested in reviving the idea. Since replacing the wing leading edge would have required an extensive wing redesign, researchers decided to find an alternate way. The selected method was to modify a ventral rudder to accommodate leading edges manufactured from Rene 41 and tantalum, and the modified rudders were ready for flight in mid – 1966. However, it is unlikely that they ever flew, given that X-15A-2 was the only aircraft to fly with the ventral rudder during the time the modified units were available.-123

Sharp-leading-edge studies that were intended to evaluate various heating theories were also part of this experiment. The standard X-15 rudder had a leading-edge radius of 0.5 inch over the very forward 0.6 inch of chord. The sharp-leading-edge modification extended the leading edge of the dorsal rudder 5.16 inches forward, resulting in an overall chord of 9.00 feet. This sharp 347- stainless-steel leading edge had a radius of only 0.015 inch at the tip, and essentially had a knife-edge shape. To ensure turbulent flow along one side of the rudder, researchers placed boundary-layer trips consisting of spot welds 0.125 inch in diameter and 0.020 inch high on the right side approximately 5 inches from the leading edge.124

To gather data on flights with the sharp rudder, researchers mounted an Inconel X shear-layer rake impact probe on the left side of the sharp-leading-edge rudder 27 inches aft of the leading edge and 12 inches from the top. Eleven 30-gage chromel-alumel thermocouples were spot – welded to the inside surface of the skin, equally spaced chord-wise on the right side of the rudder 22 inches from the top. NASA installed six 0.25-inch-diameter pressure orifices near the thermocouples and connected the surface orifices and impact probes to standard NACA manometers in the side fairing of the fuselage. Similar instrumentation on a blunt-leading-edge rudder on X-15-2 collected baseline data; however, in this case the impact probe was on the right side 95 inches from the front of leading edge and 22 inches from the top of the rudder. The location of the probes was changed because the researchers wanted to gather slightly different data.123

The sharp rudder first flew on X-15-3 on 7 November 1963 (3-23-39) with Bob Rushworth at the controls. Several flights using X-15-2 had already gathered baseline data with the standard configuration. The X-15-3 would carry the sharp rudder through flight 3-33-54, when NASA removed it to install additional instrumentation. A normal rudder borrowed from X-15-1 replaced it for flight 3-34-55. NASA reinstalled the sharp rudder in time for flight 3-35-57, and X-15-3 continued to fly with it until the airplane was lost. The tests allowed researchers to validate various heating theories for both the blunt – and sharp-leading-edge shapes. In general, the theories fell into two groups: those that closely predicted the flight results (Moeckel and Love), and those that overestimated the heat transfer by 30-50% (Eckert).123

Experiment #9: Landing Computer

completion, but combined elements of it with experiment #14.-1127 Experiment #10: Infrared Exhaust Signature

The Air Force Geophysics Research Directorate sponsored experiment #10, with Leonard P. Marcotte as the principal investigator, to determine the infrared characteristics of a liquid- oxygen-ammonia rocket engine. This was conceptually similar to experiment #3 except that it involved the infrared spectrum instead of the ultraviolet. Measurements had been made of the signatures from Atlas and Titan ICBM engines; however, no measurements from oxygen-ammonia engines were available. Researchers wanted the data to use as part of a missile-detection system. The primary instrument was a Block Associates E-8 infrared radiometer that measured radiation in four spectral regions by focusing radiation through a calcium fluoride lens and four selective filters onto a lead sulfide detector. The range of the detectors was 2.5-7.0 microns. Personnel from the Cambridge Research Laboratory accomplished pre – and postflight checkouts of the package.-^128-

The experiment was carried in the tail-cone box of X-15-3 on seven flights during 1963 and early 1964, but because of mechanical problems, data were obtained on only a single mission. Researchers asked for four additional flights during late 1964, but apparently no flights were made. The detailed results are still classified. -1129

Experiment #11: High-Temperature Windows

The ASD sponsored experiment #11 to investigate various transparent materials in the high – temperature environment. The rapid buildup of temperature and dynamic force as cold structures reentered the atmosphere at hypersonic velocities created severe problems for the window designers. The window design and installation technique were critically important since both affected the heat transfer between the airframe and the transparency, as well as between the outer and inner window surfaces. NASA instrumented the X-15-2 canopy windows, as well as the center-of-gravity compartment windows, to provide precise temperature data. Among other things, the experiment tested the fused silica windows used on the photo optical degradation experiment (#5). The experiment acquired useful data on several flights during 1963.[130]

Proposals were later made to modify the experiment to test an X-20 window and retainer during high-speed flights on the X-15. Researchers wanted to install the window on one of the X-15-2 lower speed brakes and expose it to variable dynamic pressures on several Mach 6 flights during 1964. These plans never came to fruition after Secretary of Defense Robert McNamara canceled the Dyna-Soar program in December 1963. Nevertheless, X-15A-2 carried an instrumented window in the fixed portion of its ventral stabilizer for five flights during early 1966. Among other things, researchers used these flights to investigate whether ablator smoke and residue would adhere to the glass enough to hinder vision through the windshield; they concluded that it would.-1181-

Experiment #12: Atmospheric-Density Measurements

Given the increased operations of both high-altitude manned vehicles and military missiles, the Air Force considered it important to determine the atmospheric density at altitudes above 100,000 feet as well as the day-to-day variation. As originally envisioned, the experiment would have used an alphatron ionization gage in a modified wing tip (this experiment predated the wing-tip pod concept) on X-15-2 that was outside the contamination caused by the APU and

ballistic control exhausts. The measurements placed no constraints on the flight path or trajectory.-1132!

The engineers could not find a reasonable way to mount the ionization gage, so the researchers rescoped the experiment to perform analytical research using air data gathered by the normal X – 15 ball nose and stable platform. Density-height profiles in the stratosphere and mesosphere were obtained from measurements of impact pressure, velocity, and altitude on two flights (2­14-28 and 2-20-36) in 1961 and four more (3-16-26, 3-20-31, 3-21-32, and 3-22-36) in 1963. The researchers noted that the modern recorders in X-15-3 provided more precise data, but the X-15 pressure-measuring system had a substantial lag in it, which made it difficult to perform an exact analysis. The density computations used a form of the Rayleigh pitot formula, and the data agreed well with measurements made by Arcas rocketsondes launched at Point Mugu around the time of the X-15 flights. The X-15 data generally indicated 5-7% greater densities than the standard predicted values at altitudes between 110,000 and 150,000 feet.31333

The Air Force Geophysics Research Directorate sponsored a follow-on experiment to determine the atmospheric density at high altitudes to provide data for the designers of future aerospace vehicles. The wing-tip pods finally allowed researchers to measure atmospheric impact pressure with a densatron ionization gage installed in the nose of the right wing-tip pod on X-15-1. The College of Engineering at the University of Michigan built the experiment under Air Force contract. Researchers used two flights (1-50-79 and 1-51-81) to check out the installation and measure temperatures in the instrument. NASA then installed a small amount of radioactive tritium in the gage to measure the atmospheric density above 90,000 feet.-1343

The intended goal of obtaining atmospheric density profiles on a regular basis was never realized; in fact, the experiment only flew on three more flights (five flights in four years). As the researchers later commented, "The research activity undertaken here was valuable if for no other reasons than to point out the numerous restrictions associated with a manned rocket vehicle."-11333

An analysis of the data showed that despite predictions that the wing-tip pods would be outside the interference area, the experiment was limited below 100,000 feet by the bow shock-wave interference, and above 240,000 feet by the residue from the ballistic control-system thrusters. In between those altitudes, the thrusters intermittently biased the gage output; however, researchers could still obtain sufficient data for useful analysis.31363

Experiment #13: Micrometeorite Collection

The Air Force Geophysics Research Directorate sponsored experiment #13 to collect samples of micrometeorites and extraterrestrial dust at altitudes above 150,000 feet. This was the initial impetus to manufacture the wing-tip pods, and researchers installed a collector in the nose of the left wing-tip pod on X-15-1. At high altitude and low dynamic pressure, the lid opened from the rear to a vertical position on top of the wing. As it lifted, rotating upward toward the front, it also swiveled so that the underside of the lid faced the aircraft fuselage and exposed the collector to the air stream. The collector then "broke seal" to expose a rotating collection surface behind an orifice in the side of the collector unit. The unit rotated to six different positions during the collection, and the location served to indicate the time of the event.31373

During flight 1-50-79 the collector door inadvertently opened during the exit phase and remained so for the remainder of the flight, but fortunately did not cause serious damage. The collector was flown on flight 1-51-81, without exposing the collection device, to determine the amount of contamination resulting from ground handling. The plan was to operate the collector on as many high-altitude flights of the X-15 as possible.-1138!

The experiment flew on flight 1-63-104, but the altitude attained on the flight was not sufficient to provide meaningful data, and an engine problem forced an emergency landing on Delamar Lake. After Jack McKay landed the X-15, the ground crew noticed that the collector box had extended, although they could not determine when this occurred. A postflight inspection revealed that the retraction mechanism was not functioning properly, and NASA returned the experiment to North American for repair.-139!

The experiment malfunctioned during preflight testing prior to flight 3-55-82 and NASA removed it from the aircraft. After it was modified to increase its reliability, the experiment flew on flight 1-65-108 to an altitude of 241,800 feet, but the collection rotor jammed in its second position. Subsequently, the experiment flew on both X-15-1 and X-15-3 and collected some particles during six flights. Unfortunately, residue from the ballistic control-system thrusters had contaminated the particles, and the Air Force canceled the experiment.-3401

Experiment #14: Advanced Integrated Flight-Data and Energy-Management Systems

The ASD and FRC jointly sponsored experiment #14. "A [principal] objective of this program is to obtain information to be applied to problems of design and use of advanced flight control equipment for vehicles which reenter the atmosphere from Earth orbits. Accordingly, a primary goal in the EMS design work has been to include the features of advanced orbital re-entry energy management systems to the maximum extent compatible with the X-15 vehicle and the flight control hardware to be tested." To this end, the Air Force contracted with Bell Aerosystems to develop a suitable unit targeted at the Dyna-Soar program. Robert W. Austin and John M. Ryken at Bell led the work on Advanced Technology Program (ATP) 667A.-141

James E. Love and Melvin E. Burke from the FRC, and Lieutenant Colonel Elmer F. Smith, director of the X-15 Project Office at Wright-Patterson AFB, worked out an MoU for including the Advanced Integrated Flight Control System (AIFCS) in the X-15 flight program. Smith signed the MoU on 9 September 1963 and Paul Bikle signed it on 12 September.-142!

Essentially the MoU indicated that the Air Force would be responsible for funding the development program, testing the system prior to its installation in an X-15, and maintaining the system after it was delivered. The FRC would handle the actual flight research program and provide a digital computer to upgrade the fixed-base simulator. The MoU stated that the X-15 Joint Program Coordinating Committee would determine the installation and flight schedule after "a reasonable reliability shall be demonstrated… as evidence in laboratory tests, rocket sled tests and finally flight tests in a Douglas F5D Skyray prior to the initiation of installation modifications of the X-15 airplane."-143!

The Bell system was extensively simulated using an analog system to experiment with different control-loop arrangements, and an IBM 7090 digital computer to work out the problems associated with the digital programming. The results showed that the system performed well in a range of missions covering the X-15 flight envelope. Although Bell would design the system,

Litton Industries would program it into one of their digital flight computers. The energy – management system (EMS) used slightly more than 3,000 words of memory and "about 15- percent of real-time on the Litton Flight Data System computer." The X-15-3 carried the system because it required the MH-96 adaptive flight-control system.144

Probably the most significant change from the system designed for Dyna-Soar was the use of an artificial dynamic pressure limit to ensure that the X-15 stayed within dynamic (q) and thermal limits. The decision to use a q-limit instead of directly using temperature as a control variable (as in the case of the Dyna-Soar) was the result of discussions among Air Force, Bell, and NASA personnel. The use of q-limits eliminated the need to instrument the exterior of the X-15 to obtain additional temperature data. The only inputs the system needed were dynamic pressure and altitude-rate information. The EMS performed four basic functions:[145

1. Computation of vehicle total maneuver potential, formation of a nondimensional ground area attainable, and generation of angle of attack and bank commands for vehicle destination maneuvering.

2. Computation of the minimum value of dynamic pressure attainable at the next pullout (perigee) point and generation of override commands required to insure that pullout conditions do not reach critical values.

3. Computations to nondimensionalize measured dynamic pressure and generation of override commands for a [angle of attack] and [bank angle] to ensure that present dynamic pressure and aerodynamic heating do not reach critical values. (A similar loop for control of "g" loading was not contained within the EMS since this was already provided in the Honeywell [MH-96] adaptive flight control system for the X-15.)

4. Computations to nondimensionalize measured rate of change of altitude and generation of commands to damp phugoid motions (long-period oscillations along the longitudinal axis).

The pilot could select either an automatic or manual energy-management mode. In the manual mode, the system displayed the results of the energy-management computations to the pilot but did not take any independent action. This allowed the pilot to fly the correct energy-management profile or to deviate from it as needed. In the automatic mode, the system displayed the same information to the pilot but also sent commands directly to the MH-96 to fly the desired reentry profile. The system was programmed to arrive at high key with "sufficient energy for the pilot to accomplish the final descent and landing with considerable energy reserve." Interestingly, the system did not direct the X-15 toward any particular heading over high key, so the pilot had to use some of the excess energy to establish a heading that would allow him to land.-1146

As development progressed, there were concerns that the system was requiring too much power and cooling. Jim Love and Lannie D. Webb from the FRC first voiced these concerns during a meeting on 17 September 1962 with Captain Hugh D. Clark and Captain James H. Smith from the ASD. Love indicated that the electrical demands were so high that the X-15-3 electrical system would have to be "beefed up" to accommodate the new system. Whereas the original Sperry stable platform required 1.4 pounds per minute of cooling, the new system required over 6.3 pounds per minute. The original Litton computer was finally tested in the NASA F5D (BuNo 142350/NASA 213) in late 1964, despite an initial intent to begin testing in January 1964. The F5D portion of the program ended on 31 March 1965 after 17 flights.-1^47

This experiment was reoriented in October 1964 to use Honeywell equipment instead of the originally procured Litton components. The centerpiece was an H-387 digital computer hooked to a new Lear Siegler instrument panel. In addition to conducting the experiments that were initiated under ATP 667A, researchers later included studies of pilot displays, energy management, and piloting problems during the exit phase of high-performance vehicles. The program expected to make 16 flights in X-15-3 to cover most of the flight envelope.-1^48

As finally defined for the X-15 program, this experiment was an evaluation of vertical-tape displays, energy-management concepts and techniques, and command guidance for boost and trajectory control. The equipment consisted of a Honeywell inertial system, coupler, and computer; a Honeywell AN/AYK-5 Alert digital computer; a Lear Siegler cockpit instrument panel with vertical-tape displays; the Honeywell MH-96 adaptive control system; and the ball nose.

NASA installed the system in X-15-3 during the weather down period in early 1966.-1149

Another part of the experiment was to test a boost-guidance technique and display that had been developed by the Ames Research Center and was called, logically enough, the Ames boost – guidance evaluation. For the most part, the experiment consisted of additional programming for the Alert computer. Data was displayed on the horizontal pointer of the three-axis attitude indicator, making it a "fly-to-null" display of altitude error plus altitude rate error. This change ultimately confused Mike Adams, and on flight 3-65-97 contributed to the loss of X-15-3. Researchers flew it for the first time on flight 3-58-87 to evaluate needle movement on the display. A postflight review of the cockpit film showed that the cross-pointer was moving as expected since the guidance parameters stored in the computer were not representative of the planned flight. Subsequent flights programmed the boost-guidance software to match the desired flight profile. On future flights, the pilot was to fly the boost portion using the boost-guidance program as long as the display of pitch attitude was within +2 degrees of the planned flight path. The experiment seemed to function as expected.[150]

Overall, the entire integrated flight-data system appeared to work well enough during the next 14 flights. Its performance on its last flight is more open to debate.

Experiment #15: Heat-Exchanger System or Vapor-Cycle Cooling

The ASD sponsored experiment #15 to verify performance estimates for evaporators and condensers at zero gravity. Researchers wanted to mount the experiment in the instrument compartment of X-15-1 during four high-altitude flights with a large zero-g parabola at the top. The first of the Garrett AiResearch heat exchangers (excess units from the canceled Dyna-Soar) arrived in early November 1964. North American conducted the initial performance tests in Inglewood during late November, and the unit underwent centrifuge tests at the Rocket Propulsion Laboratory at Edwards in mid-December 1964. Engineers tested the units aboard a KC-135 in early 1965 and scheduled the installation in X-15-1 for mid-1965.-1151

However, the experiment faced several challenges. The most pressing was that starting the large compressor needed to cool the equipment required more power than was available on either the X-15 or the NB-52. Engineers thought that installing larger alternators in the NB-52 might be possible, but the wiring on the carrier and the X-15 would have to be upgraded to a heavier gage to handle the load. Another possible method would be to start the compressor using ground power before takeoff since the X-15 APUs could supply the operating load, without starting the compressor. The compressor was equipped with an automatic shutoff feature that could detect a failure of one of the X-15 APUs; a single unit could not supply both the experiment and the airplane, and the airplane came first.-1152

Difficulties in bringing the experiment up to the safety standards demanded by the X-15 program delayed the experiment for over a year. As it ended up, NASA never installed the hardware on an X-15 and the experiment was moved to the Apollo Applications Program, which itself never got off the ground.-1153

Experiment #16: Rarefied Wake-Flow Experiment

The FRC sponsored a rather fanciful concept known as the "rarefied wake-flow" experiment.

Initially the plan was to tow an inflatable plastic sphere behind the X-15. By measuring the tension on the tow rope and analyzing photographs, the researchers hoped to determine the atmospheric density above 200,000 feet and the drag characteristics of a towed sphere in free – molecular-flow regions, assess the effect of vehicle flow fields, and study supersonic wakes. Additional investigations included the motion of a towed drag body and the viability of inflatable reentry vehicle deceleration devices.-11541

The experiment was modified so that a small Mylar balloon could be released (instead of towed) from the tail-cone box on X-15-3 at altitudes above 250,000 feet to investigate the properties of supersonic wakes at low densities. The experiment would require two flights above 300,000 feet using balloons originally procured for Project Mercury, and researchers wanted four additional flights above 250,000 feet using somewhat sturdier balloons. Two unsuccessful attempts (flights 3-21-32 and 3-22-36) to release a Mercury balloon occurred in mid-1963, marking the end of this idea.-1155-

The experiment ended up using a Pace flow transducer mounted in the forward section of the X – 15 left wing-tip pod. This installation negated many of the original secondary objectives of the experiment. The revised experiment called for flights above 300,000 feet, which resulted in very few flight opportunities, and by December 1964 it was determined that flights above 250,000 feet would be sufficient. (Only four program flights were above 300,000 feet, while 15 others got above 250,000 feet.) The experiment was an evaluation of a mechanical transducer for rarefied – flow measurement and measured upper-atmosphere ambient density. NASA carried the experiment on a "standby" status to replace experiment #13 if opportunity allowed, but by the end of 1965 the experiment apparently still had not flown. In April 1966 the ballast nose cone for the wing-tip pods was modified to accept the Pace transducer, allowing the experiment to be installed in either wing-tip pod on either X-15-1 or X-15-3. The experiment flew several times on each airplane during 1966 and 1967.-1561

Experiment #17: MIT-Apollo Horizon Photometer

The Office of Manned Space Flight sponsored experiment #17 to measure the Earth’s horizon – intensity profile as a function of altitude to different wavelengths in the visible spectrum. This was officially called the "simultaneous photographic horizon scanner experiment," and was in many respects a follow-on to the Langley horizon definition experiment (#4) using much more sophisticated equipment. The MIT project was large and wide-ranging, using various aircraft, sounding rockets, as well as Mercury and Gemini spacecraft, to carry radiometers to measure the Earth’s infrared horizon. Of these, the X-15 carried the largest and most sophisticated package to define the Earth’s limb for use as an artificial horizon for the space sextant carried aboard the Apollo spacecraft. Researchers designed the sextant as a backup device in the event of a radar or communications failure. NASA installed a single Phase I and two Phase II experiments on X-15- 1.H5Z1

The interim Phase I system was a fixed platform in the tail-cone box supporting three MIT Instrument Laboratory-designed photosensitive instruments (a photomultiplier photometer, a solid-state photometer, and a camera) pointing aft and approximately aligned with the aircraft thrust axis. Researchers evaluated the fixed platform during flight 1-51-81, and flew four additional flights to obtain photometer output levels.-1581

horizon-scan rates to obtain the most useful data independent of aircraft maneuvering. A door that opened above 100,000 feet covered all of the instruments during the X-15 exit phase. NASA installed the Phase II experiment in X-15-1 during the weather down period in early 1966. The initial plan was to fly a single flight to 220,000 feet as a checkout of the system, and then fly four data-gathering flights to 250,000 feet under various seasonal sun-angle and atmospheric conditions with the system pointed approximately true north.-159

Flight 1-63-104 was the checkout for part 1 of Phase II, and postflight inspection showed that the experiment was in good condition despite the emergency landing. The experiment flew on flights 1-65-108, 1-66-111, 1-67-112, and 1-68-113, but did not obtain data on flights 1­65-108 and 1-67-112 because of electrical power problems, or on flight 1-68-113 due to a loss of the scan signal. An evaluation of the data from flight 1-66-111 indicated that the photometer functioned properly but the star tracker did not acquire Polaris as programmed. The experiment subsequently flew on four additional flights and gathered good data on all of them.-160

Five flights (part 2 of Phase II) added a Barnes infrared edge tracker to measure the 14-40-micron infrared profile. The Manned Spacecraft Center sponsored this part of the experiment using an instrument designed for spacecraft attitude stabilization in the Apollo Applications Program. The Barnes instrument was essentially a telescope employing a 2.4-inch-diameter silicon lens mounted on the elevator under the skylight hatch of X-15-1. North American installed this hardware, collocated with the WTR launch-monitoring experiment, in early 1967. Researchers checked out the experiment on flight 1-76-134, and made four data-gathering flights between June and September 1968. Flight 1-80-140 was the last flight of the experiment, and Paul Bikle reported that "star recognition was not achieved."-161-

One of the more interesting aspects of the experiment was that the High Range could not provide sufficiently accurate radar data to meet the needs of MIT. Instead, NASA arranged for the Sandia Corporation to track the X-15 using the MPS-25 radar at Cactus Flats, Nevada. This radar could track the airplane with 0.10-milliradian-attitude accuracy and a range accuracy of several yards.-1162-

The experiment concluded that the concept was feasible for use as a space-navigation technique, but because the most stable portions of the radiance were in the near-ultraviolet range, it was usable only during daylight portions of an orbit. To verify that the idea worked from greater distances, NASA asked the astronauts on Apollo 8, 10, and 11 to make visual sightings of the Earth’s horizon using the onboard spacecraft sextant. This exercise was conducted several times en route to and returning from the Moon, and revealed that the sextant had relatively good accuracy compared to radar positioning.-162-

Experiment #18: Supersonic Deceleration Devices

Initially, NASA Langley sponsored experiment #18 to test the concept of inflatable devices. During the late 1950s, engineers thought they could use internal pressure to erect and stabilize structures in space because of the lack of atmosphere and gravity. The inflation of these structures, however, was difficult to investigate on the ground. A test would consist of carrying the structure either internally or externally on the X-15, ejecting it at high altitude under conditions of zero-g and zero dynamic pressure, and then photographing the inflation of the structure. It was expected that the experiment could be packaged in place of the ventral rudder if the equipment was not too large; otherwise, an external store might be required.-164-

After more thought, this concept seemed a bit far-fetched. The experiment was reoriented away from inflatable structures and toward inflatable decelerator devices. In this incarnation, the experiment was sponsored by the FRC to evaluate the drag, stability, and deployment characteristics of various decelerator configurations at Mach numbers as high as 5 and altitudes as high as 200,000 feet. Dr. Heinrich at the University of Minnesota had developed a variety of such devices, and researchers at Langley studied a number of configurations in wind tunnels to determine which ones held the most promise for actual flight tests. The possibilities included inflatable spheres and cones, and various self-inflating parachutes. In December 1964 the plan was to fly the first X-15 decelerator tests during the early summer of 1965 and deploy the decelerator at Mach 4 following burnout. The tests would require the installation of a decelerator tow kit in the tail-cone box. NASA fabricated the modification kits for two X-15 airplanes and gathered preliminary data in April 1965 using an F-104 to drop a decelerator at Mach 1.8 from

57.0 feet. Engineers made some modifications to X-15-3 to support the experiment during the weather down period in early 1966, but apparently never installed the experiment.-1165

Experiment #19: High-Altitude Sky Brightness

The ASD sponsored experiment #19 to determine the intensity, polarization, and spectral distribution of the daytime sky at high altitudes. Researchers would use the information to develop electro-optical tracking systems that were capable of discriminating a star’s optical signal from the surrounding sky’s brightness. Northrop Nortronics was developing a spectrophotometer for use on a Lockheed U-2 reconnaissance aircraft as part of the High Altitude Daytime Sky Background Radiation Measurement Program to survey the sky at altitudes between 20,000 and

70.0 feet in 10,000-foot increments. The Air Force, however, desired data obtained at up to

200.0 feet, and in 1962 the service modified the Nortronics contract to develop instrumentation

for the X-15. The goal was to survey the sky in the range of 3,500-7,500 , with a spectral

resolution of approximately 2 , to support the design of future star trackers. Researchers

extrapolated the data gathered by the U-2 to higher altitudes and used it to predict and verify data acquired by the X-15 since the effects of high-speed aerodynamics were largely unknown. The researchers wanted the X-15 to acquire data from 40,000 feet to 200,000 feet.-166

The High-Altitude Sky Brightness Experiment (#19) surveyed the sky in the range between 3,500 to 7,500 angstroms, with a spectral resolution of approximately 2 angstroms to support the designs of future star trackers. Researchers extrapolated the data gathered by the U-2 to higher altitudes and used it to predict and verify data acquired by the X-15. The spectrophotometer sensor was located in the rear portion of the left wing-tip pod, and flew on both X-15-1 and X – 15-o. (NASA)

Researchers first flew the spectrophotometer in the rear portion of the left wing-tip pod of X-15- 1 on flights 1-50-79 and 1-52-85 to check out its operation. The experiment flew on flight 1­63-104, but the emergency landing precluded the acquisition of any meaningful data.

Researchers obtained data on flight 1-65-108, and the experiment flew on flight 1-66-111; however, no useful results were obtained because a slow-blow fuse failed. Engineers conducted several tests in an environmental chamber to investigate the fuse, which consistently failed at

140,0 feet and -158°F. They eventually traced the problem to a power connector on the experiment. After repairs were made, the instrument flew several flights aboard X-15-3 beginning with 3-56-83, and acquired useful data on at least two flights.-1167!

Experiment #20: Western Test Range Launch Monitoring

The ASD funded experiment #20 under the name "Pacific Missile Range (PMR) launch monitoring." The goal was to measure from high altitude the signature of an ascending ballistic missile to determine the feasibility of using the ultraviolet spectrum for space-based detection and tracking systems. There was initial concern regarding this experiment because the timing requirements seemed very critical given the short duration of X-15 flights and the acceleration profile of an ICBM. Nevertheless, the Air Force deemed the experiment important for national security and requested six flights in excess of 250,000 feet. In mid-1964 the Air Force awarded a contract to the Northrop Space Laboratories to design and fabricate equipment. A review of the preliminary design revealed that the experiment package and its recording equipment were too large to fit on X-15-1, so the Air Force, NASA, and Northrop were reevaluating the problem as 1965 ended.[168]

Eventually Northrop worked through the problems and NASA installed the experiment during the weather down period in early 1966. The experiment consisted of an optical system, a vidicon camera, a four-spectral-band radiometer, and a servo-driven scanning mirror installed on the extensible elevator under the skylight hatch of X-15-1. The experiment first flew on 15 June 1967 (flight 1-72-125), but an electrical malfunction within the experiment precluded a complete operational checkout. The X-15-1 subsequently carried the experiment on eight additional flights.-116^

The primary target for the experiment would be a Minuteman II ICBM launched from Vandenberg AFB, although some thought was given to trying the experiment against a Titan II target. The Air Force also wanted the X-15 to track multiple Minuteman ICBMs launched from Vandenberg in rapid sequence (simulating an actual wartime response). In each case, the X-15 portion of the experiment would be secondary to other reasons for launching the missiles. Whatever experiment the Air Force was conducting involved the use of a B-52 in addition to the target ICBMs.[170]

The most ambitious of the follow-on experiments was the Western Range Launch Monitoring Experiment (#20) installed under the Skylight hatch on X-15-1. The X-15 was supposed to track a Minuteman ICBM launched from Vandenberg AFB, but the timing of getting the X-15 in position at the exact moment the ICBM was launched never worked. (NASA)

On 22-23 May 1968, representatives from the Air Force, NASA, and Northrop met to discuss various aspects of the upcoming flights. The first order of business was to discuss the security classification surrounding the project, and the Air Force agreed that the only classified data the FRC would receive would be the actual launch time of the targets. The representative from the Strategic Air Command (SAC), Lieutenant Colonel John McElveen, indicated that SAC "will do everything possible to insure a successful coordination with the exception of compromising their primary objective." This would include allowing Vandenberg to adjust its launch times to coincide with X-15 launches as long as the delays were a reasonable length of time.-1171

The attendees spent most of the meeting discussing how to make sure the ICBM and X-15 would be in position at the right time. They decided that, whenever possible, the experiment should be scheduled for between 1000 and 1400 hours Pacific daylight time. The X-15 flight planners would purposefully schedule the X-15 so that it would arrive at its launch point either on time or slightly late, since the Air Force could hold off on launching the target but could not recall it once it was launched. For the multiple-target missions, Vandenberg would launch the Minuteman

ICBMs 30 seconds apart. Procedures allowed the Air Force B-52 to hold while the NB-52/X-15 got into position for launch, and to time the launch of the target ICBMs. Nevertheless, this experiment would have required extraordinary luck to have everything in place at exactly the right time.-1172!

The Air Force apparently put a high priority on this experiment since it was one of the two reasons listed for extending Air Force funding of the X-15 program into 1968. Unfortunately, the first nine attempts to coordinate this aerial ballet failed. On at least two occasions, equipment on the X-15 failed to operate as expected, and on another Vandenberg could not launch the target because of a technical problem. The experiment also required very precise flight-path control. For instance, during flight 1-79-139 the experiment extended 129 seconds after launch. It immediately began searching for the target, but quickly failed after the elevator and azimuth torquers drove against their stops. It was later determined that Bill Dana deployed the experiment slightly before the airplane achieved the 0 2-degree pitch and roll attitude requirement.

Engineers warned Dana and Pete Knight not to extend the experiment until the airplane was stable as it approached apogee.-1172!

As the flight went on, more difficulties arose. About 208 seconds after launch, NASA-1 requested Bill Dana to retract the experiment. Things appeared normal at first, and the experiment retracted without the delays noted on some previous flights. However, the timing was unfortunate since the call was made a bit later than planned, and the automatic timer interrupted the normal action and initiated an emergency-retract sequence. Nevertheless, the experiment successfully retracted. Since a demonstration of the normal retraction sequence was required before the experiment could become "operational," NASA scheduled a flight to check out the mechanism. On flight 1­80-142, Pete Knight extended the experiment 162 seconds after launch and the sensor went into track mode 5 seconds later. At 240,000 feet, Knight commanded the experiment to retract, but indications at 220,000 feet showed that it had not. Knight activated the emergency mode, with satisfactory results.-11742

Finally, the Air Force and NASA managed the first coordinated launch of the X-15 and a WTR target. Flight 1-81-141 launched from Smith Ranch on a magnetic heading of 169 degrees, within 3 seconds of the optimum time. Bill Dana reached the planned 36-degree pitch angle 30 seconds after launch and held it until burnout at 5,400 fps. The flight experienced a nose-left thrust misalignment that caused 4.5-degree of sideslip, but Dana did not use any rudder input during the exit phase, resulting in a 3-degree error in ground track. The experiment was extended at approximately 235,000 feet as planned (roughly 137 seconds after X-15 launch), but 2.8 seconds later all power was lost to the system and the experiment retracted. The flight did not acquire any useful data.-11752

The last attempt was on the 200th X-15 flight. The launch attempt on 21 November 1968 was coordinated with Vandenberg, and the Air Force launched a Minuteman II at 1028 hours; unfortunately, the X-15 never left the ground because of a problem with the NB-52A. By this time the Air Force had spent $700,000 on the experiment, not counting the normal flight costs of the X-15 (which carried other experiments as well) or the cost of the Minuteman ICBMs (which were being launched anyway).-11762

Experiment #21: Structural Research

hypersonic outer wing panel was required to withstand temperatures beyond Mach 8 without the use of ablative coatings. Both panels needed extensive instrumentation for loads, stresses, and temperatures. The FRC received proposals in late 1964, but never built or tested the panels. By the end of 1965, NASA placed this experiment on "inactive" status.-177

Experiment #22: Air-Breathing Propulsion

Very early on, a small group of researchers believed that the X-15 was a potentially useful test bed for various air-breathing propulsion system components, including complete ramjet engines. The airplane was capable of speeds in the Mach 3-5 region, in which inlet and exit problems were greatest, and a ramjet engine was considered a desirable method of propulsion. The X-15 would provide testing under true atmospheric conditions (ground-test facilities were seldom able to achieve the proper stagnation temperatures and Reynolds number). The X-15 would also permit closer control of test conditions than was possible with ground-controlled rockets, such as those launched at the Pilotless Aircraft Research Division (PARD).178-

The most desirable position for the propulsion test package appeared to be in place of the ventral rudder, although it had to be jettisoned before landing to provide adequate clearance for the landing gear. At this point Dick Day and Bob Hoey had not proposed to fly the X-15 with the ventral removed, so this was one of the larger unknowns of the initial engine proposal. Two wing – root tanks, each holding about 100 gallons of liquid hydrogen, carried fuel for the ramjet. Other positions for the engine would be possible if permanently attached engines were required. For example, a small engine could replace one of the wing root tanks or a pair of engines mounted under the wing tips.179

The FRC proposed the first truly serious version of this experiment as "an extensive air-breathing engine development program… in which one or more sub-scale modular experimental engines would be flown in a true flight environment aboard the X-15." Somehow, the experiment took on a life of its own and morphed into the hypersonic research engine (HRE) project (discussed separately below).

Experiment #23: Infrared Scanning Radiometer

The ASD and later the Air Force Research Technology Division sponsored experiment #23 as a follow-on to the infrared exhaust signature experiment (#10) to determine the feasibility of an infrared imaging instrument operating at Mach 3-5 at altitudes between 90,000 and 120,000 feet. NASA installed a Singer scanning radiometer in the lower portion of the instrument compartment of X-15-1 during mid-March 1965. The experiment looked through an Iratran IV window in the lower fuselage and recorded the reflected solar radiation as well as radiation emitted by Earth.-1180-

The Infrared Scanning Radiometer Experiment (#10) was used to determine the feasibility of an infrared imaging instrument operating at Mach 3-5 at altitudes between 90,000 and 120,000 feet. A Singer scanning radiometer was installed in the lower portion of the instrument compartment of X-15-1 during mid-March 1965. The experiment looked through an Iratran IV window in the lower fuselage and recorded the reflected solar radiation as well as radiation emitted by Earth. (NASA)

The first of six flights was made on 26 March 1965 (1-53-86); the last was flight 1-60-99 on 30 September 1965. Actually, flight 1-59-98 was supposed to be the last flight, but a broken wire had precluded the acquisition of any useful data. The Air Force decided to leave the experiment on the airplane for Pete Knight’s familiarization flight (1-60-99), although Knight did not attempt to fly the profile normally required for the experiment. Despite this, the experiment obtained good data. Although the experiment only generated a crude, two-dimensional image, it proved that it was possible to perform infrared reconnaissance at hypersonic speeds. The development of a Germanium metal window that was transparent to infrared photography offset the masking effect of an aerodynamically heated window. This work reportedly advanced the development of infrared line scanners, such as the Texas Instruments AN/AAS-18, that went on to operational service on various Air Force reconnaissance aircraft. The Earth Resources Development Agency (ERDA) also capitalized on this technology by contracting with the Mead Corporation to develop several portable suitcase-size scanners for use on general aviation aircraft to detect various forms of pollution.-1181!

Experiment #24: High-Altitude Infrared Background Measurements

Experiment #24 was sponsored by the Air Force Research Technology Division to obtain high – altitude infrared measurements of the Earth, horizon, and sky in the 3-5- and 8-14-micron regions for use in various surveillance applications (i. e., target tracking). The measuring device was a simple dual-channel, solid-state radiometer with a flat rotating mirror that provided a circular scan. A self-contained liquid-helium system cooled the experiment. The Autonetics Division of North American built the experiment, and NASA installed it in the right wing-tip pod on X-15-1 during the weather down period in early 1966. Researchers requested three flights to altitudes above 150,000 feet, but the only verifiable attempt was on the aborted 200th flight.11821

Experiment #25: Optical Background Measurements

The Air Force Research Technology Division sponsored experiment #25 as an extension of the ultraviolet exhaust plume experiment (#3). The objective was to obtain narrow-band optical – background measurements covering the spectral region between 0.3 and 1.3 microns. Northrop modified the existing Barnes high-resolution spectrometer and associated equipment from experiment #3 to operate at visible wavelengths.11831

Researchers installed the experiment in the X-15-3 tail-cone box to determine the background characteristics of the atmosphere and Earth when viewed with a narrow-band receiver. The data was applicable to future laser systems for space vehicles. The experiment had flown twice by the end of 1965, but had gathered little usable data because of system noise. Researchers modified their equipment and the experiment flew on two additional checkout flights in mid-1966.11841

Flights 3-53-79 and 3-54-80 carried the experiment. The first flight failed to acquire useful data due to improper instrumentation, and Bill Dana inadvertently turned off the experiment after only 131 seconds on the second. The experimenter reported, however, that the limited data collected was satisfactory. The experiment was last flown on flight 3-56-83, and good data were collected.11851

Experiment #26: Supersonic Transport (SST) Structural Demonstration Techniques

The Air Force Research Technology Division sponsored experiment #26 to evaluate a new technique for determining the mechanical loads and thermal stress experienced by aerospace vehicles exposed to a thermal environment. Republic Aviation developed an experimental analytical procedure that enabled the determination of loads, deformation, and stresses from given strain and temperature measurements. Laboratory tests on a box beam and frame structure yielded data with a calculated accuracy of 10%. This procedure could be proof-tested on the X – 15 and then used to validate the analytical design methods and structural load criteria used for the SST and other advanced aerospace vehicles.11861

Researchers proposed to install thermocouples and strain gages in the fuselage-wing attachment structures and fabricate one horizontal stabilizer with strain gages and thermocouples installed on the spars. Approximately 360 sensors would have been required to perform the tests.11871

The researchers forwarded a suggested program for using this technology to the Federal Aviation

Administration (FAA) for possible funding. The FAA endorsed the requirement but thought it would be more appropriate for NASA to fund the experiment. NASA reviewed the experiment and agreed that a well-verified means of interpreting flight loads and thermal stress data was essential for the future SST, and that NASA should be responsible for developing the technique. However, NASA did not believe that a specific experiment of this magnitude was required to assess the Republic method.-1188-

Eventually, however, the FRC approved and sponsored at least part of the experiment, which was broken into two parts called, logically enough, Phase I and Phase II. The Phase I program used a slightly instrumented set of horizontal stabilizers during several flights to gather baseline airplane data. The tests began on flight 3-52-78 on 18 July 1966 and concluded on flight 3-61-91 on 20 July 1967. Not every flight collected data, due to a variety of malfunctions, but sufficient data were gathered. On several Phase I flights the pilots noted a slight buffet and beta excursion under some flight conditions, a phenomenon the researchers could not explain.-189-

Phase II included a new set of horizontal stabilizers that were manufactured by North American during May 1966. NASA instrumented the left-hand unit with 128 strain gages and 125 thermocouples, and tested it in the High Temperature Loads Calibration Laboratory before installing it on X-15-3 in time for flight 3-62-92. To investigate buffet and beta excursions experienced during the Phase I portion of the experiment, pilots performed maneuvers at Mach 2.5, 3.7, and 4.0 with a pull-up to approximately 12 degrees angle of attack made at each Mach number. The pilots did not notice a buffet or beta excursion at the two higher Mach numbers, but at Mach 2.5 they experienced results similar to those encountered on the two previous flights.

The beta excursion registered about 3 degrees, but the pilot was not positive that buffet occurred during this maneuver. Buffet had been experienced at 10.5 degrees on the previous flight. The only configuration change that occurred between the flights was the replacement of the Phase I horizontal stabilizer with the Phase II units. To evaluate this, NASA reinstalled the original horizontal stabilizers for flight 3-63-94. The pilot did not notice any buffet, leading researchers to suspect some minor manufacturing flaw in the new horizontal stabilizers. Unfortunately, X-15- 3 was lost before researchers could complete any further work. Since the experiment depended on the PCM telemetry system in X-15-3, researchers could not move it to X-15-1.[190]

Another test in this series was to study of the effect of various discontinuities on local surface heating between Mach 4 and Mach 6. To avoid having to make detailed local measurements, the experiment was designed to determine the ratio of the heating rates on two symmetrically located panels under the center fuselage and on the wing tips. One panel in each location would have the discontinuity while the other would not. Discontinuities included forward and aft facing steps, wavy surfaces (sinusoidal distortions), streamwise corners, and antenna posts. At least two X-15- 3 flights included the step panels, and the wavy panels made at least three flights.-119^

Experiment #27: Hycon Camera

The Air Force Research Technology Division sponsored experiment #27. It was conceptually an extension of experiment #5, which had used KC-1 and KS-25 cameras to acquire optical data at speeds between Mach 6 and Mach 8. This experiment used X-15-2 and was approximately 80% complete at the time of Jack McKay’s accident in the second airplane. The experiment, however, continued after X-15A-2 returned to service.-192

resulting data permitted the investigation of contrast attenuation at high altitudes and showed the feasibility of performing aerial photography from supersonic vehicles. These tests began as early as 9 October 1962 (flight 2-30-51) when the 6-inch oblique camera photographed the Las Vegas area from very high altitude using black and white film. During flight 2-39-70 on 22 June 1965, the 6-inch camera used color film to take a similar photo, and the 12-inch camera photographed Indian Springs AFB using color-infrared Ektachrome film. These tests included the evaluation of a special film, Kodak SO-190, which had a resolution of almost 200 lines per millimeter, a speed index of 6, and very low granularity.193-

In late December 1965, a new Maurer model 500 camera replaced the Hycon in the center-of – gravity compartment on X-15A-2. NASA installed the camera during the weather down period during early 1966, with the intent to carry it throughout the envelope-expansion flights beginning with flight 2-49-86. Preflight tests of the system indicated that the experiment was functioning satisfactorily, but checks of the system before launch showed that the platform would not erect properly. Despite this, the camera data were satisfactory and the quality of the resulting photographs was excellent. The X-15A-2 carried the camera on two more flights, also with satisfactory results.-194!

A Hycon KA-51A "Chicago Aerial" camera then replaced the Maurer, which only flew one time on flight 2-52-96. For the next flight of X-15A-2, NASA removed the Hycon experiment and installed an aft-viewing Millikan 16-mm camera to photograph the dummy ramjet.195-

Experiment #28: X-Ray Air Density

There is no record of what organization sponsored experiment #28. The experiment consisted of an X-ray tube and detector located in the forward portion of the right wing-tip pod. The wing-tip pod skin scattered the X-rays, and solid-state cells measured the backscatter to determine air density. The design and fabrication of this experiment began in late 1965 and several flights during 1967 and 1968 apparently carried it, although no results could be ascertained.196

Experiment #29: JPL Solar-Spectrum Measurements

The JPL sponsored experiment #29, which consisted of a spectrometer containing 12 sensors and a servo-positioning system installed in the rear section of the left wing-tip pod of X-15-1. Researchers wanted to use the data to improve the methods of correcting for atmospheric absorption, determine the absolute energy of the sun, and calibrate solar cells to validate solar simulation. JPL built the experiment in early 1966, but a pop-up hatch used to expose the spectrometer failed the qualification test in April 1966. Researchers subsequently redesigned the experiment to use a quartz window in the pod instead of a hatch to eliminate the problem. At the same time, researchers modified the experiment to use the new PCM telemetry system in X-15-

3.1197]

The experiment first flew on flight 3-58-87, and later on two additional flights. A preliminary review of the data showed excessive electrical noise on the data channel, but researchers considered the data acceptable.198-

Experiment #30: Spectrophotometry

have a sponsor of formal approval, although it did apparently receive an experiment number. By the end of 1966, NASA had canceled the experiment before any actual hardware development was undertaken.[199]

Experiment #31: Fixed Alpha Nose

The FRC sponsored the fixed-ball-nose experiment to investigate the feasibility of using a fixed – sphere-cone sensor to measure air data parameters in extreme flight environments. Rodney K. Bogue and John P. Cary built the experiment hardware.-1200

The standard X-15 ball nose proved to be remarkably reliable given its operating environment, performing less than satisfactorily on only one of its first 70 flights. Nevertheless, in retrospect, the ball nose was an overly complicated solution to the problem. All that was really needed was a way to compute the difference in pressure between opposing ports, not to drive the entire sensor to seek the null pressure.

Late in the program, NASA flew an experiment that used a non-moving sensor to detect the angle of attack. Researchers attached a fixed ball nose on the left wing-tip pod, permitting the use of the normal ball nose for comparison purposes. The sensor consisted of a ported sphere, 4.36 inches in diameter, mounted on the nose of the pod. The total length of the sensor was 18.75 inches, but it looked like a simple extension of the pod. Five pressure ports were located on the pod. One port was 5 degrees below the zero angle-of-attack stagnation point, and the remaining four ports were located symmetrically around this point in the vertical and horizontal planes. The vertical ports were used to measure the angle of attack. Researchers planned to use the horizontal ports for the angle of sideslip, but this was never implemented. The sensor flew on a single flight (1-53-86) to Mach 5.17 with Bob Rushworth at the controls.-1200

The standard ball nose had a demonstrated measurement error of less than 0.25 degree over its entire operating range. On its single flight, the fixed nose did not return the same absolute data as the ball nose. This was not surprising since the wing-mounted device and the nose-mounted unit operated in different flow fields. Several factors affected the performance of the wing – mounted device, including 1) flow disturbances and shock-wave impingement from the forebody of the X-15, 2) rotational flow about the lifting-wing surface (the latter effect was particularly noticeable during approach and landing), and 3) suspected small deflections (bending and twisting) of the wing that created a variable offset between the normal – and fixed-ball-nose devices. Nevertheless, the fixed-ball-nose data showed the same trends as the ball-nose data. Researchers concluded that the fixed ball nose was a feasible alternative to the ball nose.-1200

Confidence was high enough that NASA manufactured a "fixed alpha nose" and installed it on a wing-tip pod for six of the last seven X-15-1 flights. Again, the data did not precisely match those obtained with the ball nose, but were repeatable enough that researchers could make consistent correlations. A conceptually similar system was used on the Apollo launch escape system to provide limited air data to the astronauts in case of an abort forced them to separate the capsule from the Saturn booster. NASA designed and installed a similar system, using ports in the nose cone, on the Space Shuttle Columbia as the Shuttle Entry Air Data System (SEADS) experiment between 1986 and 1991.-1200

Scott Crossfield flew the X-15 for 18 months, from 8 June 1959 until 6 December 1960, making 14 flights. These included one glide flight, 10 flights with the XLR11, and three flights with the XLR99. Crossfield reached Mach 2.97, a speed of 1,960 mph, and an altitude of 88,116 feet. His accomplishments include the first X-15 glide flight, the first powered flight, the first flight with the XLR99, and the first emergency landing.

Albert Scott Crossfield was born on 2 October 1921 in Berkeley, California. He began his engineering training at the University of Washington in 1940, but interrupted his education to join the U. S. Navy in 1942. Following flight training, he served as a fighter and gunnery instructor, and maintenance officer before spending six months in the South Pacific without seeing combat duty. After the war, Crossfield was the leader of a Navy acrobatic team that flew FG-1D Corsairs at various exhibitions and airshows in the Pacific Northwest.-17

He resumed his engineering studies in 1946 and graduated with a bachelor of science degree in aeronautical engineering from the University of Washington in 1949. He earned a master of science degree in aeronautical science the following year from the same university, and received an honorary doctor of science degree from the Florida Institute of Technology in 1982.

Crossfield joined the HSFS as a research pilot in June 1950. During the next five years he flew the X-1, X-4, X-5, XF-92A, D-558-1, and D-558-2 aircraft, accumulating 87 rocket-powered flights in the X-1 and D-558-2, and 12 in the D-558-2 with jet power only. On 20 November 1953, Crossfield became the first pilot to exceed Mach 2, in the D-558-2 Skyrocket. Crossfield left the NACA in 1955 to work for North American Aviation on the X-15 as both pilot and design consultant.[8]

In 1960, Crossfield published his autobiography (written with Clay Blair, Jr.), Always Another Dawn: The Story of a Rocket Test Pilot (Cleveland and New York: World Publishing Company,

1960; reprinted New York: Arno Press, 1971; reprinted North Stratford, NH: Ayer Company

Publishers, 1999). The book covers his life through the completion of the early X-15 flights and is a fascinating story for anybody who is interested in that period of flight test.

Crossfield also served for five years at North American as the director responsible for systems test, reliability engineering, and quality assurance for the WS-131 Hound Dog missile, the Paraglider, the Apollo command and service module, and the Saturn booster. From 1966 to 1967 he served as technical director of research engineering and test at North American Aviation.

Crossfield served as an executive for Eastern Airlines from 1967 to 1973, and as senior vice president of Hawker Siddeley Aviation during 1974-1975. From 1977 until his retirement in 1993, Crossfield served as technical consultant to the House Committee on Science and Technology, advising committee members on matters related to civil aviation. In 1993 he received the NASA Distinguished Public Service Medal for his contributions to aeronautics and aviation over a period spanning half a century.

Crossfield was a joint recipient of the 1961 Robert J. Collier Trophy presented by President John F. Kennedy at the White House in July 1962. Other awards included the International Clifford B. Harmon Trophy for 1960, the Lawrence Sperry Award, the Octave Chanute Award, the Iven C. Kincheloe Award, and the Harmon International Trophy. He has been inducted into the National Aviation Hall of Fame (1983), the International Space Hall of Fame (1988), and the Aerospace Walk of Honor (1990). In 2006 the American Astronautical Society awarded Crossfield and David Clark the Victor A. Prather Award for the development of the full-pressure suit. Crossfield died on 19 April 2006 when his Cessna 210 crashed during a severe thunderstorm over Georgia.191

Bob White flew the X-15 for 32 months from 13 April 1960 until 14 December 1962, making 16 flights. These included six flights with the XLR11 and 10 with the XLR99. White reached Mach 6.04, a maximum speed of 4,093 mph, and an altitude of 314,750 feet. His accomplishments include the maximum Mach number (3.50) and maximum altitude (136,000 feet) with the XLR11, the first Mach 4 flight (of any manned aircraft), the first Mach 5 flight, the first Mach 6 flight, the first flight over 200,000 feet (of any manned aircraft), the first flight over 300,000 feet, and an FAI record flight of 314,750 feet (which still stands as of 2006).

Robert Michael White was born on 6 July 1924 in New York, New York. He entered the Army Air Forces in November 1942 and received his wings in February 1944. White subsequently joined the 354th Fighter Squadron in July 1944 flying the P-51 Mustang. In February 1945, the Germans shot White down during his 52nd combat mission. He was captured by the Germans and remained a prisoner of war for two months.

White returned to the United States and enrolled in New York University, where he received a bachelor’s degree in electrical engineering in 1951. The Air Force recalled him to active duty in May 1951 as a pilot and engineering officer with the 514th Troop Carrier Wing at Mitchel AFB,

New York. In February 1952, the Air Force sent him to Japan and assigned him to the 40th Fighter Squadron as an F-80 pilot and flight commander until the summer of 1953.

White became a systems engineer at the Rome Air Development Center in New York. In January 1955, he graduated from the Experimental Test Pilot School and stayed at Edwards to test the F – 86K, F-89H, F – 102A, and F-105b. He became the deputy chief of the Flight Test Operations Division, and somewhat later became assistant chief of the manned spacecraft branch. Following the death of Iven Kincheloe, backup pilot White was designated the primary Air Force pilot for the X-15 program in 1958.

In October 1963, White became the operations officer for the 36th Tactical Fighter Wing at Bitburg, and then served as the commanding officer of the 53rd Tactical Fighter Squadron. He returned to the United States in August 1965 to attend the Industrial College of the Armed Forces in Washington, where he graduated in 1966. That same year, he received a master of science degree in business administration from The George Washington University. White went to Southeast Asia in May 1967 as deputy commander for operations of the 355th Tactical Fighter Wing, and flew 70 combat missions.

In June 1968, he went back to Wright-Patterson as director of the F-15 Systems Program Office. Brigadier General-selectee White assumed command of the AFFTC on 31 July 1970. White commanded the AFFTC until 17 October 1972 when he assumed the duties of commandant of the Air Force ROTC. In February 1975 he received his second star, and in March he became chief of staff of the Fourth Allied Tactical Air Force. White retired from active duty as a major general in February 1981.-131

White was a joint recipient of the 1961 Robert J. Collier Trophy presented by President John F. Kennedy at the White House in July 1962. He also received the NASA Distinguished Service Medal, the Harmon International Trophy from the Ligue Internationale des Aviateurs for the most outstanding contribution to aviation for the year, and the Iven C. Kincheloe Award. Among his many military decorations are the Air Force Cross, the Distinguished Service Medal, the Silver Star with three oak leaf clusters, the Legion of Merit, the Distinguished Flying Cross with five oak leaf clusters, and the Knight Commander’s Cross of the Order of Merit of the Federal Republic of Germany.-1321