Category X-15 EXTENDING THE FRONTIERS OF FLIGHT

Walter Charles Williams was born on 30 July 1919 in New Orleans, Louisiana. He earned a bachelor of science degree in aerospace engineering from Louisiana State University in 1939 and went to work for the NACA in August 1940, serving as a project engineer to improve the handling, maneuverability, and flight characteristics of World War II fighters. Williams became the project engineer for the X-1 in 1946 and went to the site that eventually became Edwards AFB to set up flight tests for the X-1.[33]

He was the founding director of the organization that became the Dryden Flight Research Center{AQ8}. In September 1959, he became the associate director of the new NASA Space Task Group at Langley, which was created to carry out Project Mercury. He later became director of operations for the project, and then associate director of the NASA Manned Spacecraft Center in Houston (subsequently renamed the Johnson Space Center).

In January 1963, Williams moved to NASA Headquarters as deputy associate administrator of the Office of Manned Space Flight, and received an honorary doctorate of engineering degree from Louisiana State University. From April 1964 to 1975, he was vice president and general manager of The Aerospace Corporation. Williams returned to NASA Headquarters as chief engineer in 1975 and retired from that position in July 1982. Twice Williams received the NASA Distinguished Service Medal. He died at his home in Tarzana, California, on 7 October 1995.

[1] Memorandum for the files (Langley), subject: minutes of the meeting with ARDC representatives, 16 July 1954.

[2] Letter, NACA Headquarters to Langley, subject: research authorization, 21 July 1954.

[3] Letter, Richard V. Rhode, NACA Headquarters, to Robert R. Gilruth, Langley, no subject, 4 August 1954; telephone conversation, John V. Becker with Dennis R. Jenkins, 7 March 2002.

[4] Memorandum for the files (Langley), subject: new research airplane visits, 18 August 1954.

[5] Letter, Colonel Paul F. Nay, Acting Chief, Aeronautics and Propulsion Division, Deputy Commander of Technical Operations, ARDC, to Commander, WADC, subject: New Research

Not surprisingly by today’s standards, the original cost estimates for the X-15 and the XLR99 had been hopelessly optimistic. The first Air Force estimate for development and two airplanes totaled only $12,200,000. By the time the Air Force issued the letter contracts, the estimates stood at $38,742,500 for the airframe, $9,961,000 for the engine, and $1,360,000 for the High Range.

By the time the government and North American signed the final contract, the total cost had already risen to $40,263,709 plus $2,617,075 in fee. This had increased to $64,021,146 by the beginning of 1959. During the next six months, the estimates increased first to $67,540,178, then to $68,657,644, and by 1 June to $74,500,000-almost double the letter contract amount. The three airframes ended up costing $23.5 million; the rest represented research and development expenses.-1158!

The engine was worse. In 1955 the Air Force estimated the engine costs would ultimately be about $6,000,000. The letter contract was for $9,961,000, and by the time the Air Force and Reaction Motors signed the final engine contract this had risen to $10,160,030, plus an additional $614,000 fee. At the end of FY58, the amount was over $38,000,000, and FY59 brought the total to $59,323,000. The cost for FY60 alone was $9,050,000. As of June 1959, the engine costs were $68,373,000-over five times the 1955 estimate for the entire program and almost a sevenfold increase over the initial Reaction Motors contract value. Each of the 10 "production" engines cost just over $1 million.-1159!

While it was not nearly as bad as the engine, the stable platform ran significantly over budget as well. The original contract price was $1,213,518 plus an $85,000 fee. By May 1958, the cost had increased to $2,498,518 and a year later was at $3,234,188 plus $119,888 in fee. The auxiliary power units cost $2.7 million, the ball nose another $600,000, the MH-96 adaptive control system $2.3 million, and the David Clark full-pressure suits more than $150,000.-160

During the first five years of development, the government spent $121.5 million on the X-15 program, not including laboratory and wind-tunnel testing at Wright Field, the Arnold Engineering Development Center, NADC Johnsville, and the various NACA/NASA laboratories. The funding was broken down as follows: Ї161-

Together with approximately $11,500,000 for the High Range, it was obvious that the cost of the X-15 project was going to exceed $150,000,000 before the flight program got underway. When the original development and manufacturing contracts were closed out in FY63 (replaced by sustaining engineering and support contracts), the total came to $162.8 million. By the time it was all over in 1968, the total would almost double when all operational costs and modifications were included. Most published comparisons use the final program cost of approximately $300 million, but this is an unfair comparison to the original $12.2 million because the scope was extremely different.116^

On 9 November 1962, Jack McKay launched X-15-2 from the NB-52B on his way to what was supposed to be a routine heating flight (2-31-52) to Mach 5.55 and 125,000 feet. Just after the X-15 separated, Bob Rushworth (NASA-1) asked McKay to check his throttle position, and McKay verified it was full open. Unfortunately, the engine was only putting out about 35% power. In

theory, the X-15 could have made a slow trip back to Rogers Dry Lake, but there was no way of knowing why the engine had decided to act up, or whether it would continue to function for the entire trip. The low power setting seriously compounded the problems associated with energy management since the flight planners had calculated the normal decision times for an emergency landing at each of the intermediate lakebeds based on 100% thrust. The computer power at the time was such that there was no way to recompute those decision points in real time, so the mission rules dictated that the pilot shut down the engine and make an emergency landing.

McKay would have to land at Mud Lake.-194-

As emergency landing sites went, Mud Lake was not a bad one, being about 5 miles in diameter and very smooth and hard. When Rushworth and McKay decided to land at Mud, the pilot immediately began preparing for the landing. The engine was shut down after 70.5 seconds, the airplane turned around, and as much propellant as possible was jettisoned. It was looking like a "routine" emergency until the X-15 wing flaps failed to operate. The resulting "hot" landing (257 knots) caused the left main landing skid to fail, and the left horizontal stabilizer and wing dug into the lakebed, resulting in the aircraft turning sideways and flipping upside down. Luckily, McKay realized he was going over and jettisoned the canopy just prior to rolling inverted. The unfortunate result was that the first thing to hit the lakebed was McKay’s helmet.195

As was the case for all X-15 flights, the Air Force had deployed a rescue crew and fire truck to the launch lake. Normally it was a dull and boring assignment, but on this day they earned their pay. The ground crew sped toward the X-15, but when they arrived less than a minute later, they found that their breathing masks were not protecting them from the fumes escaping from the broken airplane. Fortunately, the pilot of the H-21 recovery helicopter noted the vapors from unjettisoned anhydrous ammonia escaping from the wreck and maneuvered his helicopter so that his rotor downwash could disperse the fumes. The ground crew was able to dig a hole in the lakebed and extract McKay. By this time, the C-130 had arrived with the paramedics and additional rescue personnel. McKay was loaded on the C-130 and rushed to Edwards, and the ground crew tended to the damaged X-15. At this point the airplane had accumulated a total free flight time of 40 minutes and 32.2 seconds.-11961

It had taken three years and 74 flights, but all of the emergency preparations had finally paid off. In this case, as for all flights, the Air Force had flown the rescue crew and fire truck to the launch lake before dawn in preparation for the flight. The helicopter had flown up at daybreak. The C – 130 had returned to Edwards and carried another fire truck to an intermediate lake (they were possibly the most traveled fire trucks in the Air Force inventory). The C-130, loaded with a paramedic and sometimes a flight surgeon, then began a slow orbit midway between Mud Lake and Edwards, waiting. Outside the program, some had questioned the time and expense involved in keeping the lakebeds active and deploying the emergency crews for each mission. The flight program was beginning to seem so routine. Inside the program, nobody doubted the potential usefulness of the precautions. Because of the time and expense, Jack McKay was resting in the base hospital, seemingly alive and well. Had the ground crew not been there, the result might have been much different.-197-

Jack McKay made an emergency landing at Mud Lake on 9 November 1962 after the XLR99 stuck at 35-percent power on Flight 2-31-52. Unfortunately, the wing flaps failed and the airplane was heavy with unjettisoned propellant, resulting in a very high 257-knot landing speed. As McKay touched down, the left rear skid failed and the airplane flipped over. Since Mud was a designated emergency landing site for this flight, fire trucks were standing by and paramedics were orbiting in a C-130 transport. McKay was airlifted to the hospital at Edwards with serious injuries. McKay recovered and flew 22 more X-15 flights and the X-15-2 was rebuilt into the advanced X-15A-

2. (NASA)

Although the post-flight report stated that the "pilot injuries were not serious," in reality Jack McKay had suffered several crushed vertebra that made him an inch shorter than when the flight had begun. Nevertheless, five weeks after his accident, McKay was in the control room as the NASA-1 for Bob White’s last X-15 flight (3-12-22). McKay would go on to fly 22 more X-15 flights, but would ultimately retire from NASA because of lasting effects from this accident.-1128!

X-15-2 had not fared any better-the damage was major, but not total. On 15 November 1962, the Air Force and NASA appointed an accident board with Donald R. Bellman as chair. The board released its findings, which contained no surprises, in a detailed report distributed during December 1962. Six months after the Mud Lake accident, the Air Force awarded North American a contract to modify X-15-2 into an advanced configuration that eventually allowed the program to meet its original speed goal of 6,600 fps (Mach 6.5). Because of the basic airplane’s ever – increasing weight, it had been unable to do this, by a small margin.!199!

One of the few areas of research that were handled almost exclusively by the Air Force was studying the physiological responses of the pilots to the demanding flight profiles required for high-performance aircraft. Although NASA monitored the results of the biomedical program, the Air Force was entirely responsible for the conduct of the research.

Before the beginning of the X-15 flight program, a Convair TF – 102A (54-1354, subsequently redesignated JTF-102A) was modified to evaluate the new David Clark MC-2 full-pressure suit (and later the A/P22S-2). The David Clark Company had designed the MC-2 pressure suits with 24 electrical contact points to facilitate connections between the sensors and the telemetry system. The system monitored helmet pressure versus suit-pressure differential, cockpit pressure versus suit pressure differential, body surface temperatures, and electrocardiogram data.

Beginning in December 1958, the Air Force used the JTF-102A to familiarize the X-15 pilots with the MC-2 pressure suit and to develop baseline physiological data for each of the pilots. Researchers also used the aircraft to evaluate additional physiological instrumentation and test the operational suitability of the MC-2 for future weapons systems (unrelated to the X-15). This initial JTF-102 test program lasted several months and eventually accumulated approximately 15 hours of flight time by pilots wearing the MC-2 ensemble, although the Air Force continued to use the JTF-102 through the end of the flight program.-1151

In addition to the "numbered" experiments formally approved by the Research Airplane

Committee, the X-15s carried several other experiments that were often funded by the FRC as part of its own normal research activities.

Bill Dana flew the X-15 for 35 months from 4 November 1965 until 24 October 1968, making 16 flights. All of these were with the XLR99 engine. Dana reached Mach 5.53, a maximum speed of 3,897 mph, an altitude of 306,900 feet, and flew the last flight of the program.

William Harvey Dana was born on 3 November 1930 in Pasadena, California. He received his bachelor of science degree from the U. S. Military Academy in 1952 and served four years as a pilot in the Air Force. He joined NASA after receiving a master of science degree in aeronautical engineering from the University of Southern California in 1958.

During the late 1960s and the 1970s, Dana was a project pilot on the manned lifting-body program, for which he received the NASA Exceptional Service Medal. In 1976 he received the Haley Space Flight Award from the AIAA for his research work on the M2-F3 lifting-body control systems. In 1986 Dana became the chief pilot at the FRC, and later was an assistant chief of the Flight Operations Directorate. He was also a project pilot on the F-15 HIDEC (highly integrated digital electronic control) research program, and a co-project pilot on the F-18 high-angle-of – attack research program. In August 1993, Dana became chief engineer, a position he held until his retirement in 1998.1101

He was inducted into the Aerospace Walk of Honor in 1993 and received the NASA Distinguished Service Medal in 1997. In 1998 the Smithsonian Institution’s National Air and Space Museum honored Dana when he delivered the Charles A. Lindbergh Memorial Lecture. On 23 August 2005, Dana finally received astronaut wings for his two X-15 flights above 50 miles altitude.-1111

By January 1958, everything had moved into high gear and North American was assembling the three model NA-240 airplanes at its facility in Inglewood, adjacent to the Los Angeles International Airport. The company had released over 6,000 engineering drawings-including one that was 50 feet long-by the end of 1957, although it continued to make minor changes to the configuration. North American subcontracted about 200 items to various vendors, but manufactured the majority of the airplane on the premises.-11

ROLLOUT

On 15 October 1958, North American rolled out the first X-15 (56-6670) in Inglewood to great pomp and circumstance. It was ironic, in a way. The NACA had given birth to a concept and had nurtured the X-15 for over four years, but two weeks earlier the committee itself had ceased to exist. In its place, the National Aeronautics and Space Administration (NASA) was created effective 1 October 1958. The X-15 had been the largest development program at the NACA; it would soon be one of the smallest at a moon-destined NASA.

X-15-1 was presented during the roll-out ceremony. The air-data boom on the nose would be

used until the ball nose was ready. The bug-eye camera ports located behind the canopy and under the fuselage in the center-of-gravity compartment would provide some breathtaking views of the early flights courtesy of National Geographic. (North American Aviation).

The master of ceremonies at the rollout was Raymond H. Rice, vice president and general manager of the Los Angeles division of North American Aviation. The keynote speakers included Major General Victor R. Haugen, deputy commander of the ARDC; Brigadier General Marcus F. Cooper, commander of the AFFTC; Walt Williams, chief of the HSFS; and Harrison Storms, chief engineer for the Los Angeles division. Also in attendance were six future X-15 pilots: Neil A. Armstrong, A. Scott Crossfield, John B. McKay, Captain Robert A. Rushworth, Joseph A. Walker, and Captain Robert M. White.[2]

Congressmen and senators sat in the grandstands and Vice President Richard M. Nixon was on hand to proclaim that the X-15 had "recaptured the U. S. lead in space." There were special exhibits featuring a David Clark full-pressure suit and a mockup of the Reaction Motors XLR99 engine. Guests could sit in the X-15 fixed-base simulator, and attend a gala luncheon where everybody praised the efforts of all involved. For the X-15 team it was a moving occasion and a much-needed respite from the years of hard work.[3]

Bob White, the man who felled every Mach number and altitude milestone in the X-15, later remembered eloquently, "The X-15 … was in the public eye from its inception and grew almost asymptotically from the day of its manufacture. Witness the presence of the vice president of the United States at the X-15 rollout ceremony. The X-15 was not controversial; it was audacious. It literally vibrated the imagination that this aircraft would double the fastest speed by more than three whole Mach numbers and… fly out of the atmosphere, into space, and back again to an on – Earth landing. The X-15 did these things and many more….,,[4]

The space race had already begun, and the United States was eager to show any progress toward besting the Soviet accomplishments. Newspapers, magazines, and newsreels all heralded the X – 15 as the American entry in the space race. Considering that only four years earlier researchers had wanted to remove the "space leap" from the X-15 concept, it was ironic that many now portrayed this small black airplane as America’s response to the Soviet threat. It may have been small, but it had not come cheaply. Despite the original $12,200,000 estimate prepared by the WADC in 1954, at the time of the rollout Major General Haugen estimated that the government had spent nearly $120 million-and the airplane had not yet flown.-15

Haugen also pointed out that the X-15 rollout was taking place two weeks ahead of the schedule established in June 1956, calling this "a tribute to all of the government and industry team." The general then summed up the spirit of the program: "It has been said that there are two extremes to research or exploratory flying-the approach that, for example, would strap a man on an ICBM and see what happens, and the super safe approach that would have us take tiny steps into the unknown and be absolutely sure of each step. We believe the solution is neither of these but rather a bold step into the future within the known technical capabilities of our engineers. We believe that the X-15 represents such a bold step… that will help us build better air and space vehicles in the future."[6]

Perhaps because his base would host the flight testing, Brigadier General Cooper was a little more cautious in his remarks: "I wish to point out here that this research program will be one of long duration, and the type of flights which excite the imagination and make newspaper headlines are many, many months away." However, the general could not resist riding the space bandwagon, at least a little, by calling the program "the first major breakthrough in sustained piloted space

Given the recent successes of the Soviets with Sputnik, the rollout of the X-15 was considered sufficiently important for the vice president of the United States to show up. Richard M. Nixon presided over the ceremonies along with distinguished speakers from the Air Force and the state of California. (North American Aviation)

Not to be outdone, Stormy Storms was even more direct: "The rollout of the X-15 marks the beginning of man’s most advanced assault on space. This will be one of the most dramatic, as in the X-15 we have all the elements and most of the problems of a true space vehicle." Describing the potential performance of the airplane, Storms said, "The performance of the X-15 is hard to comprehend. It can out fly the fastest fighters by a factor of three, a high-speed rifle bullet by a factor of two, and easily exceed the world altitude record by many times."81

Following the conclusion of the official ceremonies, North American moved the first X-15 back inside and prepared it for delivery. On the night of 16 October, covered completely in heavy-duty wrapping paper, X-15-1 traveled overland by truck through the Los Angeles foothills to Edwards for initial ground-test work.

Joe Walker would fly the maximum altitude flight (3-22-36) of the program on 22 August 1963, his second excursion above 300,000 feet in just over a month. The simulator predicted that the X-15 could achieve altitudes well in excess of 400,000 feet, but there was considerable doubt as to whether the airplane could successfully reenter from such heights. A good pilot on a good day could do it, but if anything went wrong, the results were usually less than desirable. In order to

provide a margin of safety, NASA decided to limit the maximum altitude attempt to 360,000 feet, providing a 40,000-foot pad for cumulative errors. This might sound like a lot, but the flight planners and pilots remembered that Bob White had overshot his altitude by 32,750 feet. The X – 15 was climbing at over 4,000 fps, so every second the pilot delayed shutting down the engine would result in a 4,000-foot increment in altitude. The XLR99 also was not terribly precise – sometimes the engine developed 57,000 lbf, while other times it developed 60,000 lbf. An extra 1,500 lbf for the entire burn translated into an additional 7,500 feet of altitude. A 1-degree error in climb angle could also result in 7,500 feet more altitude. Add these all up and it is easy to understand why the program decided a 40,000-foot cushion was appropriate.12051

Walker had made one build-up flight (3-21-32) prior to the maximum altitude attempt in which he overshot his 315,000-foot target by 31,200 feet through a combination of all three variables (higher-than-expected engine thrust, longer-than-expected engine burn, and a 0.5-degree error in climb angle). Walker commented after the flight, "First thing I’m going to say is I was disappointed on two items on this flight, one was that I was honestly trying for 315,000, the other one was I thought I had it made on the smoke bomb on the lakebed. I missed both of them." Although he missed the smoke bomb on landing, it was well within tolerance. As for missing the altitude, the 40,000-foot cushion suddenly did not seem very large.12061

The flight was surprisingly hard to launch, racking up three aborts over a two-week period mainly because of weather and APU problems. On the actual flight day, things began badly when both the Edwards and Beatty radars lost track on the NB-52 during the flight to the launch lake, but both reacquired it 4 minutes prior to the scheduled launch time. The launch itself was good and Walker began the long climb to altitude. Although this was the first flight for the altitude predictor,

Walker flew the mission based on its results, changing his climb angle several times to stay within a predicted 360,000 feet. When the XLR99 depleted its propellants, X-15-3 was traveling through 176,000 feet at 5,600 fps. It would take almost 2 minutes to get to the top of the climb, ultimately reaching 354,200 feet.12071

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It was not uncommon for X-15 altitude flights to miss their expected altitude. The X-15 climbed at over 4,000 fps, so every second that the pilot delayed shutting down the engine resulted in a

4,0- foot increment in altitude. The XLR99 also was not terribly precise – sometimes the engine developed 57,000-lbf; other times it developed 60,000-lbf. An extra 1,500-lbf for the entire burn translated into an additional 7,500 feet of altitude. A 1-degree error in climb angle could also result in 7,500 feet more altitude.

To give the reader a sense of what reentry was like on this flight: The airplane was heading down at a 45-degree angle, and as it descended through 170,000 feet it was traveling 5,500 fps-over a mile per second. The acceleration buildup was non-linear and happened rather abruptly, taking less than 15 seconds to go from essentially no dynamic pressure to 1,500 psf, then tapering off for the remainder of reentry, and reaching a peak acceleration of 5 g at 95,000 feet. Walker maintained 5 g during the pullout until he came level at 70,000 feet. All the time the anti-g part of the David Clark full-pressure suit was squeezing his legs and stomach, forcing blood back to his heart and brain. Walker said that "the comment of previous flights that this is one big squeeze in the pullout is still good." The glide back to Edwards was uneventful and Walker made a perfect landing. The flight had lasted 11 minutes and 8 seconds, and had covered 305 ground miles from Smith Ranch to Rogers Dry Lake. Although Walker had traveled more than 67 miles high, well in excess of the 62-mile (100-kilometer) international standard supposedly recognized by NASA, no astronaut rating awaited him. This was apparently reserved for people who rode ballistic missiles at Cape Canaveral, and it would take 42 years to correct the oversight.-1208!

By the end of 1963, the program had gathered almost all of the data researchers had originally desired and the basic research program was effectively completed. The program would now push into the basic program extensions phase using X-15A-2 to gather similar data at increasingly high speeds while the other two airplanes continued the follow-on experiments. The basic program extensions were a set of experiments that had not been anticipated when the Air Force and NASA conceived the basic program. Some were truly follow-ons to issues that were uncovered during the basic program; others were the result of new factors, such as the increased capabilities of the modified X-15A-2. In general, researchers continued all of the original research into aerodynamics, structures, and flight controls for the rebuilt airplane. The FRC paid for many of the experiments from general research funds, not from a separate appropriation from Headquarters or Congress.-1209

Despite the progress and future plans, there was no uniform agreement that the X-15 program should continue. At least privately, several officials (including Paul Bikle) argued that the value of the projected research returns was not worth the risk and expense, and that the program should be terminated at the conclusion of the basic research program, or as soon as the X-15A-2 had completed its basic program. This body of opinion was the same that had initially led NASA to argue against modifying X-15-2 into the advanced configuration. However, by this time the X – 15A-2 was well under construction and researchers had proposed an entire series of follow-on experiments, making it unlikely that the program would be terminated any time soon.-129

Although the point would be moot after the Department of Defense canceled the Dyna-Soar on 10 December 1963, at the end of 1963 the X-15 program was making plans for four unnamed future X-20 pilots to make high-altitude familiarization flights in X-15-3 during the first half of 1964. Several of the Dyna-Soar pilots had already flown the X-15 simulator in preparation.-121

When the Air Force approved the X-15 program in December 1954, the aviation medical community in the United States had already embarked on research into the physiological effects of weightlessness in anticipation of technological developments that would permit manned space flight. This research consisted largely of obtaining physiological measurements from human subjects while they flew Keplerian trajectories in a modified Lockheed F-94C Starfire and attempted to perform certain psychomotor tasks. The maximum duration of weightlessness in these early experiments was 30-40 seconds, and it was difficult to separate the subject’s responses to the weightless state from his responses to the pre – and post-trajectory accelerations. Nausea and vomiting, for example, occurred in the majority of test subjects in these experiments, probably due to the relatively rapid transitions between hypergravic and hypogravic states. Despite the amount of uncertainty surrounding the experiments, some medical researchers nevertheless concluded that weightlessness would induce nausea and vomiting in most people.

The Air Force widely reported this conclusion, which greatly influenced several early manned space studies.-161

Because the X-15 flight profiles would provide longer periods of weightlessness than were possible with lower-performance aircraft, acquiring physiological data became an early objective of the program. As North American finalized the X-15 configuration, there were additional reasons for monitoring biomedical data from a safety standpoint. Since the cockpit of the X-15 was engineered for a 3.5-psi differential between the inside of the cockpit and the outside atmosphere (or lack thereof), it was not considered feasible to use a breathable atmosphere. At sea level, oxygen accounts for approximately 20% of the normal atmospheric pressure of 14.7 psi. A breathable atmosphere therefore requires 20% of the normal 14.7 psi-about 3 psi of oxygen in the 3.5-psi cockpit.-171 Engineers considered the problems of combustion and fire associated with this 86% oxygen atmosphere to be insurmountable. As a result, North American pressurized the X-15 cockpit and ventilated the full-pressure suit with nitrogen, supplying breathing oxygen to the helmet area only. A neck seal (MC-2 suit) or a face seal (A/P22S-2 suit) separated the breathing space from the remainder of the suit. In order to prevent the leakage of nitrogen into the breathing space, technicians adjusted the breathing-oxygen regulator to deliver oxygen at a pressure 1 inch of water higher than the suit pressure.-181

The maintenance of this helmet-suit pressure differential was vital, since otherwise the pilot could develop an insidious hypoxia that would lead to serious impairment or unconsciousness. The suit pressure regulator maintained 3.5 psi in the suit, the same pressure maintained in the cockpit. In the event of loss of cockpit pressure, the suit would automatically inflate, thus preventing a catastrophic decompression of the pilot. It was not particularly unusual for the suit to inflate partially as the X-15 cabin differential changed during exit or reentry. The suit/cabin-pressure differential provided an indication of the proper functioning of the suit and suit-pressure regulator, and the cabin-pressure regulator. In the event of failure of the suit regulator or breathing-oxygen regulator, the pilot could select the emergency oxygen system that pressurized both the suit and helmet with oxygen; this was the same emergency system used during ejection.-1191

North American designed and fabricated the original biomedical instrumentation system as part of the basic X-15 contract. The system monitored eight parameters, including the ECG, oxygen flow rate, helmet/suit-pressure differential, cabin/suit-pressure differential, and pilot skin temperature, from four locations. The helmet/suit-pressure differential also served as an excellent respirometer; since the breathing space in the helmet was relatively small, the pilot’s respiration produced pressure fluctuations that the 0-0.5-psi transducer could follow, providing a real-time indication of respiratory rate. The ECG, oxygen flow rate, and skin temperatures were recorded using an onboard oscillograph recorder. The two pressure differentials were sent to the ground via PDM telemetry and displayed in the control room, along with cabin pressure (obtained via vehicle, not biomedical, instrumentation) on a heated stylus stripchart recorder. The first physiological and environmental data recorded on the X-15 program were obtained during flight 1-6-11 on 6 May 1960 with Bob White at the controls.-1291

One of the first things that researchers assessed on the X-15 was whether the cockpit environment adequately protected the pilot. The requirement was to keep the pilot’s skin temperature below 100°F even though the aircraft’s outer skin could heat to nearly 1,000°F. In fact, researchers found that the cockpit outer wall was reaching 750°F, but the cockpit itself remained in a temperature range between 36°F and 81°F. The Air Force removed the skin- temperature sensors after the first round of flights when it became obvious that the mission was not exposing the pilot to any significant thermal stress.1211

The original biomedical signal-conditioning package, mounted in the instrumentation compartment behind the cockpit, was 5 by 6.5 by 11.5 inches in exterior dimensions and weighed 11 pounds. In general, this instrumentation functioned well, but as researchers gained experience they corrected minor deficiencies and simplified the system. For example, the original ECG used five electrodes that simulated the clinical I, II, III, and V4 leads. However, since the ST segment and T(minus) wave changes are essentially uninterpretable under dynamic conditions, a one-channel ECG gave just as much information as a multi-channel system. Therefore, the ECG was simplified to a three-electrode configuration (two 0.75-inch-diameter stainless-steel screen mid-axillary leads and a reference electrode on the lower abdomen). A silicone potting compound ring surrounded the metal mesh electrode, a conductive paste assured good contact with the skin, and pressure-sensitive adhesive secured a plastic cap over each electrode to keep it in place.

Beginning with flight 2-18-34 on 12 September 1961, the Air Force installed a Tabor Instruments amplifier on the ejection seat. Amplifying the signals closer to the pilot resulted in much better data.1221

Researchers found the pilot’s heart rate during flight usually increased from the normal 70-80 beats per minute to 140-150 per minute, but with no apparent physiological effect. One interesting finding, later confirmed on Mercury flights, was that the pilot’s heart rate decreased during the period of zero g. The reduction, however, was not great (to about 130 beats per minute). The respiration rate followed similar trends, increasing to three or four times the resting rate, but researchers considered this less meaningful because talking influences the respiratory system and has a poor dynamic response rate in any case. On almost all flights, there was a large peak in respiration rate during the powered portion of the flight when the pilots tended to breathe rapidly and shallowly.[23]

During the initial phases of the flight program, researchers only installed the biomedical package in the X-15 on a non-interference basis. As a result, it frequently did not work correctly since technicians had not allocated sufficient time to its installation and checkout. Most of the difficulties were traced to shorts and broken wires. Although the biomedical team coordinated with the Air Force and NASA, the next flight frequently suffered the same problems. As a result, in early 1961 the Air Force and NASA assembled a dedicated team to work on biomedical issues, and the system became much more reliable.[24]

The researchers requested that the biomedical instrumentation package fly on all XLR99 flights that expanded the envelope. In a meeting held at the FRC on 2 December 1960, the Air Force and NASA agreed that the acquisition of physiological data was important from both a flight-safety and research perspective. However, NASA did not make the acquisition of biomedical data mandatory, mainly because it did not want to have to cancel a flight because the biomedical package failed.-1251

After Paul Bikle approved the concept of installing an FM-FM telemetry system dedicated to the biomedical package, the Air Force awarded a $79,000 contract to the Hughes Aircraft Company to develop and manufacture the system.-126 The system included an FM radio transmitter rather than a hardwire link to the aircraft telemetry transmitter. This was done to demonstrate the feasibility of the radio link in order to permit the mobility expected on future spacecraft. The final Bendix TATP-350 unit measured 9.30 by 3.95 by 0.70 inches and weighed 0.84 pound. The first unit was delivered in March 1962, and the third and final unit was delivered in July 1962. Researchers demonstrated the system during flights of the JTF-102A using MC-2 suits, and in an unusual test the system received a telemetered ECG from a free-falling parachutist.-1271

NASA installed the new FM-FM system in all three X-15s during the summer of 1962. This installation permitted the ECG to be telemetered and displayed in the control room along with the helmet/suit – and cabin/suit-pressure differentials, cabin pressure, and two axes of aircraft acceleration (vertical and longitudinal). The system multiplexed these signals onto a single FM channel and then displayed them on a six-channel Sanborn stripchart recorder in the control room.-126

In 1962, the AFFTC began providing biomedical system expertise to the Dyna-Soar program. Because of severe space and weight limitations on the X-20, miniaturization was an absolute necessity. Based on its success in providing the X-15 FM-FM system, the Air Force awarded Hughes Aircraft a contract to fabricate two prototype signal-conditioning units designed around X-20 requirements. Researchers first used the system to monitor environmental and physiological data during dynamic simulations on the centrifuge at NADC Johnsville. When North American rebuilt X-15-2 into its advanced configuration, the company installed a Hughes signal­conditioning system to test the new system prior to its use on the X-20. After the cancellation of the Dyna-Soar program in December 1963, Hughes modified the design to incorporate interchangeable modules that could meet a variety of requirements. Hughes repackaged the system so that all of the modules were a common size and used identical connectors.-1291

The final package measured 4.0 by 3.5 by 0.7 inches and weighed only 0.6 pound. Like the earlier

Hughes system, this package used an FM transmitter link to the aircraft telemetry system, although a hardwire link could also be used if needed. For X-15 use, the package provided the ECG, helmet/suit – and cabin/suit-pressure differentials, Korotkoff sounds, and partial pressure of oxygen in the breathing space. When required, researchers could substitute modules that provided the partial pressure of CO2 and an impedance pneumogram.[30]

During the summer of 1963, the Air Force again modified the biomedical instrumentation, this time by adding a blood-pressure monitoring system developed by the Air Force School of Aerospace Medicine at Brooks AFB, Texas. The system used an occlusive cuff crystal microphone to determine arterial pressure in the upper arm. An electro-pneumatic programmer that cycled once per minute automatically inflated the cuff. During deflation of the cuff, a microphone detected the Korotkoff sounds, and a display showed these sounds simultaneously with the cuff pressure trace and the ECG. The system could be turned on or off by the pilot and had a fail-safe feature that could dump the pressure in the cuff in the event of a power failure, preventing a tourniquet effect from the cuff. Surprisingly, the first few flights of the package did not yield meaningful blood-pressure information, since the pilot’s pressures exceeded the maximum reading available on the instrumentation. The school modified the cuff inflation pressure to allow up to 240 millimeters of mercury to obtain useful systolic pressure end-points.-131

The school had used the blood-pressure monitoring system for in-flight studies using conventional jet aircraft for some time, and it had been very reliable in service. However, the initial use in the X-15 was not completely satisfactory because of a generally inadequate signal-to – noise ratio. The X-15 environment proved to be particularly severe; the combination of frictional noise from the suit, vibration, acoustic noise, and pilot movement artifacts produced a high background noise and a low signal-to-noise ratio. Researchers experimented with several filters and amplifiers, and eventually found a satisfactory combination.-32

In addition to the ECG and various cockpit and suit pressures and temperatures, the researchers added blood pressure, skin temperature (on the calf, abdomen, forearm, and axilla), respiratory rate, radiation, and partial pressures of oxygen and carbon dioxide in the helmet. A $47,000 Bendix Aviation mass spectrometer determined the partial pressure of oxygen, carbon dioxide, carbon monoxide, nitrogen, and water vapor.[33] A linear pneumotachometer provided by Spacelabs, Inc., under a $23,000 Air Force contract341 furnished a rapid method for determining the total oxygen consumed by measuring changes in the pilot’s breathing rate.35

As researchers evaluated the biomedical data during the flight program, it became apparent that the initial objective of obtaining data on the physiological response to weightlessness was not feasible using the X-15. The duration of weightlessness (3-4 minutes) was too short and the pilot’s responses were conditioned by too many uncontrollable variables that occurred simultaneously for any conclusions to be made concerning the physiological response to weightlessness. In addition, the manned space programs initiated shortly after the X-15 began its flight program provided a much longer weightlessness duration without the attendant stresses of having to fly the airplane; this portion of the X-15 data was instantly obsolete. Nevertheless, the X-15 data provided researchers a unique opportunity to observe the basic physiological responses of pilots in manned vehicles flying exit and reentry profiles-something that Mercury did not, since the astronaut was simply along for the ride during those periods.-1361

The "Saturn insulation" experiment exposed various types of insulation material from the Saturn launch vehicles to the hypersonic environment. Some documentation shows this as experiment #41. The X-15-3 made at least five flights with pieces of Saturn insulation material. By flying the material on the X-15, researchers could examine it after a flight, which was not possible with the expendable Saturn boosters. Generally, researchers installed variable-thickness panels on the upper speed brakes with two thermocouples on the left side, and seven thermocouples, two static-pressure transducers, and one pitot probe on the right side. They also installed additional constant-thickness insulation panels on the lower speed brakes with two thermocouples on the right side and seven thermocouples on the left side. NASA installed a camera in the right wing-tip pod to look at the upper speed brakes, and a second camera in the left pod pointed at the lower speed brakes. Some of the tests were decidedly unsuccessful. For instance, NASA applied Saturn insulation to the upper left speed brake on the aborted flight attempt on 31 October 1967 (3-A – 96); the bond failed and the insulation came off during the captive flight. Researchers replaced the insulation before Mike Adams’s fatal flight (3-65-97).[204]

The test of insulation for the Saturn launch vehicles is usually heralded as one of the X-15’s contributions, but in reality the tests were minimal and concentrated more on the adhesives behind the insulation. Here the Saturn insulation is installed on the upper speed brakes of X-15-3 on 31 October 1967, just before its last flight. Note the tail cone box behind the speed brakes. (NASA)

After X-15-3 was lost, NASA transferred the experiment to X-15-1. Researchers installed 16-

mm movie cameras in each wing pod to photograph the insulation on the upper speed brakes, and installed 18 thermocouples in the speed brakes themselves. Several flights carried the insulation until the end of the program, although sometimes it was on the lower speed brakes (and other times on both).-1205!

Since these tests were conducted fairly late in the Saturn development program (1966-1967), it is unlikely that any unexpected information was gained. More probably, the researchers just achieved final confirmation of the material’s ability to withstand high dynamic pressures without losing its thermal properties.