The XLR99 Arrives

The first ground-test XLR99 (s/n 101) arrived at Edwards on 7 June 1959, and the first hot test was accomplished without an actual X-15 at the Rocket Engine Test Facility on 26 August 1959. X-15-3 arrived at Edwards on 29 June 1959. It was essentially identical to the other two airplanes in that it was equipped with a standard Westinghouse stability augmentation system, a stable platform, and a normal cockpit instrument panel. What made it different, at this point, was that it had the XLR99 engine. X-15-3 was never equipped with the XLR11 engines. At the same time, North American removed the second X-15 from flight status after its ninth flight (2-9-18) on 26 April 1960 in anticipation of replacing the XLR11 engines with the XLR99. This left only X-15-1 on active flight status, although the XLR99-powered X-15-3 would soon be joining it.[90]

North American made the first ground run with the XLR99 in X-15-3 on 2 June 1960 at the PSTS. Subsequent inspection revealed damage to the liquid-oxygen inlet line brackets, the result of an unexpected, but easily corrected, water-hammer effect. After repairs were completed, the company conducted another ground run with satisfactory results. For all of the ground runs during the program, a pilot had to be in the cockpit since the nearby blockhouse could not operate the engine by remote control. For the early tests, the pilot was Scott Crossfield, although all of the pilots would participate in ground runs prior to their first flights. The MC-2 full – pressure suit was an order of magnitude more comfortable than earlier pressure suits, but Crossfield still had little desire to wear it more than necessary. Since there was no need for altitude protection during the engine runs on the ground, Crossfield generally wore street clothes in the cockpit. All other personnel required for the tests were in the blockhouse, with the exception of Air Force fire crews a relatively safe distance away.-191

The third ground run began on 8 June at approximately 1930 hours. The objectives were to demonstrate the restart capability and throttling characteristics of the XLR99. All pre-test operations, servicing, and APU starts were successful and all systems were operating normally.

The engine was primed, set to idle, and then ignited at 50% thrust. After the chamber pressure stabilized for 7 seconds, Crossfield advanced the throttle to 100% for 5 seconds and then moved the throttle to idle for 5 seconds before shutting down the engine. Nobody noted anything abnormal during these events. After 15 seconds, Crossfield moved the throttle to the 50% position. The turbopump started normally, first-and second-stage ignition occurred, and the main chamber start appeared normal. After the main chamber pressure stabilized, it rapidly fell off and the engine shut down automatically. At this time, a valve malfunction light came on in the cockpit, so Crossfield moved the throttle to the off position and the light went out. In order to

restart the XLR99 after a malfunction shutdown, the pilot had to push a switch that reset the automatic safety devices. As Crossfield wrote in his accident statement, "the reset button was depressed at which time the airplane blew up." It was approximately 1945 hours.-192

Crossfield later observed, "During this entire sequence except for the malfunction shut down, there was no evidence in the cockpit of difficulty." The explosion appeared to be centered forward of the engine compartment, and caused the aircraft to separate around fuselage station 483.5, just forward of the liquid-oxygen tank. Don Richter, who was in the main blockhouse, indicated that he observed the explosion originating 5 feet forward from the aft end of the airplane, with the fireball quickly expanding to about 30 feet in diameter.-192

The explosion threw the entire forward fuselage about 30 feet forward. Crossfield said, "In the explosion, which is not describable, the cockpit translated abruptly forward and to the right with an acceleration beyond the experience of this pilot." The basic X-15 airframe had been designed – largely at Crossfield’s urging-to protect the pilot in case of an emergency; it appeared to work well. Ever the competent test pilot, Crossfield turned on his Scott airpack, turned off the engine switches, and pulled all the circuit breakers. He attempted to contact personnel inside the blockhouse, but the explosion had severed communications with the ground.-194

The fire truck that had been standing by was on the scene within 30 seconds, water pouring from its overhead nozzle, and a second fire truck arrived a minute or two later to help extinguish the fires. Art Simone and a suited fireman rushed to the cockpit and Crossfield was rescued uninjured. Simone had inhaled ammonia fumes and received minor burns to his hands, but suffered no lasting effects. The fires were largely out within a few minutes of the explosion, and Crossfield was safe. It was time to figure out what had happened.-192

Representatives from the Edwards provost marshal’s office, the North American industrial security office, and the Edwards air police arrived on the scene and roped off the area pending an investigation. Around 2110 hours, North American photographer Stan Brusto arrived to photograph the wreckage; after this was complete, the Air Force removed the data recorders from the aircraft for analysis. The air police withdrew after putting into place procedures to limit access to the area, leaving one fire truck on standby just in case. Personnel spent the next 24 hours finding all the bits and pieces blown from the aircraft, tagging them, and preparing to move the remains of the aircraft back to Inglewood. Major Arthur Murray from the X-15 project office authorized the move on 10 June.-196

Engineers removed the XLR99 from the wreckage on 13 June and took it to hangar 1870 at Edwards for inspection. North American transported the remains of X-15-3 by truck from Edwards on 15 June, parking overnight at the intersection of Sepulveda and San Bernardo Road before continuing on to Inglewood on 16 June.-192 By 4 August the company had assessed the damage and determined that the airframe would have to be replaced from fuselage station 331.9 aft. The dorsal and ventral stabilizers, all four speed brakes, both horizontal stabilizers, both main landing skids, and both propellant tanks would be replaced. The company considered the wings repairable, as were the APUs and stable platform. All of the miscellaneous equipment in the rear and center fuselage, along with most of the research instrumentation in the aft fuselage, also required replacement. Reaction Motors did not consider the XLR99 repairable, although the company salvaged some parts for future use. The Rocket Engine Test Facility required major repairs, but was back on line by the end of June.-192

Force had incorporated a vapor-disposal system into the PSTS to allow the ammonia fumes to be vented from the airplane during engine testing without endangering people. Essentially the disposal system consisted of a 90-foot pipe that connected the airplane ammonia vent to a water pond where the ammonia was diluted. At the time of the explosion, the ammonia tank pressurizing gas regulator froze or stuck in the open position while the vent valve was operating erratically or modulating only partially open. North American had considered this condition a potential failure on the airplane itself, and had addressed the problem during development. However, when combined with the back pressure created by the vapor-disposal system attached to the ammonia vent, the tank pressure surged high enough to rupture the tank. In the process, debris damaged the hydrogen-peroxide tank, and the mixing of the peroxide and ammonia caused an explosion.-199

Post-accident analysis indicated that there were no serious design flaws in either the XLR99 or the X-15. The Air Force determined that the cause of the accident was a failure of the pressure regulator, exacerbated by the unique configuration required for the ground test. Nevertheless, North American devised several modifications to preclude similar failures in the future. These included redesigning the pressurizing gas regulator to reduce maximum flow through an inoperable regulator, providing the regulator with additional closing forces in the event of freezing, relocating the regulator to minimize the chances of moisture accumulation and subsequent freezing, and redesigning the relief valve and its surrounding plumbing.-11"

Rebuilding the aircraft was not as straightforward as it sounded. Besides the estimated $4.75 million cost, there would be a considerable delay in obtaining suitable replacement parts. The X – 15s were not mass-produced items, and structural spares were nonexistent. The time required to repair the airplane meant it would miss most of the envelope expansion program and was, therefore, somewhat redundant.

There had been considerable interest in testing a new Minneapolis-Honeywell MH-96 adaptive flight control system in a high-speed vehicle prior to its use on the X-20 Dyna-Soar. Given the unfortunate event, the Air Force took this opportunity to modify X-15-3 to include the system. Complicating this was the fact the X-15 program was operating under a "reduced budget"-$8.6 million for FY61 instead of the $10.5 million that had been requested. However, the X-15 program still enjoyed considerable support within the Pentagon, and in early August, Air Force Headquarters authorized the ARDC to release $1 million from existing funds (i. e., the $8.6 million) to cover the procurement of long lead items needed for the repairs. The remaining $3.75 million, along with the restoration of the $1.9 million removed from the program earlier, was to follow "at a later date." In the interim, the Pentagon directed the X-15 program to "operate on a fiscal 1961 schedule compatible with… funds of $10.5 million plus an additional $4.75 million to cover the repair of the damaged aircraft." Although money never came easily for the X-15 program, it always came.-1"

The XLR99 Arrives

Scott Crossfield was at the controls of X-15-3 when it suffered a catastrophic explosion during a ground run of the XLR99. Fortunately, Cross field was not injured. Subsequent investigation showed there was nothing wrong with either the engine or airframe design and that the explosion had been caused by the failure of a minor component and the unique configuration required for ground testing. The X-15-3 was subsequently rebuilt to include the advanced MH-96 adaptive flight control system. (AFFTC History Office)

On 10 August, the Air Materiel Command requested that North American submit an estimate for the repair of X-15-3. Twelve days later the Air Materiel Command ordered the repair using the $1 million authorized by the Pentagon, and North American proceeded with the work. The company estimated that the aircraft could be completed in August 1961 and available for flight in October. The Pentagon came through at the end of March 1961, funding the X-15 program at $15.25 million-the original $10.5 million request plus the cost of rebuilding the damaged airplane.-1102!

The new money allowed the AFFTC to increase the propellants it had ordered because of 1) the high consumption of propellants required for component testing at the PSTS, 2) the high level of development testing of the APU and ballistic control system, and 3) the increased development testing of the XLR99 at the Rocket Engine Test Facility. A quick review shows the quantities and costs involved in this usually overlooked matter;!103!


Original FY61

Revised FY61

Alcohol (gal)

48,000 @ $0.51 = $24,480

60,000 @ $0.51 = $30,600

Ammonia (gal)

140,000 @ $0.28 = $39,200

256,000 @ $0.28 = $71,680

Peroxide (lbs)

261,000 @ $0.60 = $156,600

420,000 @ $0.60 = $252,000

Helium (sfc)

2,400,000 @ $0.02 = $48,000

5,400,000 @ $0.02 = $108,000

Nitrogen (tons)

1,500 @ $15.00 = $22,500

3,500 @ $15.00 = $52,500

At Inglewood, North American was installing the XLR99 in X-15-2 and incorporating several other changes at the same time. These included a revised vent system in the fuel tanks as an additional precaution against another explosion, revised ballistic control system components, and provisions to install the ball nose instead of the flight-test boom used so far in the program. The company had been looking to conduct the first flight in early September, but discovered corrosion in the engine hydrogen-peroxide tank. While North American was taking care of the corrosion, Reaction Motors tore down one of the ground-test engines to determine the condition of the individual components after 2 hours of engine operation. The inspection revealed no outstanding deficiencies or indications of excessive wear, clearing the way for the first X-15 flight with the million-horsepower engine.-1104

The installation of the ball nose presented its own challenges since it had no capability to determine airspeed. The possibility of a failure in the ball-nose steering mechanism also made it unsuitable as a total-pressure port to derive airspeed. The X-15 was designed with an alternate airspeed probe just forward of the cockpit, although two other locations-one well forward on the bottom centerline of the aircraft, and one somewhat aft near the centerline-had also been considered. Several early flights compared the data available from each location, while relying on the data provided by the airspeed sensors on the flight-test boom protruding from the extreme nose. The primary location exhibited some velocity-indication sensitivity at speeds over 345 mph and angles of attack over 4 degrees. At 8 degrees alpha the indicated airspeeds were generally about 25 mph low. The tests indicated that the data from all three locations were about the same, so the engineers decided to retain the original location. An interesting discovery was that the error was substantially less after the ball nose was installed, which led to a theory that the extended nose boom was contributing to the errors. Fortunately, the airspeed indications were consistent at the speeds and angles of attack encountered in the landing pattern, so researchers simply adjusted the instruments to compensate. After NASA installed the ball nose, engineers compared angle-of-attack data (based on the horizontal stabilizer position) with those from previous flights using the flight-test boom. The data were generally in good agreement, clearing the way for operational use of the ball nose.-105

Did it Work?

From the Martin Marietta post-flight report: "The actual flight environment in the area of the modified ventral fin proved to be much more severe than anticipated. The condition was directly attributable to interaction effects of the shock waves generated by the dummy ramjet, the ventral, and the pressure probes. The ablator applications in this area were inadequate to protect the structure under these flow conditions, and the vehicle suffered localized damage in the area."!330!

The flight had completely eroded the ablator application, including both the molded leading-edge detail and the sprayed MA-25S layer, from the forward portion of the ventral. The vehicle skin sustained major damage due to the excessively high heating in the shock impingement, which burned through at the leading edge and on the sides of the ventral at the torque box assembly. This also damaged the torque box and destroyed the wiring and pressure lines in the forward compartment.-!3331

A study of the thermocouple responses in the area of the ventral indicated that the ablator had provided at least some protection for the first 140 seconds of flight. Continual erosion of the ablator surfaces was occurring during this period, and by approximately 160 seconds the degradation was such that all protection broke down. The ablator materials should have had zero surface recession, but instead eroded away. The particles from the forward sections of ablator, in turn, caused severe impact erosion of the downstream ablator layer. The lower speed brakes were bare of ablator, and the material on the inboard edges of the main landing skids and the undersides of the side fairings experienced considerable abrasion.[352]

Otherwise, the ablator had performed well enough. The flight had uniformly charred the details over the leading edges of the wings, horizontal stabilizers, canopy, and dorsal stabilizer along their lengths. All of the parts had retained their shape, and the char layer attachment was firm. There were some signs of localized surface melt in areas of shock impingement during peak heating, but because of a continually varying velocity during the flight, shock presence in any one area was limited and the degradation was "insignificant." The nose-up trim attitude degraded the lower surface of the wing details more heavily than the upper surfaces; the reverse was true for the horizontal stabilizers.-1353

The lower, fixed portion of the dorsal stabilizer leading edge charred more heavily than the upper, movable rudder, and some evidence of unsymmetrical heating of the rudder was present, with the left side sustaining a higher heat load. The ablator details for both vane antennas were heavily charred and experienced local erosion or spallation of the char from their surface. They looked worse than they were; measurements showed that more than half an inch of ablator remained on the antennas, which were undamaged in any case.[354]

The sprayed MA-25S layer over the fuselage and side fairings showed varying degrees of effects. Thermal degradation, with the resultant reticulation of the ablator surface, occurred only on the forward areas of the nose. Ablator fissuring extended along the fuselage belly to approximately the forward vane antenna. The ablator on the crown of the fuselage and the belly aft of the vane antenna showed no evidence of thermal exposure.[355]

Engineers could easily correlate the varying amounts of charring experienced over the fuselage with their location or proximity to the various design features of the airplane. For instance, heavily charred areas were directly behind the pressure orifices in the ball nose. These openings were apparently sufficient to "trip" the flow, causing a rapid transition to turbulent boundary-layer conditions. The holes for the ballistic control-system thrusters greatly increased heating effects in their vicinity. Localized stagnation within the recesses apparently permitted burning of the ablator, evidenced by a surface discoloration. The thickness of the material behind the nose-gear door was seriously degraded.-1356

The various stacks and vents protruding from the airplane caused localized heating problems. Stagnation shock and trailing-wake damage were evident downstream from an external tank disconnect door that failed to close after the tanks were jettisoned. The ablator surface on the lower wing experienced varying degrees of charring over the whole area. This was heaviest adjacent to the molded leading edges, and some blistering was evident near the wing tips. However, the upper wing surfaces thermally degraded only near the leading edge details; the remainder of the surface was unaffected. Again, the ablator on the upper surface of the horizontal stabilizers degraded more heavily than the lower surfaces. Along the inboard edge of the stabilizers, next to the side fairings, sections of ablator were missing from both the top and bottom surfaces, forward of the torque tube. The open cavity of the stabilizer’s inboard closing rib and the adjacent fairing formed a channel to trap the airflow during flight. This resulted in severe heating within the cavity and caused degradation of the ablator from the back face.[357]

In addition to the thermal degradation, the stabilizer upper surfaces sustained a significant amount of impact damage. Some of the abrasions obviously occurred during landing since the exposed ablator was virgin material, while others had occurred early in flight and the exposed ablator had become charred. Engineers thought the likely cause was spallation of small pieces of upstream ablator of fluid droplets from the various vents and drains. As expected, ablation residue partially covered the unprotected right-hand windshield.13581

Pull tests were conducted at random locations on the surface of the ablator to determine whether it was still well bonded to the airplane. The results were generally acceptable. In the end, Martin Marietta believed that the ablator "performed satisfactorily except in the area of the modified ventral fin." Nevertheless, Martin went on to suggest a series of minor modifications that would solve some of the problems experienced on these two flights.-13591

The ablator obviously was not completely successful. Unexpectedly, the ablator actually prevented cooling of the airframe by preventing heat from absorbing into the underlying hot structure. The post-flight condition of the airplane was a surprise to Jack Kolf, an X0-15 project engineer at the FRC, who noted, "If there had been any question that the airplane was going to come back in that shape, we never would have flown it."13601

Engineers had not fully considered possible shock interaction with the ramjet shape at hypersonic speeds. As it turned out, the flow patterns were such that a tremendous shock wave impinged on the ramjet and its supporting structure. Researchers later estimated that the heat in the ventral stabilizer was 10 times higher than normal. The warning signs had been there in various wind – tunnel tests and previous flights, but researchers had not recognized them.13611

It is interesting to note that post-flight photographs of the X-15A-2 damage normally highlight two areas. The first is the ventral stabilizer and ramjet. Heating effects unquestionably damaged this area, although there had been indications on the previous flight that something was not right. The second area shown is the large fissures around the nose. When NASA replaced the ball nose before this flight, it used an outdated batch of MA-25S because it was all that was available. Although its application characteristics, cure rate, and appearance were the same as those of the "fresh" ablator used elsewhere, thermal exposure resulted in a greater shrink rate than the newer material. This produced much more pronounced fissuring, but it appeared that the ablator provided sufficient protection.13621

The original contract with Martin Marietta indicated the company was responsible for "touching up" the ablator twice to allow three flights with the initial application. The damage sustained by the ventral stabilizer precluded the aircraft from flying again in the near future. Consequently, the Air Force directed Martin to remove the ablator so that it could return the aircraft to North American for inspection and repair. NASA technicians under the direction of a Martin engineer, however, performed the actual removal. The technicians removed the MA-25S-1 strips from the service panel peripheries, cleaned the panel edges, and then applied polyethylene tape to protect the aircraft interior from contamination. They stripped the ablator layer using plexiglass scrapers and scrubbed the surface to remove all residual ablator material. The final cleaning was performed with aluminum wool and nylon pads with powdered cleanser, and wooden toothpicks proved useful for dislodging the ablator material from skin gaps and the heads of permanent fasteners.13631

Did it Work?

This is the ventral stabilizer after Flight 2-53-97; the ramjet had fallen off during landing. The X – 15A-2 skin sustained major damage due to the excessively high heating in the shock impingement, which burned through at the leading edge and on the sides of the ventral at the torque box assembly. This also damaged the torque box and destroyed the wiring and pressure lines in the forward compartment. (NASA)

NASA sent X-15A-2 to North American for repair and general maintenance. The airplane returned to Edwards on 27 June 1968, and a series of nondestructive load and thermal tests on the instrumented right wing began on 15 July in the FRC High Temperature Loads Calibration Laboratory. As it turned out, the airplane would never fly again.-1364-

Some of the problems encountered with the ablator were non-representative of possible future uses. North American had designed the X-15 with an uninsulated hot structure, but researchers expected to design any future vehicle with a more conventional airframe that would eliminate some of the problems encountered on this flight. However, other problems were very real. The amount of time it took to apply the ablator was unacceptable. Even considering that after they gained some experience the technicians could cut the application time in half or even more, the six weeks it took to coat the relatively small X-15 bode ill for larger vehicles.-1365-

Did it Work?

This is the nose of X-15A-2 after Flight 2-53-97. NASA had replaced the ball nose before this flight because of a maintenance issue, and had used an outdated batch of MA-25S to patch the area because it was all that was available. Although its application characteristics, cure rate, and appearance were the same as the "fresh" ablator used elsewhere, thermal exposure resulted in a greater shrink rate than the newer material. This produced much more pronounced fissuring, but analysis indicated that the ablator provided sufficient protection, despite appearances. (NASA)

The use of an ablative coating on X-15A-2 came at an interesting time. The development of what became the space shuttle was just beginning, with various study efforts being initiated under the auspices of NASA and the Air Force. It was obvious that some sort of reusable thermal protection system was going to be required on a space shuttle, and a great deal of attention initially turned to ablatives because they were the most mature technology available at the time. The experience with the X-15 provided very meaningful insights into the problems that the space shuttle undoubtedly would have encountered using this technology. Nevertheless, various contractors continued to propose the use of ablators on their space shuttle concepts, in decreasing quantity, until 1970 when several forms of ceramic tiles and metal "shingles" became the preferred concepts. Based at least partially on the results of the X-15 tests, the space shuttle program decided to go down a different road; whether that road was truly superior is open to debate. At least it represented a different set of problems.

At 10:30:07.4 on 15 November 1967, X-15-3 dropped away from the NB-52B 45,000 feet over Delamar Dry Lake. Major Michael J. Adams was at the controls, making his seventh X-15 flight. Adams had spent slightly over 23 hours in the fixed-base simulator practicing this particular mission (3-67-95), which was intended to evaluate the Ames boost guidance display and conduct several experiments, including measuring the ultraviolet plume of rocket exhausts at high altitude. About 1 minute after launch, as X-15-3 passed through 85,000 feet, an electrical disturbance caused the MH-96 dampers to trip out. It was later determined the disturbance most probably had emanated from electrical arcing in the experiment in the nose of the right wing-tip pod that was being flown for the first time. Adams reset the dampers and continued.-366

As planned, Adams switched the cockpit sideslip attitude indicator to an alternate display mode. One of the more controversial aspects of the attitude indicator was a second use for the cross­pointers, which were developed late in the program to allow precise pointing of several experiments. In this mode the cross-pointers displayed vernier attitude errors (pitch error on the alpha needle, and bank error on the beta needle). A switch allowed the pilot to control the display mode. During the climb, the pilot switched the display to the vernier-attitude-error mode, and would normally have switched back to the sideslip mode prior to reentry.367-

Unlike the other two airplanes, X-15-3 automatically blended the ballistic control-system thrusters with the aerodynamic controls as needed using the right side stick, allowing the pilot to largely ignore the dedicated ballistic controller on the left. The electrical disturbances fooled the flight-control system into believing that the dynamic pressure was higher than it actually was, resulting in the system failing to engage the ballistic control system as would normally occur at high altitude. Adams felt the lack of response as the airplane approached maximum altitude and began using the left side stick to operate the thrusters. Unfortunately, Adams reverted to flying the vertical needle on the attitude indicator as if it were still showing sideslip instead of its actual vernier-attitude-error display.366

Pete Knight was NASA-1 on the ground. As the X-15 climbed after engine shutdown, Adams initiated a wing-rocking maneuver to sweep the ultraviolet plume experiment up and down across the horizon. Because Adams was apparently interpreting the attitude indicator incorrectly, he began rocking the wings excessively. After Adams stopped the wing rocking, the X-15 began to drift toward its peak altitude, flying with a 15-degree sideslip to the right. As Adams descended, the drift began again and X-15-3 yawed at a right angle to the flight path. The airplane entered a hypersonic spin as it encountered rapidly increasing dynamic pressure at 130,000 feet.369

The designers of the NASA control room had not thought to provide a heading indication, so the controllers were unaware of the attitude of the airplane. Everybody knew the ball nose did not accurately align with the relative wind at altitudes above 250,000 feet, so there was little concern when the angle of attack and angle of sideslip began drifting off nominal values near peak altitude. In reality, the airplane was yawing wildly, eventually turning completely around. Fifteen seconds later Adams reported that the airplane "seems squirrelly" and at 1034 hours he advised, "I’m in a spin, Pete." Adams radioed again, "I’m in a spin," followed by groans as the pilot was subjected to heavy accelerations. Engineers knew very little about the hypersonic spin characteristics of the X-15, and there was no recommended spin recovery technique.-1370-

Did it Work?

At 10:30:07.4 on 15 November 1967, X-15-3 dropped away from the NB-52B 45,000 feet over Deiamar Dry Lake with Major Michael J. Adams at the controls. Technical problems combined with possible piloting issues caused the X-15-3 to break-up at approximately 62,000 feet with a velocity of about 3,800 fps and a dynamic pressure of 1,300 psf. The wreckage fell near Johannesburg, California. (NASA)

Realizing that X-15-3 would never make it back to Rogers Dry Lake, the chase pilots-Hugh M. Jackson and Bill Dana-shoved their F-104s into afterburner and raced for Ballarat and Cuddeback, the most likely emergency landing lakes. In the X-15, Adams used the combined power of the aerodynamic and ballistic controls against the spin. Eventually, largely through a weathervane effect, the airplane recovered at 120,000 feet and 140 psf. It then entered an inverted Mach 4.7 dive at an angle of nearly 45 degrees. At this point, it looked like Adams might pull out of the dive. However, a technical problem emerged as the MH-96 entered a limit-cycle oscillation when the airplane emerged from the spin. This prevented the system from reducing the pitch gain in response to the increasing dynamic pressure. While descending at over 2,700 fps, the X-15 began to exhibit an increasingly severe rapid pitching motion. The severe oscillations in the flight – control system effectively blocked pilot inputs. As it passed through 65,000 feet, X-15-3 was descending in an inverted dive at Mach 3.93 and approaching both the side-load and normal-load limits. At 1034:57.5, the airplane broke up at approximately 62,000 feet with a velocity of about 3,800 fps and a dynamic pressure of 1,300 psf. An Air Force pilot spotted the wreckage near the town of Johannesburg. Mike Adams was dead, and X-15-3 was destroyed.-1371!

accident, an unofficial search party from the FRC found the cockpit camera but not the film cartridge. Since the film cassette was lighter than the camera, engineers theorized that the cassette must have been blown north by winds at altitude. A search party organized by Victor Horton converged on the area on 29 November, and Willard E. Dives found the cassette. The film was flown to the EG&G laboratory in Boston for processing.

Johnny Armstrong and Jack Kolf began analyzing the cockpit film when it returned. Armstrong later recalled, "We had the time history from the flight recorded in the control room. We could see the vertical needle on the attitude indicator in the film and correlated the time of the film and the recorded time history. It became clear to us that the pilot was making manual ballistic inputs as if the vertical needle was sideslip rather than roll angle. His inputs were in the correct direction to make sideslip zero if it had been sideslip. However since it was roll angle his inputs drove the nose further from away from the flight path and eventually into… a spin."372

Did it Work?

Mike Adams flew the X-15 for 13 months from 6 October 1966 until 15 November 1967, making seven flights. All of these were with the XLR99 engine and he reached Mach 5.59, a maximum speed of 3,822 mph, and an altitude of 266,000 feet. Adams died on Flight 3-65-97. The Air Force posthumously awarded Mike Adams an astronaut rating for his last flight in X-15-3, which had attained an altitude of 266,000 feet (50.38 miles). This was the only fatality during the program’s 199 flights. (NASA)

The accident board concluded that Adams misinterpreted his instruments, and combined with distraction and possible vertigo, this led him to allow the heading of the X-15-3 to deviate unexpectedly. The overall effectiveness of the MH-96 had been degraded by the electrical disturbance early in the flight, further adding to the pilot’s workload. The MH-96 then caused the airplane to break up. The board made two major recommendations: install a telemetered heading indicator in the control room, visible to the flight controller, and medically screen X-15 pilot candidates for labyrinth (vertigo) sensitivity. Because of the crash, NASA added an attitude indicator in the control room to display real-time heading, pitch, roll, sideslip, and angle-of – attack information. Although it was not specifically called out in the accident report, many engineers came away with a more important lesson: do not use the same instrument to display multiple different indications in a high-workload or high-stress environment.-1373

The Air Force posthumously awarded Mike Adams an astronaut rating for his last flight in X-15- 3, which had attained an altitude of 266,000 feet (50.38 miles). This was the only fatality that occurred during the program’s 199 flights.-1374!

And a Couple More

Researchers considered X-ray photographs important for understanding the problems of the solar atmosphere, which led to the "X-ray mapping of the sun" experiment. Instruments on sounding rockets had obtained similar photographs of the sun, but the excessive motion of the vehicle had greatly complicated measurements. NASA installed a small pinhole camera in one of the upper bug-eye camera bays on the X-15 in January 1962. This experiment flew above 150,000 feet several times between March 1962 and September 1963.[78]

The "electron-distribution determination" experiment measured electron distribution in the upper atmosphere using radiofrequency techniques. These measurements of the ionosphere D-layer (often as low as 50 miles) were important for investigators seeking to gain a basic understanding of the ionosphere. Since the temporal variation of the electron distribution was important, a series of flights was desirable; however, there appears to be no record indicating that the experiment actually flew or acquired any useful data.[79]

Selected Biographies

Although 15 pilots were assigned to the X-15 program, only 12 of them actually flew the airplane. Al White was the backup pilot for Scott Crossfield and never needed to take over. Iven Kincheloe was the initial Air Force project pilot, but he died in an accident before the first airplane was delivered. NASA reassigned John Manke to the lifting-body program after the loss of X-15-3, before he was able to fly the X-15. In each of the four groups of government pilots, an equal number came from the Air Force and NASA. The following table shows the pilots in the order of their selection by the program:


Pilot at Edwards

Assigned to X-15

Left the X-15

Scott Crossfield


September 1955

December 1960

Al White


September 1955

December 1960

Iven Kincheloe


April 1958

July 1958

Bob White


April 1958

December 1962

Bob Rushworth


April 1958

July 1966

Joe Walker


April 1958

August 1963

Jack McKay


April 1958

September 1966

Neil Armstrong


April 1958

August 1962

Forrest Petersen


August 1958

February 1962

Joe Engle


June 1963

April 1966

Milt Thompson


June 1963

August 1965

Pete Knight


May 1965

December 1968

Bill Dana


May 1965

December 1968

Mike Adams


July 1966

November 1967

John Manke


July 1966

November 1967

There were also plans to allow four Dyna-Soar pilots to fly the X-15 before Robert McNamara canceled that program, and some sources have indicated that Jacqueline Cochran attempted to get permission to fly the X-15 to set the women’s speed and altitude records.-11


Hartley A. Soule was born on 19 August 1904 in New York City. He received a bachelor of science degree in mechanical engineering from New York University in 1927 and joined the staff at Langley in October 1927 after working briefly for the Fairchild Airplane Company in Long Island. Soule concentrated his research on stability and control, and became chief of the Stability Research Division in 1943. He became assistant chief of research in 1947 and assistant director of Langley in August 1952.

Soule was a coinventor of the stability wind tunnel and directed the construction of three other wind tunnels at Langley. He pioneered the use of computing machinery for analytical and data reduction. He was also instrumental in establishing the Pilotless Aircraft Research Division at Wallops Island. Soule became chairman of the Interlaboratory Research Airplane Projects Panel, and in that role he directed research on the Bell X-1 program and was instrumental in managing the early years of the X-15 program. Later he became project director for the Mercury worldwide tracking and ground instrumentation system. Soule retired from NASA on 16 February 1962 and passed away in 1988.

Back to Flying

In its own way, the X-15 program was "politically correct," even if the term did not yet exist. Paul Bikle had decided that a NASA pilot should make the first government X-15 flight, but he would later give the honor of performing the first government XLR99 flight to an Air Force pilot. The initial piloting duties were split evenly between one NASA pilot and one Air Force pilot. It seemed only fitting, therefore, that the third government pilot to qualify in the X-15 should be from the Navy.

Forrest Petersen checked out in the airplane while Joe Walker and Bob White conducted the envelope-expansion phase with the XLR11 engine. Like all of the early pilot familiarization flights, Petersen’s first flight would be low and slow, if that describes Mach 2 and 50,000 feet. The flight plan showed Petersen launching over Palmdale, heading toward Boron, turning left to fly back toward Mojave, and making another left turn toward Edwards. The launch went well, but as the airplane approached Boron the upper engine began to fail; soon it stopped altogether. Petersen reported that he "believed erroneously that the lower engine was still running, but the inability to hold altitude, and airspeed variations from values expected for single engine operation forced the pilot to the inevitable conclusion that both engines were shut down." Milt Thompson, who was NASA-1 for the flight, advised Petersen to head directly for Rogers Dry Lake. Petersen arrived at high key with only 25,000 feet altitude, much lower than desired, and Joe Walker tucked a chase plane into formation and coached Petersen through a tight turn onto final. The landing was almost perfect, and Petersen handled the entire incident with his usual aplomb. Petersen’s final report was understated: "Nothing during the flight surprised the pilot with the exception of early engine shutdown." The only Navy pilot was an excellent addition to the team.-1106

It was time for Crossfield to go back to work with the ultimate engine. The first flight attempt of X-15-2 with the XLR99 was on 13 October 1960, but a peroxide leak in the no. 2 APU ended the day prior to launch. Just to show how many things can go wrong on a single flight, there was also liquid-oxygen impingement on the aft fuselage during the prime cycle, manifold pressure fluctuations during engine turbopump operation, and fuel-tank pressure fluctuations during the jettison cycle. Two weeks later, Crossfield again entered the cockpit with the goal of making the first XLR99 flight. More problems with the no. 2 APU forced an abort.

On 15 November 1960, everything went right and Crossfield made the first flight (2-10-21) of X – 15-2 powered by the XLR99. The primary flight objective was to demonstrate engine operation at 50% thrust. The launch was at Mach 0.83 and 46,000 feet, and the X-15 managed to climb to 81,200 feet and Mach 2.97 using somewhat less than half the available power. The second XLR99 flight (2-11-22) tested the engine’s restart and throttling capability. Crossfield made the flight on 22 November, again using the second X-15. During the post-flight inspection of the aircraft and its engine, engineers found that, like most of the ground-test engines, the XLR99 was beginning to shed some of the Rokide coating on the exhaust nozzle.[107]

Despite being fast-paced, the X-15 program was never reckless. As North American prepared X – 15-2 for its next flight during December 1960, AFFTC commander Brigadier General John Carpenter heard rumors about the Rokide coating and called a meeting to discuss the matter. Representatives from the Air Force, NASA, North American, and Reaction Motors were present.

Each gave his opinion, which was that it appeared safe to continue. Carpenter dismissed the meeting but asked Scott Crossfield and Harrison Storms to stay. During this session he questioned Crossfield on his feelings about making the flight given the condition of the engine. Scott did not show any concern and indicated he was willing to go ahead with the flight. Carpenter excused Crossfield but asked Storms to stay.-1108

Storms recalled, "When we were alone, General Carpenter asked my opinion. I told him that earlier this day on my arrival at Edwards that I had inspected the thrust chamber in question and did not have any great concerns. Yes, some of the insulation was gone, but not to any great extent and the individual areas were small. It had not all been lost in one area, but the loss was fairly evenly well distributed over the entire area. Further, it certainly had not caused any negative comments from the manufacturer or their test engineers. The General’s comment was, ‘Very well, we will make it a joint decision to proceed with the flight.’ … Seriously, there is a point to be made here. That is, there is a very fine line between stopping progress and being reckless. That the necessary ingredient in this situation of solving a sticky problem is attitude and approach. The answer, in my opinion, is what I refer to as ‘thoughtful courage.’ If you don’t have that, you will very easily fall into the habit of ‘fearful safety’ and end up with a very long and tedious-type solution at the hands of some committee. This can very well end up giving a test program a disease commonly referred to as ‘cancelitis,’ which results in little or no progress." It was an excellent observation, and is as applicable today as it was in 1960.[109]

With the blessing of Carpenter and Storms, North American conducted the third and final XLR99 demonstration flight (2-12-23) using X-15-2 on 6 December 1960. Crossfield successfully accomplished the engine-throttling, shutdown, and restart objectives. This marked the last X-15 flight for North American Aviation and Scott Crossfield. The job of flying the X-15 was now totally in the hands of the government test pilots. Crossfield, the engineer, transferred to testing the Hound Dog cruise missile and then to the Apollo program.-1110

After this flight, the program established a work schedule that would allow an early XLR99 flight with a government pilot using North American maintenance personnel. Bob White would make the flight as early as 21 December 1960, assuming North American could accomplish the necessary maintenance work in time. This included replacing the engine, which had suffered excessive chamber coating loss; installing redesigned canopy hooks and a reinforced vertical stabilizer; rearranging the alternate airspeed system; and relocating the ammonia tank helium pressure regulator into the fixed portion of the upper vertical. The company made good progress until engineers found a pinhole leak in the chamber throat of the replacement engine during a ground run. Although Reaction Motors considered the leak acceptable, it became increasingly worse during a subsequent test. Since a spare XLR99 was not available, the program canceled the flight and established a schedule to deliver the aircraft to the government prior to another flight. As a result, North American formally delivered X-15-2 to the Air Force and turned the airplane over to NASA on 7 February 1961. On the same day, X-15-1 was returned to the North American plant for conversion to the XLR99, having completed the last XLR11 flight (1-21-36) of the program the day before with Bob White at the controls.-111

The first two years of the flight program showed five major reasons for flight cancellations: problems with the APUs and their fuel system, XLR11 problems, propellant system (less engine) difficulties, weather, and heating and ventilation troubles. When the ultimate engine came on line, the top five reasons changed slightly to XLR99 problems, propulsion system (less engine) difficulties, miscellaneous, problems with the APU and its fuel system, and stable platform failures. It was not surprising that the engine became a major source of delays, since the XLR99 was a major leap forward in rocket engine technology and growing pains were to be expected. Many of the propulsion-system problems were a direct result of the XLR99, such as some plastic seal materials being incompatible with anhydrous ammonia. Although the XLR99 was performing satisfactorily in flight, by the end of December 1960, maintenance personnel had discovered ammonia leaks in the thrust chambers of three engines. Reaction Motors dispatched technicians to Edwards to correct the problems while the Air Force, NASA, North American, and Reaction Motors all looked for a cause.112

Back to Flying

Major Robert M. White flew the last XLR11 flight of the program (1-21-36) on 7 February 1961. This was the fastest XLR11 flight, reaching 2,275 mph and Mach 3.50. Six months earlier White had gone to 136,500 feet using the XLR11s. Bob White holds the distinction of being the first man to fly Mach 3, Mach 4, Mach 5, and Mach 6, and the first pilot to fly to 200,000 feet and 300,000 feet, all in the X-15. (NASA)

From the beginning of the X-15 flight program in 1959 until the end of 1960, seven pilots had made 31 flights with the first two airplanes. The NB-52s had carried the two X-15s 55 times, including two scheduled captive flights and 22 aborted launch attempts. However, X-15-1 was experiencing an odd problem. When the pilot started the APU, the hydraulic pressure was either slow in coming up or dropped off out of limits when he moved the control surfaces. The solution to the problem was found after researchers placed additional instrumentation on the hydraulic system. The bootstrap line that pressurized the hydraulic reservoir was freezing, causing a flow restriction or stoppage. Under these conditions the hydraulic pump would cavitate, resulting in little or no pressure rise. The apparent cause of this problem was the addition of a liquid-nitrogen line to cool the stable platform. Since North American had installed the nitrogen line adjacent to the hydraulic lines, it caused the Orinite hydraulic oil to freeze. The solution was to add electric heaters to the affected hydraulic lines, since there was not enough room in the side tunnel to separate the lines sufficiently to prevent the problem.

Some problems defied all efforts to fix them. For example, North American tested the APU and its fuel system for many hours on an exact replica of the airplane installation. Yet, over the course of the program, the APUs caused more schedule delays and cancellations than any other system. One of the major problems was a critical pressure switch. Although the switch had been thoroughly (and correctly) qualified by the vendor, the program had to replace it by the dozen. Even with improvements, the switch continued to be a problem.-113

Paul Bikle closed the year by saying that he was generally pleased with the progress made: "The data coverage within this envelope has been fairly complete in the areas of performance, flight dynamics, control, and structural loads, but somewhat limited in structural heating due to the low heating rates encountered." Bikle cautioned, however, that the short duration and transient nature of each flight had generally precluded the acquisition of extensive or systematic measurements under selected flight conditions, as was possible with conventionally powered aircraft.-114-

Almost the End

On 13 October 1960, the government established the Aeronautics and Astronautics Coordinating Board (AACB) to coordinate various activities between the Department of Defense and NASA. The deputy administrator of NASA and the assistant secretary of the DDR&E served as cochairmen of the AACB; initially this meant Hugh Dryden and Herbert F. York, respectively. In an indirect way, the Research Airplane Committee that was created in 1954 to manage the X-15 program fell under the auspices of the AACB. However, given that the X-15 program existed prior to the creation of the AACB, the board had little direct impact on the program. The Research Airplane Committee continued to function much as it always had until sometime in 1965.[375]

The AACB Aeronautics Panel began discussing the issue of continued funding for the X-15 in early 1966. Charles W. Harper from NASA made a good case for continuing Air Force funding for the X-15 since both the HRE and delta-wing projects were of potential value to the Air Force as well as to NASA. Both projects were part of a joint national hypersonics program organized in May 1965 by John Becker from NASA Langley and R. E. Supp from the Air Force Systems Command. Becker and Supp made a presentation to the Aeronautics Panel on 13 June 1966 showing that the HRE and delta-wing projects would be the principal users of the X-15 after the end of 1967, although a number of other experiments also continued. After a brief discussion, the Aeronautics Panel endorsed these projects and recommended that the AACB develop a cost-sharing plan that would allow the X-15 program to continue.-1376

The next meeting of the AACB on 5 July 1966, in fact, would influence the X-15 program greatly, but not the way the Aeronautics Panel had expected. Instead, the meeting essentially defined the date the X-15 program would end. In rejecting the recommendation of the Aeronautics Panel, the AACB indicated that the two most important approved Air Force experiments (20 and 24) would conclude at the end of 1967, and the AACB saw little need for continued Air Force support of the program past that date. Beginning on 1 January 1968, the program would become the

responsibility of NASA exclusively.13771

Rather quickly, however, it became apparent that the planned completion of the two Air Force experiments would run well into 1968. Consequently, at the 24 August 1967 meeting of the AACB, the participants attempted to work out some compromise that would allow the X-15 program to continue. The agreement changed little on the surface. From a monetary perspective, NASA agreed to begin funding the sustaining engineering contracts the Air Force maintained with North American, Reaction Motors, and the other original contractors. Both agencies concluded it was easier to allow the Air Force contracts to continue than to terminate them and restart them as NASA contracts. Instead, NASA would reimburse the Air Force for the cost of the contracts. The FRC agreed to continue its maintenance responsibilities for the airplanes and most of their systems, while the AFFTC agreed to continue maintenance of the carrier aircraft, rocket engines, and other systems it had been responsible for.13781

The largest change was the dissolution of the Research Airplane Committee that had guided the X-15 program since the signing of the original 1954 memorandum of understanding. The X-15 Joint Operations Committee and the X-15 Joint Program Coordinating Committee that had reported to the Research Airplane Committee would now report to the Aeronautics Panel of the AACB.13791

All in attendance agreed the X-15 program would continue at least through the middle of 1968. How long the program would continue after that depended upon the status of the Air Force experiments and the NASA funding situation. On 26 October 1967, the Air Force and NASA signed a new memorandum of understanding, replacing the original 1954 MoU that had governed the X – 15 program for 13 years. Charles W. Harper (NASA deputy associate administrator for the Office of Advanced Research and Technology) worked with Thomas C. Muse (assistant director OSD,

DDR&E) to get the new agreement signed by Dr. John S. Foster (director, DDR&E) and Dr. Robert C. Seamans, Jr. (NASA deputy administrator). The new MoU reestablished Air Force responsibility for X-15 costs, and spelled out the specific responsibilities of the two organizations. However, instead of ending with a statement of national priority, the new MoU contained the ominous proviso, "funds permitting." To most NASA managers, this meant that NASA would still have to face up to the total funding of the X-15 program as soon as the last two Air Force experiments ended.13801

Charles Harper and his boss at the Office of Advanced Research and Technology, Mac Adams, made one last effort to find funds for the program during the fall of 1967. They solicited help from the NASA Office of Manned Spaceflight (OMSF) because both the HRE and the delta-wing projects would produce new technology for the Space Shuttle. The attempt failed, however, because the OMSF was already having trouble promoting the space shuttle concept and did not want to add to its problems by supporting a potentially attractive-sounding alternative.13811

The accident involving Mike Adams underscored the concerns long expressed privately by Paul Bikle and others regarding the high costs and risks associated with extending the X-15 program. In the discussions that followed the accident, Bikle convincingly speculated on the enormous costs of the HRE flight program involving years of delay in getting started, malfunctions, and repairs. In December 1967, the Air Force and NASA both agreed to abandon the HRE flight program and to terminate the X-15 program at the end of 1968. On 13 March 1968 the Air Force announced that it would allow its X-15 funding to expire at the end of the year, but that it would continue to support flight tests to the "completion of Air Force IR [241 and WTR [201 experiments."13821

NASA allocated $1,500,000 for X-15 operations in FY68, with the Air Force contributing another $777,000. It appeared the program could save $150,000 by not returning X-15A-2 to flight status, and by flying a minimum number of other flights using X-15-1. The first six months of 1969 would require approximately $400,000 to catalog and dispose of spare parts, ground equipment, and prepare the two remaining vehicles for shipment to museums. The X-15 program would transfer some parts and ground equipment to other programs, and scrap the remainder.-138^


The X-15 program would only fly another eight missions. During 1968, Bill Dana and Pete Knight took turns flying X-15-1. However, even within NASA, not everyone was certain the flights were worth the risk and $600,000 cost.-1384

X-15A-2 returned to Edwards on 27 June 1968. On 15 July, a series of nondestructive load and thermal tests began on the instrumented right wing in the FRC High Temperature Loads Calibration Laboratory. The airplane would remain grounded forever.-1385

Nevertheless, during the first part of 1968 the AFFTC and FRC worked together to see if there was sufficient interest to extend the program. By October 1968, they had surveyed the current users of the airplane and potential future researchers, and found some programs that could likely benefit from the X-15 being available. Two of the Air Force experiments (20 and 24) might need more time, especially the WTR launch monitoring, which would require extraordinary luck to get the X-15-1 and an ICBM in the air at the same moment. The groups investigating the impingement heating on the last flight of X-15A-2 also would have been happy to keep that airplane flying, since they had little other means of conducting experiments to understand the problem.-1385

Technically, NASA had already canceled the HRE flight program, but most everybody acknowledged that the ramjet experiments could also benefit from flight testing. However, NASA was a bit gun-shy after the bad experience on X-15A-2, and the flight ramjet development was running well behind schedule. Several other programs within the defense community were studying advanced propulsion concepts (ramjets, turbo-ramjets, or similar engines), and most of them potentially could have used the X-15 as a platform if it was still flying. There was even some talk about reviving the delta-wing concept that had been canceled after the loss of X-15-3.-1387

Despite this minor interest, in the end the AFFTC report concluded that "no known overpowering technological benefits will be lost if [the X-15] program ends on 31 December 1968." It noted that there was a firm requirement for the completion of the two Air Force experiments, and that "many USAF/USN technological activities [were] underway or planned for the Mach 4-6 regime," but the report failed to identify any specific requirements for the use of the small black airplanes.

It noted that "the future value of the X-15 as a hypersonic test capability should be more evident by mid-late 1969" and that the "option to use X-15 resources after 1969 should be protected."[388]

Bill Dana completed the 199th—and as it turned out the last-X-15 flight, reaching Mach 5.38 and 255,000 feet on 24 October 1968. The program made 10 attempts to launch the 200th flight, but maintenance and weather problems forced cancellation every time. The attempt on 12 December actually got airborne (1-A-142), but the X-15 inertial system failed before launch. On 20 December 1968, things looked dismal, but everybody geared up for an attempt. Bill Dana began taxiing an F-104 for a weather flight, but John Manke noted that snow was falling-at Edwards! Manke recalled Dana before he took off and canceled the mission. Later that afternoon, technicians at the FRC demated X-15-1 from the NB-52A for the last time. After nearly 10 years of flight operations, the X-15 program ended.[389]

By the end of the program, the two remaining airplanes were tired. In absolute terms, they were still young airframes-just 10 years old and with only about 10 flight hours each. The total free – flight time for all three airplanes was only 30 hours, 14 minutes, and 57 seconds. Even counting all the time spent under the wing of the two NB-52s, the total barely reached 400 hours. Despite early Air Force estimates of 300-500 flights, that had not been the original idea. Bob Hoey remembers asking North American project aerodynamicist Edwin W. "Bill" Johnston how long North American expected the airplanes to last. Johnston responded that the company had "expected that each airplane would only see 5 or 6 exposures to the design missions [i. e., Mach 6 or 250,000 feet]." They did much better.[390]

The X-15s accumulated much more flight time than most of the high-performance X-planes, and the environment they flew in was certainly extreme. They frequently experienced dynamic pressures as high as 2,000 psf, and as low as (essentially) 0 psf. The airframes endured accelerations ranging from -2.5 g to over +8.0 g. Temperatures varied from -245°F to over 1,200°F. It had been a rough life.

In addition, NASA tested the airplanes-a lot. After each flight, NASA removed, disassembled, and thoroughly checked almost every system. Then each was reinstalled and tested some more. If the technicians noted any anomalies they made the appropriate repairs and retested. Milt Thompson wrote, "[M]y personal opinion is that we wore the airplanes out testing them in preparation for flight." The space shuttle would suffer much the same fate.[391]

It is interesting to note that although the X-15 is generally considered a Mach 6 aircraft, only two of the three airplanes ever exceeded Mach 6, and then only four times. On the other hand, 108 flights exceeded Mach 5 (not including the four Mach 6 flights), accumulating 1 hour and 25 minutes of hypersonic flight. At the other end of the spectrum, only two flights were not supersonic (one of these was the first glide flight), and 14 others did not exceed Mach 2. It was a fast airplane. Similarly, there were only four flights above 300,000 feet (all by X-15-3), but only the initial glide flight was below 40,000 feet.[392]


During the summer of 1961, the Air Force ASD and NASA Headquarters proposed a new initiative to use the X-15 to carry scientific experiments that were unforeseen when John Becker conceived the aircraft in 1954. For instance, researchers at the FRC wanted to use the X-15 to carry high – altitude experiments for the proposed Orbiting Astronomical Observatory, while others wanted to carry a hypersonic ramjet for air-breathing propulsion studies. Of particular interest was the ability of the X-15 to carry experiments above the attenuating effects of the atmosphere.-180

On 15 August 1961, the Research Airplane Committee signed a memorandum of understanding (MoU) to form the X-15 Joint Program Coordinating Committee with Air Force and NASA representatives as cochairmen. The MoU included the following statements:^

1. The X-15 is a program of national importance undertaken in accordance with the terms of a Memorandum of Understanding dated 23 December 1954 among the Department of the Air Force, Department of the Navy, and the NACA (now the NASA). It is recognized that the X-15 flight research program will soon complete the initial phase of flight research.

2. It is necessary that an optimum follow-on research program be formulated to insure maximum benefit to the national objectives accrue from the research program.

3. An X-15 Joint Program Coordinating Committee with the NASA and USAF representatives in the role of co-chairman is hereby assigned the responsibility to formulate the optimum follow-on research program for the X-15. The program will be transmitted to the participating departments through normal channels and will be jointly reviewed by HQ [Headquarters] USAF and the NASA RAPL [Research Airplane Project Leader (Hartley Soule)] prior to submittal to the Research Airplane Committee.

4. The X-15 Joint Program Coordinating Committee is recognized by the Research Airplane Committee as the focal point of the subject project for continuous evaluation and formulation of program objectives for approval of the Research Airplane Committee. The establishment of a Joint Program Coordinating Committee is not intended to change the functions or responsibility of the NASA FRC-AFFTC Flight Test Steering Committee [later called the X-15 Joint Operations Committee].

The initial cochairs of the X-15 Joint Program Coordinating Committee were Lieutenant Colonel E. F. Pezda, chief of the X-15 project office at the ASD, and Paul Bikle from the FRC. The committee held its first meeting on 23-25 August 1961, during which the scientific community suggested over 40 experiments as suitable candidates. Hartley Soule and John Stack proposed separating the experiments into four groups.-182!

• Group I consisted of desirable experiments that did not require special aircraft modifications or special flight profiles. It was also initially limited to experiments that could be prepared within three to four months of approval.

• Group II consisted of experiments that required "appreciable aircraft modifications" or a relatively long lead time for preparation.

• Group III was a holding area for experiments that were not well defined.

• Group IV included experiments that supported other programs (such as the Dyna-Soar or Apollo).

By November 1961, a long list of possible experiments had been divided among the first three groups; the fourth group was not populated pending coordination with other programs. The X-15 Joint Program Coordinating Committee met four more times (9 May 1962, 7-8 January 1963, 18 September 1963, and 16 October 1963), and initially forwarded proposals for 28 experiments to the Research Airplane Committee for approval. The committee subsequently approved at least three other proposals for implementation, and it appears that several others were assigned experiment numbers; however, the nature or purpose of some of them is unknown.-183!


Mike Adams flew the X-15 for 13 months from 6 October 1966 until 15 November 1967, making seven flights. All of these were with the XLR99 engine and he reached Mach 5.59, a maximum speed of 3,822 mph, and an altitude of 266,000 feet. Adams died on flight 3-65-97.

Michael James Adams was born on 5 May 1930 in Sacramento, California, and enlisted in the Air Force on 22 November 1950 after graduating from Sacramento Junior College. Adams earned his pilot’s wings and commission on 25 October 1952 at Webb AFB, Texas. He served as a fighter- bomber pilot in Korea, flying 49 missions during four months of combat service. For 30 months Adams served with the 613th Fighter-Bomber Squadron at England AFB, Louisiana, and for six months he served rotational duty at Chaumont Air Base in France.-12

In 1958 Adams received a bachelor of science degree in aeronautical engineering from Oklahoma University. In 1962, after 18 months of astronautics studies at the Massachusetts Institute of Technology (MIT), Adams attended the Experimental Test Pilot School at Edwards, where he won the Honts Trophy for being the best in his class. He subsequently attended the Aerospace Research Pilot School (ARPS), graduating with honors on 20 December 1963, and was assigned to the Manned Spacecraft Operations Division at Edwards AFB in the Manned Orbiting Laboratory program. During this time he was one of four Edwards aerospace research pilots to participate in a five-month series of NASA Moon-landing practice tests conducted by the Martin Company in Baltimore, Maryland.

In July 1966 Adams came to the X-15 program with 3,940 hours of total flight time, including 2,505 hours in single-engine jets (primarily the F-80, F-84F, F-86, F-104, F-106, and T-33) and an additional 477 hours in multiengine jets (primarily the F-5, T-38, and F-101). Unfortunately, Mike died during flight 3-65-97 on 15 November 1967, and The Air Force posthumously awarded Adams an astronaut rating for his last flight in X-15-3, which had attained an altitude of 266,000 feet (50.38 miles). In 1991, the Astronaut Memorial at the Kennedy Space Center in Florida added Adams to its list of astronauts who had been killed in the line of duty.


Harrison A. "Stormy" Storms, Jr., was born in 1915 in Chicago, Illinois. He attended Northwestern University and graduated with a master of science degree in mechanical engineering in 1938. Storms then attended the California Institute of Technology (Caltech), earning a master of science degree in aeronautical engineering. At Caltech he studied under Theodore von Karman and worked in the wind tunnels at the Guggenheim Aeronautical Laboratory (GALCIT).

In 1940, Storms went to work on the P-51 Mustang at North American Aviation, where he developed a reputation as an expert on wind flow and high-speed aircraft. He subsequently worked on the F-86 and F-100 jet fighters. In 1957, Storms became vice president and chief engineer of the Los Angeles Division, where he led the development of the XB-70 bomber. In 1959, he became vice president for program development, in charge of the development of the Apollo spacecraft. Between 1961 and 1967, he served as president of the Space and Information Systems Division, an organization that peaked at more than 35,000 employees in 1965. Storms took the brunt of the blame for the Apollo 1 fire and stepped out of the public eye, although he continued as a company vice president. The AIAA honored him with the 1970 Aircraft Design Award. Storms died in Los Angles in July 1992.[25]