At the Edge of Space

by Milton O. Thompson

  This ballooning tendency was one of the bad characteristics of the MH-96 flight control system that tended to surprise every new pilot. We had developed a special trim technique to minimize this tendency, but Mike forgot to utilize it. It required two or three flights in the number three aircraft to learn the system and become proficient flying it. After that, it was a nice airplane to fly.

  Mike’s third flight was made in the number one aircraft. It was another pilot checkout flight to expose Mike to flight at a higher altitude. Four experiments were carried and operated on this flight. It was planned to be flown out of Mud Lake near Tonapah, Nevada. The flight plan called for a two step climb coming level initially at 100,000 feet altitude at 5,500 feet per second. The engine would then be shutdown and the pilot was to pull up to 15 degrees angle of attack and maintain that angle of attack until he peaked out in altitude at 133,000 feet at 157 seconds after launch. After reaching peak altitude, Mike was to hold 15 degrees angle of attack until he descended back through 115,000 feet and then he was to open the speed brakes and maintain a constant rate of descent while vectoring to high key at Edwards.

  During the actual flight, Mike lost cabin pressure while climbing through 77,000 feet on the way up to peak altitude. This caused his pressure suit to inflate, which in turn made it more difficult to fly the airplane. As he went over the top at 133,000 feet, his inertial computer failed and he lost his cockpit readouts of rate of climb, altitude, and velocity. He made his reentry without this information. In spite of these failures, Mike managed to fly a successful flight and acquire the desired flight data. During his approach to landing, Mike commented over the radio, “I thought you said every once in a while something goes wrong, Pete.” Mike was obviously getting more than his share of problems in-flight.

  During the postflight debriefing, Mike indicated that he had suffered from vertigo during the climbout. He indicated that after the pushover at 60,000 feet on the way up, he thought he was going straight up. Pete had warned him that he might have this sensation during boost. Mike had indeed suffered severe vertigo on this flight. He commented, “I did not know what the hell I was doing”—an ominous pronouncement. Mike had momentarily lost control of the situation. The bull only bucked once this time.

  Mike’s fourth flight was another altitude buildup flight out of Delamar Lake north of Las Vegas. In addition to the altitude buildup, on this flight Mike was to operate the PMR (Pacific Missile Range) experiment to check out the system. This experiment was a very complex experiment used to monitor ballistic missile launches from the PMR with equipment installed in the X-15. This experiment required a coordinated launch of a missile and the X-15, such that both would be above the atmosphere simultaneously. This was attempted on several flights but was never accomplished due to the inability to coordinate a simultaneous launch of both vehicles.

  On this flight, Mike was to extend the experiment as he climbed through 170,000 feet on the way to his planned peak altitude of 180,000 feet. The flight went off as planned except that Mike had problems controlling his climb angle due to an apparent stickiness in the indicator needle. As a result, his climb angle was 1 to 2 degrees low. He did not get high enough to safely open the experiment doors. Mike did obtain data on an MIT experiment, however. The flight back to Edwards was uneventful. Mike had finally gotten a nice peaceful flight.

  Mike’s fifth flight was made in the number one aircraft. It was his third altitude buildup flight. The flight was also planned to obtain data on the MIT horizon scanner experiment and to attempt to checkout the PMR experiment again. The planned maximum altitude was 220,000 feet. The flight was flown as planned, except that Mike was one second late in shutting the engine down. This resulted in an overshoot of 7,000 feet in peak altitude. Data was obtained on the MIT experiment, but a fuse failed in the PMR experiment, deactivating the video recorder.

  Mike indicated in the debriefing that he had trouble maintaining precise pitch and roll attitudes and heading while going over the top and, in fact, had a slight oscillation going as he peaked out. This was not unusual in this airplane since the pilot was flying with both hands. He was controlling the aerodynamic controls with his right hand and the reaction controls with his left hand. If the aerodynamic controls were not properly positioned, the aircraft would not maintain an attitude or angle of attack, but would diverge requiring extensive reaction control usage to counteract the small aerodynamic control moments. It was relatively easy to excite an oscillation while doing this two-fisted flying. Mike did make a successful reentry and brought the aircraft home without any further problems.

  Mike’s sixth flight was made in the number three aircraft. It was a low-altitude flight to evaluate a boost guidance system and to obtain data on horizontal tail loads. Two other experiments were to be activated during flight—one to measure the noise in the fuselage boundary layer and another to measure the heat transfer rate on a cold wall surface. The flight was a rather benign flight to a maximum speed of 4,500 feet per second at 78,000 feet altitude. After shutdown, Mike was to perform a rapid pull-up to 15 degrees angle of attack and then push over to 0 g to vary the load on the horizontal tail for data gathering purposes. The flight plan called for this same maneuver at three other speeds while slowing down, during the approach to Edwards.

  Unlike his first flight, this flight did not start out with a bang. In fact, Mike got no noise at all out of the engine when he tried to start it after launch. The engine had a vibration sensor system that monitored the vibrations during engine operation. If these vibrations exceeded a preset g level, this system shut the engine down automatically to prevent catastrophic damage to the engine, and possibly the aircraft. For some unexplained reason, this system sensed a vibration spike during the start sequence and prevented the engine from starting.

  Mike had to quickly try a restart. He went through the restart sequence automatically. Each of the X-15 pilots had that sequence burned into their memory bank. “Throttle off.” “Engine reset.” “Prime switch on and hold until the igniter-ready light came on.” This required roughly 5 seconds, but in an emergency it seemed like 5 hours. Once the igniter-ready light came on, he could move the throttle to the on position.

  Mike managed to get the engine lit on his second try, sixteen seconds after launch. The airloads were quite high during his roundout to the desired climb angle, but he finally got back on his desired profile and the flight proceeded as planned. The boost guidance experiment was cancelled prior to flight due to a problem with the system computer. This boost guidance system was intended to provide the pilot with simple steering commands during boost to reduce the pilot’s workload. This type of system would potentially enable a pilot or an astronaut to manually fly a spacecraft into orbit. This capability has still not been demonstrated since all manned spacecraft have relied on automatic guidance and control to achieve orbit. The astronauts do have a manual backup capability in the shuttle, but it has never been used. Mike obtained good data on the other three experiments.

  Mike’s seventh flight was his fourth altitude flight. It was to be made in the number three aircraft to an altitude of 250,000 feet. The aircraft carried seven different experiments on this flight—the boost guidance experiment, which was carried on Mike’s previous flight, a solar spectrum measurement device, an ultraviolet plume detector, a micrometeorite collector, a tip pod deflection camera, Saturn booster ablative material, and a traversing probe in one of the wing tip pods.

  The solar spectrum measurement experiment was an experiment to obtain solar spectrum data outside of the atmosphere in order to improve methods of correcting for atmospheric absorption. This experiment was a Jet Propulsion Laboratory experiment to obtain data needed before launching spacecraft to Venus or Mars. The ultraviolet exhaust plume experiment measured the ultraviolet characteristics of the X-15 rocket engine exhaust plume against an earth background and a sky background. The micrometeorite collector was a small experiment mounted in a wing tip pod. This experiment was exposed a
t high altitude to measure the size, velocity, and frequency of micrometeorites impacting the experiment collector. The fifth experiment, the tip pod camera, was an experiment to measure the deflection of the tip pod during flight by photographing it from a camera located in the fuselage side fairing. The Saturn booster ablative material was installed on the speed brakes to determine whether it would survive the aerodynamic and thermal loads imposed during hypersonic flight. The seventh experiment, the traversing probe, was an experiment to measure the stand-off distance of the bow shock on a blunt nose cone. In this experiment, a small needlelike probe was cycled in and out of the tip pod nose cone to measure the stand-off distance of the bow shock produced by the tip pod. The majority of those experiments were classified as scientific piggyback experiments. They were independent of the X-15 and were simply carried by the X-15 to obtain data in and out of the atmosphere.

  The flight was originally scheduled to be launched out of Delamar Lake on October 31, but the flight was aborted just prior to launch because the engine would not cycle into the igniter idle mode. Following the abort, the X-15 was de-mated from the B-52 to troubleshoot the engine. The engine was finally replaced and a ground run made to check out the new engine. This new engine also had to be replaced due to a fuel leak. A successful ground run was made with the second replacement engine on November 9 and the flight was rescheduled for November 15.

  Mike’s wife and mother came over to NASA on the morning of the flight to monitor the flight from the viewing area outside the control room. Walter “Whitey” Whiteside escorted them up to the control room and explained the control room operation and the progress of the activity in preparation for the flight.

  Takeoff was scheduled for 9:00 A.M., but actually occurred at 9:12 A.M. The weather conditions in the southern Nevada and Mojave desert region included some scattered clouds at 12,000 to 16,000 feet and some higher broken clouds with a thin overcast. The clouds initially appeared to be a problem that might force an abort, but the clouds tended to dissipate as the captive flight progressed. The captive portion of the flight was uneventful with only a minor delay due to a late takeoff by the rescue C-130 aircraft. This minor delay required Mike to reset his command pitch and roll attitudes to compensate for the change in sun position. This command attitude change would later become a significant factor.

  Mike launched the X-15 at 10:30:07. The aircraft rolled off to the right about 20 degrees, but Mike immediately rolled back to wings level. He had the throttle on within a second after launch, before leveling the wings. The engine lit a half-second second later and was up to full thrust within one second. The radio conversation after launch, and significant events, are listed below:

  10:30:07 [Launch.]

  10:30:09 [Engine light.]

  10:30:12 NASA-1 “Good light here, Mike.”

  10:30:14 NASA-1 “Check alpha, heading.”

  10:30:21 NASA-1 “Right on track, Mike, coming up on profile.”

  10:30:30 NASA-1 “Standby for theta.”

  10:30:33 NASA-1 “How do you read, Mike?”

  10:30:39 NASA-1 “Check your boost guidance null, Mike, and how do you read?”

  10:30:42 [Aircraft velocity is 2,000 feet per second and altitude is 60,000 feet.]

  10:30:44 NASA-1 “OK, Mike, we have you right on track, on the profile.”

  10:30:45 B-52: “You’re on track and profile, Mike.”

  10:30:52 Adams: “Roger.” [This was Mike’s first radio call since launch and was apparently in response to the B-52 radio relay of NASA-1’s call.]

  10:30:54 B-52: “I’ll relay, Pete.” [Pete Knight was the controller in NASA-1 The B-52 copilot was offering to relay radio calls to Mike.]

  10:30:56 NASA-1 “OK”

  10:31:01 NASA-1 “Standby for 83,000 feet, Mike.”

  10:31:04 B-52: “Standby for 83,000.”

  10:31:07 [An electrical disturbance causes a transient motion in all three control system servo actuators at this time and drives the system gain down below 50 percent, which deactivates the normal reaction controls. The electrical noise apparently emanated from the traversing probe experiment. This electrical noise would persist for two minutes and 46 seconds. While this noise persisted, it would tend to keep the normal automatic reaction controls deactivated. The electrical noise also affected the inertial system computer and the boost guidance computer causing significant errors in the inertial data displayed on the cockpit instrument panel. The reaction controls occasionally became functional fortuitously, or insidiously, when Mike had to make a special maneuver, but they were not working for a major portion of the climb to altitude. They were not available to prevent the aircraft from slowly drifting in heading during ascent. The malfunctioning of the flight control system and the inertial system computer tended to distract Mike throughout the remainder of the climb to peak altitude.]

  10:31:09 NASA-1: “Do you read us at all, Mike?”

  10:31:12 NASA-1: “OK, you’re right on track.”

  10:31:13 B-52: “Right on track, Mike.”

  10:31:19 NASA-1: “Coming up on 110,000.”

  10:31:21 B-52: “Coming up on 110,000.”

  10:31:22 NASA-1: “On the profile, on the heading.”

  10:31:24 B-52: “On profile, on heading.”

  10:31:26 NASA-1: “Standby for shutdown.”

  10:31:27 B-52: “Standby for shutdown.”

  10:31:28 [The inertial system computer and instrument failure lights came on at this time as a result of the electrical noise. This malfunction light would tend to be another distraction to Mike.]

  10:31:30 [Engine chamber pressure starts to decrease, indicating shutdown of the engine by the pilot. Actual velocity at shutdown was 5,236 feet per second, which was higher than the planned 5,100 feet per second. This would result in a higher than planned peak altitude. The engine was shut down 4 seconds later than planned, probably as a result of the pilot waiting for the proper indicated velocity for shutdown. The electrical noise caused the computed velocity to lag the actual velocity. Actual altitude at shutdown was 150,000 feet, which was also higher than the planned 140,000 feet.]

  10:31:33 NASA-1: “Precision attitudes, Mike.”

  10:31:35 B-52: “Precision attitudes, Mike.”

  10:31:36 [Mike attempts to reset the computer malfunction light.]

  10:31:39 NASA-1: “Alpha to zero.”

  10:31:40 B-52: “Alpha to zero.”

  10:31:42 NASA-1: “And rock your wings and extend your experiment, Mike.”

  10:31:45 B-52: “Extend your experiment, Mike.”

  [The wing rocking maneuvers were to obtain data for the ultraviolet exhaust plume experiment. The experiment to be extended was the JPL solar spectrum experiment.]

  10:31:50 NASA-1: “On the heading, on the profile.”

  10:31:52 NASA-1: “Have you going a little bit high. That’s all right.”

  10:31:54 B-52: “On the heading, on the profile. Maybe a little bit high.”

  10:31:54 [The X-15 is climbing through 200,000 feet altitude.]

  10:31:58 Adams: “I am reading him now. I got a computer and instrument light now.”

  10:32:03 NASA-1: “OK, Mike.”

  10:32:08 NASA-1: “We’ll go ahead and try computed alpha at 230, [230,000 feet altitude] Mike.” [The ball nose could not sense any airflow above 230,000 feet altitude. Angle of attack and angle of sideslip had to be computed from inertial data at higher altitudes.]

  10:32:10 [Aircraft heading begins to deviate slowly. The automatic reaction controls are inactive due to the electrical noise and do not resist this deviation. Heading drift continues to peak altitude.]

  10:32:14 NASA-1: “Check your computed alpha now.”

  10:32:18 NASA-1: “And you’re right on track, Mike.”

  10:32:27 NASA-1: “I lost my pitch and roll dampers.” [Pitch and roll stability augmentation. A severe electrical transient caused the dampers to disengage at this time.]

  10:32:32 NASA-1: “OK, Mike let’s try to get them o
n.”

  10:32:32 Adams: “They reset.” [The dampers reengaged satisfactorily.]

  10:32:35 NASA-1: “Did they reset?”

  10:32:35 Adams: “Yep.”

  10:32:36 NASA-1: “OK.”

  10:32:37 NASA-1: “And I’ll give you a peak altitude, Mike.”

  10:32:42 NASA-1: “Have you coming over the top. You’re looking real good. Right on the heading, Mike.”

  10:32:51 NASA-1: “Over the top at about 261 [261,000 feet altitude], Mike. Check your attitudes.”

  10:33:00 [At this time, the aircraft actually peaks out at 266,000 feet altitude. The heading drift stops due to a momentary reactivation of the automatic reaction controls. The aircraft heading is now misaligned 15 degrees to the right of the flight path. Aircraft velocity is approximately 4,600 feet per second.]

  10:33:02 NASA-1: “You’re a little bit hot, but your heading is going in the right direction, Mike. Real good.”

  [The control room is unaware of the aircraft misalignment since they do not have heading displayed in the control room. Aircraft heading outside the atmosphere does not effect the ground track, so there was no deviation of the track to alert them to the heading misalignment.]

  10:33:05 [At this time Mike makes three yaw reaction control inputs with the left- hand manual controller. He apparently realizes that the normal reaction controls are not working properly. The control inputs that he makes are, however, in the wrong direction to correct the heading error. They are actually in the direction to increase the heading error. A slow, steady heading drift to the right begins as a result of these control inputs.]

  10:33:09 NASA-1: “Real good. Check your attitudes. How do you read, Mike?”

  10:33:14 NASA-1: “OK, let’s check your dampers, Mike.”

  10:33:17 Adams: “They’re still on.”

  [Mike reached down and cycled his damper switches turning the dampers off, then on. This was another distraction.]