When Paul Bikle grounded the M2-F1 permanently in mid-August 1966, a ground swell of interest in lifting-body re-entry vehicles had been growing for over two years within NASA. The initial flights of the M2-F1 had shown that the lifting-body shape could fly. As early as two weeks after the first car-tows of the M2-F1 in April 1963, Bikle had shared his confidence in lifting bodies with NASA Headquarters, writing Director of Space Vehicles Milton Ames that the more the Flight Research Center got into the lifting body concept, the better the concept looked.
Bikle also mentioned that he was noticing "a rising level of interest" in the lifting-body concept at the Ames and Langley centers. By 1964, NASA Headquarters and these two Centers had considerably increased their participation in the lifting-body concept through the Office of Advanced Research and Technology (OART) under the direction of NASA Associate Administrator Raymond Bisplinghoff.
By this time there were also many lifting-body advocates within the aerospace industry and the Air Force. The successful flights of the M2-F1 had accelerated the aerospace community's interest in the possibility of applying the concept of lifting re-entry to the next generation of spacecraft. After our M2-F1 success, the lifting body quickly rose toward the top of the Air Force's priorities in re-entry designs. Although there were still many in the Air Force holding out for variable geometry wings and jet engines to assist in landing recovery, wingless and unpowered vehicles had become more prominent in both NASA and Air Force studies. 1
Change in Plans: On to Rocket Flight
I had originally planned to fly three lightweight lifting-body shapes. Once the M2-F1 had been built, I was ready to move on to the other two shapes, the M1-L and the lentricular. By this time, however, interest in building the other two shapes into vehicles had waned, replaced by the urge to fly a rocket-powered lifting body at transonic speeds.
After the M2-F1 was built in 1962, I went to NASA Ames and NASA Langley to confer with other engineers about developing lifting re-entry configurations. At NASA Langley, I discovered that the leading lifting-body advocates among the engineers were rapidly making progress. Eugene Love was leading the lifting-body interest at NASA Langley, with Jack Paulson, Robert Rainey, and Bernard Spencer conducting  studies and wind-tunnel tests on candidate designs. Although they were still considering deployable wings and jet engines, a powered and wingless lifting-body configuration-the HL-10 (for Horizontal Lander)-emerged as a strong contender after our success in flying the M2-F1.
NASA Headquarters assigned Fred DeMerritte as program manager for coordinating lifting-body activities at various sites, including the Flight Research Center, Ames, and Langley. We felt fortunate to have DeMerritte as program manager, for he was a good team worker who listened to us. His skill in cutting through red tape helped us move the lifting-body program along. We set up a planning team composed of three members, one for each of the three NASA sites. While I represented the Flight Research Center, George Kenyon and Bob Rainey represented Ames and Langley, respectively. Since John-son Space Center in Houston, Texas, had become the leading Center for manned space exploration, the planning team met at Johnson with its representatives.
After Kenyon, Rainey, and I presented the views of our colleagues, we quickly narrowed in on two important objectives. First, future flight tests on lifting bodies should be at wing loadings or weights five to ten times more than those of the M2-F1. Secondly, flight-test vehicles should be capable of the higher speeds in the transonic and lower supersonic speed ranges where large changes in lifting-body aerodynamics occur.
After my return to the NASA Flight Research Center, I put together a plan for a heavyweight M2-F1 with the same dimensions as the original vehicle, proposing to launch the heavyweight version from the Center's B-52 in a way similar to how the X-15 was launched. The X-15 program was no longer using the LR-11 rocket engines, and we could use them now in our lifting-body pro-gram. The LR-11 engine consists of four separate barrels or chambers, each barrel developing some 2,000 pounds of thrust for a total thrust of about 8,000 pounds. The pilot had four increments of throttling capability since each barrel could be operated separately. Two LR-11 engines in the X-15 had achieved 16,000 pounds of thrust, the engines burning a combination of water and alcohol, with liquid oxygen employed as the oxidizer. The 33,000-pound X-15, including the 18,000 pounds of fuel and oxidizer that it carried aloft, had achieved Mach 3.50 with the two LR-11 engines. We figured that if we could achieve our transonic speed objective by using one LR-11 to get close to Mach 2 flight in an aluminum version of the M2-F1. 2
To get a simple weight estimation for the aluminum lifting body, I compared the wingless weights of two aircraft that had used the LR-11s earlier, the X-1 and the D-558,  coming up with a target weight of about 10,000 pounds. I estimated the vehicle weight of the aluminum M2-F1 would be 5,000 pounds, including one LR-11 engine. Given the large volume inherent in the lifting-body shape, I foresaw little difficulty in installing tanks to carry another 5,000 pounds of fuel and oxidizer, bringing the launch weight up to about 10,000 pounds.
One problem arose right away in designing the vehicle. In the unpowered M2-F1, the pilot and ejection seat had been positioned on the aircraft's center of gravity, where the fuel tanks would need to be in the rocket-powered version. Fortunately, there was enough depth in the basic M2-F1 shape to move the pilot and canopy forward of the center of gravity. Earlier I had hoped that we could preserve the M2-F1's original shape in the aluminum version so that the wind-tunnel and flight data measured on the original version would remain valid for the aluminum follow-on. Moving the canopy forward, however, meant aerodynamic changes that made new wind-tunnel tests mandatory.
I calculated the aircraft's performance, assuming an air launch of a 10,000-pound M2-F1 from a B-52 at 45,000 feet, with an 8,000-pound-thrust LR-11 engine burning down to a burnout weight of 5,000 pounds. The result showed that a speed close to Mach 2 could be achieved.
Birth of the M2-F2
The cost of a rocket-powered lifting-body program could be cut substantially, I found, by using the present facilities and personnel for maintaining and operating the LR-11 engines and by using NASA's B-52 as a mothership for launching the lifting body. We could design and fabricate an adapter to be used in launching the lifting body that would attach to the B-52's wing pylon used in air-launching the X-15. When I presented my idea for the rocket-powered lifting-body program to Paul Bikle, he said it sounded good and suggested I try the idea out on others at the NASA Ames Research Center.
I presented the idea to members of the NASA Ames wind-tunnel team, including Clarence Syvertson, George Kenyon, and Jack Bronson. While they liked the idea, they said the "elephant ears" on the M2-F1 would have to go because they would burn off during re-entry from space. They were concerned that these outer horizontal elevons would create a serious heating problem from shock-wave and boundary-layer interaction as well as shock-wave impingement. I tried to talk them into leaving them on, knowing the elevons worked very well for roll control on the M2-F1 and provided a lot of roll damping to help retard any potential problems in roll oscillation. But they insisted that they had to go, saying there were no materials that could take the potential heat that would be generated on the elevons' leading edge and the slot between the elevon and vertical tail. After the NASA Ames team presented the M2-F2 configuration that it recommended for space re-entry, the team said we should use the M2-F2 in place of the M2-F1 shape in a rocket-powered transonic research program.
 The roll control on the M2-F2 consisted of split upper flaps of the sort we had originally built on the M2-F1 but abandoned before we had started flight-testing. The NASA Ames team also added an extra body flap on the lower surface so that the upper split flaps and the lower body flap could be opened like feathers on a shuttlecock to give the longitudinal stability needed at transonic speeds.
Even though the extra body flap caused increased drag, the NASA Ames team members defended their decision made on the basis of wind-tunnel test results. I expressed concern about adverse yaw from the split-flap roll control. They said we could cancel it out by designing an aileron-rudder interconnect into the control system. This sounded reasonable in theory to us all, but those flaps would complicate our lives greatly when we actually flew the M2-F2. The simplest and most straight-forward design solutions had always appealed to me, and keeping the "elephant ears" still seemed to me the simplest and most direct option.
Not giving up easily, I asked the NASA Ames engineers about the pressure on the upper-body flaps caused by the aerodynamic interaction of the rudders. They said I shouldn't worry about that, for they had prevented that problem by making the rudders operate like split flaps with outward movement only. The stationary inner surface of the vertical fin adjacent to the rudder would shield the split elevon upper flaps from rudder pressure, they claimed. They defended the feature, saying the transonic shuttlecock effect was needed in both yaw and longitudinal axes. Moving both rudders outboard, they added, provided directional stability in the transonic speed region-and added more drag, of course.
By now, the lifting-body program was snowballing. We were getting even more input continually from NASA engineers at other sites who were experienced in aircraft and spacecraft design. I began to feel it might be time for me to back off from my simple approach and let more of these experts contribute to the program. Designing control systems for lifting bodies was going to be a major effort requiring a lot of expert help, I felt. As a result, we froze the M2-F2 configuration with the forward canopy location and the greatly modified aerodynamic controls on the aft end of the body.
Paul Bikle, Milt Thompson, and I put together a program proposal for NASA Headquarters. Because of the growing importance of our activity to the future of lifting re-entry, we suggested that two M2-F2s be built at the same time to provide us with a backup in case one vehicle was damaged and to allow us to do separate experiments  simultaneously. We presented our proposal to Fred DeMerritte and his bosses at NASA Headquarters. After listening to us, DeMerritte said they'd rather we substituted the NASA Langley HL-10 for the second M2-F2.
Gene Love and the contingent from NASA Langley had made presentations to NASA Headquarters the week before we presented our proposal. Given the close proximity of the Langley Research Center in Hampton, Virginia, to NASA Headquarters in Washington, D.C., it was common for Langley representatives to be at the Washington headquarters almost daily. Unofficially, NASA Langley had always been considered the "mother" research center, and NASA Headquarters seemed to be more influenced by Langley than by any other NASA research center.
Birth of the HL-10
In 1957, while Al Eggers and his NASA Ames team were studying half-cone re-entry configurations, NASA Langley researchers were conducting broader re-entry studies, including winged and lifting-body vehicles. Hypersonic studies conducted at Langley's aero-physics division were evaluating various aerodynamic shapes. Preliminary goals at Langley in design features for a re-entry vehicle included minimization of refurbishment in time and money, fixed geometry, low deceleration loads from orbital speeds, low heating rates, ability for roll and pitch modulation, and horizontal powered landing.
According to these studies at Langley, a re-entry lifting-body vehicle with negative camber (that is, with the curved portions of wing surfaces turned upside-down) and a flat bottom might have higher trimmed lift-to-drag ratios over the angle-of-attack range than those of a blunt half-cone design. The negative-camber concept was used in 1957 in developing a vehicle-initially referred to as a Manned Lifting Re-entry Vehicle (MLRV), but now referred to simply as a lifting body-that was stable about its three axes and retained a flat lower surface for better hypersonic lifting capability. These studies at Langley found that a vehicle with an aerodynamic flap, a flat bottom, and a nose tilted up at 20 degrees would be stable about the pitch, roll, and yaw axes and trim at angles of attack up to approximately 52 degrees at a lift-to-drag ratio in excess of 0.6.
In a paper presented at the 1958 NACA Conference on High-Speed Aerodynamics, NASA Langley's John Becker described a small winged re-entry vehicle embodying all of the features that had earlier been identified as design goals at Langley, including low lift-to-drag ratio for range control, hypersonic maneuverability, and conventional glide-landing capability.3 The vehicle in Becker's paper also  included a flat-bottomed wing with large leading-edge radius and a fuselage crossing the protected lee area atop the wing. This configuration, however, wasn't selected to carry the first American astronaut into space. Officials at Johnson Space Center opted instead for a ballistic capsule, the Mercury "man in a can." Their decision, however, did not deter researchers at NASA Langley from continuing to develop concepts and design goals for a lifting re-entry vehicle.
In the early 1960s in its space mission studies, Langley's astrophysics division began moving away from winged to lifting-body configurations. The first seven refined mission vehicle goals of 1962 echoed the desirable characteristics of re-entry vehicles described in these studies. One goal was a hypersonic lift-to-drag ratio near 1 without elevon deflection, thus avoiding heating problems near the elevons in the maximum heating portion of the trajectory. Another goal was high trimmed lift at hypersonic speeds, providing high-altitude lift modulation. A subsonic lift-to-drag ratio of approximately 4 was desirable for horizontal runway landings without power during emergencies. Furthermore, the vehicle's body should provide high volumetric efficiency (the ratio of the useful internal volume to the total exterior volume encompassed by the external skin) with a 12-person capability, and it should have acceptable heating rates and loads at all speeds, possibly including super-orbital ones. Also essential were launch-vehicle compatibility and stability and control over the speed range.
Evolving configurations at Langley were refined to meet these mission goals. Trade-off studies interrelated sweep, thickness ratio, leading-edge radius, and location of maximum thickness. The negatively cambered HL-10 lifting-body design emerged in 1962. It then entered an intermediate stage of evolution, involving nearly every research division at Langley in intensive efforts to identify and find solutions for problems associated with this type of configuration. Interestingly enough, much debate still raged over negative camber versus no camber (or symmetrical shape), fueling even more detailed studies. In the end, negatively cambered and symmetrical (no camber) configurations were evaluated in terms of the mission goals. Three more mission goals were also added, becoming serious issues in selecting camber: lower heating rates and loads comparison, lower angle of attack for a given subsonic lift-to-drag ratio, and reduced subsonic flow separation. The negatively cambered HL-10 met nine of the ten mission goals, the symmetrical design meeting only five. The only goal not met by the HL-10 was the lower angle of attack for a given subsonic lift-to-drag ratio.
The HL-10 evolved as a flat-bottomed, fixed-geometry body with rounded edges and a split trailing-edge elevon capable of symmetric upward deflection, providing the pitch trim and stability required for hypersonic re-entry and subsonic flight. The trailing-edge elevon would also deflect differentially for roll control. For even more directional stability, tip fins were added. The lower surface was negatively cambered, assuming a rocking-horse shape to provide longitudinal trim. The aft end of the upper surface was gradually tapered, or boat-tailed, reducing subsonic base drag and decreasing problems in transonic aerodynamics. There was enough forward volumetric  distribution within the HL-10 to meet center-of-gravity requirements for subsystems and crew in balancing the vehicle for flight.
As research and development on the final vehicle design began at Langley, research centered on such issues as trajectory analysis and entry environment, heat transfer, structures and thermal protection, aerodynamics, dynamic stability and control, handling qualities, landing methods, emergency landings on land and water, equipment and personnel layout, and viscous effects including Mach number, Reynolds number aerodynamic scaling factor, and vehicle length.
Because the shape resembled that of a hydroplane racing boat, Langley also conducted tests with HL-10 models for horizontal landings on water, using its water test basin facility. However, even more water-landing tests would have been needed to optimize the HL-10's shape for water landings.
A disadvantage then and now of lifting bodies is that they suffer an aerodynamic heating penalty due to the fact that they spend more time within the entry trajectory than do ballistic missiles. Consequently, methods of thermal protection were extensively researched. Using small and thin-skinned Inconel models, engineers also made detailed wind-tunnel tests, measuring heat-transfer distributions at Mach 8 and 20. In great detail, experimental heating was measured on the models' shapes.
The volumetric efficiency for the proposed HL-10 was relatively high in several designs. One 12-person configuration had an estimated length of 25-30 feet, a span of 21 feet, and a pressurized volume of 701 cubic feet. It also had an attached rocket adapter module and a full-length raised canopy. Some vehicle designs were 100 or more feet long.
The camber issue settled, by 1964 the HL-10 had assumed a sway-backed shape, like that of a child's rocking horse. To determine the best fin configuration, Langley conducted studies using ten wind-tunnel models-ranging from a 4.5-inch hypersonic one with twin vertical fins to a 28-foot low-speed version with a single central dorsal fin. Researchers investigated single-, twin-, and triple-fin arrangements, both lower-outboard and dorsal, along with various modifications to the aft end of the vehicle's body. Finding an acceptable fin arrangement involved a compromise between subsonic trimmed performance and hypersonic trim and stability. Langley proposed that we build the configuration that offered the best compromise, a triple-fin HL-10.
NASA-Northrop Program: Building the M2-F2 and HL-10
I formed a team at the NASA Flight Research Center that then wrote a Statement of Work for designing and fabricating the M2-F2 and HL-10. Besides furnishing the LR-11 rocket engines, NASA would provide all wind-tunnel data as well as aerodynamic load and B-52 captive-load specifications. NASA would also do all control-system analysis and simulation needed for specifying control laws and gains in the automatic functions of controls. The contractor's main responsibility would be to design and build the hardware in concert with the NASA analytical team.
 Fortunately, operations engineers and technicians on the X-15 program helped us write the specifications on pilot life-support, electrical power supply, hydraulic control, landing gear, rocket, and rocket fuel subsystems. One of my long-time friends, John McTigue, then operations engineer on the third X-15, helped me specify the work for operational systems. Milt Thompson and Bruce Peterson helped me write the portions relating to the pilot's controls and cockpit displays.
In February 1964, having authorization from the NASA Associate Administrator, Raymond Bisplinghoff, we went "on the street" with a Request for Proposal (RFP), soliciting bids from 26 aerospace firms for designing and fabricating the two rocket-powered lifting bodies. Fortunately, several companies were interested in our program, believing that the next generation of spacecraft would have horizontal landing capability and that any aerospace contractor participating in our experimental lifting-body program would have an edge over other firms in later space programs. Five companies submitted bids, and our choice eventually was narrowed to two of them: North American Aviation (later to become Rockwell International, Rockwell's aeronautics and space divisions now part of Boeing) and Northrop Corporation.
Many supposed that North American (later selected as the prime contractor on the Apollo program) would be a shoo-in for the job, since North American had built the X-15. However, the Norair Division of Northrop clearly had the superior bid, the NASA Flight Research Center awarding the contract to Northrop on 2 June 1964. The RFP's timing worked in both Northrop's and NASA's favor. Northrop had intact the team that had just finished developing the prototype T-38 aircraft. A 19-month interval between the T-38 and another major program allowed Northrop to assign this team of their best people to our lifting-body program. Consequently, Northrop could keep this team together while NASA got the best bargain in skilled people for its program. Northrop's proposal listed all key persons from this team that would be working on our program, providing us as well with their resumes. Ralph C. Hakes of Northrop was assigned as Project Director with Fred R. Erb serving as Northrop's chief systems and mechanical designer.
Northrop's proposal presented a detailed preliminary design with drawings showing the use of many off-the-shelf components, including modified T-37 ejection seat, Northrop's T-38 canopy operating/locking mechanism and ejection system, T-38 stick grip, modified T-39 dual-wheel nose gear, Northrop's F-5 main gears with T-38 wheels and brakes, Northrop's X-21 hydraulic control actuators, and silver-zinc batteries for hydraulic and electrical power. Northrop signed a fixed-price contract requiring delivery of the two vehicles in 19 months for $1.2 million each, a bargain-basement price for NASA, even in the 1960s. According to one aerospace spokesman, at that time the M2-F2 and HL-10 could have cost $15 million each. In the mid-1960s, Northrop was non-union, giving the corporation flexibility in adapting the most economical and efficient methods for producing the two lifting bodies. Northrop not only delivered the vehicles on time but also did so with no cost overruns, two out-of-the-norm accomplishments for aerospace programs to that time and since.
 Northrop purposely kept its project organization lean and flexible, with an average of 30 engineers and 60 shop personnel, each averaging 20 years of aerospace experience. As Ralph Hakes later recalled, the engineers involved were "all twenty-year men who had worked to government specifications all their lives and knew which ones to design to and which to skip." He added that NASA's "people and ours would talk things over and decide jointly what was reasonable compliance with the specifications. Decisions were made on the spot. It didn't require proposals and counter-proposals." 4
NASA and Northrop's program managers devised a Joint Action Management Plan accenting five guidelines for efficiency: keep paperwork to a minimum, keep the number of employees working on the project to a minimum, have individuals- not committees-making decisions, locate the project in one area where all needed resources could be easily and quickly gathered, and fabricate the vehicles using a conservative design approach. Consequently, engineering and factory areas were located in the same building, and veteran shop technicians fabricated and assembled components from a minimum of formal drawings and-in some cases-solely from oral instructions. A special photographic process transposed drawings onto raw metal stock, avoiding costly jigs and fixtures. Northrop's project personnel maintained a very close operational relationship with NASA's personnel, maximizing the joint team's ability to react swiftly in solving problems and making changes.
The overall tone of cooperation in this joint NASA-Northrop program had been established from the beginning by Paul Bikle and Northrop's Richard Horner. The two men had much respect for each other and a good person-to-person under-standing of how the program was to be conducted. Horner and Bikle had worked together often in the past. Horner had worked for the Air Force from 1945 until June 1959, when he became NASA associate administrator until July 1960. Afterwards, he became executive vice president of Northrop. Together, Bikle and Horner agreed to do away with red tape and unnecessary paperwork, a simplification that had a dramatic effect on keeping costs low and efficiency high. Both men had impeccable reputations and credibility, keeping their word on agreements. Even though this was a fixed-price contract, Bikle and Horner agreed that it would be to both NASA's and Northrop's best interests to build these lifting bodies in the most cost-effective and timely manner.
The Program That Almost Was: Little Joes and the M2
About this time, another opportunity arose to conduct a low-cost program using surplus equipment. Four Little Joe solid rockets, used to test the Apollo capsule's escape system, were available at the NASA White Sands rocket testing facility in New  Mexico. I began to explore the possibility of mounting an M2-F2 configuration on top of a Little Joe booster for a vertical launch and possible flight to Mach 6.
Earlier, before it was assembled with the steel-tube carriage structure, I had had a fiberglass mold made from the M2-F1 wooden shell, just in case it was damaged in flight tests or we wanted to build another and heavier M2 out of fiberglass instead of wood. Using this mold, I could make a vehicle with a thick fiberglass skin capable of withstanding speeds up to Mach 6. The vehicle would be made much like a boat, its thick skin acting like an ablative coating to cool the structure from aerodynamic heating at high speeds. It would be unpiloted with a rocket climb and push-over trajectory followed by a pre-programmed turn.
Also available for recovering the M2 after it had slowed down to about Mach 2 were some surplus parachute systems from the Gemini program. John Kiker of the Johnson Space Center, in charge of developing the parachute spacecraft recovery systems for NASA's Gemini and Apollo programs, offered his services in adapting the parachute systems for recovery of the M2. Once we found out we had mutual interests in flying experimental radio-controlled model airplanes, Kiker and I became and have remained friends. In the early days of Shuttle development, Kiker had constructed flying scale models of the Boeing four-engine 747 and the Enterprise, then demonstrated a successful launch of the model Enterprise from the back of the model 747 at Johnson Space Center. This test, using Kiker's models, was done before the approach-and-landing tests of the full-scale Enterprise at Edwards AFB in October 1977.
After I talked with Kiker, I telephoned Dick Thompson, the manager of the NASA White Sands facility, about using the Little Joe boosters to launch an M2. Thompson liked the idea and said he could furnish the personnel for servicing the rockets, preparing them for launch, and conducting the launch operation, if the Flight Research Center would be responsible for the M2 payload. I found myself trying hard to restrain my excitement, for I had already located a surplus hydraulic control system and a programmable missile guidance system. It was all going too smoothly, too quickly, too easily to be believable. About then, a big dose of reality intruded, ending this tiny program before it had even begun.
Dick Thompson contacted me, saying the Little Joe rockets were out-of-date and would require an inspection before they could be used. Being naive about how much such things cost, it didn't occur to me that it would cost very much to inspect something as simple as a solid rocket. So it blew my mind when Thompson told me that an inspection would cost about $1,000,000 per rocket-about half the cost of the Northrop contract for the two lifting bodies. Apparently, the inspection involved much more than simply x-raying the solid propellant for cracks.
I reasoned with Thompson, trying to find a way to use an abbreviated inspection since the test flight would be unpiloted. Thompson was adamant, however, opposed to allowing even the potential for an explosion on the launch pad, NASA space policy having become very conservative after the early days of numerous rocket explosions on the pad.
 Thus ended the program that almost was. It had been a good idea, just not a practical one. In the future, others' ideas would have better chances for success.
NASA-Air Force Lifting-Body Program
Since 1960, the Air Force had also been conducting studies of piloted, maneuverable lifting-body spacecraft as alternatives to the ballistic orbital re-entry concepts then in favor. Given the long history of cooperation and joint ventures between the Air Force and the NASA Flight Research Center at Edwards AFB, it was only natural for them eventually to pool their resources in the flight-test portion of the lifting-body program, much the way they had in the X-15 and earlier X-plane programs.
Much as Walt Williams had done before him, Paul Bikle had always worked closely and effectively with others at the Air Force Flight Test Center. This spirit of cooperation extended to all personnel levels. Since the early days of the NACA station at Muroc in the late 1940s, there had been few, if any, disagreements at the work-level between NASA and Air Force personnel, and any that existed had been imposed from above.
In the early spring of 1965, as Northrop entered its final months of fabricating the first of the two heavyweights, Paul Bikle recognized that the lifting-body program was, like the X-15 program before it, becoming too large for the Flight Research Center (FRC) to manage and operate alone and that NASA and the Air Force had similar interests in the lifting bodies. Bikle met with his Air Force counter-part, Major General Irving Branch, commander of the Air Force Flight Test Center (AFFTC), throughout the early spring.
From those meetings emerged a memorandum of understanding between the two centers on 19 April 1965, nearly two months before the M2-F2 was completed at Northrop's plant in Hawthorne, California. Drawing on the two centers' shared experience with the X-15 program and alluding not only to the excellent working relationship between NASA and the Air Force but also to similarities between the X-15 and lifting-body programs, the memorandum of understanding created the Joint FRC/AFFTC Lifting-Body Flight Test Commit-tee. Ten members made up the committee headed up by Bikle as chairman and Branch as vice-chairman. Six of the remaining eight members included one representative each from the NASA and Air Force pilots, engineers, and project officers. A NASA instrumentation representative and an Air Force medical officer completed the committee.
The joint flight-test committee had responsibility not only for the test program but also for all outside relations and contacts. Maintenance, instrumentation, and ground support for the vehicles remained the responsibility of the Flight Research Center. The Air Force Flight Test Center assumed responsibility for the launch and support aircraft, the rocket power plant, the personal equipment of the pilots, and medical support. The two centers assumed joint responsibility for research flight planning, flight data analysis, test piloting, range support, and overall flight operations.
 Career Decision: Manager or Engineer?
As the lifting-body program grew larger, it needed a full-time manager to coordinate activities among the NASA Flight Research Center, the Air Force Flight Test Center, and the contractor, Northrop. Called into Paul Bikle's office one day, I was confronted with a career decision. Bikle gave me a choice. I could move into management of the program, which would pull me away from involvement in day-to-day technical and engineering activities, or I could stay with engineering.
Bikle told me that he thought I would be happier and NASA would benefit more if I remained in engineering, free to continue generating new technical ideas. He said that if I continued working within the program's technical engineering team, I could serve as NASA's project engineer, coordinating all technical activities for the NASA and Northrop engineering teams. He gave me a few days to make my decision, saying that if I opted to remain in engineering, he would appoint John McTigue as lifting-body project manager. I decided to stay with engineering.
As an operations engineer on the X-15, McTigue had gained experience in scheduling crews and technicians to meet flight schedules. Bikle believed McTigue would make good use of this experience in building up and servicing all systems needed to operate the lifting bodies. McTigue was also very familiar with the rocket, hydraulic, and life-support systems of the X-15s, which were, in most cases, identical to those of the lifting bodies. Furthermore, Bikle earlier had created a competitive spirit among the three X-15 operations engineers in meeting or beating flight schedules by betting against these engineers. On several occasions, Bikle had lost his bet and McTigue had won. Obviously, Bikle was impressed with McTigue as a manager who would keep the program on schedule.
NASA and Northrop Single-Team Engineering
Having a flight-test facility at Edwards AFB for testing F-5s, T-38s, and X-21s, Northrop ran a little commuter-plane operation daily between its plant in Hawthorne in the Los Angeles basin and Edwards AFB, using a couple of Piaggio twin-engined airplanes. During the 19 months of the lifting-body contract, I and the rest of the NASA engineering team commuted almost daily by Northrop's planes to the Hawthorne plant, where I spent nearly half of my time during this period.
In the lifting-body program, NASA engineers did not have the "do-as-I-say" relation-ship with Northrop engineers that was typical between customer and contractor in the aerospace industry. Instead, we worked together as a single team to make the best possible product. The keys to our success were mutual respect, trust, and cooperation. The Northrop engineers respected and trusted not only the expertise of the NASA engineers in aerodynamics and in stability and control analysis but also our operational experience with rocket-powered aircraft. Equally, the NASA engineers trusted and respected the outstanding ability of the Northrop engineers in fabricating  airframes. Working one-on-one in small groups, we made on-the-spot decisions, avoiding the usual time-consuming process of written proposals and counterproposals in solving problems and making changes.
One day, we were called together by a Northrop engineer named Stevenson who was responsible for the M2-F2's weight and balance. He showed us through his latest calculations that maintaining weight balance on the M2-F2 was becoming a large problem, given the twin challenges of a narrow nose area, limiting space for systems, and the requirement for locating multiple actuator systems in the aft end with all control surfaces. We needed to do something drastic to restore balance by putting ballast, or weight, in the nose. Otherwise, the vehicle would be tail-heavy.
An aircraft designer usually considers having to add ballast to a new vehicle as a negative reflection on his or her ability to provide an efficient design. Ballast adds nothing desirable. It puts higher loads on the structure and decreases the aircraft's performance.
We faced a large dilemma. The usual solution would have been to put depleted uranium around the pilot's feet in the aircraft's nose. Having a much higher density than lead, depleted uranium is commonly used for balance in aerospace vehicles when there is limited room for ballast. However, NASA pilots Milt Thompson and Bruce Peterson, as well as the chief Air Force lifting-body pilot, Jerry Gentry, didn't like the idea of cooking their feet in radiation, so we had to come up with another solution.
Stevenson did a cost trade-off study for using gold as ballast in the nose. He also demonstrated how the high-density gold bricks could be cut and fitted into the structure around the pilot's feet without blocking the pilot's vision through the nose window. The $35-per-ounce price for gold at the time was still cheaper than the labor costs would be for balancing the vehicle by redesigning the structure in the aft portion of the M2-F2 and moving equipment forward.
The little group of NASA and Northrop engineers sat around a table, equally desperate to solve this problem. By the time this problem arose, the two teams of engineers had coalesced into one. Everyone focused on solving the problem, not pointing fingers at others' mistakes. Thinking aloud, I suggested that if we could actually put something useful in the nose, rather than simply adding ballast, we might salvage our pride as designers. Immediately, another engineer suggested we put some extra structure around the pilot to give him added protection in case of a crash. As a group, we jumped on that idea, with no debate or dissent, and within thirty minutes we had solved the problem by changing the design, replacing the 50G cockpit with a nearly 300G cockpit that had a very heavy steel frame around the pilot. As it turns out, the decision to add the protective cage-like structure around the pilot helped to save pilot Bruce Peterson's life when the M2-F2 crashed two years later. Only the cockpit remained intact in that horrendous accident that left the rest of the aircraft looking like a crumpled beer can at a Hell's Angels' party.
In similar ways, we approached and solved other engineering problems as they arose. Time used for casting blame and engaging in agonizing debates over proposed  solutions simply leaves that much less time for designing and building. Furthermore, the NASA engineers mainly considered themselves to be support and backup for the Northrop team working at the Hawthorne plant. For example, rather than asking the Northrop team to come to Edwards AFB for meetings or for looking at hardware, we would hold the meetings or take the hardware to Hawthorne, minimizing loss in time.
Things were going so smoothly, unlike typical aerospace projects, that something just had to happen-and it did.
NASA Langley Modifies the HL-10
After the contract had been signed by Northrop and the Flight Research Center, NASA Langley continued wind-tunnel tests on the HL-10 and discovered that the trimmed subsonic lift-to-drag ratio was only slightly more than 3, considerably below Langley's established goal of 4. Furthermore, negative directional stability showed up at low supersonic speeds and at some angles of attack.
To fix these problems, Langley initially considered adding an ejectable tip-fin scheme, only to discard the idea, finding it unacceptable to be ejecting tip fins during the final phase of a mission. Then, working from wind-tunnel test results, Langley engineers changed the tip-fin shape, developing a configuration that increased area, toe-in angle, and roll-out angle. They also added simple two-position flaps to the trailing edge of the tip fins and upper elevon to vary the base area. Closing these flaps would also minimize the subsonic base drag. This modification brought the maximum lift-to-drag ratio to nearly 3.4, still short of the target 4.0. However, it improved the directional stability.
On 3 February 1965, nearly 10 months into the 19-month contract with Northrop, Langley presented its proposed HL-10 modification at a meeting held at the Flight Research Center. Attending the meeting were several of the top Langley engineers--including Eugene Love, Robert Rainey, and Jack Paulson-as well as NASA Headquarters' Fred DeMerritte, chief of the lifting-body program for the Office of Advanced Research and Technology, through whom we received our funding for the follow-on lifting-body program. The proposal was to add six more control surfaces to the HL-10. These would be two-position surfaces consisting of elevator flaps, located on the upper surface of the elevon, and outboard tip-fin flaps.
The result was a required design change and modification to the contractual agreement with Northrop. The modification was done as required, but it was done minus the wholehearted support of NASA and Northrop program managers and engineers. However, later in the HL-10 program, the required change came to be seen as an excellent decision. The modification simplified the flight-control design. It also allowed the pilot to move during flight from subsonic to supersonic speeds simply by throwing a switch, requiring less trim change in the pilot's control-stick position. The pilot could now easily convert the HL-10 from a "shuttlecock" to a low-drag subsonic configuration.
 Included in the modification was an enlargement of the center and tip fins that improved trim and stability at transonic and supersonic speeds and increased the lift-to-drag ratio in the approach to landing. At subsonic speeds and during landing, the two-position flaps on the upper elevon surface, split rudder, and tip fins retracted for maximum boat-tailing (minimum base area) on the aft portion of the vehicle. At high subsonic, transonic, and supersonic speeds, the movable flaps deflected outwardly, minimizing flow separation at control surface areas.
The modification to the HL-10 meant that the M2-F2 was the first to be finished, rolling out of Northrop's Hawthorne plant on 15 June 1965. The next day, it was trucked over the mountains north of Los Angeles to Edwards AFB. At its unveiling, the M2-F2 lacked the LR-11 rocket engine, but we planned to fly it first as a glider, then modify it for powered flight.
Made of aluminum, the M2-F2 weighed 4,630 pounds, was 22 feet long, and had a span of 9.4 feet. Its retractable landing gear used high-pressure nitrogen to rapidly extend the landing gear just before touchdown. The boosted hydraulic control system was pressurized by electric pumps running off a bank of nickel-silver batteries. A Stability Augmentation System (SAS) in all three axes helped the control system in damping out undesirable vehicle motions. For instant lift to overcome drag momentarily during the prelanding flare, the pilot could use the vehicle's four throttleable hydrogen-peroxide rockets, rated at 400 pounds each. The M2-F2 also had a zero-zero seat, a modification by Weber of the one used in the F-106 Delta Dart.
We put the M2-F2 next to the M2-F1 for a family photograph. Except for being identical in size, there were few similarities. The M2-F2 lacked the M2-F1's "elephant ears," had an extended boat-tail and forward canopy, and would eventually weigh 10 times as much as the M2-F1.
M2-F2 Wind-Tunnel Tests
Soon after the first heavyweight lifting body arrived at the NASA Flight Research Center, more team members were assigned to the M2-F2, including operations engineer Meryl DeGeer, crew chief Bill LePage, and assistant crew chief Jay L. King. In helping to ready the M2-F2 for flight testing and research, Bill Clifton did the instrumentation engineering and John M. Bruno, Al Grieshaber, and Bob Veith installed the flight research instrumentation.
Since full-scale testing of the M2-F1 had worked out well, the NASA Ames wind-tunnel team suggested that we measure the M2-F2's aerodynamic character-is-tics at landing speeds in the 40-by-80 wind tunnel. DeGeer and LePage agreed, wanting to test under wind-tunnel conditions the vehicle's control system, landing-gear deployment, and emergency ram-air turbine that would provide hydraulic power for operating  the controls if the battery driving the pumps failed in flight. By August 1965, 100 hours of wind-tunnel tests would be completed on the M2-F2 within a period of two weeks.
In late July, the M2-F2 was loaded on a truck for its trip north to the NASA Ames Research Center, stirring up memories for many of us of the similar trek two years earlier with the M2-F1. This time, however, the wind-tunnel testing would be more complex than that done on the "flying bathtub." Several changes replaced nearly everything done by the person who had sat in the cockpit throughout the M2-F1's tests-as well as much of the hand-plotting of test data-allowing the wind-tunnel tests on the M2-F2 to move along more rapidly.
Hoses ran from an aircraft hydraulic power cart to the vehicle atop the pedestal, powering its control system. Pilot linkages from the cockpit to the hydraulic servos were replaced with miniature electric screw jack actuators. Toggle switches in the wind-tunnel's control room activated these actuators that, in turn, controlled the hydraulic actuators moving the control surfaces to various settings.
We also made use of the flight instrumentation onboard the M2-F2, parking one of our mobile ground-receiving stations outside the wind tunnel and hard-wiring it to the vehicle's instrumentation. In this way, sensors inside the aircraft allowed air speed, angle of attack and sideslip, and control positions to be recorded along with data from the wind tunnel's measuring system. With all this help replacing what had earlier been done only by human hand during the M2-F1's tests, Bertha Ryan could assume sole responsibility for assimilating all wind-tunnel data on the M2-F2. Nevertheless, there still remained a lot of data-plotting that had to be done by hand.
We began with testing the operational systems, which required a person in the cockpit to operate the landing-gear deployment handle and the ram-air turbine unit. DeGeer volunteered and climbed into the cockpit. However, the vehicle's canopy had been covered with paper to protect it from scratches during the tests, and DeGeer began to get claustrophobic right away. LePage opened a peephole in the paper so DeGeer could see outside.
After the wind tunnel was brought up to speed, it began to get hot in the cockpit, seemingly due to all the bright lights used to illuminate the vehicle. Trying to cool the interior of the cockpit, DeGeer opened the ram-air doors. Of course, the air coming into the cockpit was even hotter, the tunnel actually heating the air. Despite his discomfort, DeGeer deployed the landing gear and the ram-air turbine. Both systems worked well, and we could move along to the aerodynamic testing that didn't require literally having a warm body in the cockpit. Afterwards, DeGeer said he had gained great appreciation from his own experience for what Dick Eldredge must have endured two years earlier, sitting in the cockpit of the M2-F1 in the wind tunnel for eight hours.
 Wind-Tunnel Tests of M2-F2, HL-10, and B-52 Models
Because of the potential for either heavyweight lifting body to collide with the B-52 motherplane immediately following launch, we conducted another set of wind-tunnel tests in 1965, this time at NASA Langley, using models of the B-52 bomber and the M2-F2 and HL-10 lifting bodies. During these tests, the airflow around the lifting body hanging in launch position was deflected upstream by the B-52's nose as well as (near and just above the lifting body) by the B-52's wing. This indicated that angular flow could cause the lifting body to roll and pitch immediately following hook release from the B-52. Since this could occur in a mere fraction of a second, the pilot would not be able to react fast enough to avoid a roll-off and possible vertical-fin contact with the B-52's launch pylon. In some cases, the automatic and gyro-driven rate damper might be able to react that quickly, the controls preset before launch to counter any unwanted motions after launch, but it was just as likely to be too slow to keep the lifting body from making contact with the B-52.
Launch studies by Wen Painter and Berwin Kock found that the M2-F2's vertical fins would make contact with the B-52's pylon used in launching the X-15. Consequently, the adapter used for launching the M2-F2 from the pylon was modified to lower the lifting body. In the wind tunnel, the lifting-body model was positioned at different points below the B-52 as well as in launch position, with forces and moments measured on the M2-F2 then used to calculate the vehicle's flight path and attitude as it fell away from the B-52. Similar wind-tunnel tests much earlier on a model of the X-15 had also succeeded in predicting the motions of the X-15 after launch from the B-52. Our tests used the same B-52 model that had been used in the X-15 wind-tunnel tests.
Years later, Jerry Gentry, one of only four pilots to fly the M2-F2, recalled how he and others downplayed the fear that still existed after the wind-tunnel tests that the lifting body might fly back up into the B-52 after it separated from the pylon. "There was no question which way you were going when the B-52 dropped you," he said. "One guy used to say that if they dropped a brick out of the B-52 at the same time [he] released, [he]'d beat the brick to the ground." 5
Moving Toward Flight
After we trucked the M2-F2 back to Edwards AFB, we began preparing for its first glide tests. Our staff expanded to meet these needs. Added to assist DeGeer were Norm DeMar, who acted as lead systems engineer, and Northrop's Jim Crosby, systems electrical engineer for the yet-to-be-installed rocket engine. The crew under the direction...
....of crew chief LePage and assistant crew chief King grew to include mechanics Chet Bergner and Orion Billeter, electrician and electronic technician Millar I. Lockwood, and inspectors Bill Link and John E. Reeves. For seven months, Jack Cates, Mil Lockwood, and Wen Painter worked on the problems remaining in the Stability Augmentation System, resolving them by May 1966.
As with the M2-F1, Milt Thompson was selected by Bikle and Chief of Flight Operations Joe Vensel to pilot the M2-F2 in its first glide test. A list of five more future pilots for the M2-F2 was also drawn up, including NASA pilots Bruce Peterson, Bill Dana, and Fred Haise as well as Air Force pilots Donald Sorlie and Jerry Gentry. As the "angry" qualities of the M2-F2 revealed them-selves later in actual flight, only three of these pilots-Peterson, Sorlie, and Gentry-would, in addition to Thompson, actually get to fly the M2-F2.
As part of the pilot preparation for the first flights of the M2-F2, Ken Iliff and Larry Taylor designed a flight experiment, using a highly modified and variable-stability Lockheed T-33A jet trainer from the Cornell Aeronautical Laboratory of Buffalo, New York, to simulate the flight characteristics of the M2-F2. When the petal-shaped surfaces called "drag petals" that had been installed on the T-33A's wing-tip tanks were extended in flight, the aircraft's lift-to-drag ratio varied from its usual 12-14 to as low as 2, approximating the lift-to-drag ratio of the M2-F2. The T-33A was part of a cooperative pilot training and aircraft simulation program that the NASA Flight Research Center had launched earlier with Cornell, the T-33A used initially to....
....simulate the low lift-to-drag ratio characteristic of the X-15 during re-entry. The T-33A was used at the Flight Research Center for in-flight simulation of the M2-F2 in the spring and summer of 1965, with Cornell's test pilot Robert Harper and then Thompson, Peterson, Dana, and Haise executing typical lifting-body approaches in the T-33A.
The flight experiment pinpointed a potential lateral control problem, alerting Thompson, Peterson, Dana, and Haise before the actual M2-F2 flights began in July 1966. Lateral control of the M2-F2 required considerable attention and technique from the pilot. We had had Northrop install a small wheel in the left side of the cockpit so the pilot could adjust the rudder aileron interconnect in flight. Thompson and Peterson believed that they could rely on their skills as test pilots to manually adjust the rudder aileron interconnect ratio during flight.
The interconnect ratio had to be high to roll the M2-F2, due to its extremely high dihedral at high angles of attack as well as adverse yaw of the differential upper flaps (elevons). At low angles of attack and high speed, however, using too much rudder for roll control would result in a pilot-induced oscillation. If the pilot did not set the interconnect wheel properly to match flight conditions, he could have serious problems controlling the vehicle in roll. During the T-33A flight-simulation experiment, we did not consider the possibility that a pilot would use the rudder pedals for roll control, Navy-carrier and glider pilots typically making heavy use of the rudder pedals in flying. Indeed, we were asking a lot from the M2-F2 pilots.  Little did we know then that in the M2-F2 we had created a monster.
We weren't in a rush to make the first glide flight, preferring to be absolutely sure that everything was in order. We did seven captive flights with Milt Thompson sitting in the M2-F2 attached to the B-52's X-15 pylon. Operational anomalies turned up on each of the captive flights that had to be corrected on the flight that followed. The captive flights turned out to be excellent rehearsals for everyone involved in the control room, on the ramp, in the B-52, and, of course, in the cockpit of the M2-F2.
1 Entire three paragraphs above, including quotation, based upon Hallion, On the Frontier, pp. 151-53.
2 Paragraph based in part on Thompson, At the Edge of Space, pp. 46-47, 85, but that source gives information on the LR-11 engines that were not uprated. The powered lifting bodies used uprated engines with upwards of 8,000 lbs. of thrust versus the 6,000 lbs of the original LR-11. See Frank Winter, "'Black Betsy': The 6000C-4 Rocket Engine, 1945-1989. Part II," Acta Astronautica 32, No. 4 (1994): 314-317 and David Baker, Spaceflight and Rocketry: A Chronology (New York: Facts on File, 1996), p. 167.
3 John V. Becker, "Preliminary Studies of Manned Satellites--Winged Configurations," NACA Conference on High-Speed Aerodynamics: A Compilation of Papers Presented (Moffett Field, Calif.: Ames Aeronautical Laboratory, 1958), pp. 45-57.
4 Quoted in Hallion, On the Frontier, p. 154.
5 Wilkinson, "Legacy of the Lifting Body," p. 55.