The Re-entry Problem
Returning from space is a battle against physics. A spacecraft in low Earth orbit is not simply “up”; it’s “sideways,” moving at over 17,500 miles per hour, or roughly Mach 25. To come home, it must shed all of that colossal kinetic energy. That energy doesn’t just disappear; it converts almost entirely into heat – an inferno of compressed atmosphere capable of vaporizing any unprotected material. In the late 1950s, as the space age was dawning, engineers faced a fundamental choice: how to bring an astronaut back through this barrier.
Three primary paths were available, each with its own set of advantages and severe drawbacks.
The first and most straightforward option was the ballistic capsule. This was the “cannonball” approach. Engineers, particularly H. Julian Allen at NASA’s predecessor, the National Advisory Committee for Aeronautics (NACA), had already determined that a blunt, rounded shape was far superior to a sharp, pointed one for surviving reentry. This blunt body created a powerful shockwave that stood off from the vehicle, allowing the superheated, compressed air to flow around the spacecraft, carrying the majority of the heat with it. This concept was proven effective. It was passively stable, relatively simple to build, and formed the basis for the Mercury, Gemini, and Apollo programs.
The problem with the ballistic capsule was its complete lack of control. It was a rock, falling along a predictable, unchangeable path. The astronaut inside was a passenger, subjected to massive deceleration forces, or g-loads, and having almost no ability to steer. The landing “footprint” was a small, pre-calculated patch of ocean. If the capsule missed, it missed.
The second option was the winged spaceplane, the most intuitive solution for any pilot. This approach, exemplified by the X-15 rocket plane and later the Space Shuttle, would have a vehicle re-enter the atmosphere and fly like a glider. Its wings would provide high lift, giving the pilot excellent maneuverability and the ability to land on a specific runway. The problem was the wings themselves. These large, thin structures were a thermal nightmare. They were incredibly difficult to shield from the multi-thousand-degree heat of reentry, and protecting them would add immense weight and complexity to the vehicle.
This left a third, radical, and mostly theoretical option: the lifting body. This concept tried to split the difference, capturing the best of both worlds. It was a vehicle with no wings at all, giving it the compact, sturdy, and heat-resistant shape of a capsule. But it was a vehicle whose body – its fuselage – was meticulously shaped to generate aerodynamic lift. It was a flying fuselage.
The fundamental challenge was not just survival; it was control. The goal of the space program wasn’t just to get astronauts back to Earth; it was to create a reusable, operational system. That meant moving away from splashing down in the middle of the ocean and being fished out by the Navy. The goal was to have a spacecraft that a pilot could fly back from orbit and land at a pre-determined site, just like an aircraft.
This is where the lifting body concept entered the scene. It was not a universally celebrated idea. In fact, it was born from deep skepticism. While many engineers at NASA’s research centers were toying with the idea, the high-level bureaucracy was unconvinced. In 1961, a blue-chip panel of the Scientific Advisory Board recommended to the Air Force that it finance only winged reentry vehicles, not lifting bodies. The panel, and many others, questioned the control characteristics of such a strange, wingless shape, believing conventional landings would be hazardous, if not impossible. The lifting body program was not a logical next step. It was a maverick idea, pushed by a small, dedicated group of engineers who had to fight an uphill battle against the established consensus.
What is a Lifting Body?
A lifting body is an aircraft or spacecraft configuration in which the body, or fuselage, itself is designed to produce the aerodynamic lift required for flight. It’s a simple definition for a concept that fundamentally rethinks the design of an airplane.
On a conventional aircraft, the components are specialized. The fuselage, typically a tube, exists to hold people, cargo, or fuel; it generates very little lift and, in fact, creates a lot of drag. The wings, in contrast, are specialized lift-generating surfaces. A “flying wing” is one extreme, an aircraft that seeks to maximize efficiency by eliminating the non-lifting fuselage entirely. A lifting body is the absolute opposite. It’s a design that eliminates the wings, forcing the fuselage to do all the work.
It does this by its shape. Instead of a non-aerodynamic tube, a lifting body’s fuselage is shaped like a flattened, rounded, or sometimes cone-like airfoil. While a wing generates lift by creating a pressure differential between its top and bottom surfaces, a lifting body functions in a cruder but effective way. It’s designed to fly at a high “angle of attack,” meaning its nose is pointed significantly upward relative to its direction of flight. This angle causes the vehicle’s large, specially shaped bottom surface to deflect a massive amount of air downward. In accordance with Newton’s third law, this downward push of air results in an upward push on the vehicle. This is lift.
It’s not good lift. The primary metric for this kind of flight is the lift-to-drag ratio, or L/D. A modern sailplane might have an L/D ratio of 60:1, meaning for every 1 foot it falls, it can glide 60 feet forward. A lifting body, by contrast, has a terrible L/D ratio, often as low as 3:1 or 4:1. This is why they were famously, and accurately, described as “flying bricks.”
But the point was never to soar. The lifting body concept represents a deliberate engineering trade-off. It “trades coefficient of lift for strength.” It sacrifices the high efficiency of a thin wing for the structural simplicity, volumetric efficiency, and heat-resistant properties of a compact, wingless body. It didn’t need to glide well; it just needed to glide enough to be steerable.
This steerability was the entire reason for its existence, and it’s expressed in a concept called “cross-range capability.” A ballistic capsule, like Apollo, re-enters with almost no lift. Once it begins its descent, it’s committed to a landing footprint that is very small. It cannot decide to land somewhere else.
A lifting body, by using its modest amount of lift, can perform maneuvers during its reentry glide. By rolling into a bank, it can direct its lift vector to the side, causing it to fly “laterally” – or, to the left or right of its original orbital ground track. This ability expands its landing footprint from a small patch of ocean to a massive area, potentially covering thousands of miles. A lifting body de-orbiting over the Pacific could, in theory, choose to land at any number of runways across the entire western United States.
This cross-range capability was the first major advantage. The second was volumetric efficiency. By eliminating wings, the vehicle is more compact and has more usable internal volume for its size. It also avoids the immense challenge of reentry heating on wings, which, as engineers noted, carried a “consequent weight penalty.” A lifting body was, in short, a tough, controllable, and efficient reentry shape.
The Birth of an Idea
The origin of the lifting body can be traced back to 1957, not to a grand aerospace summit, but to a specific engineering problem at NASA’s Ames Aeronautical Laboratory in California. At the time, NACA was intensely studying the problems of missile nose cone reentry. The initial assumption was that a sharp, needle-like nose would be best, to “pierce” the atmosphere.
Engineer H. Julian Allen made the counter-intuitive discovery that a blunt nose cone was far better. The blunt shape would create a powerful detached shockwave, and the friction-induced heat would form in this compressed air in front of the vehicle, not directly on its skin. Most of the heat would then be carried away by the superheated air as it flowed around the body.
This was the solution for surviving reentry. But it was another Ames engineer, Dr. Alfred J. Eggers Jr., who had the next breakthrough. Eggers was looking at these symmetrical, blunt nose cones and considered a simple modification: What if the shape wasn’t symmetrical? What if it was a “half-cone,” flat on top and rounded on the bottom? He found that this modified shape would not only survive the heat of reentry just as well, but it would also use the atmosphere to generate lift. By simply changing its shape, the nose cone went from a falling rock to a steerable glider.
This was the theoretical birth of the lifting body reentry vehicle. But a theory on paper, even a good one, is a long way from a flying machine. The idea was met with abundant skepticism. The official design studies of the era, the ones with government funding, were not focused on lifting bodies. Many engineers believed that any such vehicle would be hopelessly unstable at the low speeds required for landing. They argued that a lifting body would, at a minimum, need a set of deployable “pop-out” wings, or perhaps even deployable turbojet engines, to make a conventional landing practical.
These additions, of course, would have defeated the entire purpose of the design, which was to be simple, light, and wingless. The lifting body concept was intriguing, but it lacked official support and was stalled by institutional doubt.
The idea was rescued from this bureaucratic limbo by a small, passionate group of engineers at NASA’s Flight Research Center (FRC) at Edwards Air Force Base in the high desert of California. This was a place where people “got their hands dirty working on aircraft,” a place for pilots and engineers who liked to “kick the tires.” A small team, led by engineer R. Dale Reed, was fascinated by the lifting body concept. Unable to get official permission, they famously began their work in their spare time, building models and dreaming of a full-scale test. They were the mavericks who would prove the skeptics wrong, not with complex computer models, but by building and flying the real thing.
The “Flying Bathtub”
In 1962, FRC Director Paul Bikle, a pragmatic leader, was convinced by Reed’s passionate advocacy. He approved a small, low-budget program to build a lightweight, unpowered lifting body prototype. The goal was simple: to flight-test the wingless concept and see if a pilot could actually control it. The vehicle, nicknamed the “flying bathtub” for its ungainly shape, was designated the M2-F1.
This was a “skunkworks” project in its purest form. It was not a sleek, billion-dollar aerospace machine. It was a masterpiece of “build-it-and-see” engineering, a testament to the hands-on, low-budget innovation that defined the FRC. The M2-F1 was built like a garage project. It featured a plywood shell, which gave it its smooth, rounded shape, constructed by Gus Briegleb, a local sailplane builder from El Mirage, California. This wooden skin was fitted over a simple, strong tubular steel frame crafted in-house by FRC technicians. Construction was completed in 1963 for a remarkably low price.
With the M2-F1 built, the team faced its next challenge: how to test it. The solution was as ingenious and low-tech as the vehicle itself. The initial “flight tests” were ground tows across the vast, flat expanse of Rogers Dry Lake. The team attached the M2-F1 to a “hopped-up” Pontiac convertible with a long tow rope. NASA research pilot Milt Thompson climbed into the cockpit. The Pontiac then sped across the lakebed at speeds up to 120 mph.
It worked. The M2-F1 lifted off the ground, flying just a few feet in the air, but it was enough. Thompson used the vehicle’s simple control surfaces – fins and rudders – to stabilize and maneuver it. These initial tests, over 400 of them, generated the first real-world flight data. They proved the wingless concept was not the unstable death trap the skeptics had feared. It was flyable.
The success of the Pontiac tows gave the team approval to take the next step. They graduated from the car to a NASA R4D tow plane (the Navy’s version of the C-47). The R4D would tow the M2-F1 up to an altitude of 12,000 feet, at which point Thompson would release the tow rope. He would then be in a completely unpowered, plywood, wingless glider, and his only option was to fly it back to Rogers Dry Lake. These glide flights typically lasted several minutes and reached speeds of 110 to 120 mph.
The M2-F1 performed 77 of these aircraft-tow flights before it was retired. As a lightweight, unpowered prototype, it had done its job perfectly. It demonstrated, beyond any doubt, that a pilot could safely maneuver and land a wingless vehicle. The “flying bathtub” had, with its plywood skin and car-towed flights, kicked open the door. Its success was the key that unlocked the funding for a full-scale, joint NASA-Air Force program to build and fly the “heavyweights” – the rocket-powered lifting bodies that would fly to the edges of space.
The Heavyweights Arrive
The success of the M2-F1 transformed the lifting body from a back-of-the-envelope curiosity into a major research program. This next phase, based at the Flight Research Center, was a joint effort between NASA and the U.S. Air Force, and its goals were far more ambitious. The “heavyweights” would not be made of plywood, and they wouldn’t be towed by a C-47. They would be all-metal, rocket-powered research vehicles, built by major aerospace contractors, and designed to fly at supersonic speeds and high altitudes.
This program ultimately produced five distinct vehicles, which, combined with the M2-F1, made up the fleet of six lifting bodies flown at FRC between 1963 and 1975. The program was not centered on a single design, but was a broad investigation of different lifting body shapes, each with different theoretical properties.
The fleet of heavyweights included:
- The M2-F2: Built by Northrop Corporation, this was the all-metal, rocket-powered successor to the M2-F1, based on the “Manned” “Flight” version of the Ames M2 shape.
- The HL-10: Also built by Northrop, this vehicle was based on a competing design from NASA’s Langley Research Center. The “HL” stood for “Horizontal Landing,” and “10” was for the tenth lifting body model Langley had investigated.
- The X-24A: Built by the Martin Company for the Air Force, this was a third, distinct design concept – a bulbous, teardrop-like shape.
- The M2-F3: This was not a new vehicle, but the M2-F2, which was rebuilt with significant modifications after it crashed.
- The X-24B: In a similar fashion, this was the X-24A, which was later returned to Martin and rebuilt with a radically different “flying flatiron” shape.
A typical flight profile for one of these heavyweights was a spectacular and demanding event. The lifting body would be carried aloft by a modified B-52 “mothership,” tucked under its right wing between the fuselage and the inboard engines. The B-52 would fly to a height of about 45,000 feet and a launch speed of around 450 mph.
The research pilot, already strapped into the lifting body’s cockpit, would then be “dropped” from the B-52. After falling clear, the pilot would ignite the vehicle’s XLR-11 rocket engine. This was the same reliable, four-chambered engine that had powered the Bell X-1 past the sound barrier decades earlier. The rocket would fire for several minutes, accelerating the lifting body up to speeds approaching Mach 2 and altitudes as high as 90,000 feet.
After the rocket engine shut down, the most important part of the mission began. The pilot was now at the controls of a heavy, unpowered glider, executing a steep, high-speed descent back to Rogers Dry Lake. This unpowered glide and landing was the entire point, simulating the return from orbit. The vehicles would touch down on the lakebed at speeds well over 200 mph.
This fleet of vehicles and their 12-year flight program created the foundational database for all future lifting body and spaceplane design.
The “Angry Machine” and the Crash
The heavyweight program began with the M2-F2, the sleek, all-metal successor to the “bathtub.” Pilots quickly discovered that this new machine was dangerously unstable. It was described as a particularly “angry machine.” Its primary problem was a violent, oscillating motion known as “Dutch roll,” a sickening combination of side-to-side yawing and side-to-side rolling.
The plywood M2-F1 had large, external “elephant ear” elevons that, while simple, provided good roll control and helped damp out these motions. When the M2-F2 was designed, these were removed, and the vehicle was left without adequate roll-damping. Pilots compared flying it to a lumberjack trying to spin a log in the water without spiked boots or a stabilizing board. The vehicle was constantly threatening to roll over.
On May 10, 1967, this instability led to the program’s only serious accident. NASA research pilot Bruce Peterson was on his 16th flight in the M2-F2, making his final approach to the lakebed. The vehicle entered a severe Dutch roll. Peterson, distracted by a rescue helicopter that he thought was in his path, fought to regain control. He couldn’t.
The M2-F2 struck the dry lakebed at over 250 mph. It cartwheeled, tumbling violently end-over-end across the desert floor. The crash was horrific, demolishing the vehicle. Miraculously, Peterson survived, though he was critically injured and would later lose sight in one eye.
The footage of the M2-F2’s crash was so spectacular and terrifying that it became a piece of pop culture history. Years later, the grainy film of the M2-F2 tumbling across the desert was used in the opening credits of the popular 1970s television show, The Six Million Dollar Man, as the “backstory” for the show’s cyborg hero, Steve Austin.
A crash of this magnitude could have ended the M2 program, and perhaps the entire lifting body concept, permanently. It was a clear demonstration of the dangers the 1961 review panel had warned about. But the culture at the Flight Research Center was not to shy away from failure, but to learn from it. The crash of the M2-F2 was not seen as a failure of the concept, but as the most valuable, if costly, data point the program had yet produced. It provided undeniable, real-world data on a dangerous instability that wind tunnels and simulations had not fully predicted.
The response was to rebuild. The Northrop team, with the backing of NASA management, was authorized to take the wrecked M2-F2 and convert it into a new vehicle: the M2-F3. The most important modification was the one suggested by the crash data: the addition of a tall center fin. This fin, along with an improved stability augmentation system, was designed to “give the lumberjack his spiked boots back.”
It worked. The M2-F3 flew 27 times, piloted by NASA’s Bill Dana and John Manke, and the Air Force’s Jerauld Gentry and Cecil Powell. The center fin completely tamed the M2’s angry personality, solving the lateral stability problem. The M2-F3 was a stable, reliable research machine. The lesson had been learned, paid for by the M2-F2, and implemented on the M2-F3. This resilience, this process of breaking a vehicle, understanding why it broke, and fixing it, was essential for building the knowledge base that would make future spaceplanes safe.
Taming the Shapes: HL-10 and X-24
While the M2 program was grappling with its stability issues, the other two designs in the heavyweight fleet were also producing a wealth of data. The existence of three different, competing designs (M2, HL-10, and X-24) was not an accident. It was a deliberate, brilliant strategy of parallel development.
NASA didn’t bet on a single horse. The M2 was an Ames Research Center design. The HL-10 was a Langley Research Center design. The X-24A was an Air Force Flight Dynamics Laboratory design. All three were built and flown at the same time, by the same group of pilots, at the same flight center. This created a high-speed, competitive, and collaborative research environment. The pilots could directly compare the “feel” of each vehicle, providing invaluable subjective feedback to complement the engineering data. This parallel approach allowed NASA to gather a wide, robust database on multiple shapes, rather than getting locked into a single design that might have had a hidden flaw.
The star performer of the program turned out to be the HL-10. This was the vehicle from Langley, its name signifying “Horizontal Landing, 10th Design.” It had a unique shape, with a very flat bottom and a rounded top, much like a crude airfoil. Its first flight was on December 22, 1966, with Bruce Peterson at the controls. After some initial flights and modifications to its fins, the HL-10 “attracted the attention of the pilots.” It was eventually judged to be the best handling of the three original heavyweights.
The HL-10 flew 37 times and became the program’s record-setter. On February 18, 1970, Air Force test pilot Major Peter Hoag pushed the HL-10 to 1,228 mph, or Mach 1.86, the fastest speed any lifting body achieved. Just nine days later, NASA’s Bill Dana flew the HL-10 to an altitude of 90,303 feet, the highest altitude reached in the entire program. The HL-10’s successful flights contributed substantially to the later decision to design the Space Shuttle without “air-breathing” jet engines for landing.
The Air Force’s entry, the Martin X-24A, tested a completely different “bulbous… teardrop” shape. It was a chunky vehicle with three vertical fins at its blunt rear. It first flew on April 17, 1969, piloted by Air Force Major Jerauld Gentry. The X-24A was flown 28 times, reaching Mach 1.6 and an altitude of 71,400 feet. It, too, successfully validated the concept of an unpowered lifting reentry.
But the X-24A’s story didn’t end there. In another prime example of the program’s cost-saving, iterative approach, the vehicle was not retired to a museum. It was sent back to Martin for a complete rebuild. Its bulbous shape was converted into the radically new X-24B. This vehicle resembled a “flying flatiron,” with a rounded top, a flat bottom, a double-delta planform, and a long, pointed nose. This shape was specifically proposed by the Air Force Flight Dynamics Laboratory to test a design with a higher lift-to-drag ratio. This conversion saved the program millions in construction costs and allowed the team to test a fourth major shape using a proven airframe. The X-24B would go on to fly 36 missions, and it was this “flying flatiron” that would perform the program’s final, and most important, act.
Flying the “Falling Brick”
The lifting body program was, at its heart, a human endeavor. The vehicles were flown by a small, elite group of research pilots, including NASA’s Bill Dana, John Manke, and Bruce Peterson, and the Air Force’s Jerauld Gentry, Peter Hoag, Cecil Powell, and Mike Love. It was their job to take these theoretical, rocket-powered gliders and find out what it was really like to fly them.
The experience was unlike anything in aviation. The nickname “falling brick” became popular, a phrase later inherited by the Space Shuttle. It was a direct, and accurate, description of the vehicles’ abysmal lift-to-drag ratio. The pilots were essentially flying a falling brick through the sky.
The most demanding part of every flight was the landing. After the XLR-11 rocket engine shut down, the pilot had between five and ten minutes to get the vehicle on the ground. There was no engine, which meant there was no thrust to correct a bad approach. There was no “go-around” for a second try. It was a one-shot, unpowered, “dead-stick” landing, every single time.
The landing profile was steep and incredibly fast. Pilots couldn’t just glide gently to the ground like a sailplane. They had to dive at the runway to build up and maintain speed, which was their only source of energy. On the final approach, they would execute a high-speed “flare” maneuver, pulling the nose up at the last second. This would bleed off the excess speed and slow the vehicle from over 300 mph to a touchdown speed that was still a blazing 200 to 250 mph.
Training for such a demanding, short, and dangerous flight was a major challenge. Pilots couldn’t just take the lifting body up for practice. Their training relied on two key tools. The first was a heavy dependence on ground-based simulators. These simulators were constantly updated with data from the previous flight, allowing pilots to “fly” the mission dozens of times before ever being dropped from the B-52.
The second tool was a “simulator in the sky.” Pilots used modified F-104 Starfighter jets, which they would fly in a “dirty” configuration – with landing gear down, flaps extended, and speed brakes out. This intentionally created a high-drag, low-lift profile that closely mimicked the steep, high-speed approach of a lifting body, allowing them to practice the nerve-wracking flare maneuver in a real aircraft.
But the pilots were not flying alone. They were assisted by an unsung hero: the Stability Augmentation System, or SAS. These wingless vehicles were inherently unstable, especially in roll. They were flyable onlywith the help of these primitive, early flight computers. The SAS would take the pilot’s commands from the control stick and rudder pedals and translate them to the vehicle’s control surfaces (elevons and rudders). It would also simultaneously make thousands of tiny corrections per second to damp out oscillations, like the Dutch roll, long before the human pilot could even sense them.
This relationship between the pilot, the simulator, and the SAS reveals the real job of the test pilot. It wasn’t just to fly the vehicle. It was to validate the simulator. The engineers would program the simulator based on wind tunnel data, but no one knew if it was right. After a five-minute flight, the pilot would debrief the engineers. “The dynamics feel as good as the simulator,” one report on the HL-10 noted. Or, “The longitudinal stick is too sensitive.”
This human feedback, the pilot’s “feel,” was fed directly back to the engineers, who would then update the simulator’s code. The pilots were the biological sensor package in a complex feedback loop. This iterative process, this “calibration” of the simulator against a real pilot’s experience, is what allowed NASA to build the confidence that they could predict how a future vehicle, like the Space Shuttle, would fly before it was ever built.
The Final Milestone: The Runway Landing
By 1973, the lifting body program had answered almost every question. The M2-F1 had proven a wingless vehicle could fly. The M2-F3 had solved the critical lateral stability problem. The HL-10 had set speed and altitude records and proven to be an excellent-handling machine. The program had generated a massive database on unpowered, supersonic flight.
But one big question remained.
All 199 flights to that point had ended with a landing on the 44-square-mile expanse of Rogers Dry Lake. The lakebed was a massive, forgiving, and perfectly flat landing strip. You couldn’t miss it. But a real, operational spaceport, like Kennedy Space Center or Edwards Air Force Base, has a concrete runway. For the Space Shuttle concept to be viable, NASA had to prove that a “falling brick” could be landed with pinpoint accuracy on a narrow, 15,000-foot strip of concrete.
This would be the final mission for the lifting body program, and the task fell to the X-24B, the “flying flatiron.” This vehicle, with its higher lift-to-drag ratio, was the most promising candidate for a precision landing.
In a series of flights in 1975, NASA pilot John Manke and Air Force pilot Major Mike Love flew the X-24B on its final, most important missions. They were dropped from the B-52, ignited the rocket, and performed the same steep, unpowered glide, but this time, they aimed for the main concrete runway at Edwards Air Force Base.
The results were a “bullseye.” Both pilots successfully landed the X-24B exactly on the runway.
These flights were the final milestone. They were the climax and the ultimate validation of the entire 12-year, six-vehicle program. They “demonstrated that accurate unpowered reentry vehicle landings were operationally feasible.” The final powered flight of the program was on September 23, 1975, with Bill Dana at the controls of the X-24B. The data was in. The question had been answered.
The Bridge to the Space Shuttle
The 199 flights of the six lifting bodies were not just an academic exercise. This research “generated… the data base that led to development of the space shuttle program.” The lifting body program was the essential bridge between the Apollo capsules and the winged Space Shuttle.
During the Space Shuttle’s design phase in the early 1970s, one of the most contentious debates was whether the Orbiter should carry air-breathing jet engines. Many engineers argued that it must have them. They believed an unpowered, “dead-stick” landing from orbit was too risky, and that pilots would need jet engines to “go around” for a second attempt if they botched the approach.
But adding jet engines would have made the Shuttle Orbiter significantly heavier, more complex, and more expensive. It would have meant less room and weight for the real reason the Shuttle existed: its payload.
The lifting body program provided the verdict. The 37 successful flights of the HL-10, and most important, the two precise runway landings of the X-24B, gave NASA management the hard data and the confidence they needed to make a final decision. The lifting body pilots had proven, conclusively, that a heavy, wingless (or nearly wingless) vehicle could be landed unpowered on a conventional runway.
The Space Shuttle was designed without jet engines for landing.
When the Shuttle flew, its return from orbit was a perfect echo of the lifting body missions. The Shuttle was, in effect, a hybrid lifting body with wings. It held a high angle of attack during reentry, just like the conceptual lifting bodies. It performed a steep, unpowered, “falling brick” glide. It executed the same high-speed flare maneuver to bleed off energy just before touchdown. The flight plan for the Shuttle’s landing had been written, tested, and proven by the pilots of the M2-F3, the HL-10, and the X-24B.
The program’s true contribution was something less tangible than data charts but just as important: pilot confidence. The program took the lifting body concept from an idea that was actively recommended against by high-level panels in 1961, to a vehicle that pilots “wanted their shot at flying” by 1968, to a vehicle that could be landed on a runway with “operational feasibility” by 1975. This shift, from “too risky to attempt” to “a repeatable, predictable procedure,” was the real breakthrough. It was this confidence, shared by the test pilots and the astronaut corps, that was the final, essential component that made the Space Shuttle possible.
The Legacy That Lives On
The end of the lifting body flight program in 1975 was not the end of the concept. The data gathered was too valuable to be left in an archive. The influence of those six vehicles is still shaping spaceflight today, and it has continued down two distinct, parallel tracks.
The first thread of legacy involves the X-24A. In the 1990s, NASA began designing a “lifeboat” for the International Space Station (ISS). This was known as the Crew Return Vehicle, or CRV. Its mission was to be a simple, reliable vehicle that could be permanently docked to the station, ready to return the crew to Earth in an emergency.
A capsule, like the Russian Soyuz, was a possibility, but it had a major drawback: its limited cross-range. If an astronaut had a severe medical emergency, a capsule might have to “loiter in space for up to 24 hours,” waiting for the Earth to rotate until its landing zone in Kazakhstan was in the right place. For a medical emergency, this was unacceptable.
NASA’s Johnson Space Center began the X-38 program to build a lifting body CRV. A lifting body, with its high cross-range, could de-orbit at any time and have enough gliding range to reach a landing site near a major hospital. When it came time to choose a shape, the engineers didn’t start from scratch. They “borrowed” the shape of the X-24A. The decades-old data from the “bulbous teardrop” was pulled off the shelf, saving the X-38 program millions in new aerodynamic research. The X-38 prototypes, uncrewed, were drop-tested from a B-52, just like their ancestor, and were designed to land automatically using a massive, steerable parafoil. The X-38 program was ultimately canceled in 2002 due to budget cuts, but it proved the enduring value of the X-24A’s design.
The second, and more prominent, thread of legacy comes from the HL-10. In the 1980s and 1990s, NASA’s Langley Research Center began studying a concept for a small, reusable “space taxi” to ferry crews to and from the space station, complementing the larger, more complex Space Shuttle. This concept was called the HL-20 Personnel Launch System. Its shape was a direct descendant of the HL-10 and M2-F3. A full-scale mockup was built for human-factors testing, allowing engineers to study how crews would get in and out and what their visibility would be.
The HL-20 was an archived NASA study, but the design was adopted by a private company, SpaceDev, which was later acquired by the Sierra Nevada Corporation (now Sierra Space). That company has spent the last two decades developing the HL-20 concept into a modern, commercial spaceplane: the Dream Chaser.
After a long development program, which included its own partnership with NASA and drop-tests at Armstrong Flight Research Center (the modern name for the FRC), the Dream Chaser is now a reality.
In a moment that brings the lifting body story full circle, NASA has selected the uncrewed cargo version of Dream Chaser as one of its commercial vehicles to resupply the International Space Station. It is designed to launch vertically on a rocket and land horizontally on a conventional runway – the exact mission profile envisioned by Alfred Eggers in 1957. The “flying bathtub” that was once towed by a Pontiac on a dry lakebed has, through a long and arduous journey of engineering, sacrifice, and innovation, finally earned its place as a cornerstone of 21st-century spaceflight.
Summary
The history of NASA’s lifting body research is a 60-year story of how a radical, skeptically-viewed idea became a fundamental part of human spaceflight. It began in 1957 as a theoretical breakthrough at NASA’s Ames Research Center: the realization that a blunt reentry capsule could be shaped to fly.
This theory was brought to life in the 1960s by a passionate, hands-on team at the Flight Research Center, who, with a plywood-and-steel prototype nicknamed the “flying bathtub,” proved the concept was flyable by towing it behind a Pontiac convertible.
This initial success spawned a 12-year, joint NASA-Air Force program that flew five “heavyweight” rocket planes. This program systematically, and at times dangerously, solved the problems of wingless flight. It survived a catastrophic crash, used the data to fix a fatal flaw, and tested four different competing shapes in parallel.
The data, and just as important, the pilot confidence, from these 199 flights were the key that allowed NASA to make one of the most important design decisions of the Space Shuttle: to have it land as an unpowered glider. The lifting body program wrote the flight plan for the Shuttle’s landing.
Today, that legacy lives on. The designs for the X-24A and HL-10, developed in the 1960s, became the direct ancestors of the 1990s X-38 “lifeboat” and the 21st-century Dream Chaser commercial spaceplane. The Dream Chaser is now poised to fly cargo from the International Space Station to a runway landing, completing the journey that the M2-F1 started on a dry lakebed more than half a century ago.
