The HL-20: NASA’s Unbuilt Lifting Body Spaceplane

HL-20 Personnel Launch System

In the archives of NASA‘s Langley Research Center sits a full-scale, 30-foot-long model of a spacecraft that looks like a futuristic shuttle, yet it has no wings. This is the HL-20, a vehicle that represents a fascinating and persistent branch of spacecraft design. Though it never flew, the HL-20 Personnel Launch System (PLS) was a serious proposal, born from a period of crisis, that promised a safer, more economical way to get astronauts to and from orbit.

This article explores the HL-20, tracing its origins from high-risk atmospheric tests, its surprising Cold War design inspiration, its detailed mission profile, and its ultimate cancellation. It’s a story of a concept that was not wrong, but was perhaps ahead of its time, as its design lives on today in a new generation of commercial spaceplanes.

The Problem: A Post-Challenger NASA

The story of the HL-20 begins with the darkest day in NASA‘s crewed spaceflight history: January 28, 1986. The Space Shuttle Challenger disaster wasn’t just a human tragedy; it was a systemic shock that exposed a deep flaw in the United States’ space program. The nation’s entire capacity for human spaceflight rested on a small fleet of highly complex, and as it turned out, vulnerable vehicles.

When the Space Shuttle fleet was grounded for nearly three years, the U.S. had no other way to send its own astronauts into space. This lack of “assured access” was a strategic liability.

Furthermore, the Space Shuttle program had not lived up to its original operational promises. It was intended to be a frequent, low-cost “space truck.” In reality, the orbiters required immense, time-consuming, and expensive refurbishment between flights. The thousands of delicate thermal tiles, the complex main engines, and the solid rocket boosters all demanded painstaking inspection and repair. The system was neither cheap nor rapid.

In the wake of Challenger, NASA and the United States Congress recognized the need for a different kind of vehicle. They didn’t necessarily need another heavy-lift cargo hauler; the Space Shuttle (and expendable rockets) could handle that. What they needed was a dedicated “personnel carrier” – a safe, reliable, and cost-effective “space taxi” that could ferry crews to and from the planned Space Station Freedom.

This new concept was formalized as the Personnel Launch System (PLS). The PLS would be a small vehicle, launched on top of an expendable launch vehicle (ELV). This “capsule-on-a-rocket” design was inherently safer. If the booster failed, the vehicle could be pulled away by a launch escape system, a capability the Space Shuttle tragically lacked.

The key question was: what form should this PLS take? One option was a traditional “blunt-body” capsule, like the Apollo command module, which would re-enter and land under parachutes. The other, more advanced option was a lifting body. This concept, championed by engineers at NASA Langley, offered the safety of an ELV launch combined with the precision and gentle runway landing of an airplane. The leading lifting bodydesign was the HL-20.

A Legacy of Lift: The American Lifting Body Precursors

The HL-20 didn’t emerge from a vacuum. It was the evolutionary product of decades of high-risk, boundary-pushing research conducted by NASA and the United States Air Force in the 1960s and 1970s. The core idea was to build a spacecraft that re-entered the atmosphere like an airplane, using its own body to generate lift rather than conventional wings.

The problem with wings is that they are delicate and must be heavily protected from the searing heat of re-entry. A lifting body, by contrast, is a more compact, robust shape. It’s essentially a “flying bathtub.”

The research began at NASA‘s Dryden Flight Research Center (now Armstrong) in the California desert. The first vehicle, the NASA M2-F1, was a lightweight, unpowered glider made of plywood. In 1963, it was famously towed down a dry lakebed by a souped-up Pontiac convertible, lifting off the ground and proving the ungainly shape could actually fly.

This success led to a fleet of “heavyweight” lifting bodies. These were rocket-powered test vehicles dropped from a B-52 bomber at high altitude. Pilots like Bruce Peterson, Bill Dana, and future Apollo astronaut John W. Young flew these craft, pushing them to supersonic speeds and high altitudes to simulate a return from space.

The program was incredibly dangerous. The vehicles were notoriously difficult to fly and had the glide ratio of a stone. The M2-F2, a metal successor to the M2-F1, was famously involved in a horrific crash in 1967. Test pilot Bruce Peterson survived, but the incident (captured on film) became the basis for the opening credits of the 1970s television show The Six Million Dollar Man.

Despite the risks, the research was invaluable. The Northrop HL-10 (the “HL” standing for Horizontal Lander, designed at Langley) proved to be a stable and successful design. Its designation is the direct ancestor of the HL-20. The Martin Marietta X-24A and its successor, the X-24B, explored different body shapes. The X-24B‘s “flying flatiron” shape was particularly successful, demonstrating remarkable precision. Its test pilots were able to consistently land on a specific point on the runway.

This research program demonstrated two fundamental truths:

1. A wingless vehicle could successfully fly and maneuver in the atmosphere.
2. Pilots could safely guide an unpowered, gliding vehicle to a precise runway landing.

This data was directly incorporated into the Space Shuttle program. The Shuttle’s unpowered “dead-stick” landings were a direct legacy of the lifting body tests. But the idea of a pure lifting body as a crew vehicle was shelved. The Space Shuttle was a “winged” vehicle, a compromise between a lifting body and a traditional aircraft. It wouldn’t be until the 1980s that NASA would dust off the pure lifting body concept for the PLS.

The Surprising Soviet Connection: BOR-4

When NASA Langley engineers began conceptual work on a lifting body for the PLS program, they didn’t just look at their own 1960s-era designs. In a fascinating twist of Cold War history, they found inspiration in an operational Soviet spaceplane.

Throughout the 1980s, the Soviet Union was aggressively developing its own reusable spaceplane, the Buran. As part of that effort, they flew a series of subscale test articles called BOR (a Russian acronym for “Unpiloted Orbital Rocket-plane”). The BOR-4 was a small, uncrewed lifting body launched on a rocket. It would orbit the Earth, re-enter the atmosphere, and be recovered.

In 1982, a BOR-4 vehicle designated Kosmos 1374 splashed down in the Indian Ocean. A Royal Australian Air Force P-3 Orion patrol plane photographed the vehicle extensively as a Soviet recovery fleet steamed towards it. The resulting images, clear and detailed, were shared with the United States.

NASA engineers were stunned. The Soviets were actively flying a lifting body design. Later, in 1983, another BOR-4 was recovered, this time from the Black Sea. In 1984, Kosmos 1517 splashed down in the Indian Ocean again. Western intelligence had a very clear picture of the vehicle’s shape.

Intrigued, NASA Langley researchers reverse-engineered the shape from the photographs and data. They created models and tested them in their wind tunnels. The results were impressive. The BOR-4 shape, a flattened cone with a rounded top, had excellent aerodynamic characteristics. It offered a good balance of hypersonic stability during re-entry and subsonic handling for landing. It was, in many ways, a superior shape to some of the earlier U.S. lifting bodies.

This Soviet design, refined and scaled up for a crew of ten, became the NASA HL-20. The name “HL” was chosen to honor the HL-10 from the 1960s, and the “20” designated it as the next in Langley‘s series of lifting body studies.

Anatomy of the HL-20

The HL-20 was designed from the ground up with two principles in mind: crew safety and “aircraft-like operations.” It was a direct response to the Space Shuttle‘s complexities and vulnerabilities.

Overall Design and Philosophy

The core philosophy was simplicity and robustness. Unlike the Space Shuttle, the HL-20 would not be a “jack of all trades.” It had one job: get people to and from orbit safely. It wouldn’t deploy satellites or have a complex robotic arm. This specialization allowed for a much smaller, simpler, and theoretically safer vehicle.

Crew Safety: The HL-20 would launch on a rocket like a Titan IV or the proposed Advanced Launch System. This design separated the crew from complex and failure-prone systems like the Shuttle’s external tank and solid rocket boosters. Most importantly, the HL-20 was designed to incorporate a launch escape system (LES). In an emergency on the pad or during ascent, powerful rocket motors would fire to pull the entire orbiter and its crew safely away from the failing booster, allowing it to glide to a landing.

Aircraft-Like Operations: This was the program’s mantra. The Space Shuttle required an “army” of technicians and months of work between flights. The HL-20 was designed for a quick turnaround. After landing on a runway, it would be towed to a hangar. Its systems were designed to be non-toxic and easily accessible. The goal was to refuel its maneuvering thrusters, perform automated checkouts, and have it ready for its next flight in days or weeks, not months. This would dramatically lower the cost-per-flight.

Physical Specifications and Layout

The HL-20 was compact. It was about 30 feet (9 meters) long, with a body width (wingspan) of about 23.5 feet (7.2 meters). It weighed approximately 22,000 pounds (10,000 kg) at landing, a fraction of the Space Shuttleorbiter’s 172,000 pounds.

Its aerodynamic shape did all the work. The bottom was flat, while the top was highly curved. This difference created a pressure differential as air flowed over it, generating lift. For control in the atmosphere, it had a large central vertical fin, two smaller outboard “winglets” that also acted as rudders, and two flaps on the “boat tail” that acted as elevons (a combination of elevators and ailerons) for pitch and roll.

Crew Accommodations and Interior

A key part of the HL-20 program was “human factors” research. How do you comfortably and safely fit 10 people inside a small, windowless, cone-shaped vehicle?

NASA Langley managed the construction of a full-scale engineering mock-up to figure this out. The interior was surprisingly spacious for its small outer dimensions. The 10 seats (two pilots upfront, eight passengers behind) were arranged on two levels, similar to a mini-theater, to make the most of the curved hull.

The environment was “shirt-sleeve.” Astronauts wouldn’t need to wear bulky pressure suits, making the ride to orbit more comfortable. The mock-up was used for extensive tests. Volunteers of all sizes would practice getting in and out of the seats. They ran emergency egress drills, timing how long it would take for all 10 crew members to exit the vehicle on the launch pad or after a landing. These tests provided important data on hatch design, seat placement, and interior lighting. The cockpit, unlike the Space Shuttle‘s “glass dash” of the 1970s, was designed with modern, multi-function digital displays, similar to a modern jetliner.

Thermal Protection System (TPS)

Like any vehicle re-entering from orbit, the HL-20 would face hellish temperatures. Its Thermal Protection System (TPS) was designed to be a major improvement over the Shuttle’s.

The Space Shuttle‘s black silica tiles (LI-900) were notoriously fragile. They were brittle, absorbed water, and a small impact from foam during launch could lead to a catastrophic failure, as was later proven by the Columbia disaster.

The HL-20 plan called for a more modern, robust TPS.

• Leading Edges: The nose cap and the edges of the fins, which faced the highest temperatures, would use reinforced carbon-carbon (RCC), similar to the Shuttle.
• High-Heat Areas: The vehicle’s belly would be protected by high-temperature, mechanically tougher tiles, such as Fibrous Refractory Composite Insulation (FRCI). These were stronger than the Shuttle’s tiles and more resistant to impact.
• Low-Heat Areas: The upper surfaces of the vehicle would be covered in Advanced Flexible Reusable Surface Insulation (AFRSI). These are quilted, blanket-like materials that are much easier to apply, inspect, and repair than individual tiles.

This “smart” TPS, combined with the vehicle’s smaller size, was key to achieving the “aircraft-like operations” goal. It would require far less inspection and maintenance than the Space Shuttle.

Flight Profile: Launch, Orbit, and Landing

The HL-20‘s mission profile was a hybrid, taking the best parts of capsules and spaceplanes.

Launch: The HL-20 orbiter, with its launch escape system armed, would be mounted atop an expendable rocket. After the rocket did its job, the HL-20 would detach and use its own small Orbital Maneuvering System(OMS) thrusters to navigate into its final orbit.

Orbit: It was designed to rendezvous and dock with Space Station Freedom. It could remain in orbit for a short free-flight (up to 72 hours) or stay docked to the station for extended periods, serving as a “lifeboat” or Crew Rescue Vehicle (CRV) in case the station needed to be evacuated.

Re-entry and Landing: This is where the lifting body design shined. After firing its OMS thrusters to de-orbit, the HL-20 would hit the atmosphere. Its shape would allow it to “fly,” generating lift and giving it significant maneuverability.

This capability is measured in “cross-range.” A ballistic capsule like Apollo or Soyuz has very little cross-range; it lands near the point its trajectory dictates. The HL-20 was designed with a cross-range of over 1,200 nautical miles. This means it could deviate from its direct orbital path to the left or right, allowing it to “steer” towards a designated landing site. This wide “landing corridor” meant it could reach a runway at the Kennedy Space Center or Edwards Air Force Base from many different orbits, offering tremendous flexibility.

The final approach would be unpowered, just like the Space Shuttle and the X-planes before it. The pilots would guide the glider onto a steep approach, deploy landing gear, and touch down on any standard 10,000-foot runway. The program also invested heavily in autoland technology, with the goal of having the HL-20 capable of landing itself in any weather, even if the pilots were incapacitated.

This gentle runway landing (around 1.5 Gs) was a major advantage over a “hard” parachute landing (which can be 4-8 Gs). It would be far less stressful on crews returning from long-duration stays in zero gravity, who are often weak and deconditioned.

Building the Dream: Mock-ups and Contractor Studies

The HL-20 program progressed far beyond paper sketches. In 1990, NASA commissioned the full-scale engineering mock-up for human-factors testing. In a unique partnership, NASA Langley worked with North Carolina State University and North Carolina A&T State University. Students and faculty from the universities helped design and build the 1:1 model, which was delivered to Langley for outfitting.

This mock-up was the centerpiece of the program, allowing astronauts, engineers, and test subjects to physically interact with the design. It helped validate the cockpit layout, the seating arrangement, and emergency escape procedures.

The program was gaining serious momentum. NASA awarded “Phase B” study contracts to two aerospace giants: Rockwell International (the prime contractor for the Space Shuttle) and Lockheed Martin (then Lockheed). Their job was to take NASA‘s design and flesh it out into a fully-realized, buildable spacecraft. They analyzed subsystems, manufacturing processes, and operational timelines.

By the early 1990s, the HL-20 was one of the most well-defined and mature spacecraft concepts NASA had. It was the leading contender for the PLS and was seen as the logical, safe, and modern complement to the aging Space Shuttle fleet.

The Political and Budgetary Shutdown

If the HL-20 was such a promising solution, why was it never built? The answer has little to do with engineering and everything to do with geopolitics and money.

Two major events conspired to kill the HL-20.

First, the Soviet Union collapsed in 1991. The Cold War was over. The primary political justification for Space Station Freedom – competing with and surpassing the Soviets‘ Mir space station – evaporated overnight. Congress began looking for a “peace dividend,” and NASA‘s large, expensive programs were a prime target for budget cuts.

Second, Space Station Freedom was itself in deep trouble. It was massively over budget, behind schedule, and facing cancellation year after year. In 1S993, the new Clinton administration ordered a complete redesign of the program.

The solution was a radical one: merge the Space Station Freedom program with Russia’s Mir-2 program. This new partnership would create the International Space Station (ISS). This move was politically brilliant. It saved the station, gave the U.S. access to Russia’s vast experience in long-duration spaceflight, and provided work for thousands of Russian rocket scientists, keeping them out of “rogue states.”

But this new partnership defined a new architecture. Russia would provide crew transport using its cheap and reliable Soyuz capsule. The U.S. Space Shuttle fleet would be used to launch the large, heavy station modules.

In this new framework, there was simply no role and no budget for a third crew vehicle like the HL-20. The Personnel Launch System program was quietly canceled. The HL-20, its most promising candidate, was shelved. The full-scale mock-up was eventually moved, ending up on loan to the North Carolina Museum of Life and Science. The dream of a NASA-built lifting body spaceplane was over.

The Lingering Legacy: From X-38 to Dream Chaser

The HL-20 research was not a waste. The data and design principles were too good to ignore, and the concept of a lifting body “lifeboat” persisted.

The Immediate Descendant: X-38

Even with the Soyuz as a transport, NASA was still worried about crew rescue on the ISS. A Soyuz could only stay docked for about six months, and what if an emergency happened when the crew was larger than the Soyuz could hold?

This led to the X-38 Crew Return Vehicle (CRV) program in the late 1990s. The X-38 was another lifting body, heavily based on the X-24A shape. It was a simplified, automated vehicle designed to be a “lifeboat” permanently docked to the ISS.

The X-38 successfully completed several atmospheric drop tests from a B-52, proving its automated flight systems. However, its landing system was different. Instead of a runway, it would deploy a massive, steerable parafoil for a soft landing on the ground. Like the HL-20 before it, the X-38 program was canceled in 2002 due to ISS budget overruns.

The Commercial Rebirth: Sierra Space’s Dream Chaser

The HL-20‘s story finds its true conclusion in the 21st century. After the Space Shuttle Columbia disaster in 2003, NASA decided to retire the Shuttle fleet and turn to the private sector to resupply the ISS.

This new commercial approach gave companies a chance to innovate. A small company named SpaceDev, which was later acquired by Sierra Nevada Corporation (SNC), proposed a small, reusable lifting body spaceplane. They didn’t start from scratch.

SNC signed a Space Act Agreement with NASA. This agreement gave them exclusive access to the entire HL-20 database: all the wind tunnel research, the aerodynamic models, the simulation data, and the human-factors studies from the full-scale mock-up.

SNC, and its later spin-off Sierra Space, used this NASA-funded data as the foundation for their new vehicle: the Dream Chaser.

The Dream Chaser is the HL-20 brought to life with 21st-century materials. It uses modern composites, a revolutionary new “ceramic matrix” TPS, and state-of-the-art avionics. But its shape, its aerodynamic soul, is the HL-20.

Sierra Space competed for NASA‘s Commercial Crew Program to fly astronauts. While NASA ultimately selected the capsule designs from SpaceX (Crew Dragon) and Boeing (Starliner), Sierra Space won a major contract for the Commercial Resupply Services 2 (CRS-2) program.

An uncrewed cargo version of the Dream Chaser is now contracted to fly multiple missions to the ISS, launching on a Vulcan Centaur rocket. Its unique advantage is the one the HL-20 championed decades ago: a gentle, low-G re-entry and a runway landing. The Dream Chaser is the only cargo vehicle that can bring sensitive science experiments and hardware back from the ISS and have them on a lab bench hours after landing at the Kennedy Space Center‘s Shuttle Landing Facility.

Summary

The NASA HL-20 is one of the great “what-ifs” of space history. It was a well-researched, mature, and practical design that promised a new era of safe and routine human spaceflight. Born from the ashes of the Challenger disaster, it combined decades of American X-plane research with a design captured from a Soviet rival.

The HL-20 was not canceled because of a technical flaw. It was a victim of its time, made redundant by the end of the Cold War and the global restructuring of the space station program. Its systems were sound, its purpose was clear, and its human-factors research was thorough.

But the story of the HL-20 is ultimately one of vindication. The data collected by the NASA Langley team was not lost. It was preserved, and three decades later, it became the foundation for a new commercial spaceplane. When the Sierra Space Dream Chaser glides to a landing on a runway, it will be the fulfillment of the vision set forth by the HL-20 team – a concept not defeated, just waiting for its moment.