Since the earliest days of the space age there has been something inherently attractive in the idea of a spacecraft that could glide back after its mission and land like an aeroplane. From Sanger’s Silbervogel onwards, a succession of spaceplanes sporting various shapes and configurations have flowed from the minds of aerospace designers.
Sierra Nevada Corporation recently announced that it is preparing its Dream Chaser spaceplane for a new round of flight tests. If Dream Chaser makes it into space, it will mark the culmination of a long evolution for a wingless ‘lifting body’ shape going back over 50 years and involving both Cold War superpowers…
While wings are fantastic for atmospheric flight producing the lift needed to keep a craft airborne, they can be something of a liability for a spacecraft. Unless the design proposes to use lifting flight on the way to space, they are generally only of use following re-entry into the sensible atmosphere. If the craft is launched on a booster then wings can be at best additional weight, at worst an aerodynamic handicap. Worse still, large wings can be problematic in terms of re-entry heating and require elaborate thermal protection to safeguard their survival. But what if there was a way of retaining the lift and controllability required to make pinpoint horizontal landings while removing some of the problems inherent with winged craft?
Early work on Lifting Re-entry
Our story begins with NASA’s predecessor, the National Advisory Committee for Aeronautics (NACA) and the work of engineers at the Ames Aeronautical Laboratory in California. Studies being carried out to determine the optimum shapes for survivable ballistic warheads by H. Julian Allen and Alfred Eggars suggested that blunt shapes would stand up to the intense energy generated by re-entry by producing a large shockwave ahead of the object, keeping the highest temperatures away from the re-entry body. Additional studies suggested that a 30-degree half cone shape with a blunt nose could not only survive re-entry at low-G loads, but with the addition of flight control surfaces would actually produce sufficient lift from the body shape alone to provide controllable, albeit high-drag, aerodynamic flight providing limited cross-range – deviations from the original ballistic path. These shapes became known as Lifting Bodies.
Following the launch of Sputnik in 1957, thoughts turned to the possibility of a manned satellite capable of orbiting the Earth and returning a passenger safely. As the NACA became NASA in 1958, research on this mission became consolidated under Project Mercury. Lifting bodies seemed a logical direction for more research given that their relatively benign re-entry characteristics and controllability both seemed to lend themselves to the safe return of an astronaut. Unfortunately, the pressing need to move the programme forward and the limited payload capabilities of the available boosters meant a simpler ballistic capsule approach was chosen for America’s first foray into orbit.
In spite of this early setback, NASA engineers at Ames and Langley Centres continued their research into wingless vehicles and these coalesced into a number of designs flight tested during the 1960’s. At NASA’s Flight Research Centre (part of Edwards AFB) Dale Reed decided to put theory into practice, first with a small hand launched model then with a full-scale craft based on the Ames M2-F1 shape. With the involvement of NASA test pilot Milt Thompson (a veteran of X-15 and X-20 programmes) a flight test programme began, initially with the lightweight wooden craft being towed across the dry lake behind a souped up Pontiac, then with air launched glide tests behind a NASA C-47 transport. Although somewhat marginal in stability with a tendency to ‘dutch-roll’, by the time of its retirement in 1966 the M2-F1 proved the point that a wingless craft was indeed controllable and more research into lifting bodies was warranted.
Flight testing expands
Interest in lifting bodies now grew steadily. The M2-F1 was superseded by a ‘heavyweight’ version of the shape, the rocket powered M2-F2. This was joined by a second design, this time featuring a flat base and curved upper section devised at Langley. This design was the HL-10, with the HL denoting Horizontal Landing. Both of these craft were constructed by Northrop and would be air-launched from the B-52 Motherships used for the X-15 programme at Edwards. Both craft experienced control problems resulting in re-designs to improve their flight characteristics. In the case of the M2-F2 these problems were a contributing factor to a harrowing crash which badly injured pilot Bruce Peterson in 1967. Eventually both lifting bodies were able to demonstrate approach and landing from high altitude supersonic flight – the final phase for such a craft returning from orbit.
Air Force involvement
Perhaps unsurprisingly the United States Air Force had held an interest in the idea of a military spaceplane since the early 1950’s. Initially their thoughts were more directed towards a winged craft and they followed this route from Bell Aircraft’s initial I proposals through into the Dyna-Soar project (See: Death of the Dyna-Soar). While pursuing this direction, they had also continued to monitor the NACA (and later NASA) research into lifting bodies.
In conjunction with the Martin Company they developed their own lifting body shape, the SV-5D and initiated a two stage programme named Spacecraft Technology and Advanced Reentry Tests (START) to test both it’s manoeuvrability during a hypersonic lifting re-entry and its low speed characteristics during approach and landing. The first part of this programme, Precision Recovery Including Manoeuvring Entry (PRIME) was achieved during 1966-67 using small sub-orbital models launched by Atlas missiles, reaching maximum speeds exceeding Mach 24 before recovery by parachute. These vehicles are now often referred to under the designation X-23A, although it appears this name was only applied retrospectively.
The second phase, Piloted Low-speed Tests (PILOT) involved an air-launched lifting body, the X-24A. This had a successful test career alongside the NASA lifting bodies at Edwards AFB, first flying in 1969. Later, the Air Force decided to use the X-24A airframe as the basis for a more advanced shape developed by their Flight Dynamics Lab. This craft had an extended triangular planform and flew successfully until 1975 when it became the final rocket powered research plane to fly over Edwards. A follow on X-24C programme was proposed, with design work done by the famous Lockheed Skunk Works, but this was cancelled due to lack of funding.
The United States was not alone in its interest regarding spaceplanes. Across the world in the Soviet Union, designers also wondered about the possibilities of lifting re-entry reaching similar conclusions as their counterparts at NACA and NASA. Ironically, the Soviets also recognised that simpler ballistic shapes offered the quickest route to a manned satellite and so were adopted for the early programmes, Vostok and Voshkhod. But, as in the U.S. research continued, mainly under the auspices of OKB-23 under the leadership of Myasishchev. Although prototype winged spaceplanes were designed, none reached production and eventually, as was often the case in the Soviet Programme, political intervention led to the project being diverted to the politically favoured bureau – Chelomei’s OKB-52.
Chelomei had been a long time advocate of spaceplanes or Raketoplan and partly thanks to his timely employment of Kruschev’s son Sergei, found his star on the rise in the early 1960’s. Unfortunately Chelomei’s ambitions often exceeded the technology available and his plans were viewed as slightly too exotic by a leadership wanting a steady succession of space achievements on the back of Korolev’s achievements at OKB-1. Although Chelomei had hoped to create a Soviet equivalent of the USAF’s Dyna-Soar, his bureau was working at capacity on other missile and ballistic spacecraft projects until he too fell from favour following Krushchev’s removal from power.
The demise of Chelomei’s Raketoplan did not signal the end of Soviet interest in spaceplanes though. Following its cancellation, the research materials and workforce from this and Myasishchev’s previous work were transferred to the famous OKB-155 Mikoyan-Guryevich (MiG) bureau. Here a new and even more ambitious project was born under the name Spiral. In spite of the cancellation of Dyna-Soar, the Soviets saw great potential in a similar system giving them a small spaceplane that could carry out reconnaissance, interception or satellite inspection missions at short notice, before returning to land like an aeroplane. But unlike Dyna-Soar, the Soviet designers felt the best way to achieve this flexibility was to develop an air-launched system consisting of a large hypersonic carrier aircraft and a small lifting body spaceplane with booster stage.
As with the American START programme, the Soviets decided to break development on Spiral into smaller parts and test each of the systems separately. The spaceplane design borrowed heavily on Myasishchev’s early designs, but also bore some resemblance to the NASA HL-10 design (much of the NASA work was publicly available, but it is difficult to discern how direct an influence this had on Soviet designers). It featured a flat-bottomed shape with an upturned nose, earning it the nickname ‘Lapot’ after a wooden Russian shoe. A series of sub-scale models were prepared under the name Bezpilotniye Orbitainiye Raketoplan (BOR) and three of these were launched during 1969 from the Plesetsk launch facilities in the North of Russia. A piloted prototype, the MIG 105.11, was also constructed to carry out approach and landing tests and was flown on a number of occasions.
Unfortunately for Spiral, external events worked against the programme with the ill-fated Soviet lunar effort diverting what funding was available. OKB-155’s Chief, Artyom Mikoyan died in 1970 and a subsequent review of the Spiral programme led to its cancellation.
In the early 1980’s Western Intelligence became aware of a number of tests carried out under the generic Kosmos designation which appeared to suggest spaceplane development. In March 1983 an Australian maritime patrol plane flying over the Indian Ocean spotted a Soviet vessel involved in a recovery operation. Moving in for a closer look, they saw was a small lifting body spaceplane being recovered from the water. This was the BOR-4 vehicle and gave western analysts their first good look at the wingless shape originally intended for Spiral. The question was, why were the Soviets flying these tests now? There had long been speculation in the West that the Soviet Union was developing a spaceplane to rival the Shuttle, but at the time another possibility troubled analysts…
As development of the American Shuttle moved ahead in the 1970’s, the Soviets were well aware of the influence the US Military was exerting on the design (See: Blue Shuttle: How the Air Force influenced the STS design process). Soviet analysts were concerned by the US Air Force’s proposed Shuttle launches from Vandenberg AFB, which would put it into polar orbit and therefore allow overflights of the USSR. The Air Force had expressed a wish to fly single-orbit missions from Vandenberg and the Soviets were concerned that the Shuttle was a potential first-strike weapon. Even if this wasn’t the case, the potential for the Shuttle to snatch Soviet satellites was enough to alarm the Kremlin.
Rumours began to circulate in the West that the Soviets were working on a small space interceptor that would be launched vertically on a booster and could intercept the Shuttle using missiles to disable or destroy the American vehicle. The name attached to this alleged spaceplane was Uragan (Hurricane) and its design was supposedly based on the lifting body configuration of the cancelled Spiral spaceplane – the same shape used by the BOR-4.
Following the unveiling of the Soviet Buran Shuttle and the fall of the USSR in the late 1980’s it was recognised that the BOR-4 tests were related to this programme. Little firm information has surfaced regarding Uragan and it remains entirely possible that it was either an example of Soviet Maskirovka or simply Western intelligence seeing patterns in the shadows that simply didn’t exist.
BOR-4 Switches sides
While intelligence officials worried about the possible existence of Uragan, engineers at NASA Langley examined the classified images of the BOR-4 recovery. Intrigued by the spaceplane’s shape they created models of the vehicle and subjected them to wind-tunnel testing. What they discovered was that the Soviet design was highly advanced, offering superior control and re-entry characteristics. The upturned nose that gave the design its ‘Lapot’ nickname created a strong shockwave that reduced heating on the vehicle’s after body. Quick to recognise the potential in the Soviet work, the Langley engineers set about using what they had discovered and applying it to a new set of lifting body designs resulting in the HL-20.
HL-20 and the Personnel Launch System
As a decision was made in 1984 to push ahead with the construction of Space Station Freedom (The U.S. precursor to what eventually became the ISS) NASA turned its attention to a craft capable of carrying crews to and from this orbital outpost. While the Shuttle was capable of carrying out this mission, it couldn’t be left attached to the station indefinitely and given its size, costs and cargo capacity using it for this role represented a poor use of resources. NASA started to look for a smaller craft that could offer a cheaper option and also an alternative to the Shuttle should that system suffer more failures.
This initiative became known as the Personnel Launch System (PLS) and NASA Langley submitted a small spaceplane, the HL-20, as their preferred solution. Measuring 19 feet in length and capable of carrying a crew of 10, the HL-20 bore a striking resemblance to the BOR-4 shape while also representing an evolution of Langley’s previous lifting body research. While NASA’s Johnson Space Centre proposed a blunt capsule for PLS, the HL-20’s supporters felt it offered a number of advantages including the ability to make low-g re-entries and pinpoint landings – important if injured or incapacitated crew members were being evacuated from orbit. The concept also grew to encompass other missions beyond the space station support role, although the design offered no cargo bay as per the Shuttle Orbiter. As such the HL-20 was designed to complement rather than replace the Shuttle.
The HL-20 was to be launched atop a Titan III booster, already man-rated from the Dyna-Soar programme, although as the Air Force moved from this booster to the Titan IV, so did the HL-20. The Bush Administration proposed a new booster, the National Launch System (NLS) in 1991 to serve the needs of NASA and the Military and the HL-20 could also have used this.
One of the HL-20’s key advantages over the Shuttle as a crew transport was that it offered a launch escape capability, with the craft being propelled away from it’s booster and descending under parachute in the event of launch failures. This extra safety was offset somewhat by the fact that the Titan boosters used highly toxic hypergolic fuels making them less than ideal as launchers for crewed missions.
A study of the HL-20 concept was carried out by Rockwell International in 1989, followed by further operational assessments by the Lockheed Skunk Works in 1991. At this point a full-size mockup of the vehicle was constructed by NASA, North Carolina State University and North Carolina A&T University. This mockup was used extensively in human-factors trials, but this was as close as the HL-20 or it’s proposed follow on the HL-42 would get to production.
As Space Station Freedom morphed into the co-operative ISS project during the 1990’s, the availability of more affordable Russian Soyuz capsules for the crew ferry and lifeboat roles undercut the need for a second American spaceplane. For a while a simpler lifting body design, the X-38 (based on the Air Force’s old SV-5 shape) was considered for the lifeboat role, but this too faced cancellation. While the Shuttle continued to operate, it would be difficult to justify the developmental costs of the PLS and for future needs NASA began looking to fully reusable craft such as the Lockheed Martin VentureStar (See: The X-33:Nothing ventured, nothing gained). But this wasn’t the end for this lifting body design.
In 2006 a commercial spaceflight firm SpaceDev examined the HL-20 with an eye to resurrecting the concept. After signing a licensing deal for the design with NASA they began developing it under the name Dream Chaser. By 2006 NASA had moved towards a model of employing commercial service providers to ship cargo and ultimately crew to the ISS. The Commercial Orbital Transportation Services (COTS) initiative was announced in 2006 and SpaceDev put together a proposal to use Dream Chaser in this station cargo resupply role, but were ultimately unsuccessful. Undeterred, SpaceDev formed a partnership with booster manufacturer United Launch Alliance (ULA) to allow Dream Chaser to be launched atop their Atlas V rocket.
With an effective booster/vehicle combination in place and a merger between SpaceDev and Sierra Nevada Corporation (SNC) in 2008, Dream Chaser was now able to compete for a contract under NASA’s Commercial Crew Development (CCDev) initiative. Following selection for Phase 1 funding SNC were able to conduct structural testing of Dream Chaser before moving into Phase 2 which included captive flight testing of the vehicle.
SNC received further funding in 2012 under the Commercial Crew Integrated Capability (CCiCap) Programme and work continued to move forward including the test article’s first free flight which ended in a landing mishap with one of the main gears failing to fully deploy. In September 2014 the successful candidates for the next round of the Commercial Crew Development Programme were announced by NASA, but unfortunately Dream Chaser was not selected.
Work on the vehicle continues with interest from a number of directions including the European Space Agency (ESA) and the Japanese Space Agency JAXA. At the time of writing, SNC continue to prepare Dream Chaser for a second phase of flight testing. Hopefully we may still see this most persistent of designs finally fly.
- The X Planes: X-1 to X-45 – Jay Miller
- Secret Projects: Military Space Technology – Bill Rose
- Wingless Flight: The lifting Body Story – R. Dale Reed
- Developing and Flight Testing the HL10 Lifting Body – Robert W. Kempel, Weneth D. Painter, Milton O. Thompson
- The Soviet BOR-4 Spaceplanes and their Legacy – Bart Hendrickx
- Personnel Launch System (PLS) Study: Final report – Carl F. Erlich