A spaceplane is a vehicle that can fly and glide like an aircraft in Earth's atmosphere and maneuver like a spacecraft in outer space.[1] To do so, spaceplanes must incorporate features of both aircraft and spacecraft. Orbital spaceplanes tend to be more similar to conventional spacecraft, while sub-orbital spaceplanes tend to be more similar to fixed-wing aircraft. All spaceplanes to date have been rocket-powered for takeoff and climb, but have then landed as unpowered gliders.
Four types of spaceplanes have successfully launched to orbit, reentered Earth's atmosphere, and landed: the U.S. Space Shuttle, Russian Buran, U.S. X-37,[2] and the Chinese CSSHQ. Another, Dream Chaser, is under development in the U.S. As of 2019 all past, current, and planned orbital vehicles launch vertically on a separate rocket. Orbital spaceflight takes place at high velocities, with orbital kinetic energies typically greater than suborbital trajectories. This kinetic energy is shed as heat during reentry. Many more spaceplanes have been proposed, but none have reached flight status.
Spaceplanes must operate in space, like traditional spacecraft, but also must be capable of atmospheric flight, like an aircraft. These requirements drive up the complexity, risk, dry mass, and cost of spaceplane designs. The following sections will draw heavily on the US Space Shuttle as the biggest, deadliest, most complex, most expensive, most flown, and only crewed orbital spaceplane, but other designs have been successfully flown.
Launch to space
The flight trajectory required to reach orbit results in significant aerodynamic loads, vibrations, and accelerations, all of which have to be withstood by the vehicle structure.[citation needed]
If the launch vehicle suffers a catastrophic malfunction, a conventional capsule spacecraft is propelled to safety by a launch escape system. The Space Shuttle was far too big and heavy for this approach to be viable, resulting in a number of abort modes that may or may not have been survivable. In any case, the Challenger disaster demonstrated that the Space Shuttle lacked survivability on ascent.
Space environment
Once on-orbit, a spaceplane must be supplied with power by solar panels and batteries or fuel cells, maneuvered in space, kept in thermal equilibrium, oriented, and communicated with. On-orbit thermal and radiological environments impose additional stresses. This is in addition to accomplishing the task the spaceplane was launched to complete, such as satellite deployment or science experiments.
Buran spaceplane rear showing rocket engine nozzles, attitude control thrusters, aerodynamic surfaces, and heat shielding
Orbital spacecraft reentering the Earth's atmosphere must shed significant velocity, resulting in extreme heating. For example, the Space Shuttle thermal protection system (TPS) protects the orbiter's interior structure from surface temperatures that reach as high as 1,650 °C (3,000 °F), well above the melting point of steel.[3]Suborbital spaceplanes fly lower energy trajectories that do not put as much stress on the spacecraft thermal protection system.
An air-breathing orbital spaceplane would have to fly what is known as a 'depressed trajectory,' which places the vehicle in the high-altitude hypersonic flight regime of the atmosphere for an extended period of time. This environment induces high dynamic pressure, high temperature, and high heat flow loads particularly upon the leading edge surfaces of the spaceplane, requiring exterior surfaces to be constructed from advanced materials and/or use active cooling.[citation needed]
The first (STS-1) of four orbital test flights occurred in 1981, leading to operational flights (STS-5) beginning in 1982. Five complete Space Shuttle orbiter vehicles were built and flown on a total of 135 missions from 1981 to 2011. They launched from the Kennedy Space Center (KSC) in Florida. Operational missions launched numerous satellites, interplanetary probes, and the Hubble Space Telescope (HST), conducted science experiments in orbit, participated in the Shuttle-Mir program with Russia, and participated in the construction and servicing of the International Space Station (ISS). The Space Shuttle fleet's total mission time was 1,323 days.[5]
The first orbiter, Enterprise, was built in 1976 and used in Approach and Landing Tests (ALT), but had no orbital capability. Four fully operational orbiters were initially built: Columbia, Challenger, Discovery, and Atlantis. Of these, two were lost in mission accidents: Challenger in 1986 and Columbia in 2003, with a total of 14 astronauts killed. A fifth operational (and sixth in total) orbiter, Endeavour, was built in 1991 to replace Challenger. The three surviving operational vehicles were retired from service following Atlantis's final flight on July 21, 2011. The U.S. relied on the Russian Soyuz spacecraft to transport astronauts to the ISS from the last Shuttle flight until the launch of the Crew Dragon Demo-2 mission in May 2020.[6]
The Buran programme (Russian: Буран, IPA:[bʊˈran], "Snowstorm", "Blizzard"), also known as the "VKK Space Orbiter programme" (Russian: ВКК «Воздушно-Космический Корабль», lit. 'Air and Space Ship'),[7] was a Soviet and later Russian reusable spacecraft project that began in 1974 at the Central Aerohydrodynamic Institute in Moscow and was formally suspended in 1993.[8] In addition to being the designation for the whole Soviet/Russian reusable spacecraft project, Buran was also the name given to orbiter 1K, which completed one uncrewed spaceflight in 1988 and was the only Soviet reusable spacecraft to be launched into space. The Buran-class orbiters used the expendable Energia rocket as a launch vehicle.
The Buran programme was started by the Soviet Union as a response to the United States Space Shuttle program[9] and benefited from extensive espionage undertaken by the KGB of the unclassified US Space Shuttle program,[10] resulting in many superficial and functional similarities between American and Soviet Shuttle designs.[11] Although the Buran class was similar in appearance to NASA's Space Shuttle orbiter, and could similarly operate as a re-entry spaceplane, its final internal and functional design was different. For example, the main engines during launch were on the Energia rocket and were not taken into orbit by the spacecraft. Smaller rocket engines on the craft's body provided propulsion in orbit and de-orbital burns, similar to the Space Shuttle's OMS pods. Unlike the Space Shuttle, Buran had a capability of flying uncrewed missions, as well as performing fully automated landings. The project was the largest and the most expensive in the history of Soviet space exploration.[8]
X-37
The sixth X-37B mission with a Service module placed inside its payload fairing
An X-37 first flew during a drop test in 2006; its first orbital mission was launched in April 2010 on an Atlas V rocket, and returned to Earth in December 2010. Subsequent flights gradually extended the mission duration, reaching 780 days in orbit for the fifth mission, the first to launch on a Falcon 9 rocket. The sixth mission launched on an Atlas V on 17 May 2020 and concluded on 12 November 2022, reaching a total of 908 days in orbit.[14] The seventh mission launched on 28 December 2023 on a Falcon Heavy rocket, entering a highly ellipticalhigh Earth orbit.[15][16]
Chongfu Shiyong Shiyan Hangtian Qi
The Chinese reusable experimental spacecraft (Chinese: 可重复使用试验航天器; pinyin: Kě chóngfù shǐyòng shìyàn hángtiān qì; lit. 'Reusable Experimental Spacecraft'; CSSHQ) is the first reusable spacecraft produced by China. It embarked upon its initial orbital mission on 4 September 2020.[17][18][19][20] According to media reports, the CSSHQ is launched into Earth orbit in a vertical configuration while enclosed within the payload fairings of a rocket like a traditional satellite or space capsule, but it returns to Earth via a runway landing like a conventional aircraft; the landing is conducted autonomously (unlike the Space Shuttle). In the absence of any official descriptions of the spacecraft or photographic depictions thereof, some observers have speculated that the CSSHQ may resemble the X-37B spaceplane of the United States in both form and function.[21][22]
Two piloted suborbital rocket-powered aircraft have reached space: the North American X-15 and SpaceShipOne; a third, SpaceShipTwo, has crossed the US-defined boundary of space but has not reached the higher internationally recognised boundary. None of these crafts were capable of entering orbit, and all were first lifted to high altitude by a carrier aircraft.
On 7 December 2009, Scaled Composites and Virgin Galactic unveiled SpaceShipTwo, along with its atmospheric mothership "Eve". On 13 December 2018, SpaceShipTwoVSS Unity successfully crossed the US-defined boundary of space (although it has not reached space using the internationally recognised definition of this boundary, which lies at a higher altitude than the US boundary). SpaceShipThree is the new spacecraft of Virgin Galactic, launched on 30 March 2021. It is also known as VSS Imagine.[23] On 11 July 2021 VSS Unity completed its first fully crewed mission including Sir Richard Branson.
The Mikoyan-Gurevich MiG-105 was an atmospheric prototype of an intended orbital spaceplane, with the suborbital BOR-4 subscale heat shield test vehicle successfully reentering the atmosphere before program cancellation.
HYFLEX was a miniaturized suborbital demonstrator launched in 1996, flying to 110 km altitude, achieving hypersonic flight, and successfully reentering the atmosphere.[24][25]
History of unflown concepts
United States Gemini tested the use of a Rogallo wing rather than a parachute. August 1964.
Various types of spaceplanes have been suggested since the early twentieth century. Notable early designs include a spaceplane equipped with wings made of combustible alloys that it would burn during its ascent, and the Silbervogelbomber concept. World War II Germany and the postwar US considered winged versions of the V-2 rocket, and in the 1950s and '60s winged rocket designs inspired science fiction artists, filmmakers, and the general public.[26][27]
In 1961, NASA originally planned to have the Gemini spacecraft land on a runway[30] with a Rogallo wingairfoil, rather than an ocean landing under parachutes.[citation needed] The test vehicle became known as the Paraglider Research Vehicle. Development work on both parachutes and the paraglider began in 1963.[31] By December 1963, the parachute was ready to undergo full-scale deployment testing, while the paraglider had run into technical difficulties.[31] Though attempts to revive the paraglider concept persisted within NASA and North American Aviation, in 1964 development was definitively discontinued due to the expense of overcoming the technical hurdles.[32]
The Rockwell X-30 National Aero-Space Plane (NASP), begun in the 1980s, was an attempt to build a scramjet vehicle capable of operating like an aircraft and achieving orbit like the shuttle. Introduced to the public in 1986, the concept was intended to reach Mach 25, enabling flights between Dulles Airport to Tokyo in two hours, while also being capable of low Earth orbit.[33] Six critical technologies were identified, three relating to the propulsion system, which would consist of a hydrogen-fueled scramjet.[33]
The NASP program became the Hypersonic Systems Technology Program (HySTP) in late 1994. HySTP was designed to transfer the accomplishments made in hypersonic flight into a technology development program. On 27 January 1995 the Air Force terminated participation in (HySTP).[33]
The Lockheed Martin X-33 was a 1/3 scale prototype made as part of an attempt by NASA to build a SSTO hydrogen-fuelled spaceplane VentureStar that failed when the hydrogen tank design could not be constructed as intended.[citation needed]
In 2011, Boeing proposed the X-37C, a 165 to 180 percent scale X-37B built to carry up to six passengers to low Earth orbit. The spaceplane was also intended to carry cargo, with both upmass and downmass capacity.[37]
The Soviet reusable spacecraft programme has its roots in the late 1950s, at the very beginning of the space age. The idea of Soviet reusable space flight is very old, though it was neither continuous nor consistently organized. Before Buran, no project of the programme reached operational status.
The first step toward a reusable Soviet spacecraft was the 1954 Burya, a high-altitude prototype jet aircraft/cruise missile. Several test flights were made before it was cancelled by order of the Central Committee. The Burya had the goal of delivering a nuclear payload, presumably to the United States, and then returning to base. The Burya programme was cancelled by the USSR in favor of a decision to develop ICBMs instead. The next iteration of a reusable spacecraft was the Zvezda design, which also reached a prototype stage. Decades later, another project with the same name would be used as a service module for the International Space Station. After Zvezda, there was a hiatus in reusable projects until Buran.
The Buran orbital vehicle programme was developed in response to the U.S. Space Shuttle program, which raised considerable concerns among the Soviet military and especially Defense Minister Dmitry Ustinov. An authoritative chronicler of the Soviet and later Russian space programme, the academic Boris Chertok, recounts how the programme came into being.[38] According to Chertok, after the U.S. developed its Space Shuttle program, the Soviet military became suspicious that it could be used for military purposes, due to its enormous payload, several times that of previous U.S. launch vehicles. Officially, the Buran orbital vehicle was designed for the delivery to orbit and return to Earth of spacecraft, cosmonauts, and supplies. Both Chertok and Gleb Lozino-Lozinskiy (General Designer and General Director of NPO Molniya) suggest that from the beginning, the programme was military in nature; however, the exact military capabilities, or intended capabilities, of the Buran programme remain classified.
Like its American counterpart, the Buran orbital vehicle, when in transit from its landing sites back to the launch complex, was transported on the back of a large jet aeroplane – the Antonov An-225 Mriya transport aircraft, which was designed in part for this task and was the largest aircraft in the world to fly multiple times.[39] Before the Mriya was ready (after the Buran had flown), the Myasishchev VM-TAtlant, a variant on the Soviet Myasishchev M-4Molot (Hammer) bomber (NATO code: Bison), fulfilled the same role.
MiG-105 crewed aerodynamics test vehicle
The Soviet Union first considered a preliminary design of rocket-launch small spaceplane Lapotok in early 1960s. The Spiral airspace system with small orbital spaceplane and rocket as second stage was developed in the 1960s–1980s.[citation needed]Mikoyan-Gurevich MiG-105 was a crewed test vehicle to explore low-speed handling and landing.[40]
In the early 2000s the orbital 'cosmoplane' (Russian: космоплан) was proposed by Russia's Institute of Applied Mechanics as a passenger transport. According to researchers, it could take about 20 minutes to fly from Moscow to Paris, using hydrogen and oxygen-fueled engines.[41][42]
United Kingdom
An artist's depiction of HOTOL
The Multi-Unit Space Transport And Recovery Device (MUSTARD) was a concept explored by the British Aircraft Corporation (BAC) around 1968 for launching payloads weighing as much as 2,300 kg (5,000 lb) into orbit. It was never constructed.[43]
In the 1980s, British Aerospace began development of HOTOL, an SSTO spaceplane powered by a revolutionary SABRE air-breathing rocket engine, but the project was canceled due to technical and financial uncertainties.[44] The inventor of SABRE set up Reaction Engines to develop SABRE and proposed a twin-engined SSTO spaceplane called Skylon.[45] One NASA analysis showed possible issues with the hot rocket exhaust plumes causing heating of the tail structure at high Mach numbers.[46] although the CEO of Skylon Enterprises Ltd has claimed that reviews by NASA were "quite positive".[47]
Bristol Spaceplanes has undertaken design and prototyping of three potential spaceplanes since its founding by David Ashford in 1991. The European Space Agency has endorsed these designs on several occasions.[48]
European Space Agency (1985–)
France worked on the Hermes crewed spaceplane launched by Ariane rocket in the late 20th century, and proposed in January 1985 to go through with Hermes development under the auspices of the ESA.[49]
In the 1980s, West Germany funded design work on the MBB Sänger II with the Hypersonic Technology Program. Development continued on MBB/Deutsche Aerospace Sänger II/HORUS until the late 1980s when it was canceled. Germany went on to participate in the Ariane rocket, Columbus space station and Hermes spaceplane of ESA, Spacelab of ESA-NASA and Deutschland missions (non-U.S. funded Space Shuttle flights with Spacelab). The Sänger II had predicted cost savings of up to 30 percent over expendable rockets.[50][51]
Hopper was one of several proposals for a European reusable launch vehicle (RLV) planned to cheaply ferry satellites into orbit by 2015.[52] One of those was 'Phoenix', a German project which is a one-seventh scale model of the Hopper concept vehicle.[53] The suborbital Hopper was a Future European Space Transportation Investigations Programme system study design[54] A test project, the Intermediate eXperimental Vehicle (IXV), has demonstrated lifting reentry technologies and will be extended under the PRIDE programme.[55]
Japan
HOPE was a Japanese experimental spaceplane project designed by a partnership between NASDA and NAL (both now part of JAXA), started in the 1980s. It was positioned for most of its lifetime as one of the main Japanese contributions to the International Space Station, the other being the Japanese Experiment Module. The project was eventually cancelled in 2003, by which point test flights of a sub-scale testbed had flown successfully.[citation needed]
Shenlong (Chinese: 神龙; pinyin: shén lóng; lit. 'divine dragon') is a proposed Chinese robotic spaceplane that is similar to the Boeing X-37.[59] Only a few images have been released since late 2007.[60][61][62]
European Union
A test project, the Intermediate eXperimental Vehicle (IXV), has demonstrated lifting reentry technologies and will be extended under the PRIDE programme.[55]
The FAST20XX Future High-Altitude High Speed Transport 20XX aims to establish sound technological foundations for the introduction of advanced concepts in suborbital high-speed transportation with air-launch-to-orbit ALPHA vehicle.[63]
The Space Rider (Space Reusable Integrated Demonstrator for Europe Return) is a planned uncrewedorbitallifting body spaceplane aiming to provide the European Space Agency (ESA) with affordable and routine access to space.[64][65][66] Contracts for construction of the vehicle and ground infrastructure were signed in December 2020.[67] Its maiden flight is currently scheduled for the third quarter of 2025.[68]
Development of Space Rider is being led by the Italian Programme for Reusable In-orbit Demonstrator in Europe (PRIDE programme) in collaboration with ESA, and is the continuation of the Intermediate eXperimental Vehicle (IXV) experience,[69][70] launched on 11 February 2015. The cost of this phase, not including the launcher, is at least US$36.7 million.[71] At the ESA Ministerial Council held in Seville in November 2019, the development of the Space Rider was subscribed by the participating member states with an allocation of €195.73 million.[72]
As of 2018, Japan is developing the Winged Reusable Sounding rocket (WIRES), which if successful, may be used as a recoverable first-stage or as a crewed sub-orbital spaceplane.[76]
US
Dream Chaser flight test vehicle in 2013
Dream Chaser is an American reusablelifting-body spaceplane developed by Sierra Space. Originally intended as a crewed vehicle, the Dream Chaser Space System is set to be produced after the Dream Chaser Cargo System cargo variant is operational. The crewed variant is planned to carry up to seven people and cargo to and from low Earth orbit.[77]
The Dawn Mk-II Aurora is a suborbital spaceplane being developed by Dawn Aerospace to demonstrate multiple suborbital flights per day. Dawn is based in the Netherlands and New Zealand, and is working closely with the American CAA. On December 9, 2020, the Civil Aviation Authority of New Zealand, working alongside the New Zealand Space Agency, issued a license allowing the vehicle to fly from a conventional airport.[80] On August 25, 2021, the first test-flight campaign of five successful flights using surrogate jet engines was announced.[81] As of August 15, 2022, 35 test flights have been complete, validating the vehicles aerodynamics, avionics, rapid deployment and various piloting modes.[82] A qualified 2.5 kN.s pump-fed HTP/kerosene engine is being installed for high-performance high-altitude flights. Dawn Aerospace previously demonstrated multiple low-altitude rocket-powered flights per day on their Mk-I vehicle.[83]
^"China launches reusable experimental spacecraft". Xinhuanet. Jiuquan. 4 September 2020. Retrieved 19 September 2020. After a period of in-orbit operation, the spacecraft will return to the scheduled landing site in China. It will test reusable technologies during its flight, providing technological support for the peaceful use of space.
^"我国成功发射可重复使用试验航天器" [Our country successfully launched a reusable experimental spacecraft]. Xinhuanet. 4 September 2020. Archived from the original on 4 September 2020. Retrieved 4 September 2020.
^"HOTOL History". Reaction Engines Limited. 2010. Archived from the original on 8 August 2010. Retrieved 29 September 2010.
^"Skylon FAQ". Reaction Engines Limited. 2010. Archived from the original on 28 August 2010. Retrieved 29 September 2010.
^Unmeel Mehta, Michael Aftosmis, Jeffrey Bowles, and Shishir Pandya; Skylon Aerodynamics and SABRE Plumes, NASA, 20th AIAA International Space Planes and Hypersonic Systems and Technologies Conference 6–9 July 2015, 2015,
^Aeroshape Trade-Off and Aerodynamic Analysis of the Space RIDER Vehicle M. Marini, M. Di Clemente, G. Guidotti, G. Rufolo, O. Lambert, N. Joiner, D. Charbonnier, M.V. Pricop, M.G. Cojocaru, D. Pepelea, C. Stoica, and A. Denaro, 7th European Conference for Aeronautics and Space Sciences (EUCASS) 2017
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