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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. 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 but then landed as unpowered gliders.
Three types of spaceplanes have successfully launched to orbit, reentered Earth's atmosphere, and landed: the Space Shuttle, Buran, and the X-37. Another, Dream Chaser, is under development. 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 at least 50 times greater than suborbital trajectories. Consequently, heavy heat shielding is required during reentry as this kinetic energy is shed in the form of heat. Many more spaceplanes have been proposed, but none have reached flight status.
At least two suborbital rocket-powered aircraft have been launched horizontally into sub-orbital spaceflight from an airborne carrier aircraft before rocketing beyond the Kármán line: the X-15 and SpaceShipOne. [a]
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.
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.
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.
The Space Shuttle used dedicated engines to accomplish orbital maneuvers. These engines used toxic hypergolic propellants that required special handling precautions. Various gases, including helium for pressurization and nitrogen for life support, were stored under high pressure in composite overwrapped pressure vessels.
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. Suborbital spaceplanes fly lower energy trajectories that do not put as much stress on the spacecraft thermal protection system.
The Space Shuttle Columbia disaster was the direct result of a TPS failure.
Aerodynamic flight and horizontal landing
Air-breathing orbital spaceplane concept
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.
The Space Shuttle is a retired, partially reusable low Earth orbital spacecraft system operated from 1981 to 2011 by the U.S. National Aeronautics and Space Administration (NASA) as part of the Space Shuttle program. Its official program name was Space Transportation System (STS), taken from a 1969 plan for a system of reusable spacecraft where it was the only item funded for development. 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, 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 construction and servicing of the International Space Station (ISS). The Space Shuttle fleet's total mission time was 1,323 days.
Space Shuttle components include the Orbiter Vehicle (OV) with three clustered Rocketdyne RS-25 main engines, a pair of recoverable solid rocket boosters (SRBs), and the expendable external tank (ET) containing liquid hydrogen and liquid oxygen. The Space Shuttle was launched vertically, like a conventional rocket, with the two SRBs operating in parallel with the orbiter's three main engines, which were fueled from the ET. The SRBs were jettisoned before the vehicle reached orbit, while the main engines continued to operate, and the ET was jettisoned after main engine cutoff and just before orbit insertion, which used the orbiter's two Orbital Maneuvering System (OMS) engines. At the conclusion of the mission, the orbiter fired its OMS to deorbit and reenter the atmosphere. The orbiter was protected during reentry by its thermal protection system tiles, and it glided as a spaceplane to a runway landing, usually to the Shuttle Landing Facility at KSC, Florida, or to Rogers Dry Lake in Edwards Air Force Base, California. If the landing occurred at Edwards, the orbiter was flown back to the KSC atop the Shuttle Carrier Aircraft (SCA), a specially modified Boeing 747.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.
The Buran program (Russian: Буран, IPA: [bʊˈran], "Snowstorm", "Blizzard"), also known as the "VKK Space Orbiter programme" (Russian: ВКК «Воздушно-Космический Корабль», lit. 'Air and Space Ship'), 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. In addition to being the designation for the whole Soviet/Russian reusable spacecraft project, Buran was also the name given to Orbiter K1, 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. They are generally treated as a Soviet equivalent of the United States' Space Shuttle, but in the Buran project, only the aeroplane-shaped orbiter itself was theoretically reusable (unlike the Shuttle system's ability to reuse solid rocket boosters).The Buran programme was started by the Soviet Union as a response to the United States Space Shuttle programme. The project was the largest and the most expensive in the history of Soviet space exploration. Development work included sending BOR-5 test vehicles on multiple sub-orbital test flights, and atmospheric flights of the OK-GLI aerodynamic prototype. Buran completed one uncrewed orbital spaceflight in 1988, after which it was recovered successfully. Although the Buran class was similar in appearance to NASA's Space Shuttle orbiter, and could similarly operate as a re-entry spaceplane, its internal and functional design was distinct. 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.
The Boeing X-37, also known as the Orbital Test Vehicle (OTV), is a reusable robotic spacecraft. It is boosted into space by a launch vehicle, then re-enters Earth's atmosphere and lands as a spaceplane. The X-37 is operated by the United States Space Force, and was previously operated by Air Force Space Command until 2019 for orbital spaceflight missions intended to demonstrate reusable space technologies. It is a 120-percent-scaled derivative of the earlier Boeing X-40. The X-37 began as a NASA project in 1999, before being transferred to the United States Department of Defense in 2004.The 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 latest mission, the sixth, launched on an Atlas V on 17 May 2020.
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 Chinese reusable spacecraft. It was launched on 4 September 2020 at 07:30 UTC on a Long March 2F from the Jiuquan Satellite Launch Center, in the Gobi Desert of northwestern China. Xinhua News Agency said in a report, "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".Unofficial reports indicate that the spacecraft is part of the Shenlong programme, which is claimed to be similar to the Boeing X-37B.
Suborbital rocket planes
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, SpaceShipTwo VSS 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 it is launched in 30 March 2021. Its is also known as VSS Imagine. It will have its test in this summer. 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.
In 2021 Dawn Aerospace test flew its Aurora Mk II, a small uncrewed single-stage suborbital spaceplane, temporarily fitted with small engines. The Aurora takes off and lands horizontally using conventional runways. The next development step is to fit it with a hydrogen peroxide/kerosene liquid-fuel rocket engine to reach supersonic speeds and suborbital altitudes with a payload of up to 3U.
History of unflown concepts
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 Silbervogel bomber 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.
United States (1950s–2010s)
The U.S. Air Force invested some effort in a paper study of a variety of spaceplane projects under their Aerospaceplane efforts of the late 1950s, but later reduced the scope of the project. The result, the Boeing X-20 Dyna-Soar, was to have been the first orbital spaceplane, but was canceled in the early 1960s in lieu of NASA's Project Gemini and the U.S. Air Force's crewed spaceflight program.
In 1961, NASA originally planned to have the Gemini spacecraft land on a runway with a Rogallo wing airfoil, rather than an ocean landing under parachutes. The test vehicle became known as the Paraglider Research Vehicle. Development work on both parachutes and the paraglider began in 1963. By December 1963, the parachute was ready to undergo full-scale deployment testing, while the paraglider had run into technical difficulties. 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.
The Space Shuttle underwent many variations during its conceptual design phase. Some early concepts are illustrated.
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. Six critical technologies were identified, three relating to the propulsion system, which would consist of a hydrogen-fueled scramjet.
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).
In 1994, a USAF captain proposed an F-16 sized single stage to orbit peroxide/kerosene spaceplane called "Black Horse". It was to take off almost empty and undergo aerial refueling before rocketing to orbit.
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.
On 5 March 2006, Aviation Week & Space Technology published a story purporting to be the "outing" of a highly classified U.S. military two-stage-to-orbit spaceplane system with the code name Blackstar.
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.
Soviet Union (1960s–1991)
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. Mikoyan-Gurevich MiG-105 was a crewed test vehicle to explore low-speed handling and landing.
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.
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.
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. The inventor of SABRE set up Reaction Engines to develop SABRE and proposed a twin-engined SSTO spaceplane called Skylon. One NASA analysis showed possible issues with the hot rocket exhaust plumes causing heating of the tail structure at high Mach numbers. although the CEO of Skylon Enterprises Ltd has claimed that reviews by NASA were "quite positive".
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.
European Space Agency (1985–)
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.
Hopper was one of several proposals for a European reusable launch vehicle (RLV) planned to cheaply ferry satellites into orbit by 2015. One of those was 'Phoenix', a German project which is a one-seventh scale model of the Hopper concept vehicle. The suborbital Hopper was a Future European Space Transportation Investigations Programme system study design A test project, the Intermediate eXperimental Vehicle (IXV), has demonstrated lifting reentry technologies and will be extended under the PRIDE programme.
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.
AVATAR (Aerobic Vehicle for Hypersonic Aerospace Transportation; Sanskrit: अवतार) was a concept study for an uncrewed single-stage reusable spaceplane capable of horizontal takeoff and landing, presented to India's Defence Research and Development Organisation. The mission concept was for low cost military and commercial satellite launches. No further studies or development have taken place since 2001.
Current development programs
A test project, the Intermediate eXperimental Vehicle (IXV), has demonstrated lifting reentry technologies and will be extended under the PRIDE programme. 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.
Winged Reusable Sounding Rocket
As of 2016[update], the Indian Space Research Organisation is developing a launch system named the Reusable Launch Vehicle (RLV). It is India's first step towards realizing a two-stage-to-orbit reusable launch system. A space plane serves as the second stage. The plane is expected to have air-breathing scramjet engines as well as rocket engines. Tests with miniature spaceplanes and a working scramjet have been conducted by ISRO in 2016.
Shenlong (Chinese: 神龙; pinyin: shén lóng; lit. 'divine dragon') is a proposed Chinese robotic spaceplane that is similar to the Boeing X-37. Only a few images have been released since late 2007.
Dream Chaser is an American reusable lifting-body spaceplane being developed by Sierra Nevada Corporation (SNC) Space Systems. Originally intended as a crewed vehicle, the Dream Chaser Space System is set to be produced after the cargo variant, Dream Chaser Cargo System, is operational. The crewed variant is planned to carry up to seven people and cargo to and from low Earth orbit.The cargo Dream Chaser is designed to resupply the International Space Station with both pressurized and unpressurized cargo. It is intended to launch vertically on the Vulcan Centaur rocket and autonomously land horizontally on conventional runways. A proposed version operated by ESA would launch on an Arianespace vehicle.
The Space Rider (Space Reusable Integrated Demonstrator for Europe Return) is a planned uncrewed orbital lifting body spaceplane aiming to provide the European Space Agency (ESA) with affordable and routine access to space. Contracts for construction of the vehicle and ground infrastructure were signed in December 2020. Its expected maiden flight is in the fourth quarter of 2023.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, launched on 11 February 2015. The cost of this phase, not including the launcher, is at least US$36.7 million. 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.
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