Space flight

(aerospace engineering) Travel beyond the earth's sensible atmosphere; space flight may be an orbital flight about the earth or it may be a more extended flight beyond the earth into space.

The penetration by humans into the reaches of the universe above the terrestrial atmosphere and investigation of these regions by automated, remote-controlled and crewed vehicles.

The purpose of space flight is to provide significant contributions to the physical and mental needs of humanity on a national and global basis. Such contributions fall specifically in the areas of (1) Earth resources of food, forestry, atmospheric environment, energy, minerals, water, and marine life; (2) Earth and space sciences for research; (3) commercial materials processing, manufacturing in space, and public services. More general goals of space flight include expansion of knowledge; exploration of the unknown, providing a driving force for technology advancement and, hence, improved Earth-based productivity; development and occupation of new frontiers with access to extraterrestrial resources and unlimited energy; strengthening of national prestige, self-esteem, and security; and providing opportunity for international cooperation and understanding.

This article focuses on crewed space flight. For discussion of other missions See also Communications satellite; Meteorological satellites; Military satellites; Satellite (spacecraft); Satellite navigation systems; Scientific satellites; Space probe.

To conduct crewed space flight, the two leading space-faring nations, the United States and Russia, formerly the Soviet Union, have developed spacecraft systems and the necessary ground facilities, research and development base, operational know-how, planning experience, and management skills. In the United States, crewed space programs are conducted by the National Aeronautics and Space Administration (NASA), a federal agency established in 1958 for the peaceful exploration of space. In Russia, crewed space flights have been under the auspices of the U.S.S.R. Academy of Sciences; they are now the responsibility of the Russian Space Agency (RKA). The first spacecraft with a human on board, the Vostok 1, piloted by Yuri A. Gagarin, was launched on April 12, 1961, from the Baikonur Cosmodrome in Kazakhstan and returned after completing one revolution of the Earth. The first American space flight of a human took place 3 weeks later, when NASA launched Alan B. Shepard on May 5 on the Mercury-Redstone 3 for a 15-min suborbital test flight.

The early spacecraft of both nations were built for only one space flight. The first multiply reusable space vehicle, the space shuttle, was launched by the United States on April 12, 1981.

In November 1987, the 13 member nations of the European Space Agency (ESA) agreed to become the third major power engaging in human space flight. European efforts today focus on a two-pronged program: participation as a partner in the International Space Station (ISS), primarily with the Columbus Orbital Facility (COF), and extension of the Ariane family of expendable launch vehicles with the heavy-lift carrier Ariane 5. By joining the original partnership behind the space station and assigning astronauts to United States space shuttle missions (as did the European Space Agency and Russia), Canada and Japan have also entered the ranks of space-faring nations, while other countries, such as Brazil, are preparing to join. On October 15, 2003, the People's Republic of China launched Yang Liwei on a 21-hour orbital flight aboard the spacecraft Shenzou 5.

Crewed spacecraft

A crewed spacecraft is a vehicle capable of sustaining humans above the terrestrial atmosphere. In a more limited sense, the term crewed spacecraft is usually understood to apply to vehicles for transporting and sustaining human crews in space for time periods limited by prestored on-board supplies, as distinct from orbital space stations which support theoretically unlimited habitation of humans in space by autonomous systems, crewed maintenance, and periodic resupply.

The basic requirements of crewed spacecraft are quite different from those of uncrewed space probes and satellites. The presence of humans on board necessitates a life-sustaining environment and the means to return safely to Earth. The major common feature of all crewed spacecraft, therefore, is the atmospheric return element or reentry module. It consists basically of a pressure-tight cabin for the protection, comfort, and assistance of the crew, similar to the cockpits of fighter aircraft, but shaped externally in accordance with the desired airflow and its forces, and surrounded by heat-resistant material, the thermal protection system (TPS), to cope with the high frictional and radiative heating accompanying the energy dissipation phase of the atmospheric return flight to Earth.

The main system that distinguishes crewed spacecraft from other spacecraft is the environmental control and life support system. It provides the crew with a suitably controlled atmosphere. Because all atmospheric supplies must be carried into space, it is essential to recirculate and purify the spacecraft atmosphere to keep the total weight of the vehicle within reasonable limits.

Space suits or pressure suits are mobile spacecraft or chambers that house the astronauts and protect them from the hostile environment of space. They provide atmosphere for breathing, pressurization, and thermal control; protect astronauts from heat, cold, glare, radiation, and micrometeorites; contain a communication link and hygiene equipment; and must have adequate mobility. The suit is worn during launch, docking, and other critical flight phases.

Because of the potential hazards of space flight to personnel, crewed spacecraft must meet stringent requirements of safety and hardware reliability. Reliability is associated with the probability that the spacecraft systems will operate properly for the required length of time and under the specified conditions. To assure survival and return in all foreseeable emergencies, the design of a crew-rated spacecraft includes standby systems (double or triple redundancy) and allows for launch escape, alternative and degraded modes of operation, contingency plans, emergency procedures, and abort trajectories to provide maximum probability of mission success. The priority order of this reliability requirement is (1) crew safety, (2) minimum achievable mission fulfillment, (3) mission data return, and (4) minimal degradation. See also Reliability, availability, and maintainability.

Soviet/Russian programs

After the first Sputnik launch on October 4, 1957, developments of crewed space flight capability followed in quick succession, leading from the first-generation Vostok (East) to the second-generation Voskhod (Ascent) and to the third-generation Soyuz (Union) spacecraft. Originally engaged in an aggressive program to land a cosmonaut on the Moon before the United States lunar orbit mission of Apollo 8 in December 1968, the Soviet Union redirected its aims, after four test failures of its N1 heavy-lift launcher, toward the development of permanent human presence in Earth orbit.

The Vostok, a single-seater for short-duration missions and ballistic reentry from Earth orbits, consisted of a near-spherical cabin, having three small viewports and external radio antennas. The 7-ft (2-m) sphere of the cabin was attached to a service module. The second-generation Voskhod, essentially a greatly modified Vostok, was a short-duration multiperson craft and was designed to permit extravehicular activity or spacewalking by one of the crew.

The Soyuz design is much heavier, larger, and more advanced in its orbital systems, permitting extended orbital stay times. It consists of three main sections or modules: a descent vehicle, an orbital module, and an instrument-assembly module. The three elements are joined together, with the descent vehicle in the middle. Shortly before atmospheric reentry, the two outer modules are jettisoned.

Soyuz spacecraft carried originally up to three cosmonauts. However, when an accidental explosive decompression of the descent cabin during reentry caused the death of the Soyuz 11 crew in 1971, the third seat was removed to make room for the necessary additional life-support equipment, and the Soyuz thereafter carried only two cosmonauts. An improved version, the Soyuz T (for “Transport”) was introduced in 1980. A new version, the Soyuz-TM, with extended mission duration and new subsystems, replaced this vehicle in February 1987, after a crewless test flight in May 1986.

Between 1971 and 1981, five Salyut space stations operated in low Earth orbit successively. The most successful of them, Salyut 6, was the first of a “second generation” of such stations. Unlike its predecessors, it had two docking ports, instead of only one. This enabled it to receive visiting crews and resupply ships. Together with other new on-board systems, this feature was the key to missions of considerably extended duration. Its successor, Salyut 7, was launched in 1982.

On February 19, 1986, the Soviet Union launched the core vehicle in its Mir (Peace) space station complex series. This complex represented a new-generation space station which evolved from the Salyut and Kosmos series vehicles. The core, an advanced version of Salyut, had six docking ports and consisted of four sections. Connected to various docking ports were four laboratory modules, which were launched separately between 1989 and 1996. These modules were dedicated to different scientific and technical disciplines or functions, including technological production with a shop, astrophysics, biological research, and medical research.

In its later years, Mir required increasing maintenance and repairs by its crews, particularly after two serious emergencies in 1997. When U.S. support of Mir ended at the conclusion of the joint Shuttle/Mir program (ISS Phase 1), further crewed operations of the space station were increasingly difficult and impractical for the Russian Space Agency (RSA). The last crew returned to Earth on August 27, 1999, and the station was deorbited on March 20, 2001. See also Space station.

With the successful first test flight, from Baikonur, of the powerful expendable heavy-lift launcher Energia on May 15, 1987, the Soviet Union gained a tremendous new launch capability. With its second, and last, flight on November 15, 1988, the Energia launched the Soviet space shuttle Buran on its only (crewless) orbital test flight. After the collapse of the Soviet Union, the Energia/Buran programs were terminated.

United States programs

During the first decade after its inception in 1961, the United States crewed space program was conducted in three major phases—Mercury, Gemini, and Apollo.

Mercury was in its basic characteristics similar to the Soviet Vostok, but it weighed only about a third as much, as necessitated by the smaller missiles of the United States at that time (the Redstone and Atlas). The one-person Mercury capsules used ballistic reentry and were designed to answer the basic questions about humans in space: how they were affected by weightlessness, how they withstood the gravitational forces of boost and entry, how well they could perform in space. See also Weightlessness.

The second United States step into space was the Gemini Program. With the two-person Gemini capsule, for the first time a crewed spacecraft had been given operational maneuverability in space. Its reentry module flew a lifting reentry trajectory for precise landing point control. In addition, its design permitted extravehicular activity by one of the crew.

The third-generation spacecraft, Apollo, had five distinct parts: the command module (CM), the service module (SM), the lunar module (LM), the launch escape system (LES), and the spacecraft/lunar module adapter (SLA). The three modules made up the basic spacecraft; the LES and SLA were jettisoned early in the mission after they had outlived their function. The command module served as the control center for the spacecraft and provided living and working quarters for the three-member crew for the entire flight, except for the period when two persons entered the lunar module for the descent to the Moon and return. The command module was the only part of the spacecraft that returned to Earth, flying a lifting trajectory with computer-steered maneuvers. The lunar module carried two astronauts from the orbiting command/service module (CSM) down to the surface of the Moon, provided a base of operations there, and returned the two astronauts to a rendezvous with the command service module in orbit. On the last three lunar landings, Apollo 15–17, lunar exploration was supported by the lunar roving vehicle.

A more powerful booster was required to lift the Apollo spacecraft to Earth orbit and thence to the Moon. At the Army Ballistic Missile Agency (ABMA) in 1958, a team of engineers under Wernher von Braun set out to prove that vastly more powerful space rockets could be built from existing hardware by clustering engines and tanks. The project evolved into the Saturn Program of NASA. The Saturn 5, which became the Apollo lunar launch vehicle, had the capability to lift 250,000 lb (113 metric tons) into low Earth orbit and to send 100,000 lb (45 metric tons) to the Moon.

In addition to its lunar mission in the Apollo program, the Saturn 5, in a two-stage version, served also—in its last and thirteenth flightz—to launch the first United States space station, Skylab.

Skylab

The experimental space station Skylab was the largest object placed in space up until that time, and the first crewed project in the U.S. Space Program with the specific purpose of developing the utility of space flight in order to expand and enhance humanity's well-being on Earth. To that end, Skylab's equipment included an Earth resources remote sensing instrument and the first crewed solar telescopes in space. A total of three crews of three astronauts each carried out experiments and observations on Skylab. Skylab was launched uncrewed by Saturn 5 in 1973. The space station underwent repair in orbit, a first for the space program.

Space Transportation System

After the end of the joint American-Soviet space mission, attention began to focus on the routine application of newly acquired know-how systems and experience, specifically in the form of the emerging Space Transportation System (STS), with the ability to transport inexpensively a variety of useful payloads to orbit, as the mainstay and “work horse” of the United States space program. The two major components of the Space Transportation System were the space shuttle and the Spacelab.

The space shuttle is a reusable system. It has three major elements: the orbiter, an external tank (ET) containing the liquid propellants to be used by the orbiter main engines for ascent, and two solid-propellant rocket boosters (SRBs) “strapped on” to the external tank. The orbiter and solid rocket booster casings are reusable; the external tank is expended on each launch. See also Space shuttle.

The orbiter Columbia made its first orbital flight on April 12–14, 1981. Three additional shuttles were added by the end of 1985. With the launch of the twenty-fifth shuttle mission, 51-L on January 28, 1986, tragedy struck the American space program. At approximately 11:40 a.m. EST, 73 s after liftoff, the flight of Challenger, on its tenth mission, abruptly ended in an explosion triggered by a leak in the right solid rocket booster, killing the seven member crew. Continuation of the United States crewed space program was suspended pending a thorough reassessment of flight safety issues and implementation of necessary improvements. Shuttle flight operations resumed on September 29, 1988.

On February 1, 2003, Columbia, on its twenty-eighth flight, was lost with its crew during reentry when it violently disintegrated in the skies over Texas. The Columbia Accident Investigation Board (CAIB) concluded that one of the left wing's leading-edge reinforced-carbon-carbon elements had been punctured during ascent to orbit by a chunk of foam insulation blown off the external tank by the supersonic air stream, rendering the wing unable to withstand reentry heating longer than about eight minutes after entry interface. Further shuttle operations were halted for the duration of the CAIB investigation and subsequent intensive return-to-fight efforts by NASA and its contractors.

The Spacelab was a major adjunct of the shuttle. Developed and funded by member nations of the European Space Agency, the large pressurized Spacelab module with an external equipment pallet was designed to be the most important payload carrier during the space shuttle era, and was used on numerous shuttle missions between 1983 and 1997. With its large transport capacity (in weight, volume, and power supply), the Spacelab was intended to support a wide spectrum of missions is science, applications, and technology by providing versatile and economical laboratory and observation facilities in space for many users. Another objective was to reduce significantly the time from experiment concept to experiment result, compared with previous space practice, and also to reduce the cost of space experimentation. It allowed the direct participation of qualified men and women scientists and engineers to operate their own equipment in orbit.

International Space Station

Interest in the development of a permanent crewed platform in Earth orbit dates back to the very beginnings of human space flight. While the practical realization of the concept was accomplished and proven by the Soviet Salyut/Mir and the American Skylab programs, the real breakthrough happened on January 29, 1998, when representatives of 16 nations signed a partnership agreement for the joint development and operation of an International Space Station (ISS). The goal of the ISS program is to establish a permanent platform for humans to live and work in space in support of science and technology research, business, education, and exploration. Its objectives are to provide a world-class laboratory complex uniquely located in a microgravity and vacuum environment where long-term scientific research can be carried out to help fight diseases on Earth, unmask fundamental processes leading to new manufacturing processes and products to benefit life on Earth, and observe and understand the Earth's environment and the universe. When completed, the International Space Station (see illustration) will have a mass of about 1,040,000 lb (470 metric tons). It will be 356 ft (108 m) across and 290 ft (108 m) long, with almost an acre (0.4 hectare) of solar panels to provide up to 110 kilowatts of power to six state-of-the-art laboratories.

International Space Station with its solar arrays deployed, photographed from the space shuttle Endeavour following undocking on December 9, 2000. (NASA)

The on-orbit assembly of the ISS began with the launch of the Functional Cargo Block (FGB) Zarya (“Dawn”) on November 20, 1998.

On October 31, 2000, a Soyuz-U carrier lifted off from Baikonur and placed in orbit Soyuz TM-31, carrying the first resident crew for the Space Station. Since then, each crew has remained on the station for about six months before rotating with the subsequent crew. Early in 2003, further progress in ISS assembly was halted by the stand-down of space shuttles after the Columbia loss. As a consequence of the reduction in resupply missions to the station, crew size was reduced from a three- to a two-person caretaker crew per expedition.