flights into space; the aggregate of the branches of science and technology used in the exploration of space and extraterrestrial objects by means of various types of spacecraft. Space exploration includes subjects of astronautics, such as problems of the theory of space flight (calculation of trajectories) and scientific and technical problems (the design of space rockets, engines, on-board control systems, launch complexes, unmanned probes, piloted craft, scientific instruments, ground-based flight control systems, and tracking and telemetry services, as well as the organization and supply of orbital stations). Also studied are medical problems (the development of on-board life-support systems; compensation for unfavorable effects of acceleration, weightlessness, and radiation on the human body) and problems of international law connected with the regulation of the use of space and the planets.
Historical survey. Mankind has long dreamed of penetrating the cosmos, as is reflected in the dreams contained in fairy tales, legends, and science-fiction novels. The numerous and usually unrealizable inventions of the past attest to this. Stories of flight are encountered as early as Assyrian-Babylonian epics, as well as in ancient Chinese and Iranian legends. The Sanskrit epic poem Mahabharata contains instructions for a flight to the moon. The Greek myth about Icarus’ flight to the sun on wings fastened together with wax is widely known. In the second century B.C., Lucian described a flight to the moon on wings.
In the late 19th century the Russian scientist K. E. Tsiolkov-skii was the first to provide a theoretical basis for space flight. In his Investigation of Interplanetary Space by Means of Jet Devices (1903) and in subsequent works, Tsiolkovskii solved a number of basic problems of space flight and demonstrated its technical feasibility. In addition to Tsiolkovskii’s works, those of I. V. Meshcherskii (beginning in 1897), lu. V. Kondratiuk (1919-29), F. A. Tsander (1924-32), N. A. Rynin (1928-32), and other Russian scientists were devoted to the problems of space flight. Outside the USSR, early works in the field were published by R. Esnault-Pelterie (France, 1913), R. Goddard (USA, 1919), and H. Oberth (Gemany, 1923). The first space exploration societies were founded in the 1920’s—in the USSR in 1924, Austria in 1926, Germany in 1927, and Great Britain and the USA in 1930. They worked to promote the ideas of space exploration, as well as to assist in solving practical problems.
Work in rocket technology in the USSR began in 1921; the Gas Dynamics Laboratory (GDL) was organized during that period. Flight tests of rockets using smokeless grainy powder began in 1928, under the direction of N. I. Tikhomirov (the founder of the Gas Dynamics Laboratory). In 1929, V. P. Glushko developed rockets with electric and liquid-propellant motors. The first tests of electric and liquid-propellant rocket motors took place in 1929 and 1931, respectively. In 1932 the Moscow Group for the Study of Jet Propulsion (GIRD) was formed. In 1933, S. P. Korolev directed the first launches of Soviet liquid-propellant rockets designed by M. K. Tikhonravov and F. A. Tsander. In late 1933 the GDL and GIRD were merged to form the Jet Scientific Research Institute. These three organizations made the major initial contribution to the development of Soviet rocketry. The subsequent development of rocket and space technology in the USSR came from the experimental design bureau for the development of liquid-propellant rocket motors, that had grown out of the GDL, as well as from other experimental design bureaus, institutes, and factories.
Experimental work on liquid-propellant rocket motors in the USA was began in 1921 by R. Goddard, and launches of liquid-propellant rockets began in 1926. Bench tests of liquid-propellant motors were begun in Germany by H. Oberth in 1929 and flight tests by J. Winkler in 1931. Germany used liquid-propellant rockets with a range of 250–300 km (the V-2 rocket, designed by W. von Braun) during World War II (1939–45). The potential of the new weapon caused many countries to intensify their efforts in rocket technology after the war, resulting in the development of intercontinental and other ballistic missiles armed with nuclear warheads. This work indirectly furthered the development of the technological basis for space flight.
The space age. Oct. 4, 1957, the date on which the USSR launched the first artifical earth satellite, is considered the dawn of the space age. A second important date is Apr. 12, 1961, the date of the first manned space flight, by Iu. A. Gagarin, the start of man’s direct penetration into space. The third historical event is the first lunar expedition, by N. Armstrong, E. Aldrin, and M. Collins (USA), July 16–24, 1969.
A number of countries have developed and are using spacecraft: the USSR since 1957, and USA since 1958, France since 1965, Japan and the People’s Republic of China since 1970, and Great Britain since 1971. The scale of space research may be judged from the number of satellites of the earth, the sun, the moon, Mars, and Venus launched by the USSR (about 900 as of Jan. 1,1976); earth escape velocity has been imparted to 41 space probes, with a total mass of 110 tons (167 tons, including the final stage of the launch vehicle). Space research is conducted on a similar scale in the USA. As of Jan. 1, 1976, 34 soviet cosmonauts had made space flights in 26 spacecraft and three orbital stations of the Salyut series, and 43 American astronauts had flown in 31 spacecraft and one orbital station. The number of satellites orbited by other countires is as follows: 10 by France, six by Japan, and three by the People’s Republic of China (as of Dec. 1, 1975).
S. P. Korolev was the founder of practical astronautics. By 1957 he had directed the construction of a space center, which made possible the launching of the first artificial earth satellite; later, a number of unmanned spacecraft were successfully orbited. By 1961 the Vostok spacecraft, on which Iu. A. Gagarin made the first flight, had been developed and launched. Korolev directed the development of unmanned interplanetary probes for the study of the moon (up to Luna 9, which made the first soft lunar landing), the first spacecraft of the Zond and Venera series, and the Voskhod spacecraft (the first multiseat spacecraft, from which the first space walk was made). Not limiting his work to the development of launch vehicles and spacecraft, Korolev exercised overall technical supervision of work that created the basis for the first space programs. Important contributions to the development of Soviet rocket technology were also made by design bureaus headed by M. K. Iangel’, G. N. Babakin, A. M. Isaev, and S. A. Kosberg. V. P. Glushko, the founder and head of the experimental design bureau affiliated with the GDL, supervised the development of powerful liquid-propellant rocket motors used by all Soviet launch vehicles (1957-73).
Modern space flight theory is based on celestial mechanics and the theory of vehicle control. In contrast to classical celestial mechanics, this new field is called astrodynamics. Space flight gave rise to the need to develop optimum spacecraft trajectories (selection of the launch time and type of trajectory in order to minimize fuel consumption by the launch vehicle). Changes in trajectory caused by perturbational forces—particularly gravitational fields and the aerodynamic braking effect, which results from interaction of the spacecraft with the rarefied upper layers of the atmosphere (for artificial satellites of planets)—and under the influence of solar radiation pressure (for interplanetary flights) are taken into account. The optimality requirement sometimes results in fairly complex trajectories, with extended interruptions in launch vehicle engine operation (for example, for a lunar, Mars, or Venus launch the spacecraft is first inserted into the earth parking orbit and then injected into a planetary trajectory) and with the use of the gravitational field of a planet (for example, for a lunar mission, which requires an arched trajectory for earth return without firing the rocket motor).
The theory of trajectory corrections is an important branch of astrodynamics. Deviation of the actual trajectory from the calculated trajectory is the result of two factors: distortion of the trajectory by perturbational forces that cannot be predicted (slowing of a satellite by the atmosphere, whose density varies unevenly) and the technically unavoidable minor errors in speed and direction of the spacecraft at the moment of shutdown of the launch vehicle engine (in interplanetary flights, the effect of errors gradually increases). Trajectory correction is accomplished by a short burn of the rocket motor. The theory of correction involves questions of optimizing the correction maneuver (the most advantageous number of such maneuvers and the location of correction points along the trajectory). Knowledge of a spacecraft’s actual trajectory is needed in order to make corrections and perform maneuvers. If the actual orbit is determined on board the spacecraft, such a determination is an integral part of the self-contained navigational system and involves the measurement of angles between stars and planets, the distances of planets, the times of setting and rising of the sun and stars relative to the edge of planets, and the processing of the measurements by an on-board computer, using methods of celestial mechanics.
The development of space centers is a complex scientific and technical problem. Large launch vehicles may have a launch mass of as much as 3,000 tons and may be more than 100 m tall. In order to carry the necessary fuel reserves (90 percent of the total mass), a rocket’s structure must be extremely light; this is achieved through appropriate design and judicious reduction of rigidity and durability requirements. As fuel is consumed in flight, the empty parts of the fuel tanks become superfluous, and their further acceleration results in unwarranted expenditure of fuel. Therefore, multistage launch vehicle configurations (usually two to four stages) are advisable; the stages are jettisoned successively as their fuel tanks become empty.
A modern launch vehicle is a complex package of systems, of which the power plant and the control system are the most important. Chemical liquid-propellant rocket motors are normally used; solid-propellant motors are used less frequently. Motors that use nuclear power are still in the experimental stage (1973); however, there is no doubt that nuclear power will actually be used on future space expeditions. Manned flights to Mars (including a Mars landing) and other similar space programs require tremendous amounts of energy, which can be supplied only by nuclear power sources in combination with chemical sources. Launch vehicle power plants are rated at tens of millions of kilowatts. In the development of powerful and economical liquid-propellant rocket motors for launch vehicles, scientists are concentrating their efforts on the selection of optimum energy-producing fuels and the provision of sufficiently complete combustion in the combustion chamber under high pressures and temperatures. In connection with this, solutions must be found to difficult problems, such as in-flight engine cooling and the achievement of stability of fuel combustion.
Launch vehicle power plants usually consist of several engines, whose operation is synchronized by the guidance system. Guidance systems are normally self-contained—that is, they operate independently of ground stations. They consist of gyroscopic and other primary information sensors, which continuously measure the attitude of the launch vehicle and the accelerations acting on it. Using this information, a computer determines the actual trajectory and controls the vehicle in order to achieve the required combination of coordinates and velocity vector of the rocket at the moment of engine shutdown. The control of a launch vehicle’s attitude is complicated by the vehicle’s low structural stiffness and the large proportion of its mass that is liquid. Therefore, the flexural oscillations of the rocket’s hull and the movement of liquids in the fuel tanks must be taken into account.
The flight readiness of a launch vehicle is checked in the field assembly area of the cosmodrome (in the assembly and testing building), and then the vehicle is transported to the launching pad, where it is erected on the launch pedestal, undergoes pre-launch tests, and is fueled and launched. A spacecraft is considered to have been inserted into orbit if it has exceeded orbital velocity (about 7.91 km/sec) for earth satellites or has attained velocity of the order of earth escape velocity (11.19 km/sec) for spacecraft on missions to the moon, Mars, or Venus. (For flights to the remote planets or the sun a speed considerably greater than earth escape velocity is needed.) During orbital insertion the launch vehicle separates from the spacecraft, which continues its orbital flight mainly by inertia, according to the laws of celestial mechanics.
Spacecraft inserted into orbit may be divided into two groups, earth satellites and space probes for flight to the moon or planets. If significant changes in speed are planned, such spacecraft may be equipped with rocket stages of various degrees of power for braking during planet approach (if the flight plan calls for planetary satellite orbit), for soft landing on a planet lacking an atmosphere, for blastoff from the planet, and for accelerating the spacecraft to the velocity required for its return to earth. It is presumed that in the future economical electric rocket motors will accelerate spacecraft from orbital to higher velocities. A shortcoming of the electric motor is its small thrust, as a result of which acceleration from orbital to escape velocity (or braking from escape to orbital velocity) may last several months. High-capacity sources of nuclear-derived electric power are needed to produce the necessary thrust; this causes additional difficulties connected with the need to protect instruments and crew from harmful radiation.
Spacecraft must be capable of long-term independent operation in space. A number of systems are needed for this purpose: a system for maintaining a specified temperature range; a power-supply system using solar radiation (solar batteries), fuel (electrochemical current generators), or nuclear energy to produce electric power; a system for communicating with earth and other spacecraft; and a guidance system. In addition, a spacecraft carries a wide variety of scientific equipment, from small instruments for studying the properties of space to large telescopes.
The on-board control system integrates the operation of these instruments and systems.
Guidance involves solutions to a number of problems such as attitude control and control of engine burns for trajectory correction during ascent and landing, as well as during rendezvous and other maneuvers performed by two spacecraft. Special control is required for descent to the surface of a planet with an atmosphere. A distinction is made between two kinds of atmospheric descent in which the atmosphere itself is used to slow the spacecraft—controlled descent and uncontrolled (ballistic) descent. The former is characterized by a high degree of touchdown accuracy and a smaller g-load during atmospheric braking. Heat shields are used to protect the descent vehicle from the heat generated by atmospheric braking.
In addition, a number of medical problems arise in the case of a manned spacecraft. It must provide protection of the crew from the space environment (vacuum, harmful radiation, and so on) and must be equipped with a life-support system, which maintains the necessary atmospheric composition and the correct temperature, humidity, and pressure inside the spacecraft. Food and water reserves are provided on short-term flights; for long-term flights, food production—as well as water and oxygen regeneration—must take place on board. Space flight places increased demands on the human body (the effect of weightlessness and of the g-load during the launch and landing phases). Therefore, medical criteria must be used in the cosmonaut selection process. The problem of long-term manned flight under conditions of weightlessness has not yet been resolved.
Descent to the surface of heavenly bodies involves the solution of a number of problems: setting up scientific equipment, conducting experiments using stationary and mobile automatic robots, and—in the future—manned expeditions requiring the construction of temporary or permanent bases.
Space flights usually require a broad network of ground-based control services. Space communications centers are located all over the globe, and where this is not feasible, as in the ocean, ships equipped with communications gear (for example, the Iurii Gagarin and Kosmonavt Vladimir Komarov) are used.
After a spacecraft has returned to earth, the recovery team goes into operation. Its mission is to find and recover the descent vehicle and, in the case of manned flights, to recover the crew, render medical assistance if needed, and take quarantine measures (for crews returning from other planets). To facilitate location of the descent vehicle, it is equipped with a radio beacon whose signals are used for homing by the ships, airplanes, and helicopters of the recovery team. Control of a flight from launch to touchdown involves the efforts of a large number of various services. The job of the administrative technical personnel in charge of a flight is to organize and integrate on-board spacecraft control systems with the numerous ground-based services.
The goals of space exploration may be divided into two groups: scientific studies and practical applications. In addition to the indirect influence of space research on the practical sphere through fundamental scientific discoveries, space exploration makes possible the direct use of spacecraft for practical applications. Artificial satellites circling the globe in high orbits and equipped with repeaters receive signals from a ground station and, after appropriate amplification, return it to earth, where it is received by a station located thousands of kilometers away from the transmitting station. Such communications satellites relay television programs and handle telephone and telegraph communications. Satellites are used in meteorology to produce cloud distribution and earth heat radiation maps, as well as to track cyclones. The information is continuously fed to world meteorological centers and is used for weather forecasting. Satellites whose orbital paths have been determined with great accuracy are used for marine and aviation navigation services; they transmit their precise coordinates to ships and aircraft during periods of radio contact. Any object can establish its own coordinates by determining its position relative to the navigation satellite.
Satellites are playing an ever-increasing role in surveying the earth’s natural resources and in continuous checks on their condition. Photography of the earth’s surface through various light filters, as well as other research methods, makes it possible to see the distribution of vegetation and changes in the snow cover, as well as river flooding and the condition of crops and forests; to observe the progress of work in the fields; to estimate the expected harvest; and to record the occurrence of forest fires. Oceanographic and hydrological studies may also be conducted using satellites. The use of satellites is of particular value in geodesy and topography—for precise fixing of points located at great distances from each other and the fast updating of topographic maps through photographs from space, as well as for setting up geodetic reference networks by tracking satellites (whose coordinates are known precisely at every moment) from various ground stations. The particular features of space flight, such as weightlessness and vacuum, may be used for certain particularly delicate industrial processes. For this purpose appropriate industrial equipment will be placed on satellites, and space shuttles will supply them with raw materials and transport the manufactured products to earth.
A considerable number of specialized unmanned satellites (astronomical, solar, geophysical, geodetic, weather, communications, and others), as well as long-term multipurpose manned orbital stations, are needed to solve the problems associated with the exploration of near-earth space. Crew transfer will be carried out as required, by space shuttles making regular trips between an orbital station and ground space centers.
The immediate goal of lunar and planetary exploration is to produce new scientific data. Plans include the continued study of the moon by both manned and unmanned spacecraft, followed by the establishment of a scientific base on the lunar surface. Flights to Mercury, Venus, Mars, Jupiter, and other planets of the solar system are being made by unmanned crafts, and manned landing missions to Mars (with an expedition time of about three years) are seen as possible in the 1980’s and 1990’s. The study of remote planets and flights out of the solar system and to the sun will long remain feasible only for unmanned spacecraft. The very long duration of such flights requires a new step forward in technological progress in order to develop equipment of very high reliability. In the future, space exploration will make it possible for man to harness the material and energy resources of the universe.
Space exploration, by its very nature, is a field involving the efforts of all mankind, and even if carried out within the framework of national interests, it affects the interests of many counties. (See Table 1 for the major events of the space age.)
V. P. GLUSHKO and B. V. RAUSHENBAKH
| Table 1. Major events of the space age | |
|---|---|
| Date of launch | Type of mission |
| Oct. 4, 1957 | First artificial satellite, Sputnik (USSR) |
| Nov. 3, 1957 | Biological satellite Sputnik 2 with the dog Laika on board (USSR) |
| Feb. 1, 1958 | First satellite of the American Explorer series |
| May 15, 1958 | Sputnik 3 satellite (geophysical laboratory) (USSR) |
| Jan. 2, 1959 | Lunar fly-by of unmanned Luna 1 probe; first artificial satellite of the sun (USSR) |
| Mar. 3, 1959 | Pioneer 4, first American artificial satellite of the sun |
| Sept. 12, 1959 | Impact of Luna 2 probe on the lunar surface, Sept. 14, 1959 (USSR) |
| Oct. 4, 1959 | Circumlunar flight of Luna 3 probe; transmission to earth of first pictures of the far side of the moon (USSR) |
| Apr. 1, 1960 | Weather satellite of the Tiros series (USA) |
| Apr. 13, 1960 | Navigation satellite of the Transit series (USA) |
| Feb. 12, 1961 | Fly-by of Venus by Venera 1 probe; May 19–20, 1961 (USSR) |
| Apr. 12, 1961 | First manned orbital flight, by lu. A. Gagarin aboard the Vostok spacecraft (USSR) |
| May 5, 1961 | First suborbital flight, by A. Shepard aboard the Mercury spacecraft (USA) |
| Aug. 6, 1961 | Day-long orbital flight, by cosmonaut G. S. Titov aboard the Vostok 2 spacecraft (USSR) |
| Feb. 20, 1962 | First orbital flight, by astronaut J. Glenn aboard the Mercury spacecraft (USA) |
| Mar. 7, 1962 | First orbiting solar observatory (USA) |
| Mar. 16, 1962 | First satellite of the Cosmos series (USSR) |
| Apr. 23, 1962 | First lunar probe of the Ranger series; photographs of lunar surface before impact (USA) |
| Aug. 11–12, 1962 | First group flight, by cosmonauts A. G. Nikolaev and P. R. Popovich aboard the Vostok 3 and Vostok 4 spacecraft (USSR) |
| Aug. 27, 1962 | Venus fly-by of first probe of the Mariner series, Dec. 14, 1962 (USA) |
| Oct. 31, 1962 | Anna 1B geodetic satellite (USA) |
| Nov. 1, 1962 | Mars fly-by of the Mars 1 probe, June 19, 1963 (USSR) |
| June 16, 1963 | Orbital flight by the first woman cosmonaut, V. V. Tereshkova, aboard the Vostok 6 spacecraft (USSR) |
| Nov. 1, 1963 | First maneuvering unmanned satellite of the Polet series (USSR) |
| Aug. 19, 1964 | Insertion of Syncom 3 communications satellite into stationary orbit (USA) |
| Oct. 12, 1964 | Orbital flight by cosmonauts V. M. Komarov, K. P. Feoktistov, and B. B. Egorov aboard the three-place Voskhod spacecraft (USSR) |
| Nov. 28, 1964 | Mars fly-by and study by the Mariner 4 probe, July 15, 1965 (USA) |
| Mar. 18, 1965 | Space walk by A. A. Leonov outside the Voskhod 2 spacecraft, commanded by P. I. Beliaev (USSR) |
| Mar. 23, 1965 | First orbital maneuvers by the Gemini 3 spacecraft, with astronauts V. Grissom and J. Young aboard (USA) |
| Apr. 23, 1965 | First communications satellite of the Molnia 1 series in synchronous orbit (USSR) |
| July 16, 1965 | First heavy research satellite of the Proton series (USSR) |
| July 18, 1965 | Zond 3 probe photographs far side of moon and transmits pictures to earth (USSR) |
| Nov. 16, 1965 | Venera 3 probe lands on Venus, Mar. 1, 1966 (USSR) |
| Nov. 26, 1965 | First French A-1 satellite |
| Dec. 4–15, 1965 | Rendezvous of Gemini 7 and Gemini 6 spacecraft with astronauts F. Borman, J. Lovell, W. Schirra, and T. Stafford aboard (USA). |
| Jan. 31, 1966 | First soft lunar landing, by Luna 9 probe, Feb. 3, 1966; pictures of lunar landscape transmitted to earth (USSR) |
| Mar. 16, 1966 | Manual docking of Gemini 8 spacecraft, piloted by astronauts N. Armstrong and D. Scott, with an Agena rocket (USA) |
| Mar. 31, 1966 | Luna 10 probe, first lunar satellite (USSR) |
| May 30, 1966 | First soft lunar landing by a probe of the Surveyor series (USA) |
| Aug. 10, 1966 | Insertion of first probe of the Lunar Orbiter series into lunar orbit (USA) |
| Jan. 27, 1967 | During testing of the Apollo spacecraft on the launching pad, fire broke out in the craft’s cabin, killing astronauts V. Grissom, E. White, and R. Chaffee (USA) |
| Apr. 23, 1967 | Flight of Soyuz 1 spacecraft, with cosmonaut V. M. Komarov aboard. Parachute system failure caused the death of the cosmonaut during reentry (USSR) |
| June 12, 1967 | Descent of unmanned Venera 4 probe into Venusian atmosphere, Oct. 18, 1967, accompanied by transmission of scientific data (USSR) |
| June 14, 1967 | Fly-by of Venus (Oct. 19, 1967) by Mariner 5 space probe (USA) |
| Sept. 15 and Nov. 10, 1968 | Circumlunar navigation and return to earth by Zond 5 and Zond 6 spacecraft, using ballistic and controlled descent (USSR) |
| Dec. 7, 1968 | First orbiting astronomical observatory (USA) |
| Dec. 19, 1968 | Stationary communications satellite of the Intelsat 3B series (USA) |
| Dec. 21, 1968 | Circumlunar flight, including lunar orbit insertion (Dec. 24, 1968) and return to earth, by Apollo 8 spacecraft, piloted by astronauts F. Borman, J. Lovell, and W. Anders (USA) |
| Jan. 5 and 10, 1969 | Studies of atmosphere of Venus by Venera 5 (May 16, 1969) and Venera 6 (May 17, 1969) unmanned probes (USSR) |
| Jan. 14–15, 1969 | First orbital docking of Soyuz 4 and Soyuz 5 spacecraft, with cosmonauts V. A. Shatalov, B. V. Volynov, A. S. Eliseev, and E. V. Khrunov aboard. The last two cosmonauts exited their craft and transferred to the other spacecraft (USSR). |
| Feb. 24 and Mar. 27, 1969 | Fly-by of Mars by Mariner 6, July 31, 1969, and Mariner 7, Aug. 5, 1969 (USA) |
| May 18, 1969 | Apollo 10 circumlunar flight, with astronauts T. Stafford, J. Young, and E. Cernan aboard; selenocentric orbit insertion, May 21, 1969; orbital maneuvers and return to earth (USA) |
| July 16, 1969 | First lunar landing, by Apollo 11 spacecraft. Astronauts N. Armstrong and E. Aldrin spent 21 hr 36 min on the lunar surface in the Sea of Tranquillity (July 20–21, 1969). M. Collins remained in selenocentric orbit in the command module. Having accomplished the flight program, the astronauts returned to earth (USA) |
| Aug. 8, 1969 | Circumlunar flight and return to earth by Zond 7 probe using controlled descent (USSR) |
| Oct. 11, 12, and 13, 1969 | Group flight with maneuvers of the Soyuz 6, Soyuz 7, and Soyuz 8 spacecraft, with cosmonauts G. S. Shonin and V. N. Kubasov; A. V. Filipchenko, V. N. Volkov, and V. V. Gorbatko; and V. A. Shatalov and A. S. Eliseev (USSR) |
| Oct. 14, 1969 | First research satellite of the Intercosmos series, carrying scientific instruments from socialist countries (USSR) |
| Nov. 14, 1969 | Apollo 12 lunar landing in Oceanus Procellarum (Ocean of Storms). Astronauts C. Conrad and A. Bean spent 31 hr 31 min on the lunar surface (Nov. 19–20, 1969). R. Gordon remained in selenocentric orbit (USA) |
| Feb. 11, 1970 | Ohsumi, the first Japanese satellite |
| Apr. 11, 1970 | Apollo 13 circumlunar flight by astronauts J. Lovell, J. Swigert, and F. Haise. Planned lunar landing cancelled as a result of an emergency aboard the spacecraft (USA) |
| Apr. 24, 1970 | First Chinese satellite |
| June 1, 1970 | Soyuz 9 flight, lasting 425 hr, by cosmonauts A. G. Nikolaev and V. I. Sevast’ianov (USSR) |
| Aug. 17, 1970 | Soft landing on surface of Venus by Venera 7 unmanned probe (USSR) |
| Sept. 12, 1970 | Soft lunar landing by Luna 16 unmanned probe in Mare Fecunditatis (Sea of Fertility), Sept. 20, 1970; spacecraft drilled into the surface, took soil samples, and successfully launched payload to earth (USSR) |
| Oct. 20, 1970 | Circumlunar flight and return to earth on northern hemisphere side by Zond 8 (USSR) |
| Nov. 10, 1970 | Unmanned Luna 17 probe landed remote-control Lunokhod 1 roving vehicle, with scientific instrumentation. During 11 lunar days it traveled 10.5 km, studying an area in Mare Imbrium (Sea of Rains) (USSR) |
| Jan. 31, 1971 | Apollo 14 lunar landing in the vicinity of the Fra Mauro crater. Astronauts A. Shepard and E. Mitchell spent 33 hr 30 min on the lunar surface (Feb. 5–6, 1971). S. Roosa remained in selenocentric orbit (USA) |
| Apr. 19, 1971 | First Salyut long-term piloted orbital station (USSR) |
| May 19, 1971 | First Mars landing. Mars 1 probe orbited the planet on Nov. 27, 1971 (USSR) |
| May 28, 1971 | Mars 3 probe orbited the planet Dec. 2, 1971; ejected first soft-landing Mars lander |
| May 30, 1971 | Mariner 9, first artificial satellite of Mars, inserted into Mars orbit Nov. 13, 1971 (USA) |
| June 6, 1971 | 570-hr flight by cosmonauts G. T. Dobrovol’skii, V. N. Volkov, and V. I. Patsaev in the Soyuz 11 spacecraft and the Salyut orbital station. During descent to earth, the cosmonauts perished as a result of depressurization of the cabin (USSR) |
| July 26, 1971 | Apollo 15 lunar landing. Astronauts D. Scott and J. Irwin spent 66 hr 55 min on the lunar surface (July 30-Aug. 2, 1971). A. Worden remained in lunar orbit (USA) |
| Oct. 28, 1971 | Prospero, first British satellite, launched by British launch vehicle |
| Feb. 14, 1972 | Luna 20 probe brought to earth lunar soil samples from area adjoining Mare Fecunditatis (USSR) |
| Mar. 3, 1972 | Pioneer 10 probe explored asteroid belt (July 1972-February 1973), flew by Jupiter (Dec. 4, 1973), and left the solar system (USA) |
| Mar. 27, 1972 | Venera 8 probe made soft landing on Venus, Jul. 22, 1972. Planet’s atmosphere and surface studied (USSR) |
| Apr. 16, 1972 | Apollo 16 lunar landing. Astronauts J. Young and C. Duke spent 71 hr 02 min on the lunar surface (Apr. 21–24, 1972). T. Mattingly remained in selenocentric orbit (USA) |
| Dec. 7, 1972 | Apollo 17 lunar landing. Astronauts E. Cernan and H. Schmitt spent 75 hr 00 min on the lunar surface (Dec. 11–15, 1972). R. Evans remained in selenocentric orbit (USA) |
| Jan. 8, 1973 | Luna 21 probe delivered Lunokhod 2 to the moon, Jan. 16, 1973. Roving vehicle traveled 37 km during five lunar days (USSR) |
| Apr. 6, 1973 | Fly-by of Jupiter by Pioneer 11 probe on Dec. 3, 1974, at a distance of 43,000 km, or three times closer than Pioneer 10. The probe then left the solar system (USA) |
| May 14, 1973 | Skylab long-term orbital station. Astronauts C. Conrad, P. Weitz, and J. Kerwin spent 28 days on board beginning May 25. Another crew, consisting of A. Bean, O. Garriot, and J. Lousma, boarded the station on July 28 and spent 59.5 days there, and the third crew (astronauts G. Carr, E. Gibson, and W. Pogue) spent 84 days on board, beginning November 16 (USA) |
| Nov. 5, 1973 | First fly-by of Mercury by Mariner 10 probe (Mar. 29, 1974); the gravitational field of Venus, an intermediate planet, was used for the first time on Feb. 5, 1974, to reach another planet (USA) |
| Apr. 13, 1974 | The first regional system communications satellite in the USA and the third in the world (after the USSR and Canada) was put into operation after the insertion of Westar 1 satellite into synchronous orbit (USA) |
| May 17, 1974 | First synchronous weather satellite, SMS-1, providing weather data for a hemisphere every 30 min (USA) |
| May 30, 1974 | Multipurpose ATS-6 synchronous satellite. On July 2 the satellite began relaying educational programs directly to commercial TV sets in remote areas in the USA and India. ATS-6 was successfully used during the experimental flight of the Soyuz and Apollo spacecraft (EPAS) in July 1975 |
| Aug. 30, 1974 | First Dutch satellite, ANS, placed in orbit by an American launch vehicle |
| Nov. 15, 1974 | First Spanish satellite, lntasat-1, placed in orbit along with two American satellites by an American launch vehicle |
| Dec. 10, 1974 | Helios 1, first space probe in Western Europe (Federal Republic of Germany), placed into orbit by an American launch vehicle |
| Dec. 26, 1974 | Salyut 4 long-term piloted orbital station. Cosmonauts A. A. Gubarev and G. M. Grechko spent 29.5 days on board, beginning Jan. 12, 1975. P. I. Klimuk and V. I. Sevast’ianov boarded the station on May 26 and spent about 63 days there (the longest flight in Soviet space exploration). On November 19, automatic docking of Soyuz 20 unmanned spacecraft (launched on November 17) with Salyut 4 orbital station took place (USSR) |
| Feb. 6, 1975 | Second synchronous weather satellite, SMS-2. Combined with the SMS-1, it provides round-the-world weather monitoring every 30 min (USA) |
| Apr. 19, 1975 | First Indian satellite, Aryabhata, placed in orbit by a Soviet launch vehicle |
| June 8, 1975, and June 14, 1975 | Venera 9 and Venera 10, first artificial satellites of Venus (inserted into Venus orbit on Oct. 22 and 25, 1975, respectively). Soft landing of Venus landers ejected from the spacecraft; first pictures of the planet at the landing site (USSR) |
| July 15, 1975 | First international space experimental program (EPAS) involving manned spacecraft Soyuz 19 (USSR) and Apollo (USA) |
| Aug. 25, 1975, and Sept. 5, 1975 | Flight to Mars of Viking 1 and Viking 2 unmanned probes for the purpose of detecting any signs of life on the planet (USA) |