One of the most dramatic moments of the twentieth century occurred on October 4, 1957. The Soviet Union sent a small shiny sphere with four long antennas into space. They called it Sputnik I. Sputnik is a Russian word that means “traveling companion.” The satellite traveled so fast that its ballistic flight continued all the way around Earth. A radio transmitter on board sent a simple beeping signal that could be heard everywhere as it passed overhead. It was an artificial moon. Since then, satellites have come to be a vital part of human development. Communications, national defence, space exploration and other areas of human activity are today closely linked with satellites.
The first series of unmanned U.S. space probes designed chiefly for interplanetary study was Pioneer. Whereas the first five Pioneers were intended to explore the vicinity of the Moon, all other probes in the series were sent to investigate planetary bodies or to measure various interplanetary particle and magnetic-field effects.
The Midas program was a series of 12 unmanned U.S. military satellites developed to provide warning against surprise attacks by Soviet ICBMs. Midas (an abbreviation of Missile Defense Alarm System) was the first such warning system in the world. To provide global coverage, the Midas satellites were placed into polar orbits. Because of launch and mechanical failures, the Midas satellites were unable to provide the desired continuous coverage of the Soviet Union. The infrared sensors could not distinguish between missile launches and sunlight reflected off of clouds in the upper atmosphere.
The Venera probes were a series of unmanned Soviet planetary probes that were sent to Venus between 161 and 1983.
Cosmos is a series of unmanned Soviet and then Russian satellites launched from the early 1960s to the present day. As of 2017, there were 2,500 satellites in the series. The first satellite in the series was launched on March 16, 1962. Cosmos satellites have been used for a wide variety of purposes, including scientific research, navigation, and military reconnaissance.
The probes in the U.S. Mariner series were sent to the vicinities of Venus, Mars, and Mercury between 1962 and 1973.
The 12 U.S. Velas were reconnaissance satellites developed to detect radiation from nuclear explosions in Earth’s atmosphere. Launched from 1963 to 1970, the Vela satellites were supposed to make certain that no countries violated the 1963 international treaty banning the testing of nuclear weapons on the ground or in the atmosphere. Although their primary function was military reconnaissance, the Velas made several significant astronomical discoveries, including the discovery of gamma-ray bursts.
Zond was a series of eight unmanned Soviet lunar and interplanetary probes. Zond 1 and Zond 2 were aimed at Venus and Mars, respectively, but failed to send back data on the planets. Zond 3 transmitted close-up photographs of 7,800,000 square km (3,000,000 square miles) of the lunar surface, including the hidden side, before going into solar orbit. The remaining flights in the Zond program were tests of Soyuz spacecraft modified for flights around the Moon.
The seven Surveyor U.S. space probes were sent to the Moon between 1966 and 1968 to photograph and study the lunar surface.
Helios was a series of two unmanned solar probes developed by West Germany in cooperation with NASA. Helios 1 and Helios 2 were launched by NASA from the John F. Kennedy Space Center in Cape Canaveral, Florida. Both traveled closer to the sun than any other spacecraft.
The two U.S. Viking spacecraft were launched by NASA for extended study of the planet Mars. The Viking project was the first planetary exploration mission to transmit pictures from the Martian surface.Viking 1 and Viking 2, which lifted off on Aug. 20 and Sept. 9, 1975, respectively, each comprised an instrumented orbiter and lander.
The satellites of the 1980s were built upon the knowledge gained in previous decades. The U.S.-British-Netherlands satellite Infrared Astronomical Satellite (IRAS) was the first space observatory to map the entire sky at infrared wavelengths.
The U.S. satellite Cosmic Background Explorer (COBE) was placed in Earth orbit in 1989 to map the “smoothness” of the cosmic background radiation field and, by extension, to confirm the validity of the Big Bang theory of the origin of the universe. In 1964 Arno Penzias and Robert Wilson—working together at Bell Laboratories in New Jersey to calibrate a large microwave antenna prior to using it to monitor radio-frequency emissions from space—discovered the presence of microwave radiation that seemed to permeate the cosmos uniformly. Now known as the cosmic background radiation, this uniform field provided spectacular support for the Big Bang model.
The joint European-U.S. space probe Ulysses was the first spacecraft to fly over the poles of the sun and return data on the solar wind, the sun’s magnetic field, and other activity in the sun’s atmosphere at high solar latitudes. Understanding such solar activity is important, not only because the sun is an average star that is available for close scrutiny, but also because its activity has important consequences for Earth and its inhabitants. Clementine was a joint project of the Department of Defense’s Strategic Defense Initiative and NASA. The ingenious mission design used the Moon as a “target” for testing various sensors and spacecraft components intended for ballistic-missile-defense applications. In the process, it returned a vast amount of scientific data.
The Infrared Space Observatory (ISO) was a satellite of the ESA that observed astronomical sources of infrared radiation from 1995 to 1998. ISO was launched by an Ariane 4 rocket and was placed into a highly elliptical 24-hour orbit. This enabled it to spend most of its time both far from terrestrial thermal interference and in communication with the control centre at Villafranca, Spain. ISO’s program included both solar-system and deep sky objects.
The U.S. Mars Global Surveyor spacecraft launched to the planet Mars to carry out long-term study from orbit of the entire surface, the atmosphere, and aspects of the interior. High-resolution images returned from the spacecraft indicated that liquid water may have existed on or near the planet’s surface in geologically recent times and may still exist in protected areas.
The U.S.-European space mission to Saturn, Cassini-Huygens, was launched in 1997. The mission consisted of NASA’s Cassini orbiter, which was the first space probe to orbit Saturn, and the ESA’s Huygens probe, which landed on Titan, Saturn’s largest moon.