Space Exploration

Automated space probes and human spaceflight have provided a wealth of scientific data on the nature and origin of the solar system and the universe. Although studies from earth using optical and radio telescopes had accumulated much data on the nature of celestial bodies, it was not until after World War II that the development of powerful rockets made direct space exploration a technological possibility.

Imagined for centuries, the era began with the first artificial satellite (Sputnik, 1957) and the first manned flight (Gagarin, 1961), with subsequent rapidly evolving capabilities in Earth orbit and Solar System exploration (initiated by Mariner 2, 1962). It is an arena of intense international competition and, recently, co-operation. The utilitarian uses of space - communications and meteorology - are now taken for granted; astronomy and Earth remote-sensing capabilities provide a new perspective on the universe and our own planet.

Solar System exploration has provided reconnaissance as far as Neptune, in-depth exploration of Mars and Venus, and detailed study of the Moon; the study of comets and asteroids is less advanced. Human activity has been demonstrated even to the point of crewed lunar landings (Apollo programme, 1969-72) and continuing space station occupancy (Salyut and Mir space stations), but remains dangerous and costly.

Launch vehicle advances have achieved a re-usable crewed orbiter (US space shuttle), but inexpensive, reliable transportation is still in the future. The two dominant participants have been the USA and USSR (now Russia), with the Europeans and Japanese becoming increasingly influential. Space physiological effects on humans are likely to limit the rate at which future exploration proceeds.

Rocket Propulsion

The father of modern rocket propulsion is the American physicist, Robert Hutchings Goddard. Along with Konstantin Eduordovich Tsiolkovsky of Russia and Hermann Oberth of Germany, Goddard envisioned the exploration of space. During World War I (1914-1918) he began experimenting with rockets. By 1918 he had improved rocket design by using smokeless powder instead of black powder and by adding a nozzle that improved the rocket motor's efficiency. In memory of this brilliant scientist, a major space science laboratory, NASA's Goddard Space Flight Center, Greenbelt, Maryland, was established on May 1, 1959.

Rocket engines are reaction engines. The basic principle driving a rocket engine is the famous Newtonian principle that "to every action there is an equal and opposite reaction". A rocket engine expels mass in one direction and moves with the reaction that occurs in the other direction as a result.

A rocket is propelled by the expulsion of gases generated in a combustion chamber. A rocket develops thrust independent of its surroundings, unlike jet engines that need oxygen from the atmosphere to burn fuel. A rocket engine is self-contained and is currently the only type of device suitable for space flight.

Rockets may be divided into two classes: solid-propellant rockets and liquid-propellant rockets. In both types the combustion chamber is called the motor. In a liquid-propellant rocket, the propellants are carried in separate tanks and transferred to the rocket motor; in solid-propellant rockets, the propellant charge is stored and burned in the motor.

Artificial Satellites

The space age began on October 4th, 1957, when the USSR launched Sputnik 1, the world's first artificial satellite. One month later on November 3rd, Sputnik 2 was launched carrying Laika, a black and white dog. Explorer 1 was launched by the U.S. in January 1958. In October 1958 the National Aeronautics and Space Administration (NASA) was created in the U.S.

Earth-orbiting satellites have improved global communications, weather forecasting, navigational aids, and reconnaissance of the earth's surface for the location of mineral resources and for military purposes.

Hundreds of communications satellites reflect or relay radio signals, providing transmission of television signals, telephone conversations, and digital data. Weather satellites provide daily reports of temperatures and cloud patterns. The U.S. Landsats observe the earth, returning information on soil characteristics, water and ice quantities, pollution, insect blights of crops, and even forest fires. Study of the earth's crust helps geologists to identify deposits of oil and minerals. Navigation satellites can locate a position on earth within a few yards. See lower down for Astronomy from Space.

Manned Spaceflight

The first space flight by a human was on April 12th, 1961. Yuri Gagarin, a Soviet cosmonaut, orbited Earth once in the Vostok 1 spacecraft. Manned spaceflight started with suborbital and orbital flights by a single astronaut (USA: Mercury) or cosmonaut (USSR: Vostock); subsequent flights include

On July 20th, 1969, the USA were the first to land men on the Moon and return them safely to Earth. By that time, probes had been sent to Venus and Mars.

The Space Shuttle

The Space Shuttle is a reusable rocket-launched vehicle designed to transport people and cargo between Earth and orbiting spacecraft, and then to return to the Earth's surface by gliding down and landing on a runway.

The Shuttle was selected in the early 1970s as the principal space launcher and carrier vehicle to be developed by the National Aeronautics and Space Administration (NASA).

Planned as a replacement for expensive, expendable booster rockets, it would complete NASA's new Space Transportation System (STS). The program finally got under way in the early 1980s.

Astronomy from Space

Orbiting astronomical observatories permit observations of distant cosmic objects high above the interference and distorting effects of the Earth's atmosphere. Astronomical satellites have studied the sun's radiation, cosmic radiation, the solar wind, the electromagnetic characteristics of space, stellar radiation, and other information not available through the earth's atmosphere.

The unmanned Infrared Astronomy Satellite (IRAS), launched in 1983 by the United States in collaboration with the United Kingdom and The Netherlands, has discovered much about infrared sources far beyond the limits of the solar system. That same year, the Soviet Union placed in Earth orbit another advanced observational satellite, called Astron. Equipped with an ultraviolet telescope developed by France, Astron has studied cosmic radiation from galactic and extragalactic sources.

The Hubble Space Telescope

HST - a joint ESA/NASA project - is a 2.4-meter reflecting telescope which was deployed in low-Earth orbit (600 kilometers) by the crew of the space shuttle Discovery (STS-31) on 25 April 1990. It is a long-term spacebased observatory. The observations are carried out in visible, infrared and ultraviolet light. During its years of operation HST has managed to become one of the most important science projects ever. HST has enabled scientists to make many astronomical discoveries, including the first observations of a black hole.