History of Space Exploration

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People dreamed of space flight for millennia before it became reality. Evidence of the dream exists in myth and fiction as far back as Babylonian texts of 4000 bc. The ancient Greek myths of Daedalus and Icarus also reflect the universal desire to fly. As early as the 2nd century ad, the Greek satirist Lucian wrote about an imaginary voyage to the Moon. In the early 17th century the German astronomer Johannes Kepler wrote Somnium (Sleep), which might be called a scientific satire of a journey to the Moon. The French writer and philosopher Voltaire, in Micromégas (1752), told of the travels of certain inhabitants of Sirius and Saturn; and in 1865 the French author Jules Verne depicted space travel in his popular novel From the Earth to the Moon. The dream of flight into space continued unabated into the 20th century, notably in the works of the English writer H. G. Wells, who published The War of the Worlds in 1898 and The First Men in the Moon in 1901. More recently, fantasies of space flight have been nourished by science fiction.

Contents:

1. Early Developments

2. Scientific Discoveries

3. Rocket Propulsion

Early Developments

During the centuries when space travel was only a fantasy, researchers in the sciences of astronomy, chemistry, mathematics, meteorology, and physics developed an understanding of the solar system, the stellar universe, the atmosphere of the Earth, and the probable environment in space. In the 7th and 6th centuries bc, the Greek philosophers Thales and Pythagoras noted that the Earth is a sphere; in the 3rd century bc the astronomer Aristarchus of Samos asserted that the Earth moved around the Sun. Hipparchus, another Greek, prepared information about stars and the motions of the Moon in the 2nd century bc. In the 2nd century ad Ptolemy of Alexandria placed the Earth at the centre of the solar system in his cosmic scheme, now called the Ptolemaic system.

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Scientific Discoveries

Not until some 1,400 years later did the Polish astronomer Nicolaus Copernicus systematically explain that the planets, including the Earth, revolve about the Sun. Later in the 16th century the observations of the Danish astronomer Tycho Brahe enabled Kepler to formulate the laws of planetary motion. Galileo, Edmond Halley, Sir William Herschel, and Sir James Jeans were other astronomers who made contributions pertinent to astronautics.

Celestial Models by Ptolemy and Copernicus

In the 2nd century ad, Claudius Ptolemy proposed a detailed version of the geocentric, or earth-centered, picture of the universe, already ancient in his day. His model (shown left) depicts the earth as stationary, with the planets, moon, and sun moving around it. Ptolemy’s system was accepted by astronomers and religious thinkers alike for over a thousand years. It was not until the 16th century that Nicolaus Copernicus revived another ancient idea, the heliocentric, or sun-centered, model of the universe. The new model was rejected by the church, but it gradually gained scientific acceptance. Copernicus’ data were no more accurate than Ptolemy’s, but his ideas fitted in better with the new physics that was developed in the 17th century.

Physicists and mathematicians also helped to lay the foundations of astronautics. In 1654 the German physicist Otto von Guericke proved that a vacuum could be maintained, refuting the old theory that nature “abhors” a vacuum. In the late 17th century Sir Isaac Newton formulated the laws of universal gravitation and motion. Newton’s laws of motion established the basic principles governing the propulsion and orbital motion of modern spacecraft.

Despite the scientific foundations laid in earlier ages, however, space travel did not become possible until the advances of the 20th century provided the actual means of rocket propulsion, guidance, and control for space vehicles.

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Rocket Propulsion

The techniques of rocket propulsion also originated long ago. Ancient rockets used gunpowder as fuel, very much as in fireworks today. In ad 1232 in China, the city of Kaifeng was reportedly defended against the Mongols by the use of rockets. From the Renaissance onwards, references were made to the proposed or actual military use of rockets in European warfare. As early as 1804 the British army established a rocket corps equipped with rockets that had a range of about 1,830 m (6,000 ft).

In the United States, the foremost pioneer in rocket propulsion was Robert Goddard, a Professor of Physics at Clark College (now Clark University). He began experimenting with liquid fuels for rocketry in the early 1920s and launched the first successful liquid-propelled rocket on March 16, 1926. During the same general period, studies on spaceships and rocket propulsion were being conducted in several parts of the world. About 1890 Herman Ganswindt, a German law student, conceived of a solid-propellant spaceship that demonstrated his marked awareness of the stability problem. Konstantin Tsiolkovsky, a Russian schoolteacher, published in 1903 A Rocket into Cosmic Space, which proposed the use of liquid propellants for spaceships. In 1923 a German mathematician and physicist, Hermann Oberth, published Die Rakete zu den Planetenräumen (The Rocket into Interplanetary Space). The book was supplemented by Walter Hohmann, a German architect, who published in 1925 Die Erreichbarkeit der Himmelskörper (The Possibility of Reaching Celestial Bodies), which contained the first detailed calculation of interplanetary orbits.

World War II provided the impetus and motivation for the development of long-range sub-orbital rockets. The United States, the USSR, Great Britain, and Germany simultaneously developed rockets for military purposes. The most successful were the Germans, who developed the V-2 (a liquid-propellant rocket used in the bombardment of London) at Peenemünde, a village near the Baltic coast. At the close of the war, the US Army brought back a number of the V-2s, which were then used in the United States, in vertical flights, for experimental research. Some German engineers went to the USSR after the war, but the leading rocket experts, including Walter Dornberger, and Wernher von Braun, went to the United States.

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