(See Cover) When the Soviet Lunik raced past the moon and free of the earth last week, it did more than win a triumph for its designers. It also marked a turning point in the multibillion-year history of the solar system. One of the sun's planets had at last evolved a living creature that could break the chains of its home gravitational field.
After a few more moments on the evolutionary time scale, earth's restless social primate, man, can almost surely make himself felt throughout the system. Earth's life will no longer be confined to the earth. This startling development took place with explosive suddenness. Boys still in high school remember a time when sensible citizens considered space flight as impractical as hunting leprechauns. Only ten years ago the altitude record for rockets, 250 miles, was held a brilliant achievement. Only two years ago, the earth satellite, that humblest of space vehicles, seemed an almost impossible project.
Newton's Rails. But the basic rules of space flight have been known for centuries. The Chinese, who invented rockets about 1200, did not theorize about them, but Sir Isaac Newton's laws of motion, published in 1687, not only explained the principle that makes rockets fly but gave the essential sailing directions for space ships of the future. When a U.S. Atlas or an even bigger (for the present) Soviet space rocket roars into the sky. it runs on rails devised by the ill-tempered Sir Isaac, who sat in his English garden nearly 300 years ago and wondered why things move as they do, and why things fall. When a rocket engine shoots a jet of gas out of its tail cone, Newton's third law takes over: For every action there is an equal and opposite reaction. Acting in the opposite direction to that of the racing gases, a mighty force lifts the rocket off its launching pad. As long as the engine fires, the rocket climbs faster and faster, obeying Newton's second law: An unbalanced force acting on a body makes it accelerate in the direction of the force . . . When the engine burns out, the rocket continues upward under the control of Newton's first law: . . . A body in motion continues to move at constant speed in a straight line unless acted upon by an unbalanced force. As it rises, it slows and curves because an unbalanced force, the earth's gravitation, keeps pulling at it in obedience to Newton's law of gravity: Each particle of matter attracts every other particle with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.
Although the magic laws of Newton pointed clearly into the sky, no one apparently followed their lead until a shy, deaf, self-educated Russian schoolteacher, got to thinking about air travel in the 1890s. Konstantin Eduardovich Tsiolkovsky, born in 1857, wrote about space flight with amazing prescience. He chose the rocket as the only possible space engine and derived mathematically the speed that its exhaust gases would have to attain. He decided that it should burn liquid fuel. This conclusion he published in 1898, when not even an airplane had left the ground.