Physics behind Spacecrafts

Repulsion
        The rocket engines that launch and propel spacecraft are of two main types: solid-propellant rockets, which use chemicals that burn in a fashion similar to gunpowder, and liquid-propellant rockets, which use liquid fuels and oxidizers carried in separate tanks. Most of the rockets that have launched American spacecraft have had several separate rocket stages; each stage is separately powered with its own fuel. After the fuel in each stage has been consumed, the empty stage drops away from the spacecraft.
      Because the technology to build space-launch vehicles is closely akin to that for long-range ballistic missiles, the United States and the USSR were the only two countries that had the ability to launch satellites from 1957 to 1965. In subsequent years France, Japan, India, and China launched Earth satellites of ever-increasing sophistication, and in May 1984 the 13-member European Space Agency began its own launch programme from a space centre at Kourou in French Guiana. The United States and the USSR, however, remained the only nations with launch vehicles capable of placing in orbit payloads of many tonnes-the prerequisite for manned space flight.
Launching and Re-entry

A space vehicle is launched from a specially constructed launchpad, where the space vehicle and the rocket that propels it are set up and carefully inspected before launching. The operation is supervised by engineers and technicians in the nearby control centre. When all preparations are complete, the rocket engines are fired and the rocket and spacecraft lift off.
            Re-entry poses the problem of slowing down a returning spacecraft so that it lands on Earth without being destroyed by aerodynamic heating. The space flights of the US Mercury, Gemini, and Apollo programmes overcame the problem of re-entry by protecting the leading surface of the returning capsule with a specially developed heat shield, made of metals, plastics, and ceramic materials that melt and vaporize during re-entry, thereby carrying off or dissipating the heat without damage to the capsule or the astronauts. The heat shield developed to protect the space shuttle during re-entry consists of a covering of ceramic tiles individually cemented to the shuttle's hull. Before the development of the space shuttle, which lands on a runway (see "Space Shuttle" below), all American manned spacecraft used the ocean to cushion the impact of landing; the astronauts and the capsules were retrieved quickly by helicopter and taken aboard waiting naval vessels. Soviet cosmonauts have landed on solid ground in various sites in Siberia.