NASA launch vehicles (through 1989)
Rockets, Missiles, and Launch Vehicles
A rocket is a type of power plant, or engine, that is used to propel something (called a payload) by the high-velocity ejection of matter, usually exhaust gases. Burning some type of fuel in most types of rockets produces the exhaust gases. Rockets produce their power by the principle expressed in Newton's third law of motion-for every action there is an equal and opposite reaction. This reaction forces the rocket and its payload in the opposite direction. Some more advanced rockets produce their action in other ways.
A rocket is called a missile when it carries a weapon or warhead as the payload, which may be a nuclear weapon or a simple explosive charge. A ballistic missile is one that assumes a free-falling trajectory (or path) after an internally guided, self-powered ascent.
A rocket is called a launch vehicle when carrying a satellite or spacecraft. Some rockets begin as missiles and later become launch vehicles. For example, the Titan II rocket was originally designed to carry a nuclear warhead and was then called the Titan II missile. Later, the National Aeronautics and Space Administration (NASA) began using the Titan II to launch spacecraft. It was then called the Titan II booster or the Titan II launch vehicle.
There are two basic categories of launch vehicles-expendable launch vehicles and reusable launch vehicles, or ELVs. Rockets that are used only once are considered ELVs. ELVs have included the Scout, Saturn, Titan, Atlas, and Delta. The Space Shuttle is, in 2001, the only reusable launch vehicle.