What is Spacecraft propulsion?
[[File:RS-68 rocket engine test.jpg|thumb|An RS-68 rocket engine during a test at a NASA facility]] '''Spacecraft propulsion''' is the method that a [[spacecraft]] uses to control its movement through [[outer space]]. A spacecraft with no means of propelling itself is typically considered derelict. The problem of propelling a spacecraft has, predictably, existed since spacecraft themselves. Most spacecraft are propelled by [[Rocket engine|rocket engines]], which combust an explosive liquid fuel with liquid oxidizer (oxygen in a liquid state) to generate hot gas which expands and propels the spacecraft forward. == Methods == Many methods of spacecraft propulsion have been developed and practiced. Most work by accelerating a propellant to a very high speed and ejecting it from the spacecraft through a nozzle. === Chemical rocket === A chemical rocket works by mixing an explosive propellant with [[Oxygen|liquid oxygen]] and burning it under [[pressure]]. This releases a great amount of heat. It results in a rapidly expanding gas. This gas is then funneled out of the rocket's [[nozzle]] (usually a bell shape) and off into space. === Ion thruster === An [[ion thruster]] works by using [[static electricity]] or [[magnetism]] to accelerate [[Ion|ions]] ([[Atom|atoms]] with an [[electric charge]]) to very high speeds, and out of the thruster's nozzle. Ion thrusters make very little thrust but are very efficient. === Nuclear thermal rocket === A [[nuclear thermal rocket]] heats a propellant with heat from a [[nuclear reactor]] before expelling it through a nozzle. Nuclear thermal rockets are currently experimental, but will have decent [[thrust]] and high efficiency once put into practice. {{Emerging technologies}} [[Category:Spacecraft]]