Editing Rocket (section)

===Engines===
{{Main|Rocket engine}}
[[File:Viking 5C rocketengine.jpg|thumb|upright|[[Viking (rocket engine)|Viking 5C]] rocket engine]]

Rocket engines employ the principle of [[jet engine|jet propulsion]].<ref name="RPE7"/> The rocket engines powering rockets come in a great variety of different types; a comprehensive list can be found in the main article, [[Rocket engine]]. Most current rockets are chemically powered rockets (usually [[internal combustion engines]],<ref>{{cite web |author=Charles Lafayette Proctor II |url=http://concise.britannica.com/ebc/article-9368065/internal-combustion-engine |title=internal combustion engines |publisher=Concise Britannica |access-date=2012-12-10 |url-status=dead |archive-url=https://web.archive.org/web/20080114004538/http://concise.britannica.com/ebc/article-9368065/internal-combustion-engine |archive-date=2008-01-14 }}</ref> but some employ a decomposing [[monopropellant]]) that emit a hot [[exhaust gas]]. A rocket engine can use gas propellants, [[Solid-fuel rocket|solid propellant]], [[liquid-propellant rocket|liquid propellant]], or a [[hybrid rocket|hybrid mixture of both solid and liquid]]. Some rockets use heat or pressure that is supplied from a source other than the [[chemical reaction]] of propellant(s), such as [[steam rocket]]s, [[solar thermal rocket]]s, [[nuclear thermal rocket]] engines or simple pressurized rockets such as [[water rocket]] or [[cold gas thruster]]s. With combustive propellants a chemical reaction is initiated between the [[fuel]] and the [[oxidizer]] in the [[combustion]] chamber, and the resultant hot gases accelerate out of a [[rocket engine nozzle]] (or [[nozzle]]s) at the rearward-facing end of the rocket. The [[acceleration]] of these gases through the engine exerts force ("thrust") on the combustion chamber and nozzle, propelling the vehicle (according to [[Newton's third law]]). This actually happens because the force (pressure times area) on the combustion chamber wall is unbalanced by the nozzle opening; this is not the case in any other direction. The shape of the nozzle also generates force by directing the exhaust gas along the axis of the rocket.<ref name="RPE7"/>