Editing Jet engine (section)

===Rocket===
{{Main article|Rocket engine}}
[[File:Rocket thrust.svg|thumb|right|Rocket engine propulsion]]
The rocket engine uses the same basic physical principles of thrust as a form of [[reaction engine]],<ref>[https://www.collinsdictionary.com/dictionary/english/reaction-engine Reaction engine] definition, Collins online dictionary: ''"an engine, such as a jet or rocket engine, that ejects gas at high velocity and develops its thrust from the ensuing reaction"'' (UK), or ''"an engine, as a jet or rocket engine, that generates thrust by the reaction to an ejected stream of hot [[exhaust gas]]es, ions, etc."'' (US) (retrieved 28 June 2018)</ref> but is distinct from the jet engine in that it does not require atmospheric air to provide oxygen; the rocket carries all components of the reaction mass. However some definitions treat it as a form of [[jet propulsion]].<ref>[https://www.collinsdictionary.com/dictionary/english/jet-propulsion Jet propulsion], Collins online dictionary definition. (retrieved 1 July 2018)</ref>

Because rockets do not breathe air, this allows them to operate at arbitrary altitudes and in space.<ref>AC Kermode; ''Mechanics of Flight'', 8th Edition, Pitman 1972, pp. 128–31.</ref>

This type of engine is used for launching satellites, [[space exploration]] and crewed access, and permitted [[landing on the Moon]] in 1969.

Rocket engines are used for high altitude flights, or anywhere where very high accelerations are needed since rocket engines themselves have a very high [[thrust-to-weight ratio]].

However, the high exhaust speed and the heavier, oxidizer-rich propellant results in far more propellant use than turbofans. Even so, at extremely high speeds they become energy-efficient.

An approximate equation for the net thrust of a rocket engine is:

:<math>F_N = \dot m\, g_0\, I_\text{sp,vac} - A_e\, p \;</math>
Where <math>F_N</math> is the net thrust, <math>I_\text{sp,vac}</math> is the [[specific impulse]], <math>g_0</math> is a [[standard gravity]], <math>\dot m</math> is the propellant flow in kg/s, <math>A_e</math> is the cross-sectional area at the exit of the exhaust nozzle, and <math>p</math> is the atmospheric pressure.

{| class="wikitable"
|-
! Type
! Description
! Advantages
! Disadvantages
|-
![[Rocket]]
|Carries all propellants and oxidants on board, emits jet for propulsion<ref>{{cite web|url=http://www.grc.nasa.gov/WWW/K-12/airplane/rockth.html |title=Rocket Thrust Equation |publisher=Grc.nasa.gov |date=2008-07-11 |access-date=2010-03-26}}</ref>
|Very few moving parts. Mach 0 to Mach 25+; efficient at very high speed (> Mach 5.0 or so). Thrust/weight ratio over 100. No complex air inlet. High compression ratio. Very high-speed ([[hypersonic]]) exhaust. Good cost/thrust ratio. Fairly easy to test. Works in a vacuum; indeed, works best outside the atmosphere, which is kinder on vehicle structure at high speed. Fairly small surface area to keep cool, and no turbine in hot exhaust stream. Very high-temperature combustion and high expansion-ratio nozzle gives very high efficiency, at very high speeds.
|Needs lots of propellant. Very low [[specific impulse]] – typically 100–450 seconds. Extreme thermal stresses of combustion chamber can make reuse harder. Typically requires carrying oxidizer on-board which increases risks. Extraordinarily noisy.
|}