Vacuum thrust

In rocket engines, vacuum thrust refers to the thrust that the engine generates in a vacuum . The vacuum thrust is different from the starting thrust. This is due to the fact that the thrust of a rocket engine depends on the pressure ratio between the combustion chamber and the environment. This pressure difference is naturally greater in a vacuum. In the case of multi-stage rockets, usually only the launch thrust is mentioned for the engines of the first stage . For the stages above, which are operated in a vacuum, usually only the vacuum thrust is mentioned.

Examples

Engine		Start thrust	Vacuum thrust	use
	Rocketdyne RS-68	2,819 kN	3,314 kN	Delta IV first stage, Ares V first stage
	NPO Energomash RD-170	7,550 kN	7,900 kN	Energija 11K25 booster
	SNECMA Vulcain 1	815 kN	1,120 kN	Ariane 5 first stage
	Kuznetsov NK-33	1,505 kN	1,638 kN	N-1 first stage, modified to the Aerojet AJ26 in Kistler K-1
	RD-107 (on the outer blocks)	821 kN	995 kN	R-7 (and variants) outer blocks

literature

• Eugen Reichl, Aydoğan Koç: Space knowledge . 1st edition. Motorbuch Verlag, Nuremberg, 2006, ISBN 978-3-613-02666-7 .