Booster (rocket propulsion)

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The boosters of a Falcon Heavy are about to land
A "GEM-40" solid matter booster before mounting on a Delta II rocket
Retrieval of a space shuttle solid rocket (SRB)

In space technology and military missiles, a booster is an auxiliary missile that is used at launch and then dropped. It can be attached to the launcher or an external tank (as with the space shuttle ). Boosters are used to generate additional thrust during take-off.

Are they burned in conventional launchers in 40-60 km altitude, they are - usually some time before the end of firing the first rocket stage - separated and fall back to the surface, in the water or on the mainland. With the Chinese LM-2 and LM-3 missiles , the latter is the rule and particularly risky, as they are operated with highly toxic hydrazine and sometimes fall on fields or in residential areas (although mostly after warning for the respective region). The speed achieved by boosters in relation to the atmosphere is usually not high enough to cause them to burn up. Some larger boosters such as those of the Space Shuttle , the Ariane 5 and the Energija rocket land or land softly with the help of parachutes in order to be inspected for errors and possibly reused. The Falcon Heavy's boosters land vertically using engine recoil and landing legs.

Boosters are also used in aircraft and other atmospheric missiles to briefly increase thrust. For example, missiles with ramjet require a different drive source to achieve the minimum speed required for the engine. Small rocket boosters are also used to jump-start aircraft. Drones like the CL-289 are started from a standing start using a rocket booster, but larger military aircraft can often be optionally equipped with boosters in order to shorten the take-off distance with a JATO start.


According to the fuel used, a distinction is made between two types:

  • Liquid propellant boosters (Engl. Liquid rocket booster , in short LRB ) are mainly used in Soviet / Russian launch vehicles as Soyuz and Proton , but also Indian ( GSLV Mk II ) and Chinese (for example, LM-2E and LM-3B used rockets). On the Russian side in particular, however, one does not speak of boosters or auxiliary missiles , but of blocks of the first stage . On the US side, the Delta IV Heavy and the Falcon Heavy use LRBs so far . Liquid-Fly-Back Booster (LFBB) is a concept for liquid fuel boosters that are intended to reduce take-off costs by returning to the take-off site as an airplane.
  • Some launch vehicles also used a mix of SRB and LRB, e.g. B. at the European Ariane 44LP . With the Japanese H-2A , the mix was planned, but not implemented.

Often, depending on the payload mass, two or four boosters are used to guarantee symmetrical thrust ratios; However, these can also be achieved with a combination of three, six or nine boosters. At Energija , the boosters were bundled in pairs and the rocket could be used with two (realized), three or four such pairs of boosters. The Delta II used 3, 4 or 9 boosters. Some missiles such as the Atlas V can also use boosters in asymmetrical ratios; in this case the thrust vector of the booster still has to lead through the center of mass of the rocket.


  • G. Brüning, X. Hafer: Flight performances. Springer Verlag Berlin Heidelberg GmbH, Berlin Heidelberg 1978.
  • Ernst Messerschmid, Stefanos Fasoulas: Space systems. Springer Verlag Berlin Heidelberg, Berlin Heidelberg 2000, ISBN 978-3-662-09675-8 .

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