Recoverable booster

A booster rocket (or engine) is either the first stage of a multistage launch vehicle, or else a shorter-burning rocket used in parallel with longer-burning sustainer rockets to augment the space vehicle's takeoff thrust and payload capability. (Boosters used in this way are frequently designated "zero stages".) Boosters are traditionally necessary to launch spacecraft into low Earth orbit (absent a single-stage-to-orbit design), and are certainly necessary for a space vehicle to go beyond Earth orbit. The booster is dropped to fall back to Earth once its fuel is expended, a point known as booster engine cut-off (BECO). The rest of the launch vehicle continues flight with its core or upper-stage engines. The booster may be recovered and reused, as was the case of the Space Shuttle.

A booster rocket or engine is either the first stage of a multistage rocket or launch vehicle, or else a shorter-burning rocket used in parallel with longer-burning sustainer rockets to augment a space vehicle's takeoff thrust and payload capability. The latter are frequently designated "zero stages".

Boosters are traditionally necessary to launch spacecraft into low Earth orbit absent a single-stage-to-orbit design, and are necessary to go beyond Earth orbit. When the booster´s fuel is empty it is dropped to fall back to Earth, a point known as booster engine cut-off (BECO). The rest of the launch vehicle continues to fly with its core or upper-stage engines. The booster may be recovered and reused, as in the case of the Space Shuttle.

The SM-65 Atlas rocket used three engines, one of which was fixed to the fuel tank, and two of which were mounted on a skirt which dropped away at BECO. This was used as an Intercontinental ballistic missile (ICBM); to launch the manned Project Mercury capsule into orbit; and as the first stage of the Atlas-Agena and Atlas-Centaur launch vehicles.

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