Liquid Fly-back Booster (LFBB)

Current proposals for the introduction of reusable components in space transportation focus on winged fly-back boosters, powered by liquid rocket engines. Such vehicles are under consideration for a Space Shuttle upgrade, and as a possible future evolution of Ariane 5. Therefore, a similar design is under investigation within the German future launcher technology research program ASTRA under the lead of DLR-SART.

Y8 boosters separating from the expendable core stage

The reference expendable core space transportation system of the DLR study is the Ariane 5 ECB with cryogenic upper stage, but skipped SRB. The basic requirement is to reach almost the same commercial GTO payload as for the launcher with solid rocket boosters. The replacement of powerful solid rocket-motors by liquid propellant engines requires the utilization of high mass flow engine designs. Such large motors considerably contribute to the total development cost of these space transportation vehicles, if a new lay-out is selected. To obtain a substantial reduction in space transportation price, the employment of existing or derived engines is of high interest.

The following table lists all reusable booster stages investigated by SART so far, sorted by propellant combinations.

LOX-Kerosene
engine type	configurraton type
RD-180	Twin Body
RD-180	Single Body Catamaran
NK-33	Single Body
RS-76	Twin Body

LOX-Methane
engine type	configurraton type
SART SE-12	Twin Body

LOX-LH2
engine type	configurraton type
Vulcain 3 - 35	Twin Body (ASTRA reference)
Vulcain 3 - 50	Single Body
Vulcain 3 - 50	Twin Body (ASTRA size variation)
RD 0120	Single Body Catamaran
SART SE - 21	Twin Body