Liquid fly-back booster
Liquid Fly-back Booster (LFBB) was a German Aerospace Center's (DLR's) project concept to develop a liquid rocket booster capable of reuse for Ariane 5 in order to significantly reduce the high cost of space transportation and increase environmental friendliness. LFBB would replace the existing solid rocket boosters, which provided the majority of thrust from liftoff to separation.