Current proposals for the introduction of reusable components in space transportation focus on winged fly-back boosters, powered by liquid rocket engines. Such vehicles were under consideration for a Space Shuttle upgrade, but are also considered for possible future evolution of Ariane 5. Therefore, a similar design was under investigation within the German future launcher technology research program ASTRA under the lead of DLR-SART from 1999 to 2004.
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.
