In order to support the reflection of DLR Space Agency concerning the next European generation of launch vehicles, the SART group is studying and pre-designing different concepts for a launch vehicle able to inject between 3 and 8 tons in a GTO (Geo-Transfer Orbit). After an analysis of the expected satellite market, it was decided to consider a reference version with a payload to GTO of 4 tons. The lower limit of 3 tons is reached by the de-loading of the launcher and the upper one by adding solid rocket boosters. Relatively small boosters have been selected in order to easily adapt the launch vehicle to payload mass between 4 and 8 tons with an adapted number of boosters.
Only two stage configurations have been studied until now and both stages use cryogenic propellant (LH2 and LOX). The design constraints imposed the use of a maximum of two engines for the first stage, to reduce recurring costs. In addition, in the reference version the launch vehicle should be able to blast-off without solid rocket booster. As a consequence the Vulcain 2 engine cannot be used and a more powerful engine with a thrust of about 1900 kN at sea level should be developed. A gas generator cycle with characteristics close to those of Vulcain 2 has been selected for this engine. It will however need to have the capability to be throttled-down in order to keep the acceleration at an acceptable level. The second stage is based on the high performance expander cycle cryogenic Vinci engine which provides a thrust of 180 kN with a specific impulse in vacuum of 464 s. The currently studied staging, determined thanks to an optimization based on trajectory analysis results is a H220-H23 (i.e. 220 tons cryogenic propellant in the first stage and 23 tons cryogenic propellant in the second stage).
The first stage has, as Ariane 5, a diameter of 5.4 m. For the second stage a smaller diameter has been chosen to allow the use of an integral LH2 tank, aiming at reducing the structural index.