Two new launchers, Soyuz and Vega, are scheduled to enter operation in the coming months at Kourou spaceport, increasing the range of missions able to be launched by Western Europe. It is however already foreseen that improvements of Vega might be required to at least partially fill the performance gap with the Soyuz launch vehicle and to allow, for instance, Galileo satellite replacement single launch missions. Indeed, the Soyuz launch vehicle which will be launched from the French Guiana Space Centre, with its over 2700 kg payload capacity in GTO, is oversized for such a mission.
A promising concept is currently being investigated by DLR’s group for Space Launcher Systems Analysis (SART), namely a two-stage to orbit launch vehicle (TSTO) based on technologies already existing in Europe and aiming at exploiting synergies with other European programs, in order to keep development and production costs low. All the studied configurations are based on a solid rocket motor first stage, derived from the P80 FW used on Vega. The second stage is based on the 180 kN expander cycle cryogenic Vinci engine.
First estimations done by SART in 2007 showed that a P80 (first stage of Vega) with a H18 propelled by Vinci (also referred to as VENUS F) could inject up to almost 2700 kg in the reference orbit of the Vega launch vehicle 700 km x 700 km, 90°. Considering a P100 for the first stage and an upper stage with the optimized propellant loading H17, more than 3000 kg can be injected into the reference orbit of the Vega launch vehicle. For a Galileo replacement mission a MTO (medium transfer orbit) (250 km x 23216, 56°) will be probably used. The payload performance of a P100 + H17 in this orbit is almost 1000 kg. This performance decreases to almost 950 kg for a GTO orbit. However this would not be sufficient for a Galileo replacement satellite equipped with an apogee engine for the circularization and the corresponding propellant.
Since late 2010, new variants of TSTO launch vehicle with bigger first stage engines are investigated. First stage solid rocket motors with up to 160 tons of propellant could be produced easily with the same techniques as P80 and with only minor adaptations of the production facilities. In a first step, the diameter of the first stage has been set to 3 m, as for the P80 and for the EAP (Ariane 5 solid rocket booster). In the next steps of study, a modification of this diameter is however foreseen for several reasons. Versions with two additional strap-on boosters have also been considered to assess a potential increase of the performance. After an optimization of the propellant loading of the second stage, a pre-sizing of the selected launch vehicles has been done. Using the DLR-SART in house programs, the feed and pressurization system and the structure of launcher, among others, have been pre-sized.
The targeted payload performance was set at around 1500 kg to GTO with the reference version and up to 3000 kg to GTO with the help of strap-on boosters.