EURASTROS ascent trajectory and abort analysis

The EURASTROS study [1] was a joint study between Ariane Group GmbH and the German Aerospace Center (DLR), exploring astronautic transport capabilities of Ariane 6. The study included the preliminary design of a crew module (CM) [2], a service module (SM) [3], a performance analysis of possible Launch Abort System (LAS) concepts and a cost analysis [4]. This paper presents the work performed with the purpose to define the general ascent strategy and to design suitable end-to-end abort strategies compatible with the mission and system requirements. It shows the selected reference ascent trajectory and covers detailed preliminary analyses of the exo- and endo-atmospheric abort scenarios regarded within the EURASTROS project. All analyses were closely tied to continuous optimization of the Ariane 6 ascent trajectory and corresponding iteration of achievable payload performances, using astronautic transport to an ISS orbit as reference study case. The conducted analyses explored multiple possibilities for performance adjustment in agreement with human rated mission requirements, while also respecting space debris mitigation standards. Eventually these investigations concluded in the proposal of 11 Mg propellant un-loading of the Upper Liquid Propulsion Module (ULPM) of the Ariane 64 (A64) with respect to standard GTO upper stage fuel, yielding a trajectory enabling for maximum performance and also sufficient safety. The crew module, envisioned for a total crew of up to three astronauts, was designed with close resemblance to the Apollo CM, with a Service Module (SM) for exo-atmospheric flight at the rear and a Launch Abort System (LAS) for endo-atmospheric abort at the front, but with volume reduced by 28 %. For the LAS design, the most promising configurations were designed towards minimum thrust allowing to reach a minimum safety distance of 200 m to the launch vehicle within 3.5 seconds after separation and to fulfill further safety requirements in case of an abort from launch pad. Simulations conducted at DLR concluded that the bare minimum thrust should exceed 950 kN for both concepts in order to meet imposed safety requirements. Based on these results a subsequent mass budget estimation yielded a total mass estimate between 4700 – 5400 kg for the LAS. The SM is based on the ASTRIS kick stage and utilizes the engine BERTA running on storable fuel. This module is dimensioned to provide continuous exo-atmospheric launch abort capabilities while preventing any potential impact on populated areas on European and Eurasian soil. For such an abort scenario, the Last Direct Re-entry Point (LDR) after which an abort-to-orbit would be executed, has been defined. Influences of the corresponding maneuver pitching angles on ballistic downrange as well as on required time for abort-to-orbit are explored and the SM minimum thrust was adjusted to yield sufficient performance capabilities. Eventually, six abort modes for exo-atmospheric flight are proposed and discussed