EURASTROS capsule design and re-entry analysis
Creators: name:  P. MARQUARDT 
name:   M. FERTIG 
name:   T. REIMER 
name:   A. GULHAN 
Publisher: name: Proceedings of  the 9th European Conference for Aerospace Sciences. Lille, France, 27 June - 1 July, 2022
Year: 2022
Subjects: HUMAN
SPACEFLIGHT

description: The EURASTROS study was a joint study between Ariane Group GmbH and German Aerospace Center (DLR), exploring the astronautic transport capabilities of Ariane 6. An overview of the study is given in [1]. The study included preliminary design of a crew module (CM), a service module (SM) [2], a launch abort system concept (LAS) with end-to-end abort capability [3], and a cost analysis [4]. The crew module is a capsule design derived from the Apollo capsule reduced in volume by 28% that can accommodate up to three astronauts. The main driver of the design choice is the fast and cost-effective development of the capsule due to heritage of the Atmospheric Reentry Demonstrator (ARD) and the existing databases of the Apollo program. The lift-off mass of the capsule is approximately 5000 kg. Approximate methods were used to evaluate acceptable locations of the center of gravity for statically stable flight at a target hypersonic trim angle of attack. Furthermore, an aerodynamic database was generated using the same approach. The aerodynamic coefficients were used to analyze the trajectory of the capsule for nominal and off-nominal re-entry as well as for launch abort scenarios to identify critical trajectory points for the design of the capsule. These design points define the maximum loads in terms of heat flux, dynamic pressure, and acceleration. The points are identified by analyzing return scenarios for ISS return and launch abort at different altitudes for controlled and uncontrolled/ballistic re-entry. A detailed analysis of the ascent trajectory and the resulting atmospheric and exo-atmospheric abort trajectories is presented in [3]. High resolution, steady-state, 3-dimensional computational fluid dynamics (CFD) simulations including real gas effects and chemical nonequilibrium have been carried out to determine the heat flux distribution on the front and back shell of the capsule at the critical trajectory points and to cross validate the aerodynamic database. For the simulations, the CFD solver TAU was used. The computational grid comprises a structured grid layer to allow for the determination of the surface heat flux with high accuracy. The normal resolution of the grid on the capsule surface is of the order of the local mean free path length. Furthermore, the grid is adaptively refined to accurately capture the Mach number and pressure gradients in the flow field, e.g., the bow shock. Turbulent flow and chemical equilibrium is assumed for the simulations at peak dynamic pressure. The points of maximum heat flux occur at much higher Mach number and altitude such that laminar flow and chemical nonequilibrium is considered. For the TPS design, the ablator material ZURAM was selected as baseline which has been developed by DLR and is comparable in properties and performance to materials like PICA and ASTERM. For the TPS sizing, the total recession of the ablator material and the thermal insulation of the TPS material were analyzed. A transient thermal finite element method (FEM) simulation identified the thermal insulation as the main driver for the TPS sizing. The structure of the capsule is designed as a highly integrated metallic structure consisting of a cylindrical part with horizontal floor and a conical part on top, reinforced with orthogrid stiffeners on the outside of the pressure vessel. Two load cases, i.e., pressure difference between capsule internal and outside vacuum, and deceleration load during reentry, were investigated via FEM. The analysis results showed that the differential pressure load case is the dominating one for the assumptions made. Preliminary thickness values and masses for TPS and structure were determined. [1] Ali Gulhan, Marco Wolf, et.al.; An Overview of the EURASTROS Study, EUCASS-3AF CONFERENCE, LILLE, FRANCE, 2022. [2] Alex Plebuch, Pascal Marquardt, Marco Wolf; System design of EURASTROS reference configurations and mission, EUCASS-3AF CONFERENCE, LILLE, FRANCE, 2022. [3] Ingrid Dietlein, Pascal Marquardt, Kevin Bergmann; EURASTROS ascent trajectory and abort analysis, EUCASS-3AF CONFERENCE, LILLE, FRANCE, 2022. [4] Andy Braukhane, Alex Plebuch, Thomas Renk; EURASTROS demonstration plan and cost analysis, EUCASS-3AF CONFERENCE, LILLE, FRANCE, 2022.