ESA GNC Conference Papers Repository

The paper describes the work performed by SENER Ingeniería y Sistemas to design a reusable orbital vehicle thruster configuration and control strategy. The reusable orbital vehicle is meant to carry out missions lasting from few days up to two months with automatic re-entry. The vehicle's mission scenarios include microgravity experimentation, earth observation and rendezvous and capture of payloads deployed by the International Space Station. The thruster configuration design is carried out in 4 steps. 1. The starting point of the Reaction Control System (RCS) design is the identification of the requirements. This is performed defining all the Guidance, Navigation and Control (GNC) Use Cases (UC) and capturing from each UC the RCS requirements. 2. An initial configuration of thrusters is selected to fulfill each UC requirement. This approach involves different trade-off since the re-entry UC requires quite energetic force and torques, while controlling the vehicle's position during rendezvous and capture requires dim forces and torques 3. The initial configuration is refined to be fail operational and additional thrusters are included. 4. A final optimization of the RCS configuration is performed following a holistic approach. This optimization lead to the following improvements: - The most efficient thruster's combination is always selected to be nominally used. - Smaller thrusters are selected for the vehicle's front side in order to simplify their installation, improve fine pointing with thrusters in orbit and reduce consumption. - The thruster locations are fine tuned to be completely out from the lower part of the vehicle covered by ceramic material. The thruster's configuration optimization is performed under strict control strategy constraints. The designed algorithms, allow to translate the required GNC force and torques to thrusters firings. In particular the optimization account for: - Consumption minimization, - Agility maximization, - Simultaneous thrusters actuation minimization, - Number of firings minimization, - Thrust resolution maximization. Space Rider has been selected as application for this work. Space Rider is the space program managed by ESA under Thales Alenia Space primeship for the development of a reusable robotic spacecraft. The program has successfully passed ESA Preliminary Requirements Review. The configuration proposed for Space Rider requires 8x20N thrusters located in the front of the vehicle and 12x90N thrusters located in the rear of the vehicle. The configuration fulfills all identified requirement. In particular the requirement of being Fail Operational is also satisfied. The configuration layout is unusual for orbital vehicles in order to comply with the limitations imposed by a reentry vehicle and the specific needs of each mission scenario.