Analysis of Effectiveness of Phoenix Entry Reaction Control System

Interaction between the external flowfield and the reaction control system thruster plumes of the Phoenix capsule during entry has been investigated. The analysis covered rarefied, transitional, hypersonic, and supersonic flight regimes. Performance of pitch, yaw, and roll control authority channels was evaluated, with specific emphasis on the yaw channel due to its low nominal yaw control authority. Because Phoenix had already been constructed and its reaction control system could not be modified before flight, an assessment of reaction control system efficacy along the trajectory was needed to determine possible issues and to make necessary software changes. Effectiveness of the system at various regimes was evaluated using a hybrid direct simulation Monte-Carlo-computational fluid dynamics technique, based on direct simulation Monte-Carlo analysis code and general aerodynamic simulation program, the Langley aerothermal upwind relaxation algorithm code, and the fully unstructured 3-D code. Results of the analysis at hypersonic and supersonic conditions suggest a significant aeroreaction control system interference, which reduced the efficacy of the thrusters and could likely produce control reversal. Very little aeroreaction control system interference was predicted in rarefied and transitional regimes. A recommendation was made to the project to widen controller system deadbands to minimize (if not eliminate) the use of reaction control system thrusters through hypersonic and supersonic flight regimes, where their performance would be uncertain.