EXPERIMENTAL STUDY OF THE ARIANE 5 ATTITUDE CONTROL SYSTEM (SCA) PASSIVATION.

On the request of CNES, ESA/ESTEC has led a study on the disposal of the hydrazine reservoirs of the Ariane 5 Attitude Control System (SCA). ESTEC has asked ONERA to propose an experimental assessment of risks of icing in piping and of generation of large debris in space during the process. After an examination of test conditions that would be representativ e of the reality, some campaigns have been realized at ONERA - Center of the Fauga-Mauzac. The objectives were the validation of the disposal system conceived for the SCA, also the general understanding of phenomena and consecutively a definition of the general trends to observe for ejection of liquids in space, and the constitution of a validation database for the modeling of hydrazine venting Validation tests of the flight ejector performed with hydrazine have demonstrated that the passivation process could be done without obstructing the piping. Further tests proved that this kind of phenomenon could be simulated without hazards by using water as similarity fluid. An effervescent type injector could be appropriate in order to guarantee a fine pulverization of a liquid ejected in a vacuum.