Experimental study of the Ariane 5 attitude control system (SCA) passivation

Abstract

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 representative 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.

Thermodynamic Model of Hydrazine that Accounts for Liquid-Vapor Phase Change

“…A Helmholtz potential that exhibits regions of instabilities, that is, regions in which the stability conditions [Eqs. (3) and (4)] are infringed, in a given (T ; v) domain of interest contains in principle all of the required information pertinent to the single-and multiphase thermodynamics of the medium it describes. In particular, and of much signi cance here, it allows to perform a complete quantitative analysis of the phase equilibria of the medium.…”

“…The need to nd qualitatively meaningful and quantitatively accurate answers imposes the necessity to study numerically the liquid N 2 H 4 ow eld in critical portions of the SCA venting lines with the supporting complement of experimental investigations. 3 In this regard, a mandatory ingredient for successful analysis is the availability of a thermodynamic model of N 2 H 4 with the theoretically builtin capability to account for phase changes. The main purpose of this paper is to describe the work performed to develop a preliminary model applicable to liquid-vapor phase transition.…”