Fluid Mechanics of Zero-G Propellant Transfer in Spacecraft Propulsion Systems

Abstract

The basic requirement of a transfer system for storable propellants is to provide propellant in sufficient quantity to assure proper engine operation. The main propulsion systems of advanced spacecraft will make many restarts after long coast periods during which the propellant is in a weightless state. Various vehicle motions, such as rotational maneuvers, may result in dislocation of propellant from the region of the outlet of un-baffled tanks. In this paper a promising method of propellant relocation, settling by means of an induced gravitational field, is considered. Small axially directed rockets are used to generate a low g-field for settling the propellant. The value of the acceleration that must be exceeded to assure propellant flow from top to bottom of the tanks (the critical acceleration) has been determined by a numerical solution of the interface equation. This acceleration is exceeded by several orders of magnitude for practical settling rocket systems. The fluid mechanics of the ensuing “settling” flow and the subsequent rebound or “geysering” is discussed and a criterion for settling time is suggested. These results were obtained through scaled experiments conducted at 1-g conditions.