Cryogenic Propellant Management during Ballistic Flight Phases

Abstract

In low gravity flight phases without main thrust activations, the liquid tends to wet or migrate along the walls or interior structures within the spacecraft tanks. In many cases a combination of buoyancy effects, e.g. during RCS firing, and capillarity becomes effective. Proper propellant management of liquid and gas is essential in order to ensure provision of bubble-free liquid to the engines under all specified conditions. This becomes even more difficult when cryogenic liquids (e.g. LH2 and LOX) are being stored in the tanks. Propellant vaporization and bulk boiling then have to be taken into account. In cryogenic tanks vaporization can be caused by incident heating through the tank walls, heating from the engine to connected lines and equipment, and by pressure fluctuations in the tank due to venting or pressurant cooling. An additional aspect is pure gas venting, e.g. to depressurize the tank or to run an RCS system. At Astrium different concepts concerning propellant management in tanks were matured with the goal to reach a TRL 6 technology readiness level in 2012. In this context a development program, named Cryogenic Upper Stage Technologies (CUST) was initiated by ESA in order to develop promising concepts to a level such that they can be considered as a potential application e.g. for the next generation of upper stages. The present study focuses on the recent advances at Astrium in this field of development. Two Propellant Management Device (PMD) concepts for cryogenic liquids are being discussed. Goal of the PMDs is to provide bubble free propellant to the engine in case of engine restart. Details concerning the maturation, including an overview concerning verification tests are being given. Testing concerned experiments under 1g as well as 0g conditions (drop tower and sounding rocket). The presented results show the readiness of the proposed concepts.