Nebula Public Library

Propulsion passivation is most of the time feasible for running missions, using thrusters and existing AOCS modes, whatever the number of tanks and for both monopropellant and bipropellant systems.
For monopropellant systems the propulsion passivation may be:
-Partial for tank(s) with membrane. All the hydrazine under the membrane may be depleted but the pressurant gas above the membrane cannot be depleted. The final tank pressure is close to typically 5 bars at the end of mission.

All spacecraft in Earth orbit are exposed to the risk of impact with Micrometeoroids and Orbital Debris (M/OD). Because of the large collision velocities, Hypervelocity Impacts (HVI) with M/OD may cause significant damage to various subsystems and components up to mission failure.

The APPS study work focusses on the critical technologies required to provide both servicing and support functions to a seismometer payload located on the lunar surface. Although the baseline payload (and by extension the reference mission) has specific requirements, the technology focus of the study allows the outputs to be of broader application to exploration missions to the moon and beyond.

The purpose of the study is to investigate the use of ASTs as sensors in modern AOCS. Relatively recently ASTs have developed into a mature technology offering high-performance autonomous attitude determination in relatively small packages.

The investigations into using ASTs used two different types of mission for reference. A large, high- performance scientific mission XMM, as one, and a typical geostationary telecoms mission as the other. Using baseline specifications for ASTs (AD(2) & AD(3)) the studies were performed with focus upon different aspects including: