Initial Galileo propulsion system in-flight characterization

The Galilee RetroPropulsion Module (RPM) has performed excellently throughout the first three years of mission operations. The RPM is a state-of-the-art, pressure-fed, bipropellant propulsion system, provided to NASA by Germany. Due to efficient navigation, propellant margin has substantially increased since launch, enabling extensive contingency maneuvering and the second asteroid flyby while maintaining the confidence level for successfully completing the orbital tour of the planet Jupiter, beginning in 1995. The RPM has responded very well to the challenges brought about by the attempts to deploy the Galileo High Gain Antenna. No thruster thermal instabilities have been observed during maneuvers through the end of 1992; however, lateral thruster performance shifts have been nonnegligible and remain unexplained. Nearly all Galileo thrusters are exceeding ground performance test levels by 1-7 percent.