LIQUID GAUGING IN-SPACE - THE G-22 EXPERIMENT

As the life of a satellite is terminated when its onboard propellants are depleted, accurate knowledge of those remaining propellants throug hout a mission is essential. Whereas the measurement of propellant con tents ('liquid gauging') is a trivial matter on the ground, it is a mo st difficult task in space because of the microgravity conditions that prevail. , Motivated by the need to develop an accurate method of liq uid gauging in space, ESA sponsored the development at TechnoSystem (I taly) of two thermodynamic methods of liquid gauging: the Periodic Vol ume Stimulus Method (PVSM) and the Foreign Mass Injection Method (FMIM ). These methods were subsequently tested in space as the G-22 Get-Awa y-Special (GAS) Experiment aboard Shuttle flight STS-57 in June 1993. The space test was completely successful and showed good correlation w ith the results of ground experiments. The PVSM proved to be a precise method with good repeatability; the fill-factor error (difference bet ween actual and measured contents) was less than 0.6%. The FMIM proved to be less accurate, due to temperature effects and pressure-transduc er inaccuracies. Improvements to the FMIM have since been evaluated th eoretically.