Optimization of immunity to helium tidal influences for the STEP experiment test masses

This paper describes an optimization strategy for the design of the three pairs of test masses in the STEP (satellite test of the equivalence principle) experiment. Using these designs, the allowable helium tidal amplitude is calculated for a STEP accelerometer sensitivity of , based on a worst case distribution of the liquid helium in the satellite's dewar. It is found that the hybrid belted/straight-cylinder geometry can be dimensioned such that the quadrupole moment and differential hexadecapole moment are identically zero. The resulting test mass designs are technically feasible. Some practical problems relating to their manufacture are discussed.