Direct measurement of STEP test mass quadrupole moments

A cryogenic torsion balance method is suggested to measure the residual quadrupole moments of the STEP test masses directly. The individual masses are placed on a torsion balance and the torque exerted by a rotating set of source masses is analysed. Conservatively, assuming a torque sensitivity of 10-13 N m, it appears that a quadrupole moment of 10-7 kg m2 can be detected.