Gravity gradient suppression in spaceborne atomic tests of the   equivalence principle
  The gravity gradient is one of the most serious systematic effects in atomic tests of the equivalence principle (EP). While differential acceleration measurements performed with different atomic species under free fall test the validity of EP, minute displacements between the test masses in a gravity gradient produces a false EP-violating signal that limits the precision of the test. We show that gravity inversion and modulation using a gimbal mount can suppress the systematics due to gravity gradients caused by both moving and stationary parts of the instrument as well as the environment, strongly reducing the need to overlap two species. 
Sheng-wey Chiow, Jason Williams, Nan Yu and Holger M\"uller
physics.atom-ph gr-qc physics.space-ph quant-ph