DC Cancellation As a Method of Generating a t^2 Response and of Solving   the Radial Nonobservability Problem in a Concentric Free-Falling Two-Sphere   Equivalence-Principle Experiment in a Drag-Free Satellite
  This paper solves two major problems which have blocked a free-fall Equivalence-Principle (EP) in a satellite for 25 years: a semimajor-axis error between the two proof masses cannot be distinguished from an EP violation and the response to an EP violation only grows as t not t^2. Using the cancellation method described in this paper, the nonobservability problem can be suppressed and a t^2 response can be generated which lasts between 10^4 and 10^6 seconds depending on the cancellation accuracy. t^2 response times between 10^5 and 10^6 seconds are equivalent to a very tall (0.1 to 10 AU) drop tower with a constant gravitational field of 3/7 ge. 
Benjamin Lange