The Laser Interferometer Space Antenna (LISA) Pathfinder experiment successfully demonstrated that a future gravitational wave detector in space is possible with current technology. Results from a selection of the many experiments performed by this state of the art gravity gradiometer are presented in this thesis.

In the first half, groundwork for projection of test mass charging to the LISA mission will be provided by an analysis of the Pathfinder radiation monitor data. To do this, an existing GEANT4 model for the monitor is developed and a new component representing the on board processing of signal hits added.

The second half of this thesis relates to fundamental physics with gravity gradiometers, with an emphasis on measuring the gravitational constant in space. The measurements will be presented with arguments for a number of improvements so that future gradiometers can improve on the results outlined in this work.