  Precise control over the potential of an electrically isolated proof mass is
necessary for the operation of devices such as a Gravitational Reference Sensor
(GRS) and satellite missions such as LISA. We show that AlGaN UV LEDs operating
at 255 nm are an effective substitute for Mercury vapor lamps used in previous
missions because of their ability to withstand space qualification levels of
vibration and thermal cycling. After 27 thermal and thermal vacuum cycles and 9
minutes of 14.07 g RMS vibration, there is less than 3% change in current draw,
less than 15% change in optical power, and no change in spectral peak or FWHM
(full width at half maximum). We also demonstrate UV LED stimulated
photoemission from a wide variety of thin film carbide proof mass coating
candidates (SiC, Mo2C, TaC, TiC, ZrC) that were applied using electron beam
evaporation on an Aluminum 6061-T6 substrate. All tested carbide films have
measured quantum efficiencies of 3.8-6.8*10^-7 and reflectivities of 0.11-0.15,
which compare favorably with the properties of previously used gold films. We
demonstrate the ability to control proof mass potential on an 89 mm diameter
spherical proof mass over a 20 mm gap in a GRS-like configuration. Proof mass
potential was measured via a non-contact DC probe, which would allow control
without introducing dynamic forcing of the spacecraft. Finally we provide a
look ahead to an upcoming technology demonstration mission of UV LEDs and
future applications toward charge control of electrically isolated proof
masses.
