Title UV LED charge control of an electrically isolated proof mass in a GRS at 255 nm Publication Type Journal Article Year of Publication Submitted Authors Balakrishnan K, Sun K-X, Alfauwaz A, Almajed M, Alrufaydah M, Althubiti S, Aljibreen H, Buchman S, Byer R, Conklin J, DeBra DB, Hanson J, Hultgren E, Al-Saud T, Shimizu S, Soulage M, Zoellner A Abstract 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 smaller size, lower power draw, higher dynamic range, and higher control authority. 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$\times10^{-7}$ one week after coating and 1.1-1.4$\times10^{-7}$ after 16 months of storage in a dry N₂ environment, and reflectivities of 0.11-0.15. 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 charge control without introducing dynamic forcing of the spacecraft. Finally we provide a look ahead to an upcoming technology demonstration mission of UV LEDs. URL http://arxiv.org/abs/1202.0585