UV LED charge control of an electrically isolated proof mass in a Gravitational Reference Sensor configuration at 255 nm

TL;DR

This paper demonstrates the use of UV LEDs at 255 nm for charge control of proof masses in space, showing their durability, effectiveness with various coatings, and potential for future space missions.

Contribution

It introduces UV LEDs as a space-qualified alternative to mercury lamps for proof mass charge control and evaluates their performance with different carbide coatings.

Findings

UV LEDs withstand space qualification tests with minimal performance change.

Carbide coatings exhibit quantum efficiencies of 3.8-6.8×10^-7 and reflectivities of 0.11-0.15.

Proof mass potential can be controlled remotely in a GRS-like setup.

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 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.