Ground testing and flight demonstration of charge management of insulated test masses using UV-LED electron photoemission

Abstract

Abstract.The UV-LED mission demonstrates the precise control of the potential of electrically isolated test masses that is essential for the operation of space accelerometers and drag-free sensors. Accelerometers and drag-free sensors were and remain at the core of geodesy, aeronomy and precision navigation missions as well as gravitational science experiments and gravitational wave observatories. Charge management using photoelectrons generated by the 254nm UV line of Hg was first demonstrated on Gravity Probe B and is presently part of the LISA Pathfinder technology demonstration. The UV-LED mission and prior ground testing demonstrates that AlGaN UVLEDs operating at 255 nm are superior to Mercury vapor lamps because of their smaller size, lower power draw, higher dynamic range, and higher control authority. We show flight data from a small satellite mission on a Saudi Satellite that demonstrates AC charge control (UV-LEDs and bias are AC modulated with adjustable relative phase) between a spherical test mass and its housing. The result of the mission is to bring the UV-LED device Technology Readiness Level (TRL) to TRL-9 and the charge management system to TRL-7. We demonstrate the ability to control the test mass potential on an 89 mm diameter spherical test mass over a 20 mm gap in a drag-free system configuration. The test mass potential was measured with an ultra-high impedance contact probe. Finally, the key electrical and optical characteristics of the UV-LEDs showed less than 7.5% change in performance after 12 months in orbit.

Effective decrease of photoelectric emission threshold from gold plated surfaces

“…Photoelectric emission is used for charge control of test bodies in a number of applications, both realised, such as Gravity Probe B (GP-B) 1 , UV-LED 2 and LISA Pathfinder (LISAPF) 3 , and proposed, such as STEP 4 , LISA 5-7 , DECIGO 8 , BBO 9 , TAIJI 10 However GP-B, UV-LED and LISAPF were validated through empirical testing 2,14,15 , and subsequent in-flight performance 2,16,17 . This study reports on a proposed 'working' model to describe the sub-threshold electron emission from gold (section II), an experimental measurement campaign to validate the model (section III) and the results from it (section IV).…”

“…However GP-B, UV-LED and LISAPF were validated through empirical testing 2,14,15 , and subsequent in-flight performance 2,16,17 . This study reports on a proposed 'working' model to describe the sub-threshold electron emission from gold (section II), an experimental measurement campaign to validate the model (section III) and the results from it (section IV).…”

Differential optical shadow sensor for sub-nanometer displacement measurement and its application to drag-free satellites

“…We note that the DOSS does not occupy the top and bottom faces of the housing. These faces will be used for UV-LED based charge management [26], and a caging mechanism [27]. An additional interferometric displacement sensor required for state of the art gravitational wave detection would be accommodated in a corner of the housing.…”

Au(111) Surface Contamination in Ambient Conditions: Unravelling the Dynamics of the Work Function in Air

“…[ 5 ] This airborne contamination is known to form a layer that changes the wettability of these surfaces rendering them hydrophobic upon air exposure. [ 1,6 ] Gold is widely employed both in applied and fundamental research (e.g., optoelectronic device fabrication, adsorption studies, and electrochemical detection) and it is also a suitable material for gravitational waves detection (Gravity Probe B, [ 7 ] UV‐LED, [ 8 ] and LISA Pathfinder [ 9 ] ). The control of adventitious contamination is of critical importance for the above‐cited applications, as surface cleanliness and uniformity are among the key requirements to obtain reliable and reproducible results.…”