Paper 13093-240
In-orbit selection of cryocooler drive frequencies for XRISM/Resolve
Abstract
The XRISM/Resolve instrument cooling system uses adiabatic demagnetization refrigerators (ADRs) to cool the detectors to 50 mK and Joule-Thomson and Stirling cryocoolers to reduce heat load on the He tank supporting the ADRs. Resolve was designed with tunable cryocooler drive frequencies so that interference could be avoided. The cryocooler generated micro-vibration changes with drive frequency and that micro-vibration causes interference and degrades instrument performance. Poor drive frequency choices have been shown to dramatically impact ADR cooling power, temperature stability, detector noise, and degrading spectroscopic performance. However, some choices are free of these features, allowing the instrument to satisfy its performance requirements with significant margin. Thus, the choice of drive frequencies is critical to achieving peak instrument performance. The drive frequencies of the Joule- Thomson cooler, near 52 Hz, and the Stirling coolers, near 15 Hz, were adjusted in three scan sequences while measuring interference to narrow candidate frequency options. Choices were based on stability of the 50 mK control thermometer, changes in the ADR demagnetization rate, and changes in detector noise. These scans were performed routinely during ground testing. Surprisingly though, the results were not repeatable after the Dewar was warmed and recooled but were repeatable when remeasured during the same test campaign. Since the good/bad drive frequencies change during Dewar warmup/cooldown, and possibly after vibration events, the drive frequencies could not be finalized before launch. This paper describes the cryocooler frequency scan measurements and compares the results during instrument commissioning to those performed during ground tests.
Presenter
Gary A. Sneiderman
NASA Goddard Space Flight Ctr. (United States)
Gary Sneiderman is NASAs lead Instrument Systems Engineer and engineering authority for the Resolve instrument for the X-Ray Imaging and Spectroscopy Mission (XRISM). He served in the same role on the two preceding missions, the SXS instrument for Astro-H/Hitomi, and the XRS instrument for Astro-E2/Suzaku. His experience on these projects and their international instrument developments spans two decades and three complete project life cycles. Gary began his professional career at Goddard Space Flight Center’s Special Payloads Division in 1988 where he supported the rapid development of numerous small satellites and Shuttle attached payloads. He served as the lead mechanical engineer for the Sub-millimeter Wave Astronomy Satellite from selection to launch, and then transitioned to instrument systems engineering with his assignment to Astro-E2 in 2000. Gary holds a MS in Mechanical Engineering from George Washington University, and a BS in Mechanical Engineering from Tulane University.