Ground test results of the microvibration interference for the x-ray microcalorimeter onboard x-ray imaging and spectroscopy mission

Abstract

Resolve is a payload hosting an X-ray microcalorimeter detector operated at 50 mK in the X-Ray Imaging and Spectroscopy Mission (XRISM). It is currently under development as part of an international collaboration and is planned to be launched in 2023. A primary technical concern is the micro-vibration interference in the sensitive microcalorimeter detector caused by the spacecraft bus components. We conducted a series of verification tests in 2021-2022 on the ground, the results of which are reported here. We defined the micro-vibration interface between the spacecraft and the Resolve instrument. In the instrument-level test, the flight-model hardware was tested against the interface level by injecting it with micro-vibrations and evaluating the instrument response using the 50 mK stage temperature stability, ADR magnet current consumption rate, and detector noise spectra. We found strong responses when injecting micro-vibration at about 200, 380, and 610 Hz. In the former two cases, the beat between the injected frequency and cryocooler frequency harmonics were observed in the detector noise spectra. In the spacecraft-level test, the acceleration and instrument responses were measured with and without suspension of the entire spacecraft. The reaction wheels (RWs) and inertial reference units (IRUs), two major sources of micro-vibration among the bus components, were operated. In conclusion, the observed responses of Resolve are within the acceptable levels in the nominal operational range of the RWs and IRUs. There is no evidence that the resultant energy resolution degradation is beyond the current allocation of noise budget.