In-orbit operation of Resolve Filter Wheel and MXS

The Resolve soft X-ray spectrometer is the high spectral resolution microcalorimeter spectrometer for the XRISM mission. In the beam of Resolve there is a filter wheel containing X-ray filters. Also in the beam is an active calibration source (the modulated X-ray source (MXS) which can provide pulsed X-rays to facilitate gain calibration. The filter wheel consists of 6 filter positions. Two open positions, one 55Fe source to aid in early mission spectrometer characterisation and three transmission filters: a neutral density filter, an optical blocking filter and a beryllium filter. The X-ray intensity, pulse period and pulse separation of the MXS are highly configurable. Furthermore, the switch–on time is synchronized with the space–craft’s internal clock to give accurate start and end times of the pulses. One of the issues raised during ground testing was the susceptibility of an MXS at high voltage to ambient light. Although measures were taken to mitigate the light leak, the efficacy of those measures must be verified in–orbit. Along with an overview of issues raised during ground testing, this article will discuss the calibration source and the filter performance in–flight and compare with the transmission curves present in the Resolve calibration database.