Micrometeoroids are micron-sized dust particles orbiting at hypervelocities of a few tens of kilometers per second. Impacts on sensitive x-ray astronomical devices in space can degrade their performance and even lead to fatal loss of at least parts of their functionality, like in the case of two CCDs of the EPIC MOS1 camera aboard XMM-Newton. We summarize here the main parameters and effects of such micrometeoroid impacts on x-ray astronomical instrumentation in space, to serve as quick reference on this subject, e.g. for subsequent comparative studies. In particular, we list all related SRG/eROSITA events registered during the first two years of operations at the sun-Earth L2 point. None of these seven events has lead to any failure or significant reduction of instrument performance. Only bright pixels and column segments developed. They were either set to bad onboard or could be cured by computation of new offset maps or commanding of higher thresholds for individual pixels. Only one case was clearly associated with an intense optical light flash. Finally, we compare the number of registered events to predictions from interplanetary dust models of sporadic meteoroids from the interplanetary dust cloud and cometary meteoroid streams. The modelled dust fluxes for approximately 1 µm sized sporadic particles are in rough agreement with the number of events registered by eROSITA, while cometary meteoroid streams can most likely be excluded as origin of eROSITA hits.
eROSITA (extended ROentgen Survey with an Imaging Telescope Array) is the soft X-ray scientific payload on board the SRG (Spektrum-Roentgen-Gamma) mission. It was successfully launched from Baikonur in July 2019. Following a 101 days cruise phase, SRG reached its final orbit around the Sun-Earth Lagrangian point L2, from where it has carried out already four full-sky surveys. eROSITA is a complex instrument composed of seven identical co-aligned X-ray telescopes with a focal length of 1600mm and an aperture of 350mm. Each telescope is equipped with an independent CCD camera. The cold redundant ITC (Interface and Thermal Controller) manages all seven cameras as well as the thermal control of the telescope and the interface to the spacecraft. The cruise phase of SRG was used to verify that all systems had survived launch and no degradation in the functionality was present. Following that, the main science mission, comprised of an early Calibration and Performance Verification Phase, followed by the all-sky survey. This paper presents the performance of the eROSITA telescope during the first four complete all-sky surveys. It presents the challenges encountered during the telescope operations as well as the operations and mitigation strategies put in place to understand or minimize the effects of the space environment in L2, such as micrometeoroid hits and radiation damage of the detectors.
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