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Abstract

eROSITA (extended ROentgen Survey with an Imaging Telescope Array) is the primary scientific payload on board the SRG (Spektrum Röntgen Gamma) mission, successfully launched from Baikonur in July 2019. Following a 101 days cruise phase, SRG reached its final orbit around the Lagrangian point L2, where it will carry out its mission of making a full survey of the X-ray sky. 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. In addition, the critical one-time operations of opening the telescope cover and cooling the CCD detectors to -90°C were carried out during this phase. The extreme reliance on the instrument controller (ITC) for the survival of the telescope, in addition to the thermal control an data handling systems that are under control of the ITC, make it pertinent to report on how these systems behaved in the initial phases of the mission. This paper presents an overview of the telescope operations during the early phase and commissioning that verified functionality of thermal and electrical systems and commissioned the cameras before the important Calibration and Pointed Verification phase started. In addition, it reports on the challenges encountered and summarizes the results from this phase of eROSITA operations.