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Abstract

eROSITA aboard the Spectrum-Roentgen-Gamma satellite, successfully launched in July 2019, is the first X-ray astronomical telescope operational at the Sun-Earth Lagrange point L2. A prime scientific goal of eROSITA is the detection of 100000 clusters of galaxies, which at the fainter luminosity end appears as weak and slightly extended objects. For a reliable detection and characterization of the sources also a detailed knowledge of the instrumental background is required. In the light of the upcoming ESA Athena mission and other future X-ray missions, eROSITA can play a role as pathfinder in terms of space environment and non-X-ray background at L2.. Initial results related to the eROSITA in-flight background have been obtained during Commissioning and subsequent Calibration and Performance Verification phases. The eROSITA background is composed of various components, such as from the electronics, from particle induced radiation inside the camera, external particles registered (and rejected) onboard, stray-light from celestial sources, and general X-ray background. By means of dedicated variations of the set-up (e.g., filter wheel, on-board processing) and viewing direction we started to disentangle the components and origins. Particle background variations appear to be low, which may be expected due to the low solar activity at the moment. The general background level appears to exceed pre-launch expectation. This is currently under investigation.