One million satellites in the sky: Light contamination on space telescopes

Rapidly growing satellite mega-constellations have raised strong concerns among the scientific community. Reflections from satellites are visible to the human eye and extremely bright for professional telescopes. These trails already affect astronomical observations across the complete electromagnetic spectrum, with a noticeable cost for operations and mitigation efforts. Despite the common misconception, satellite trails affect not only ground-based observatories, but also space observatories, like Hubble . However, the current number of satellites is only a fraction (<10%) of those to be launched in the next decade. Here we show a forecast of the satellite trail contamination levels for a series of international low earth orbit telescopes, based on the proposed telecommunication industry constellations. Our results show that if these constellations are completed, one fourth ofHubble's images will be contaminated, while the space telescopes SPHEREx, ARRAKIHS, and Xuntian will have 94% of their exposures affected, with 5.9 ^{+0.6 _-0.6} , 32 ⁺¹⁷ _-13 and 86 ⁺²⁰ _-19 trails per exposure respectively, with an average surface brightness of μ = 18+-2 mag arcsec ^-2 . Our results demonstrate that light contamination is a growing threat for space-telescope operations. We propose a series of mitigation measures to minimize their impact, allowing researchers to predict, model, and correct unwanted satellite light pollution from science observations.