A multi-facted approach to mitigating the challenge of satellite constellations on optical astronomy

Connie Walker (IAU CPS/NSF NOIRLab)

As many are acutely aware, satellite constellations in LEO create bright streaks impacting optical/infrared observations and create the potential for space debris to scatter sunlight and increase the diffuse night sky brightness. Operators’ push to offer direct-to-cell services requires very large antennas, such as the BlueWalker 3 prototype, which was measured as among the brightest objects in the night sky. However, satellite brightness measurements also show some voluntary mitigations like specialized coatings are able to effectively reduce visibility. In the radio regime, no regulations currently extend radio-quiet zone protections to include downlinks from orbit. Since all transmitters above the horizon are visible to radio telescopes, we are witnessing a steady loss of certain frequency ranges to opportunistic observations. Further, unshielded electronics and motors create low-frequency transmissions that are detectable from the ground. To address these and related concerns, the International Astronomical Union’s Centre for the Protection of the Dark & Quiet Sky against Satellite Constellation Interference (IAU CPS) is taking multiple approaches to mitigate negative impacts. For example, the CPS facilitates regular meetings for at least 12 operators to share best practices and understand astronomical concerns. The CPS SatHub organizes observing campaigns and develops predictive software for position and brightness of satellites impacting planned observations. In addition, educational videos about satellite constellations are available, and ongoing efforts are underway to engage with impacted indigenous groups. CPS-affiliated policy and space law experts have developed and are refining recommendations for ultimately turning best practices into a model regulatory framework. Because of IAU raising awareness, a United Nations committee on the peaceful use of outer space has adopted a five-year agenda item to consider astronomy and satellite constellations and an international entity that licenses satellite launches is taking up some key issues of protection. The CPS has laid the groundwork for effective responses to this issue. We welcome your involvement to continue this work to protect the night sky for generations to come.