The impact of large satellite constellations on astronomy: five years on

Topic: Other Topics

Session Title: The impact of large satellite constellations on astronomy: five years on


The Low Earth Orbit space environment has changed dramatically since 2019, with the advent of satellite constellations such as OneWeb and Starlink. Starlink alone has already doubled the total number of satellites ever launched into space, and there are proposals to regulators that, when combined across all operators, request the launch of over a million satellites in the coming years.
These satellites affect astronomy in many different ways – in the optical, sunlight reflections can cause them to be very bright (often mags 3-5, even mag 0 for very large satellites like BlueWalker 3, with mag 7 being the recommended target brightness). In the radio, they use broadband transmissions at frequencies around 10GHz – and with each constellation using a different frequency, this will extend to 20, 30, 40, even 190GHz in the future. They also cause unintended low frequency emission that can be detected by instruments such as LOFAR and SKA, and we do not yet know their impact in other parts of the electromagnetic spectrum.

Various collaborations exist to understand and mitigate the effects of satellites on astronomy, and to engage with the satellite operators to reduce satellite interference. In particular, the IAU Centre For The Protection Of The Dark And Quiet Sky From Satellite Constellation Interference (CPS) has been working on observations and policy input, and is open for volunteer involvement.

RAS working groups contribute to the CPS and to policymaking in general, noting the particular responsibility of the UK government as a part-owner of OneWeb (now part of Eutelsat).

Despite the significant effort by astronomers around the world, constellations continue to grow, and there is little prospect of global regulation to contain their impact, and no guarantee that the measures taken by existing operators will be replicated by future constellations.
However, some mitigations have taken place to reduce satellite brightness’s, particularly by SpaceX with VisorSat and Bragg reflectors on Gen2 mini satellites, and conversations with operators are ongoing to define good practices here, with astronomer feedback vital to improving the situation in the long term.



Session 1: Tuesday 16th July, 15:00 – 17:00