Satellite constellations will ‘fundamentally’ disrupt astronomy

Satellite constellations are groups of artificial satellites operating as a system. While most operational constellations have a small number of satellites (for instance, GPS has just 24 in six planes) there are now plans for constellations with hundreds or thousands of satellites such as Starlink and OneWeb. SpaceX is launching 60 satellites at a time and aiming to have 1,584 satellites providing high-speed internet connectivity across the globe around late 2021, with the possibility of a total of 30,000 satellites.

This has thrown SpaceX into a dispute with much of the astronomical community – including the USA's National Radio Astronomy Observatory and the International Astronomical Union – which asserts that the brightness of these satellites in optical and radio wavelengths will have a severe impact on observations. As Starlink satellites can autonomously change orbits, observations cannot be scheduled in advanced to work around them.

“[We embrace] the principle of a dark and radio-quiet sky as not only essential to advancing our understanding of the universe of which we are a part, but also as a resource for all humanity and for the protection of nocturnal wildlife. We do not yet understand the impact of thousands of these visible satellites scattered across the night sky - and despite their good intentions, these satellite constellations may threaten both,” the International Astronomical Union said in a statement last year.

In response to these concerns, SpaceX CEO Elon Musk has offered to provide orientation adjustments on-demand if necessary and to introduce a sunshade to reduce the brightness of the satellites. The company has been experimenting with painting the satellites black and altering the position of their solar panels in order to minimise reflectivity, and has offered to share satellite tracking data with astronomers to help plan for undisrupted observations.

Now, hundreds of astronomers have jointly warned that Starlink and other large satellite constellations could prove highly disruptive to scientific progress.

The American Astronomical Society hosted the Satellite Constellations 1 (Satcon1) workshop, bringing together more than 250 astronomers, satellite operators (including SpaceX, Amazon and OneWeb), and dark-sky advocates. A report from the workshop (Impact of Satellite Constellations on Optical Astronomy and Recommendations Towards Mitigations) concluded that constellations of bright satellites will change the nature of ground-based optical and near-infrared astronomy.

The report said that these constellations could even change the appearance of the night sky for casual stargazers.

“Existing and planned large constellations of bright satellites in low-Earth orbit will fundamentally change astronomical observing at optical and near-infrared wavelengths,” the Satcon1 report said. Particularly severely affected projects will include planned space observatories such as the Vera C Rubin Observatory currently under construction in Chile.

The report explicitly mentioned SpaceX’s Starlink, warning that this constellation alone may double the number of moving objects detectable by the naked eye at night.

The report suggested six options for reducing the impact of satellite constellations on the night sky, with the only option which could eliminate the impact being to not launch further satellites: “However impractical or unlikely, this is the only option identified that can achieve zero astronomical impact,” the report said.

Alternative possibilities were darkening the satellites’ surfaces (e.g. with SpaceX’s 'VisorSat'), setting an altitude limit for the satellites, orienting them to reflect less sunlight, removing the impacts during image processing, and working with operators to avoid the satellites. However, the report warns that no combination of these alternatives will eliminate the impact of satellite trials on astronomical observations.

The American Astronomical Society has been working with SpaceX to try to address the issue amicably. Satcon1 co-chair Dr Jeffrey Hall welcomed SpaceX’s collaboration with the astronomical community and said that he hoped to see other operators follow suit.