New Report Offers Roadmap to Mitigate Effects of Satellite Constellations on Astronomy

25 August 2020

An international team of experts, including ESO staff, has produced a new report that explores practical ways to address the impact of large satellite constellations on astronomy. The report concludes that large constellations of bright satellites in low Earth orbit will fundamentally change ground-based optical and infrared astronomy and could impact the appearance of the night sky for stargazers worldwide. It also offers a roadmap for observatories and satellite operators to work together to lessen these impacts.

The report offers two main findings. First, low-Earth-orbiting satellites disproportionately affect science programmes that require twilight observations, such as searches for Earth-threatening asteroids or for the visible-light counterparts of fleeting gravitational-wave sources. Satellites orbiting below 600 kilometres have limited interference with astronomical observations during the night’s darkest hours. But satellites at higher altitudes, such as the 1,200-km-high constellation planned by OneWeb, can be illuminated all night long during summer and for much of the night in other seasons. These constellations could have serious negative consequences for many research programmes at the world’s premier optical observatories. Depending on their altitude and brightness, constellation satellites could also affect the views of starry skies for astrophotographers, amateur astronomers, and other nature enthusiasts.

Second, the report offers a number of ways to mitigate harm to astronomy from large satellite constellations. Operators could launch fewer satellites, deploy satellites at altitudes below 600 km, darken spacecraft or use sunshades to shadow their reflective surfaces, and control each satellite’s altitude to reflect less sunlight towards Earth. The astronomical community, on the other hand, could contribute to the mitigation efforts by helping operators identify lower limits for satellite brightness and calculate how effective different ways of lowering that brightness would be. The report also recommends that observatories support the development of a tool to remove or mask satellite trails and their effects in astronomical images, and another to calculate satellite trajectories and avoid their trails. ESO, along with other observatories, are assessing the costs of these mitigation efforts.

The report is the outcome of the SATCON1 virtual workshop, organised by NOIRLab, a US National Science Foundation astronomy centre and the American Astronomical Society. It brought together more than 250 scientists, engineers, satellite operators, and other stakeholders from 29 June to 2 July to discuss the impacts of mega-constellations and explore ways to mitigate them. ESO experts Olivier Hainaut, Andrew Williams and Angel Otarola were amongst the participants in the workshop and are authors in the new report.

Earlier this year, following concerns raised by the astronomy community on how satellite constellations would affect scientific research, ESO released a study by Hainaut and Williams on their impacts, focusing mostly on observations with ESO telescopes in the visible and infrared. It considered a total of 18 representative satellite constellations under development by SpaceX, Amazon, OneWeb and others and found that large telescopes like ESO's Very Large Telescope and ESO's upcoming Extremely Large Telescope will be "moderately affected" by these constellations. The study, which also explored impacts on non-ESO facilities, found that the greatest impact could be on wide-field surveys, in particular those done with large telescopes, like NOIRLab’s Vera C. Rubin Observatory.

Hainaut and Williams, together with Otarola (previously at the Thirty-Meter International Observatory), contributed to the new report by conducting detailed simulation work, summarising the impacts for ESO facilities, and participating in the working groups assembled to author the report. ESO’s VISTA telescope was used to conduct observations of Starlink satellites to support the simulation work. Having detailed simulations of satellite constellations is important as it allows impact calculations to be made rapidly in the future, and will support the creation of tools for telescope operators to schedule observations to avoid satellite trails. Rescheduling observations cannot avoid all impacts and relies on accurate information from the satellite companies, but it can minimise the effects.

ESO will continue its active, ongoing work with the international astronomy community to understand the impacts of mega constellations and develop solutions in partnership with industry and government agencies. SATCON2, which will tackle the significant issues of policy and regulation, is tentatively planned for early to mid-2021.

More Information

The report “Impact of Satellite Constellations on Optical Astronomy and Recommendations toward Mitigations”, was presented to the US National Science Foundation and has been published today, 25 August 2020.

The team is composed of ​C. Walker (NOIRLab, US), J. ​Hall (Lowell Observatory, US), L. Allen (NOIRLab, US), ​R. Green (University of Arizona, US), ​P. ​Seitzer (University of Michigan, US), ​A. Tyson (University of California, Davis, Vera C. Rubin Observatory, US), A. ​Bauer (Vera C. Rubin Observatory, US), ​​K. Krafton (American Astronomical Society [AAS], US), ​J. ​Lowenthal (Smith College, US), ​J. ​Parriott (AAS, US), ​P. ​Puxley (Association of Universities for Research in Astronomy [AURA], US), T. Abbott (NOIRLab, US), ​G. Bakos (Princeton University, US), ​J. ​Barentine (The International Dark-Sky Association [IDA], US), ​C. ​Bassa (ASTRON, The Netherlands), J. ​Blakeslee (Gemini Observatory, US), A. ​Bradshaw (SLAC, US), J. ​​Cooke (Swinburne University, Australia), ​D. ​Devost (Canada-France-Hawaii Telescope, US), D. ​​Galadí (Icosaedro working group of the Spanish Astronomical Society, Spain), F. ​​Haase (NOIRLab, US), O. ​Hainaut (European Southern Observatory [ESO], Germany), ​S. ​Heathcote (NOIRLab, US), M. ​Jah (University of Texas at Austin, US), ​H. ​Krantz (University of Arizona, US), ​D. ​Kucharski (University of Texas at Austin, US), J. ​McDowell (CfA, US), P. ​​Mróz (Caltech, US), A. ​​Otarola (ESO, Chile), ​E. ​Pearce (University of Arizona, US), ​M. ​Rawls (University of Washington, Vera C. Rubin Observatory, US), C. Saunders (Princeton University, US), ​R. ​Seaman (​Catalina Sky Survey, US), J. ​​Siminski (ESA SpaceDebris Office, US), ​A. Snyder (Stanford University, US), L. ​Storrie-Lombardi (​Las Cumbres Observatory, US), ​J. ​Tregloan-Reed (University of Antofagasta, Chile), ​R. ​Wainscoat (University of Hawaii, US), A. ​Williams (ESO, Germany), ​P. ​Yoachim (University of Washington, Vera C. Rubin Observatory, US).



Olivier R. Hainaut
ESO Astronomer
Garching bei München, Germany
Tel: +49 89 3200 6752
Cell: +49 151 2262 0554

Andrew Williams
ESO External Relations Officer
Garching bei München, Germany
Tel: +49 89 320 062 78

Angel Otarola
ESO Atmosphere Scientist
ESO La Silla Paranal Observatory, Chile
Tel: +56 55243 5311

Bárbara Ferreira
ESO Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6670

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