Washington, D.C., July 2025
On behalf of over 8500 members of the American Astronomical Society, we are writing to express our strong support for provisions in the EU Space Act related to the protection of dark and radio-quiet skies. We are encouraged by this legislation’s recognition of the growing challenges that satellites pose for the natural night sky and for astronomical observations. The protections for dark and quiet skies within the EU Space Act represent a critical step forward in balancing commercial innovation with responsible stewardship of our shared space environment.
Article 72 sets forth a useful framework for addressing the growing impact of satellites on astronomical observations by requiring that satellites’ visual magnitude be no brighter than 7th magnitude, which corresponds to about the faintest an object can be and still be visible to the unaided human eye, through design requirements on low reflectivity coating or shielding. We support the requirement for spacecraft operators to develop plans to limit light and radio pollution, including technical descriptions of the measures taken to reduce impacts on optical and radio astronomy. US companies have already been voluntarily leading the way with mitigations aimed at protecting dark and quiet skies. Namely, major satellite providers like SpaceX Starlink, Amazon Kuiper, and AST SpaceMobile have signed coordination agreements with the National Science Foundation to mitigate the impact to ground-based astronomical observatories, spurring successful technological innovations such as the development of dielectric films to reduce scattered light, and real-time coordination to protect radio observatories. These requirements from the EU would stimulate further innovation in the sector and contribute to a more sustainable space for all. It is beneficial to both US companies and the scientific community that other countries are requiring similar technical specifications for their spacecraft.
There are no borders in space, and as such, the brightnesses of and radio frequency interference from satellites will impact US astronomy regardless of who owns the satellite. The Vera C. Rubin Observatory, for example, is a flagship US observatory located in Chile that is preparing to begin an unprecedented time-lapse movie of the Universe with the world’s largest digital camera in late 2025. Simulations suggest that at least 10% of all Rubin images will contain at least one satellite streak, and the majority of images in twilight would contain streaks (https://www.lsst.org/content/lsst-statement-regarding-increased-deployment-satellite-constellations). These satellite streaks can appear millions of times brighter than the objects
Rubin is meant to observe, thereby potentially saturating images and rendering a portion of Rubin data scientifically useless. If all satellites adhered to the 7th magnitude brightness limit, the impacts to Rubin science, as well as many other US astronomical facilities, would be significantly reduced. We understand that not every satellite manufacturer or operator may feel prepared to adopt technical measures to limit light and radio pollution; however, we are very willing to offer the astronomical community’s assistance with this process. In addition to the deep expertise held within the National Science Foundation, members of the AAS Committee for Protection of Astronomy and the Space Environment (COMPASSE, https://compasse.aas.org/) and the International Astronomical Union’s Centre for the Protection of the Dark and Quiet Sky (IAU CPS, https://cps.iau.org/) are happy to share their knowledge with satellite companies to assist in the development of technical plans. For example, the IAU CPS Industry and Technology (I&T) Hub is leading the way in collaborative practice with participation from SpaceX, Amazon Kuiper, Planet, and other space industry members who are very willing to share their experience from and strategies for developing mitigation measures. The CPS I&T Hub facilitates an “Astronomer Guide” program, where expert astronomers sign NDAs to provide free consultations to companies on issues like Bidirectional Reflectance Distribution Function (BRDF) testing. In addition, CPS SatHub offers an open repository of brightness measurements and tools to help assess mitigation efficacy. SatHub’s free open source software includes SatChecker (a satellite position prediction tool, satchecker.readthedocs.io) and SCORE (Satellite Constellation Observation Repository, score.cps.iau.org), and the hub welcomes collaboration with observers and operators alike.
Thank you for the opportunity to provide feedback on the EU Space Act. We hope that the Office of Space Commerce will continue to support US companies in demonstrating leadership and a commitment to responsible space operations by adopting mitigations to support dark and quiet skies, and we are glad to assist in these efforts.