The Air and Space Academy (AAE) established a working group to elaborate a statement on the impact of large satellite constellations on Earth-based astronomical observations and space-based observations of the Earth. The group was led by Alain Hauchecorne, president of Section 1 of the AAE. It was composed of AAE members (Michel Blanc, Michel Courtois, Tanja Masson-Zwaan, Karl-Ludwig Klein, Sylvie Vauclair) and external experts (Olivier Hainaut, ESO; Eric Lagadec, SF2A; Hervé Roquet, Meteo France DESR/DAP).
The working group met about ten times between March 2020 and spring 2021 and consulted several external experts I. Thomas, Station de radioastronomie de Nançay; J.Mariez, CNES; P. Baiocco, CNES; L. Vigroux, MESRI). AAE is grateful for their help. The following text is the statement by AAE based on the report of the working group.
Statement on the impact of megaconstellations on astronomical observations of the sky and geophysical observations from space
The advent of large satellite constellations, with several hundreds of elements deployed so far, and tens of thousands to come in the near future, leads to an unprecedented change of the vision of the night sky. It concerns ground-based, and to some extent space borne astronomical observations of the sky, as well as geophysical observations from space. The present text has been elaborated by a working group of the Air and Space Academy based in France, gathering experts in astrophysical and geophysical research, in legal issues concerning space, and in satellite design and operations.
The working group has taken note of the impact of large constellations on scientific observations:
- Reflection of sunlight by satellites affects observations of the night sky in visible light and at infrared wavelengths. The impact varies with the diameter of the field of view of the instrument and the exposure time. In view of the foreseeable numbers of satellites in the near future as planned by SpaceX (Starlink) or other companies like OneWeb, detailed quantitative investigations have been undertaken by astronomers. They suggest that the impact on telescopes with small fields of view, like those operated by the European Southern Observatory (ESO), will be manageable. Wide-angle observations, such as those planned with the Vera Rubin Observatory presently under construction in Chile, will be strongly affected by saturation from the brightest satellites, and by the numerous fainter trails that will streak the images. Complex techniques for the partial removal of parasitic signals must be developed, without any prospective to completely solve the problem. The Rubin Observatory will obtain the deepest maps of the sky with an almost daily rate, which will make it possible to build astronomical catalogues several orders of magnitude richer than before and providing unprecedented insight in the time domain. 1. Astronomers expect performance loss despite cooperation with SpaceX on the detector saturation problem caused by the brightest satellites.
- The sheer number of satellites and their emission near 14 GHz (Starlink) will have an impact on radio astronomy, even if the satellites emit and receive in authorised bands. The need for greater sensitivity for deep-space research drives projects that can only be realised when a broad range of frequencies is accessible, both because integration over a broad frequency range enhances sensitivity and because characteristic signatures at a specific frequency are Doppler-shifted to a different frequency when emitted by a distant galaxy. These observations are not protected by international agreements on the allocation of individual frequencies. The strategy chosen by professional astronomers is to build new instruments at sites far away from any terrestrial interference. 1. While interference with signals from a limited number of satellites can be managed at these sites, the huge number of transmitters in large constellations will jeopardise this strategy.
- The proximity of frequencies used by present and potential future constellations to spectral regions used for passive observations of the Earth’s atmosphere and surface from space is also a source of concern, in particular around 19 GHz and 37 GHz. To preserve scientific observations, strict compliance with the specifications by individual satellites will be crucial. Experience with past satellite constellations, such as Iridium, shows that this respect is not guaranteed, and is impossible to enforce once the satellite is deployed. Today, licences are granted to satellite operators without addressing these negative effects or imposing constraints on satellite design and operations to mitigate these effects. 1. It would be advisable for licensing entities to take these aspects into consideration during the licensing process.
- It appears that constructive cooperation has been developed between SpaceX and professional astronomers, and similar efforts are starting with OneWeb and Kuiper. This demonstrates a real will on the part of the industry to limit the impact of their operations on astronomical observations. However it is clear that these limitations will reduce, but not remove the impact, especially on optical instruments with a large field of view. It is furthermore by no means guaranteed that all satellite operators will consider engaging in a similar dialogue with research. Such cooperation appears to be an expression of goodwill by the industry, which is the only instance with real decision-making power. 1. This could destroy the possibilities of improved astronomical observations from Earth.
Conclusions and recommendations
- The Air and Space Academy calls upon authorities in charge of space policy and regulation of satellite operators to address the problem. The Academy is aware that no legal regulation protects the vision of the sky. There is, however, a need to preserve scientific research and more generally the vision of the night sky by the general public. This need is not supported by economic interests, and society has no leverage on decision makers. It is therefore important that States adopt regulatory measures to enable a fair balance between economic, scientific and cultural interests. The Academy encourages the Member States of the UN Committee for the Peaceful Uses of Outer Space (COPUOS) to support the proposal of the International Astronomical Union (IAU) to include this topic on the agenda of the next COPUOS meeting, in order to develop a series of recommendations or policy guidelines for operators of satellites in low-Earth orbit that would minimise their interference with astronomical and geophysical observations.
- The Air and Space Academy recommends that the scientific community quantitatively assess the impact of large constellations in low-Earth orbit on astronomical and geophysical observations together with satellite manufacturers and operators of such constellations. This is only possible through discussions based on sound technical information and a real scientific and engineering expertise. This work must be recognised by the bodies evaluating scientific activity. The existing cooperation between astronomers and SpaceX engineers can serve as a model. 1. In France, the observation services under the auspices of CNRS/INSU provide an adequate framework for such activities.
- The European Space Agency (ESA) and national space agencies such as the French CNES should address this problem and provide their expertise and support to determine realistic technical solutions to minimize interference in the radio frequency and optical domain, such as solutions in the design of satellites to minimize the reflection of sunlight or the establishment of quiet zones for the emission of radio waves.
- The Air and Space Academy recommends establishing means to monitor operators’ compliance with licensing rules governing the development and operation of satellite constellations, in particular with respect to the use of radio frequencies.
- The Air and Space Academy recommends that the impact on scientific activities related to astronomical observations and observations of the Earth and operational meteorology be considered in the licensing process for large satellite constellations, within the context of Article VI of the 1967 Outer Space Treaty,