The artificial constellations impacting on astronomical science

The ISC chats to Piero Benvenuti, Past Secretary General at International Astronomical Union, about Dark and Quiet Skies, and the three artificial interferences that are affecting astronomy.

Starlinks constellation in the night sky

Piero Benvenuti is passionate about astronomy for humanity, and is part of a growing movement that is organizing international efforts to ensure there is a dialogue around the increasing interference artificial light at night and Low Earth Orbit objects are having on astronomical science.

We’re hearing a lot about new constellations made of thousands of Low Earth Orbit satellites being launched by private companies and governments that are critical for telecommunications advances here on Earth. How is this affecting astronomical science? 

These new constellations have a serious impact on the appearance of the night sky and on astronomical observations. The problem is primarily related to the large number of satellites that in a few years is foreseen to be as high as 100.000. The visibility and brightness of a satellite during the night depends on the altitude of its orbit (currently ranging from ~350 to ~1200 km) and on its surface reflectivity and attitude with respect to the observer. A fraction of the satellites will be visible by the naked eye (those with magnitude < 7th), but all of them are potentially detectable by highly sensitive telescopes’ detectors. Therefore, they leave traces of their transit on astronomical images, significantly decreasing the scientific usability of the collected data. Post-processing of the affected images does not prove to be a solution: the brighter trails may saturate the detectors, making portions of images unusable, while the removal of the fainter trails leaves residual effects that seriously affect important scientific programs, as, e.g., statistical automatic surveys of faint galaxies.  

Tell us about Dark and Quiet Skies for Science and Society. How did the campaign start, and who is behind the campaign to raise awareness about what is going on in Earth’s orbit and how it affects science and humanity? 

The International Astronomical Union (IAU), representing more than 12,000 professional astronomers from about 90 countries, has in its mission the promotion and safeguard of the science of astronomy in all its aspects. In 2017, the IAU approached the UN Committee for the Peaceful Use of Outer Space (COPUOS) proposing to include the protection of the astronomical sky within its mandate. The COPUOS agreed to co-organize a Conference with the title “Dark and Quiet Skies for Science and Society” with the aim to assess the impact of any artificial interferences affecting the visibility of the sky and the detection of cosmic radio signals.

At the time, the potential interference by the large satellite constellations was not yet known, but, by the time the first Conference was organized in October 2020, it had become the most serious problem and the closer one to the primary mission of the COPUOS. The advantages to society that the communication constellations are offering cannot be disputed, but their impact on the pristine appearance of the night sky and on astronomy must be considered with great attention because they affect both the cultural heritage of humanity as well as the progress of science.

The results of the Conference (organized online because of the Covid-19 pandemic), included specific recommendations for mitigating the impact of artificial interferences. They were presented to the Scientific and Technical Sub Committee of COPUOS (STSC) in April 2021 and received the attention of several Delegations. Hence a second Conference, also co-organized by UNOOSA, IAU and the Government of Spain, took place last October focusing on the feasibility of implementing adequate mitigating measures. These will be presented to the next meeting of the STSC in February 2022.  

The exploration of our solar system includes both ground and space-based astronomical facilities. You speak of three categories of artificial interferences that are negatively impacting astronomical observations. Can you tell us what they are and their impacts on astronomy? 

The three categories of artificial interferences that negatively impact the astronomical observations are:

  1. The urban illumination or ALAN (Artificial Light At Night);
  2. The optical/infrared trails of the satellites in low-Earth orbits (LEO);
  3. The radio transmission by ground and space emitters that affects radio astronomy.

The interference by ALAN, that affects both amateur and professional astronomers, has become an acute problem with the advent of the LED (Light Emission Diodes), particularly by those with a high level of blue light. The International Astronomical Union has established a recommended maximum tolerable threshold of light pollution for astronomical sites of 10% above natural background levels. Light pollution is growing globally at an estimated rate of 2 to 6 % per year and is reducing darkness everywhere, including at observatory sites where world-class sites risk hitting the 10% threshold in the next decade. In addition to the impact on astronomy, artificial light at night may have significant biological effects, to flora and fauna, vertebrates and invertebrates, which requires further study by appropriate experts. 

The impact of the large satellite constellations on optical/infrared astronomy has already been mentioned: it is especially affecting telescopes with large field of views as well as the automatic searches for fast moving objects, like the International Asteroid Warning Network (IAWN), a programme initiated and supported by the UN Office of Outer Space Affairs and aimed at detecting potentially dangerous Near-Earth Objects (NEOs).

The protection of radio astronomical observations, a.k.a. spectrum management, is the responsibility of the Radio Communication Sector of the International Telecommunication Union (ITU-R).  The Radio Regulations provides allocations for various services, including radio astronomy under the radio astronomy service (RAS). Indeed, radio astronomy has a long history of negotiation activity aimed at protecting frequency bands of astronomical interest from harmful interference generated by artificial radio emissions within the wavelength range of astronomical interest.

However, the situation created by the new large constellations of telecommunication satellites poses new threats to radio astronomy which deserve further study. In particular, the Dark and Quiet Skies reports to protect recommend that satellite designs should have the capacity to avoid direct illumination of radio telescopes and radio quiet zones and the cumulative background electromagnetic noise created by the constellations should be kept below the limit agreed by the ITU. 

We have intergovernmental bodies, such as UNOOSA – the United Nations Office for Outer Space Affairs and its Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space, as well as COPOUS – The Committee on the Peaceful Uses of Outer Space. Are the intergovernmental bodies and private enterprise working together closely enough to ensure that exploration and the use of outer space is being carried out for the benefit – and in the interests – of all countries and humanity? Or has the private enterprise ship already sailed? Are we too late to prevent the interference of Low Earth Orbit constellations? 

The STSC, in its last Report, has encouraged the UNOOSA to engage with all relevant stakeholders, like the IAU and others, on the matter of dark and quiet skies, as it relates to the mandate of the Committee and its subcommittees. It also highlighted that the second Conference on Dark and Quiet Skies could provide inputs to a focused discussion on opportunities for international cooperation. Indeed, the private companies that are currently launching or planning to launch the constellations were invited to participate in the conference and contributed effectively to the discussion about the mitigating measures that could be implemented. Some of them already tried to modify the design of their satellites in order to lower their apparent luminosity in orbit.

More work has to be done, but it is clear that, in parallel with the definition of internationally agreed guidelines, a close collaboration between industry and the astronomical community will be instrumental in mitigating the negative effects. This action is particularly important for the future foreseeable constellations: the Industry Subgroup of the conferences concluded that satellite operators were more likely to adopt voluntary practices or mitigation tools if they engaged with astronomers early in their project cycle, before spacecraft designs were finalized and when modifications to architectures, spacecraft design or operations could be introduced at less cost or schedule impact. In order promote this action, the IAU has recently announced the constitution of a Coordination Centre that will continue to foster the dialogue with all the stakeholders and the astronomers. 

The International Telecommunications Union is held its annual Internet Governance forum in early December, where Low Earth Orbit satellites were discussed in the name of access to information and accessing the internet. How can the ITU, COPUOS, UNOOSA and the international science community work together to ensure dialogue on the impact of satellite constellations on science and society? 

As already mentioned, the new large constellations of telecommunication satellites are creating unprecedented challenges to both the spectrum management, which is under the responsibility of ITU-R, and to the space traffic management, which is under the responsibility of COPUOS. As discussed above, the combination of these two aspects is negatively affecting astronomy. We do hope therefore that ITU and UNOOSA will jointly assess the new situation and confirm or redefine their mutual responsibilities in such a way the IAU will know to which organization it should formally appeal.  

Find out more:

Watch the webinar, Addressing the Impact of Satellite Constellations on Astronomy and Society: Pathways Forward with the National Academies of Science and the International Astronomical Union

Image by Jeff Bryant on Flickr CC BY-NC 2.0


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