The boom of low Earth orbit satellites – a critical reminder of the dangers of space debris, as explained by the International Astronomical Union

Satellites are increasingly a global-communications lifeline, allowing people in remote areas, even war zones, to make phone calls and get online without the need for ground-based infrastructure. Services such as SpaceX’s Starlink, by far the largest of the networks of telecommunications satellites in low Earth orbit, have been booming during the past decade. The companies requested access to the spectrum for more than one million satellites.

This success comes at a cost, with mounting concerns about safety and sustainability. As things stand, most satellites are single-use products with a lifetime of 15 years or less. Moreover, space debris is a growing problem, as physicists Richard O. Ocaya at the University of the Free State in Bloemfontein, South Africa and Thembinkosi D. Malevu at North-West University, Potchefstroom, South Africa, describe in a Comment article. The boom of satellites raises questions about whether humans could mess up the environment without regulation.

Rubin has a powerful camera and telescope that will take about 1,000 nightly exposures of the sky, each 45 times the area of the full Moon. That is more wide-field photos of the sky than any observatory has ever taken. Simulations suggest that if satellite numbers in low Earth orbit rise to around 40,000 over the 10 years of Rubin’s survey — a not-impossible forecast — then at least 10% of its images, and the majority of those taken during twilight, will contain a satellite trail3.

The pace needs to quicken, as work towards this is under way. Three years ago, the International Astronomical Union (IAU) established a centre for the protection of dark and quiet skies, in Paris. It is a hub for scientific, policy, industry and community discussions about satellite swarms, and it has put forward common-sense recommendations that are already being adopted. French satellites will be less bright after France updated its national space law last year.

The first step is raising awareness. Finance is not the only thing. The IAU centre is run on a small budget with donations and time given by astronomy. Funders should step up with more support, as the US National Science Foundation did last year with a US$750,000 grant to the IAU to develop software tools that predict when satellites will appear in telescopes’ fields of view.

Some say there needs to be a discussion about regulation, or rather the lack of it. Most companies don’t dimming their satellites because there aren’t many regulations that say so. There are several regulatory agencies for satellites, but they have limited, if any, enforcement power when it comes to the impacts of satellites on astronomy.

Beyond the clash with the astronomer, the future of satellite swarms need to be talked about in broader terms. That includes integrating perspectives from Indigenous peoples, many of whom have important connections with the night sky, but who have long been marginalized from decision-making and economic power in outer space.

The number of working satellites has soared in the past five years to around 11,000, mostly because of constellations of orbiters that provide Internet connectivity around the globe (see ‘Satellite surge’). Just one company, SpaceX in Hawthorne, California, has more than 7,000 operational Starlink satellites, all launched since 2019; OneWeb, a space communications company in London, has more than 630 satellites in its constellation. On paper, tens to hundreds of thousands more are planned from a variety of companies and nations, although probably not all of these will be launched1.

Satellites play a crucial part in connecting people, including bringing Internet to remote communities and emergency responders. The rising number of satellites can be a problem for scientists because they interfere with ground based astronomy by creating bright streaks on images and jamming radio telescopes. The satellite boom also poses other threats, including adding pollution to the atmosphere.

Tools such as SatChecker help telescope operators to avoid problems by allowing them to target a different part of the sky when a satellite passes overhead or by simply pausing observations as it flies by. It would aid astronomers if SatChecker had even more accurate information about satellite positions, but there are constraints on improving the system. SatChecker data come from the US Space Force, which draws on a global network of sensors that tracks objects in orbit and issues updates on satellite locations as often as several times a day. The frequency of these updates is limited by factors such as how often a sensor can observe an object and whether the sensor can distinguish what it’s looking at.

SpaceX took early steps to try to mitigate the problem. Changes to the design and position of Starlinks were tested by the company and Rubin as they tried to keep their brightness under a threshold. The retail and technology giant, based in Seattle, Washington, is testing a number of different solutions for the proposed Kuiper constellation. The problem is that the changes don’t eliminate it.

For other observatories, the IAU CPS is working on tools to help astronomers identify and correct satellite streaks in their data. One is a new database of crowdsourced observations of satellite brightnesses called SCORE, which is currently being beta tested and is planned for wider release in the coming months. Peel says that this will help scientists to work backward, so they can figure out what’s puzzling in their past observations.