Jure Japelj
astronomy, blog, satellites
EAS 2020: Mega-constellations and astronomy
The annual meeting of the European Astronomical Society EAS 2020 hosted a session on the impact of the upcoming commercial satellite constellations on professional astronomy. Astronomers, engineers, and representatives of companies discussed the future coexistence of astronomy and satellites. My takeaway from the meeting is: it never rains, but it pours.
For more than a year, astronomers tried to come to terms with the new reality: the sky will never again be as it was. Placing tens of thousands of telecommunication satellites in the low-Earth orbit (LEO) in the next five to ten years will undoubtedly interfere with astronomical observations. The jury is still out on the severity of the problem. Will it be only a nuisance or a complete disaster?
During the meeting, the speakers addressed several topics:
How badly will the satellites affect astronomical observations?
What can we do to mitigate the problem?
Relationship between industry and astronomy community
In favor of brevity, I focus on optical observations in this post. Satellites will also not go unnoticed by radio astronomers, and the sheer number of new satellites poses a threat to future handling of space debris. For a more general background, I refer you to my other post.
Bright satellite trails also pollute space observatories (note: Starlink does not necessarily cause these trails). High-altitude (>1000 km) satellite networks would significantly impede our ability to carry out observations efficiently. Credit: a slide from the talk of Mark McCaughrean.
Satellites are especially problematic for observations in the visible light because they leave bright trails on images. The trails are difficult to remove and prevent us from taking sensitive measurements; it depends on the exact science we do, but we may have to discard the images polluted by the satellites entirely. Telescopes on Earth will be affected the most, though space-based telescopes in LEO aren't completely impervious to the pollution either.
Many companies have announced their plans to enter the new commercial space race, but right now, Starlink and OneWeb are the ones in the limelight.
Starlink is a company owned by Elon Musk. The network of more than thirty thousand satellites will orbit the Earth in the lower part of the LEO at the altitudes of less than 600 km. Starlink has launched about 500 satellites into orbit in the past year. The unexpectedly bright satellites inflamed the astronomical community, but also initiated the collaboration between astronomers and the company engineers, resulting in possible solutions to mitigate the problem. Due to their relatively low altitudes, the satellites will disturb observations mostly at the beginning and end of the night.
After launching its first batch of satellites, the British company OneWeb went bankrupt a few months ago. But recently it made a comeback. The company announced a new plan to place about fifty thousand satellites at an altitude of about 1000 kilometers. While the FCC hasn't approved their request yet, we learned just a few days ago that the British government is becoming a 45 % owner of the company. That is reassuring because the government's involvement ensures that the project will be carried out responsibly in consultation with experts, including astronomers. Oh, wait… Never mind.
The British government believes that the OneWeb network will provide both fast broadband internet and deliver a precise Positioning, Navigation, and Timing service, a sort of replacement for the European Galileo navigation system; UK will lose the Galileo membership in January when it leaves the EU.
As far as astronomers are concerned, OneWeb is a disaster. The satellites will disturb astronomical observations throughout the night because of their high altitude orbits; the higher the satellite orbits the Earth, the longer it gets illuminated by the Sun. Simulations performed by Olivier Hainaut (ESO) show that the Starlink network itself will significantly impact the Vera Rubin Observatory, the transient discovery machine of the next decade. The other wide-field surveys, employing smaller telescopes, will suffer to a lesser extent, but most observatories in the world will only experience a marginal annoyance. OneWeb changes that. The small field-of-view telescopes will be affected as well, and the wide-field surveys will be crushed under the burden of the satellite trails. Hours into the night, 20 – 70 satellite trails will pollute each of the Rubin Observatory images.
As Olivier Hainaut summarized: "Low altitude we can live with. […] Higher altitudes are a catastrophe."
Artist's impression of VisorSat, a satellite equipped with a visor that is supposed to shield the satellite from the Sun. Credit: SpaceX
The satellite constellations are the reality we will have to live with. Whether it is Starlink or OneWeb, or any other of the many companies with their eyes on LEO, the space near Earth will soon be swarming with satellites. Accepting that, astronomers are seeking solutions to mitigate the problem and to prevent the worst from happening.
What can companies do? Starlink engineers have worked together with astronomers to reduce the albedo of their satellites, that is, to reduce the amount of reflected solar light from the satellites' surfaces. Paint it black, was the first solution. The most reflective surfaces on a test satellite were coated with a non-reflective substance, and it kind of worked—the brightness of the DarkSat satellite reduced three times compared to his non-painted cousins. That is still not good enough, but it is a step in the right direction. The problem is that such a satellite absorbs more light and heats up, which is not good for the satellite itself. Besides, the heated satellite emits infrared light, which could disturb infrared observations. Starlink recently launched the first batch of satellites carrying a visor that is supposed to block most of the solar light from reaching the satellite. If it works, the solution will make the satellites darker while avoiding the negative byproducts of the black paint.
Note that the darkening won't remove the satellite trails on images of big telescopes altogether. But let's be pragmatic: a faint trail is better than a bright trail.
Other companies must adopt or develop similar solutions to darken their satellites. The big unknown is again OneWeb. So far, the company hasn't responded to the appeals from astronomers. Given the possibly detrimental effect of OneWeb's constellation, the astronomical community has to do everything to make the company and the UK government listen. We should discuss, advise, annoy, poke, bite, bribe—hopefully we stop at "advise". A lot is at stake.
Besides advising companies, what can astronomers do? An obvious action is to schedule observations in a sequence that would avoid pollution from satellites. This requires full cooperation with companies who need to communicate the positions of their satellites. Rescheduling will result in less efficient observations—programs will have to run longer to achieve their scientific goals. The scheduling won't help if there are a hundred thousand new satellites in the sky. Provided that the companies manage to produce darker satellites, we can improve our algorithms to better remove the trails from images and have other unwanted camera effects under control. The most sensitive observations will likely still be affected.
So far, it seems no legal actions have been considered to protect the darkness itself, enforcing the satellite brightness to stay below a certain threshold. It would take a lot of time to adopt and put such a requirement in practice; serious discussions should commence as soon as possible before it is too late.
Credit: OneWeb
Representatives from Starlink and ESOA presented their views on the future of satellite constellations and commented on the clash with astronomy community. Understandably, their interests are not the same as astronomers' interests; their contributions were interesting, but in line with expectations. I want to end this post with a few of my own thoughts concerning some of the arguments that typically arise in these kinds of discussions.
What will it be, astronomy or satellites?
Whenever I discussed this topic, either in academia or elsewhere, I was confronted with the remark of an absolutist: why do I think astronomy is more important than internet access in remote places in the world? I don't believe that it is, nor does any other astronomer I know. Shocking. Why do we have to choose one or the other? It is not that satellites and astronomy can't coexist. The problem, as usual, is that an action is taken without making a comprehensive study of the effects on the environment, either deliberately or due to negligence. That is why we raised our voices, and we will continue to shout until proper actions are taken. From the Starlink's efforts, we already see that the problem of brightness can be mitigated, perhaps even more than what we imagine. With a bit more effort, many of the issues can be solved, and that is all we ask.
Speaking of internet access, Starlink claims that their constellation is built to deliver the internet to the poor and unprivileged. This philanthropic stance would be more believable if they wouldn't aim for a low-latency connection intended for online gaming and capital markets. If the internet to remote areas were the primary concern, the constellation wouldn't need to have the current scope. Again, their interest is understandable. But alluding that astronomers are selfish because we don't want the poor to have access to the web is perverse.
From the legal point of view, the space isn't ready for the current increase in all kinds of satellites. There seem to be regulations, but many are either not international or are challenging to enforce. I am not a legal expert—I would advise that future panels about satellite constellations involve a more active presence of a legal expert because it seems to be a topic about which many of us would all like to hear more.
As pointed out by the ESOA representative, we live in an increasingly connected world. Connectivity improves our lives, and the new constellations, as well as many individual commercial satellites, are necessary for a better world. Hopefully, in a few years, astronomers will still have a place in this grand unified world.
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