Satellites vs astronomy
Meredith Rawls reveals the impact of artificial satellites on the night sky
Even with the best intended regulations controlling what frequencies are being used by satellite companies, it’s going to have some pretty serious effects on radio astronomy.
You are working on the Legacy Survey of Space and Time (LSST). What will this survey study? The Vera C. Rubin Observatory is the site in
Chile where we are building this giant telescope. It’s going to survey the entire night sky of the Southern Hemisphere, so every few days there will be a new image of pretty much every chunk of sky. After ten years – which is how long the survey is going to last – we will have a high-resolution full-colour movie of the night sky. We will be able to see lots of things that are changing, maybe discover new science that we didn’t know about and also see really faint structures that we haven’t been able to see before.
It’s everything from asteroid discovery and
Solar System science to figuring out the fate of the universe. It really encompasses all areas of astronomy, which is why it is super cool.
The data is going to be published and made available to all astronomers in the US and Chile. It will be immediately made public, and then a subset of it will be going public globally. Then it will be made fully public two years after the fact, so we really want to enable science on a large scale.
How will the planned ten-year survey at the Vera C. Rubin Observatory be affected by lowEarth orbit satellites?
It turns out that the aspects of the Vera Rubin Observatory that make it so amazing as a discovery engine for the unknown are the same characteristics that make it vulnerable to low-Earth orbit satellites that are bright and everywhere. It’s hard to predict exactly what the effects are going to be, but I think they’re going to be significant, especially as more and more satellites go up.
How can the interference from these satellites be reduced?
Astronomers have been in dialogue with some folks from different satellite operator companies, and generally when we have been in contact with these operators they have been receptive to not wanting to ruin the night sky, but they do also want to deliver their product and make money.
If it’s not too technically difficult to do some small to medium things to make it a little easier for astronomy to not be totally messed up they’ve been willing to do it, which has been really nice. I don’t think that is going to necessarily fix it, but it is going to somewhat mitigate it. For example, we have worked with SpaceX where we were coming up with different darkening mitigations, and we were observing the results and reporting back on whether they made a difference or not.
The first generation of that was called DarkSat, when SpaceX painted a whole satellite in dark, black paint. It did make it a little darker, but the issue from their end was that it made the satellite too hot, and it didn’t function well. The next thing SpaceX tried was installing a little visor flap that would shield the reflective parts so they wouldn’t reflect as much sunlight, but there were not as many observations of VisorSat because of the pandemic, as many of the groundbased observatories were closed. Some of the data suggested that the visors were able to reduce the brightness of the satellites by an order of magnitude, which is good, but not good enough.
There are ongoing discussions about other potential darkening mitigation options, because these satellite companies really do move fast. One thing that has really struck me as I have become
familiar with this whole situation is how fast satellite companies move compared to astronomy and science, which tends to be on a much longer timescale to get a project up and running. But then regulation moves on even longer timescales, so they are really mismatched.
If low-Earth orbit satellites are problematic, should the companies just place the satellites higher up?
Actually that would be worse. It’s a little complicated because you could think that maybe a lower orbit satellite would be brighter because it is closer, which is true, but the trick is that it moves faster in a lower orbit because it has to not fall out of the sky. That means that when you are taking a picture it will move out of the way faster and the pixels won’t linger long enough to make as bright of a streak in the image, which is better.
I was personally disappointed that OneWeb decided to keep its satellites at a higher altitude, whereas SpaceX has been more willing to keep its satellites at lower altitudes. Though space debris will become an even bigger problem at these lower altitudes as the lower the orbit, the more crowded it gets.
Could these satellites be influencing not only ground-based astronomy, but also general enjoyment of the night sky?
These low-Earth orbit satellites are fundamentally changing the night sky. My kids are going to have a very different experience of what it means to go to a dark site and stargaze. Even if you are far away from a city and there’s not much traditional light pollution, you’re going to find a whole bunch of moving things in the sky. If satellite companies manage to get the brightness below seventh magnitude, or at least close, they might not be super bright, and you won’t necessarily be able to see the satellites unless they are glinting at certain times of the night. But even in a best case scenario where all of the satellite operators agree to reduce the brightness, you’re still ruining astrophotographers’ views of the night sky.
And even if they can manage to make them seventh magnitude or fainter when they are at their main orbital altitude, they still have to launch them. When they are launched, the satellites have to spend a little bit of time at a really low altitude – which is when they’re at their brightest – before they manoeuvre up into a higher orbit. At the end of their lifetime, which is usually about five years, they’re also going to be brighter when they are on their way back down. You might say that’s only a month in a five-year lifetime, but it’s constant. They’re going to be replenishing the satellites that are up there. They’re always going to be launching some and deorbiting others, and there are a number of companies doing this at once.
Something else that I would like to stress is the bigger picture of all of this. I obviously care a lot about the science, but I do really care a lot about the impacts on the human experience of the night sky. There are a whole bunch of folks who have not been invited to any of the discussions about this – in particular indigenous folks and religious practitioners. People have all kinds of different relationships with the night sky, and I think that it’s really important to seek out and listen to those folks as well, because they are not getting a say at all. It’s really just a bunch of companies who are deciding what the future of the night sky is going to be for everyone. I don’t think that’s a great way to proceed.
Do you think these satellites could make ground-based observations impossible?
Some people ask: “Why can’t you just launch all these telescopes into space and solve this problem?” But unfortunately this is not realistic for a whole bunch of reasons, funding being the main one.
Also, the kind of survey that we will be doing at the Vera Rubin Observatory – where you are trying to do a wide-field survey of the night sky – you cannot do that with a space telescope because you cannot get the hardware up there – it’s that big. If anything breaks, you can’t necessarily service it. When the James Webb Space Telescope launches, it’s going to be so far out that it cannot be serviced, so if anything breaks, that’s it. It just makes us all very nervous.
I don’t think it’ll be impossible, but it will be harder. We are used to dealing with a lot of interference in our data – that’s not really fundamentally new – but I do think that we will miss discoveries that we basically don’t know we will have missed. That’s what scares me most about the scientific impact of this whole thing: that we won’t know what we cannot see.
For example, maybe we’ll miss a near-Earth asteroid. One of the many things that the LSST survey is going to do is aim to discover a whole bunch of near-Earth asteroids. But to do that search it has to do it at twilight, and it’s during this time that there are the most illuminated satellites.
If you can’t image the same asteroid three or four times, you can’t measure its orbit, and you have no idea if it’s going to come close to impacting Earth. The fact that we have tonnes of satellites may make it impossible to tell if there’s going to be a dinosaur-level asteroid situation, so that’s kind of an irony for you.
It’s really just a bunch of companies who are deciding what the future of the night sky is going to be for everyone. I don’t think that’s a great way to proceed.