# Why is Starlink polluting the night sky a big concern if we have space telescopes?

There's a lot of concern in the Astronomy community over the deployment of Starlink satellites. For a good discussion, see the related question How will Starlink affect observational astronomy?

But why is there so much concern over this problem, given that there are numerous space telescopes? Presumably a lot more will be launched in the upcoming years thanks to satellite launches becoming cheaper. Aren't space-based observations superior in the first place thanks to the lack of an atmosphere?

I understand this sucks for amateur astronomers but is it also a big problem for professional researchers?

• Look at your link and see how few of those space telescopes remain operational. Now look again at the remaining operational space telescopes and strike the duplicates. Finally, look at how many of the remaining few are small in size. The number of large operational space telescopes is very small. And except for Hubble, once they're done, they're done. Apr 19 at 21:39
• You might want to read the answers to this Q. Space telescopes are extremely expensive and adaptive optics has gotten extremely good, is the short answer. Also everyone and their dog wants observing time, but a space telescope can only be pointed in one direction at a time astronomy.stackexchange.com/questions/26610/… Apr 20 at 4:30
• It we could time-travel to pre-industrial society, we probably wouldn't survive very long, but we would be blown away by the night skies. Apr 20 at 15:13
• @EricDuminil you can also just go to the right part of the countryside, it's not THAT hard to get away from light pollution (though central Europe is one of the harder places to do so, but still easier than time travel), see lightpollutionmap.info Apr 20 at 17:14
• Ask yourself who is causing the problem (SpaceX), and who stands to gain from your proposed solution of more space-based telescopy (also SpaceX)... Apr 21 at 1:19

It's a problem because there are still lots and lots and lots of ground-based telescopes.

Ground-based telescopes are still (by far) the biggest optical telescopes, and the cost of space telescopes is prohibitive for many research projects. It will be a long time before a telescope anywhere close in size to the VLT can be launched.

Most space telescopes are specialist devices, observing in a particular part of the spectrum that is blocked by the atmosphere (so there are infra-red, ultraviolet and X-ray telescopes in space) Or doing a specific task (looking for exoplanets, or mapping the positions of stars)

Space is getting cheaper, but it will be a long time before it is as cost-effective as ground telescopes in the optical range. And so it will be a long time before all professional telescopes are in space.

So it is a problem for professional astronomers.

• There is also the issue of space debris with more launches making the problem worse which in turn creates hazards when putting space telescopes in orbit and making keeping them safe non-trivial. Apr 19 at 21:04
• There is also the less-talked about issue of radio pollution - all those RF downlinks from the Starlink satellites will have an impact on radio astronomy. There is also the hard to quantify effect on planetary protection - virtually all of the current NEO discoveries (until/if NEOSM flies) are ground-based so blanking out sky surveys with sat trails make life on Earth (slightly) more dangerous. Big report came out recently via UN Dark and Quiet Skies for Science and Society following a big workshop on this which has more info Apr 19 at 21:59
• Uplinks are pretty much focused at the satelite in question, so they are rather not a problem. But the other issues still stand. Apr 20 at 8:59
• @J... Not even remotely applicable. Light pollution is exactly that - a pollution. The telescopes are not ideal and a stray light lowers the signal to noise ratio. And the interesting things are always at the limit of the capabilities. Apr 20 at 18:06
• @fraxinus created a follow up question: astronomy.stackexchange.com/questions/43484/… Apr 20 at 19:02

To expand on the "space telescopes are expensive" aspect:

• Space telescopes cannot be maintained or repaired. This applies not just to things like optics and instruments, but also to space-specific equipment like gyroscopes and thrusters (the James Webb Space Telescope has an estimated lifetime of $$\sim 10$$ years, set by the supply of fuel for the thrusters it needs to maintain its orbit).

The sole exception to this, of course, is the Hubble Space Telescope -- but note that the repair/upgrade missions a) were incredibly expensive; b) were only possible because of its low Earth orbit; and c) are no longer possible now that the Space Shuttle is retired.

• Space telescopes cannot use the most modern electronics, because they require radiation-hardened chips to protect against the effects of the much stronger radiation environment in space. Such chips are generally several generations behind the current state of the art.

• Space telescopes do not allow for testing new instruments, which is a very important use of smaller ground-based telescopes.

An example from my own experience: in the early 1990s I worked as an assistant to some infrared astronomers at the Aerospace Corporation, who designed and built their own infrared spectrographs. To use one of these, we put it in a van, drove the van to an observatory, mounted the spectrograph on a telescope (e.g., one of the telescopes at Mt. Lemmon Observatory, or one of the telescopes at Lick Observatory, or even the Kuiper Airborne Observatory), and started taking data the same night. This is a kind of flexibility that's simply not possible with space-based telescopes.

So it's not just that we can only build the largest telescopes on the ground (which is true!), it's also that the existing stock of smaller ground-based telescopes allow for experimentation, development, and science that cannot be done with space telescopes.

• At some point we might be able to build larger telescopes on the Moon than we can build on Earth. Probably not in my lifetime. And probably by then Elon Musk III will insist on providing Starlink to everyone on the Moon too. ;-) Apr 21 at 12:46

One thing I always like to add is that ground based telescopes benefit from being able to take huge amounts of data. The Vera Rubin Observatory will have a 3.5 Gigapixel camera. There are proposals to sometimes run it in a mode with 1 second exposures. So we're talking data rates of gigabytes per second. If you have dedicated fiber lines you can deal with that. But it's really hard to move that volume of data down from orbit, it would require multiple dedicated ground stations all over the world. Keep in mind, for science images you can't use lossy compression (no turning images into JPEGS!).

• While I agree that starlink is a problem for some of the other reasons stated, the very same project requires building hundreds of ground stations around the world, capable of transferring data from and to orbit at what amounts to a total rate somewhere in the terabits/s range. So they could easily solve that problem by donating some of that capacity to science.
– mlk
Apr 22 at 6:32
• Sure, that would be cool. This is kind of explaining the current state of affairs. Since we don't have a big enough ground station network, there are no very large field of view space telescopes. Starlink is in very low earth orbit and the antennas point down. So you might need new hardware or extra satellites to make it work. There's potential, but I'm not sure it's all the way to "easy". Apr 22 at 20:00

Space telescope Astronomy research published in Science and Nature: Ground-based telescopes (31.1%), spacecrafts (27.0%), space telescopes (22.8%). (ref)

Number of professional telescopes affected: >1050. (ref) representing tens of thousands of academic physicists, cosmologists, astronomers and other scientists.

Number of amateur astronomers affected: 200,000 to 500,000 scientifically valuable people

Cost of equipment affected: 30-50 billion of equipment.

Number of Starlinks visible in the night sky to everyday people: more than 100 starlink satellites will be visible to us when we look at the sky after sunset and before morning.

(ref)

You know how distracting moving lights are, If you look at a sleeping city with thousands of little lights, and 100 planes are flying over the city, it's confusing, you have to look away. The dawn and dusk will soon consist of looking at hundreds of low flying satellites when the first stars start showing up. 1-2 hours after sunset there will still be 20-50 obvious lights still visible, you'll have to look towards the dark side of the sky to only see higher satellites.

Hale bopp, shoemeker-levy, various exoplanets, galaxies and solar system events were discovered by hobby astronomers, and just two terrestrial telescopes on their own have found 5700 asteroids, comets, variable stars and other stellar object (Pan Starrs).

The research states 0.01 starlink lights per square degree, 1-3% of photos for narrow field telescopes will messed up at dawn/dusk, and maximum 30-40% of photos for a wide field 1 billion telescope being currently built.

You won't be able to use Starlink on any mobile phones without 5kgs of lithium batteries and a dish ( >90W Starlink / <1W 4g ), it costs 1500 euros in Europe for the first year (83 per month + 400 equipment) compared to faster fiber at 300 euros. 99.9% of developed populations already have 4g internet at home, while poor nations can't afford Starlink... no monthly prices have been announced for India or African countries.

Is it necessary? Perhaps it will be a 10 billion dollar flop because 40 million yearly customers are necessary at prices exceeding ADSL/4g/fiber and pre-orders are currently low (50k out of 40 million?).

• Comments are not for extended discussion; this conversation has been moved to chat. Apr 21 at 19:47
• What is the Y axis on that chart? I'm guessing the top line is 100%? Apr 22 at 0:25
• It was a graph showing that 99% of wealthy people have 4g at home, 99% of Indians have 3g at 2% of the price of starlink, and 70% of Africans had 3g in 2020. Apr 22 at 1:54
• “while poor nations can't afford Starlink” – Starlink will be exactly as affordable as (some) people can afford, in every country. That's basically the definition of price: there's some ≈fixed supply of bandwidth for every country, and SpaceX will charge for that as much as they can, but no more than people are able to spend because unused bandwidth is wasted income. Apr 22 at 7:57