Can telescopes in space replace ground based telescopes?

[Marci]

"Astronomers should be happy about SpaceX. Cheap access to space will enable a lot of space telescopes, no worries about mega constellations disturbing ground based astronomy"


This is one of the most common answers one can read when talking about effects of starlink and other satellite constellations on ground based telescopes. Even from people like Everday Astronaut or Elon Musk himself. My feeling is that this is not a very realistic argument but I want to learn more about it and hear some thoughtfull opinions on this topic?

Let's say Starship will be flying soon and it will actually be very very cheap. Can you really replace ground based telescopes? What types of research/wavelengths could be done in space? And what types of research need to be done on the ground and why?

[Proponent]

I doubt there is anything that must be done on the ground, but even if launch is free, the cost of reconstructing humanity's collective ground-based capabilities in space would be, er, astronomical.

[TorenAltair]

I think neutrino telescopes are better on or more precise under Earth.

[su27k]

The idea is not to totally replace ground based telescopes, at least not in the short term, but to compensate the loss of the ground based observation time caused by mega constellations. This latter loss would require a lot less space telescopes than a total replacement, especially considering space telescope can work 24x7 while ground telescopes can only work at night and under good weather conditions.

[hop]

I doubt there is anything that must be done on the ground, but even if launch is free, the cost of reconstructing humanity's collective ground-based capabilities in space would be, er, astronomical.

Yeah, "we'll just put the telescopes in space" is just fantasy. All else being equal being in space would be generally better for optical and radio, but in real life things aren't remotely equal. Doing things in space is really expensive, even if the launch is free.

Large ground based telescopes are already ~billion-dollar projects, with development timelines measured in decades. The big ground based observatories that will operate though the 2030s are already being built, with billions of dollars committed in hardware and multinational agreements. Even if Starship were available tomorrow and launch was free, LSST, GMT, TMT and ELT aren't going space. Designing space missions to accomplish the same goals would mean starting over from scratch, at the cost of many billions of dollars and years (if not decades) of development. The instruments for these things can already cost hundreds of millions. Building equivalent systems to operate in space could easily cost an order of magnitude more.

It's equally absurd at the low end: A lot real astronomy is done with small telescopes on tiny budgets. The budget for something like Dragonfly would be absolutely swamped by the cost of a spacecraft bus capable of supporting it.

[ZChris13]

I doubt there is anything that must be done on the ground, but even if launch is free, the cost of reconstructing humanity's collective ground-based capabilities in space would be, er, astronomical.

Yeah, "we'll just put the telescopes in space" is just fantasy. All else being equal being in space would be generally better for optical and radio, but in real life things aren't remotely equal. Doing things in space is really expensive, even if the launch is free.

Large ground based telescopes are already ~billion-dollar projects, with development timelines measured in decades. The big ground based observatories that will operate though the 2030s are already being built, with billions of dollars committed in hardware and multinational agreements. Even if Starship were available tomorrow and launch was free, LSST, GMT, TMT and ELT aren't going space. Designing space missions to accomplish the same goals would mean starting over from scratch, at the cost of many billions of dollars and years (if not decades) of development. The instruments for these things can already cost hundreds of millions. Building equivalent systems to operate in space could easily cost an order of magnitude more.

It's equally absurd at the low end: A lot real astronomy is done with small telescopes on tiny budgets. The budget for something like Dragonfly would be absolutely swamped by the cost of a spacecraft bus capable of supporting it.

SpaceX are also trying to bring down the cost of a satellite bus, with their Starlink production line. Of course, getting good enough pointing accuracy might not be so easy, and Starlink isn't the best form factor for a telescope, but they're not alone. The costs for a cubesat is also quite low.

[meberbs]

I doubt there is anything that must be done on the ground, but even if launch is free, the cost of reconstructing humanity's collective ground-based capabilities in space would be, er, astronomical.

Yeah, "we'll just put the telescopes in space" is just fantasy. All else being equal being in space would be generally better for optical and radio, but in real life things aren't remotely equal. Doing things in space is really expensive, even if the launch is free.

...The instruments for these things can already cost hundreds of millions. Building equivalent systems to operate in space could easily cost an order of magnitude more.

Things are expensive in space because you cant fix them if they break, and other overdesigning issues that are required for special one off missions. If Starship is running cheap launch of large things, you don't have to worry about that so much, and the marginal cost of doing it in space will be in the noise relative to the rest of the project cost

It's equally absurd at the low end: A lot real astronomy is done with small telescopes on tiny budgets. The budget for something like Dragonfly would be absolutely swamped by the cost of a spacecraft bus capable of supporting it.

Yeah, not like anyone could put a hundred cheap telescopes in orbit today capable of operating 24/7. Oh wait, that has already been done, they just pointed them at the Earth. With cheap frequent launch there is no reason reasonable size telescopes like that could not be supported on equal inexpensive buses.

And as has been mentioned above, the near term bar should just be eliminating the net impact to observations due to upcoming constellations. That whole being in Earth's shadow while overhead during the night really kills the visibility impact of most satellites over most of the sky most of the time. Few telescopes have significant need for near horizon observations for science work that I know of, often it is less useful due to more interference from the air. One exception I have heard suggested was searches for PHAs, but those should be particularly helped by IR sats in orbit. In general productivity, one telescope on orbit probably could replace at least 2 slightly more capable ones on the ground completely. If all you want to do is replace the bit of interference that upcoming constellations will cause with certain observations, it doesn't take all that much.

We have another thread on actual impacts going on for a while, but I haven't read the whole thing, has anyone actually done a calculation/simulation yet showing what real impacts would be? Preferably one that accounts for the fact that satellite passes are predictable and can be dodged entirely in many cases.

[ZChris13]

No, unfortunately meberbs that entire thread is two or three people arguing the same points back and forth. It's mostly quieted down now, so it's safe to skim it, but there hasn't been a whole lot more math than pointing out that the math used to fearmonger was kind of bogus.

[meberbs]

No, unfortunately meberbs that entire thread is two or three people arguing the same points back and forth. It's mostly quieted down now, so it's safe to skim it, but there hasn't been a whole lot more math than pointing out that the math used to fearmonger was kind of bogus.

Thanks, that is what I thought, I had looked at the thread some. (And I admit to being one of the 2 or 3 people in certain other threads (usually new physics) that ended up similar, so I get how that happens.)

It has been long enough that if a specific astronomy mission was going to have major irrevocable impacts, someone probably would have quantified them by now, and knowing this site, someone would find that quickly. In my mind, the lack of such a report puts a loose bound on how severe the impacts can get. I expect one will eventually get published one way or another to guide future missions.

[woods170]

Can telescopes in space replace ground based telescopes?

Yes, technically they can. Hubble in particular is a very fine example.

A large part of the electromagnetic spectrum is not visible to ground-based telescopes anyway. Think Gamma ray, X-ray, Ultraviolet, most of the Infrared spectrum and long wavelength Radio.

In the past several decades, a very substantial number of space-based telescopes has gone into orbit to observe said parts of the electromagnetic spectrum. A whole bunch of X-ray telescopes and Ultraviolet telescopes, a good number of Infrared observatories and some Gamma ray missions as well (Compton, BeppoSAX, HETE-2, Swift, INTEGRAL, Fermi and AGILE).
Heck, there have been even a few Radio astronomy satellites: HALCA and Spekr-R.

[libra]

No. They are complementary, and adaptative optics can cancel most of atmospheric disturbance.

Also, astronomers are no idiots - the fact that  30 m and 39 m ground-based telescopes (EELT) are currently build can not only be explained by the high cost of space launch, with or without SpaceX.

Incidentally, even with BFR/BFS, sending a 30 m or 39 m mirror into space won't be easy anytime soon.

As for multiple mirror telescopes like the defunct TPF & Darwin, ground-based variants also exists. Antoine Labeyrie, a genius astronomer that pioneered visual light interferometry, has explored ground-based and spaceborne concepts.

Ground-based with adaptative optics and smaller spaceborne telescopes are complementary, not mutually exclusive.

[libra]

Yeah, not like anyone could put a hundred cheap telescopes in orbit today capable of operating 24/7. Oh wait, that has already been done, they just pointed them at the Earth.

Bouncing off this even if I don't agree with Meberbs arguments.

Fact is that the NRO launched
- 144 KH-7 and KH-8 GAMBIT spysats, each one with a 48 inch mirror
- 20 and counting, KH-11 and whatever followed them, each one with a 94-inch mirror

- plus the cancelled KH-10 DORIAN MOL
- of which six 72-inch mirrors were build and later handled to Aden Meinel for the Arizona MMT telescope.
- Plus the NRO declassified documents showing that NASA wanted these mirrors in 1969
- and also asked the spooks if, someday, they could point a KH-10 at Mars or Jupiter to try and get some interesting pictures.

So the NRO kind of launched 170 high-tech mirrors in space since the first KH-7 in 1963  ! makes one think... it is no surprise NASA was either jealous or willing to collaborate with the spooks... to get their technology. 

[meberbs]

No. They are complementary, and adaptative optics can cancel most of atmospheric disturbance.

Most is not all, this does nothing to support your argument, as you don't list a single capability that is lessened by being in space (they really isn't a meaningful one.)

Also, astronomers are no idiots - the fact that  30 m and 39 m ground-based telescopes (EELT) are currently build can not only be explained by the high cost of space launch, with or without SpaceX.

No, astronomers are not idiots, so it is simply insulting when you use their name to make such baseless assertions. The inability to launch said telescopes to space at an affordable price is plenty of reason to build them on the ground instead.  You provide no other explanation.

Incidentally, even with BFR/BFS, sending a 30 m or 39 m mirror into space won't be easy anytime soon.

Such telescopes are already built out of numerous bite sized mirrors, And if that wasn't enough, the telescope could be launched in pieces, and even have astronauts assemble it on orbit (cheap human launch is also a capability of BFR/BFS.)

As for multiple mirror telescopes like the defunct TPF & Darwin, ground-based variants also exists. Antoine Labeyrie, a genius astronomer that pioneered visual light interferometry, has explored ground-based and spaceborne concepts.

Why would ground based equivalents of some space based telescopes existing have any relevance to the question at hand, whether space based equivalents can exist for ground based telescopes?

Ground-based with adaptative optics and smaller spaceborne telescopes are complementary, not mutually exclusive.

No one has said that they are exclusive, the topic of the thread asks if there is anything that needs to be done on the ground, where interference from Starlink or other large constellations could not be mitigated by instead doing it from an on orbit telescope, given cheap, highly capable launch.

Yeah, not like anyone could put a hundred cheap telescopes in orbit today capable of operating 24/7. Oh wait, that has already been done, they just pointed them at the Earth.

Bouncing off this even if I don't agree with Meberbs arguments.

Fact is that the NRO launched ...

You seem to have missed my point, I thought it was clear that I was referring to a much more recent commercial company. You aren't exactly helping your case here either way though.

[Proponent]

A large part of the electromagnetic spectrum is not visible to ground-based telescopes anyway. Think Gamma ray, X-ray, Ultraviolet, most of the Infrared spectrum and long wavelength Radio.

A minor point about the graphic:  astronomers do observe the heavens at wavelengths below 1 mm from the ground, albeit only from very elevated portions of ground.  From a very good site like Mauna Kea, observations down to 0.3 mm are possible, say, one night in ten  -- it depends on the amount of water vapor in the atmosphere.

[Hobbes-22]

There's a list of astronomical observatories on Wikipedia. It has ~800 entries, and that's just the professionals. There's also an amateur community that provides professional-grade observations. It'll take quite a few launches to replace those.

I'm not convinced comparisons with the NRO are valid. Those sats weren't exactly cheap, and they weren't suitable for astronomy either (optimized for Earth observations at much higher light levels than astronomy).

[hop]

Things are expensive in space because you cant fix them if they break, and other overdesigning issues that are required for special one off missions. If Starship is running cheap launch of large things, you don't have to worry about that so much, and the marginal cost of doing it in space will be in the noise relative to the rest of the project cost

Cheaper, sure, but "in the noise relative to the rest of the project cost" is totally unsupported. Space is still an extreme environment. Radiation, vacuum, thermal extremes, micro gravity, launch loads all impact the cost of developing an instrument. Free-flying satellites still need a whole bunch of systems and greater reliability than some COTS electronics in a dome you can send a grad student out to bang on with a hammer.

On the ground, if a component goes bad, one low wage operator goes and swaps it out in an afternoon. That's going to be orders of magnitude cheaper than launching someone into space to do an EVA. Even if your telescope is bolted onto an already crewed space station, the overhead of a space station is going to be a lot more than a telescope operators shack.

Easy access to space doesn't completely negate the need for higher reliability. On the ground, if your software crashes someone can go and reboot it. In space, if you don't have high redundancy and complicated safing systems, it can mean LOM. Even if you have on-orbit repair capability, losing command capability will make it more complicated and run the risk of cascading failures, like batteries and propellant systems exceeding thermal limits or instruments frying themselves by looking at the sun. You can engineer your way out of all that of course, but it costs money.

Yeah, not like anyone could put a hundred cheap telescopes in orbit today capable of operating 24/7. Oh wait, that has already been done, they just pointed them at the Earth. With cheap frequent launch there is no reason reasonable size telescopes like that could not be supported on equal inexpensive buses.

Cheap launch would certainly be great for smallsat astronomy. There's interesting, useful things to be done with satellites in the class of Planet's doves. But it's a big leap from that to assuming it can replace everything that's done on the ground for similar cost. BRITE has done some cool stuff in this area, but if you read their papers, you'll find there's a lot more to it than just shoving a cubesat out the door.

That whole being in Earth's shadow while overhead during the night really kills the visibility impact of most satellites over most of the sky most of the time.

This is not as mitigating as SpaceX fans seem to think. When you think about the geometry, you need to include inclination and seasons. The reality these constellations will be a minor annoyance for some, and a significant issue for others. It is already impacting LSST planning (SpaceX is working with LSST to help mitigate the impact, but that doesn't include putting LSST into space ). The recent AAS 235 meeting had a session https://aas.org/meetings/aas235/press-kit#Sun_am and press conference on this subject.

[yg1968]

Can telescopes in space replace ground based telescopes?

Of course not. There is more and more discoveries by amateurs because it's impossible to be looking everywhere at the same time. There is strenght in numbers. Very large telescopes are still being built in Chili and elsewhere despite Hubble and other space based telescopes.

[meberbs]

Things are expensive in space because you cant fix them if they break, and other overdesigning issues that are required for special one off missions. If Starship is running cheap launch of large things, you don't have to worry about that so much, and the marginal cost of doing it in space will be in the noise relative to the rest of the project cost

Cheaper, sure, but "in the noise relative to the rest of the project cost" is totally unsupported.

Read the context of what I was responding to. They were talking about $100 milllion dollar telescopes becoming billion dollar ones. Starlink/One Web type satellites should be on the order of $1 million a piece scale that up some for bigger satellites and then down for decreasing costs as cheap launch and expanded use of space etc. In the noise seems about right compared to the driving costs including precisely ground mirrors etc contributing to the baseline cost. I never claimed that the other things you mention can be ignored completely.

Also as far as spacewalks and such for repair, there is a fundamental difference in risk between a 10% chance that you lose a $100 million instrument and a 10% chance that you spend $5 million sending someone to repair it. It fundamentally changes the acceptable risks and how much needs to be spent mitigating them.

Cheap launch would certainly be great for smallsat astronomy. There's interesting, useful things to be done with satellites in the class of Planet's doves. But it's a big leap from that to assuming it can replace everything that's done on the ground for similar cost. BRITE has done some cool stuff in this area, but if you read their papers, you'll find there's a lot more to it than just shoving a cubesat out the door.

You are mixing things here. Every capability can clearly be replicated on the ground. There is however no short term need to only do things in space. The assumption you are arguing against is a strawman.

That whole being in Earth's shadow while overhead during the night really kills the visibility impact of most satellites over most of the sky most of the time.

This is not as mitigating as SpaceX fans seem to think.

Your links do not support your assertion. In fact after looking over the linked presentations, I am becoming more convinced that this will be completely negligible. I haven't watched the whole video since it is an hour long. If there is anything in it that actually describes a real significant impact please provide the relevant time stamp. (There are a number of assertions in the video/papers that seem to be using the brightness level of the orbit raising state and applying it to everything, same presenter later makes relevant mitigating marks.) Nothing in the video says that the factors I list are not significant mitigating factors. Some are actually listed as relevant factors in fact.

When you think about the geometry, you need to include inclination and seasons.

If you think about the seasons, you see that it is better for half the year and worse for half the year. This doesn't really change anything.

The reality these constellations will be a minor annoyance for some, and a significant issue for others. It is already impacting LSST planning (SpaceX is working with LSST to help mitigate the impact, but that doesn't include putting LSST into space ).

From as far as I got in the video, it sounds like there would be no reason to put LSST in space because by planning around satellite passes and other potential mitigations, there was no assertion that there would be a net impact to the science once this was complete.

[hop]

They were talking about $100 milllion dollar telescopes becoming billion dollar ones.

You have offered no evidence that this is incorrect. Space qualifying something like the LSST camera or one of the ultra high precision spectrographs would be super expensive, even if you have a very generous mass budget.

Also as far as spacewalks and such for repair, there is a fundamental difference in risk between a 10% chance that you lose a $100 million instrument and a 10% chance that you spend $5 million sending someone to repair it. It fundamentally changes the acceptable risks and how much needs to be spent mitigating them.

Sure, it changes the risks, but $5 million is a lot more than sending your $40k/year telescope operator out to change out a $10 non-space rated electrical component they picked up at the hardware store.

Your links do not support your assertion. In fact after looking over the linked presentations, I am becoming more convinced that this will be completely negligible.

The people building LSST came to the opposite conclusion you do. The AAS abstracts unfortunately don't include the details of their analysis, but I'm sure they will be published in due course.

Fundamentally, a large number of professional astronomers believe this is a significant issue for some types of observations (though not an existential threat for most), and SpaceX enthusiasts (edit: though aside from some ill-considered tweets, not SpaceX themselves) insist it's not, often by implying astronomers don't know when satellites are visible, or saying "just put all the telescopes in space!!!!"

One of these positions is informed by deep knowledge of the relevant details.

If you think about the seasons, you see that it is better for half the year and worse for half the year. This doesn't really change anything.

That is not correct, because the value of the time at the extremes isn't equal. The point is that satellites like this can be illuminated at relatively high elevation in prime observing time.

edit:
To be clear, I agree with you that there is no need to put all ground based astronomy in space, and that many types of astronomy won't be severely impacted by mega constellations.

Where we disagree is over the idea that cheap launch would make moving ground based astronomy into space a viable option in the foreseeable future.

[meberbs]

They were talking about $100 milllion dollar telescopes becoming billion dollar ones.

You have offered no evidence that this is incorrect. Space qualifying something like the LSST camera or one of the ultra high precision spectrographs would be super expensive, even if you have a very generous mass budget.

I didn't try to prove it in general, because it is too general of a statement to do that. I gave numeric examples to support my statement though, which is significantly more evidence than your list of specific issues that you incorrectly claimed I was ignoring.

Sure, it changes the risks, but $5 million is a lot more than sending your $40k/year telescope operator out to change out a $10 non-space rated electrical component they picked up at the hardware store.

Worst case, the risk happens and you add $5 million to a $100 million budget. This is small enough relative to the budget as a whole that it is a rounding error in these order of magnitude estimates. Comparisons to what it would have cost to fix the same thing on the ground aren't relevant.

Your links do not support your assertion. In fact after looking over the linked presentations, I am becoming more convinced that this will be completely negligible.

The people building LSST came to the opposite conclusion you do. The AAS abstracts unfortunately don't include the details of their analysis, but I'm sure they will be published in due course.

The abstracts do not make the assertion that there would be non-negligible impacts to science after mitigation. Nothing I saw in the video does either. I asked for you to point specifically to where they say otherwise and you failed to do so. There is no reason to think that they have a detailed analysis which supports an assertion they don't make to begin with. As far as I can tell you are now just lying, asserting that they say something that they don't just to spread FUD.

Fundamentally, a large number of professional astronomers believe this is a significant issue for some types of observations (though not an existential threat for most), and SpaceX enthusiasts (edit: though aside from some ill-considered tweets, not SpaceX themselves) insist it's not, often by implying astronomers don't know when satellites are visible, or saying "just put all the telescopes in space!!!!"

They "believe" it is for "some types" of observations. That is about as wishy-washy of an assertion as you can get. It does not assert evidence of even a potential issue, or specifically list anything that would be negatively impacted. You then move on to talking about extreme strawmen on the other end of the spectrum rather than providing any facts.

One of these positions is informed by deep knowledge of the relevant details.

Nope, neither of them is. None of what you just listed is supported by a single fact, nor is what you just listed equivalent to what I am saying.

If you think about the seasons, you see that it is better for half the year and worse for half the year. This doesn't really change anything.

That is not correct, because the value of the time at the extremes isn't equal. The point is that satellites like this can be illuminated at relatively high elevation in prime observing time.

For what reason is the value of the observing time different? Your second statement has nothing to do with the seasons, and is the kind of thing that show be supported by math and an explanation of what you consider "relatively high elevation"

To be clear, I agree with you that there is no need to put all ground based astronomy in space, and that many types of astronomy won't be severely impacted by mega constellations.

Where we disagree is over the idea that cheap launch would make moving ground based astronomy into space a viable option in the foreseeable future.

There are a couple ways I can interpret the last sentence. One is that you are claiming that no moving of ground based astronomy to space would happen in the foreseeable  future, which is absurd because astronomy is happening in space and reduced cost of access to space will only increase how much happens there.

Another is you arguing against the point of moving all ground spaced astronomy to space in the near term, which again would just be you trying to force an idiotic strawman argument into my mouth.

I am not really sure what you could be trying to say in between, since I am only arguing that near term enough can be put into space to mitigate any impacts and you just agreed that many types of astronomy will not be severely impacted. The real disagreement seems to be whether there are any significant to severe impacts, and while I cannot go through every conceivable desired type of astronomy to prove that there is none, if there is one that is significant, it shouldn't be too hard to point out specifics, so I am not going to accept that there are such impacts without evidence. (And if there are then the question of whether those can be easily addressed with space based telescopes can be a lot more specific.)

It was mentioned above how a related thread devolved into an argument between a couple people, lets not do that again here. If you have some facts to share please do. If you are just going to argue against strawmen, or point to vocal astronomers on twitter making vague complaints, please don't.