Discussion of Future Space Telescopes

[Sesteritum]

Hey there! Great to see discussion around future space telescopes. It's exciting to think about what the future holds in terms of space exploration and discovery. And the rockets mentioned in the video, Falcon Heavy, Starship, and Super Heavy, are definitely a crucial part of getting these telescopes into space. If you're interested in diving deeper into space-related topics, I'd highly recommend checking out Science Resources. They have a wealth of information and resources on space, including the latest updates on space telescopes.

Moderator note: I checked the link and it is apparently a decent teaching resource site. As far as I can tell it is safe.

 

[ecarfan]

In another thread @JB47394 wrote:

Maybe SpaceX should create Starview satellites that form a constellation of thousands of orbiting telescopes that collectively provide absurd levels of observing power. That might keep the astronomers happy.

That is a brilliant idea. I continue to maintain that ground-based astronomy has no future. I understand that astronomers are very unhappy with the current number of LEO satellites but they cannot stop the growth of those constellations which by the end of this decade will be in the tens of thousands and continuing to increase.

The good news for astronomers is that by the end of this decade enormous space-based telescopes will be able to be launched for a few tens of millions (launch cost) and they will be vastly more powerful than anything that is in operation right now.

 

[jerry33]

In another thread @JB47394 wrote:


That is a brilliant idea. I continue to maintain that ground-based astronomy has no future. I understand that astronomers are very unhappy with the current number of LEO satellites but they cannot stop the growth of those constellations which by the end of this decade will be in the tens of thousands and continuing to increase.

The good news for astronomers is that by the end of this decade enormous space-based telescopes will be able to be launched for a few tens of millions (launch cost) and they will be vastly more powerful than anything that is in operation right now.

And I'd guess there is a market for "connect to our telescope constellation--point the telescope where you want (with certain restrictions)".

 

[JB47394]

That is a brilliant idea. I continue to maintain that ground-based astronomy has no future. I understand that astronomers are very unhappy with the current number of LEO satellites but they cannot stop the growth of those constellations which by the end of this decade will be in the tens of thousands and continuing to increase.

I wonder how much pushback there would be to moving all large-scale observatories off-planet. Would it be like the auto industry and the aerospace industry, where there is a lot of entrenched interest in keeping the status quo? Obviously, the consumers of observatory capacity are thrilled with any expansion, but I wonder who would be alienated by dumping those big ground observatories.

Edit: I just looked up optical interferometry and apparently folks are making real progress on it. One example of this is the CHARA array, which is ground-based. SpaceX already has laser interlinks between satellites, so I would think that we're knocking on the door of a vast optical/infrared interferometer that could simply replace all observatories. Just dial in the telescopes that you want to link together and go to town. Use as much or as little of the constellation as you like. Done right, the telescopes could piggyback the Starlink satellites.

A man can dream.

And I'd guess there is a market for "connect to our telescope constellation--point the telescope where you want (with certain restrictions)".

Would you want observatory time to be controlled by corporations? There's no natural price level for observation time, and I can't see too many competitors in such a market.

Edit: And now that I've suggested putting telescopes on Starlink satellites, I've gone down the rabbit hole you suggested.

 

[Grendal]

Realistically, we will soon have the opportunity to put a very big telescope on the dark side of the Moon. It's not that far away and you put a couple satellites in Moon Lagrange points to send the observational data back to Earth. That would be pretty spectacular. Add in a telescope constellation and the Universe is really opened up observationally.

I know we can't travel to other star systems within my lifetime, but I'm hoping to get some really solid observations of planets in other solar systems showing that some form of life (that we would characterize as life) exists. I know there have been some vague signs in some of the observed planets in the habitable zone, but nothing definitive. Better telescopes can make that happen.

As a science fiction reader since childhood, I remember reading a few stories about space based telescopes doing serious observations of planets. In one the telescope was so good it found a civilization in another galaxy. Granted that the observation was something like a hundred million years in the past but it showed a very advanced civilization making very big things that could be observed from that far away. After reading that, I'm hoping humanity can pull off something amazing like that soon. In our local area of course...

 

[mongo]

Realistically, we will soon have the opportunity to put a very big telescope on the dark side of the Moon. It's not that far away and you put a couple satellites in Moon Lagrange points to send the observational data back to Earth. That would be pretty spectacular. Add in a telescope constellation and the Universe is really opened up observationally.

That's handy for radio astronomy, but since the far side isn't really dark, a telescope would end up pointing sunward half the time.
Polar telescopes could avoid both light sources by pointing vertically, or at the bisection of the larger formed angle.

 

[TunaBug]

That's handy for radio astronomy, but since the far side isn't really dark, a telescope would end up pointing sunward half the time.
Polar telescopes could avoid both light sources by pointing vertically, or at the bisection of the larger formed angle.

That sounds neat, but if telescopes pointing south were desirable then why aren't there more of them in Antarctica? I know it's not a convenient environment, but it's warmer/cheaper/closer than the moon.

Putting telescopes on the dark side seems like a red-herring, though. Even if it was ok for them to be closed off due to the sun "half the time"... I would think a telescope on the moon's surface would be valuable if it was near a settlement for easier assembly or servicing. Otherwise why not leave it in orbit? And if you were going to put a settlement on the moon I'm not sure the dark side would be attractive. I use "settlement" loosely: not a colony, just something we can get to readily, like if we had regular trips from the pole to the gateway.

 

[mongo]

That sounds neat, but if telescopes pointing south were desirable then why aren't there more of them in Antarctica? I know it's not a convenient environment, but it's warmer/cheaper/closer than the moon.

It has more snow, lower elevation that current mountain sites, and is sunlit a lot (only 3 months without twilight) without the benefit of vacuum.

 

[JB47394]

Otherwise why not leave it in orbit?

I wouldn't put one big dish on orbit. I'd do the Starview thing again. You can get absolutely insane resolving power by doing interferometry. The light collection would only be as good as your willingness to put large collectors on the satellites. And if you're interested in a Moon colony, instant infrastructure. I don't know how badly the Moon's mass concentrations would mess with the satellite orbits, though. That might get ugly.

Now we just need to talk to Elon.

 

[TunaBug]

Now we just need to talk to Elon.

He'll want to put it on Mars. But why not Mars? SpaceX will probably have regular shuttles to Mars before NASA does to the moon, and at lower cost. And he needs something to do once there, although he probably already has a bucket list for that.

Trying to bring this back to the thread topic: what are the conditions that would make it more desirable to have a telescope on the surface (not earth) instead of in orbit?

 

[JB47394]

But why not Mars?

Mass and delta-v. Such a constellation of telescopes would work about as well around the Moon and at a dramatically lower cost.

Now if you were to create all the telescopes at Mars, then I'd have no argument against it.

Trying to bring this back to the thread topic: what are the conditions that would make it more desirable to have a telescope on the surface (not earth) instead of in orbit?

If an observatory requires regular access, then it is a candidate for staying on the surface. This could mean supplying consumables, tuning stuff that cannot be accomplished remotely, or even a constant desire to upgrade the technology in the observatory. The caveat here is that low cost access to orbit changes the balance there. Low cost access by automated flights is another means of changing the balance.

Then there are observatories (detectors) that leverage the fact that they are either in the atmosphere or inside the planet to be able to see only specific particles or wavelengths. Any observatory whose basic function requires gravitational acceleration. Though I suppose those could be spun up in space if they're not too sensitive to the linearity of the acceleration.

 

[Grendal]

That's handy for radio astronomy, but since the far side isn't really dark, a telescope would end up pointing sunward half the time.
Polar telescopes could avoid both light sources by pointing vertically, or at the bisection of the larger formed angle.

I just looked it up and from NASA.com: "There are some parts of the Moon that never see sunlight. These areas are called permanently shadowed regions, and they appear dark because unlike on the Earth, the axis of the Moon is nearly perpendicular to the direction of the Sun's light. The result is that the bottoms of certain craters, like here at the Moon's south pole, are never pointed toward the Sun, with some remaining dark for over two billion years."

So that might be the best place for a big space telescope.

 

[scaesare]

I wouldn't put one big dish on orbit. I'd do the Starview thing again. You can get absolutely insane resolving power by doing interferometry. The light collection would only be as good as your willingness to put large collectors on the satellites. And if you're interested in a Moon colony, instant infrastructure. I don't know how badly the Moon's mass concentrations would mess with the satellite orbits, though. That might get ugly.

Now we just need to talk to Elon.

I've wondered how interferometry would work with multiple collectors all moving in multiple curved axes relative to each other...

 

[JB47394]

I've wondered how interferometry would work with multiple collectors all moving in multiple curved axes relative to each other...

There's been some work on this for the Laser Interferometer Space Antenna (LISA). It's for detecting gravitational waves, but the system needs to know the precise distance between three spacecraft in heliocentric orbit. Here's a quote from the Wikipedia page.

A LISA-like instrument should be able to measure relative displacements with a resolution of 20 picometres—less than the diameter of a helium atom—over a distance of a million kilometres, yielding a strain sensitivity of better than 1 part in 10^20 in the low-frequency band about a millihertz.

I have no idea how expensive such satellites might be. Gravity wave detection requires that insane level of precision, but an optical telescope doesn't, so I would hope that it could be built using much more accessible technology. Then again, it might just be a fantasy for years to come.

 

[mongo]

There's been some work on this for the Laser Interferometer Space Antenna (LISA). It's for detecting gravitational waves, but the system needs to know the precise distance between three spacecraft in heliocentric orbit. Here's a quote from the Wikipedia page.



I have no idea how expensive such satellites might be. Gravity wave detection requires that insane level of precision, but an optical telescope doesn't, so I would hope that it could be built using much more accessible technology. Then again, it might just be a fantasy for years to come.

For that though can't they back out the orbital effects to find the underlying signal?

I think real time interferometry requires continuous fixed delay matching and mixing of the collected photons.

 

[scaesare]

My understanding of interferometry is that the distance between the detectors is a function of the wavelength being detected. Given that it's not a single wavelength, but a band, I assume that it's a matter of "ideal distance", not that it's a binary matter of not working at all at the "wrong" distance.

Thus, I'd expect a constantly moving constellation will have continuously variable sensitivity range... I suspect if you sample over time you could get some pretty amazing results...

 

[mongo]

My understanding of interferometry is that the distance between the detectors is a function of the wavelength being detected. Given that it's not a single wavelength, but a band, I assume that it's a matter of "ideal distance", not that it's a binary matter of not working at all at the "wrong" distance.

Thus, I'd expect a constantly moving constellation will have continuously variable sensitivity range... I suspect if you sample over time you could get some pretty amazing results...

That doesn't sound correct. Infrared's longest wavelength is 1mm. Telescope separation determines angular resolution.

They need the adjustable length paths to time/ phase match all the telescopes. If they are aren't zeroed, there is a linear phase shift with frequency that messes things up.

 

[scaesare]

I think you are right, and I was conflating it with what I had read about optical interferometry:

Astronomical optical interferometry has had to overcome a number of technical issues not shared by radio telescope interferometry. The short wavelengths of light necessitate extreme precision and stability of construction. For example, spatial resolution of 1 milliarcsecond requires 0.5 μm stability in a 100 m baseline."

 

[JB47394]

I think real time interferometry requires continuous fixed delay matching and mixing of the collected photons.

That's what's done today because that's as far as we've taken the technique. As Tom Scott emphasizes, right now it's analog. I don't believe there's anything in physics that prevents us from digitally recording the signals and then integrating them at a later time. The data requirements would be massive, and certainly the compute resources would be equally gigantic at the start, but I would expect optimizations over time as scientists and engineers develop experience. Just as they must be doing with the analog systems today.

But yes, I'm using an Appeal To Future Magic to make it work.

 

[mongo]

I think you are right, and I was conflating it with what I had read about optical interferometry:

Astronomical optical interferometry has had to overcome a number of technical issues not shared by radio telescope interferometry. The short wavelengths of light necessitate extreme precision and stability of construction. For example, spatial resolution of 1 milliarcsecond requires 0.5 μm stability in a 100 m baseline."

Radio has it Sooooo much easier
Downmix the frequency band and digitize it. Do everything else in post processing. Same deal with small phased array radar receivers like automotive radar (allows post-processed scanning).

But yes, I'm using an Appeal To Future Magic to make it work.

Indeed