Future Optical Space Telescopes - i.e. Hubble 2.0 ect

[Jim]

Don't forget hammerhead payload shroud configurations may enable larger (unusual?) monolithic types as well.

It is more than just a fairing and processing facilities.  Need spacecraft factories that can handle spacecraft larger than 5m.  Need vibe, acoustic and thermovac chambers too.  And don't forget a way of getting the spacecraft to the launch site.

[Jim]

The JWST folded approach is much easier to do, but it has hard limits on how large it can scale, relative to the payload fairing, and it's much more expensive (at n=1 anyway) than monolithic mirrors. 

Not a proper comparison.  JWST is 6.5m vs a 5m monolithic.

[RotoSequence]

Don't forget hammerhead payload shroud configurations may enable larger (unusual?) monolithic types as well.

It is more than just a fairing and processing facilities.  Need spacecraft factories that can handle spacecraft larger than 5m.  Need vibe, acoustic and thermovac chambers too.  And don't forget a way of getting the spacecraft to the launch site.

Space Power Facility at Glenn Research Center isn't large enough?

[KelvinZero]

If we are worried about the exhaust gasses from incoming rockets contaminating the mirror's surface they could dock with a spacestation several miles away. A cable could then connect the flying control room to the partially built telescope. Ordinary electric motors can carry the parts to the telescope for assembly. A small spacestation can now be purchased/long term leased for less than a billion dollars.

Getting off topic, but I was wondering if the SEP tug could actually make the Gravity movie's orbital mechanics make sense. Im referring to ISS and Hubble apparently in same orbit, or reachable with very little delta-v. That is the orbit in which you assemble it, and possibly return it for repairs. The SEP tug moves it to and from its working orbit over several months. In that universe it could make sense for the chinese station and any other LEO HSF to be in the same orbit as well, a few hundred miles apart. Shuttling between these locations would be with something not too unlike an Orion or Dragon that is usually docked to the ISS.

[Paul451]

Contamination would likely be a concern at ISS.

Contamination near ISS has been exaggerated. Long-duration exposure experiments haven't found significant issues (unless you get a direct blast from a thruster, obviously.) A 6-12 month construction would not experience significant contamination unless the mirrors were cryo-cooled the entire time.

Realistically though, the astronomy community is going to be very lucky to get a telescope that maxes out the payload of a single FH launch (let alone SLS), so on-orbit assembly is unlikely to be relevant.

That's kind of my point. The availability of cheap launch mass, but not payload-shroud-diameter, may require a change in how you think about designing spacecraft. If heavy-lift additionally frees up significant mass to "waste" on an inefficient design that is cheaper to build, you may get more telescope bang for the buck. (As my previous example of cheap electronics and heavy bulk shielding. Similarly heavy but cheaply built structural elements instead of ultra-light sculpted materials typical of spacecraft.)

SEP through the Van Allen belts is not really a great thing for the detectors either.

But again, when you've got 50 tonnes to play with in a single launch, adding a few tonnes of jettisonable shielding around the instruments isn't a big cost. (Of course, with cheap launches and on-orbit assembly, launching a fast chemical upper-stage as a separate payload might also be an option. But SEP is becoming so off-the-shelf with commercial satellites, it may be the cheaper option.)

LEO is not a destination for telescopes.

Which is why, if you read what I wrote and not what you are pretending I wrote, I didn't say that. You even quoted the part of the comment where I specifically talked about other orbits (including ESL) as the final destination.

[Sohl]

Instead of a circular mirror, is it possible to have a spinning strip or spoke?

I don't see why not... after you capture a series of images over at least a half-rotation, it would be possible to process them all together into higher-resolution approximation of what the fully-filled aperture image would be.  Re-pointing it would be a bit trickier due to gyroscopic effects, and using solar for power also trickier, or perhaps you'd confine your aim to be within something like 30 degrees of the anti-sun direction.

But this kind of setup would be best for targets where image resolution is more important than light-gathering capability... maybe resolving exoplanets separately from their parent stars, measuring star diameters, better resolve face-on binary stars, and other stuff like that.

But yes, this is an interesting idea to think about! 

[AncientU]

<snip>

Earth telescope observatories are run by consortium's. Why not space based telescopes too?

I have a proposal in for just such an observatory...

[Jim]

1.  Contamination near ISS has been exaggerated. Long-duration exposure experiments haven't found significant issues (unless you get a direct blast from a thruster, obviously.) A 6-12 month construction would not experience significant contamination unless the mirrors were cryo-cooled the entire time.


2.  Which is why, if you read what I wrote and not what you are pretending I wrote, I didn't say that. You even quoted the part of the comment where I specifically talked about other orbits (including ESL) as the final destination.

1.  Wrong context and take away.  It isn't "significant" for the experiments and vehicles that visit it and not applicable to telescope optics.    Your points on 6-12 months and optic temps are unsubstantiated.


2.  Then don't make a  claim of 50 tons with 5 tons of shielding.  The mass to those actually orbits is significantly less.  There is no need for SEP when a launch vehicle can get it there directly.  There is no real savings.

3.  This  nonsense  "heavy-lift additionally frees up significant mass to "waste" on an inefficient design that is cheaper to build"  is not proven and doesn't look like it will

[Jim]

Space Power Facility at Glenn Research Center isn't large enough?

a.  It can't do true thermal vac
b.  can't get to it.  There are too many obstructions between it and the airport.

[RonM]

Instead of a circular mirror, is it possible to have a spinning strip or spoke?

I don't see why not... after you capture a series of images over at least a half-rotation, it would be possible to process them all together into higher-resolution approximation of what the fully-filled aperture image would be.  Re-pointing it would be a bit trickier due to gyroscopic effects, and using solar for power also trickier, or perhaps you'd confine your aim to be within something like 30 degrees of the anti-sun direction.

But this kind of setup would be best for targets where image resolution is more important than light-gathering capability... maybe resolving exoplanets separately from their parent stars, measuring star diameters, better resolve face-on binary stars, and other stuff like that.

But yes, this is an interesting idea to think about! 

Sorry, that won't work. Vibrations would be a problem, ruining the resolution. Less area equals less light gathering capability.  Defeats the purpose of having a larger mirror.

If the need is for a Hubble replacement, then something a little larger with modern electronics is the solution.

If the need is to resolve exoplanets, then multiple telescopes acting as an interferometer is the solution.

[Sohl]

Instead of a circular mirror, is it possible to have a spinning strip or spoke?

I don't see why not... But yes, this is an interesting idea to think about! 

Sorry, that won't work. Vibrations would be a problem, ruining the resolution. Less area equals less light gathering capability.  Defeats the purpose of having a larger mirror.

If the need is for a Hubble replacement, then something a little larger with modern electronics is the solution.

If the need is to resolve exoplanets, then multiple telescopes acting as an interferometer is the solution.

I envisioned the long "strip or spoke" might be a relatively rigid framework for an optical long(ish)-baseline interferometer.  http://en.wikipedia.org/wiki/Astronomical_interferometer

Active vibration damping or passive rigidity could be engineered in as needed.  Might be easier than a pair or larger numbers of free-flying interferometer mirros, no?  As I pointed out, it would have its limitations though.

Edit:  That said, I would like to add that I'd like to see a somewhat bigger, better version of optical/UV Hubble flown for general-purpose astronomy too (and probably first, before the more exotic concepts I and others have shared).

[Paul451]

I envisioned the long "strip or spoke" might be a relatively rigid framework for an optical long(ish)-baseline interferometer.

If it's an interferometer, you don't need the rotation. Just two smaller 'scopes on a truss. (Or three or four on a y-arm or triangular truss.)

before the more exotic concepts I and others have shared

Oddly, this kind of interferometer would be much simpler than a large conventional telescope, it just wouldn't give you the classic HST astronomy-porn images.

It isn't "significant" for the experiments and vehicles that visit it and not applicable to telescope optics.

Jim, you know damn well that long-duration exposure experiments (including MISSE) have included mirror elements.

[Jim]

Jim, you know damn well that long-duration exposure experiments (including MISSE) have included mirror elements.

And the results can't hand waved away as not "significant"

[Sohl]

Oddly, this kind of interferometer would be much simpler than a large conventional telescope, it just wouldn't give you the classic HST astronomy-porn images.

No, not for a single interferogram image capture, but if you combine the interferogram from multiple angles, you can synthesize  something close to a conventional image.  That would be the motivation for rotating.  Multiple arms could provide even more data for better full-image estimation accuracy and low-light sensitivity.

Look, I'm not saying this is the best thing to promote as a high priority now, but the initial post struck me as an interesting and innovative approach to a capability we don't have now: ultra-high resolution from an atmosphere-free observatory.  It could be a stepping stone to massive in-space mirror telescopes.  But, yeah, for a presumed Hubble 2.0, probably not the best approach.

[llanitedave]

8 meter monolithic is not going to happen, there is no way of handling such a spacecraft in the US

That's simply not true, Jim.  You've been corrected on that claim before with specific examples.  8 meter monolithic mirrors are being produced right now in Phoenix, Arizona, and are being shipped on public roads.

[Jim]

That's simply not true, Jim.  You've been corrected on that claim before with specific examples.  8 meter monolithic mirrors are being produced right now in Phoenix, Arizona, and are being shipped on public roads.

Wrong and those were corrections were wrong too.  I have been saying spacecraft not just a mirrors.

[gosnold]

Membrane optics might be the way to go. They can give large, lightweight apertures albeit with reduced collecting efficiency (around 30% currently) and restricted bandwitdth.

[llanitedave]

That's simply not true, Jim.  You've been corrected on that claim before with specific examples.  8 meter monolithic mirrors are being produced right now in Phoenix, Arizona, and are being shipped on public roads.

Wrong and those were corrections were wrong too.  I have been saying spacecraft not just a mirrors.

The mirror is the largest single component, and the only one that would even potentially cause problems due to size.  There is no reason for NASA to be considering an 8.5 meter fairing if they have no plans to develop the capability of  handling payloads that require it.


The corrections were factual, BTW.  I listed specific examples of monolithic mirrors produced by spin casting, 8m in diameter, from the University of Arizona, that have been transported out of Phoenix and are being installed in major observatories worldwide.  Please don't misrepresent me.

[Jim]

1.  The mirror is the largest single component, and the only one that would even potentially cause problems due to size. 

2.  There is no reason for NASA to be considering an 8.5 meter fairing if they have no plans to develop the capability of  handling payloads that require it.

3.The corrections were factual, BTW.  I listed specific examples of monolithic mirrors produced by spin casting, 8m in diameter, from the University of Arizona, that have been transported out of Phoenix and are being installed in major observatories worldwide.  Please don't misrepresent me.

1.  Wrong again.  It is not just the mirror.  It would be part of a larger telescope assembly and then yet part of a spacecraft.    So, it doesn't matter if they can get a mirror around.  The issue is the telescope assembly and the spacecraft

2. Surely you jest.  The only thing they really look at was the LSAM and that could be broken down into pieces.  There are only pie in the sky ideas like ALAST.  There is no real look at the money needed to pull it off.   Why do you think JWST costs so much?  It is still within existing fairings and can use existing planes, but still needed a new dedicated container and transporter.    Itt has to be tested in the deployed configuration and there was only one place that was large enough to test it.  They had to modify the JSC thermovac chamber and build a clean room around it.

3.  No, the corrections were meaningless since I was talking about spacecraft.

[wizzzard3]

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