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Space Science

A New and Improved Hubble Telescope? 17

Posted by Hemos from the seeing-better-farther- dept.
Juda_ben_Maci writes "Foxnews.com is running this article on a plan being developed to revamp the Hubble Telescope with a new set of lenses that will boost it's magnification 10X. The stumbling block, NASA's non-existent budget."
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A New and Improved Hubble Telescope? More

A New and Improved Hubble Telescope?

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  • The amount of data/images/info generated by the Hubble 'scope has been incredible. It has also been invaluable for generating a "WOW" response from the general public and raising interest/funds in NASA. If this doesn't cost too much, then it should be funded....seems like the most bang for the buck. Funding shouldn't be too hard to get.. the public is kinda familar with Hubble and that usually makes things easier. The money spent there generates something real for them (Ooh,pretty star picture) and is there easier for them to allow/want funding for it, as opposed to something more abstract/obstruse like most basic science research.

    By the way...does NASA have any ideas/plans for a linked array of visable telescopes...multiple small telescopes all linked so that they act as a super large telescope?

  • Sounds nice on paper, but ... (Score:3)

    by hubie ( 108345 ) on Friday September 08, 2000 @06:03AM (#794475)
    The article is long on details on what one can do with a big mirror, but it doesn't go into the major technical problems you'd run into. There is a reason that mirrors have the particular thicknesses they do, which has to do with stability. You can't just arbitrarily grind off the mass of a mirror without some major consequences. The article doesn't mention what they would do to handle the stresses and strains that the very thin mirror would undergo. A glass mirror that thin is going to flop all over the place unless you can control the mirror shape, and we're talking about controlling the shape down to nanometer length scales (assuming you want diffraction-limited quality, which is something like better than 1/14 of the wavelength averaged over the useable surface).

    Keep in mind that this isn't a quick and easy retrofit for the Hubble. This is a major undertaking which would require a major budget. The article comes off sounding like it would be cheap and easy and silly not to do, whereas it would probably turn out that for the kind of money you'd be talking about, you might as well spend a little more and build a new, better telescope from scratch.

  • The array of visible telescopes is what the NGST [nasa.gov] is about (to some extent-it uses segmented mirrors acting as one). More directly, the Space Technology 3 [nasa.gov] mission is supposed to address this.
  • The bottom line is that you cannot do the job with an arbitrarily thin piece of material because the disturbances will kill you. Remember, you have to maintain the shape to nanometer-scale. Shave off most of the glass and back it with any material you want, but now you're back to a heavy mirror because of all the backing material, or you have differential expansion problems between the mirror material and the backing material. Also, if you do manage to make the mirror thin and light, you still have the problem of de-coupling the satellite disturbances from the optics system (where all the extra mass in the mirror actually turns out to help you).

    Gravity is not the limiting factor for ground-based mirrors, at least not for performance reasons. They didn't go to a segmented primary on Keck because of gravity effects, they went that way because you just cannot make a monolithic mirror that big with decent optical quality under any reasonable budget (not to mention that it would be about impossible to get it up the mountain if you did build one). And for some of the same reasons you can't just make an arbitrarily thin Keck-sized primary and back it with all the new composite materials because it will not hold the mirror shape down to nanometer levels. Believe me, it would have been done a long time ago for both ground and spaced-based telescopes.

    My original point is that this is a very tough problem, which did not come through in the Fox News story. The story made it sound like you just shave down a mirror and stick it on Hubble with some shower curtain light shields. I don't think this idea will fly because not only of the technical challenges involved in grinding, mounting, and flying it, but also because NASA is already spending good money on thin-mirror research. I personally find the most exciting areas of research here to be flying individual telescopes and combining their signals the way radio astronomers do, or the ideas on very large thin metallic films that unfurl and are kept in shape using electrostatic forces (such as in the link I provided in my earlier comment).

    (BTW, I appreciate the discussion on this. Mostly all I see on /. are postings of only one or two interesting comments (usually lost in the noise), lots of noise, or lots of "me too" comments.)

  • Or possibly a car wash. NASA execs could stand on the corner holding signs...
  • ... The article doesn't mention what they would do to handle the stresses and strains that the very thin mirror would undergo. A glass mirror that thin is going to flop all over the place unless you can control the mirror shape, ...

    And exactly what is going to make it flop around?? This is in Space remember - ie. vacuum, no wind, no gravity, ... nothing to make the mirror deform apart from temperature gradients and the telescope's own tiny pointing movements. The mirror has only got to maintain its own shape which can be accurately set before launch/install.

    The main reason big telescope mirrors are hard to build (apart from lack of money! :) is that they deform under their own weight - no such problemo up there dude.

  • I agree, I'd like to see their proposal too. And perhaps once I did I would come around on it, but I am still very skeptical that it could be pulled off as easy as they (or at least the Fox reporters) say.

    Perhaps they should be given money just to take the VLT mirror and make the primary. Then they can test it to get an idea if it should be tried. Or, if that is too expensive, maybe they could be given a spare smaller glass mirror and grind it to the correct proportional size to see if it would work.

  • Temperature gradients can be huge! Remember that you are talking about a very thin piece of glass here. You had better hope that the coefficients of expansion is isotropic too because you can get some unpleasant occurances (e.g., cracks) in thin materials if they don't expand isotroptically.

    Gyro vibration. You have to continually run the gyros to keep them pointed in particular directions, and these will cause vibrations. Thursters will shake the whole thing too. If your glass it too thin you'll start it vibrating like a drum head.

    Also keep in mind that structures behave in completely different ways in zero-G. You might have characterized all your structures on the lab and have damped out most of the disturbances, but you will find that there are whole different modes of vibration in space. Something that wasn't a problem on the ground is now a problem in space.

    Telescopes are not hard to build because they deform under their own weight; in fact, their deformation is easy to predict thanks to Mr. Newton. Large optical quality mirrors are ground to allow for their sag on the earth.

    Remember, the Hubble mirror (and other mirrors in space) is as thick as it is because it has to be that thick. Believe me, the cost per pound to put somthing in orbit is so high, they made that mirror as thin as they could. You can't just artibrarily grind off most of the mass unless you can elsewhere compensate for all the problems you introduce. Maybe they have an idea on how to correct for all the aberrations that they'll have in the mirror (such as adding an active secondary, but here you start adding more and more R&D money), but they didn't mention that in the article. Or maybe the telescope isn't supposed to be optical quality and they want to use it in front of spectrographs.

    There are many efforts all over the globe to come up with ultra-lightweight mirrors for space (see for instance some work [spacedaily.com] at the U. of Kentucky). If you have a good idea on how to do it, you can make some nice bucks for yourself. :)

  • And exactly what is going to make it flop around?? This is in Space remember - ie. vacuum, no wind, no gravity, ...

    Well, the lauch is a pretty shaky 5 g or so! Seems to me it could do a lot of damage to a big thin sheet of glass?
  • yes, temperature gradients are huge, and there are vibrations etc. But the basic point is that glass is NOT a good material for strength. Use the absolute minimum of (heavy) glass and get all the strength and stiffness from carbon fibre or a similar material that is designed for strength and light weight. Hence a thin mirror bonded to a stiff and strong backplate, NOT a thick mirror.

    If you think differential expansion is a problem then deliberately put grooves in the mirror (like the gaps in concrete pavements) to let mirror segments move apart. As long as the stiff backplate remains parabolic you have no problems.

    It just seems like a correct material for the job issue to me... ???

    BTW, mirrors on earth ARE limited by their deformability under gravity simply because they rotate and point at different angles to gravity, and so deform in a complicated way. Hence people now avoid single large mirrors and use segmented mirrors like Keck.
  • Amusement parks is the answer! I want titan rocket engines on roller coasters!

  • From a BBC Article [bbc.co.uk]:
    A task force established to assess the threat of so-called Near Earth Objects (Neo's) has concluded that the risk is not science fiction but something that should be taken seriously.


    The three-member team called on ministers to seek international partners to build a new £15m telescope dedicated to sweeping the skies for threatening objects.

    The three-metre (9.8 feet) survey telescope, based in the Southern Hemisphere, would be designed to detect objects down to a few hundred metres across.


    There's also a wire story on the study here [yahoo.com].

  • Arraying multiple 'scopes is a tough feat. The problem is this: to composite the image you have to know the distance between them in units comparable to what you're measuring — in this case, wavelengths of light which are measured in Ångstroms. Keck 1 and 2 do this, but they sit on the same mountain in Hawaii. The VLA and VLBA have been around awhile, but radio wavelengths are much longer than light.

  • The article is long on details on what one can do with a big mirror, but it doesn't go into the major technical problems you'd run into.

    I haven't read the paper, but Jim Crocker and John Trauger are both pretty smart cookies -- and they've apparently thought things through well enough that Bruce McCandless has bought off on it. Sure, the article doesn't go into this -- but the article is a Fox News article, fergawdsake, not a peer-reviewed publication!

    My money says they've thought of everything you're bringing up as an objection, and have a fix for it. Crocker even commented that his first reaction was the same as yours: "Wow, that'll never work." I doubt that any of these guys would risk their reputations on something just slopped together.

    Keep in mind that this isn't a quick and easy retrofit for the Hubble. This is a major undertaking which would require a major budget. The article comes off sounding like it would be cheap and easy and silly not to do, whereas it would probably turn out that for the kind of money you'd be talking about, you might as well spend a little more and build a new, better telescope from scratch.

    I haven't read their proposed budget, either, but the article does talk about money -- and says it should cost maybe half of what doing it from scratch would cost. Other plusses are the fact that they're using a spare mirror from the Very Large Telescope (which is a ground instrument, BTW, which speaks to some of the excess thickness) and also using a proven spacecraft and subsystems. Sounds reasonable and relatively cheap to me...

    I think the hardest, riskiest part of the proposal is the orbital refitting: working in microgee conditions is difficult, and they'll have to be extremely careful not to damage Hubble (old and new parts).

    On the whole, it's an intriguing proposal: I'd like to see some details of what they intend to do, before condemning the whole idea.

    ---

  • The main difference between the Hubble and the new super advanced telescope they're planning to launch in 2008 is that the Hubble "sees" visible and UV while the new one "sees" only infrared radiation. Having actual pictures of space is important for marketing to the public (imagine what would happen if there were publishable pictures of planets from another solar system that people could recognize and get excited about). Without visual cues that the money is being well spent, the people won't push as hard for space and NASA will get even less money from the government.

    What if there are planets out there that we could actually see? It could fundamentally shift the way we see ourselves and our celestial neighbourhood. Not to sound fanatical or anything but what if there are pre-radio civilizations out there that we could see but can't hear?

    Build and launch this mission ASAP!

  • We can waste money paying for artists to splatter paint on a canvas and decorate it with vaginal shaped manure, but we can't afford to explore the cosmos.

    NEA annual budget: ~$200 million
    NASA annual budget: ~$12 billion

  • ~$200 million too much for the NEA, there.

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