Two telescopes in the news

Two rather famous telescopes have hit the news for different reasons. The James Webb Space Telescope is the subject of an article in the Yale Daily News. The 6.5 metre infrared telescope, which will exceed Hubble in its resolving power and sensitivity, though operating on different wavelengths, is set to launch in 2014 for a decade of observation. The article, which reports on a lecture by Nobel Laureate Dr John Mather is here.

From the largest proposed space telescope to the largest existing single dish radio telescope. The Arecibo Observatory in Puerto Rico, famously felled by Pierce Brosnan’s James Bond in the closing scenes of Golden Eye, has received a glowing reference from the Near Earth Object Surveys and Hazard Mitigation Survey. The report, which details how NASA’s present surveys and facilities are in general insufficient to keep tabs on asteroids and comets above 140m in size, praises the radio telescope as the best individual tool available for imaging and tracking NEOs. The report comes as Arecibo looks to be on the brink of having its funding reduced to a level that will entail its closure. It is believed the glowing reference is a necessary but not in itself sufficient step to securing new funding, according to Astronomy Now.

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6 responses to “Two telescopes in the news

  1. Gregg Weber

    I hope that they have figured out the answer and might not get the answer here but here is a question about Webb;
    What protects those mirrors from micro meteor damage that would either produce pits that slowly lower the effective surface or produce facets that would reflect other light sources onto the sensor?

    • Space telescopes come with shielding, both a cap and the long tubes – telescopes of this kind don’t have any optical reason to have long tubes (the ground based versions don’t have them at all), they’re just there to limit the direction the damage can come from. A bit of degradation will also be allowed for, with a view towards only keeping the telescope operational for ten years. Damage to the tube doesn’t do much in terms of reflecting light into the mirror, but if reflections occur, they can be removed by ordinary post capture data processing. The position the telescope lies at will also have been taken into account. But this is an ongoing problem, and some parts of the Hubble Space Telescope, either examined in orbit or brought back during the recent servicing mission, have been under scrutiny to get more data on this problem. So in summary, a load of techniques ranging from things learnt in the past few decades of space telescopes and keeping data from ground based telescopes as pristine as possible are used to mitigate the problem, but it will still be a bit of a problem and one the engineers believe the telescope can live with.

  2. Gregg Weber

    Thank you for your reply but I still don’t like the idea of a disposible expensive space telescope. Mt. Wilson is still in operation and many others, like the Hale, which were the biggest and best at one time but is still productive in other areas than being, to mix metaphors, at the spear point of knowledge gathering.
    I had thought of eventually placing the Hubble on the moon but realized that it was not made to be under gravity. I suspect that the next thing would be to have a tug to capture, and tow it to the ISS for repair and updates, maybe even in an enclosed “shed”, “dock”, or “hanger”, and than return it and go rescue some stranded crew to go to the ISS. But that is another thought.
    The same can be done to the Webb telescope at some future time rather than throwing it away.
    Tangent: What happens to old mirrors from old telescopes? Are they reused?

    • I would prefer it that way too, but the funding simply isn’t there for an extension to these missions. There was a proposal to bring Hubble down to be put in the Smithsonian, but it was rejected out of hand as being too expensive, a lunar mission (which would involve putting Hubble on a mount and protecting it from all sorts of things) would be much more expensive and much more technologically difficult than that. On the last service mission a band was placed on Hubble to allow a tug to move it, but the only funding presently available is for the tug to pull Hubble to a fiery death in the atmosphere. One of the proposals currently before the US Human Spaceflight Plans Subcommittee is kind of like the hangar idea, with telescopes pulled into lunar orbit for repair, but again it isn’t likely to get funding. In essence we’re getting the benefit of diffraction limited astronomy, but only with time limited telescopes. These things are suggested by NASA who would love to keep sending people up there to fix things and keep them working, but these are big missions with bigger price tags. Another problem is Hubble is a relatively small telescope, it is the lack of atmosphere that gives it its boost, and its job is slowly being taken over by adaptive optics systems that remove the atmosphere in other ways, so it won’t be staying at the top for much longer. Obviously JWT is a bigger telescope, though 6.5 metres is hardly the thirty metre telescope, and NASA will look to extend it in the same way that Hubble’s life has been extended.

      Old mirrors can and often are reused where possible. Old lenses too – in the last observatory I was employed at, our telescopes dated from the end of the nineteenth century and still did occasional research even in London’s skies. If a telescope becomes too small for research (which in fact never happens, there’s always some sort of research that can be done) then it simply moves into teaching. If a telescope becomes too degraded, then it can be resilvered (mirrors) or carefully cleaned (lenses) and put back into use. There’s always someone out there who’ll pick up an old mirror of whatever quality. I remember when my offices in the atmospheric physics laboratory were moved and we had to dispose of infrared telescopes that had been flown on balloon missions twenty to thirty years ago. We gave them to the optical science laboratory who took the working bits out and put them on new instruments.

  3. Gregg Weber

    Another possibility might be to make it part of a binocular telescope by sending up a new scope plus the interconnection and merging equipment. I would imagine the longer the interconnection the better the resolution, but there would probably be a need for laser distance measuring to keep the alignment good.

    Is distance or relative speed a concern with interferometry? Two scopes some distance apart and with a relative speed comparable to the rotation of the earth as they revolve in tandem around the earth. Again comes the laser measuring even with a cable holding them against some sufficient centrifugal force.

    I would rather it put into a nearby solar orbit so later on it can be taken out of “mothballs” and used again.

    • Distance is the main concern for interferometry in general, but it would be nice to know the satellites kept pace with each other too, the two telescopes must be kept a set distance to within half of whatever wavelength they’re working in. Systems were developed for the LISA mission that never flew, the proba 3 satellite constellation will be testing such a system and the Darwin exoplanet imaging mission will be a four (each 3m) telescope infrared interferometer, but the technology won’t be ready for the JWT, plus it would mean building and launching another one and severely altering the design. You’re right that increasing the distance will give better resolution, in aperture synthesis the separation becomes the effective mirror size (except in terms of sensitivity, which still relies on the combined size of the mirrors used).

      Nearby solar orbit would still leave the telescopes open to damage from micrometeors, the solar wind and the Sun’s radiation. The Lagrange point behind the Earth tends to be the favoured spot for telescope parking at the moment (which is where Planck and Herschel are currently lying and operating). There are five Lagrange points in any two body system (Earth-Sun, Earth-Moon) areas where the gravities of the bodies add together or cancel out, satellites can orbit or park on them (the ones either side of the Earth have the STEREO sun observation telescopes for example) just as they orbit planets. But again, there’s a limit to how long anything can survive out there.

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