Re: Ground-based image of STS+ISS

From: Jeff Umbarger (jumbarger2000@yahoo.com)
Date: Thu Jun 28 2007 - 18:38:50 EDT

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    Hey George,
         A question: with some adaptive optical systems,
    you do not, necessarily, need a nearby guide star to
    monitor, to use to back out the atmospheric distortion
    with mirror actuators. In fact, I would think in this
    case, with a satellite (i.e.; the ISS/Shuttle in low
    earth orbit) you wouldn't be able utilize stationary
    guide stars unless you could work quickly. Instead,
    aren't there methods of "creating" a guide star with a
    co-axially mounted (sodium?) laser to illuminate the
    upper reaches of the atmosphere near the object being
    tracked so that you can back out the distortions of
    the new guide star/illumination point? And you are
    using coherent light. Is there a laser associated with
    this system for that purpose?
    
         Regards,
              Jeff Umbarger
              Plano, TX USA
    
    --- George Roberts <gr@gr5.org> wrote:
    
    > >I'm impressed...
    > >http://antwrp.gsfc.nasa.gov/apod/ap070628.html
    > 
    > >I've just put my 8 inch scope in the trash can !!!
    > Thanks for the chuckle!
    > 
    > ... or how to make a good satellite photography
    > system:
    > 
    > The telescope used to take this picture is a 15
    > minute drive 
    > from my house and I have visited it about 6 times. 
    > It 
    > belongs to a private school for K-12 (this isn't the
    > only 
    > impressive part of the school by a long shot - this
    > is a very 
    > rich school).  The telescope has a mirror that was
    > ground to 
    > much better smoothness and figure than typical
    > mirrors of 
    > it's size (25 inches).  The telescope has an active
    > adaptive 
    > optics system that corrects only in x and y (some
    > adaptive 
    > optics systems have hundreds of correctors). 
    > According 
    > to Ron Dantowitz who runs the telescope a single
    > corrector 
    > fixes most of the atmospheric distortion.  I don't
    > know if this 
    > system works with photographs like this one where
    > there is 
    > no reference star.  But the seeing is very good at
    > this location - 
    > the telescope is mounted on the roof of a 4 story
    > building (with 
    > a pier that runs through all 4 floors into granite
    > below - 
    > vibrationally separate from the rest of the school)
    > and 
    > this building is on top of a hill, and typical winds
    > run over 
    > a large farmer's field before hitting the hill.  All
    > this reduces 
    > turbulence.  This telescope is used by the Navy each
    > night 
    > remotely (after Ron goes home) to search for planets
    > 
    > around other stars using laser-spectroscopy and Ron 
    > seems to think it is the most accurate device on our
    > 
    > planet for this purpose because of the telescope's
    > unique 
    > features.  Located about 8 miles from light polluted
    > Boston - 
    > obviously one can do serious astronomy in light
    > polluted skies.
    > 
    > There is a picture of the building (and the
    > telescope dome) in 
    > the upper corner of this web page:
    >
    http://www.dexter-southfield.org/podium/default.aspx?t=10557
    > 
    > - George Roberts
    > http://gr5.org
    > 
    > 
    > 
    > 
    > 
    >
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