From: Stephen D. Williams (sdw@lig.net)
Date: Sat May 12 2001 - 08:30:13 PDT
kragen@pobox.com wrote:
>
> Eirikur Hallgrimsson <eh@mad.scientist.com> writes:
> > I think a space telescope could be seriously cost-reduced. The mirror, after
> > all, could be a foil or membrane of some kind, probably in an array rather
> > than as single big piece. This lends itself to focusing at different
> > frequencies, which I've not heard about anyone doing except by playing with
> > where the focus falls.
>
> I don't think mirrors focus different wavelengths of light in different places.
Defintely not, but is that what he meant?
>
> It's probably possible to build a mirror the way you're describing,
> but it isn't easy. The surface of the mirror needs to approximate a
> parabola to within a fraction of a wavelength of the light you're
> interested in focusing. (Shorter wavelengths can be focused into
> sharper images, given the same mirror.) Positioning all the elements
> of an array of large mirrors relative to one another to a precision of
> 50-100nm will not be easy.
Reactive feedback control could do it. Using more than one wavelength,
you pulse from the focal point through the mirrors and measure their
distance with calibrated hardware built in to the corners of each mirror
(or 3 points). I'm sure there is a better method, but the idea is
sound.
sdw
-- sdw@lig.net http://sdw.st Stephen D. Williams 43392 Wayside Cir,Ashburn,VA 20147-4622 703-724-0118W 703-995-0407Fax Dec2000
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