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From: truett@cup.portal.com
Newsgroups: sci.space,sci.crypt
Subject: Re: satellites
Message-ID: <2534@cup.portal.com>
Date: 17 Jan 88 10:50:40 GMT
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In order to beat the apparent diffraction limit, you don't even need a rigid
frame for the multiple mirror setup.  The method is called active optics and
it works like this:

First you drop a small corner reflector somewhere in the Lebanese highlands.
Then you put an array of mirrors and CCD detectors into orbit together with a
small laser.  Now, use the reflected signal of the laser from the corner
reflector to get the optical sensors all phase to withing a fraction of a
wavelength of light (or infrared, that's even easier).  The resulting system
has an effective appature much bigger than a sigle mirror.  I suspect that
arrays with an apparent aperture of 20-30 meters can be orbited easily.

Another note.  Each of the optical sensors is using folded optics with a very
long focal length (probably up to ten meters) and for pictures in daylight, a
very high f/stop would be used resulting in extreme depth of field.

There is also nothing that says the observation had to be in visible light.
I believe that synthetic aperture radar achieves a resolution of half the
antenna diameter.  It should not be too difficult to put a microwave radar
on a satellite that can achieve a three-dimensional image to a resolution
of a few inches.  Such a system can even provide sequential images giving
you a movie of the action below.

Now, use the reflected laser light to puat an array of synthetic aperture
radars in phase (thus overcoming the higher diffraction limit of microwaves)
and the results can be very interesting.

Truett Lee Smith, Sunnyvale, CA
UUCP:  truett@cup.portal.com