Xref: utzoo sci.space:4408 sci.crypt:782
Path: utzoo!mnetor!uunet!munnari!basser!jaa
From: jaa@basser.oz (James Ashton)
Newsgroups: sci.space,sci.crypt
Subject: Re: satellites
Message-ID: <1179@basser.oz>
Date: 19 Jan 88 10:12:00 GMT
References: <873@uop.edu> <2166@umd5.umd.edu> <4910@well.UUCP> <1952@netsys.UUCP> <7169@apple.UUCP> <1705@faline.bellcore.com>
Reply-To: jaa@basser.oz (James Ashton)
Organization: Dept of Comp Sci, Uni of Sydney, Australia
Lines: 21
Keywords: Diffraction Limit, Interferometry
Summary: Optical Interferometry

In article <1705@faline.bellcore.com> karn@faline.bellcore.com (Phil R. Karn) writes:
>You can get extremely high resolution images if you *simultaneously*
>photograph the same target from two or more widely separated satellites,
>and then *coherently* add the two images with an accuracy on the order
>of a small fraction of a wavelength. This is entirely practical at radio
>wavelengths (VLBI and SAR being two examples), but at optical
>wavelengths? Good luck!

It is true that interferometry is more difficult at optical wavelengths
but it is certainly not impossible.  The Physics department at this
university has sucessfully tested a prototype optical telescope which
uses two widely spaced plane mirrors feeding into an intricate optical
system.  The system was able to compensate for atmospheric jitter and
recombine the light to obtain very high resolution.  Work is currently
in progress on a full scale instrument which will have a maximum mirror
separation of 240 metres and the best optical resolution of any telescope.
Of course stellar images tend to be simpler than spy sat images but I
guess that a spy sat, could use a similar technique to obtain very fine
resolution.

						James Ashton.