< Now it seems to me that there's no way these spy satellites can get
< around that diffraction limit, except by having a primary lens or
< mirror that's bigger than Hubble's. But I don't expect that they do.
< So I think that the rough estimate of the spy-satellite resolution
< must be overly optimistic.
< Anybody care to comment? Some of my numbers or calculations could
< be wrong, or there could be some physics I'm missing.
Well Ted you raise a good issue and one which I frankly havent thought about
much. So last night I pulled out some of my references and took a gander.
I believe you are underclaiming Hubble and ground based resolution by about
1 order of magnitude. My copy of "the New Cosmos 4th ed" by Aldrech Unsold
gives Hubble resolution as .008 arc seconds and best ground based resolution
as .03 arc seconds in chapter 3. Now this hubble resolution is in a different
mode where spectrum and field of view are resricted and it sounds like some
sort of photomultiplier is used to enhance the image brightness.
Also I pulled out "Deep Black" by William e. Burrows, a reading of which was
the basis for earlier statements of a ballpark nature. Burrows is a science
journalist, so we need to be careful, but he has covered military technology
etc for the NY Times, Washington Post and Wall street Journal over a 25 year
period and is a professor of Science journalism at New York University. It
appears that he has developed most of his info from congressional and military
contacts (including defense contractors) and he provides 45 pages of notes
on sources.
Anyway Burrows claims Keyhole 8 has about a 1 foot resolution and one of the
later ones has 4 inch resolution. He points out that you can make out the
windows on the russian carrier photo that graced the cover of Jane's one month ( I looked at that issue a long time ago, right now all I can really remember
is being impressed) It sounds like the Keyhole 8 has about an 80 inch large
mirror and uses a configuration with a secondary mirror that increases the
focal length beyond what would be practical for a telescope on the ground.
As for orbit heights, he claims keyhole 8 has about a 100 kilometer perigee
and 300 kilometer apogee.
An interesting physics problem which spurred my interest in spy satellites
is to calculate analytically the torque applied over a period to a satellite
due to the fact that the earth is really an oblate Spheroid not a sphere.
(There are 2-3 problems related to this in chapter 3 of symon's mechanics
book, note that the torque problem 3.56 has a star by it, which is deserved
I can attest) anyway the result is that the torque depends on the angle the
satellite makes with the equator and that the satellite will precess west
each revolution. A related simple problem is quantifying the advantage of
launching east versus west.
Regards
Graham Flower ms 90-TT | Better to have convictions and act on
Hewlett-Packard 350 W Trimble Rd | them, even if they are wrong, than to
Microwave Semiconductor Division | waffle in indecision.
