[amsat-bb] More on imaging statellites...

Mark VandeWettering kf6kyi at gmail.com
Fri Oct 16 10:57:20 PDT 2009

> Getting an image is clearly possible, but only if you can get a certain
> agency known by its initials to do it.  Recall that Skylab, circa 1973, took
> some damage on launch.  Some amazing pictures were provided by said agency,
> among others, to assess what was needed for repair.  Now imagine 35 years
> later.  However, that is not going to happen, and in any case, there is
> little to be gained, though of course we are all curious.

I was interested in the details of this, and dug around on the web to
find some more information.  It appears that on May 16, 1973, a KH-8
"Gambit" spy satellite was launched.   These were apparently a "film
return" satellite, that would deorbit film cannisters.   Their
resolving power was said to be about 1/2 a meter on the ground from
orbit.   These satellites appear to operate in fairly low orbits (say,
between 220km and 350km), so let's take 300km as a reasonable orbit
height.  That means that their resolving power was around .3 arc
seconds, which implies that their imaging optics were about 15 inches
minimum in aperature.  (I am assuming a straight heads down imaging
geometry, if the resolution could be achieved at a different angle,
the imaging optics would have to be increased, and this didn't take
into account any atmospheric effects.   The reality is that .3 arc
seconds is probably fairly challenging through the atmosphere no
matter what size optics you have, at least without adaptive optics).
A bit more research bears this out: the KH-8 carried a 44 inch optic
with a 77 inch focal length.

Anyway, Skylab launched on May 14th.   The first crew launched on May
25th.     So, an interesting question was what imaging opportunities
were there between the sats?    Luckily, somebody else did all the
heavy lifting and made a nice webpage (thanks Ted Molczan!)


Ranges as low as 138km were acheived between the KH-8 and Skylab.   At
that range the nominal resolution of a 44 inch optic (which might be
achieved without atmpsheric effects) might approach just 7 cm.
Indeed, very good resolution.

Check out more info on Ted's webpage:


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