Robert Casey wrote:

Jack Harrison wrote:
Resolution of 50 cms per pixel for Mars! Excellent.

The highest resolution routinely available from NOAA satellites
orbiting Earth is 250 metres per pixel (Modis). It would be nice to
see pictures of Earth to resolution of 50 cms per pixel. Landsat?
But I can't find anything on internet.


Spysats are at least this good if not better. Spysats the
size of Hubble must be quite good. The atmosphere astronomers
complain about blurring their astro pictures probably don't
bother the spy sat guys, as sunlight on the items of interest
on the ground allow quick exposure settings in the cameras of
the spy sats. Before the atmosphere wiggles. Even at
night adaptive optics should be able to clean up the
atmospheric wiggles enough to see stuff. Someone who
knows the physics of optics for telescopes can probably make
a very good guess of the resolution one could get with say
a 1 meter reflector spy telescope.

Sure, it's not very difficult.
Assuming the following:
- No atmospheric distortion (or perfect correction)
- an altitude of about 500km (slightly lower than Hubble, but we're talking
ballpark figures here)
- a 1 meter primary mirror

then the resolving power is as follows:
Resolving power in seconds of arc is 115/D (with D = diameter in
millimeters), so here this would be 0.115 arc-seconds
1 arc second at 500 km = 500/206625 = 2.4 meters
so the max. resolving power of this scope would be 2.4*0.115 = 27.8 cm, or
about 11 inches for the Imperial-minded person.

The Hubble-telescope has a 2.4m mirror, wich would result in approx. 11.5 cm
resolving power, or 4.5 inches.

Basically, the laws of physics prevent the military from putting up a spysat
that can read license-plates or military insignia, because that would
require far too large a mirror to be launchable using existing rockets.

1cm resolving power at 1000km (remember, looking straight down won't show
license plates :-) would require a telescope with a 50 meter mirror,
something which would be somewhat noticeable if orbiting the earth...

But the other guys will
just do their dirty work inside buildings or underground...

But... think of the children, why won't anybody think of the children!!!