Re: Mars Orbiter Sees Rover Tracks Among Thousands of New Images

From: Bart Declercq (bart_at_mira.be)
Date: 09/28/04 

Date: Wed, 29 Sep 2004 00:18:23 +0200

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!!!

Relevant Pages

  • Re: Mars Orbiter Sees Rover Tracks Among Thousands of New Images
    ... >> Resolution of 50 cms per pixel for Mars! ... Before the atmosphere wiggles. ... then the resolving power is as follows: ... The Hubble-telescope has a 2.4m mirror, ...
    (sci.geo.geology)
  • Re: A new style reflecting telescope
    ... As you've known, larger the size of mirror becomes, more ... the reason for a telescope is magnification. ... Are light gathering capacity and resolution capability the same?. ... eye (or smaller receptors, but the size of the receptor is fixed ...
    (sci.physics)
  • Re: Question about telescope design.
    ... that of a 3 m strip up and down the block. ... slice from the mirror of a normal telescope. ... resolution and brightness benefits of large-aperture mirrors. ... surfaces whose radius of curvature varies all over the place. ...
    (sci.astro.amateur)
  • Re: Question about telescope design.
    ... that of a 3 m strip up and down the block. ... slice from the mirror of a normal telescope. ... support structures to that level of precision, ... resolution and brightness benefits of large-aperture mirrors. ...
    (sci.astro.amateur)
  • Re: Sony A100 to A700
    ... resolution lenses if you can get the back of the lens closer to the ... sensor than the mirror allows. ... mirror is to get the optical viewfinder, and the only reason we need ...
    (rec.photo.digital)