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[ex-ex-svin4.livejournal.com]

Откуда пошёл слух, что спутник-шпион из космоса якобы может прочитать газетный шрифт или номер машины?

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Вот дифракционный предел:

[ex-ex-svin4.livejournal.com]

All an imaging satellite is, really, is a large, space based optical telescope/camera, not unlike the Hubble Space Telescope.

The resolving power of any telescope can be calculated by the following formula:

θ = 115.8/D

where θ is angular resolution of the objective, expressed in seconds of arc, and D is the diameter of the objective in millimeters.

This is commonly referred to as the Dawes limit of the objective, and is quite a good estimate of the theoretical resolution the objective is capable of.

The Hubble telescope has an objective of 2.4 meters and this is probably pretty close to the maximum diameter that can be launched into space with currently available launch vehicles, so the NRO satellites can't be much bigger than this.

The Dawes limit of a 2.4 meter objective works out to around .05 seconds of arc.

To figure out actual size of an object from its angular size at a given distance use the formula:

angular size(in degrees) = 57.3*actual size / distance

For a distance of about 650 kilometers, which is likely a typical operating altitude for imaging satellites, this works out to right around 10 centimeters.