Message du 19/04/14 21:49 De : "jim bell"
From: Troy Benjegerdes To: jim bell
[I didn't get a bounce off of CP the first time] Izvestia'.) An approximation I once heard is that a lens or mirror of about 4.5 inch in diameter can resolve an >>angle of one arc-second. A mirror of the size of the Hubble Space Telescope (which I assume approximates >>that of the typical spy satellite today) is about 20x larger, so the resolution should be 20x better, or 1/20 arc->>second. That's 1/(57 degrees per radian)(3600arcseconds per degree)(20) = 1/4,100,000 radian. From an >>altitude of 500 kilometers, that's about 1/8 of a meter, or 120 millimeter. Maybe that's a pixel-pair, but it's far >>too large to resolve the text on a newspaper.
The best prospect to improve on this resolution would be to use a 'multiple-mirror-telescope' technology. > >Light-gathering capability isn't important in this application; high resolution is. Making a spy-telescope out of a >>few different mirrors, held precisely many meters apart, could conceivable achieve resolutions substantially >>greater than this. Jim Bell Such a mirror array would at some point reflect enough light at odd angles to be visible with the naked eye. I find it more likely that multiple-mirror-telescope tech would be implemented with a swarm of small satellites and extremely precise location tracking and a lot of signal processing later on.
I sure find that difficult to imagine! Particularly because the assemblage would presumably be flying at about 500 kilometers altitude, and would therefore be buffeted by extremely-small-but-significant orbital winds. In addition, the amount of information that would have to be interchanged (phase and amplitude, in TWO dimensions!) of an entire field of view would be phenomenal. What I suspect the US military would really like to see is a spy satellite at geosync altitude (22,000 miles) with an apparent aperture of perhaps 150 meters, so that it has roughly the same resolution on the ground as existing fast-orbital spy satellites. (orbital period circa 90 minutes or so). Jim Bell
Balloons, that's what the military uses for high resolution imagery. And they are so good to stay aloft that not even with a .50 machine gun you would be able to down it. The only way to do that is to fly a drone nearby carrying some pounds of dynamite and fire it off.