> 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.
