QUOTE (edstrick @ May 5 2005, 06:04 AM)
Lunar orbiter 2 and 3 were capable of 1 meter resolution with the high resolution frames. Orbiter 1 had it's image motion compensation system fail, and the high rez pics from low orbit were smeared.
Orbiter 4 had 50 meter rez from periapsis in it's eccentric mapping orbit. Orbiter 5 was in a higher periapse orbit than 1 through 3 for science site mapping
As far as resolution possible from Mars orbit...
Remember a bit of physics called the "diffraction limit"
Hubble-sized optics in low earth orbit have a diffraction limit of maybe 5-10 cm on vertical pointed images... Hubble sized.. that's the big recon sats. You can see a licence plate but not read it. (that's what I understand, I've never seen real performance numbers)
Mars Recon orbiter's gonna be working essentially at it's diffraction limit, I hope and expect. If you want to do better, you're gonna have to buy a spare KH-11 or some such sat from the spooks. It wouldn't be easy to get it to Mars even if you had it!
Yeah, LO 2 and 3 got 1m resolution from pericynthion, which was (IIRC) about 35 miles (or roughly 50 km). Obviously, such a low orbit is impossible around Mars... IIRC, the Apollo pancam had the potential to get about 50cm resolution from the descent orbit (15 km pericynthion), but its motion compensation system didn't work well at that low altitude, and so that theoretical resolution was never achieved. But I do recall quite clearly that the maximum resolution of the Apollo pancam was significantly softened (by alterations of the optics) from the level the camera was designed to provide -- and provided in those self-same KH's you mention.
I don't have the link handy, but there is an excellent image from one of the KH's taken of a Soviet battleship in dock that displays the quality of the system. You can count the containers on the deck and identify individuals on the ship, on other ships, and on the docks. From shadow lengths, you could even calculate every person's height. Resolution was on the average of 20cm per pixel or better (since you could make out human forms, including arms and legs). And this was taken through Earth's thick atmosphere from at least 200 km. To top it off, it was a somewhat oblique-angle shot, so it was looking through more atmosphere than a straight overhead image would have to contend with.
DOD was *really* unhappy when that image was leaked -- it indeed showed that their systems could resolve something the size of a license plate, though, as you said, you couldn't read it. For example, you could tell there were markings on most of the visible containers, but they were dark blurs, not readable.
So, while HiRise is absolutely nothing to sneeze at, and will return extraordinary images, you *could* get higher resolution. And while it would probably *not* have to be a Hubble-sized instrument, it would almost definitely be beyond our current capability of sending all the way to Mars... HiRise is remarkably capable for an instrument that we *can* send to Mars, IMHO.
-the other Doug