I have been rereading More of the Straight Dope (copyright July 1988), which mentions that spy satellites can see objects on Earth of about a 6"x6" size. Considering that Mars has a thinner atmosphere with less pollution, how come there are not better photographs of the surface? (The simple answer would be that they haven’t sent any decents satellites to orbit the place, but I guess the question is why not?)
Here’s a nice picture of Mars. 
Nasa launched the Mars Global Surveyor spacecraft in November 1996. It arrived at Mars 12 September 1997. It took pictures of practically the whole planet, with resolution down to about one metre. I’d call that a pretty decent satellite.
High resolution spy satellites are huge - roughly the size of the Hubble space telescope, which weighs about 15,000 pounds. That’s just way too big a piece of equipment to send to Mars. It would take a gigantic amount of fuel to get it on its way there and then to brake it into orbit when it arrived. Mars Global Surveyor only weighed about 2300 pounds in Mars orbit.
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Cost. The big spy satellites (KH-11) are larger than the Hubble Space Telescope. The Space Shuttle is the only heavy lift transport we have capable of hauling something that big into orbit. And then you’d have to make a second mission to haul a rocket and fuel into orbit to fire the thing to Mars.
Then there are other issues as well - For one thing, images of that high a resolution would be huge, and require a lot of bandwidth or time to transmit back to Earth. That means you can’t take all that many of them. Wanna take a guess at how many photographs you’d need to take to map the surface of Mars if each one only resolved an area of maybe 500 square feet?
And we know where to point the spy satellites - a shipyard, airport, etc. Where are you going to point your camera on Mars? Without knowing what’s on the ground in the first place, snapping pictures of random 500 foot areas is a big waste of time, because the vast majority of such photos would just show you a bland landscape.
So we take steps like we’re doing. First send a global surveyer to map the planet in low resolution. Then send another satellite to focus on temperature and chemical sensing. Send some tiny landers to actually check out some areas.
After you’ve collected and crunched all your data, you may find some areas that are extremely interesting, either because of geological features, possible vegetation or water, or whatever. Once you’ve collected enough such sites to warrant another mission, THEN maybe you send a higher-resolution orbiter to map them, or landers, or humans. We’re not anywhere near that point right now.
Besides the size issue, there’s also the money issue. An earth-orbit satellite with a 6" resolution is not cheap. The US has a nice one, the KH-12. It can do 10 cm resolution. It is also estimated to cost about $1 billion (back in 1989 even). The whole MGS project cost significantly less than that, around $200 million.
Also, the FAS has a nice page on the KH-12, if you want to see what kind of hardware you need to get those nice resoultions.
For starters. . . maybe the “Mars Face.” The canals. Then the other ancient ruins that NASA is covering up. The River Iss. The list goes on and on. . . .
Oh gosh, I hope you’re kidding …
About 3.12 trillion images. What do I win?
I though that 1 meter was about the best resolution we have with spy satellites, but I suspect I haven’t been keeping up with the technology (and on preview, I see my suspicions are confirmed). Mars has already thoroughly mapped via the Mars Global Surveyor a couple of years ago. I’m not sure what we would want a high altitude satellite for- to look into the nooks & crannies? I’m not saying that there’s no reason why we wouldn’t want to have high resolution close up glossies of martian rocks, I just can’t think of any at the moment.
Evilhanz: You’ll get NOTHING, and like it! You were supposed to guess. You gave the right answer. No cookie. Go to your room.
It would be ‘nice’ to have a KH-12 in orbit around Mars for sure. But we live in a world of finite resources. I suspect that putting such a satellite in orbit around Mars would set you back at least 3 or 4 billion dollars, which is 30 or 40 times more expensive than the Mars Pathfinder mission.
Also don’t forget that those big birds need maintenance. They need manoevering fuel, for one thing. A lot of those ‘secret’ shuttle missions are no doubt service missions for some of the larger sats, and the Shuttle has been up to service the Hubble a few times. Pretty tough to do that in Martian orbit.
Yep, NASA started there with the MGS.
Thats a great image! I’ve never seen that before. Thanks for the link!
