[davidcuddeback]

AmSat [1] is an organization of ham radio enthusiasts that are also very interested in space and satellites. They've launched a bunch of their own satellites into space that are available for anyone with a ham license to use to communicate. These satellites are usually named /^AO-\d+$/. That's what the AO-40 reference is to.

I don't know anything about the geosync or Mars sats that the GP is referencing. I'm assuming those were proposed AmSat projects that have never been launched.

Edited to add: A ham license is easy (and cheap) to get. I studied for a few hours and paid about $10 at a local testing facility to get my license (KI6BJU). The equipment is a bit more expensive, but I'm not sure how much it costs for a decent setup because I worked in a lab that already had the equipment.

Once you have a license and equipment, you can talk to other people over the AO-sats and download pictures from scientific satellites. I got my license when I worked in a satellite lab, and we used the equipment to download weather photos from NOAA satellites and helped gather data from other scientific satellites like NASA and various aerospace companies and universities. A lot of satellites have some sort of beacon with a public data format that you can decode.

[1] http://ww2.amsat.org/