RemoteTech
Community developed continuation of Kerbal Space Program's RemoteTech mod.
RemoteTech allows you to construct vast relay networks of communication satellites and remotely controlled unmanned vehicles. Your unmanned vessels require an uplink to a command station to be controlled. This adds a new layer of difficulty that compensates for the lack of live crew members.
A detailed manual is available on-line.
Questions? Try the KSP forum thread.