Radar has been used on satellites for ocean surveillance before but it takes a lot of power. That means carrying a nuclear reactor, or enormous solar panels plu

Radar has been used on satellites for ocean surveillance before but it takes a lot of power. That means carrying a nuclear reactor, or enormous solar panels plus batteries. And a huge constellation would be needed to achieve anything like continuous coverage. http://www.astronautix.com/u/us-a.html http://www.astronautix.com/u/us-a.html It probably wouldn't be feasible to have a single constellation tracking both aircraft and ships. Different types of radar operating on different frequencies would be needed for those applications.