I am seriously impressed! What an excellent application. You could put the 00:00:00:00 as default gps and disable gps until gps value has been set. Also, the map download might be nice to be on by default.

Also, if you have a look at google maps terms and conditions, it would seem that you are indeed allowed to use those maps (for non commercial purposes). But, as you have done, I don't think it's legal to provide app that does that automatically. Are NASA maps for free? You could put an option for those. Or a default setting.

Anyway. Jut an idea. Kepp up the splendid work. That app totally rocks!