Astronaut Spacewalk by Jorge Hernandez is the closest most of us will ever get to taking a no-tether trot in outer space. The delightfully complex and detailed simulation game gives you a screen filled with controls and a few simple missions to complete, then sits back and watches while you climb the impossibly high learning curve. It will take hours, not minutes, to learn how to maneuver your lone astronaut, and until you do, you'll probably feel confusion, bewilderment, and possibly a touch of anger. If you stick with it, though, you'll discover a game that shares the joys and wonders of space exploration tempered by the realism of science, and it's a wonderful experience indeed.

Orbital Defender is a great looking planetary defense game from Addictive Zone that has been acutely tuned for ease of use on mobile devices. As a lone satellite orbiting a single planet, it's your job to keep the rock safe from asteroids, comets, UFOs, and more nefarious dangers as you orbit over and over again. You can't move, only shoot, and since firing at your planet is a very bad idea, you have to play a little game of strategy as you blast foes each time you swing by.