After you finish this, try playing some Doom for space-marine training.
Last year we learned that NASA was working on an Unreal-engine powered MMO game called Astronaut: Mars, Moon, and Beyond. It's partly a recruitment tool to get the younger generation interested in space exploration and research, much like the aims are with America's Army.
The final version of the NASA MMO isn't out yet, but released this week is Moonbase Alpha as a free preview. You've got nothing to lose, so grab it on Steam if you've always wonder what it'd be like to be a space cadet.
In Moonbase Alpha, you assume the exciting role of an astronaut working to further human expansion and research. Returning from a research expedition, you witness a meteorite impact that cripples the life support capability of the settlement. With precious minutes ticking away, you and your team must repair and replace equipment in order to restore the oxygen production to the settlement.