As an astronaut, you go on space missions, eventually leading up to being the first man or woman on Mars. The missions consist of 3 or 4 major parts. Early on in the game, they include takeoff, an EVA to build the spacestation, pick up and deployment of cargo, a few science experiments, and reentry. These are the Low Orbit missions. Later, the missions include Space Station missions and Mars missions.
In this game you are in competition with other companies to be the first to reach Mars and then, once that objective has been reached, to mine Mars the most fruitfully. To win this game, you must come out on top.