The caps lock key pauses Mars Rising while you are in the middle of a game, allowing you to take a breather or switch out to another application if you desire. To resume a game after you've paused it, simply depress the caps lock key.
The esc key aborts the game you're playing. This is not a quit key, but an end the game because the boss is coming in to the office key. It is only operational when you are playing the game.