Your ship has sustained massive damage, is falling apart around you, and is drifting toward the ultimate catastrophe, a black hole. You are alone.
Your challenge in Lux Aeterna is to draw and play all of the cards in the main deck, one turn after another, without the spaceship collapsing completely or falling into the black hole. Cards have multiple functions; you will assign drawn cards to one each of these functions each turn:
As damage to a system (with six systems available to you);
As an action to help stay alive/fix the ship; or,
As movement toward the black hole.
If a ship's system collapses, the game will get harder for you; if you should repair a system, then you just might avoid the ultimate doom.
Events (called "glitches") can be seeded into the main deck to make things even more difficult, as will reducing the real time that you have to play: 12 minutes -> 10 minutes -> 8 minutes, etc.
—description from the designer