A spaceship is leaking air rapidly, and soon everyone on board will die. The local chaplain does the mass absolution thing (the name of which I cannot remember at the moment), so that all may die in a state of grace. A nearby space station, hearing the distress calls, sends a small freighter to the rescue. The pilot, however, realizes that if he rescues the ship, it is statistically likely that someone aboard (it’s a big ship) will go apostate or otherwise sin mortally, and would not achieve heaven. If he does not rescue the ship, everyone aboard will die, but hopefully they will all go to Heaven. What gives?
The reverse situation is also troublesome. A spaceship (of the EVIL COALITION OF EVIL) blows up a space station. Another ship (of the GOOD COALITION OF GOOD) chases down the first ship. Because of the nature of spaceships and space combat, a single shot strike against the ECESS Evilface will completely destroy it, without hope of any survival of anyone aboard. Also by the nature of spaceships, every crewman aboard the ECESS Evilface knowingly and willfully brought about the destruction of the GCG Civilian Space Station Jerusalem 5. It is a requirement of civil and military justice that the GCGSS Goodface destroy the Evilface. But if they fire, they will kill everyone aboard, and presumably doom them to Hell. What gives?
This sort of question always reminds me of the old line, “What if there were no such thing as a hypothetical situation?”
The answer to your first scenario is, I think, obvious. Rescue the ship. It’s not our job to second guess the future. And it is emphatically not our job to do evil in the present (the sin of omission) by refusing to save lives because of some theory about what might happen someday. That’s just consequentialism of a particularly dangerous sort. You might as well kill everybody in the world since all of them are prone to commit *some* mortal sin at some point or another.
The second scenario is slightly more complex, but not much. First, there can be no morally binding “requirement of civil and military justice that the GCGSS Goodface destroy the Evilface” since the use of deadly force is a last, not a first, resort in Catholic teaching. The idea is that, under certain circumstances, you may have to kill, not that you get to kill (something many bellicose enthusiasts for pre-emptive war are still extremely unclear about). So the first thing to do is to order the ship to surrender. It is only if they try to attack or flee that you have the right to use deadly force—which you should do in order to prevent them from harming more lives. Once again, you are not responsible for the final destinies of the the crew. That’s God’s problem. You are responsible to protect the lives of innocents from a clear and present danger.