• YOU HAVE MY SYMPATHIES Xenomorphs, facehuggers, necromorphs, predators, whatever: the threat you're up against is some kind of being you've never seen before. Perhaps they're engineered somehow, perhaps they've evolved this way. Either way, I hope you can figure out how to kill them before they kill you.
• I'M AFRAID I CAN'T DO THAT Why the hell did we think building un-tethered AI was a good idea? Your threat is an android, or a ship's AI, or I don't know, a sentient race of evil ships that want to destroy all life and suck it into tubes to make a weird baby shaped ship. WHATEVER. The point is, technology is going against you. Can you beat out something with that much processing power? Maybe having bigger firepower will help.
• I LOVE... ROCKS Your threat is environmental. An exploding sun, an alien planet with an inhospitable atmosphere, your ship's life support systems have failed, your shuttle has gone down in flames. Can you cobble together some way to fix the problem before you all die?
• THIS IS NOT A RESCUE SHIP Screw the other problems, what you're up against are HUMANS. Or, you know, whatever species/race matches yours. We're not xeno-racist here. Anyway, you're being targeted by your own. Maybe you're in the way of a scientific development, or you've become expendable, or they want to take over your ship, or they're just plain evil.
• ABOUT 15 SECONDS Holy shit. Holy... shit. You were outside your ship making repairs and you got knocked off track. Maybe your fancy magnetic boots failed. Maybe some debris from your ship took you down with it. Either way, your space walk has become a space "holy shit help I'm going to get spaced, someone get me back on board." Try not to panic.
• WE'RE THE ENEMIES You've been out in space too long. Everything is going strange and everything is a threat. Is your space sickness psychological or physiological? Is it spreading? Is there a cure?
• PLANETSIDE Crash landed. In an outpost. Building a new life. You're on a planet not your own and things are going horribly wrong. What can you do when you have no way home?
• STATION SWEET STATION Whether you're out in your ship or in a streamlined space station, things are rotten in Denmark. You'd better fix that circuitry before you all die. Just a suggestion.
• THE GAPING MAW There's nothing around you and all you can hear is your breathing. Are you calm? Panicked? What's it like floating in the vast expanse of space?
• IT'S INEVITABLE You're lost in your own head. You can be anywhere, but maybe you're the threat because you've short-circuited from being in space too long. The mind can only take so much. Try to be gentle. Try to breathe. No one's after you, it's all in your head.
As always, these are just suggestions. Also, not all examples are strictly hard sci-fi but we do what we want in these parts. Make up anything you want, as long as you're having fun!