Working up some rules for my OSR sci-fi game and writing up the entry for Astronavigation. Failure puts the ship off course by 1d10 lightyears. Failure with a roll of 95-99% puts the starship in imminent danger (comes out in an asteroid field, or just inside the atmosphere of a planet, etc). I've chosen to make a fail with 100% indicates that the starship comes out of hyper and collides with something, taking serious damage, or they phase back into real space within an object (an asteroid, another vessel, a planet, etc.), killing everyone inside.
Would this be too much for most gamers in the modern world? TPKs through combat with a superior force is one thing, but being due to the failure of a skill check by one player could be devastating for some folks, maybe. Thoughts?
I wouldn't, especially if they're expected to do so as part of normal gameplay.
Teleportation had a death percentage in D&D, true. But that was because it was a shortcut and an escape clause. The death percentage kept it from being abused trivially - you couldn't just go "oh, it doesn't matter if we get into a tough spot, we'll just teleport out" or "oh, we'll just teleport down there". It was available as a last resort, and could be used if you thought the overall odds were better than of surviving the trip to where you were going, but it wasn't a freebie.
If the only way to get from planet to planet is Astronavigation, then basically having a 1% chance of dying every session isn't very good design. I'd think about the overall structure of the game (what do players spend time doing?) and not put up artificial barriers to getting to the gameplay. If gameplay is "each session, go to a planet, explore around, and then go back" (the space equivalent of a dungeon crawl) then having a percentage chance of just nuking the session
when there's no way to avoid it isn't fun.
If Astronavigation is something that the players
can choose to do, then it's fine for it to have more risk.
If I wanted something like that, I'd probably allow the Astronavigation roll to determine basic range that you can safely pilot, as well as extended range. Traveling within basic range is safe and not an issue, and no roll is required. Traveling outside of that range has whatever failure chances you want (though I'd still avoid the TPK on this one).
In this case the tradeoff would be that you can either do one big jump with an incurred risk, or several smaller jumps, which could have whatever complications are associated with refueling/etc. That makes it more of an interesting choice and less "roll every time to see if we end the campaign".
Also, I'd keep in mind that it's generally better to have negative consequences for bad
decisions rather than bad
rolls. (Though, to be clear, choosing to engage in a mechanic that can have a bad roll is a decision, if it's actually a decision. Llike, if you play Russian Roulette, that's a decision even if the roll ends up being the thing that kills you).