How long is too long for a space mission?

Before the main payoff, that is. The New Horizons probe to Pluto is taking 10 years to get there. People seem happy with that; we’re getting interesting results along the way. But what if we could make our probes go even faster - would a 50 year mission to Alpha Centauri be acceptable? A 100 year mission?

I think more than a decade is starting to stretch things, unless, like Voyager 2, you can do some other stuff on the way to the long-term part of the mission. I think people want to see results and while I would love it if someone else had selflessly prepared the way for me to see some results, I don’t feel quite so enthusiastic about preparing for something that will reap results long after I’m dead and gone. I realise that’s pretty much the definition of ‘selfish’, but there it is.

Actually, I think it’d be pretty cool to send a probe out with a payoff 500 years later. It would be like a time capsule – people would have forgotten about it, and would be excited by its reappearance. (Unless it’s a manned probe, that is, in which case enthusiasm would be somewhat tempered.)

Consider then that a 40 year mission would fit this bill: start work in your 20s, get the results in your 60s.

I think the “Daedalus” probe concept had something like a 50-year mission life. Ah…yep.

12% of c! Woo-hoo!

I wonder if you could use a solar sail as a braking mechanism? And you’d need something to keep it all warm. Would a RTG last that long?

Sure, but you might have trouble getting the crumblies to fund it.

Yes; either use the destination star’s sunlight, or if you are using a laser-driven sail make the center of the sail detach when you need to decelerate; the laser pushes the detached center ahead, and the ship and it’s remaining sail uses the bounced-back light for deceleration.

Re the OP : As far as I’m concerned, it’s more of a technological question. There’s no point in a probe taking a 500 year journey to another star if it seems likely that in 50 years we’ll develop a probe that can do it in less than a hundred years. Right now, a voyage that will take longer than, say, 50 years ( number pulled out of air ) is probably wasted effort.

There’s precedence for a 5 year mission to explore strange, new worlds.

I’ve got three weeks vacation this year, but I might need a day or two to clean up the backyard. On the other hand, if you’re telling me I don’t have to go back to work at all, then I’ve got all the time you need.