This movie is from the late 80s, early 90s. I think it was on TV a number of times during the Disney broadcasts on Sunday night.
The premise is that earth is going through an environmental collapse. Acid rain is one of the problems mentioned specifically. So, they've decided to send a ship to a new planet that they've discovered that might have life on it. But it is going to take 50+ years to get there, so they can't send regular astronauts. Instead they pick a bunch of smart kids and one "senior" captain (who is still young - say mid twenties?).
I recall one scene where they are recruiting a kid and it is raining while they eat lunch outside somewhere. The food he is eating is very green and stains his teeth. Lots of people are waiting special rain coats because of the rain. This is one of the few scenes that takes place on earth.
On the ship they have an ion drive which lets them travel fast, but not FTL.
Anyway, there is a coup on board that they have to deal with, and I remember one scene where this girl makes a fake metallic feather as a memorial for a friend who may have died.
The movie ends with them resolving the problems on the ship, but only a few weeks/months has elapsed, so there is still a long way to go to get to the planet.
Anyone have any thoughts? Sorry for so few details.