   Lights End
  Very simple, something I haven't seen or read anywhere, only variations thereof.A planet thrown out of orbit from another solar systems somewhere else in the galaxy collides with our sun. There are materials in the planet which kills the sun forcing it to switch off and die within a few months.Yourself and a crew need to go to the cooling sun to discover what the materials are and whether it can be engineered to restart the sun.Now this can play off in the future where we have space travel or where we are now as humans, each will obviously change the story quite a bit but the other option is that a city or cities is discovered in the sun of  an alien race that is now dead. Maybe the crew can then discover a portal system that connects to other alien cities which obviously can't be traveled to because of the heat or the alien technology leads to space travel and clues as to the locations of other alien cities in other suns.But we need someone to fight obviously so the aliens from far away might discover through whatever means that something has destroyed the home of their brethren. Seeing as the humans are found on site (or clues are left after their departure) they are thought to have attacked the city.Or possibly the destruction of the sun is the work of the sun aliens enemies and then humans get pulled into the struggle, the character could have the choice of which alien to help in the struggle.Clearly there is a lot of balance required but could make for something new.   
  Been giving it a little more thought.You could make runs to get much needed resources for the humans on earth that are freezing to death, there would be construction of special biodomes that house living creatures, trees and all such things. Nuclear energy will be a good option for generating heat. Then you would need special materials that prevents pipes and such things from freezing and bursting thus the biodomes need to be kept stable.Seeing as the sun aliens, while living in the reverse of earth, did have to counter the molten conditions of the sun, you could bring samples that would be reverse engineered. But there could be parasite type creatures that live in the sun which are now loose in the destroyed city (need to have a decent reason that they can survive without the heat of the sun otherwise leave it out). Then also being a return trip, the "evil" aliens that destroyed the sun could still be there resulting in a confrontation. They could be made up of various castes.There could be moral decisions with the choice of certain missions over others which result in the death of humans on earth due to supplies not arriving or the enemy gaining ground at some strategic location which then is so much harder to retake.It would be nice if every decision affects later encounters or situations.