"Herschel has a fixed end-date because its three instruments all need to be cooled to very low temperatures" says Cardiff University's Prof Matt Griffin, one of the team working on the mission.
"That cooling is provided by a big tank of liquid helium on board. The helium is gradually boiling away, and as planned, it will eventually run out and the instruments will stop working".
One proposal is to send the craft into a controlled collision with the Moon at the end of its life. It's hoped the impact might reveal more about ice hidden below the lunar surface.
"Some people don't like the idea because they think the Moon should not be contaminated by crashing a spacecraft into it, some other people think Herschel is such a lovely spacecraft that shouldn't be destroyed by crashing into a rock like the Moon!"
"But most of the members of my team are very much in favour. We don't regard the spacecraft as the final legacy... we regard the data and the science [as the legacy]. If we can do a little bit more at the end, we'd find that very pleasing."