[quote=@uliop]
Maybe there's some large EMP field around one of the planets? Then some rebels come and shoot us down while we're EMP'd? Maybe something happens to the life support and we have to go down to the planet? Just kinda throwing some ideas out there.
[/quote]
Or maybe the rebels could have taken over an interdictor and use it's gravity well as an ambush spot? It is something reasonably similar, just maybe add an ion cannon or two and maybe it could go down.