Yep, it's frustrating to have a stupidly long SC trip imposed on you through RNG.
I made a thread about this ages ago.
Please consider putting a cap on the maximum distance that a mission target will be at for missions such as assassinations or salvage, where we know only the system from the mission description, not the actual target location. I have had three missions recently, with a combined SC travel...
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I have no issue with SC travel times in general, and in cases where a mission specifies the distance then that's fine, we can choose to take it or not. But where no distance is specified, then to decide to abandon a mission, not because it's too difficult, but because it's simply too boring and not worth the time investment seems a shame.
Would be great if they could set a distance cap on mission types where the target isn't specified in the mission description. I can't believe they think that players would enjoy sitting in SC for an extended period to do a mission that takes a few minutes to complete.
I must say I haven't tried Para Handy's suggestion to jump out and reset the instance, will try that some time to see whether it works. But this also happens for planetary scan missions where the target body is fixed once you get the initial mission critical update.