I think you're recalling Possibly Uncanny #99 & 100 when the team are captured by the Sentinels... Banshee and Co break free of their prison only to find they are actually in orbit, these two issues go into the problems of survival in space and are maybe what you remember.
Alternately (and I can't recall the details as clearly) there was that early 90s issue where Jean and Cyclops are caught by Stryfe and face an identical predicament - Uncanny #296 & X-Factor #86. I think those issues would fit what you're remembering too.
Thanks for checkin', Daveym. This is goin' to bug me for awhile still. Don't own 99-100 and kept my Executioners Song issues polybagged sealed for value (like a fool) for the longest time. So, it wasn't those. Guess it could have easily been a sci-fi TV series ep too since no other comicbook possibilities have come to mind yet. Oh well, at least got to read Executioners Song finally... blecch. The Jae Lee efforts was nice to revisit in that issue.