Ultimately, it doesn’t sound like a good idea. The fins or whatever on the capsule could get snagged and they have no feeling to guide them, unlike the extremities of a human. A human clambered into the cave through the narrows, and could and did clamber back.
Heh - have never been in that tight a spot in a cave. But have some experience in very tight spots in attics, floor / ceiling trusses, etc. :-)
(Semi “ /s “.)
In one, in about 120 deg. F heat, it either took about 15 minutes to get turned around, or one could “inchworm” backwards 30 - 40 ft. and a little past the “entrance” and then get out. Back then I was a lot skinnier (and probably lost 5 lbs. on that job!) Anyone any bigger would have probably got stuck and passed out...