Other than actual astronauts and the pilots and crew of NASA’s famous Vomit Comet, very few Earthlings have experienced more time in weightlessness than Tom Hanks, Kevin Bacon, Bill Paxton, Ron Howard, and the camera operators and other crew who filmed this movie. There are many ways to fake showing people in zero gee in a movie—such as in Gravity, where no parabolic flight trajectories were used—but there is no way other than CGI (which was still in its infancy in 1995) to mimic the behavior of liquids. You have to be actually free falling for that.
They flew 612 parabolas, with 25 seconds of weightlessness at the apex of each arc. That adds up to almost four hours of free falling. And they call it the Vomit Comet for a reason. Even people who think they have strong stomachs can find themselves hurling. Which shouldn’t surprise anyone, since almost half of the astronauts themselves feel sick for a while when they first go into orbit. And though it must have been fun in a lot of ways, it was also hard and exacting work. The cast and crew had to carefully plan out every move for those precious 25 seconds. Then they had to get into position in very small, cramped spaces, get the shot, and then get out because after the plane goes over the arc it then has to pull out, and they will experience two gees. You can hurt yourself in two gees.
So that’s the technical part. Everything else worked, too. That was due to an almost fanatical attention to detail, a lot of help from NASA, and a great script that humanizes these men, in orbit and on the ground. (I say men, because aside from Mrs. Lovell, it is practically an all-male cast. Mission Control was all men. These days, I’m happy to say, the ratio would probably be 70/30, or even 60/40.) It is hard to make a film where people are in peril and you know not only that they survived, but just how they did it, but Ron Howard achieved tension from the moment of the first explosion. If I have any criticism, it is a half-hearted complaint that there is no sound in space. But that fight was lost a long time ago. When the capsule passes by us, there will be a whoooosh!, and we might as well learn to live with it.