When Stephen Furst went in to audition for Vir, he saw that everyone else in the waiting room had done their hair up into a Centauri crest; he was the only person without one. In a blind panic, he went to the bathroom and tried to use liquid soap to create a crest. When his name was called, he stumbled in, with a disheveled, lopsided crest, eyes tearing up from liquid soap running into them. He began to apologize profusely, stammering with run-on sentences. Series show runner J. Michael Straczynski and the producers looked at each other, declared "Oh my God, it's Vir!", and offered him the role on the spot.
The Babylon 5 station is an "O'Neill class space station". Gerard K. O'Neill was a physicist and space visionary who suggested using large rotating cylindrical habitats for future space stations.
During the first season, Commander Sinclair said, "This station creates gravity by rotation, so the room never stops spinning." Reportedly, the animating team had the station spinning at a near-Earth gravity simulation. This was determined by a physicist who was also a fan of the show, who determined the approximate size of the station by comparing it to the image of a human being on the edge of the station and extrapolating.
Peter Jurasik and Andreas Katsulas got along famously on and off camera. They rarely needed more than two or three takes to shoot their scenes together. They would often play for the camera and improvise off each other (which J. Michael Straczynski often forbade while cameras were rolling) between takes or while waiting for their scenes to be shot, leaving the cast and crew in stitches, and providing some comic relief. In one instance, Jurasik and Katsulas, in character and in full costume, recorded an infomercial for The Book Of G'Kar, parodying infomercials at the time. It was later included in various blooper reels and DVD extras.
Each major character and storyline had a "trapdoor" designed into it, allowing J. Michael Straczynski to integrate unforeseen changes during production without changing the main plot.