Answer: Pulleys

It would be very easy to assume that the doors on the sets of Star Trek (in all its incarnations) were automated. After all, here in the boring, non-futuristic present, we experience automated doors in the most mundane places like gas stations, shopping malls, and the like. Although not as common in the 1960s as they are today, automatic doors like the ones we’re familiar with were invented in 1954 and the first commercially available automated door was installed in 1960.

But despite the fact that the technology existed at the time the show was created (and certainly in all the subsequent additions to the franchise like Star Trek: The Next Generation), the doors on the sets have always been manually opened by the stage crew. In the 1996 book Inside Star Trek: The Real Story, written by Herbert F. Solow and Robert H. Justman, Solow—Desilu’s Executive in Charge of Production for the original Star Trek—explained how it worked:

Superior hand-eye coordination was necessary for brain surgeons, prestidigitators, and the guy responsible for opening the various doors on the set. He accomplished it by standing out of sight of the camera and running the “mechanisms.” The mechanisms consisted of wires attached to the sides of the doors and threaded through a series of pulleys. The assistant director, standing behind camera and watching the scene, would trigger a red light that cued the offstage guy that the moment had arrived for him to open the doors. He would yank on the main wire. This activated the wires running through the pulleys and opened the doors just in time for Kirk or Spock to enter or exit.

The mechanisms always worked; the people responsible weren’t as dependable. Sometimes the cue would be given too early, and the doors would open long before the actors reached them. This “magic door” syndrome usually brought an enthusiastic laugh from everyone except, perhaps, the director, who was usually behind schedule. To him, it wasn’t funny.

Sometimes the cue would be given too late and the actors, trusting souls that they sometimes were, bounced off the unopened doors. This almost always brought an enthusiastic laugh, especially from the director. De Kelley was overheard to remark, “You can get killed walking to the coffee shop aboard this ultra-modern space cruiser.”

Later, when a builder in Santa Barbara, California, wrote to us asking for ideas on how to build sliding doors that work as quickly as those aboard the Enterprise, my recommendation to Bob was to tell the builder to get a different assistant director and a faster offstage guy.

The mechanism didn’t change much over the years, and you can find “Star Trek Door Bloopers” on YouTube showcasing actors from the franchise running into doors over the span of all the decades the franchise has existed.