"Tomorrow Is Yesterday" is the nineteenth episode of the first season of the American science fiction television series Star Trek. Written by D. C. Fontana and directed by Michael O'Herlihy, it first aired on January 26, 1967. It was the first Star Trek episode to be written solely by a woman (Dorothy Fontana had previously written the teleplay for the episode “Charlie X” but the story was credited to Gene Roddenberry). In the episode, the Enterprise is thrown back to Earth in the 1960s where the US Air Force detects it so the crew must find a way to correct the damage to the timeline. Plot The USS Enterprise is thrown back in time to Earth during the 1960s by the effects of a high-gravity "black star". Enterprise ends up in Earth's upper atmosphere, and is picked up as a UFO on military radar. A U.S. Air Force F-104 interceptor piloted by Captain John Christopher, is scrambled to identify the craft. Fearing an attack, Captain Kirk orders a tractor beam to be used on the jet, which tears the plane apart. The pilot is transported aboard the Enterprise. Fearing Christopher could disrupt the timeline if returned to Earth, Kirk at first decides that the pilot must stay with the Enterprise. When Science Officer Spock later discovers that the pilot's as-yet-unborn son will play an important role in a future mission to Saturn, Kirk realizes he must return Christopher to Earth after all. After learning of the existence of film taken of the Enterprise by Christopher's wing cameras, Kirk and Lt. Sulu beam down to the airbase to recover the film and any other evidence of their visit. They are caught by an Air Policeman, who accidentally activates an emergency signal on Kirk's communicator and is immediately beamed aboard. Kirk and Sulu continue their search, after which Kirk is captured again and Sulu escapes. Spock, Sulu, and Christopher, who knows the base's layout, beam down to recover Kirk. After Kirk's guards are subdued, Christopher grabs one of their guns and demands to be left behind. Spock, having anticipated Christopher would make such an attempt, appears behind Christopher and disables him with a Vulcan nerve pinch. After they return to the ship, Spock and Chief Engineer Scott inform Kirk of a possible escape method by slingshotting around the Sun to break away and return to their time. The maneuver is risky, since