Impulse (Star Trek: Enterprise)
"Impulse" is the fifty-seventh episode of the American science fiction television series Star Trek: Enterprise, the fifth episode of season three. The episode was written by story editor Jonathan Fernandez from a story by Fernandez and Terry Matalas. It first aired October 8, 2003 on the UPN network in the United States. The episode was described by Paramount Pictures as "as close to a horror show as Star Trek gets".

Set in the 22nd century, the series follows the adventures of the first Starfleet starship Enterprise, registration NX-01. In this episode, while investigating the Delphic Expanse for a Xindi superweapon, the Enterprise responds to the distress call of a Vulcan ship. The crew on board have undergone the effects of exposure to Trellium-D, which turns Vulcans into violent zombie-like drones because it is a toxin. T'Pol is also poisoned and it begins to affect her, however Phlox is able to reverse the effects.

Plot
Captain Archer carries Sub-Commander T'Pol into sickbay, where he and Doctor Phlox strap her to a bed. She awakes and threatens to kill Archer, and Phlox sedates her. A day earlier, Enterprise receives a distress call from the Vulcan cruiser Seleya, and upon arrival, they find the ship adrift in an asteroid belt rich in Trellium ore. Archer decides to send in a shuttlepod as Enterprise is too big to maneuver among the asteroids. En route, T'Pol informs the other members of the away team that the Vaankara had been sent into the Expanse to find the Seleya, but the crew began to attack one another and the ship was destroyed. Meanwhile, Commander Tucker and Ensign Mayweather decide to mine some Trellium ore from an asteroid.

Lieutenant Reed, T'Pol and Archer board the Seleya and are attacked by zombie-like Vulcans. Soon T'Pol begins to show the same effects as seen on the other Vulcans. Archer and the away team then fight their way to Engineering, where they attempt to re-route the bulkhead controls on the ship so they can get back to their shuttle. They discuss a general override, which would unlock the bulkheads, but also shut down the containment on the warp core, and T'Pol accuses Archer of wanting to kill all the Vulcans.

Tucker and Mayweather retrieve the ore, but their shuttlepod is damaged in the process. After they return to Enterprise they begin repairs. Meanwhile, the Vulcan crew begins to gas Engineering, forcing Reed to activate the override. Archer's away team head back to the shuttle and arrive moments before the Seleya is due to explode, but find the docking clamps locked. Tucker and Mayweather then arrive on the second shuttle and destroy the clamps and the two shuttles depart, as the Seleya is destroyed. Tucker announces enough ore was recovered to shield the forward hull, but Archer orders it stored in a bio-hazard locker until a cure can be created.

Reception and home media release
"Impulse" was first aired in the United States on UPN on October 8, 2003. It received a 2.8/4 percent share among adults. This means that it was seen by 2.8 percent of all households, and 4 percent of all of those watching television at the time of the broadcast. Enterprise was the sixth most watched program in the timeslot, behind Smallville on The WB. It was estimated that "Impulse" was watched by 4.17 million viewers, which was less than the previous episode, "Rajiin".

Jamahl Epsicokhan at his website Jammer's Reviews described the episode as "sort of a guilty pleasure" due to the "superficial visual qualities". He was positive about the visual qualities of the episode, but said that it lacked substance. He gave "Impulse" a rating of three out of four. In 2017 this episode was noted as featuring scary and/or eerie Star Trek content. In 2018, TheGamer ranked this one of the top 25 creepiest episodes of all Star Trek series.

"Impulse" was released as part of the season three DVD box set, released in the United States on September 27, 2005. The set included optional text commentary for "Impulse" from Mike and Denise Okuda. The season was released on Blu-ray in the United States on January 7, 2014.