Star Trek: Enterprise is an American science fiction television series that originally aired on the UPN network from September 26, 2001 to May 13, 2005. Until the episode "Extinction" towards the start of the third season, the series was called simply Enterprise without the Star Trek prefix. The series aired for 98 episodes across four seasons, centering on the adventures of the 22nd century starship Enterprise. They are the first deep space explorers in Starfleet, using the first Warp 5 equipped vessel. It was set within the universe of the Star Trek franchise, with the series placed earlier in the chronology than Star Trek: The Original Series.