LOS ANGELES — After four years, the mission is over for "Star Trek: Enterprise."

The prequel to the original "Star Trek" science-fiction series will air its final episode May 13, UPN and Paramount Network Television said Wednesday.

Its end means that, for the first time in 18 years, no first-run "Star Trek" series will be airing.

The series will get a send-off that "salutes its contributions to the network and satisfies its loyal viewers," said UPN Entertainment President Dawn Ostroff.

"Star Trek: Enterprise" debuted in September 2001. Scott Bakula stars as Capt. Jonathan Archer, along with (onetime Seattleite) John Billingsley, Jolene Blalock, Dominic Keating, Anthony Montgomery, Linda Park and (Walla Walla native) Connor Trinneer.

The cause of death is, as usual, low ratings. "Enterprise" has been on a steady slide, from 5.9 million in its first season to 2.9 million in its fourth. The show narrowly escaped the ax last spring when UPN revamped its lineup, dropping other action shows in favor of female-friendly dramas. "Enterprise" had to cut its price tag and move to low-profile Fridays.

The series has been sold into rerun syndication in most of the country, with a fall debut.

The studio hinted at more "Star Trek" to come: "We all look forward to a new chapter of this enduring franchise in the future," said Paramount Network Television President David Stapf.

USA Today contributed to this report