After masterfully blending horror with youthful angst, Joss Whedon now turns his eyes toward space … the final frontier.

Gene Roddenberry once described “Star Trek” as “‘Wagon Train’ in space.” Whedon launches in the same direction, creating a Western at the galaxy’s outer edges in “Firefly,” debuting at 8 tonight on Fox.

The Emmy and Academy Award nominee built critically acclaimed cornerstones for fledgling networks, “Buffy the Vampire Slayer” for WB (later pirated by UPN) and its sibling, “Angel,” still on WB. Now Fox is desperately seeking a replacement for the retired “X-Files,” and along comes Whedon with “Firefly.”

The series is set 500 years in the future, in the wake of a universal civil war. “Firefly” focuses on the crew Serenity, a small transport spaceship operating on the frontiers of space that doesn’t have a planet to call home. Captain Mal Reynolds (Nathan Fillion, “Two Guys and a Girl”), a defeated soldier who opposed the unification of the planets by the totalitarian governed Alliance, is willing to take any job to stay afloat financially.

His crew includes his loyal second-in-command Zoe (Gina Torres, “Alias”), who served beside him in the war; Wash (Alan Tudyk), the ship’s pilot and Zoe’s husband; Kaylee (Jewel Staite), the ship’s young engineer; and Jayne (Adam Baldwin), a tough mercenary whose loyalties lie, at least for now, with the captain.

In an effort to earn extra cash, the Serenity has taken on passengers. They include “companion” Inara (Morena Baccarin), whose shuttle is docked to the ship; Simon (Sean Maher), who joined the crew as medic in hopes of protecting his emotionally fragile sister River (Summer Glau), and “The Shepherd” (Ron Glass, “Barney Miller”), a preacher who is on board to spread the word of God to the far reaches of the galaxy.

At least in the early going, the crew of the Serenity stays on the side of the angels, even though times are rough financially. It’ll be intriguing to watch them try to stay one step ahead of the Alliance “feds” while extricating themselves from one fix after another.

Whedon has done it again with “Firefly,” which deserves to be a staple of Fox’s lineup. It’s a riveting change of pace for those who are tired of such moldy time-slot competitors as “America’s Funniest Home Videos,” “48 Hours” and “Providence.” But, like the too-short “Dark Angel” before it, will its demographically desirable target audience be home to watch it?

Following “Firefly” on Fox is another intriguing drama, “John Doe,” about an amnesiac with astonishing mental powers.

A man (played by Dominic Purcell) awakes on an island, to a black-and-white world (he’s colorblind). He finds his way to nearby Seattle. He has a head full of information, some trivial, some helpful, but lacks the most basic one: who he is. While attempting to figure this out, he uses his powers to help the police solve “impossible” crimes.

“John Doe” compares favorably with the NBC cult favorite “The Pretender,” as both feature lead characters with incredible abilities who are trying to recapture their pasts.

This engaging series, as conceived by writers Brandon Camp and Mike Thompson (“Dragonfly”) and director Mimi Leder (“Pay It Forward”), has a golden opportunity to succeed, as it’s up against rookies “Hack” on CBS and “That Was Then” on ABC. But it will require viewers who are patient enough for its mystery to be played out.

The WB is reinforcing its Friday “comedy” lineup with two new sitcoms tonight. Having struck the jackpot with one former Nickelodeon star, Melissa Joan Hart, in “Sabrina the Teenage Witch,” the network has recruited gifted physical comic Amanda Bynes (“The Amanda Show”) to star in “What I Like About You,” premiering at 8.

Bynes plays 16-year-old live-wire Holly Tyler, who moves in her strait-laced older sister Valerie (Jennie Garth, “Beverly Hills 90210”) when their father takes a job in Japan. It’s the umpteenth limp version of “The Odd Couple,” despite the valiant efforts of Bynes, who deserves a better vehicle for her antic style, and Garth, surprisingly capable in a comedic role. Simon Rex (“Jack & Jill”), in the role of Val’s boyfriend Jeff, and Wesley Jonathan, as Holly’s friend Gary, are largely wasted.

Also debuting tonight on The WB, but not reviewed, is “Welcome to Tucson,” a family comedy airing at 9:30.