http://en.wikipedia.org/wiki/X_Minus_One

X Minus One was a half-hour radio program broadcast in America from April 1955 to January 1958 on NBC.

A revival of Dimension X, X Minus One is widely considered among the finest radio dramas ever produced. The first 15 episodes were new versions of Dimension X episodes, but the remainder were adaptations of newly published science fiction stories by leading writers in the field, such as Isaac Asimov, Ray Bradbury, Philip K. Dick, Robert A. Heinlein, Frederik Pohl and Theodore Sturgeon with a few original scripts.

Among the best episodes are Robert Sheckley's "Skulking Permit," Bradbury's "Mars Is Heaven," Heinlein's "Universe," Pohl?s "Tunnel Under The World," J. T. McIntosh?s "Hallucination Orbit," Fritz Leiber?s "A Pail of Air" and George Lefferts' "The Parade".

Announced by Fred Collins, the listener was greeted with the following introduction to each episode, although later shows were partnered with Galaxy Science Fiction rather than Astounding Science Fiction:

    Countdown for blastoff... X minus five, four, three, two, X minus one... Fire! [Rocket launch SFX] From the far horizons of the unknown come transcribed tales of new dimensions in time and space. These are stories of the future; adventures in which you'll live in a million could-be years on a thousand may-be worlds. The National Broadcasting Company in cooperation with Street and Smith, publishers of Astounding Science Fiction presents... X Minus One.

The series was cancelled after the 126th broadcast on January 9, 1958. However, the early 1970s brought a wave of nostalgia for old-time radio, and an experimental new episode was created in 1973, "The Iron Chancellor" by Robert Silverberg, but failed to revive the series. NBC also tried broadcasting the old recordings, but their irregular once-monthly scheduling kept even devoted listeners from following broadcasts. All episodes of the show survive.