Dimension X was an NBC radio program broadcast on an unsponsored, sustaining basis from April 8, 1950 to September 29, 1951. The first 13 episodes were broadcast live, and the remainder were pre-recorded. Fred Wiehe and Edward King were the directors, and Norman Rose was heard as both announcer and narrator.
Preceded by Mutual's 2000 Plus (1950-52), Dimension X was not the first adult science fiction series on radio, but the acquisition of previously published stories immediately gave it a strong standing with the science fiction community, as did the choice of well established, respected writers in the field: Isaac Asimov, Robert Bloch, Ray Bradbury, Fredric Brown, Robert A. Heinlein, Murray Leinster, H. Beam Piper, Frank M. Robinson, Clifford D. Simak, William Tenn, Jack Vance, Kurt Vonnegut, Jack Williamson and Donald A. Wollheim. Ernest Kinoy and George Lefferts adapted most of the stories and also provided original scripts.
In Science Fiction Television (2004), M. Keith Booker wrote:
It was not until the 1950s that science fiction radio really hit its stride, even as science fiction was beginning to appear on television as well. Radio programs such as Mutual's 2000 Plus and NBC's Dimension X were anthology series that offered a variety of exciting tales of future technology, with a special focus on space exploration (including alien invasion), though both series also often reflected contemporary anxieties about the dangers of technology. 
The series opened with "The Outer Limit," an Ernest Kinoy adaptation of Graham Doar's short story from The Saturday Evening Post (December 24, 1949 issue), about alien contact. A week later (April 15, 1950), the program presented Jack Williamson's most famous story, "With Folded Hands," first published in the July 1947 issue of Astounding Science Fiction.
With a five-month hiatus from January 1951 to June 1951, the series spanned 17 months. All 50 episodes of the series survived and can be heard today. Later, NBC's X Minus One (1955-58) utilized many of the same actors and scripts.
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X Minus One was a half-hour science fiction radio series broadcast from April 24, 1955 to January 9, 1958 in various timeslots on NBC.
Initially a revival of NBC's Dimension X (1950-51), X Minus One is widely considered among the finest science fiction dramas ever produced for radio. 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, including Isaac Asimov, Ray Bradbury, Philip K. Dick, Robert A. Heinlein, Frederik Pohl and Theodore Sturgeon, along with a few original scripts.
Episodes of the show include adaptations of Robert Sheckley's "Skulking Permit," Bradbury's "Mars Is Heaven," Heinlein's "Universe" and "The Green Hills of Earth", " Pohl’s "The Tunnel under the World," J. T. McIntosh’s "Hallucination Orbit," Fritz Leiber’s "A Pail of Air" and George Lefferts' "The Parade".
The program opened with announcer Fred Collins delivering the countdown, leading into this introduction (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; a new experimental episode, "The Iron Chancellor" by Robert Silverberg, was created in 1973, but it failed to revive the series. NBC also tried broadcasting the old recordings, but their irregular once-monthly scheduling kept even devoted listeners from following the broadcasts. All episodes of the show survive.
Future Tense! was a 1974-76 radio series, produced in Kalamazoo, Michigan, with local actors performing scripts updated from X Minus One by Professor Eli Segal.  The show was a production of WMUK, the college radio station of Western Michigan University. Segal also produced X Minus One recreations on his Audion Theatre (1990).
Most recently the series was rereleased in podcast form beginning on June 22, 2007.
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