Thanks to Signor Marconi and his fellow inventors  we have the marvelous wonders of wireless telegraphy. And what better use could be made of invisible waves traveling at the speed of light than to bring you the drama from long, long ago in a galaxy far, far away.
Star Wars: the Radio Drama  Brian Daley turned the original 1977 two-hour film by George Lucas into a six-hour thirteen-part radio play for National Public Radio in 1981. John Madden directed film cast members Mark Hamill and Anthony Daniels to reprise their parts as Luke Skywalker and C-3PO; Brock Peters plays Darth Vader, and the John Williams original score is performed by the London Symphony Orchestra. It’s everything you love about the movie and more. And the story continues with radio productions of The Empire Strikes Back  and Return of the Jedi .
Perhaps the most infamous science fiction radio broadcast occurred just before Halloween 1938. Director Orson Wells led the cast of the Mercury Theater on the Air in The War of the Worlds.  Writer Howard Koch adapted the novel of Martian invaders by H.G. Wells by modernizing it and bringing the setting from England to America. Instead of the Martians landing on the Horsell Common and moving on London “in the last years of the nineteenth century” they landed in New Jersey in 1938 and started toward New York! Thousands of people, who had been twirling their dials* between stations and programs missed the opening announcements and thought they were listening to a real reporter and not an actor, who informed them,
“Ladies and gentlemen, this is the most terrifying thing I have ever witnessed. . . . Wait a minute! Someone's crawling. Someone or . . . something. I can see peering out of that black hole two luminous disks . . . are they eyes? It might be a face. It might be . . . good heavens, something's wriggling out of the shadow like a gray snake. Now it's another one, and another one, and another one. They look like tentacles to me. There, I can see the thing's body. It's large as a bear and it glistens like wet leather. But that face, it . . . ladies and gentlemen, it's indescribable. I can hardly force myself to keep looking at it, it's so awful. The eyes are black and gleam like a serpent. The mouth is kind of V-shaped with saliva dripping from its rimless lips that seem to quiver and pulsate.”
*For younger readers I need to point out before remote controls were standard issue for all manner of electronic devices, this is how listeners did their “channel surfing.”
Fast forward to the 1950s, the era of Rock 'n Roll, flying saucer sightings and other social indicators of instability or fun, depending on your point of view. Legends of Radio: Science Fiction Classics  is an impressive compilation of American science fiction radio programs from the 1950s. Three of them, “Destination Moon,” “The Day the Earth Stood Still,” and The War of the Worlds,” are adaptations of the motion pictures of the same title and vintage, but of most of them are adaptations of the stories of prominent authors of the time: Robert Heinlein, Isaac Asimov, Alfred Bester, Robert Bloch, Ray Bradbury, L. Sprague De Camp, Philip K. Dick, Gordon R. Dickson, Fritz Leiber, Clifford D. Simak, Robert Silverberg, and Theodore Sturgeon. There are also a few written originally for radio. An excellent accompanying booklet explains the emergence of the genre and then a program-by-program profile of the authors, with their portraits and a cast list.
And now for something more up to date. Solaris  is a 2007 BBC Radio 4 dramatization of Stanislaw Lem’s novel. Psychologist Kris Kelvin is sent to the space station orbiting the planet Solaris to investigate the crew’s psychological fitness for duty. What’s left of the crew are behaving very strangely. Some of them are downright anti-social. Kris spends some time gazing at the wondrously sublime ocean of the planet below, goes to sleep, and then gets a visit from his wife Rheya. This is quite unusual because she committed suicide several years before this unexpected arrival at the foot of his bed.
Turning from the wondrous to the wonderfully silly we have Earthsearch, Series I & II: The Complete Radio Series  by James Follett. One-hundred-fifteen years after it left earth, the ten-mile long starship Challenger and its crew of four returns to its home world to find that it’s gone. The moon remains alone orbiting Sol. The Sentinel on the moon tells the crew that it was dragged away by its inhabitants half-a-million years ago. In their search for the missing planet the grandchildren of the original crew encounter the mishaps of many interstellar travelers: manic robots bent on destruction, grumpy androids, galactic emperors who rule a few small asteroids, another massive starship the mirror image of their own, a shortage of oxygen, hostile humans who take them for aliens, worshipful humans that take them for gods, black hole gravity wells, time dilation, the temptation to eat forbidden fruit, starship computers who want to rule the world, androids that want to rule the universe, and ten-mile high pyramids filled with mysterious secrets, planet engulfing floods, in short, just about every science fiction cliché imaginable, and played absolutely straight faced with tongue firmly in cheek. This is a marvelously fun space opera.
Also marvelous fun is the production of Sir Arthur Conan Doyle's The Lost World  done by the Production Company Alien Voices. This item is slightly off topic because it’s not really a radio drama—but it’s so good I couldn’t resist adding it to the list. Scripted by Nat Segaloff and John de Lancie it was ”Performed at Creation Entertainment's Grand Slam V Star Trek Convention in Pasadena, Calif. on March 22, 1997.” The audience participated by acting the crowd in parts of the play. The recording was then taken to the studio, cleaned up and released directly as an audio recording. Because it was first performed at a fan convention it features a cast composed of veteran Star Trek actors: Leonard Nimoy, John de Lancie, Roxann Dawson, Richard Doyle, Marnie Mosiman, Ethan Phillips, Dwight Schultz, and Armin Shimerman.
Professor Challenger leads an expedition deep into the heart of the Amazon, complete with hostile natives and poisonous snakes, to a previously unmapped plateau compete with pterodactyls, dinosaurs, and vicious ape-men. It would be hard to match the cast’s exuberant over-the-top adaptation of Conan Doyle’s original creature feature.