Universe originally appeared in Astounding Science Fiction in May of 1941. Heinlein wrote a sequel, Common Sense, which appeared in Astounding in October of the same year. Pictured below is the 1951 paperback novelization by Dell. The two stories were later published together as Orphans of the Sky(1963).
Universe was first broadcast on Dimension X #31. It was repeated as episode 42. Most vintage radio collections of Dimension X include episode #42, but every one I have heard to date has been a fake. One tell-tale sign is a hiccup during the end credits where the plea to fans to keep the series going heard in episode 31 has been edited out.
Universe was remade for episode #4 of X Minus One. The audio is a little clearer in the latter episode, but it's hard to say which is "best." I suppose I like the Dimension X version a little better.
Dimension X #31
26 November 1950
Robert Heinlein (author), George Lefferts (adaptation), Donald Buka, Peter Kapell, Bill Griffis, Abby Lewis, Edgar Stehli, Jason Seymour, Ian Martin
X Minus One #4
15 May 1955
NBC net origination, AFRTS rebroadcast. Abby Lewis, Donald Buka, Edgar Stehli, Fred Collins (announcer), Ian Martin, Jason Johnson, John Seymore, Peter Capell, Robert Heinlein (author), William Griffis, George Lefferts (adaptor), William Welch (producer), Fred Weihe (director).