Adrift on the Sea of Rains is but the first of a quartet of novellas, then!
As the story opens, a small band of astronauts manning a permanent American base on the Moon (established as part of a natural progression from the Apollo missions, in that time frame and with that technology) find themselves marooned there when the USA and the USSR decide to go ahead and fight out World War III and destroy the planet Earth, rendering its glorious blue-white marble a desolate grey rock to match its satellite. The astronauts have (nuclear!) power, and thus life support, for 20 years, but only have freeze-dried astronaut chow to last them about two! Oh noes!
Fortunately, one of their number is not really an astronaut but a mad scientist plucked from Nazi Germany and secretly put to work continuing his experiments travel between parallel universes. He's obnoxious as hell but he's their only hope once he's completed his masterpiece (which would only work in a vacuum, hence his presence on the Moon), allowing them to start jumping from universe to universe in search of one where nobody ever actually decided to play a game of Global Thermonuclear War.
And then the fun begins. Because our astronauts have to jury-rig and re-start all that wild old Apollo-era technology to try to get themselves to their new home!
The story of this mighty effort is intercut with the previous test piloting-and-espionage experiences of the Moon Base commander, Vance Peterson, in a series of cleverly arranged flashbacks that also tell the tale of how the disaster came to be. It's good storytelling, no doubt, but what makes this novella really stand out is its visceral conveyance of the experience of trusting the analogue tech of the late 1960s and early 1970s to keep people alive and hurl them across space. Famously, the Eagle that landed in Apollo 11 had less computing power in it than the smartphone in your pocket, but that's just the beginning. Paper-thin hulls. Huge banks of switches. Ring binders full of gnarly math and densely printed instructions. Slide rules and pencils. It's utterly, utterly glorious.