Buck Rogers is put into suspended animation after being overcome by a mysterious gas while exploring a mineshaft/being frozen after crashing on a glacier/mumblemumble. He awakens in the 25th century to discover a world just beginning to claw its way back to advanced civilization after the centuries of barbarism that followed the collapse of society after the SpamBot Wars.
Little has survived from the old civilization, and much of it irrelevant to recreating modern technology. Among the most treasured of the Historical Documents is a series of illustrated texts that show the technology of the the 20th century: rockets with tail fins, analog gauges and vacuum tube electronics, rocket belts, leather flying helmets, and so on.
The engineers of the reborn civilization use the Historical Documents to recreate the technology of the past, tail fins and all. They quickly discover that single stage spaceships could not achieve interplanetary travel, or the flying belts the performance shown in the texts, through chemical rocket power alone. They deduce that the rockets were used only for maneuvering and rapid acceleration: the ancients must have had some other form of of primary propulsion!
This spurs them on to the research that accomplishes what they believe be the rediscovery of the Reactionless Drive. (Like the most practical form of artificial gravity it's something of a misnomer, but the important thing is that you don't need to carry reaction mass on board. Newton is not dissed.)
Dieselpunk hijinks ensue.