The Ragged Astronauts is a novel in which people can use a hot-air balloon for interplanetary travel between twin planets that share the same atmosphere.

[1] The feudal residents of Land have to migrate to the nearby planet of Overland due to overexploitation of resources on their homeworld.

The story is told from the perspective of nobleman Toller Maraquine who clashes with a military Prince before and during the chaotic evacuation accelerated by rioting and a global pandemic.

Dave Langford reviewed The Ragged Astronauts for White Dwarf #81, and stated that "Pi, in this book, equals 3.

Therefore the universe isn't ours, the gravitational constant is different, and physicists will kindly pipe down.