Within the universe of "The Way", the Thistledown is an asteroid starship built by hollowing out Juno and fitting it with mass-driver (Rail gun) engines and thermonuclear drives. Inside the asteroid, seven giant “Chambers” are built, of which one hosts a city for the inhabitants, while others host machinery. The asteroid is prepared 500 years in the future, as told in Bear's novel, "Eon", and is engaged on a multi-generational journey to Epsilon Eridani, around which a habitable planet is known to be circling.