Chelonauts are space explorers sent under the Great A'Tuin in an attempt to discover its gender. The only known attempts were made by Krull, the only Discworld island to hang over the Rim, and were told about in The Colour of Magic. These were lowering a glass box over the rim, and the more famous voyage in The Potent Voyager, which was taken over by Rincewind and Twoflower. It is also possible that Carrot Ironfoundersson, Rincewind and Leonard da Quirm, when they traveled in the Kite in The Last Hero can by considered chelonauts, because they did go under the Disc.
Chelonauts, according to the description, wear space costumes which look suspiciously like the ones Erich von Daniken thought he saw in prehistoric cave pictures.
They spik a längwîdj wìth löts ðøv åccëntêd kåråcters, which gives it a distinctly Scandiwegian look.
A portmanteau of Chelonii (turtles) and astronaut.