Most spacecraft in Runaway to the Stars are modular microgravity structures, and these are the 4 most common types of module.

Avian modules tend to be spheres about 10 feet wide on the interior, big enough in diameter for them to stretch their wings out. Non-flyers can sometimes find themselves flailing in the middle without a handhold. Small human modules are usually about 5 feet in diameter. Ferret modules are usually only 3 to 4 feet wide on the inside, just big enough to turn around and pass other ferrets in. The walls are covered in a spongy material that they can attach Velcro objects to, and dig their claws into for traction. Large human modules/panspecies modules are big enough to comfortably accommodate large GMHs and centaurs, being between 8-10 feet in diameter with 4 foot wide connector points.

Almost all modules are either spheres or cylinders, as they are the cheapest shape to pressurize. Having modular units instead of one large hull is also much safer, as damaged units can be easily closed off from others in case of disaster. Thank you again to hyratel@tumblr for their invaluable help with rocket science stuff!!