That thought led him off on a tangent—he wondered how they had dealt with the long-term effects of microgravity. NASA would be very interested, especially if they were seriously considering a mission to Mars. If he remembered right, spending long amounts of time in space caused a loss of bone density and muscle tone, and he thought he could remember that there were problems with the circulatory system, too, since the human body was evolved to work in earth-gravity. He hadn’t given it much thought, but she seemed to be moving around well enough—they had undoubtedly come up with a solution to the problem, either with an gravitational field on the entire ship, or a gravity wheel that the crew could exercise in. They could also have solved the problem with fast travel: if they had some sort of warp drive or could control wormholes or something they wouldn’t be in microgravity long enough for it to be a problem. Maybe everyone aboard the ship was deep-frozen, and only thawed if the ship’s computers found something of note. Cryogenics was—at best—a fringe science on Earth, but maybe the problems of cell damage weren’t insurmountable.