Chris Hadfield Space Flight Quotations

Other anatomical changes associated with long-duration space flight are definitely negative: the immune system weakens, the heart shrinks because it doesn't have to strain against gravity, eyesight tends to degrade, sometimes markedly (no one's exactly sure why yet). The spine lengthens as the little sacs of fluid between the vertebrae expand, and bone mass decreases as the body sheds calcium. Without gravity, we don't need muscle and bone mass to support our own weight, which is what makes life in space so much fun but also so inherently bad for the human body, long-term.

For the last several years and culminating in six months in orbit next year, I've been training for my third space flight. This one is almost in a category completely different than the previous two, specifically to live in on the space station for six months, to command a space ship and to fly a new rocket ship.