One of the strangest experiences in space is one of the simplest on Earth: sleeping. On the shuttle, you strap your sleeping bag to the wall or the ceiling or the floor, wherever you want, and you get in. It's like camping. The bag has armholes, so you stick your arms through, reaching outside the bag to zip it up. You tighten the Velcro straps around you to make you feel like you're tucked in. Then you strap your head to the pillow—a block of foam—with another Velcro strap, to allow your neck to relax. If you don't tuck your arms into the bag, they drift out in front of you. Sometimes you wake up in the morning to see an arm floating in front of your face and think, "Whoa! What is that?" until you realize it's yours.