This protocol involves a baseline period consisting of 14 hours of wakefulness and 10 hour nocturnal sleep episodes each 24 hours. This is followed by a forced desynchrony regimen spanning 21 calendar days and consisting of 12 cycles ("days") of a 42.85-hour wake:bedrest schedule. In each 42.85 hour cycle, there are 32.85 hours of scheduled wakefulness and 10 hour sleep opportunities. This will allow assessment of the independent contributions of circadian phase and homeostatic sleep pressure on sleep and neurobehavioral performance. This forced desynchrony regimen is followed by 10 recovery days consisting of 14 hours of wakefulness and 10 hour nocturnal sleep episodes each 24 hours.