In humans, hormone levels, alertness, and core body temperature are synchronized through a 24-hour circadian cycle. Daytime alertness is at its best when sleep/wake cycles are in sync with the circadian cycle. Thus alertness can be easily affected with a distributed work schedule, such as the one to which astronauts are subjected. It has been shown that the human circadian cycle can be delayed or advanced through light stimulus. To ensure optimal alertness, a system is designed to track astronauts’ circadian cycles and increase the quality of sleep during missions. Core body temperature can be used as an indicator of the circadian cycle. A computer model with optimum circadian body temperature variations can be compared to an astronaut’s body temperatures. Whenever a difference is detected, the astronaut is subjected to a light stimulus to advance or delay the astronaut’s circadian cycle (Mott, 2003). Draw a functional block diagram of the system. Indicate the input and output signals, intermediate signals, and main subsystems.