Part of Skylab 4’s mission objective was to study how astronauts could cope with extended time living in space. The mission dealt with diet, exercise to prevent muscle loss, and other issues associated with prolonged weightlessness. The astronauts on the mission -- Gerald Carr, William Pogue, and Edward Gibson -- faced a grueling schedule for the 84-day mission. And one day in December 1973, the astronauts just decided to take a day off. They blacked out communication with Mission Control and spent the day relaxing and taking in the spectacular views. That got NASA's attention, and a reduced workload and more autonomy for the astronauts was soon agreed upon.
Ground Control to Skylab 4: