Skylab IIISkylab III
At 84 days, 1 hour, 15 minutes and 31 seconds, Skylab III (actually oficially designated "Skylab 4") remains by far the longest American space flight, a record that will certainly stand until the permanent human occupation of space begins with the international Space Station.
To help keep the crew in physical condition during their almost three months in orbit, they walked treadmills and rode an on-board stationary bicycle, and came home in far better condition than had the previous Skylab crews.
Among the thousands of experiments they conducted during this long, long flight, the astronauts took four space walks, including one on Christmas Day to observe the comet Kohoutek.
