This 59-day mission saw the three person crew perform over 1,000 hours of science operations on Skylab and gather data on changes to and overall health of the human body on prolonged space missions. A second Apollo spacecraft was rolled out to the launch pad for potential rescue of the Skylab 3 crew when a fuel leak developed on two of the Apollo Service Module's thruster pods. A rescue was ultimately not needed. Observations of the Sun also continued on this Skylab mission. A spacewalk installed a more permanent and efficient debris and heat shield on the outside of the station.