 By seven hours into the mission , the crew was about one hour and 40 minutes behind flight plan , because of the problems in moving away from the S @-@ IVB and Lovell 's obscured star sightings . The crew now placed the spacecraft into Passive Thermal Control ( PTC ) , also called " barbecue roll " , in which the spacecraft rotated about once per hour around its long axis to ensure even heat distribution across the surface of the spacecraft . In direct sunlight , the spacecraft could be heated to over 200 ° C ( 392 ° F ) while the parts in shadow would be − 100 ° C ( − 148 ° F ) . These temperatures could cause the heat shield to crack and propellant lines to burst . Because it was impossible to get a perfect roll , the spacecraft swept out a cone as it rotated . The crew had to make minor adjustments every half hour as the cone pattern got larger and larger . 
