Complex sentence: 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.
Split into simpler sentences: The crew now placed the spacecraft into Passive Thermal Control (PTC), also known as "barbecue" roll. PTC involved the spacecraft rotating about once per hour along its long axis to ensure even heat distribution across the surface of the spacecraft.