Once on-orbit both crew members safed their ejection seats and unstrapped. The next critical event was payload bay door opening. This was essential to allow heat rejection from "Columbia"'s systems via the doors' space radiators. Failure to open these by the end of the second orbit would have resulted in a return to Earth at the end of the fifth orbit, before the limited capacity of the flash evaporator cooling system was exceeded. As they opened the doors the crew noticed that they had sustained damage to thermal protection system (TPS) tiles on the OMS pods. This was televised to the ground. Shortly afterwards Young, then Crippen doffed their emergency ejection suits.