Meanwhile, back at the launch site, Endeavour's countdown was being held at the T-minus 11 hour mark.
News came out late on Saturday afternoon that an APU thermostat had failed tests. If so, this is the better of the two most likely failures and would allow work to proceed towards a new launch attempt on Monday.
Technicians continued working late into the night to test thermostats for Endeavour's APU-1 fuel line heater to help determine what caused it to fail.
NASA flight planners also tweaked Endeavour's target liftoff time for a Monday launch attempt to 2:34 pm (7.34 pm GMT).
If a Monday launch is possible, the countdown would resume at 10:07 pm on Sunday, with fuelling starting at 5:09 am and the crew strapping in at 11:14 am on Monday.