"We will not fly this machine until it is ready - and today it was not ready." These were the words of flight director Mike Leinbach at the end of a press briefing this afternoon following the postponement of the launch of Endeavour.
At the Kennedy Space Center it was a day of highs and lows. Despite the early overcast skies there was optimism and excitement in the air.
Ironically, by the end of the day, it was the weather that was cooperating and the technology that had gone arry. An hour before the scheduled launch time clear blue skies had returned making perfect conditions for liftoff.
The Shuttle team had worked hard through the previous night, performing the Rotating Service Structure retraction at the launch pad shortly before midnight to leave Endeavour bathed in bright arch lights, looking pristine and ready to go.
The milestone in preparing the Shuttle for launch came some five hours later than planned but the team still managed to start fuelling on time first thing in the morning.
From an outside perspective it seemed as though things were all going to plan - but behind closed doors the team had been alerted at around 9 am to a potential problem with a heater associated with the Shuttle's hydraulic power system.
Blissfully unaware of the unfolding situation, things continued as normal and I was among about 150 of the reporters and photographers present signed up to witness the crew walkout at the start of their journey to the launch pad.
The Shuttle has three Auxiliary Power Units (APUs) that provide hydraulic power to steer the vehicle during ascent and entry. NASA’s launch commit criteria and flight rules require all three APUs to be fully operational for launch.