"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.
Before being allowed on the NASA buses to transport us to the viewing point all bags and equipment had to be placed in a line for inspection by an army sniffer dog. This is standard practice when being taken to any secure KSC area.
A drive of several miles brought us to the Operations and Checkout building where the astronaut crew had been quarantined in their quarters since arriving two days previously.
We had a wait of about 45 minutes, a security helicopter with a machine gunner positioned in the open door swooping overhead. When it began to hover above at about midday we knew the crew, dressed in their orange flight suits, were about to appear.
After posing for photos they were off in the silver Astrovan with military escort to the launch pad. The iconic Astrovan has been used to transport crews to launch pads at KSC since the days of the Apollo Moon programme.
We’re back on the buses in a few minutes and head along the same route back towards the press centre area. But, bizarrely, after a mile or so, we see blue flashing lights coming in the opposite direction - closely followed by a speeding Astrovan.
It could mean only one thing - the launch had been aborted and the crew were on their way back to their quarters. In the next few seconds word came through via Twitter and text message confirming a postponement.
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.
Endeavour's orange external fuel tank had to be drained of more than 500,000 gallons of liquid hydrogen and oxygen - a process taking about 24 hours - before engineers could access the area and evaluate the issue with APU 1. The only option was to postpone the launch for at least 72 hours.
