CAPE CANAVERAL, Fla. -- The launch of space shuttle Endeavour was foiled again on Sunday, this time not by lightning strikes or fuel leaks but by a slow-moving rain cloud that drifted within 20 nautical miles of its launch pad.
Canada's Julie Payette and six other astronauts were already inside the shuttle and awaiting countdown when NASA scrubbed the mission for the fourth time.
The culprit this time was like a skunk at the company picnic -- not menacing in its own right, but causing enough concern due to its proximity that the mission had to be cancelled for fear it would develop into something dangerous.
The disappointment was palpable at NASA when the cloud appeared on the weather radar map about 90 minutes before the scheduled launch at 7:13 ET. It was slow-moving, but inching ever closer to Endeavour.
The concern, a NASA official said, was not launching the shuttle with the rain cloud nearby, but what would happen if something went wrong after liftoff and the shuttle had to turn around and return to Earth.
The shuttle cannot be navigated through precipitation.
NASA will now attempt to launch the shuttle again on Monday. It has until Tuesday to send it to space before having to make way for an unmanned Russian spacecraft.
The Endeavour mission was scrubbed three times previously -- twice last month because of a potentially hazardous hydrogen fuel leak, and again Saturday because of 11 lightning strikes that touched down near the launch pad.
The mission would be Payette's second voyage to space -- she was aboard the space shuttle Discovery in 1999.
The Endeavour mission will mark another historic moment for Canada when Payette meets up at the space station with fellow Canadian astronaut Robert Thirsk.
It will be the first time Canada has had two astronauts in space at the same time.
Thirsk is spending six months at the space station, laying the groundwork for deploying Canadian robots onto other planets.
The mission will feature five spacewalks and complete construction of the Japan's Kibo laboratory. Astronauts will attach a platform to the outside of the Japanese module that will allow experiments to be exposed to space.
Payette plans to take treats from home to space -- including maple cookies, maple butter and Alberta beef jerky.
About three hours before the launch, Payette and her fellow crewmates arrived at the launch pad to prepare to board the shuttle. The astronauts smiled, waved and gave a thumbs-up as they headed to the pad.
"Look at that!" said astronaut David Wolf, gesturing to the brilliant sunshine at the time.
Once inside the launch pad, Payette beamed broadly and chatted with NASA technicians as they checked her space suit.
She also found the time to make a call to an astonished Canadian Space Agency official, thanking Anna Kapiniari for her hard work and letting her listen to the low roar of the shuttle.
The space agency began fuelling up Endeavour on Sunday morning for the scheduled 7:13 p.m. EDT launch.
"Today is our day," Steve Payne, NASA's shuttle test director, had said optimistically earlier in the day.
Stormy weather, technical failures and even a flock of woodpeckers have resulted in NASA having to delay the launch of various space shuttles over the years.
Florida, in fact, is the thunderstorm capital of the United States, and boasts a "lightning belt" between Orlando and Tampa. More people die from lightning strikes in Florida than any other state, and hurricanes are a problem in the spring and early summer.
Weather conditions must be almost perfect for NASA to launch the shuttle -- rain, low cloud cover, nearby thunderstorms and high winds will result in liftoff being scrubbed.
Technical problems are also commonplace. A fully loaded shuttle weighs almost 590,000 kilograms and includes complex circuitry and moving parts that can malfunction.
In the past, tiny failures have resulted in disasters like the destruction of Challenger in 1986 and Columbia in 2003.
