CAPE CANAVERAL, Fla. NASA started the three-day countdown clock toward launch on Thursday of the space shuttle Endeavor as the seven astronauts, a polyglot crew of four Americans, a Canadian, an Italian and a Russian, arrived at the Kennedy Space Center on Monday.

The crew, described by the U.S. space agency as the most internationally diverse ever on a shuttle mission, flew T-38 training jets from NASA's astronaut training base in Houston to Florida for a mission to deliver a gigantic robotic "inchworm" to the International Space Station, Reuters reported.

"We're all very excited to be here," said shuttle Commander Kent Rominger.

"It's a great day to be in Florida, especially with what's coming up in about three days," said Canadian Space Agency astronaut Chris Hadfield, who will become the first Canadian to make a spacewalk.

Four of the five space agencies involved in building the mammoth orbiting outpost are represented on the crew. Only Japan was left without a seat on the flight.

The weather forecast for Thursday's 2:40 p.m. EDT (1840 GMT) launch is good, with only a 10 percent chance of cross winds strong enough to delay the launch.

"It's very dry over Florida and the southeastern U.S.," shuttle weather officer Ed Priselac said. "It looks like a really good day to launch."

The astronauts will head to the space station to deliver and install the largest segment of a $900 million ($1.4 billion Canadian) robotics system that is Canada's primary contribution to the multinational orbiting research outpost.

The 58-foot (17.6-meter) robot arm stowed in Endeavor's cargo bay is a cousin of those used by shuttle crews for years, but this one will have no permanent attachment to the station.

Instead, it will be able to work its way, hand-over-hand along the station's walls, plugging into a series of power and data ports lining the station's exterior.

------------ 'Inchworm' Unlike Anything in Space ----------

The Canadian Space Agency described it as an "inchworm," but in reality it will be unlike anything ever seen in space or on earth. With seven joints and enough computer power to plan its own maneuvers, the Canadarm 2 will be able to heft multi-ton modules, handle delicate experiments or hunt for leaks and frayed cables.

The arm will eventually employ a sled it can use to more quickly traverse the length of the station, and a mini two-armed robot that can attach to one end of the arm for delicate repair work as the station ages.

Two, possibly three, spacewalks will be needed for Hadfield and colleague Scott Parazynski to mount the new arm.

Although Parazynski and pilot Jeffrey Ashby are hardly household names, both are veterans of two highly celebrated missions in the 1990s. Parazynski flew with John Glenn when the septuagenarian veteran of project Mercury returned to space as part of a shuttle crew.

Ashby was the shuttle pilot when Eileen Collins became the first woman to command a shuttle mission.

Italian Umberto Guidoni is making his second flight. He will perform some of the activities associated with an Italian-built cargo module named Raffaello, which like another cargo module, Leonardo, is named for a Renaissance master. Leonardo flew aboard shuttle Atlantis in March.

Russian Yuri Lonchakov is making his first trip into orbit. American John Phillips, formally an earth-based space scientist, is making his first space flight at age 50.