WASHINGTON (AFP) –- Countdown began Tuesday for the U.S. space agency's launch of the shuttle Endeavour, with preparations proceeding smoothly and the weather forecast looking pleasant for the Friday liftoff, NASA said.

“We're really happy to be here today,” said shuttle commander Mark Kelly, who arrived at Kennedy Space Center on Tuesday afternoon with four other American astronauts and one Italian who will fly on the Endeavour's final mission.
“We got a chance to take look at the orbiter as we first flew over the field,” said Kelly. “It's great to see Endeavour all ready to go again.”
The shuttle is set to depart on Friday at 1947 GMT from Kennedy Space Center in Florida on a 14-day mission to the International Space Station.
When it returns to Earth it will become the second of the three-shuttle fleet to enter retirement.
The launch is receiving plenty of U.S. media attention because Kelly's wife, Arizona lawmaker Gabrielle Giffords, who was shot in the head in January during a grocery store political meeting, is coming to Florida to watch the launch along with President Barack Obama and his family.
“This is something she would not want to miss,” said Giffords' spokesman CJ Karamargin.
“It represents another significant milestone in her recovery.” The countdown to Friday's launch officially began at 1800 GMT on Tuesday.
------Favorable weather for launch
NASA's shuttle launch weather officer Kathy Winters said there was an 80 percent chance of favorable weather for the Friday launch, though thunderstorms could roll through on Thursday during flight preparations.
If the launch has to be delayed, weather conditions for Saturday are 70 percent favorable and by Sunday the forecast returns to 80 percent positive.
NASA has four opportunities for launch during the April 29 to May 4 window.
The six-member all male crew includes five Americans and one Italian, astronaut Roberto Vittori from the European Space Agency.
The team will deliver the Alpha Magnetic Spectrometer (AMS), a particle physics detector designed to search the universe for dark matter and antimatter, NASA said.
The shuttle will also bring along the Express Logistics Carrier 3, a platform for spare parts which will stay at the space station. Astronauts are planning to step out on four spacewalks to do maintenance work and install new components.
The mission will be the 25th flight for Endeavour, and the 36th shuttle trip to the ISS.
Discovery flew its final mission in February and returned in March. Atlantis is scheduled for its last mission in June, after which the 30-year U.S. space shuttle program will end for good.
Once the U.S. space shuttle program ends, astronauts will rely on Russia's space capsules for transit to the orbiting research station.