NASA is preparing to launch its Endeavour shuttle for the last time. The youngest of America's reusable orbiters is set to deliver a 2 billion dollar particle physics experiment to the International Space Station. Once it completes its 14-day mission, Endeavour will be retired to a museum in Los Angeles. That will leave just the Atlantis shuttle still in active service. It is expected to make a final outing in the next few months. The US space agency is withdrawing the orbiters to make way for a fleet of vehicles provided by the commercial sector later this decade. Lift-off for Endeavour and her crew of six is targeted for today from the Kennedy Space Center, Florida.