The space shuttle Endeavour is ready to lift off from Kennedy Space Center on its final mission at 8:56 a.m Monday after NASA finished fueling shuttle in the pre-dawn hours.

Originally, the space shuttle was supposed to launch on April 19 but the launch was delayed 10 days because of a scheduling conflict with a Russian spacecraft. Following that delay, it was pushed back for the 2nd time to May 16 hours before the April 29 launch because of a problem with the heating auxiliary power unit-1 (APU-1).

The mission will be commanded by Mark Kelly, husband of congresswoman Gabrielle Giffords who was nearly shot to death earlier this year. Other crew members are Pilot Gregory H. Johnson and Mission Specialists Michael Fincke, Greg Chamitoff, Andrew Feustel and European Space Agency astronaut Roberto Vittori.

The mission will last two weeks and will include four space walks and a trip to the International Space Station. The crew will deliver the Alpha Magnetic Spectrometer-2 (AMS) to the ISS. The AMS is designed to help researchers study the origins of the universe by measuring cosmic rays. The crew will also be responsible for maintenance work and installing new components.

The flight is Endeavour's 25th since a maiden voyage in 1992. The youngest shuttle orbiter was built as a replacement for Challenger, the shuttle destroyed in a 1986 launch accident that killed seven astronauts. Endeavour has traveled 116,372,930 miles, spent 283 days in space and has had a total of 4,423 orbits since its first mission. After returning to earth in 16 days time Endeavour will be retired to a Los Angeles museum.

An estimated 500,000 people are expected to have crowded around the Kennedy Space Center to see Endeavour launch.