NASA has pushed back the earliest launch date for the Endeavour two more days, going May 8 to May 10. The space agency did not give a specific reason as to why this date has been pushed back an additional two days, other than to say it removed the Load Control Assembly-2 (LCA-2) box in the orbiter's aft compartment last night.

Managers are planning on reconvening Friday to determine a more definite launch date after the box is removed and replaced and the retest of systems has been completed. Originally, NASA said it might be able to launch May 8 because the removing and installation of the box would take several days to complete, along with a 1-2 day test period. Endeavour was originally scheduled to launch April 29.

The crew, led by Commander Mark Kelly, is motion base simulator conducting refresher ascent and entry sims prior to their planned return to Kennedy later this week for the second launch attempt. Along with Kelly, the crew members include Pilot Gregory H. Johnson and Mission Specialists Michael Fincke, Greg Chamitoff, Andrew Feustel and European Space Agency astronaut Roberto Vittori.

During the 14-day mission, Endeavour and its crew will deliver the Alpha Magnetic Spectrometer (AMS) and spare parts including two S-band communications antennas, a high-pressure gas tank and additional spare parts for Dextre. After it finishes up, NASA will conclude the space shuttle program with the Atlantis. Following that, the three remaining space shuttles and a fourth prototype will head to museums across the country.

A NASA official told, the cost of the delay would be at least $500,000, if not more. This is mainly due to the cost of de-tanking, where the fuel propellant is drained for an external tank.

The Endeavour launch will be the final one for the space shuttle. It is also the penultimate mission for the space shuttle program. It marks the end of a historic run for the spacecraft.

Kelly's presence on the flight is also significant, as he is the husband of congresswoman Gabrielle Giffords, who was nearly shot to death earlier this year. President Barack Obama was in Florida on Friday for the proposed launch and met with Commander Kelly and his team. He also met with Giffords.

Follow Gabriel Perna on Twitter at @GabrielSPerna