Space shuttle Endeavour is seen on launch pad 39a as a storm passes by prior to the rollback of the Rotating Service Structure (RSS) April 28, 2011, at Kennedy Space Center in Cape Canaveral, Florida. During the 14-day mission, Endeavour and the STS-134 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. Launch is targeted for April 29 at 3:47 p.m. EDT. (Photo by Bill Ingalls/NASA via Getty Images)

Photographers set up remote cameras near Space Shuttle Endeavour STS-134 as it sits on launch pad-39A at the Kennedy Space Center April 28, 2011 in Cape Canaveral, Florida. (Photo by Eliot J. Schechter/Getty Images)

A helicopter pours water over a wildfire with the Space Shuttle Endeavour seen through heavy smoke in the background April 27, 2011 in Cape Canaveral, Florida. (Photo by Roberto Gonzalez/Getty Images)

A large thunder storm moves over the Vehicle Assembly Building as the Space Shuttle Endeavour sits on Pad-39A on April 28, 2011 in Cape Canaveral, Florida. (Photo by Tom Pennington/Getty Images)