CAPE CANAVERAL, Fla. -- In the Space Shuttle Main Engine Processing Facility at NASA's Kennedy Space Center in Florida, three of six space shuttle main engines are prepared for the STS-134 and STS-335 missions. Postflight inspections and maintenance of each engine are conducted in the facility between shuttle missions by Pratt & Whitney Rocketdyne aerospace technicians. Three main engines are clustered at the aft end of the shuttle and have a combined thrust of more than 1.2 million pounds. Each engine utilizes liquid hydrogen for fuel and liquid oxygen as oxidizer and operates during the entire eight-and-a-half minute ride to orbit.Space shuttle Endeavour's STS-134 mission is the final planned mission of the Space Shuttle Program and will deliver the Alpha Magnetic Spectrometer, as well as critical spare components, to the International Space Station next year. Shuttle Atlantis will be prepared for STS-335, which is the planned "launch on need," or potential rescue mission, for Ende