CAPE CANAVERAL, Fla. -- This diagram of a space shuttle orbiter shows the location of avionics bay 5. Space shuttle Endeavour was scheduled to launch on the STS-134 mission to the International Space Station on April 29, but that attempt was scrubbed to allow engineers to assess an issue associated with failed heaters on a fuel line for Endeavour's auxiliary power unit-1 (APU-1). STS-134 will be the final spaceflight for Endeavour. For more information, visit www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts134/index.html. Image credit: NASA

CAPE CANAVERAL, Fla. -- This diagram of a space shuttle orbiter's avionics bay 5 shows the location of aft load control assembly-2 (ALCA-2) inside the bay. Space shuttle Endeavour was scheduled to launch on the STS-134 mission to the International Space Station on April 29, but that attempt was scrubbed to allow engineers to assess an issue associated with failed heaters on a fuel line for Endeavour's auxiliary power unit-1 (APU-1). STS-134 will be the final spaceflight for Endeavour. For more information, visit www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts134/index.html. Image credit: NASA

CAPE CANAVERAL, Fla. -- At NASA Kennedy Space Center's Launch Pad 39A, workers gain entrance to space shuttle Endeavour's aft section as teams prepare to remove and replace the aft load control assembly-2 (ALCA-2). Located in the orbiter's aft avionics bay 5, the assembly is believed to have caused heaters on a fuel line for Endeavour's auxiliary power unit-1 (APU-1) to fail April 29 during the first launch attempt for the STS-134 mission. STS-134 will deliver the Express Logistics Carrier-3, Alpha Magnetic Spectrometer-2 (AMS), a high-pressure gas tank and additional spare parts for the Dextre robotic helper to the International Space Station. The mission also will be the final spaceflight for Endeavour. For more information, visit www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts134/index.html. Photo credit: NASA/Kim Shiflett

CAPE CANAVERAL, Fla. -- Barely visible inside space shuttle Endeavour's aft section, a technician at NASA Kennedy Space Center's Launch Pad 39A helps prepare for the upcoming removal and replacement of the aft load control assembly-2 (ALCA-2). Located in the orbiter's aft avionics bay 5, the assembly is believed to have caused heaters on a fuel line for Endeavour's auxiliary power unit-1 (APU-1) to fail April 29 during the first launch attempt for the STS-134 mission. STS-134 will deliver the Express Logistics Carrier-3, Alpha Magnetic Spectrometer-2 (AMS), a high-pressure gas tank and additional spare parts for the Dextre robotic helper to the International Space Station. The mission also will be the final spaceflight for Endeavour. For more information, visit www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts134/index.html. Photo credit: NASA/Kim Shiflett

CAPE CANAVERAL, Fla. -- At NASA Kennedy Space Center's Launch Pad 39A, workers inside space shuttle Endeavour's aft section help prepare for the upcoming removal and replacement of the aft load control assembly-2 (ALCA-2). Located in the orbiter's aft avionics bay 5, the assembly is believed to have caused heaters on a fuel line for Endeavour's auxiliary power unit-1 (APU-1) to fail April 29 during the first launch attempt for the STS-134 mission. STS-134 will deliver the Express Logistics Carrier-3, Alpha Magnetic Spectrometer-2 (AMS), a high-pressure gas tank and additional spare parts for the Dextre robotic helper to the International Space Station. The mission also will be the final spaceflight for Endeavour. For more information, visit www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts134/index.html. Photo credit: NASA/Kim Shiflett

CAPE CANAVERAL, Fla. -- A technician at NASA Kennedy Space Center's Launch Pad 39A crouches in space shuttle Endeavour's aft section, where teams are preparing to remove and replace the aft load control assembly-2 (ALCA-2). Located in the orbiter's aft avionics bay 5, the assembly is believed to have caused heaters on a fuel line for Endeavour's auxiliary power unit-1 (APU-1) to fail April 29 during the first launch attempt for the STS-134 mission. STS-134 will deliver the Express Logistics Carrier-3, Alpha Magnetic Spectrometer-2 (AMS), a high-pressure gas tank and additional spare parts for the Dextre robotic helper to the International Space Station. The mission also will be the final spaceflight for Endeavour. For more information, visit www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts134/index.html. Photo credit: NASA/Kim Shiflett

CAPE CANAVERAL, Fla. -- At NASA Kennedy Space Center's Launch Pad 39A, a technician makes his way across a platform in space shuttle Endeavour's aft section as work begins to remove and replace the aft load control assembly-2 (ALCA-2). Located in the orbiter's aft avionics bay 5, the assembly is believed to have caused heaters on a fuel line for Endeavour's auxiliary power unit-1 (APU-1) to fail April 29 during the first launch attempt for the STS-134 mission. STS-134 will deliver the Express Logistics Carrier-3, Alpha Magnetic Spectrometer-2 (AMS), a high-pressure gas tank and additional spare parts for the Dextre robotic helper to the International Space Station. The mission also will be the final spaceflight for Endeavour. For more information, visit www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts134/index.html. Photo credit: NASA/Kim Shiflett