NASA Associate Administrator for Education and former astronaut Leland Melvin teaches the ABC's of living and working in space to Sesame Street's Elmo at NASA's Kennedy Space Center, Wednesday, July 6, 2011 in Cape Canaveral, FL. The pair discussed nutrition, exercise, hygiene in orbit. They also chatted about the features of the space shuttle and the various suits that astronauts wear. Photo Credit: (NASA/Carla Cioffi)

NASA Associate Administrator for Education and former astronaut Leland Melvin teaches the ABC's of living and working in space to Sesame Street's Elmo at NASA's Kennedy Space Center, Wednesday, July 6, 2011 in Cape Canaveral, FL. The pair discussed nutrition, exercise, hygiene in orbit. They also chatted about the features of the space shuttle and the various suits that astronauts wear. Photo Credit: (NASA/Carla Cioffi)

NASA Associate Administrator for Education and former astronaut Leland Melvin teaches the ABC's of living and working in space to Sesame Street's Elmo at NASA's Kennedy Space Center, Wednesday, July 6, 2011 in Cape Canaveral, FL. The pair discussed nutrition, exercise, hygiene in orbit. They also chatted about the features of the space shuttle and the various suits that astronauts wear. Photo Credit: (NASA/Carla Cioffi)

CAPE CANAVERAL, Fla. -- At Kennedy Space Center in Florida, NASA is hosting a Tweetup for 150 Twitter followers of space shuttle Atlantis' STS-135 mission to the International Space Station, selected from more than 5,500 online registrants. A Tweetup is an informal meeting of people who use the social messaging medium Twitter. Here, NASA astronaut Mike Massimino talks with Sesame Street's Elmo. Sesame Street also is at Kennedy to film Elmo, as he learns about space exploration at NASA. Atlantis and its crew of four; Commander Chris Ferguson, Pilot Doug Hurley, Mission Specialists Sandy Magnus and Rex Walheim, are scheduled to lift off at 11:26 a.m. EDT on July 8 to deliver the Raffaello multi-purpose logistics module packed with supplies and spare parts to the station. Atlantis also will fly the Robotic Refueling Mission experiment that will investigate the potential for robotically refueling existing satellites in orbit. In addition, Atlantis will return with a failed ammonia pump module to help NASA better understand the failure mechanism and improve pump designs for future systems. STS-135 will be the 33rd flight of Atlantis, the 37th shuttle mission to the space station, and the 135th and final mission of NASA's Space Shuttle Program. For more information visit, www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts135/index.html. Photo credit: NASA/Troy Cryder

CAPE CANAVERAL, Fla. -- At Kennedy Space Center in Florida, NASA is hosting a Tweetup for 150 Twitter followers of space shuttle Atlantis' STS-135 mission to the International Space Station, selected from more than 5,500 online registrants. A Tweetup is an informal meeting of people who use the social messaging medium Twitter. Here, NASA astronaut Mike Massimino talks with Sesame Street's Elmo. Sesame Street also is at Kennedy to film Elmo, as he learns about space exploration at NASA. Atlantis and its crew of four; Commander Chris Ferguson, Pilot Doug Hurley, Mission Specialists Sandy Magnus and Rex Walheim, are scheduled to lift off at 11:26 a.m. EDT on July 8 to deliver the Raffaello multi-purpose logistics module packed with supplies and spare parts to the station. Atlantis also will fly the Robotic Refueling Mission experiment that will investigate the potential for robotically refueling existing satellites in orbit. In addition, Atlantis will return with a failed ammonia pump module to help NASA better understand the failure mechanism and improve pump designs for future systems. STS-135 will be the 33rd flight of Atlantis, the 37th shuttle mission to the space station, and the 135th and final mission of NASA's Space Shuttle Program. For more information visit, www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts135/index.html. Photo credit: NASA/Troy Cryder

CAPE CANAVERAL, Fla. -- At Kennedy Space Center in Florida, NASA is hosting a Tweetup for 150 Twitter followers of space shuttle Atlantis' STS-135 mission to the International Space Station, selected from more than 5,500 online registrants. A Tweetup is an informal meeting of people who use the social messaging medium Twitter. Here, NASA astronaut Doug Wheelock talks with Sesame Street's Elmo. Sesame Street also is at Kennedy to film Elmo, as he learns about space exploration at NASA. Atlantis and its crew of four; Commander Chris Ferguson, Pilot Doug Hurley, Mission Specialists Sandy Magnus and Rex Walheim, are scheduled to lift off at 11:26 a.m. EDT on July 8 to deliver the Raffaello multi-purpose logistics module packed with supplies and spare parts to the station. Atlantis also will fly the Robotic Refueling Mission experiment that will investigate the potential for robotically refueling existing satellites in orbit. In addition, Atlantis will return with a failed ammonia pump module to help NASA better understand the failure mechanism and improve pump designs for future systems. STS-135 will be the 33rd flight of Atlantis, the 37th shuttle mission to the space station, and the 135th and final mission of NASA's Space Shuttle Program. For more information visit, www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts135/index.html. Photo credit: NASA/Troy Cryder

CAPE CANAVERAL, Fla. -- At Kennedy Space Center in Florida, NASA is hosting a Tweetup for 150 Twitter followers of space shuttle Atlantis' STS-135 mission to the International Space Station, selected from more than 5,500 online registrants. A Tweetup is an informal meeting of people who use the social messaging medium Twitter. Here, NASA astronaut Mike Massimino talks with Sesame Street's Elmo. Sesame Street also is at Kennedy to film Elmo, as he learns about space exploration at NASA. Atlantis and its crew of four; Commander Chris Ferguson, Pilot Doug Hurley, Mission Specialists Sandy Magnus and Rex Walheim, are scheduled to lift off at 11:26 a.m. EDT on July 8 to deliver the Raffaello multi-purpose logistics module packed with supplies and spare parts to the station. Atlantis also will fly the Robotic Refueling Mission experiment that will investigate the potential for robotically refueling existing satellites in orbit. In addition, Atlantis will return with a failed ammonia pump module to help NASA better understand the failure mechanism and improve pump designs for future systems. STS-135 will be the 33rd flight of Atlantis, the 37th shuttle mission to the space station, and the 135th and final mission of NASA's Space Shuttle Program. For more information visit, www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts135/index.html. Photo credit: NASA/Troy Cryder

CAPE CANAVERAL, Fla. -- At Kennedy Space Center in Florida, NASA is hosting a Tweetup for 150 Twitter followers of space shuttle Atlantis' STS-135 mission to the International Space Station, selected from more than 5,500 online registrants. A Tweetup is an informal meeting of people who use the social messaging medium Twitter. Here, NASA astronauts Mike Massimino and Doug Wheelock talk with Sesame Street's Elmo. Sesame Street also is at Kennedy to film Elmo, as he learns about space exploration at NASA. Atlantis and its crew of four; Commander Chris Ferguson, Pilot Doug Hurley, Mission Specialists Sandy Magnus and Rex Walheim, are scheduled to lift off at 11:26 a.m. EDT on July 8 to deliver the Raffaello multi-purpose logistics module packed with supplies and spare parts to the station. Atlantis also will fly the Robotic Refueling Mission experiment that will investigate the potential for robotically refueling existing satellites in orbit. In addition, Atlantis will return with a failed ammonia pump module to help NASA better understand the failure mechanism and improve pump designs for future systems. STS-135 will be the 33rd flight of Atlantis, the 37th shuttle mission to the space station, and the 135th and final mission of NASA's Space Shuttle Program. For more information visit, www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts135/index.html. Photo credit: NASA/Troy Cryder

CAPE CANAVERAL, Fla. -- At Kennedy Space Center in Florida, NASA is hosting a Tweetup for 150 Twitter followers of space shuttle Atlantis' STS-135 mission to the International Space Station, selected from more than 5,500 online registrants. A Tweetup is an informal meeting of people who use the social messaging medium Twitter. Here, NASA astronaut Mike Massimino talks with Sesame Street's Elmo. Sesame Street also is at Kennedy to film Elmo, as he learns about space exploration at NASA. Atlantis and its crew of four; Commander Chris Ferguson, Pilot Doug Hurley, Mission Specialists Sandy Magnus and Rex Walheim, are scheduled to lift off at 11:26 a.m. EDT on July 8 to deliver the Raffaello multi-purpose logistics module packed with supplies and spare parts to the station. Atlantis also will fly the Robotic Refueling Mission experiment that will investigate the potential for robotically refueling existing satellites in orbit. In addition, Atlantis will return with a failed ammonia pump module to help NASA better understand the failure mechanism and improve pump designs for future systems. STS-135 will be the 33rd flight of Atlantis, the 37th shuttle mission to the space station, and the 135th and final mission of NASA's Space Shuttle Program. For more information visit, www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts135/index.html. Photo credit: NASA/Troy Cryder

CAPE CANAVERAL, Fla. -- At Kennedy Space Center in Florida, NASA is hosting a Tweetup for 150 Twitter followers of space shuttle Atlantis' STS-135 mission to the International Space Station, selected from more than 5,500 online registrants. A Tweetup is an informal meeting of people who use the social messaging medium Twitter. Here, NASA astronauts Mike Massimino and Doug Wheelock talk with Sesame Street's Elmo. Sesame Street also is at Kennedy to film Elmo, as he learns about space exploration at NASA. Atlantis and its crew of four; Commander Chris Ferguson, Pilot Doug Hurley, Mission Specialists Sandy Magnus and Rex Walheim, are scheduled to lift off at 11:26 a.m. EDT on July 8 to deliver the Raffaello multi-purpose logistics module packed with supplies and spare parts to the station. Atlantis also will fly the Robotic Refueling Mission experiment that will investigate the potential for robotically refueling existing satellites in orbit. In addition, Atlantis will return with a failed ammonia pump module to help NASA better understand the failure mechanism and improve pump designs for future systems. STS-135 will be the 33rd flight of Atlantis, the 37th shuttle mission to the space station, and the 135th and final mission of NASA's Space Shuttle Program. For more information visit, www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts135/index.html. Photo credit: NASA/Troy Cryder

CAPE CANAVERAL, Fla. -- At Kennedy Space Center in Florida, NASA is hosting a Tweetup for 150 Twitter followers of space shuttle Atlantis' STS-135 mission to the International Space Station, selected from more than 5,500 online registrants. A Tweetup is an informal meeting of people who use the social messaging medium Twitter. Here, NASA astronauts Mike Massimino and Doug Wheelock talk with Sesame Street's Elmo. Sesame Street also is at Kennedy to film Elmo, as he learns about space exploration at NASA. Atlantis and its crew of four; Commander Chris Ferguson, Pilot Doug Hurley, Mission Specialists Sandy Magnus and Rex Walheim, are scheduled to lift off at 11:26 a.m. EDT on July 8 to deliver the Raffaello multi-purpose logistics module packed with supplies and spare parts to the station. Atlantis also will fly the Robotic Refueling Mission experiment that will investigate the potential for robotically refueling existing satellites in orbit. In addition, Atlantis will return with a failed ammonia pump module to help NASA better understand the failure mechanism and improve pump designs for future systems. STS-135 will be the 33rd flight of Atlantis, the 37th shuttle mission to the space station, and the 135th and final mission of NASA's Space Shuttle Program. For more information visit, www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts135/index.html. Photo credit: NASA/Troy Cryder

CAPE CANAVERAL, Fla. -- At Kennedy Space Center in Florida, NASA is hosting a Tweetup for 150 Twitter followers of space shuttle Atlantis' STS-135 mission to the International Space Station, selected from more than 5,500 online registrants. A Tweetup is an informal meeting of people who use the social messaging medium Twitter. Here, NASA astronaut Doug Wheelock talks with Sesame Street's Elmo. Sesame Street also is at Kennedy to film Elmo, as he learns about space exploration at NASA. Atlantis and its crew of four; Commander Chris Ferguson, Pilot Doug Hurley, Mission Specialists Sandy Magnus and Rex Walheim, are scheduled to lift off at 11:26 a.m. EDT on July 8 to deliver the Raffaello multi-purpose logistics module packed with supplies and spare parts to the station. Atlantis also will fly the Robotic Refueling Mission experiment that will investigate the potential for robotically refueling existing satellites in orbit. In addition, Atlantis will return with a failed ammonia pump module to help NASA better understand the failure mechanism and improve pump designs for future systems. STS-135 will be the 33rd flight of Atlantis, the 37th shuttle mission to the space station, and the 135th and final mission of NASA's Space Shuttle Program. For more information visit, www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts135/index.html. Photo credit: NASA/Troy Cryder

CAPE CANAVERAL, Fla. -- At Kennedy Space Center in Florida, NASA is hosting a Tweetup for 150 Twitter followers of space shuttle Atlantis' STS-135 mission to the International Space Station, selected from more than 5,500 online registrants. A Tweetup is an informal meeting of people who use the social messaging medium Twitter. Here, NASA astronaut Mike Massimino talks with Sesame Street's Elmo. Sesame Street also is at Kennedy to film Elmo, as he learns about space exploration at NASA. Atlantis and its crew of four; Commander Chris Ferguson, Pilot Doug Hurley, Mission Specialists Sandy Magnus and Rex Walheim, are scheduled to lift off at 11:26 a.m. EDT on July 8 to deliver the Raffaello multi-purpose logistics module packed with supplies and spare parts to the station. Atlantis also will fly the Robotic Refueling Mission experiment that will investigate the potential for robotically refueling existing satellites in orbit. In addition, Atlantis will return with a failed ammonia pump module to help NASA better understand the failure mechanism and improve pump designs for future systems. STS-135 will be the 33rd flight of Atlantis, the 37th shuttle mission to the space station, and the 135th and final mission of NASA's Space Shuttle Program. For more information visit, www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts135/index.html. Photo credit: NASA/Troy Cryder

CAPE CANAVERAL, Fla. -- At Kennedy Space Center in Florida, NASA is hosting a Tweetup for 150 Twitter followers of space shuttle Atlantis' STS-135 mission to the International Space Station, selected from more than 5,500 online registrants. A Tweetup is an informal meeting of people who use the social messaging medium Twitter. Here, NASA astronaut Mike Massimino talks with Sesame Street's Elmo. Sesame Street also is at Kennedy to film Elmo, as he learns about space exploration at NASA. Atlantis and its crew of four; Commander Chris Ferguson, Pilot Doug Hurley, Mission Specialists Sandy Magnus and Rex Walheim, are scheduled to lift off at 11:26 a.m. EDT on July 8 to deliver the Raffaello multi-purpose logistics module packed with supplies and spare parts to the station. Atlantis also will fly the Robotic Refueling Mission experiment that will investigate the potential for robotically refueling existing satellites in orbit. In addition, Atlantis will return with a failed ammonia pump module to help NASA better understand the failure mechanism and improve pump designs for future systems. STS-135 will be the 33rd flight of Atlantis, the 37th shuttle mission to the space station, and the 135th and final mission of NASA's Space Shuttle Program. For more information visit, www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts135/index.html. Photo credit: NASA/Troy Cryder

CAPE CANAVERAL, Fla. -- At Kennedy Space Center in Florida, NASA is hosting a Tweetup for 150 Twitter followers of space shuttle Atlantis' STS-135 mission to the International Space Station, selected from more than 5,500 online registrants. A Tweetup is an informal meeting of people who use the social messaging medium Twitter. Here, NASA astronaut Mike Massimino talks with Sesame Street's Elmo. Sesame Street also is at Kennedy to film Elmo, as he learns about space exploration at NASA. Atlantis and its crew of four; Commander Chris Ferguson, Pilot Doug Hurley, Mission Specialists Sandy Magnus and Rex Walheim, are scheduled to lift off at 11:26 a.m. EDT on July 8 to deliver the Raffaello multi-purpose logistics module packed with supplies and spare parts to the station. Atlantis also will fly the Robotic Refueling Mission experiment that will investigate the potential for robotically refueling existing satellites in orbit. In addition, Atlantis will return with a failed ammonia pump module to help NASA better understand the failure mechanism and improve pump designs for future systems. STS-135 will be the 33rd flight of Atlantis, the 37th shuttle mission to the space station, and the 135th and final mission of NASA's Space Shuttle Program. For more information visit, www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts135/index.html. Photo credit: NASA/Troy Cryder

NASA astronaut Mike Massimino, left, and Sesame Street's Elmo speak at the STS-135 Tweetup, Thursday, July 7, 2011, at Kennedy Space Center in Cape Canaveral, Fla. Elmo asked the astronauts questions about living and working in space. About 150 NASA Twitter followers attended the event. The STS-135 mission will be NASA's last space shuttle launch. Photo Credit: (NASA/Paul E. Alers)

NASA astronaut Mike Massimino, far left, Sesame Street's Elmo and NASA astronaut Doug Wheelock, far right, speak at the STS-135 Tweetup, Thursday, July 7, 2011, at Kennedy Space Center in Cape Canaveral, Fla. Elmo asked the astronauts questions about living and working in space. About 150 NASA Twitter followers attended the event. The STS-135 mission will be NASA's last space shuttle launch. Photo Credit: (NASA/Paul E. Alers)

CAPE CANAVERAL, Fla. -- At Kennedy Space Center in Florida, NASA is hosting a Tweetup for 150 Twitter followers of space shuttle Atlantis' STS-135 mission to the International Space Station, selected from more than 5,500 online registrants. A Tweetup is an informal meeting of people who use the social messaging medium Twitter. Here, Sesame Street's Elmo listens to NASA astronaut Mike Massimino (out of frame), as he learns about space exploration at NASA. Atlantis and its crew of four; Commander Chris Ferguson, Pilot Doug Hurley, Mission Specialists Sandy Magnus and Rex Walheim, are scheduled to lift off at 11:26 a.m. EDT on July 8 to deliver the Raffaello multi-purpose logistics module packed with supplies and spare parts to the station. Atlantis also will fly the Robotic Refueling Mission experiment that will investigate the potential for robotically refueling existing satellites in orbit. In addition, Atlantis will return with a failed ammonia pump module to help NASA better understand the failure mechanism and improve pump designs for future systems. STS-135 will be the 33rd flight of Atlantis, the 37th shuttle mission to the space station, and the 135th and final mission of NASA's Space Shuttle Program. For more information visit, www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts135/index.html. Photo credit: NASA/Troy Cryder

CAPE CANAVERAL, Fla. -- At Kennedy Space Center in Florida, NASA is hosting a Tweetup for 150 Twitter followers of space shuttle Atlantis' STS-135 mission to the International Space Station, selected from more than 5,500 online registrants. A Tweetup is an informal meeting of people who use the social messaging medium Twitter. This Tweetup is an opportunity to learn more about NASA, explore NASA's Kennedy Space Center in Florida and experience a space shuttle launch. Here, NASA Public Affairs Officer John Yembrick addresses the participants. Atlantis and its crew of four; Commander Chris Ferguson, Pilot Doug Hurley, Mission Specialists Sandy Magnus and Rex Walheim, are scheduled to lift off at 11:26 a.m. EDT on July 8 to deliver the Raffaello multi-purpose logistics module packed with supplies and spare parts to the station. Atlantis also will fly the Robotic Refueling Mission experiment that will investigate the potential for robotically refueling existing satellites in orbit. In addition, Atlantis will return with a failed ammonia pump module to help NASA better understand the failure mechanism and improve pump designs for future systems. STS-135 will be the 33rd flight of Atlantis, the 37th shuttle mission to the space station, and the 135th and final mission of NASA's Space Shuttle Program. For more information visit, www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts135/index.html. Photo credit: NASA/Troy Cryder

CAPE CANAVERAL, Fla. -- At Kennedy Space Center in Florida, NASA is hosting a Tweetup for 150 Twitter followers of space shuttle Atlantis' STS-135 mission to the International Space Station, selected from more than 5,500 online registrants. A Tweetup is an informal meeting of people who use the social messaging medium Twitter. This Tweetup is an opportunity to learn more about NASA, explore NASA's Kennedy Space Center in Florida and experience a space shuttle launch. Atlantis and its crew of four; Commander Chris Ferguson, Pilot Doug Hurley, Mission Specialists Sandy Magnus and Rex Walheim, are scheduled to lift off at 11:26 a.m. EDT on July 8 to deliver the Raffaello multi-purpose logistics module packed with supplies and spare parts to the station. Atlantis also will fly the Robotic Refueling Mission experiment that will investigate the potential for robotically refueling existing satellites in orbit. In addition, Atlantis will return with a failed ammonia pump module to help NASA better understand the failure mechanism and improve pump designs for future systems. STS-135 will be the 33rd flight of Atlantis, the 37th shuttle mission to the space station, and the 135th and final mission of NASA's Space Shuttle Program. For more information visit, www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts135/index.html. Photo credit: NASA/Troy Cryder

CAPE CANAVERAL, Fla. -- At Kennedy Space Center in Florida, NASA is hosting a Tweetup for 150 Twitter followers of space shuttle Atlantis' STS-135 mission to the International Space Station, selected from more than 5,500 online registrants. A Tweetup is an informal meeting of people who use the social messaging medium Twitter. This Tweetup is an opportunity to learn more about NASA, explore NASA's Kennedy Space Center in Florida and experience a space shuttle launch. Atlantis and its crew of four; Commander Chris Ferguson, Pilot Doug Hurley, Mission Specialists Sandy Magnus and Rex Walheim, are scheduled to lift off at 11:26 a.m. EDT on July 8 to deliver the Raffaello multi-purpose logistics module packed with supplies and spare parts to the station. Atlantis also will fly the Robotic Refueling Mission experiment that will investigate the potential for robotically refueling existing satellites in orbit. In addition, Atlantis will return with a failed ammonia pump module to help NASA better understand the failure mechanism and improve pump designs for future systems. STS-135 will be the 33rd flight of Atlantis, the 37th shuttle mission to the space station, and the 135th and final mission of NASA's Space Shuttle Program. For more information visit, www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts135/index.html. Photo credit: NASA/Troy Cryder

CAPE CANAVERAL, Fla. -- At Kennedy Space Center in Florida, NASA is hosting a Tweetup for 150 Twitter followers of space shuttle Atlantis' STS-135 mission to the International Space Station, selected from more than 5,500 online registrants. A Tweetup is an informal meeting of people who use the social messaging medium Twitter. Here, NASA astronauts Mike Massimino (left) and Doug Wheelock introduce a special guest to the Tweetup. Atlantis and its crew of four; Commander Chris Ferguson, Pilot Doug Hurley, Mission Specialists Sandy Magnus and Rex Walheim, are scheduled to lift off at 11:26 a.m. EDT on July 8 to deliver the Raffaello multi-purpose logistics module packed with supplies and spare parts to the station. Atlantis also will fly the Robotic Refueling Mission experiment that will investigate the potential for robotically refueling existing satellites in orbit. In addition, Atlantis will return with a failed ammonia pump module to help NASA better understand the failure mechanism and improve pump designs for future systems. STS-135 will be the 33rd flight of Atlantis, the 37th shuttle mission to the space station, and the 135th and final mission of NASA's Space Shuttle Program. For more information visit, www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts135/index.html. Photo credit: NASA/Troy Cryder

CAPE CANAVERAL, Fla. -- At Kennedy Space Center in Florida, NASA is hosting a Tweetup for 150 Twitter followers of space shuttle Atlantis' STS-135 mission to the International Space Station, selected from more than 5,500 online registrants. A Tweetup is an informal meeting of people who use the social messaging medium Twitter. This Tweetup is an opportunity to learn more about NASA, explore NASA's Kennedy Space Center in Florida and experience a space shuttle launch. Atlantis and its crew of four; Commander Chris Ferguson, Pilot Doug Hurley, Mission Specialists Sandy Magnus and Rex Walheim, are scheduled to lift off at 11:26 a.m. EDT on July 8 to deliver the Raffaello multi-purpose logistics module packed with supplies and spare parts to the station. Atlantis also will fly the Robotic Refueling Mission experiment that will investigate the potential for robotically refueling existing satellites in orbit. In addition, Atlantis will return with a failed ammonia pump module to help NASA better understand the failure mechanism and improve pump designs for future systems. STS-135 will be the 33rd flight of Atlantis, the 37th shuttle mission to the space station, and the 135th and final mission of NASA's Space Shuttle Program. For more information visit, www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts135/index.html. Photo credit: NASA/Troy Cryder