Falcon 9 flight hardware goes through final integration at SpaceX's Cape Canaveral launch site in Florida. SpaceX hide caption

itoggle caption SpaceX

At Launch Pad 39A at NASA's Kennedy Space Center in Florida, a technician performs a final check of space shuttle Atlantis' payload bay doors before they are closed for launch. Cory Huston/NASA hide caption

itoggle caption Cory Huston/NASA

Space shuttle Atlantis awaits blastoff on its launch pad as members of the media set up remote cameras for Friday's scheduled launch from Kennedy Space Center in Florida to the International Space Station. Matt Stroshane/Getty Images hide caption

itoggle caption Matt Stroshane/Getty Images

This illustration shows the asteroid 24 Themis flanked by two small fragments that broke off following a crash more than 1 billion years ago. The bottom fragment's cometlike tail comes from the sublimation of ice from its surface. Gabriel Perez, Servicio MultiMedia, Instituto de Astrofisica de Canarias, Tenerife, Spain hide caption

itoggle caption Gabriel Perez, Servicio MultiMedia, Instituto de Astrofisica de Canarias, Tenerife, Spain