A view of Earth from the Cupola on the earth-facing side of the International Space Station, June 12, 2013. Visible in the top left foreground is a Russian Soyuz crew capsule. In the lower right corner, a solar array panel can be seen. (Photo by Reuters/NASA)

Astronaut Mike Hopkins as he participates in the second of two spacewalks which took place on December 24, 2013. (Photo by Reuters/NASA)

The sun is over Earth's horizon as seen from aboard the International Space Station above a point in southwestern Minnesota, May 21, 2013. (Photo by Reuters/NASA)

The sun about to come up over the South Pacific Ocean photographed by one of the Expedition 35 crew members aboard the International Space Station a few hundred miles east of Easter Island, May 9, 2013. (Photo by Reuters/NASA)

Space tourist Anousheh Ansari while enroute to the International Space Station on September 18, 2006. (Photo by Reuters/NASA)

NASA astronaut Sunita Williams takes part in the third session of extravehicular activity outside the International Space Station, September 5, 2012. (Photo by Reuters/NASA)

A Russian cosmonaut during a mission in open space outside the International Space Station, August 24, 2012. (Photo by Reuters/Roscosmos)

A photo taken by an Expedition 28 crew member aboard the International Space Station shows Hurricane Irene off the east coast of the United States on August 26, 2011. (Photo by Reuters/NASA)

The moon appears near the earth's horizon in a photo of an orbital moonset taken from aboard the International Space Station on May 17, 2011. (Photo by Ron Garan/Reuters/NASA)

Backdropped by a night time view of the Earth and the starry sky, the Space Shuttle Endeavour is seen docked to the International Space Station on May 28, 2011. (Photo by Reuters/NASA)

A photo of the aurora australis taken during a geomagnetic storm from the International Space Station on May 29, 2010. (Photo by Reuters/ISS Crew Earth Observations experiment and Image Science & Analysis Laboratory, Johnson Space Center)

Spacewalker Ron Garan rides on the International Space Station's robotic arm on July 12, 2011. (Photo by Reuters/NASA)

Space Shuttle Endeavour astronaut Mike Fincke plays with a water bubble in microgravity aboard the International Space Station on May 29, 2011. (Photo by Reuters/NASA TV)

Astronaut Robert L. Satcher Jr. works outside the International Space Station on November 19, 2009. (Photo by Reuters/NASA)

Space shuttle Atlantis Pilot Doug Hurley moves around supplies and equipment in the Leonardo Permanent Multipurpose Module of the International Space Station on July 11, 2011. (Photo by Reuters/NASA)

A setting last quarter crescent moon and the thin line of the Earth's atmosphere as photographed from the International Space Station over Central Asia on September 4, 2010. (Photo by Reuters/NASA)

NASA astronaut Greg Chamitoff uses a laptop computer on the aft flight deck of space shuttle Endeavour during rendezvous and docking operations with the International Space Station in this photograph provided by NASA and taken May 18, 2011. (Photo by Reuters/NASA)

An unprecedented view of the space shuttle Atlantis, appearing like a bean sprout against clouds and city lights on its way home, as photographed from a window on the International Space Station on July 21, 2011. Airglow over Earth can be seen in the background. (Photo by Reuters/NASA)

The space shuttle Endeavour silhouetted against the backdrop of Earth's horizon prior to docking with the International Space Station, February 9, 2010. (Photo by Reuters/NASA)

Spacewalker Ron Garan rides on the International Space Station's robotic arm with the Earth as a backdrop as he transfers a failed pump module to the cargo bay of space shuttle Atlantis on July 12, 2011. (Photo by Reuters/NASA)

Astronaut Karen Nyberg looks through a window in the newly installed Kibo laboratory of the International Space Station on June 11, 2008. (Photo by Reuters/NASA)

NASA astronauts Greg Chamitoff (L), mission specialist, and space shuttle Endeavour Commander Mark Kelly, work on the orbiter's middeck on May 17, 2011. (Photo by Reuters/NASA)

The sun shines above the Earth's horizon with the International Space Station in the foreground in a photo taken by spacewalker Ron Garan on July 12, 2011. (Photo by Ron Garan/Reuters/NASA)

The space shuttle Discovery after it undocked from the International Space Station, in a photo taken more than 200 miles above Earth and released on March 9, 2011. (Photo by Reuters/NASA)