The International Space Station depends on a mix of U.S. and Russian parts. "I hope we can hold it together as long as we can," says former NASA astronaut Scott Kelly. NASA hide caption
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Tina Buechner da Costa (left) hopes to become Germany's female astronaut. Claudia Kessler (right), CEO of HE Space, is organizing a campaign to send the first German woman into space. Soraya Sarhaddi Nelson/NPR hide caption
With this shot of Mount Fuji, astronaut Scott Kelly tweeted, "your majesty casts a wide shadow!" Scott Kelly/NASA hide caption
Astronaut Scott Kelly reacts after returning to Earth after nearly one year aboard the International Space Station. Bill Ingalls/AP hide caption
Expedition 43 NASA astronaut Scott Kelly (left) and his identical twin, Mark Kelly, pose for a photograph in 2015 at the Cosmonaut Hotel in Baikonur, Kazakhstan. Bill Ingalls/NASA/Getty Images hide caption
'Everybody Stretches' Without Gravity: Mark Kelly Talks About NASA's Twins Study
Kelly posted this photo of an aurora taken from the International Space Station to Twitter on Aug. 15, 2015. NASA hide caption
NASA astronaut Scott Kelly takes a selfie inside the cupola, a special module that provides a 360-degree view of Earth. Kelly and Russian cosmonaut Mikhail Kornienko have spent nearly a year aboard the International Space Station. NASA hide caption
NASA astronaut Scott Kelly is seen inside a Soyuz simulator at the Gagarin Cosmonaut Training Center on March 4 in Star City, Russia. Kelly, along with Russian cosmonaut Mikhail Kornienko of the Russian Federal Space Agency, are scheduled for launch Friday aboard a Soyuz TMA-16M spacecraft from the Baikonur Cosmodrome in Kazakhstan. NASA/Bill Ingalls hide caption