The Soviet and, later, Russian space station Mir is seen in 1998 as it orbits Earth after the US space shuttle Endeavour moves away after completing five days of joint operations. The space station would be decommissioned in 2000 and reentered the Earth's atmosphere in 2001. AFP/EPA/NASA/Newscom/File
The Soviet-French space crew (l.- r.) Sergei Krikalyev, Jeab-Loup Chretien aboard the Russia's space station Mir in 1988. Itar-Tass/Newscom/File
Sputnik 2 was the first satellite to carry a living animal, Laika the dog, into space. Laika died after 5 to 7 hours. RIA Nowosti/Newscom/File
This file photo taken on April 12, 1961 shows the Soviet Vostok-1 spaceship with cosmonaut Yuri Gagarin on board blasts off on top of Rocket R-7 for the first manned trip into space from the Baikonur Cosmodrome in Kazakhstan. The 27-year-old's 108-minute flight is still remembered in Russia even after the USSR's collapse as its greatest national achievement. The first manned spaceflight allowed the Soviet leadership, fully entrenched in the cold war, to maintain the superiority of the communist system over their principal adversary, the United States. AFP/Getty Images/Newscom/File
This undated picture shows a Russian Vostok rocket on its launcher. It was the Soviet Union's own giant leap for mankind – one that would spur a humiliated America to race for the moon. It happened on Tuesday, April 12, 1961 when an air force pilot named Yuri Gagarin, traveling in a Vostok, became the first human in space. AP/File
This file photo taken on April 12, 1961 shows Soviet cosmonaut Yuri Gagarin inside the Vostok 1 command capsule. AFP/Getty Images/Newscom/File
Yuri Gagarin talks with Soviet leadership before his historic 1961 flight. Educational Images LTD/Custom Medical Stock Photo/Newscom/File
An early space capsule from the USSR is seen in this 1960s photo. Educational Images LTD/Custom Medical Stock Photo/Newscom/File
The Apollo-Soyuz Test Project was the first joint US/Soviet space mission, flown in 1975. This symbolic mission saw the two crews conducting separate experiments and helping each other conduct joint research. The mission also saw the docking of the two orbital spacecraft, as depicted in this painting NASA
A replica of Sputnik 1, the first artificial satellite to be put into outer space by the Soviet Union in 1957. NSSDC Master Catalog by NASA
This photo depicts the liftoff of the Saturn IB launch vehicle, for the Apollo/Soyuz Test Project mission, from the Launch Complex 39B, Kennedy Space Center. NASA
Visitors at the 38th Paris International Air and Space Shown at Le Bourget Airfield line up to tour a Soviet An-225 Mriya aircraft with the Space Shuttle Buran on its back. The Buran was a Space Shuttle-like reusable space vehicle that completed only one unmanned spaceflight in 1988. MASTER SGT. DAVE CASEY
This 1972 Soviet postage stamp depicts celebrating the space program is from a series titled '15 Years of Space Age.
Nikolai Nikolaevich Rukavishnikov, cosmonaut of the USSR, was captain of the 1979 Soyuz 33 mission to the Soviet Salyut 6 space station.
A model of the Salyut 7 space station, with a Soyuz spacecraft docked at the front port and a Progress spacecraft at the rear port is seen. The display is in front of one of the pavilions of the Exhibition of Soviet National Economic Achievement located across from the Kosmos Hotel on the north side of Moscow. Don S. Montgomery, USN (Ret.)
The Soyuz spacecraft and launch vehicle are installed on the launch pad at the Baikonur complex in Kazakhstan. Baikonur is the world's largest space center. This launch was part of the Apollo-Soyuz Test Project (ASTP), a cooperative space mission between the United States and the USSR. Great Images in NASA
The Soviet Cosmos unmanned satellite/spacecraft is on display. The circular viewport was installed for display purposes. The Cosmos (or Kosmos) series of satellites are a large series of unmanned orbiters launched from Russia beginning in 1962. 2,468 Cosmos satellites have been launched to date. NASA
On April 12, 1961, the era of human spaceflight began when the Cosmonaut Yuri Gagarin became the first human to orbit the Earth in his Vostock I spacecraft. The flight lasted 108 minutes. NASA
Major battlefield gains by pro-Russia rebels in eastern Ukraine may be absorbing the full attention of Kiev and Moscow, in large part thanks to an all-but-openly-acknowledged boost in Russian assistance to the rebels' cause.