Expedition 44 flight engineer and NASA astronaut Scott Kelly seen inside the Cupola, a special module which provides a 360-degree viewing of the Earth and the International Space Station. Kelly is one of two crew members spending an entire year in space. (Photo by Scott Kelly/NASA)

This image made available by the Johns Hopkins University Applied Physics Laboratory on Wednesday, May 31, 2017 depicts NASA's Solar Probe Plus spacecraft approaching the sun. On Wednesday, NASA announced it will launch the probe in summer 2018 to explore the solar atmosphere. It will be subjected to brutal heat and radiation like no other man-made structure before. (Photo by Johns Hopkins University Applied Physics Laboratory via AP Photo)

A woman walks with her child past a Soyuz rocket, installed as a monument at the Russian leased Baikonur cosmodrome, the world's first and largest operational space launch facility, in Baikonur, Kazakhstan, Saturday, November 12, 2016. The new Soyuz mission to the International Space Station (ISS) is scheduled for Friday, Nov. 18. (Photo by Dmitri Lovetsky/AP Photo)

ESA astronaut Tim Peake posted this stunning image on his social media channels, commenting: “Station passed through magnificent aurora Australis last night”. Tim is set to return to Earth on 18 June 2016, bringing his six-month Principia mission to the ISS to an end. During his stay he performed more than 30 scientific experiments for ESA and taking part in numerous others from ESA's international partners. ESA and the UK Space Agency have partnered to develop many exciting educational activities around the Principia mission, aimed at sparking the interest of young children in science and space. (Photo by Tim Peake/ESA/NASA)

This image provided by NASA shows parts of Europe and Africa very easily recognizable in this night time image shot by one of the Expedition 25 crew members aboard the International Space Station flying 220 miles above Earth on Thursday October 28, 2010. The view “looks” northward over Sicily and the “boot” of Italy, with the Mediterranean Sea representing most of the visible water in the view and the Adriatic Sea to the right of center. Tunisia is partially visible at left. Part of a docked Russian spacecraft and other components of the ISS are in the foreground. (Photo by AP Photo/NASA)

“A small British company with a dream of building a re-usable space plane has won an important endorsement from the European Space Agency (ESA) after completing key tests on its novel engine technology. Reaction Engines Ltd believes its Sabre engine, which would operate like a jet engine in the atmosphere and a rocket in space, could displace rockets for space access and transform air travel by bringing any destination on Earth to no more than four hours away”. – Chris Wickham via Reuters. Photo: Artist's impression of Skylon. (Photo by Reaction Engines Ltd)

The Hubble Space Telescope is shown following its release from the space shuttle Discovery Wednesday, February 19, 1997. The Hubble Space Telescope, one of NASA'S crowning glories, marks its 25th anniversary on Friday, April 24, 2015. With more than 1 million observations, including those of the farthest and oldest galaxies ever beholden by humanity, no man-made satellite has touched as many minds or hearts as Hubble. (Photo by AP Photo/NASA)

Virgin Galactic's new spaceship N202VG (bottom L) is seen behind the WhiteKnightTwo carrier aircraft mothership (front), which landed safely after splitting from SpaceShipTwo, in a hangar at Mojave Air and Space Port in Mojave, California, November 4, 2014. (Photo by Lucy Nicholson/Reuters)