This week's full Moon as photographed from on board the International Space Station by NASA astronaut Jeff Williams on August 19, 2016. Jeff is currently Commander of the Space Station for the Expedition 48 crew. (Photo by Jeff Williams/NASA)

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)

Russian President Vladimir Putin (R) looks through a window of a research bathyscaphe while submerging into the waters of the Black Sea as he takes part in an expedition near Sevastopol, Crimea, August 18, 2015. (Photo by Alexei Nikolsky/Reuters/RIA Novosti/Kremlin)

“Adventurers have gone deep underground to discover previously unexplored caves in these pictures. The awe-inspiring snaps show the cavers dwarfed by the huge series natural rock chambers in the Leye – Fengshan Geopark, China. Belgian photographer Francois-Xavier De Ruydts, 33, captured the team of explorers as they trekked through the deep wonderground in January 2014”. – Caters News. Here: Caving expedition in Fengshan, China, Guangxi province. (Photo by Francois-Xavier De Ruydts/Caters News)

Peter Weiss, director of the Space Department of COMEX, (c) tests a pressurized suit identical to those used in space expeditions in the lava tunnel of “Caverne Gendarme” on October 12, 2018 in Saint-Philippe, the French overseas island of Reunion. Reunion could become a training site for astronauts. (Photo by Richard Bouhet/AFP Photo)

Soyuz MS-12 spacecraft with crew members of Expedition 59/60 Russian cosmonaut Alexey Ovchinin, NASA astronauts Christina Koch and Nick Hague lifts off from the launch pad at the Russian leased Baikonur cosmodrome, Kazakhstan, 15 March 2019. Hague, Koch, and Ovchinin will spend six-and-a-half months living and working aboard the International Space Station. (Photo by Sergei Ilnitsky/EPA/EFE)

A Romanian honor guard soldier stands still as three military aircraft carriers are crossing the sky during a ceremony held at the Unknown Soldier Memorial, in Carol I Park, on the occasion of the Heroes' Day commemoration, in Bucharest, Romania, 10 June 2021. (Photo by Robert Ghement/EPA/EFE)