The United States and Russia may not be getting along so well of late, but that has not interrupted the two nations' vital space relations.

The relationship has now spanned four decades, Monica Grady, a professor of planetary and space sciences at The Open University, noted in an op-ed for CNN. The two leaders in space exploration, the U.S. and Russia depend on each other in regards to the International Space Station (ISS).

Currently, the U.S. and other nations who participate with the ISS pay the Russian Space Agency to ferry their astronauts to the floating science lab. Meanwhile, NASA has contracted private companies to fly unmanned resupply trips to the ISS.

But NASA has publicly been trying to end its reliance on Russia for transporting astronauts to and from the ISS by tasking these private companies to develop rockets and spacecraft designed for human travel.

"[The U.S.-Russia collaboration] is a very different picture of space exploration from 50 years ago, when the U.S. and the USSR were firmly gripped in a Cold War and a space race," Grady wrote. "In 1965, the U.S. was lagging behind the Soviet competition. Still smarting from losing out to Sputnik (the first artificial satellite launched in 1957), Yuri Gagarin (first man in space, 1961) and Valentina Tereshkova (first woman in space, 1963), America focused its efforts on sending a man to the moon."

To commemorate the highly successful partnership, Buzz Aldrin, one of the astronauts to travel to the moon, remembered the 1975 Apollo-Soyuz mission that started it in a piece written in Time.

"That... mission was a game-changer, bringing together two adversaries during the Cold War and the often-called 'Space Race,'" Aldrin wrote. "The competition between the U.S. and the Soviet Union was, in my view, left in the lunar dust when Neil Armstrong and I firmly planted our boots years earlier on the time-weathered Moon. Our 'one small step' translated into a U.S. victory at the lunar goal line. Nevertheless, our nation's space program represented then-and more so today-a tool to forge international partnerships not only in Earth orbit... but also beyond."