Reaching the stars just got a bit easier and a new study argues that the boundary between Earth’s atmosphere and outer space —known as the Kármán line — is 20 kilometers, or about 20 percent, closer than scientists thought, this according to an article published in the Science online infosite by Paul Voosen.
Though the new definition won’t make a difference for launching rockets and spacecraft, it could help clarify a legal debate that will set the rules for space policy — and commercial spaceflight — for years to come.
Until now, most scientists have said that outer space is 100 kilometers away. At that point, it’s been thought, the speed needed to achieve lift in the superthin atmosphere is equal to the speed needed to simply orbit the planet; once there, a spacecraft’s horizontal pace would counteract the tug of Earth’s gravity. It’s an insight that has long been credited to aerodynamics pioneer Theodore von Kármán, though he credited the term to the world’s first “space lawyer,” Andrew Haley, in 1963.
A close look shows that the traditional definition flies in the face of evidence, said Jonathan McDowell, an astrophysicist at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts. As a hobby, McDowell compiles an influential, detailed record of rocket launches online, who has been making lists of rockets since he was 13. McDowell often has to decide which launches qualify as reaching outer space, and which do not. Given how low many orbiting satellites fly, the 100 kilometer limit never seemed to be correct to McDowell. He preferred the mesopause, the coldest point in Earth’s atmosphere, located roughly 85 kilometers up. (Recent estimates have bumped the mesopause somewhat higher.)
Most people continued to use 100 kilometers as a boundary, including the World Air Sports Federation (FAI) in Lausanne, Switzerland, the keeper of outer space records. Although definitions are always points of contention in science, it seemed worthwhile to McDowell to dig deeper, knowing such companies as Virgin Galactic and Blue Origin could soon be offering tourism flights to this boundary realm.