Even the Ansari X-prize chose the Kármán line as the benchmark height required to win its $10 million prize, which was claimed when Burt Rutan’s SpaceShipOne became the first privately-built spacecraft to carry a crew back in 2004. government has been reticent to agree to a specific height, people who fly above an altitude of 60 miles (100 km) typically earn astronaut wings from the Federal Aviation Administration. The United Nations has historically accepted the Kármán line as the boundary of space. So, settling on a boundary for space is about much more than the semantics of who gets to be called an astronaut. There are no national borders that extend to outer space it’s governed more like international waters. However, the Kármán line is also where the human laws governing aircraft and spacecraft diverge. In other words, the Kármán line is where the physical laws governing a craft's ability to fly shift. Anything traveling above the Kármán line needs a propulsion system that doesn’t rely on lift generated by Earth’s atmosphere - the air is simply too thin that high up. The Kármán line is based on physical reality in the sense that it roughly marks the altitude where traditional aircraft can no longer effectively fly. However, for well over half a century, most - including regulatory bodies - have accepted something close to our current definition of the Kármán Line. What is the Kármán Line? Experts have suggested the actual boundary between Earth and space lies anywhere from a mere 18.5 miles (30km) above the surface to more than a million miles (1.6 million km) away. That's why the exact altitude where space begins is something scientists have been debating since before we even sent the first spacecraft into orbit. The answer is partly based on physical reality and partly based on an arbitrary human construct. So, how did humans come to accept this relatively nearby location as the defining line between Earth and space? It’s also well within the clutches of Earth's overpowering gravitational pull and expansive atmosphere. This boundary sits some 62 miles (100 kilometers) above Earth's surface, and it's generally accepted as the place where Earth ends and outer space begins.įrom a cosmic perspective, 100 km is a stone's throw it's only one-sixth the driving distance between San Francisco and Los Angelas. But to earn their astronaut wings, high-flying civilians will have to make it past the so-called Kármán line. And a deluge of paying space tourists should soon follow. These days, spacecraft are venturing into the final frontier at a record pace.