From a cosmic perspective, 100 km is a stone's throw; it's only one-sixth the driving distance between San Francisco and Los Angelas. It’s als

The Kármán Line: Where does space begin?

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2021-06-20 07:00:03

From a cosmic perspective, 100 km is a stone's throw; it's only one-sixth the driving distance between San Francisco and Los Angelas. It’s also well within the clutches of Earth's overpowering gravitational pull and expansive atmosphere. So, how did humans come to accept this relatively nearby location as the defining line between Earth and space?

The answer is partly based on physical reality and partly based on an arbitrary human construct. 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 Kármán line is based on physical reality in the sense that it roughly marks the altitude where traditional aircraft can no longer effectively fly. 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. In other words, the Kármán line is where the physical laws governing a craft's ability to fly shift.

However, the Kármán line is also where the human laws governing aircraft and spacecraft diverge. There are no national borders that extend to outer space; it’s governed more like international waters. So, settling on a boundary for space is about much more than the semantics of who gets to be called an astronaut.