Where Does Space Actually Begin? Depends Who You Ask

With both Richard Branson and Jeff Bezos gearing up for suborbital flights this month, a question that used to be trivia-night material is suddenly a real argument: where does space start?

The number you’ll see cited most often is the Kármán line, roughly 100 km (62 miles) above sea level. It’s named after Theodore von Kármán, who worked out that above this altitude, an aircraft would need to be moving faster than orbital velocity just to generate enough lift from the thin atmosphere to stay up — at which point it’s not really flying anymore, it’s basically orbiting. That’s a clean physical justification, and it’s why the Fédération Aéronautique Internationale (the body that certifies aviation and spaceflight records) uses it as the official boundary.

But the US has never fully signed on to that number. The US Air Force, and later the FAA, have long recognized 50 miles (about 80 km) as the threshold for awarding astronaut wings. That’s a full 20 km lower than the Kármán line — not a rounding error, a meaningfully different line in the sky.

Why does this matter right now? Because it maps almost exactly onto the two vehicles about to fly paying (or at least high-profile) passengers. Virgin Galactic’s SpaceShipTwo has topped out around 86-90 km on its test flights — well past the US 50-mile mark, but short of the internationally recognized 100 km. Blue Origin’s New Shepard, by contrast, clears 100 km on every flight, putting it on the right side of both definitions.

That gap has turned into a genuinely public spat between the two camps. Blue Origin has been pointed, publicly and repeatedly, about the fact that its vehicle crosses the “real” boundary while Virgin’s doesn’t. Virgin, understandably, leans on the FAA/Air Force standard and notes its passengers will still get astronaut wings from the US government. Both things are true simultaneously, which is what makes this more interesting than a simple gotcha.

I don’t think there’s a physics-only answer here, honestly. The Kármán line has a tidier theoretical basis, but it was also calculated decades ago with cruder atmospheric models, and some researchers have argued the “real” transition altitude is closer to 80 km once you account for atmospheric drag more precisely. If that recalculation gains traction, it would conveniently validate the exact altitude Virgin Galactic already flies to — which is either a coincidence or a reason to be skeptical of whoever’s citing it, depending on your mood.

Practically, this is a branding fight as much as a scientific one. “Went to space” is a marketable claim, and having two competing thresholds means both companies get to make it, just with different footnotes. Expect a lot of very careful wording in press releases this month. My money is that regulators eventually just pick one number and everyone stops arguing — but not before both flights happen and both companies get their headlines.