Days after Richard Branson flew to space and back, Jeff Bezos is preparing for his turn.
The dueling space billionaires share a lifelong fascination with space travel and aspire to sell customers a few glorious minutes of weightlessness, high above Earth. But on one very basic point they disagree: Where does space begin?
Bezos’s Blue Origin is designed to take passengers to a higher altitude than Branson’s Virgin Galactic. Just before Branson’s flight earlier this month, Blue Origin tweeted that it flies higher than Virgin Galactic, “so none of our astronauts have an asterisk next to their name”—suggesting that Virgin Galactic passengers don’t become “real” astronauts.
Isn’t this designation—the edge of space—something two men and, really, all other residents of planet Earth should be able to agree on? Remarkably, no, and the division doesn’t originate with Bezos and Branson.
There is no universal standard, let alone a legal definition, for the region high above the ground, where Earth’s atmosphere thins and gives way to space. NASA, the U.S. military, and the Federal Aviation Administration, which approves licenses for space launches, put the boundary at 50 miles (80 kilometers) above the ground. Virgin Galactic just passes that line. The World Air Sports Federation, or the Fédération Aéronautique Internationale (FAI), which maintains standards for aeronautical activities, puts the line at 62 miles (100 kilometers). Blue Origin claims this is where it really counts. This second altitude, known as the Kármán line, is the most-well-known definition for the edge of space—but not an inarguable fact of nature.
Until now, this definition was the subject of obscure and somewhat geeky debate. But for anyone who buys a very expensive journey with Bezos or Branson, it might matter quite a bit. Branson and Bezos built their companies in part to fulfill their personal dreams, but they’re also competing for customers. Just before Branson’s flight, Blue Origin posted a little chart listing the differences between its offering and Virgin Galactic’s, including the size of the windows, the availability of an escape system, and the peak altitude of the journey. The chart was effectively an ad, and it put a very fine point on one key perk of space tourism: bragging rights. What’s the point of paying an extraordinary amount of money to go to space if your other rich friend can deny that you went? In this context, the edge of space is not a scientific fact, but a selling point. (Elon Musk, the other space billionaire, has remained above this particular fray because SpaceX flies passengers all the way into orbit to loop around Earth.)
The discussion about the edge of space is decades old. But this level of ambiguity is unusual: “Over the past 60 years of space travel, most things have not hung out in this liminal region for long periods of time,” Jonathan McDowell, an astronomer at the Harvard-Smithsonian Center for Astrophysics, told me. No one really needed a clear definition. This region was never a premier destination—just a fuzzy region to pass through on the way to orbit.
The Kármán line—the destination of Bezos and his fellow passengers—is named for the Hungarian American aerodynamicist who is said to have come up with the boundary in the late 1950s. Despite the prominence of the definition, the lore around it is perhaps overbuilt, according to Thomas Gangale, a space lawyer who wrote a comprehensive report on the topic. Theodore von Kármán’s calculations actually came out to about 52 miles (84 kilometers), and he wasn’t trying to delineate the boundary for space travel, but rather determine the altitude at which aircraft struggled to fly. Somewhere along the way, people started rounding up, from 80 kilometers to 100 kilometers. By the 1960s, the FAI had set the bar at 100 kilometers, or 62 miles. Perhaps it stuck because it was a nice round number—in the metric system—McDowell says, or because scientists at the time thought that Earth’s upper atmosphere fluctuates more than it really does. If the atmosphere wasn’t going to stay put, what was the harm in adding a few kilometers?
McDowell, who is well known in the space community for his research on this topic, has argued that the Kármán line is not based in scientific reasoning. According to his analyses of historical data, Virgin Galactic is right—space begins about 50 miles (80 kilometers) from the ground.
Neither Blue Origin nor Virgin Galactic can put people into orbit around Earth, but the nature of orbits provides a useful way to understand this problem. Imagine you’re a satellite traveling in an elongated orbit around Earth, and your closest approach brings you less than 50 or so miles from the ground. At that point, the atmosphere will assert its presence and drag you down into a fiery plunge. But if your approach takes you above 50 miles, “you will likely survive ’til the next orbit and go around,” McDowell said. At this boundary—which I’m calling the McDowell line—gravitational forces become more important than atmospheric ones.
In 2018, the FAI said it would consider changing its standard for the edge of space based on McDowell’s work, but McDowell says the organization hasn’t stayed in touch. And governments have little incentive to draw a clear-cut line, which would have all manner of legal and political implications. If the idea of a planet’s inhabitants squabbling over where their home ends and everything else begins seems a little funny, well, that’s just the way we are; drawing bright lines helps us make sense of the boundless universe we inhabit. In this case, Bezos and Branson both have fortunes staked on whether potential customers accept one definition or the other, but they’re both still blasting people to heights where they can see the same sight: the sparkling curvature of the Earth against the inky darkness. With that view, no one will be looking for a floating sign that reads you are now entering the vacuum of space.