Businessweek: Spy Balloons Are the Slow and Silent Future of Surveillance

When Russ Van Der Werff heard about the Chinese surveillance balloon detected drifting over the US, potentially spying on sensitive installations, he was concerned, naturally. But as vice president for stratospheric solutions at Aerostar, a company that makes high-altitude balloons, he was also kind of psyched. For years Van Der Werff has been working to convince government and commercial customers that Aerostar’s products offer serious advantages as surveillance platforms. It isn’t always easy. “There’s always someone saying, ‘Oh, now the balloon kooks are here,’” he says. “Well, now it looks like other people think it’s a good idea, too.”

For all the furor caused by China’s ill-fated balloon, its turn in the spotlight has been something of a coming-out party for a technology that’s spent the past decade quietly polishing its abilities. “We don’t believe a stratospheric balloon is the be-all and end-all,” Van Der Werff says, “but there are times when it’s a better fit.”

Balloons have been used for military surveillance since 1794, when France deployed one during its war with Austria. Both sides used them during the American Civil War, and the US Navy used blimps to hunt Nazi submarines during World War II. But the development of airplanes and high-altitude spy planes made lighter-than-air craft seem quaint, and the US Navy retired its last airship in 1962.

In time new technology would bring balloons back around. In the late 1990s, NASA started testing superpressure or ultra long duration balloons (ULDBs) that could stay aloft in the stratosphere for months at a time. Thanks to new high-strength polymers, the craft could carry payloads weighing thousands of pounds to heights above 100,000 feet.

In 2012, Google hired Aerostar to build ULDBs for Project Loon, a fleet of dozens of stratospheric balloons that provide internet connectivity to remote areas. By pumping air into or out of a smaller balloon within the outer envelope, the Loon ULDBs could rise or sink as needed to catch winds moving in a desired direction. That meant they could go (more or less) where they wanted to and remain (more or less) over a given target area.

Aerostar’s current model, called Thunderhead, brings the same technology to reconnaissance and surveillance missions. “I can keep it in an area for weeks at a time without interruption,” says Van Der Werff. From their launchpad in South Dakota, Aerostar’s solar-powered balloons can find their way to anywhere in the world; the longest flight to date lasted 150 days.

To understand how useful performance like this can be, consider the alternatives. Low-Earth-orbit satellites whiz along at 17,500 mph about 150 miles above the ground, meaning that they can cover the whole surface of the Earth but only stay over a particular target for a matter of minutes. “The value of the intelligence you collect goes up exponentially with the loiter time,” says Arthur Holland Michel, author of the book Eyes in the Sky, about high-altitude surveillance. “If you can hang out over an adversary’s sensitive facility for days, you’re able to see temporal patterns—where people go, how they move, what sort of schedules they have.”

Geosynchronous satellites are good at maintaining a steady gaze, as they’re permanently fixed above a certain spot on the globe. The problem is that they’re 22,000 miles up—too far to get a detailed look at things.

Then there are airplanes. These can get to an area of interest quickly and remain on station over a specific spot. But their endurance is limited and you can’t fly them through hostile airspace. “The US has quite a lot of experience in flying not over a country, but sort of along its borders and looking diagonally to the territory,” Michel says. But that approach is pretty useless when it comes to a big country like China, Russia or the US.

Stratospheric balloons can overcome many of these problems. Because they fly higher than planes and are mostly made of material that’s transparent to radar, they’re much harder to spot when they slip over the borders of unfriendly countries. “The radar cross-sectional area of the balloon is very low,” says David Stupples, a professor of electronic engineering at the University of London who specializes in space-based surveillance. What Stupples is saying essentially is that from the perspective of a radar antenna, the balloon is very small and hence difficult to detect.

And balloons move more slowly, on the order of 40 to 50 mph, which is actually an advantage when it comes to avoiding detection. “Air defense radars are looking for fast-moving metal aircraft,” Stupples explains. Because the velocity of a target changes the frequency of the returned signal, radar operators can filter out slow-moving targets like rainstorms and flocks of birds by ignoring everything with a small frequency change. But doing so also filters out balloons. “Something slow is going to get lost in the clutter,” he says.

If a country suddenly decides it wants to detect high-altitude balloon systems—as the US apparently has—then it needs to look at everything with a small frequency change and try to pick out potential targets from amid a great deal of noise. That means a lot of false positives. “We don’t have any evidence that there has been a sudden increase in the number of objects in the sky,” said President Joe Biden in a speech about the balloon shoot-downs on Feb. 16. “We’re now just seeing more of them, partially because the steps we’ve taken to increase our radars—to narrow our radars.”

Because they’re unmanned, high-altitude balloons are more or less expendable. Even if one is detected and shot down, there isn’t going to be an international incident on the scale of earlier ones involving spy planes, such as when the Soviets captured U-2 pilot Gary Powers in 1960, or when the Chinese seized a US surveillance plane in 2001. “Yes, China’s balloon sparked an international incident,” Michel says, “but it does not even come close to what would have happened if China flew a human-crewed jet over the US.”

Having an aircraft that can get closer to its target than a satellite may have been especially important to China, if it was trying to sniff out America’s newest secure communications technology. This technology, called LPI/LPD, or “low probability of intercept/detection,” works by transmitting at very low power so that a signal is deliberately lost against background noise.

Ultimately, the one advantage of stratospheric balloons that could really change the game is cost. “We have to brace ourselves for the fact that this is going to become an increasingly available technology available to friends and foes alike,” says Michel, adding: “States and nonstate actors alike.”

“What you’ve done is, you’ve brought signals intelligence to the midrank countries of the world,” Stupples says.

Between that and all the recent free publicity, the odds just got a lot better that a high-altitude spy balloon could be coming your way soon. You probably won’t realize it, though.

This article originally ran in Bloomberg Businessweek on February 21, 2023.