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Why Chinese Spy Balloon’s Flight Path Was Not An Accident – And What It May Have Been Doing

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China has insisted that the balloon shot down by a U.S. F-22 Raptor off South Carolina was nothing but a weather balloon with "limited self-steering capability" which "deviated far from its planned course." At a press briefing Monday, U.S. General Glen VanHerck said the military immediately identified it as a spy balloon and that its flight path, which took it over sensitive military sites, was no accident. How can we know who is telling the truth?

“We had a good indication that it was a surveillance balloon from the beginning,” VanHerck, commander of North American Aerospace Defense Command, told reporters, adding, "I do think their path was purposely built.”

The stratosphere is so called because it is stratified, divided into narrow layers, each with its own wind pattern. These air currents can move at very high speed: jet streams can reach more than 275 mph and it would seem that a balloon would have little control over where it went. Even at much lower altitude, wind has always been a major problem for airships. German Zeppelins attempting to bomb Britain in WW1 struggled even to reach their targets. One raid in 1917 ran into a gale and only seven of the eleven airships made it back.

Things have changed with a greater understanding of the stratosphere. Atmospheric modeling and smart algorithms allow a balloon to change altitude to catch wind in any desired direction, and even to circle around a given point on the ground. Google GOOG parent Alphabet’s Project Loon used steerable stratospheric balloons to provide internet access to 100,000 people in Puerto Rico after Hurricane Maria in 2017 using this technique.

“The balloons dance on the winds in small loops to remain where needed,” according to a blog post by project lead Astro Teller.

The U.S. military has been trialing similar balloons for years. By 2018 the algorithms allowed a balloon to stay within in a 30 mile circle for 24 hours at a time, and it has been steadily improving since then. DARPA developed a new type of laser sensor to detect wind speed and direction remotely in its Adaptable Lighter-Than-Air program, which is likely to be a game-changer in terms of rapidly locating favorable winds.

China has also been working on steerable stratospheric balloons. In particular, the Academy of Opto-Electronics in Beijing, part of the Chinese Academy of Sciences in Beijing, has a Lighter Than Air Vehicle Center founded in 2005. This is working on high-altitude balloon systems and “Modern airship including stratospheric airship.”

Few of the Center’s papers have been released publicly, although there are studies on solar power panels for high-altitude balloons (like those on the one which was shot down), control systems, preventing icing, and strengthening the balloon’s plastic envelope. A 2011 study, looked at how stratospheric balloons could keep station over a point on the ground.

While U.S. stratospheric systems rely on altitude change, the Chinese may also provide theirs with auxiliary propellers, making them genuine airships – some recent scientific papers mention Chinese work on this approach. While it is hard to see how this would work, National Security Council spokesman John Kirby told reporters that the Chinese balloon did have propellers that may have improved its ability to steer a course.

In 2017, the South China Morning Post reported that researchers from the Beijing Lighter Than Air Vehicle Center had launched two drones from a stratospheric balloon. An electromagnetic launcher fired the "bat-sized" drones at over 60 mph, the first at over 80,000 feet, the other from 30,000 feet. The drones give the balloon a close look capability to check out objects below; the article mentions search and rescue but there are obvious military applications.

“The goal of our research is to launch hundreds of these drones in one shot, like letting loose a bee or ant colony,” the lead researcher, Professor Yang, told the SCMP.

However, Yang did not published any open-source papers on this work and no further details are available. Again, the U.S. military has similar plans, including a project to rain down large numbers of tiny electronic sensors behind enemy lines from stratospheric balloons.

U.S. sources have been keen to downplay any suggestion that the Chinese could have gained any intelligence they had not already gleaned from satellite observation.

“We did not assess that it presented a significant collection hazard beyond what already exists in actionable technical means from the Chinese,” VanHerck told the press conference.

However, he also noted that “we took maximum precaution to prevent any intel collection,” which would seem unnecessary unless the balloon might have sensing capabilities above and beyond regular spy satellite transits.

A major operation is now under way to retrieve debris from the downed balloon and find out as much as possible about its capabilities. This may tell us whether it might have been carrying drones or other dropped sensors and relying information from them back to China.

Exactly what the Chinese balloon was doing and what capabilities it possessed remain open questions. However, at this point the Chinese assertion that it was just a civilian research craft which was blown off course rings pretty hollow.

CORRECTION 21 Feb: An earlier version of this article stated that the 2011 paper on station keeping "was a collaboration between Beihang University and MIT" — this is not correct, but was caused by ResearchGate confusing individuals with similar names. We wish to make it clear MIT was not involved in this research, and that all the researchers were from Beijing University of Aeronautics and Astronautics.

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