There's a high altitude balloon in the news recently. It seems to have come from the Pacific, passed over Canada and is now over the US. I don't have any official tracking data but notional trajectories are shown in screenshots below. The CNN graphic is labeled conservatively:

Potential trajectory: suspected spy balloon

Question: Balloons certainly have a place in the history of warfare and intelligence gathering, but these days are there really noted, plausible modern instances of spy balloonery? And are investigative balloons (spy or otherwise) of this size really maneuverable?

screenshots from CNN's February 4, 2023 See path the suspected spy balloon may have taken showing a "potential trajectory" of a "suspected spy balloon" and some high resolution photos showing the balloon and an array of panels that seem likely to be for solar power.

screenshot from CNN's February 4, 2023 "See path the suspected spy balloon may have taken" https://www.youtube.com/watch?v=vP7JlAG5o6U screenshot from CNN's February 4, 2023 "See path the suspected spy balloon may have taken" https://www.youtube.com/watch?v=vP7JlAG5o6U

screenshot from CNN's February 4, 2023 "See path the suspected spy balloon may have taken" https://www.youtube.com/watch?v=vP7JlAG5o6U screenshot from CNN's February 4, 2023 "See path the suspected spy balloon may have taken" https://www.youtube.com/watch?v=vP7JlAG5o6U

A different hypothetical map from Sky News's February 4, 2023 Spy balloon: China wanted 'to be noticed' says Professor Michael Clarke showing a trajectory for an object at 40,000 feet ending up in Montana

screenshot from Sky News' "Spy balloon: China wanted 'to be noticed' says Professor Michael Clarke" https://youtu.be/EaxiA7529vE

Screenshot from the April 30, 2020 NASA Wallops video B-Line to Space: The Scientific Balloon Story showing the payload and its solar panels. I don't know which balloon mission this is, but we can see images of another similar one in Space SE's What cosmic ray sensor is attached to this Balloon?

From the video:

NASA’s Wallops Flight Facility in Virginia manages the agency’s Scientific Balloon Program with 10 to 15 flights each year from launch sites worldwide. Northrop Grumman, which operates NASA’s Columbia Scientific Balloon Facility (CSBF) in Texas, provides mission planning, engineering services and field operations for the program. The CSBF team has launched more than 1,700 scientific balloons in the over 35 years of operation.

screenshot from NASA Wallops' "B-Line to Space: The Scientific Balloon Story" https://www.youtube.com/watch?v=sPQ-tMoAHkY


3 Answers 3


To what extent is modern "maneuverable spy balloonery" really a thing?

To the extent that it helps to sell news and stoke irrational fear of secret Chinese technology.

Much of what a "spy balloon" can accomplish can be done better with a satellite. But there is maybe one thing for which a balloon is the better option: Signal intelligence, meaning the listening in on radio signals. This could be anything from intercepting radio communications to provoking air defenses in order to learn what frequencies and tactics are used.

The "navigating" part is rather limited. Other than changing altitude in order to catch a different wind direction there is nothing a balloon can do for flying into a certain direction. Altitude changes happen automatically with the heating of the balloon from solar radiation and cooling again during the night. In order to deliberately change altitude, ballast must be carried along in order to be dropped when the balloon should climb.

To me it looks as if the balloon flew into US airspace by chance and not by active control.

EDIT (Feb. 18, 2023): Aviation Week cites an ex-Google Loon engineer with the information that in the most recent balloons altitude is controlled by a ballonet, an internal gas bag that can be in- or deflated to change the pressure (and thus the buoyancy) of the balloon:

The most advanced ultra-long-endurance, high-altitude balloons seldom use propellers for directional control. Instead, such aircraft pump regular air into an internal ballonet envelope to descend or release the air to climb, Bowen says. Altitude adjustments are made to find wind currents moving in other directions. The system provides a limited capability for directional control.

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    $\begingroup$ @JohnPankowicz In principle yes, but given the massive drag of a large balloon, this would be rather inefficient and only allow only for small distances of powered travel. $\endgroup$ Commented Feb 4, 2023 at 16:38
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    $\begingroup$ In addition to signal intelligence, being 10x closer than the lowest-dipping spy satellites and moving 50x more slowly and being in the atmosphere also allows one to pick up other information as well. A sensitive single crystal germanium detector can pick up trace signatures of radioisotopes (if there's some unshielded activity or transportation) and one can "sniff" the air for particulates. Yes this sounds a bit like a Michael Crichton novel I know, but with spook stuff we (us non spooks) really never know for sure. $\endgroup$
    – uhoh
    Commented Feb 5, 2023 at 11:29
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    $\begingroup$ It seems that a team of researchers from Loon, an ex "Google X" project, used deep learning to predict wind currents in the stratosphere to move balloons around by changing altitude (See also here, "Sailing the stratosphere" paragraph). It sounds plausible that the Chinese military is able to do something similar. $\endgroup$
    – GBathie
    Commented Feb 5, 2023 at 16:00
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    $\begingroup$ @uhoh And this is how such model outputs can be used to optimize balloon trajectories ready.noaa.gov/READY_balloon.php $\endgroup$ Commented Feb 5, 2023 at 16:57
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    $\begingroup$ @PeterKämpf Just an FYI, I have significant experience with balloons that altitude station-keep for one full sun cycle. The balloon has a small amount of ballast and a controllable gas vent. We vent gas as solar radiation heats the envelope to maintain a fixed GPS altitude. At night, we dump ballast as the lack of solar radiation cools the envelope. The certification on our balloons only allowed us to carry enough ballast weight for one cycle, but by planning launch times we could get 30-ish hours at an altitude. That's about 900 linear miles of flight at FL 1200 in the US latitudes. $\endgroup$
    – Max R
    Commented Feb 9, 2023 at 5:38

to what extent is modern maneuverable spy balloonery really a thing?

While it is certainly debatable whether or not recent balloons in the news were maneuverable or not, technology does exist to attempt it.

Goal: drift over Montana from around 10,000 km away

Montana is around 1000 km × 400 km. Prevailing winds would favor a broad side approach.

Error margin: +/- 500 km. $arc$ $sine$ (500/10000) = +/- 3 degrees.

check the weather before you go flying

Weather forecasting has grown in leaps and bounds in recent years, and world wide wind field maps are available.

moving with the air mass.

An all-time Aviation Stack Exchange favorite. Use buoyancy for lift, ride the wind. This is exactly what this airship did during its 1929 round the world flight along a similar trans-Pacific route. Knowing the weather helps.


A 10,000 km trip at 100 km/hr will take 100 hours. Gently moving in the airmass at 5 km/hour perpendicular to the ground speed would allow 500 km in either direction of manuverability. Montana or bust!

is it really a thing?

It is technologically possible, but one can only ask that the science of this site not be dragged down into the political folly of the day. Returning to 1929 may not be the best course, returning to 1914, worse still.

  • $\begingroup$ While the " +/- 3 degree" would make sense in the context of a ballistic trajectory, in fluid dynamics I don't think anything short of a simulation (some combination of Monde Carlo for the large-scale turbulence at boundaries and best available atmospheric model for the general wind directions vs altitude can address this. I agree that this site is Aviation SE and politics doesn't belong, thankfully I don't see it anywhere on this page. Anyway +1 and thanks! $\endgroup$
    – uhoh
    Commented Feb 20, 2023 at 23:04

For intelligence gathering a balloon would have a couple of advantages and several disadvantages. The disadvantages first. Limited maneuverability, most balloons can only float on the wind. You could add the ability to change altitude hoping to find winds blowing the direction you want to go. This leads to the second issue weight. To keep the size reasonable the mass of the payload must be limited. limited mass means things like large high resolution cameras are not feasible. this would include large motor for propulsion and equipment to change altitudes. Now for the advantages. They are much cheaper than satellites, high performance spy planes, or even drones. They are harder to detect. Ours defensive radar networks were simply not looking for them. Our radars were optimized to look for aircraft and missiles, not balloons. I assume that is being changed. Finally because we did not initially detect them we did not take any measures to "hide" ay activities. When I was in the USAF we knew when Soviet satellites were passing over head and made sure no aircraft were transmitting radar, radio, or ECM, and that all exterior panels were closed. We would sometimes even suspend work during the time they were overhead.

  • $\begingroup$ Wow, closing the exterior panels? So the satellite couldn't see inside? $\endgroup$ Commented Feb 20, 2023 at 18:12
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    $\begingroup$ Correct, I never said what the military did made sense. The only thing I could see that they might learn is that a given plane was undergoing some type of repair. $\endgroup$
    – Jim
    Commented Feb 20, 2023 at 19:48
  • $\begingroup$ @Jim or that it was or was not there or somewhere else at the time? $\endgroup$
    – uhoh
    Commented Sep 17, 2023 at 23:54
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    $\begingroup$ @uhoh Most air force bases were relatively small. You could typically view the flight line from roads just off base. It was not unusually to have people parks by fences to observe aircraft taking off and landing. Most simply wanted to see the planes. We had little doubt others were sending reports to the USSR. We never did, but some units would occasionally change the markings and even tail numbers to try and confuse them. The number of SR-71 and U2 aircraft were often incorrectly reported because of this. $\endgroup$
    – Jim
    Commented Sep 18, 2023 at 18:54
  • $\begingroup$ @Jim yikes! It seems that times were a little different then :-) $\endgroup$
    – uhoh
    Commented Sep 18, 2023 at 21:27

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