The Amazing Technology Of Pico Balloons


If there was anything good about three or four days of obsessing over unidentified balloons last weekend, it’s that we all learned about a fascinating niche of amateur radio that marries tiny radio transmitters to featherweight hydrogen balloons capable of sailing around the globe—sometimes many times.

In this hour-long video—really a published Zoom conference—radio amateur Brian Basura explains the fascinating hobby of pico ballooning, a unique marriage of physics, meteorology, electronics and radio communication. The sport came to light when an Illinois-based pico club revealed that one of its balloons was in the same area that an F-22 shot down an unidentified flying object on Feb. 11. The Northern Illinois Bottlecap Balloon Brigade isn’t claiming its pico was splashed by the Raptors, but the coincidence suggests that it could have been.

So what is a pico balloon? (That’s pronounced pee-coh, not pye-coh, and refers to the size of the thing: small.) As Basura explains, a pico balloon is an ultra-lightweight plastic balloon suspending a tiny, lightweight amateur radio transmitter. The envelope is filled with a breath of hydrogen, which is used in place of helium because it leaks less. The balloon has a free lift capacity of about 15 or 16 grams—a little over half an ounce. When launched, it appears to be barely inflated but expands to a larger sphere when it reaches planned stasis altitude of about 40,000 feet. Basura explains that the difference between too little inflation and too much is barely a squirt of hydrogen. It’s determined by careful weighing on a gram scale.

The electronics package, which dangles under the balloon on a light filament, is called the tracker. It consists of a transmitter, a GPS chip and a small computer with programing instructions. Total weight? Just under a half ounce, including a light solar array to power the system. The device trails a long dipole antenna made of 0.005-inch fine wire.

Pico balloons communicate through various protocols, but two popular ones are called APRS and WSPR. The Automatic Packet Reporting System is a kind of single-frequency network system that allows any ham to check on local activities in that region. There are numerous APRS nets in the U.S. and many countries have some version of it. In the U.S., it operates on 144.39 MHz in the 2-meter band, but on different frequencies elsewhere in the world so the transmitters have to be smart enough to adapt. The balloon trackers transmit continuously when the sun is up to energize their solar arrays and report position, altitude and other parameters that the bandwidth allows. APRS is integrated with the internet.

So is WSPR or Weak Signal Propagation Reporting, pronounced whisper. It’s a software protocol designed for sniffing out very low-powered one-way signals. It has miniscule bandwidth and reports station power and position by grid reference. With WSPR, it takes 110 seconds to transmit 50 characters at 1.46 baud. That might be so 1970s, but it gets the job done with the low-powered transmitters pico balloons have. Some countries don’t allow transmissions from balloons, so picos following the rules have to be emissions geo-fenced. And by the way, pico balloons, by dint of their light weight, are exempt from 14 CFR 101 that regulates balloons. Picos typically transmit at about 10 milliwatts—1/50th the power of a Christmas tree light. Still, explains Basura, transmit distances of up to 5000 miles have been achieved and 1200 to 2000 miles are routine.

Success with a pico balloon is anything but. Sometimes they never reach altitude or don’t survive the first night. They can develop leaks and sink out of the stratosphere or just disappear without a trace. On the other hand, when this video was recorded last April, Basura had been tracking one of his balloons for 51 days and 4.5 global circumnavigations. Not bad. This site tracks known pico launches, but doesn’t claim to be complete.

Pilots naturally wonder if pico balloons represent a threat to aircraft. Politics being what they are, the Pentagon thought so and ordered three of what may or may not have been pico or research balloons shot down. The first question to ask, however, is are standard NOAA radiosondes a threat because they’re 30 times heavier and far more numerous? In the conterminous U.S. alone, some 138 are launched daily from 69 sites. The little Styrofoam box containing the hardware weighs about 17 ounces, max. It has a parachute and a return address.

No crashes have been caused by aircraft/weather balloon collisions in the U.S., but one was recorded in Russia in 1970 when an AN-24 airliner collided with a radiosonde just after takeoff. There were no survivors. The size of the radiosonde doesn’t appear in accident reports.

For amazing as pico technology is, just as astonishing is that U.S. radar can find such a thing and an AIM-9X can target it and bring it down.

If, indeed, that actually happened.

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  1. Can radar pick up a pico balloon? No if it is an electrically non-conductive material. Add aluminized plastic and a trailing antenna and it becomes the same question but favoring a positive response. The problem is that if the “aperture” is opened up enough to capture those returns a lot of other stuff appears, including some atmospheric phenomena. If the radar is looking for fast aircraft perhaps one would not normally want to see small balloons.

    Did you notice that one of the missiles missed? This indicates that the radar on the missile was not as “good” as that in the aircraft. Exactly what one would think. Now the Chinese, and the rest of the world, knows more about our air defense capabilities. Or maybe the AF is cagey enough to fire an old dud just to screw them up. Spy vs. spy vs. spy.

    • Radars can pick up balloons just fine, so long as they have sufficient sensitivity and so long as the tracking algorithms are tuned recognize such slow movers as something to track. (The material of the balloon envelope doesn’t have nearly as much to do with it as you seem to believe.). But, none of that really matters very much with the missiles in this case, since they have IR seeker heads (a.k.a. “heat seekers”) rather than RF (“radar”) seekers.

  2. Great article, Paul. As far as radar tracking the actual physical balloon-payload package, I suspect the radio transmissions would be what gets tracked.

    Waiting for the price point of ADS-B units to reflect the price point of the referenced disposable launch-and-forget GPS gear before I commit… LOL

  3. An unfortunate last name, Basura = trash en espanol. I had to go back and look because I couldn’t figure out why you’d be goofing in the article that was otherwise serious (and very informative)!

  4. That’s fascinating stuff you’ve pulled together on pico ballooning and weather balloon trash accumulations in the middle to upper atmosphere more generally. (Like the famed Sargasso Sea and mid-Pacific junk gyres, respectively.) I’d like to know more about the trajectories that get balloons to the stratosphere and which they then follow. Where do hobbyists in Illinois launch from, and what configuration of those big ole airmasses does it take to wind them up to the polar latitudes where things stabilize and they can circumnavigate repeatedly?

    • In the video, Basura covers HYSPLIT, the super-computer driven wind model that pico ballooners use to project trajectory. Anyone has access to it, perhaps including the Chinese. This raises an interesting question. The Washington Post reported that the Chinese balloon may have taken an unintended course, flying further north than planned.

      Or did the Chinese know that was coming and launched from Hainan to intentionally ride the wave? We may never know.

      • A good question to be sure. But it would be a mistake to assume that the first balloon shot down was completely at the whims of the winds like those (admittedly still fascinating) Pico balloons. Apples and oranges.

  5. With regards to APRS – a number of pilots have been using APRS transmitters as a ‘free’ tracking device in lieu of subscription-based satellite trackers such as SPOT or InReach. They’re not quite an equal substitute. But for those with the technical knowledge and desire to tinker it’s a very low-cost way to allow the non-flying spouse to keep track of your whereabouts.

  6. Now that we’ve got airline pilots looking UP while cruising along, we’ll doubtless get a huge upsurge in sightings. Someone needs to come up with a way to monetize this.

  7. One of the benefits of being consumed by this particular interest, at least for a few days, is the opportunity to learn about the technology and science behind it. From the physics of buoyancy and atmospheric pressure to the intricacies of radio transmission and reception, there’s a lot to study and discover in affordable amateur radio ballooning. Now in my retirement days, I find all this rejuvenating. Thank you, “Bien Hoa” Paul.👍