March 25, 2023

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The Chinese post a lot about stratospheric balloons

On February 22, the US Department of Defense suddenly released a photo of a Chinese stratospheric balloon taken from a U-2 plane. Before you could say “balloon” again, he was already standing up Wikipedia: with high precision. It was 18 days after the damned spy case was blown out of the sky by a Sidewinder missile and his remains were recovered from the sea.

The U-2 pilot took his self-portrait while flying between the sun and the balloon until his plane’s shadow, 60 feet (19.2 m) high from head to tail, fell completely on the balloon. Suddenly you can tell that it was 150 feet in diameter, not 200 feet as previously claimed, and that the payload suspended underneath was probably the size of an Embraer Regional Jet (100 feet) but certainly not its weight (25 tons). experts He estimated that the payload might be less than 900 kg (2,000 lb).

The solar panels were held well perpendicular to the sun and that was no accident. They were showing off the sun Put, perhaps with a pair of recognizable thin cables. Or with the four fans recommended by the experts Aviation Week It is believed to be seen in four white dots, left and right of the white satellite dish that provides communication between the balloon and the satellites. American speakers already mentioned beginning of February That the balloon had propellers and a rudder, which must have been derived from better photos of U-2 than those we saw. The presence of the rudder has not been confirmed.

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The balloon itself could, of course, be driven by the four propellers, but it didn’t seem like much could be expected from that. Anyway, the balloon wasn’t moving relative to the sky when the picture was taken: a loose cable hanging straight down.

Navy men Retrieving the balloon shot from the sea.
Ministry of Defense photo via AFP

Somewhat heavy plastic

Something strange is happening with solar panels. on registration From a Sidewinder effect captured with a telephoto lens on February 4, we see them fall from the balloon. However, it appears that the Marines who retrieved the balloon from the sea later that day also towed a broken solar panel onto their boat, including the pier on which it was mounted. Wikipedia has a picture of it.

The same photo shows that the skin (“encapsulation”) of the balloon is made up of a fairly heavy plastic, certainly not the light, clear, low-pressure polyethylene used in the “normal” Zero pressure balloons Uses. It is 23 micrometers thick and has a mass of about 22 grams per square metre2 The quality of the chips used in the sandwich bags. The opaque white skin of the Chinese balloon weighs much more, perhaps 75 gsm2. Considering also the shape of the balloon, which resembles a pumpkin, including its typical parts (‘gores’), it is certainly modern. Super pressure balloon used to be. Unlike zero-pressure balloons, super-pressure balloons are subjected to excessive pressure relative to the environment. They are closed balloons that, thanks to their skin taut with helium, can stay in the air for months and basically maintain the same altitude. Zero pressure balloons respond to the rhythm of day and night solar heat.

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The Chinese airship floated 18 to 20 km in five or six days from northwest to southeast over the United States at an average speed of less than 30 km/h. Whether she actually followed the jet stream, as has been said, is questionable. the A jet stream turns From day to day and at its location around the tropopause (9 to 14 km high) it has wind speeds much higher than 160 km/h. The balloon may have flown away above And the next jet stream. (So ​​it’s a mystery from which the Americans deduced that balloon In reality He was on his way to Guam.)

The main question is whether the balloon allows itself to be carried away by the wind or can determine its trajectory from time to time. The Americans said that sometimes he could completely slow down on one land object interesting for eavesdropping and espionage. hanging outThis is called. The evidence is not presented and the question is whether the humble propellers succeeded in driving the giant to the wind.

A balloon within a balloon

single now common technique It is the use, after airships, of a “balloon net”, a balloon inside a balloon into which an electric compressor can pump air as ballast. With a sophisticated system of “pump and vent”, the stratosphere air layer can be found where the wind is blowing in the right direction based on information gathered by real weather balloons. It is also possible to keep the balloon in one place for the task of observing while ascending and descending (“Save the station‘). But the alleged spy balloon’s vertical movements were not reported.

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The knowledge and mastery of the Chinese in this technology is evidenced by the huge amount of posts about stratospheric balloons that can be found on Google Scholar. China annually releases twenty balloons from the stratosphere with sizes of up to 600,000 square meters3. In addition to the aforementioned “Station Keeping” and analysis of the stratospheric wind field, the publications describe the balloon’s thermal management, its sensitivity to ozone and UV radiation, the use of solar panels, potential ice buildup, and much more.

What do the Chinese want with balloons? Earth observation, their literature says. Stratospheric research, astronomy, communications and observation. But there will be also considered To provide the stratosphere with radar installations that, in conjunction with ground-based installations, can penetrate the stealth protection of aircraft such as the US B-2. Perhaps the spy balloon was a pilot balloon.