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On flightradar24 I saw a plane flying as high as 59,700 ft at a bit more than 40 kn (pretty slow to fly at such altitude) over north-east Missouri at 1:18 am CST. Fr24 didn't tell what plane that was and I guess it's an experimental plane or drone. It could also have been an espionage balloon, but it was portrayed as a winged aircraft. Does anyone know or have an idea what that could be?

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    $\begingroup$ Any conventional aircraft capable of flying as slow as 40kn is not going to be capable of reaching 60,000ft. Probably, you saw a weather balloon, assuming that it wasn't just an artifact of FR24's systems. There are many questions here about such artifacts. $\endgroup$ Jan 29, 2022 at 9:03
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    $\begingroup$ @CatchAsCatchCan But it didn't have to be a conventional one. I once saw a U2 on fr24. The experimental NASA Pathfinder and Helios can/could reportedly reach higher altitudes at slower speeds. en.wikipedia.org/wiki/NASA_Pathfinder Weather balloons are usually portrayed as balloons on fr24, but this one was portrayed as an airplane so if anything it might be an espionage balloon I guess. $\endgroup$ Jan 29, 2022 at 9:52
  • $\begingroup$ @CatchAsCatchCan It couldn't have been an artifact, for it had a route (it flew from the north) showing where it launched from and the aircraft's values changed with time. $\endgroup$ Jan 29, 2022 at 9:54
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    $\begingroup$ A screenshot and link to FR24 would be great. $\endgroup$
    – Bianfable
    Jan 29, 2022 at 11:26
  • $\begingroup$ @Bianfable I'm using fr on another medium where there aren't the cookies to register into this account so I wouldn't have the SE account on the other medium. But anyone can trace it back since fr allows for that. Just set the filter to planes above 59,000 ft for instance and enter the time (01/29 1:18 CST which is 7:18 GMT). $\endgroup$ Jan 29, 2022 at 14:29

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A high-altitude balloon, identifier HBAL577, registration N257TH.

Screenshot showing track of a high-altitude balloon launched from Sioux Falls on January 28 2022 and traveling southeastbound

ADS-B Exchange track
FR24 track
FR24 replay

(FR24 may be storing "altitude" as an unsigned 16-bit integer; notice how the altitude seems to wrap around back to zero in the vicinity of 65,500 feet.)

More information available at this FR24 blog post. Notice how they say "Because the balloons do not necessarily transmit their type, some may appear as aircraft icons until we are able to update our database."

The FAA's N-number Inquiry site shows that "N257TH" has been reserved by Raven Aerostar, who formerly collaborated with Google on Project Loon (although it is not actually shown as assigned to any aircraft, which is why FR24 did not know to show it with a balloon icon). This article from The Drive notes that Project Loon was shut down in January 2021 but Raven Aerostar continues to develop its balloon technology for military applications.

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    $\begingroup$ You know you're flying high when your flight causes integer overflow. $\endgroup$
    – void_ptr
    Jan 30, 2022 at 4:00
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    $\begingroup$ They still use 16 bit ints in 2022? $\endgroup$ Jan 30, 2022 at 8:07
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    $\begingroup$ @void_ptr kudos for choosing that username for posting this comment $\endgroup$
    – DeepSpace
    Jan 30, 2022 at 9:26
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    $\begingroup$ @KevinKostlan, smaller ints are used more often in practice than you'd think. It makes sense for fr24: there are about 10,000 planes in the sky at any given moment, and fr24 logs every 5-ish seconds. If speed, direction, and altitude all are stored in 16 bits instead of 64-bit doubles, that saves about 1 GB of data storage per day, which adds up when you've got a few years of data, plus backups, indexes, bandwidth considerations, etc. $\endgroup$
    – Jason
    Jan 31, 2022 at 5:21
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    $\begingroup$ @Jason I'd expect any long term data storage to losslessly compress data - greatly reducing data needs. Using 16, 32 or 64 bit raw data makes little difference then in terms of compressed data size. $\endgroup$ Jan 31, 2022 at 6:33

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