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Comment by yabones | Hacker News Reader

Even a radar reflector would have helped a lot. ADS-B is off-limits for balloons, ultralights, hang-gliders, etc, and it seems like now that radio beacons can be manufactured very cheap & low power all those non-commercial aerial vehicles should be equipped.

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For a 2.5 lb ground weight balloon, a radar reflector is likely still too heavy. The lightest weight marine radar reflector [1] I could find is about half a pound.

[1] https://www.westmarine.com/plastimo-tubular-radar-reflector-...

Marine applications care a lot about durability and pretty much zero about weight, so I wouldn’t expect that to be representative of how light they can be. You could make a radar reflector from a bit of cardboard and aluminum foil.

you can make one out of cardboard and aluminum foil (better yet, aluminized mylar (space blanket) on foam) on the order of a few oz. https://www.instructables.com/Lightweight-Radar-Reflector/

A radar reflector such as that, or this (https://overlookhorizon.com/product/radar-reflector/, which is ~300g) has roughly the same RCS as a small (piper cherokee) to medium (gulfstream) sized aircraft.

That being said, detection isn't everything; primary radar cannot make accurate altitude measurements, only bearing and range. While that's enough to route traffic around, it could be also mistaken for a false return.

Any idea how much that homemade one weighs? 300g for the commercial one is more than half a pound, similar to the one I linked but a different shape.

Off limits? What's the reason? Why not ADS-B everything in the air and let the computers sort it out?

It's not off-limits. But, it's not required (for most balloons, ULs, etc). And due to cost and/or weight, people don't always use it when it's not mandatory.

The comments I was reading at ArsTechnica suggested that adding transponders was off-limits to balloons. The argument was that balloon operators wanted to add transponders but that it was resisted by FAA worrying about there being too many non-plane transponders for pilots/ATC to keep track of.

I obviously don't know which is right, but it does show that there is definitely confusion out there about the issue.

It's not off limits in the regulatory sense. Balloons are generally exempted due to their size and power constraints. Per the submission, the balloon weighs 2.4 lbs at launch. That doesn't give them much room to add a transponder and battery for ADS-B while staying within the target weight limit.

47 CFR 87.107 requires that radios transmitters in aircraft broadcast an identification number, and the allowed forms of identification aren't permissive enough for non-registered aircraft.

ADS-B out is still relatively new (especially in aviation terms) so I expect we'll see this continue to evolve.

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