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Comment by jamieplex | Hacker News Reader

Approximately 8' diameter (other commenters pointed out a more reasonable size) solid steel ring gear (riveted together from 4 parts). Doesn't look anything like a "separation ring", and certainly isn't large enough. Plus it is solid steel. I am kinda doubting the whole story at this point. No way it is from a rocket (too heavy, too low-tech, no ring gears in rocketry), and doubtful from any commercial aircraft (again, too low-tech and too heavy).

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For reference, here is a ring which is believed to have come from China's Long March BuNo Y77. Note the similar scale, and similar discoloration. https://spacenews.com/india-examining-crashed-space-debris-s...

I design and build all sorts of hardware relating to air-breathing (jet) propulsion, including gears. I agree with mkl. Those are not gear teeth. They have flat flanks, and no involute profile. No one makes gears with a gigantic U shaped root. They appear to me to most likely be clearance slots, to go around protruding bolt heads on a mating part. I have designed similar counterbore features myself.

What makes you claim that this part is steel? The article does not say that. Is that a fact, or are you guessing?

The appearance of rust on the surface of the article's main photo suggests steel. I guess heat from reentry may lead to that appearance on other materials?

Inconel looks just like that after exposure to heat, and is much more likely to have been used to build an aerospace vehicle than carbon steel. Most jet aircraft exhaust systems are made of Inconel and oxidize to a dull brown at 1200F or so. Like on this 737NG:

https://aviation.stackexchange.com/questions/90974/what-are-...

The exhausts that turn iridescent purple for a while due to heat are titanium, for example this 787. So I would suspect the debris is not titanium based on lack of heat marking.

https://www.reddit.com/r/aviation/comments/b77f5x/b787_its_s...

So if I were to guess what kind of metal it was solely based on coloration and suspected use case, I’d say Inconel.

But I wouldn’t make a guess at all, because it’s naive to assume that you can identify a type of metal based on a grainy freeze-frame of a cell phone video that has been re-encoded an unknown number of times before publication.

An earlier article [1] linked in this one says about 1.2m radius, so ~2.4m or ~8ft diameter. At 48 seconds in the video there's a man standing next to the propped up side and it comes up to his chest, so that seems believable (the other side is down a slope).

It seems surprising it weighs 500kg though, as it's held up by a thin iron/steel pipe/bar. If it's solid mild steel at 7850kg/m^3, with an outer radius of 1.2m and inner radius of 1.05m, and a thickness of 4cm, that would be (π*1.2^2 - π*1.05^2)*.04*7850 ≈ 333kg. If the inner radius is 1.0m and thickness is 5cm, that would be ~543kg, so maybe it is that heavy.

Edit: The tooth profile looks strange for a gear. There's a clear but potato-resolution view at 36s in the video. The teeth have flat tops with sharp corners, the sides are pretty vertical, and the gaps have very rounded bottoms.

[1] https://nation.africa/kenya/counties/makueni/mystery-object-...

Lots of rocket components look like gears. The outside skin of the rocket often had internal vertical stringers and so components need cutouts that end up looking a bit like gears

true, but I guess I have never heard of an 8' diameter rocket before...

SpaceX notwithstanding, it's pretty common for orbital rockets to "neck down" for upper stages.

You're just making stuff up? Photos show diameter is larger than human height, maybe 8'. Only indication it's "solid steel" is you said it is.

sorry, I estimated from the grainy footage. Relax, man...

No, you're deliberately being a contrarian. Dismissing the official story, witnesses, and other experts, because you feel like you're smarter.

Then you tell people to relax when they dare question you. How about you relax, man?

The rust does stand out as kind odd, not many aerospace materials rust???

How fast would you have to spin a gear ring to say, launch it on a ballistic trajectory and have it go supersonic? Maybe a factory somewhere had a _really_ catastrophic accident?

Maybe that was the "rumbling" they all heard! lol

There have been a bunch of very powerful non-nuclear explosions. Perhaps a part of an exploding ship such as in the halifax explosion or the Princess Irene?

Where is the rest of the exploded ship, in that case?

Things tend to burn up in re-entry if they're not designed for it, and this wasn't designed for it. Many metals oxidize when super heated

2.5 m (8 ft 2 in) in diameter:

https://en.m.wikipedia.org/wiki/M-V

Maybe it was something like this?

https://old.reddit.com/r/nextfuckinglevel/comments/1bmpxaq/t...

The diameter seems to match.

I thought it might be an jet-engine cowl, but I don't know enough about planes.

Cowlings are generally thin aluminum or composite materials, never steel. Cowlings are considered "fairings", generally to smooth the air-stream in and around the engine.

Do you have a theory on where the rest of the airplane went?

My assumption was that it landed sans-cowl.

But it turns out it might be from an Ariane upper stage after all.

The rivets and joints are very much aerospace style.

ok....

Could be from a concrete mixer. (Credit: rando YouTube comment.)

Bearings are single cast.

From that concrete mixer the Mythbuster's blew up? It took a while to come down...

Haha, had it been a cement mixer ring bearing, then there would have been another explanation for the reports that it fell red hot from the sky — that they were as fanciful as the reports of mysterious drones infesting New Jersey (which seem to have actually been real planes). For instance, a broken cement mixer part got dumped there and somebody made up a colorful story.

But maybe it really is Space Junk! https://www.youtube.com/watch?v=Z2dcVIEQwEE ("and now my Sally's dead...")

Proper scientific inquiry demands both an open mind and skepticism. That's why I didn't claim "it's definitely a cement mixer ring bearing" with the usual certainty of people arguing on the internet, but attempted to convey the unreliability of my source.

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