For one thing, the Apollo shield started in the very thin upper atmosphere, and they came in at an angle that meant they bled off as much speed/energy as possible in that thin upper atmosphere before going into the thicker atmosphere.
I don't know that that makes a huge difference to the physics involved, though it certainly may have.
But in that case we're talking about human survivability, and a chunk of solid iron is going to survive a whole lot longer than humans or delicate instrumentation. It might look a little worse for the wear, but it's much more likely to be recognizable after the whole experience than anything designed for people.
The layer of air you're talking about at the front of the spacecraft was what heated up the heat shield. Instead of causing heating via friction, the heat was the result of compressing the air.
But after initial heating, the air cushion begins heating itself up instead of the object, reducing the amount of heat the object receives.
The amount of compression you're talking about would be orders of magnitude higher for something starting at 40 km/s in the thick lower atmosphere.
But it would also tail off as the bore cap heated, reducing stresses on it as it went higher.
Also, the Apollo heat shield did heat up to 5000F or 2800C but was designed to be ablative, so that the hot layers burned off and flew off to the sides leaving new material to be heated up and burned off.
True, but on the other hand the a Apollo heat shield wasn't designed to convect heat to other parts of itself. And again, it had a much harder job (keep the Apollo command module at human-survivable temperatures) than the bore cap (not reach the boiling point of iron).
This concrete and metal plug wouldn't have been designed the same way. Concrete apparently melts at 1200C, and steel is approximately the same, so it's very likely some of it melted or vaporized, the question is how much.
All the stuff I read only mentioned the iron, but keep in mind that it has to not only reach the melting point but also undergo phase change, which requires a lot more energy.
I don't know where you're getting the maximum of 22MJ of energy.
11 kJ per m² per second was the peak amount of energy that the Apollo heat shield encountered. Double that for the approximately two seconds it would've been in atmosphere, and it's a pretty handy approximation since the bore cap was about a meter itself.
The whole point of Apollo not going directly into the atmosphere was to take as long as possible to slow down, going through the thinnest part of the atmosphere for as long as possible. [...] One reasonable first approximation of the energy would be to integrate the entire energy per second / power for Apollo's re-entry over the entire 7 minutes (or however long it took until parachutes deployed) and then divide that energy by 2 for the 2 seconds the plug was in the atmosphere.
You're right, the total amount would've been a way better approximation than the peak. Worth looking into.
My guess is that that would have been temperatures well in excess of 1200C which would have made the outer surface start to melt, and most likely a temperature where it just turns to plasma.
I don't have any argument with that. I think the outer surface would definitely have begun to melt.
Would it all have melted / vaporized / plasmafied away? I don't know, it's a huge plug.
Yep. Even just considering the amount of time it would take for the heat to excite all the molecules in the massive chunk of iron, and then for them all to undergo phase change, I just don't think it could've made it.
Since it was launched vertically, anything remaining would probably have come right back down. But, that's assuming it stayed in one piece. I'm guessing it broke apart due to the stresses on it, and breaking apart would have meant more surface area, which would have meant more areas exposed to massive heating, which would have meant more breaking apart.
That's something I couldn't find information on: is iron's tensile strength high enough to prevent the thing shattering apart on contact with air? I'm inclined to think it is—chunks of meteorites bigger than a meter have made it through the atmosphere, for instance. The Hoba meteorite is estimated to only be slightly bigger than it is now before its atmospheric entry, and it's way bigger than the bore cap. Similar composition, too.
TL;DR: I doubt it made it out of the atmosphere.
Either way, I like researching it.
Edit: also, the bore cap starting at the bottom of the atmosphere means that it's likely it experienced less fracture stress, since the air would've accelerated with it rather than being static.
I literally just remembered that ChromeOS is a thing. I bet a big chunk is people seeing that they're cheaper and deciding to switch to those. So, in a way, it kind of is Linux.
Yeah, probably the switches that are making any meaningful impact to the statistics are Windows 11 users buying a Mac (edit: or a Chromebook). I don't doubt that there is a higher than usual number of Windows users switching to Linux because of Microsoft's latest nonsense, but you're right that it's probably not the biggest part of this stat.
My guess is either people are downgrading, or enough people are dropping Windows entirely after previously using Windows 11 (whether by switching to Mac or Linux, or by deciding that they don't need laptops at all and can get by with just an iPad or something) to affect the percentages.
Edit: oh, also Chromebooks. I bet it's a lot of people switching to ChromeOS.
Yes, although the protocol is already open, which I think mitigates the risk slightly. Bluesky is also organized as a public benefit corp, which mitigates the risk almost not at all but is interesting. If Bluesky begins to go the way of Twitter, other corporations or entities can make interoperable replacements easily. That was not so for Twitter.
But in general, yes. This is the same song but a different verse. People have been so blinded by the brokenness of the internet as it is now that an interoperable protocol doesn't make any sense to them.
Let's compare with the Apollo Command Module heat shield, a remarkably close analogue for the bore cap. They're a similar weight (3,000 lb for the heat shield, 2,000 lb for the bore cap) and have melting points within an order of magnitude of each other (5,000°F for the AVCOAT heat shield and about 2,800°F for the iron bore cap). They're even both of a similar shape and aerodynamic profile (disc-shaped and blunt). Both had to travel 62 miles (the distance from sea level to the Karman Line, where atmosphere becomes negligible).
The Apollo CM made that distance in about seven minutes; at 130,000mph, the Pascal B bore cap took at most 1.72 seconds to make the trip.
What was discovered during the development of the Apollo heat shield is that the blunt shape caused a layer of air to build up in front of the spacecraft, which reduced the amount of heating that convected into the heat shield directly. This reduced the amount of heat load that the heat shield needed to bear up under.
Further, it's also worth noting that the Apollo command modules weren't tumbling, which the bore cap likely would have been, allowing brief instants during its ascent for the metal to cool before being subjected again to the heat of the ascent.
But probably most critical at all is the remarkably brief amount of time that the bore cap spent in atmosphere. This person did the math on how much power it would take to vaporize a cubic meter of iron, and the answer is 25,895,319 kJ. Now, the bore cap isn't quite a cubic meter, but we can use all of his calculations and just swap in 907kg (2000lbs):
To heat the bore cap to iron's melting point: 0.46 kJ/kg * 907 kg * (1808K-298K) = 630,002 kJ
To phase change the iron from solid to liquid: 69.1 KJ/kg * 907 kg = 62,674 kJ
To heat the bore cap to iron's boiling point: 0.82 kJ/kg * 907 kg * (3023K-1808K) = 903,644 kJ
To phase change the iron from liquid to gas: 1520 kJ/kg * 907 kg = 1,378,649 kJ
So, in total, 2,974,969 kJ. The Apollo heat shield encountered a peak of 11,000 kJ/m^2/s. Since the Pascal B bore cap was about a meter in diameter and was traveling through the atmosphere for about two seconds, we can very neatly estimate that it absorbed a maximum of 22,000 kJ due to atmospheric compression--not even close to enough to get it to melting temperature.
I just wish this was a native function of one or both platforms. What a feather in Bluesky's cap to say that they're interoperable with Threads, for instance.
In order to get a similar experience to Twitter, you need to follow a lot more people on Mastodon than you did on Twitter, because you never get that algorithmic backfill (and, in fairness, because there are fewer people using it).
Even if it does preserve your momentum, with some really good trigonometry, you could teleport to a location that would result in that momentum landing you softly and exactly at the top of a cliff. If you can redirect the momentum, it can be any cliff. If you can't, you'll have to choose a cliff in another part of the world so that gravity burns off all your inertia at just the right time.
There are a lot of people on it, it doesn't feel empty like I have often found Mastadon.
Mastodon isn't empty. People just have to follow folks to actually get any content. Now, Bluesky definitely does the onboarding better in that regard, but this almost certainly comes down to people not knowing that they have to follow accounts to get content.
I don't know that that makes a huge difference to the physics involved, though it certainly may have.
But in that case we're talking about human survivability, and a chunk of solid iron is going to survive a whole lot longer than humans or delicate instrumentation. It might look a little worse for the wear, but it's much more likely to be recognizable after the whole experience than anything designed for people.
But after initial heating, the air cushion begins heating itself up instead of the object, reducing the amount of heat the object receives.
But it would also tail off as the bore cap heated, reducing stresses on it as it went higher.
True, but on the other hand the a Apollo heat shield wasn't designed to convect heat to other parts of itself. And again, it had a much harder job (keep the Apollo command module at human-survivable temperatures) than the bore cap (not reach the boiling point of iron).
All the stuff I read only mentioned the iron, but keep in mind that it has to not only reach the melting point but also undergo phase change, which requires a lot more energy.
11 kJ per m² per second was the peak amount of energy that the Apollo heat shield encountered. Double that for the approximately two seconds it would've been in atmosphere, and it's a pretty handy approximation since the bore cap was about a meter itself.
You're right, the total amount would've been a way better approximation than the peak. Worth looking into.
I don't have any argument with that. I think the outer surface would definitely have begun to melt.
Yep. Even just considering the amount of time it would take for the heat to excite all the molecules in the massive chunk of iron, and then for them all to undergo phase change, I just don't think it could've made it.
That's something I couldn't find information on: is iron's tensile strength high enough to prevent the thing shattering apart on contact with air? I'm inclined to think it is—chunks of meteorites bigger than a meter have made it through the atmosphere, for instance. The Hoba meteorite is estimated to only be slightly bigger than it is now before its atmospheric entry, and it's way bigger than the bore cap. Similar composition, too.
Either way, I like researching it.
Edit: also, the bore cap starting at the bottom of the atmosphere means that it's likely it experienced less fracture stress, since the air would've accelerated with it rather than being static.