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’m not so sure… At those speeds, it would’ve taken under 10 seconds to completely clear the atmosphere. Even with intense compressional heating, I don’t think it would’ve been in contact with the atmosphere long enough to completely vaporize — although it probably didn’t look much like a manhole cover anymore by the time it escaped.
I don’t think melting is the issue here. I think it literally disintegrates at those speeds. Like, this is Mass Effect mass driver level of impact with the atmosphere.
For reference, RICK ROBINSON’S FIRST LAW OF SPACE COMBAT: “An object impacting at 3 km/sec delivers kinetic energy equal to its mass in TNT.”
Assuming the lid is travelling 55km/s, it’s well beyond that point. The atmosphere it’s travelling through is basically a solid at that speed. Even if it isn’t heating due to the friction (and waiting for heat flow), it is heating due to the compressive force of being slammed into the atmosphere. It’s very likely the whole thing vaporized.
But I could be wrong, and some alien SOB is going to have a bad day when the manhole cover slams into their ship in interstellar space.
And for reference, the earth escape velocity from the surface is 11.2 km/s or 25,000 mph, not 7,000 mph.
To escape the solar system from the earth surface, the minimum speed is 16.6 km/s, or 37,100 mph. But this assumes that you launch in the correct direction to take the most advantage of the Earth’s 30 km/s. If you launch in the most disadvantageous direction, you can add another 60 km/s to escape.
Sadly, the cover likely did burn up in the atmosphere at those speeds, like a meteorite in reverse.
I’m not so sure.
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.
Interestingly, early missiles actually did use solid metal heat shields; not iron, but titanium, beryllium, and copper. They were effective, but abandoned due to their weight.
I’m not so sure… At those speeds, it would’ve taken under 10 seconds to completely clear the atmosphere. Even with intense compressional heating, I don’t think it would’ve been in contact with the atmosphere long enough to completely vaporize — although it probably didn’t look much like a manhole cover anymore by the time it escaped.
I don’t think melting is the issue here. I think it literally disintegrates at those speeds. Like, this is Mass Effect mass driver level of impact with the atmosphere.
For reference, RICK ROBINSON’S FIRST LAW OF SPACE COMBAT: “An object impacting at 3 km/sec delivers kinetic energy equal to its mass in TNT.”
Assuming the lid is travelling 55km/s, it’s well beyond that point. The atmosphere it’s travelling through is basically a solid at that speed. Even if it isn’t heating due to the friction (and waiting for heat flow), it is heating due to the compressive force of being slammed into the atmosphere. It’s very likely the whole thing vaporized.
But I could be wrong, and some alien SOB is going to have a bad day when the manhole cover slams into their ship in interstellar space.
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And for reference, the earth escape velocity from the surface is 11.2 km/s or 25,000 mph, not 7,000 mph.
To escape the solar system from the earth surface, the minimum speed is 16.6 km/s, or 37,100 mph. But this assumes that you launch in the correct direction to take the most advantage of the Earth’s 30 km/s. If you launch in the most disadvantageous direction, you can add another 60 km/s to escape.