| ▲ | hooo 17 hours ago |
| What’s the core technology that enables them? It is crazy how deep the GBU-57 can get before detonating |
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| ▲ | ggm 17 hours ago | parent | next [-] |
| Case hardening. Making something which if propelled fast enough (secondary issue) and with a G force resisting detonator (secondary issue) which has sufficient integrity and inertia to penetrate as deeply as possible before exploding. Materials science in making aerodynamic rigid, shock tolerant materials to fling at the ground. I am sure the materials science aspects have come along since ww2, as has delivery technology, but I'd say how it goes fast, hits accurately and explodes is secondary to making a case survive impact and penetrate. I would posit shaped charges could be amazing in this, if you could make big ones to send very high energy plasma out. I'm less sure depleted uranium would bring much to the table. (Not in weapons engineering, happy to be corrected) |
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| ▲ | giantg2 17 hours ago | parent [-] | | I'm not sure you would want a shaped charge unless you guarantee it was pointing in the right directionatthe right time. Modern bunker design usually includes deflection tactics. |
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| ▲ | kragen 17 hours ago | parent | prev | next [-] |
| According to public information, Eglin steel. I was guessing either tungsten or depleted uranium, as for APDS, but the bomb's average density is only about 5 g/cc (14 tonnes in 3.1 m³). Length of 6.2 m times 5 tonnes per cubic meter gives a sectional density of 31 tonnes per square meter, which is about 15 meters of dirt. So Newton's impact depth approximation would predict a penetration depth one fourth of the reported 60-meter depth. I don't know how to resolve the discrepancy. The plane wouldn't fly if the bomb weighed four times as much. Maybe most of the bomb's mass is in a small, dense shaft in the middle of the bomb, which detaches on impact? |
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| ▲ | creato 15 hours ago | parent | next [-] | | > Length of 6.2 m times 5 tonnes per cubic meter gives a sectional density of 31 tonnes per square meter, which is about 15 meters of dirt. So Newton's impact depth approximation would predict a penetration depth one fourth of the reported 60-meter depth. This seems to assume that the weapon would penetrate until it displaced an equal amount of dirt by mass, which seems like nonsense. Why would that be the case? | | | |
| ▲ | barrkel 16 hours ago | parent | prev | next [-] | | How much does refinements of shape, terminal velocity, target characteristics change the calculation? | | |
| ▲ | kragen 16 hours ago | parent | next [-] | | I don't know. Shape can change it to be arbitrarily bad; 14 tonnes of 5-micron-thick Eglin steel foil spread over a ten-block area wouldn't penetrate anything, just gently waft down, although it could give you some paper cuts. I suspect it can't make it much better, except in the sense of increasing sectional density by making the bomb longer and thinner, which we already know the results of. Velocity doesn't enter into Newton's impact depth approximation at all. It does affect things in real life, but you can see from meteor craters that it, too, has its limits. Target characteristics, no idea, but in a fast enough impact, everything acts like a gas. It's only at near-subsonic time scales that condensed-matter phenomena like elasticity come into play. Even at longer time scales the impact can melt things. This of course comes into conflict with the design objective of the bomb acting solid, so that it penetrates the soil instead of just mixing into it, and can still detonate when it comes to rest. I feel like buried plates of the same metal would have to be able to deflect it? And there are plenty of other high-strength alloys. | |
| ▲ | tguvot 14 hours ago | parent | prev [-] | | A system described in the 2003 United States Air Force report called Hypervelocity Rod Bundles[10] was that of 20-foot-long (6.1 m), 1-foot-diameter (0.30 m) tungsten rods that are satellite-controlled and have global strike capability, with impact speeds of Mach 10.[11][12][13] The bomb would naturally contain large kinetic energy because it moves at orbital velocities, around 8 kilometres per second (26,000 ft/s; Mach 24) in orbit and 3 kilometres per second (9,800 ft/s; Mach 8.8) at impact. As the rod reenters Earth's atmosphere, it would lose most of its velocity, but the remaining energy would cause considerable damage. Some systems are quoted as having the yield of a small tactical nuclear bomb.[13] These designs are envisioned as a bunker buster.[12][14] As the name suggests, the 'bunker buster' is powerful enough to destroy a nuclear bunker. https://en.wikipedia.org/wiki/Kinetic_bombardment?useskin=ve... |
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| ▲ | jiggawatts 14 hours ago | parent | prev [-] | | I did some quick calculations: The energy of the impact from the stored kinetic energy gained by falling fro 15,000m is about the same as half a kiloton of TNT going off. That's focused into a circle just 80cm in diameter. | | |
| ▲ | kragen 14 hours ago | parent [-] | | Yet setting off half a tonne of TNT on the ground, or even just under it, won't penetrate 60 meters deep, or even 15; it will just blast open a shallow crater. A shaped charge will do only a little better. |
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| ▲ | giantg2 17 hours ago | parent | prev | next [-] |
| It's not that crazy. It's simple physics. Drop a 15 ton metal lawn dart from 50,000 feet and it has a lot of energy. |
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| ▲ | algorithmsRcool 16 hours ago | parent | prev [-] |
| No real secret sauce, the weapon weighs almost 30,000lbs and most of it is just hardened metal to make it heavy. The warhead is only ~5,300lbs of explosive |
