Air Force 'rods from god' kinetic weapon could hit with nuclear-weapon force | Hacker News Reader

Air Force 'rods from god' kinetic weapon could hit with nuclear-weapon force

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34 pointsvezycash57 comments

> 20 feet long, 1 foot in diameter tungsten rods

I was curious about the price of this so I did some monster math (FYI complete arms layman, serious errors are likely).

Raw materials: Volume is 15.7 cu ft = 444,574.5 cm3. Density is 19.3g/cm3 = 8,580 kg. Estimated price of $30.3k per metric ton [1] = $260k in tungsten. Cheap.

Now for launch price. SpaceX advertises $90 million for 8 metric tons launched into low-earth orbit [2]. Yowza.

A single Trident submarine based missile is in the order of $65-$100 million depending on various sources. So cost-wise these seem within the same order of magnitude as nukes.

1: https://www.metalary.com/tungsten-price/ 2: https://spacenews.com/wp-content/uploads/2016/05/spacex-pric...

That price per ton doesn't include making it in the desired shape, though, right? Tungsten is very tough to work with, so I imagine that'd add significantly to the price, though I've no idea how much.

It would be eclipsed by the price of getting it into orbit, making it a rounding error.

It just needs to be more or less a rod. The exact shape doesn't matter much, so there's not going to be much working it, just melt it into a rod and done. (There are some ceramics that can handle the necessary temperature.)

You can also sinter it, it doesn't need to be especially strong, just hold itself together while falling, and sintering can make it strong enough.

The strength plays no part at all when it impacts. At the energy involved it might as well be a noodle. It just needs to handle the heat and resistance of reentry. Mainly heat.

> The strength plays no part at all when it impacts. At the energy involved it might as well be a noodle. It just needs to handle the heat and resistance of reentry.

So why tungsten, rather than a tungsten skin on a lead bar?

when it impacts. You want your missile to reach the ground in one part, and you want it to have low air resistance, so that most potential energy goes into the kinetic energy at impact, rather than say, heating or melting your projectile or the air.

Also, the density of tungsten is about 75% larger than that of lead. Iridium and osmium are about 15% heavier still, at about twice the density of lead (osmium is heavier, but by only 0.12%)

The shape matters because you want to maximize the impact speed which means minimizing resistance of reentry. A simple rod will not keep its orientation while falling down, it needs either fins or a different shape.

You actually have to decelerate rapidly, so you warheads fall at a steep angle. Gliding reentry is inaccurate

At which point there’s no reason putting this thing in orbit instead of launching it as a regular ballistic missile.

To hit one target on the ground you are going to need thousands of rods in orbit to ensure that one is available to use on the target. This is necessary because things in orbit will only be able to de-orbit on top of things that are close to their orbital plane.

It'd be funny if someone would try to cast it in shape by melting it.

SpaceX is trying to reduce launch costs though. The closer they get to their goal of 10 million / launch, the cheaper this thing gets.

How accurate can it be - or does it only work when there is almost no wind? Also, isn't there a maximum velocity based on air drag - if so, can something similar not be dropped from a plane?

Rod-shaped means very little drag. And at the speeds that would produce such an energetic effect, wind isn’t going to cause much drift.

I'd imagine at that speed (mach 8) it spends only a few short seconds in the part of the atmosphere that is dense enough to cause it to deviate from wind. Maybe a few metres? The thing I was more curious about is how they drop it from non-geostationary orbit and still have it entering the atmosphere and landing at the right place.

It would need a precise retrograde burn at a precise orbital location. This means it will be slower than surface based nukes and have a highly variable time to target. At a low orbit this could be 90 minutes, at geostationary orbit it could be almost a day, but it will always vary based on the location of the target and the weapons orbital position when the order is issued.

I think they'd just get very strategic about the direction they launch it from the satellite. They mentioned 15 minutes in the article but that would require multiple satellites in the sky. The idea of putting rocketry and guidance systems omboard seems plausible too.

You can't deorbit something just by "dropping" it from a satellite. If you want to target a single "rod" they would need independent onboard guidance and propulsion.

A better orbit is retrograde solar, just inside or outside the Earth's orbit. With 183 of them in orbit, one would pass by the Earth every day. With a week or so advance notice, aiming would be easy.

But why, there are already more than enough ways to kill people. And yet somehow sane and affordable healthcare is out of reach.

To be fair, coming up with new weapons is a lot simpler than fixing the world's healthcare systems.

In what sense? In the "we have the technology, medicine and money for people to live healthy well into their seventies but we choose to spend it on doomsday machines instead" sense? In the "our armed forces are now so well-equipped and well-funded they would simply take over if we tried to cut funding to reasonable levels" sense? In the "everybody else is an enemy" sense? What a lot of nonsense.

I meant in the "give billions of dollars to weapon manufacturers and they'll keep inventing crazy shit, but you can't even begin to enumerate the number of organizations and agencies you'd have to give funding to in order to effect change in our systemically flawed healthcare status quo" sense.

In other words, it's a complexity problem. It's easy to take money, throw it at a defense contractor, and get weapons out the other end. But to change healthcare, thousands of laws would have to be changed, and hundreds of government agencies would have to change their daily operations. And politicians would use the change to polarize their voter base.

What we need is to educate the younger generations on the benefits of universal healthcare, show them how it's the inevitable way of the future, and eventually they'll get into office and do the hard work of making the necessary changes. It may take generations.

This way you can kill a lot of people without irradiating the territory or the atmosphere.

I'm pretty skeptical that the energy dispersed from a tungsten rod impact would be dispersed in a manner similar to a nuclear weapon. That is to say, while they may both be just as energetic, the nuclear bomb might be dumping most of it's energy into thermal radiation while the tungsten rod, I would expect, is dumping a lot of it's energy into shattering bedrock as it burrows half a kilometer deep into the earth's crust. Yes, ultimately that energy is dispersed as heat, the rocks pierced by the rod would get hotter, but instead of the thermal energy being emitted in one horrible microsecond in the atmosphere above the target, it would be dispersed over a longer time period and over a larger area straight into rock.

That's just my intuition. I don't think these would actually be as effective as the raw energy values might suggest.

> I'm pretty skeptical that the energy dispersed from a tungsten rod impact would be dispersed in a manner similar to a nuclear weapon.

You're right, it wouldn't. See below.

> the tungsten rod, I would expect, is dumping a lot of it's energy into shattering bedrock as it burrows half a kilometer deep into the earth's crust

Yes, that's the point: the expected use for these weapons is to hit hardened targets underground, so you want the energy to be concentrated, not dispersed like in a nuclear blast.

What's to say it would have the desired terminal effects when it hits the underground bunker, instead of simply piercing the bunker and continuing deeper underground? If the underground bunker is built with bulkheads, would one portion of the bunker getting pierced by a rod necessarily turn people in another section into hamburger meat?

Guessing by lethal shockwaves are from relatively small explosions (like packets of C4), I'm going to go ahead and guess the energy dispersed from this would easily shatter all the concrete of the bunker and instantly kill anything living.

Maybe, but I'm not convinced. With enough velocity, a ping pong ball can blow a clean neat circular hole straight through a ping pong paddle. Fast moving objects can cause extremely localized damage. On the other hand if you shoot a fast at a plastic jug full of water, an incompressible fluid, it will shred the water jug specifically because that water is incompressible. Fill the jug with air or sand and you'll then find that the jug remains intact when you shoot it, save for two bullet-sized holes through both sides.

If the tungsten rod is able to borrow through hundreds of meters of bedrock, it seems to me that's a sufficiently efficient penetrator that it might 'ice pick' straight through the target bunker dumping only a small fraction of it's energy into the bunker, as it then goes deeper through more bedrock.

Your ping pong ball example is fairly counter to everything I've ever seen but I'm no physicist. I would be very surprised if there's any velocity that would put the ball through the paddle without completely destroying both

I have my doubts. You would have to stop it from orbiting first (8km/s). What kind of rocket would be needed to get 8km/s deceleration of 12 tons on LEO? And it would only gain 10km/s. Why not go directly from the ground then?

It doesn't even take 1km/s to deorbit.

https://space.stackexchange.com/questions/12011/how-could-a-...

Yeah but you'd want your orbital kinetic weapon to pass through as little atmosphere as possible to minimize aerodynamic breaking and to reduce the accuracy problems inherent in those aerodynamic effects. The steeper the reentry, the better, which means a greater delta-v requirement.

Maybe highly elliptical orbits?

There's an economic incentive for the moon base! Since it's so expensive to bring heavy payloads up by rocket we can just mine them on the moon. It surely won't be too long until the US needs to mass-produce the godrods anyway.

From the moon, you don’t need high quality weapons; you can compensate by increasing mass. And that moon base could become independ3nt because of its ability to launch rocks (https://en.m.wikipedia.org/wiki/The_Moon_Is_a_Harsh_Mistress...)

Independence requires more than the ability to “drop rocks” it requires total self-sufficiency. Without that you’re bombing the people who can kill you just by withholding essentials like food, water, and air. No one is even pretending that a colony on the moon or Mars could be self-sufficient to thst degree with anything like our current technology.

No village or small city is self-supporting nowadays. Why would a moon base of similar size be different?

What matters is whether enough money flows in to buy elsewhere what you can’t produce.

If (a big if, but an assumption in Heinlein’s novel) a moon base can be made profitable, and kids get born there, so that people end up thinking of themselves as citizens of them moon, would it be fair if most of those profits keep ending up on earth?

In Heinlein’s novel, the idea is not that those living permanently on the moon bomb those on earth (even though that does happen), but that they use the threat of bombing them to get a fairer deal.

Carl Sagan argued against developing the technological methods that would be needed to defend against asteroids hitting the Earth because the methods proposed would more likely be used as weapons against the Earth.

Pretty soon we’ll just dropping small meteors. Farming them might not be cheap, but we’re not going to run out of them.

Always have been curious about bringing outerspace stuff to earth.

Lets say we learn to mine asteroids, wouldnt the extra weight added to earth affect its orbital mechanics in anyway?

The entire asteroid belt weighs less than 5% of the moon, and most of the material would have little economic justification for bringing it down.

Considering that lots of stuff already ends up on Earth from outer space, I doubt it has a meaningful effect. We also throw stuff from Earth into space (the planet does so without us as well).

If this has "nuclear weapon force", then the rocket used to launch it also contains that much energy.

A quick bit of match says the space shuttle energy is about 1 kiloton of TNT equivalent. That's a pretty small bomb.

Maybe the new launch systems are more powerful.

Although it seems simpler to just fly a rocket full of fuel at the target.

With a series of rocket launches, bringing multiple boosters up to the rod, you could raise it to a higher orbit incrementally than a single rocket would permit. But this would be very expensive and I'm skeptical of the practical value of this sort of weapon in the first place, even if we assume the rod is given equivalent energy.

"the moon is a harsh mistress"

The cost thing, they need to do inflation-adjusted dollars. They wrote this bit really badly. The cost of launch as dropped, kg for $, over time. But, also inflation happens so a million $ isn't the big deal it was.

Interesting that this was literally the major plot point in one of the GI Joe movies. I wonder if they got the idea from the movie. If you google around, the weapon in the movie created a lot of discussion about the real life viability and physics involved about this exact topic.

Here’s a clip of the weapon being used in the movie: https://m.youtube.com/watch?v=jOKf5r_JMAo

"During the Vietnam War, the US used what it called "Lazy Dog" bombs. "

Sure, they got the idea from the GI Joe movies /s

Not the op, but just wanted to note various technologies in the past have been inspired by fiction: https://screenrant.com/star-trek-real-life-gadgets/

It’s a symbiotic relationship at times. Eg Computers became a thing, fiction ran with it and made up hand held tablet computers, Tricorders, universal translators etc, which materially (not always exclusively) influence future technology designs and directions. Today we have real tablet computers, universal translators etc which were inspired by fiction.

Edit: I missed the specific point being made that the Vietnam War was well, well before the GI Joe movies in question. Apologies!

Are you sure it's not because they are the obvious things?

They seem that way now, but when a computer was the size of a building, perhaps not.

Sure. I just wanted to point out that the linked article describes similar weaponry used by the US in Vietnam, so the point about inspiration from a movie is kinda moot.

Ah right, apologies I missed that! You make a fair comment given the GI Joe movies came out decades after the Vietnam war.

It is a much older idea than that:

https://en.m.wikipedia.org/wiki/Kinetic_bombardment

Rod of god sounds funnier than rods from god. Let's call it that.

lance of Longinus?

A $220 million per shot rod of God can burrow deep. How do you maximize the value of that shot? Wiping out a city? Taking out military target? Pfft, nay.

How can you make a $200M shot free up trillions in liquidity?

You target the bunkers of billionaires and wipe out all of the blackmail they store. That'll justify the high cost per shot eaaily.

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