this post was submitted on 14 Nov 2023
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[–] [email protected] 57 points 1 year ago (15 children)

The rods from God's idea is insane and won't work.

We had this back when the Russians announced they were going to drop conventional ordinance from space, and everyone pointed out that they would be lucky to hit the right continent, let alone Ukraine. In order to make this actually work, you would have to have an active aiming system. Which you know, is a missile.

[–] [email protected] 19 points 1 year ago* (last edited 1 year ago) (7 children)

The launch platform can aim it and use math to account for gravity, the atmosphere and all that jazz to hit the target at least close enough. Just like we already do to safely crash/burn up space debris.

[–] Patches 20 points 1 year ago (1 children)

at least close enough

To whose standards exactly? Dick Cheney's?

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[–] [email protected] 12 points 1 year ago

No, they can't. The atmosphere is an unknown state, different temperatures, different densities, different wind directions, none of which can be known ahead of time. That's why weather forecasting is always approximate. You get a percentage chance that it'll rain. You don't get a definite time stamp with 100% accuracy.

We cannot predict atmospheric disturbances to the level necessary to make this a practical system. When they burn up space debris they do it "somewhere over the middle bit of the Atlantic" That's about the level of definition you get. It's not accurate at all.

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[–] [email protected] 43 points 1 year ago (15 children)

From a purely physical point of view, is that realistic?

If all of its energy is kinetic, it means that the energy must result from it's potential energy+any fuel it is propelled with. Ignoring air-friction and terminal velocity for free falling objects, that means that still the energy of a nuclear weapon is required to bring this thing up into space, or stored as fuel for its propulsion.

So unless the projectile is assembled in space, any rocket bringing it into space will contain at least the energy of a nuclear warhead. Gotta be a very nervous launch, knowing that any failure will result in a fire with the energy of a nuke.

[–] [email protected] 41 points 1 year ago (1 children)

A lot of the energy comes from orbital speeds.

The Hypervelocity Rod Bundles project proposed 6,1x0,3 m tungsten rods, weighing about 8200 kg, impacting at about 3000 m/s, meaning about 42 GJ of energy per projectile [wikipedia].

The weakest recorded nuke, the Davy Crocket Tactical Nuclear Weapon, is estimated at about twice that (84 GJ), and the largest, Tsar Bomba, at about 3 000 000x the yield (210 PJ).

[–] [email protected] 35 points 1 year ago (2 children)

That’s their point, how do you get such a heavy thing to orbital speed without spending all that energy? You can’t unless you build it from materials harvested in space.

[–] [email protected] 29 points 1 year ago* (last edited 1 year ago) (9 children)

Oh, I apologise, I suffered some curse of knowledge there, the answer is time.

A blast is a release of energy over a short time, the whole point of building weapons is to store and handle energy in safe amounts over time.

Global electric energy consumption is about 200 PJ a day, approximately the same as the Tsar Bomba, but there's no risk for a huge explosion neither when you incinerate trash or turn off the AC.

Because time.

Although we could explode a nuke and propel things ballistically, it turns out it's a lot easier to use rockets. A rocket, although carrying frightening amounts of fuel and exploding spectacularly when it fires wrong, has several safeguards to not expend all that fuel at once. And also gives the opportunity to correct course along the way.

Now imagine that the same amount of energy has been expended many many many times over the course of the space era, and almost any mass in orbit has serious potential for damage.

For example, the MIR was 130 tons, orbiting at about 7,8 km/s, for a kinetic energy of 4 TJ, and another 235 GJ of potential energy. Totalling about a tenth of Little Boy that levelled Hiroshima.

Edit: Specifying and correcting the global energy consumption.

[–] [email protected] 13 points 1 year ago (2 children)

Right, and tungsten rods are dangerous because they don’t slow down and burn up in the atmosphere like most spacecraft do (like you said, spreading out that energy over time and space). As long as you can deorbit them accurately, they are devastating since they convert the entire orbital potential energy into surface kinetic energy all at once. (Oddly, orbital potential energy and surface kinetic energy are the same thing, just from different points of reference.)

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[–] [email protected] 11 points 1 year ago (1 children)

One of the things that's stuck with me during my time on Lemmy is someone remarking that the only difference between a battery and a bomb is how controlled the release of energy is. Having seen what happens when you puncture a LiPo battery, I believe it 😰

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[–] [email protected] 13 points 1 year ago (2 children)

The mass to orbit isn't the hard part. A reusable Falcon 9 can put 18,400 kg in low Earth orbit. That should cover two rods, plus hardware to hold and deploy them.

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[–] [email protected] 11 points 1 year ago

So a little bit of looking around, and some "Close enough, fuck it" math suggests that the Saturn V over the duration of it's launch emitted about the same amount of energy (190 Gigawatts over 2.5 minutes = 2.85x10e+13 joules, close to 7000 tons of TNT at 2.93E+13 joules) as 1/3 the yield of the Fat Man dropped on Nagasaki (FM = 20,000 tons of TNT = 8.36e+13 joules).

Now I'm not math inclined, so you should take all this with more salt than your doctor recommends, but if the rocket's output is comparable to 1/3 of an actual nuke, then it's not unreasonable to think that converting all of that back into kinetic energy would get you roughly 1/3 of a nuke's output, which could be said to be "the force of a nuclear weapon." It would take a launch of something Saturn V sized or bigger to put one up there, but supposedly Starship would be up to the task if it ever stops exploding itself and/or it's launch pad.

What I'm saying is, it's plausible enough for a blurb on some article.

[–] [email protected] 9 points 1 year ago (1 children)

And friction would cost some work both way

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[–] [email protected] 32 points 1 year ago (1 children)

There has actually been multiple occasions were Russia was caught trying to break that treaty, kind of interesting to think about. The question is if Russia does actually mobilize an orbital nuclear weapon someday like an advanced Sarmat or some kind of space bomber, will the nations of the world act in unison or watch in silence?

Have fun with that existential dread while I work on my laundry.

[–] baked_tea 13 points 1 year ago (3 children)

They are super far from having that kind of money. Anyways the US would know early enough to stop it.

[–] [email protected] 18 points 1 year ago

True I bet the Russian Oligarchs would secretly siphon that project's funds in moments, just like they did to the Russian Navy.

[–] [email protected] 10 points 1 year ago (1 children)

Nah, the USA would join them and try it.

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[–] [email protected] 30 points 1 year ago (2 children)

What about the Jewish Space Lasers that MTG said started the wildfires?

[–] [email protected] 28 points 1 year ago

Magic The Gathering has a lot to answer for.

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[–] [email protected] 28 points 1 year ago (18 children)

The problem I remember is that it is expensive to get the rod up there in the first place.

Also every other nation would hate us and make jokes about the collective small penis of the US state.

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[–] [email protected] 25 points 1 year ago (1 children)

If anyone wants some good sci-fi, I recommend The Expanse, both the books and the show. They make great use of kinetic impactors, especially Nemesis Games.

[–] [email protected] 11 points 1 year ago (5 children)

Doors and corners, kid.

Other recommended book series for scifi physics:

  • Expeditionary Force
  • Bobiverse
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[–] [email protected] 22 points 1 year ago (2 children)

Except you can't just drop it. You need to push it out of orbit, and then push yourself back in

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[–] [email protected] 20 points 1 year ago (2 children)

Fun fact, everything with a high velocity (and a certain mass) has a lot of kinetic energy.

(Now think of space ships going light speed. You don't need photon torpedoes)

[–] [email protected] 15 points 1 year ago

Inyalowda love rocks, so let's give dem sum, sasa ke

[–] [email protected] 10 points 1 year ago (3 children)

True, but to hit things within the atmosphere it needs high mass and low drag. The ISS re-entering would have high mass but high drag, and most of it would fall apart when entering and be slowed down by drag so the energy gets spread through a long streak on the atmosphere instead of on the target

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[–] skeeter_dave 18 points 1 year ago (2 children)

We should just build space colonies and just drop those when needed

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[–] [email protected] 14 points 1 year ago

So no one considers moon a weapon of m.ass destruction? All it needs is a fairly good booster on the far side ...

[–] AMillionNames 14 points 1 year ago (3 children)

Science fiction always challenges my suspension of disbelief is when people land on planets to skirmish with conventional weapons instead of, say, throw a big heavy aerodynamic solid rock from space.

[–] [email protected] 18 points 1 year ago (1 children)

In the Expanse series Earth and Mars are at war. They can easily throw rocks and totally destroy the other side. Not just beat them in a war, like totally wipe them out. But Mars knows if they start throwing rocks all bets are off and Earth will wipe them out. Just as Earth knows the same, if they wipe out Mars, Mars will make sure the Earth is destroyed.

It's an analogy of the current situation we have with nuclear weapons. During the Cold War Russia made sure they could wipe out the US if the US ever tried a first strike and the US made sure they could wipe out Russia if they ever tried something. The Mutually Assured Destruction (MAD) prevented anyone from taking the first step. These days the playing field is a bit more complex, but the same principles hold for now.

Of course in the Expanse there is a third party with nothing to lose that at one point employs such a weapon of mass destruction. But let's just hope that part isn't a mirror for reality.

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[–] Evilsmiley 11 points 1 year ago

You can make good reasons or at least plausible ones. 40k has planetary shields. There could be a civil war so neither side might want to destroy the surfaces of each planet and civilians. Battletech has spaceship tech being rare and irreplacable, and there are treaties limiting orbital and nuclear bombardment.

Sometimes the most realistic route just isnt fun though so i can usually look past the contrivances.

[–] [email protected] 9 points 1 year ago (1 children)

Good sci-fi usually treats this on par with using nuclear weapons (which it kinda is?). In Babylon 5, mass drivers are banned by intergalactic treaty, and when one race uses them anyway it literally bombs their victims back into the stone age, and it's treated as a horrifying event --one of the character's defining moments in the show is just him looking on silently in horror.

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[–] [email protected] 9 points 1 year ago (4 children)

Neil Tyson said this is entirely impractical.

[–] [email protected] 60 points 1 year ago

Neil Tyson needs to shut the fuck up and stop cockblocking me from having based weapons

[–] [email protected] 13 points 1 year ago (2 children)

I mean you have to put a nuclear amount of energy into the rods with chemical energy. Why not skip a step and just drop a big conventional explosive?

[–] [email protected] 16 points 1 year ago (2 children)

The idea is that it's too fast to ever intercept, is extremely penetrating, and you don't have to send a bomb to orbit in violation of treaty.

But all the really cool versions use rail guns and asteroid mining.

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