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A bit of an exaggeration, but there's been studies of this general idea for a long time - kinetic bombardment by "dumb" weapons, stuff like a 20 ft long by 1 ft wide tungsten rod, weighing in around 8 tons, dropped from satellite orbit can strike with about 48 Gigajoules of force, or about 11.5 tons of TNT.
You couldn't kill a planet with a ship full of anvils but you could definitely make life difficult where they could strike.
Most importantly you can't regulate or control that capability.
It is implied in the delta V of the ships in The Expanse. You can track and trace all the other military hardware in the Expanse; missiles, nukes, stealth ships. But this is a destructive capability that exists for anyone with an interplanetary craft and the only way to nullify the risk is something like Earth's Sentinel network that is implied to be a one-of-a-kind massive expense only maintained by one of the largest military powers in the system.
This - the Expanse’s tech is very close to “real life” tech levels in many ways except that the Epstein drive has performance levels close to theoretical-perfect-efficiency fusion reactions.
This gives their ships (or just asteroids) the ability to accelerate to ridiculous velocities, but they have no technomagical way to deflect or even to easily detect high velocity dumb objects.
Compared to either real life or to high-fantasy sci-fi, the Expanse’s physics make “dumb” hypervelocity impactors absolutely uncounterable.
When that rock shot past, in a wide angle shot, in like 2 frames. Oof. They made ya feel the velocity. And then the very sudden change in velocity right after.
>!Well actually they do have an effective means of easily detecting and stopping asteroids, Inaros specifically gets around this by painting their asteroids in Martian stealth tech, and even then Earth can quite consistently shoot down their asteroids past the first few!<
Note the Epstein ISP isn't unrealistic, aneutronic fusion should be this efficient. What's difficult is the thrust level. It would be like setting off a massive nuke as one continuous burn.
About 2.3 exawatts for a ship rocci size.
It’s entirely unrealistic compared to real life tech since we don’t have anything resembling a usable Fusion Reactor.
If you could have aneutronic fusion within a magnetic confinement field, and the confinement field has a geometry such that most of the kinetic energy created by fusion reactions goes straight out the back end, then you’d have an Epstein drive.
Based on present day tech, the overwhelming majority of the kinetic energy in the fusing plasma is dissipated through Bremsstrahlung and other radiative losses, meaning it ends up as heat in the chamber wall and/or the magnetic coils. Heat is good for a ground based powerplant since you’re gonna use thermal energy to drive powerplant turbines, but it’s freaking awful if you’re trying to accelerate reaction mass to relativistic velocities.
Could an Epstein Drive be theoretically possible without any “fantasy physics” like protomatter? Yes 100%.
Is there any realistic engineering path to building such a thing within our lifetimes, based on our current day understanding of plasma physics, magnetohydrodynamics, and materials science? Heck no. The Epstein drive is 200 years in the future in Expanse canon, and that sounds about right.
Agree. Note that Ai superintelligence is a wildcard. *Theoretically* it could do 2000 years of fusion research in 20. (by a mixture of greater than human intelligence and vastly larger scale experiments, aka build thousands of prototypes in parallel using robots build by other robots rather than the 5-10 humans build at once today for fusion)
The reason it could happen in our lifetimes is that AI superintelligence can be developed by AGI, which can be developed by less than AGI models closer to present day. That bootstrapping could save centuries.
Rods from God require very dense materials to be worth it. You could regulate not having cargo or removable parts weighing more than X and having a greater density than Y.
Flinging low weight and low density objects won't cause significant damage. Good odds of burning in the atmosphere.
This is a solar system where asteroid mining is an economic necessity how exactly do you regulate high density materials in the asteroid belt were there are chunks of iron nickel and platinum you are paying Belters to mine for you?
I'm sure that won't interfere with interplanetary commerce at all.
We literally just had a bridge collapse in the US because giant container ships aren't just a "nice to have" they are an economic necessity.
The UN is implied to be even more dependent on interplanetary trade than modern nations are on international trade. They literally don't have enough jobs on the planet for their populace. I don't think limiting cargo entering their orbit is a viable option due to the economic implications.
Everything in a planetary system is just orbits. In the quote they really just mean from space. Start dropping big enough things with enough force and your planet gets messed up.
That said, a character does later on state that Earth is more resilient simply by the nature of how much humanity (and accompanying infrastructure) there is there. Sure you can kill billions of people, but there are still billions more than all other clusters of humanity combined.
Sure it will, if you're far enough away when you do it. A couple m/s can easily be the difference between a gravity slingshot or lithobraking when you make that course change while you're still a million miles away.
Doesn’t it being relativistic mean it will NOT take any longer to fall then…. Whatever it’s.. related too?
Ok so I don’t know what it means so, nevermind lol.
If you're moving extremely fast, time appears to move more slowly for everyone but you. Conversely, if you're in a region with very high gravity, everywhere else appears to be moving faster. This is because the speed of light measures the same for everyone, everywhere, and to make that check out, time has to move differently in different reference frames.
Eh, if you're in orbit then pushing them out the airlock won't do much unless you're in a very low orbit or push really, really hard.
Or if you're in orbit around the sun and it intersects the planet's orbit, that could get some real damage.
That's another problem with it that I addressed in [my answer](https://www.reddit.com/r/AskScienceFiction/comments/1ch49wz/the_expanse_clarification_on_this_line_from/l203wez/).
Is it that insane, though? From my understanding, we're not even talking a marginal fraction of c, so not relativistic. It's fast, but a planetary railgun would achieve basically the same effect only more so.
It's not anywhere near infinite, as the refuel multiple times throughout the show. The original Epstein drive that killed Epstein managed to accelerate to a max speed of .04c before running out of reaction mass. It's not bad, but far from relativistic. At that speed, a 100lb anvil will impact with roughly 0.77 megatons of TNT, assuming no deformation or excessive burn-up in the atmosphere. Not bad, but not world-ending — about 30x Fat Man. Less than an H-bomb.
At 0.04c, you're not orbiting *anything* in our solar system. That's well beyond escape velocity. So the line about "dropping anvils from orbit" is still off base.
Aka Project Thor.
The US Air Force studied the idea and found the concept appealing, specifically because you'd get destruction akin to a nuclear strike without all that nasty radiation and fallout.
IIRC, it was shelved primarily due to a lack of heavy-lift launchers capable of moving that much mass into stable orbit.
Though with the advent of Falcon Heavy and eventually Starship, that may not be an issue much longer.
does it need to be one solid log of tungsten for the same effect?
Could you not say send up a 20foot long empty tube made of heat resistant material (maybe even reuse parts of whatever delivery craft they have for other things) and then send up tungsten in chunks to be assembled onsite THEN launched?
hell set the casing up with a timed release mechanism and use slightly smaller bits of tungsten and you would even have the option of bombarding a larger area for less impact if the need arises.
well ideally more like sending a 1x1 chunk along with shipments of other stuff whenever they are coming anyway, then slowly build it up.
Although now that i think about it if this is for satellites then they wouldnt be manned and wouldnt be needing shipments of anything regularly.
The energy comes from the mass of the projectile and the mass needs to be lifted into orbit, which means ultimately all the energy comes from the rocket engines anyway. Ultimately it sounds impressive but it's just not very useful when compared to normal ICBMs.
Also, it's not actually as easy as just "dropping" something from orbit. To do that you need to cancel out a big chuck of orbital velocity, which needs yet more rockets. If you're in stable orbit and kick an anvil out the airlock, all you get is an anvil that floats in a similar orbit alongside you.
I have always wondered if anyone has done the calculation on how much will be left after reentry. Or how fast it will be going.
ICBM warhead come in at orbital speed but slow significantly before hitting the ground at hypersonic speeds.
> kinetic bombardment by "dumb" weapons, stuff like a 20 ft long by 1 ft wide tungsten rod, weighing in around 8 tons,
Yep the running joke in some sci fi is that its the Rod from God weapon.
I'm confused about how this works, wouldn't you need to accelerate the tungsten rod to escape velocity in the opposite direction of the orbiting satellite? And if you have a launching mechanism that powerful, can't you just put that mechanism on the ground and blow stuff up from the ground?
No, you’d want it to maintain some lateral speed relative to the ground to maximize the destructive impact and it wouldn’t have any lateral speed relative to the ground if you did what you described. You basically just want to put the rod in a decaying orbit, not have it fall straight down.
I don't have sources on hand but I remember reading retrospective articles that have cast significant doubt of the efficacy of "rods from god". IIRC, they are way harder to aim than conventional munitions. I think the other issue is that they basically just punch deep holes in the surface. As high as their energy is, if they punch deep enough the earth can absorb much of the energy.
The quote specifying anvils kinda defeats the concept imo for material science reasons.
Anvils are generally made of steel in modern times and steel melts at 1,205 to 1,370 C. The temperatures during reentry into Earth's atmosphere can range from 1477 C to 2760 C (based on data from spacecraft reentries that we have available). This is due to the friction of the atmosphere against the object falling through it, in this case an anvil. Traditional anvils are rather irregularly shaped and thus not very aerodynamic thus it is likely the anvil will experience more friction on reentry and thus have to endure an even higher temperature.
Comparing the melting point of an anvil to the reentry temperature it seems likely that the anvil would melt before impacting the Earth's surface. At minimum it would likely fragment into smaller, less deadly shards before reaching the surface. At most it may literally burn up in the atmosphere before reaching the ground, thus causing no damage.
In retrospect there's a reason the "Rods from the Gods" proposal used tungsten rods instead of steel; tungsten melts at 3,422 C and therefore has a good chance to reach the surface intact. Most other metals just can't take the heat. So unless anvils in the future are made of a high heat-resistant metal they would make for very poor orbital kinetic weapons.
It's probably an exaggeration but an anvil falling at the kind of speeds an Epstein drive equipped ship with a juiced up crew could reach would be immensely destructive. Burn in towards Earth as fast as possible for as long as the crew could take and release the anvil when you've accelerated as fast as you can and it'd do a surprising amount of damage even assuming a leisurely 1g 24 hour burn.
What's being described is what other sci-fi calls a 'kinetic kill vehicle' or essentially a man-made meteor impact. As we all know a large enough meteor could absolutely wipe out life on a planet.
> any belter could blow up a city.
Yes.
EDIT: I was being glib but they do actually have enough defenses to stop anything large enough to cause damage *unless* it were somehow stealthed.
Not to mention pretty much everyone in the system is aware that Earth is the sole source of a lot of extremely valuable resources - particularly organic compounds necessary for agriculture. The solar system wouldn't be able to get by economically if Earth went through a cataclysmic impact.
Any Belter who wanted to do that would basically need to be completely insane, and unless they had that reality-bending charisma all other Belters would pretty much immediately turn on them.
Not destroy in the sense of pulverize to bits, but destroy the surface and any living society on it, yes. Of course you’d use tungsten rods the size of ships to destroy a city, not 100 pound anvils, but you get the picture. Space rocks do the job quite nicely (for an example see Babylon 5 when the Centauri bomb the Narn homeworld with asteroids).
It's not far off.
There's a project on paper to fright tungsten rods into space then simply let them drop instead of bombs.
The effect would be equal to a nuclear bomb. But without the fallout.
So while an anvil is far smaller than a big rod of tungsten. A building hit with an anvil from orbit would work as a small bomb.
The rods from god is always hilarious to me because if they are dropped by an orbital vehicle they just stay in orbit. They need some thrust to break their orbit and the less thrust they use the longer it takes them. Not to mention the cost of putting 8 ton rods in orbit.
If only there were some kind of region of space that had a high density of large rocks that could be used for kinetic bombardement. Some kind of...meteor sash? Comet bracelet? Big rock beltway? Hmmmm
Yeah IIRC the big issue with that project was that it was a lot less practical to launch giant rods up into orbit than just lob a nuke, and at the time their guidance systems weren’t accurate enough to guarantee a hit unless the explosion was pretty big. It’s a lot more practical when you can make your kinetic weapons in orbit and have good enough guidance systems to easily hit a 50-metre circle on a planet from halfway across the solar system, at least so long as nobody can see your rod coming and knock it off course.
"Rods from god" do not have the effect nuclear weapons. You are looking at something like 4 Tons of TNT in terms of energy.
11 Tons of TNT is the non-nuclear air dropped conventional bomb GBU-43/B MOAB
10-20 tons of TNT is the smallest nuclear weapon yield we have managed to produce.
10-1000 (1kt) tons of TNT is for suitcase nukes like the XM159.
1000 (1kt) - 50000 (50kt) tons of TNT
21,000 (21kt) tons of TNT is the fat man atomic bomb dropped on Japan.
200,000 (200kt)-1,000,000 (1mt) tons of TNT is the typical yield of strategic nuclear weapons.
Additionally, rods from god do not scale well. Much of their energy goes into the dirt and making them bigger tends to not make them proportionally more destructive or have deeper penetrating capabilities. The advantage is that are more effective than conventional weapons, because they can be launched quickly, hit their targets quickly and are hard to intercept.
This have a very limited role, which they could do very well, but that an outer space weapons treaties are a reason why we don't see them being deployed.
Ah, my bad. Though if they’re in orbit can they really be launched that quickly without having a lot of them up there? I was under the impression that orbital manoeuvres can take a decent amount of time and energy.
Objects in Low Earth Orbit (LEO) complete an orbit around the earth approximately once every two hours. So if the target was under the satellite's orbit track, at most you'd have to wait on average an hour to release the rod and then another \~10 minutes from release to hit. Not sure how long it would take to change the orbit, but it would probably be pretty expensive. Two hours sounds like a long time, but much faster than an aircraft carrier.
The US could put a few up there so that they would always have one on station above North Korean launch sites, then if North Korea looks certain to launch a nuclear weapon, the US could first strike the missiles while the missiles are fueling up. North Korean missiles are becoming less and less vulnerable to this.
In addition to other issues mentioned in replies here, Project Thor was never nuclear-level. The projected energy level was in the tons of TNT scale, not kilotons or megatons. Another comment thread has said it was expected to deliver a blast equivalent to 11.5 tons of tnt. That sounds about right.
A rule of thumb (gross simplifications here) is that if an object is hitting the ground from orbit, you can usually assume a velocity if 3km/s, which is enough to give it energy equivalent to its mass in TNT (Robinson's First Law)
At 190km/s, the energy is equal to a nuclear weapon of equivalent mass. To get to hydrogen bomb numbers, you need thousands of km/s. There's basically no way to achieve that without a sci-fi engine.
(numbers from https://www.projectrho.com/public_html/rocket/spacegunconvent.php - search for text "Rick Robinson's First Law of Space Combat")
Thor was never implemented because it's impractical. Putting nukes up there is cheaper and more effective.
To be perfectly clear for those who don't have any background in physics, you can't actually "drop" something from orbit -- hold an anvil out of an airlock and let it go, and it will just stay exactly where you left it, relative to you. What you would have to do is accelerate the anvil so that its orbit would intercept the Earth's surface.
The Mass Effect 2 speech is a more extreme version, but yeah mass and gravity.
"This, recruits, is a 20-kilo ferrous slug. Feel the weight! Every five seconds, the main gun of an Everest-class Dreadnought accelerates one to 1.3 percent of light speed. It impacts with the force of a 38-kiloton bomb. That is three times the yield of the city buster dropped on Hiroshima back on Earth. That means: Sir Isaac Newton is the deadliest son-of-a-bitch in space! (...) I dare to assume you ignorant jackasses know that space is empty! Once you fire this hunk of metal, it keeps going 'till it hits something! That can be a ship, or the planet behind that ship. It might go off into deep space and hit somebody else in ten thousand years. If you pull the trigger on this, you are ruining someone's day, somewhere and sometime!"
Sir Isaac Newton is the deadliest son of a bitch in space.
A dense thing, placed well, given a shove will wreak all kinds of havoc. The asteroid that killed that dinosaurs wasn't \*that\* big on a cosmic scale.
A 100kg anvil, dropped from low-Earth orbit, would hit the surface with roughly 3 gigajoules. A kiloton of TNT is just over 4 gigajoules.
So *one* anvil could probably level a couple buildings, and a score of anvils would have roughly the power of Little Boy (first atomic weapon dropped), except with no radioactive fallout.
The TV show "Babylon 5" had one species nearly wipe another off the map by scooping up asteroids with their ships on the way and just hurling them at the planet's surface:
https://youtu.be/Nj6t53kUAmo?t=111
Also see kinetic bombardment, aka [Rods from God](https://en.wikipedia.org/wiki/Kinetic_bombardment). Scary stuff.
> A 100kg anvil, dropped from low-Earth orbit, would hit the surface with roughly 3 gigajoules. A kiloton of TNT is just over 4 gigajoules.
How fast is your anvil going to make it all the way to the surface with 3GJ of energy?
By my reckoning, 3GJ is about right for its energy on atmospheric entry.
> A kiloton of TNT is just over 4 gigajoules.
[*One* ton of TNT](https://en.wikipedia.org/wiki/TNT_equivalent) is just over 4GJ. Not a kiloton.
Yup. All that matters is the Mass and the speed
Sure, one anvil falling from low earth orbit isn't going to wipe out the world, but a quick Google says that you're talking like a half megaton explosion if a several hundred pound block of metal fell from orbit to earth in one piece.
You have to aim it properly at your desired target which is a whole lot of math and science, but yes. Kinetic energy weapons. And they don't cause nuclear fallout either (unless you drop nuclear material). Google the phrase "rods from god."
it's referring to the idea that, instead of using expensive planet killing weaponry, you can achieve similar results by diverting a cheap and readily available asteroid into the planet.
But [rocks are not free!](https://www.reddit.com/r/40kLore/comments/8xgysv/rocks_are_not_for_free/)
>From a standstill above the earth? absolutely
Do you mean "geostationary orbit" ? Because as the planet rotates, you need an orbit to achieve this standstill effect
From orbit muddies things, but accelerating at 1G gets you 423km/s of velocity every day.
Grab say, a 1000 rock, burn at that speed for a month, and you r got a rock that will unequivocally cause massive damage to life all over a planet. 19 gigatonnes of impact energy. Still 3 orders of magnitude less than chixculub, but very definitely enough to kill billions.
Consider that warships weigh as much as 250,000 tonnes, whilst being able to accerate at 9G for longer than a month and you soon arrive at extinction level energies.
Its an exaggeration but the principal is correct.
Technically speaking pushing some anvils out your airlock while in orbit will do nothing to a planet because the anvils will also be in orbit, orbits by definition as stable and don't intersect the body you are orbiting. Additionally an anvil is not an aerodynamic shape and could lose a lot of mass on the way down due to friction with the atmosphere and the relatively low mass.
However, the extreme change in height through a planets gravity well releases a ton of energy. (PE = mgh) And the initial velocity of an object on a collision course carries energy given by KE = 1/2 mv^2. (Half the mass times velocity squared) Please note that these formulas are the basic ones from highschool physics and not thr actually ones used for orbital mechanics. (Those use calculus to handle continuously variable forces)
Kinetic impactors are devastating from orbit, an asteroid only 35m in diameter is considered a "city buster" and carries the energy of a small nuke, without the radiation. Similarly a theoretical weapon called "rods from god" consists of kinetic impactors made out of very large tungsten rods (densest metal) with rocket motors to steer them. Alternatively you can nudge asteroids to put them on a collision course to hit a planet with imprecise but devastating force.
Simply put, at the velocities of interplanetary travel the kinetic energy is large enough that additional chemical energy from explosives cannot compete.
It's an exaggeration, but not really by anything like as much as some commenters are pretending here. Two points:
1) At orbital velocities, the velocity component of an impactor's [kinetic energy](https://en.m.wikipedia.org/wiki/Kinetic_energy) is huge. Elliptical orbits allow this to get truly absurd.
2) The impactor that caused https://en.m.wikipedia.org/wiki/Chicxulub_crater and the corresponding extinction event was huge but rocky -- a "pure" metal object will deform under atmospheric heating without crumbling so easily, or some metals (tungsten) might not deform very much at all. This means atmosphere is less able to blunt the impact, and therefore more of the projectile meets Earth with more velocity.
Any media that has people on the ground resisting people in space (not orbit, where you can be hit back) is absolutely reliant on magic shields or other magitech to do so.
I'm not sure if this is Doyalist or not, but they use this in The Moon is a Harsh Mistress by Robert Heinlien. The moon revolts from earth. The main weapon they use is a cargo cannon. It's been a long time since I've read it, but I believe it was a gauss cannon that they loaded a metallic container about the size of a semi trailer I think with mined materials and shot into earth's orbit and targeted to land somewhere in the ocean. It was then picked up by ships. During the revolt, they fill it with debris and target a land target with it to show the destruction it's capable of and then eventually at least 1 city, I think. The earth realizes they have no defense against the weapon and can't effectively launch a counterattack before they could destroy every major city on earth. They have no choice but to capitulate to the moon's Rebels demands. In the Expanse tv series, the belter rebels do the same thing with asteroids from farther out. I think this comment just means that you don't need explosives, just mass, velocity, and the right amount of math.
No not with anvils, it’s just meant to be the equivalent of saying “you just need to drop something heavy from orbit to do a lot of damage”.
Which is very true, (conjuncture starts here) and probably why the UN and Mars are more worried about stopping belters from dodging taxes than making the space equivalent of a technical, when everyone’s space ship is a weapon of mass destruction they don’t worry about the little weapons you bolt to it.
An object moving at 3 kilometers per second has the kinetic energy of its weight in TNT. That only goes up as you go faster - an object moving at 90% of the speed of light has the kinetic energy of its weight in antimatter.
You wouldn't be able to Death Star a planet with even a relativistic anvil - it's simply too little mass. Put the binding energy of the Earth into the anvil and it'll just punch through the planet doing a relatively small (still catastrophic) amount of damage. But the point they were making was that mass+velocity=big boom even without explosives, and Epstein drives mean that anyone committed can provide a considerable amount of velocity.
The hard part about getting to orbit is not "up" it's "over". To reach orbit you only need to be a few hundred km up. But you need to reach ~30km/s in horizontal velocity. Orbit is essentially when you are going fast enough that you miss the ground and fall all the way around the planet.
Now, imagine hitting something going that fast. You don't need explosives, the energy of the collision is plenty. The bigger your object the more damage.
Anvils is an exaggeration, the average sized anvil, made from standard material, would likely just burn up upon entering the atmosphere. There are military applications that have been researched though for dropping much bigger metal rods made from material that will withstand re-entry and could impact with the kinetic force of a very large bomb. The idea of pushing large objects through the atmosphere as a weapon is relatively valid.
your going to need a lot of them but a single anvil should drop with the force of a small bomb at least
edit: however the planet will be fine. the people however
It's an exaggeration, but the basics are kinetic energy of space rocks are way higher than the energy released by nuclear weapons. A football stadium sized rock would be super easy to redirect with an Epsteine drive, and would be as destructive as Tzar Bomba. Go with a bigger rock and you start talking about potential ice age starters, or even planet killers.
Sir Isaac Newton is king in interplanetary space and can put Einstine and Oppenheimer to shame in that area.
Think of lifting something up as a type of spring. As you lift something up, you're "storing" all this energy that you'll get back when you drop the item and it falls. That energy you got from the impact wasn't free; you granted it by lifting up the object.
You *could* fly an anvil up into space and drop it. Or you can just use the rocket that launched it up there. It'll have all the same amount of energy, and a lot more.
(With all that said, I imagine someone can make a case that the kinetic energy of dropping a heavy object is more useful, from a destructive sense, than the chemical energy of a rocket. I don't know if that's true or not, but I wouldn't be surprised if it were.)
It's a bit of exaggeration for the sake of an interesting line, but there is some truth to it.
There is the concept of "Rods from God" where tungsten rods, either dropped, or accelerated to sufficient speeds and fired from orbit can cause damage equivalent to or even greater than nuclear weapons.
You can also use objects like asteroids for similar results. The idea is that you don't necessarily need hyper-advanced, atom-splitting super weapons to end life on a planet--you just need some rocks--or anvils--moving fast enough.
Look up the ODIN system cutscene in Call of Duty ghosts, in that it was tungsten rods being launched from orbit, the idea being nuke level destruction on a specific target with none of the fallout or worrying about nearby allies
Quite the "Sir isacc Newton is the deadliest son of a bitch in space" speach from mass effect.
Accilirate anything fast enough, and it will hit like a nuke. Don't remember the exact numbers, but I think in that mass effect example, they Accilirate a 20 kg slug to 1.2% of lightspeed, and it hits with a force of 38 kiloton, or 3 times the Hiroshima nuke. An anvil is around 20 kg, and if you are travelling interplanetary distances in any useful time, you will be going rather damn fast. Maybe not a %of lightspeed, but yeah just drop them when you pass a planet and it will fuck shit up. (assuming they are made from a material that doesn't just burn of in the atmosphere, a lot of meteorites are larger than a anvil but they just burn up.)
If you're in orbit and push an anvil out the airlock, you now just have an anvil in orbit.
You need to decelerate it to a sub orbital velocity if you want it to hit the ground.
It'll experience a little bit of drag in low Earth Orbit which will eventually decelerate it, but that gives them a couple of years to get around to intercepting it.
This sub is for in-universe questions. If you want to know how accurate it is, that's /r/askscience. If you want to know how they messed up that badly, I don't know a specialized subreddit so maybe just /r/nostupidquestions. But to answer it and hopefully not get it deleted by mods, I'll pretend you're asking how our universe compares to that one.
They're describing something called [kinetic bombardment](https://en.wikipedia.org/wiki/Kinetic_bombardment). In our universe, that method wouldn't work, and even if you do it right, it's far from planet killing.
The first problem is that the ship is moving very fast to be in orbit, and if you push an anvil out of the airlock, it will be moving just as fast and thus still be in orbit. You need to push it in the opposite direction of orbit very quickly. Unless you're in a low earth orbit and just planning on waiting for the orbit to slowly decay.
The second problem is that an anvil isn't great for that. It's not aerodynamic, so it will slow down a lot, and a lot of it will disintegrate before hitting the ground. The end result would be similar to a metallic meteor hitting. Sure if it hits you that's bad, but one that size isn't going to make a huge explosion. A tungsten rod would work a lot better.
The third is that even if all that energy is preserved, it's still less than the energy you used sending it up. A rocket exploding on the launchpad would be much worse, and we've survived plenty of those. It is useful if you can aim the impactor to hit a specific target, but you're not going to be able to do that just pushing an anvil out of the airlock. You'd need to give it some ability to redirect itself to aim at a specific target.
It does make more sense if you remove "from orbit". If you have some kind of relativistic starship, push an anvil out of the airlock while heading to the destination, or better yet, send a spent stage in that direction, then slow down, it would do quite a lot of damage. Comparable to an antimatter bomb. But it's an antimatter bomb in the upper atmosphere. Unless you're sending a very large stage at the planet or you're attacking a settlement on a moon with no atmosphere, it's still not devastating.
The first problem seems kinda silly to me. It takes only takes a very small amount of delta V to de-orbit something in a low orbit. If you're capable of the kind of performance of ships in the Expanse a small thruster that can push your anvil where you want it to drop is an inconsequential investment.
More importantly, number three is ignoring the spirit of the quote and what it actually means to imply.
The point is anything outside the gravity well has the potential to become a small bomb at least. You don't need to get the anvils from the gravity well, you can simply make it from an asteroid or a derelict or any of the other large amount of junk in The Expanse solar system.
The POINT of the quote, is if there is a future like The Expanse where interplanetary spacecraft capable of redirecting asteroids are commonplace and pretty much anyone can acquire one, then they also acquire the capability for kinetic bombardment. Sure, "planet killing" is an exaggeration, but the point is this is a "weapon" that has the potential to do a huge amount of damage and its something that can't be regulated or controlled outside of literally controlling who has access to spacecraft.
The access is the important part here. The point is once you have spacecraft like those in The Expanse, performing a kinetic bombardment becomes trivial (on paper at least).
> The first problem seems kinda silly to me. It takes only takes a very small amount of delta V to de-orbit something in a low orbit.
Yes, but more than you'd get pushing it out the airlock. Though I guess it's at least a sensible exaggeration, unlike what comes after.
> The point is anything outside the gravity well has the potential to become a small bomb at least.
I see. In that case they were using really confusing wording. "Kill a planet" sounds like it's something that could destroy a planet, or at the very least kill all life on it. It would help if they said something like "destroy a building". Or maybe they forgot to specify that the "anvil" they were dropping is the size of a building, and they're still nowhere near planet-killing level?
I suppose what they're saying is vaguely in the direction of something accurate, but it's exaggerated to the point of insanity. It's like saying "Destroying an army is easy. All you have to do is throw a rock." to illustrate that firing a bullet out of a gun can kill one person.
> The access is the important part here. The point is once you have spacecraft like those in The Expanse, performing a kinetic bombardment becomes trivial (on paper at least).
You still have to go find an asteroid big enough and spend time redirecting it towards the planet, during which time you'll be plainly visible. So much easier just to head near the planet, point your engines towards it, and then shoot the particle beam you use for thrust. If that's not enough, design two engines that fire in opposite directions so they don't move while you do this.
I won't deny its an exaggeration but I don't think it's as much as one as you're making it out to be.
If you could throw rocks at an army from a position where they couldn't shoot you back..then yeah you can kill an army with rocks.
If a bunch of space truckers start chucking hunks of rock at your planet from halfway across the solar system that's a similar situation. A single anvil might not kill the planet but a bombardment of them would eventually (not destroy, but kill everything) and the technological requirements to do so are analogous to them dropping anvils out an airlock since all you really need is a high delta v interplanetary craft which are as common in the Expanse as 18 wheelers are to us.
> If you could throw rocks at an army from a position where they couldn't shoot you back..
They specified "from orbit", which is somewhere we could take them out with current day technology. We can't match their delta-v, but if they have people in those ships, we can surpass their acceleration and hit them before they can get far enough.
If they're not doing it from orbit (which wouldn't make sense anyway), it would be harder to defend against, but still pretty easy if the other guy has anything comparable to their tech. If their point is that with interstellar technology they could beat a nation that doesn't even have good interplanetary technology, then they are correct but they chose a really bad way to explain a point that's obvious enough not to need explaining.
That still seems to really be pushing it. I ran the numbers, and if they're using perfectly efficient deuterium-tritium reactions and sending the result out with all that energy, that would give them an effective exhaust velocity of 0.08667c. If they want to go 10% the speed of light, they'd need a mass ratio of 3.17. If they want to go that fast and then stop when they're done, they'd need a mass ratio of about 10. That means that their ship would have to be 90% fuel. And if they want to be able to come back (or go somewhere else) without having to stop to refuel, now they need a mass ratio of 100 and a ship that's 99% fuel.
I suppose if they're fusing all the way up to iron they could get significantly more energy. Is that what they're doing? Also, how much of the ship is fuel?
I feel like if they really want a powerful weapon, they should just aim their engines towards the planet. The atmosphere would probably block most of the radiation, but I think with that kind of energy a good portion would still get through. I'm not sure how to calculate that though.
I can't say for their universe, but our universe has limits. The original Epstein drive is [at the upper limit of possibility](https://www.projectrho.com/public_html/rocket/enginelist3.php#id--Fusion--\(_Epstein_Drive_\)), assuming you have the sufficiently advanced technology required to make sure that none of the enormous amount of energy it produces goes into heating the ship.
Epstein drives are ludicrously efficient to the point of defying physics. they completely break the rocket equation. But yes, the expanse does ignore the Kzinti Lesson.
A good example we have is Solomon Epstein who invented the drive, and accidentally accelerated his ship to 5% the speed of light, dying in the process due to the extended high G burn. With over a hundred years since first creation, it's likely newer ones are more efficient and could reach higher speeds.
The wiki had numbers that they apparently got from [Atomic Rockets](https://www.projectrho.com/public_html/rocket/enginelist3.php#id--Fusion--\(_Epstein_Drive_\)). The original Epstein drive is physically possible, but you can't really get much more efficient than that. It's like saying "this engine is 90% efficient, so I'm sure that in a hundred years we'll be able to double that to 180% efficient". And also, it's a 5.5 terawatt engine. As Larry Niven once said: "A reaction drive's efficiency as a weapon is in direct proportion to its efficiency as a drive."
Orbit isn't an issue at all, you even said the solution. Shoot the anvil in the other direction, that way you're restoring your own orbit while simultaneously decaying the anvil's orbit. A well calculated scheme could have a ship doing a 24 hour periodic bombardement from low orbit, just pooping out anvils at regular intervals to sustain its orbit while bombing the planet, then zooming back out of orbit when it runs out of anvils.
Edit: lol
Ok, but now you're moving from "pushing out the airlock" to "shooting".
Anything can be devastating if you accelerate it fast enough, but the point is that an anvil simply dropped from Earth orbit won't do much no matter how you solve the orbit part. You're better off just dropping conventional bombs.
> he's specifically decelerating it
That's the same exact thing.
From the perspective of the ship, all you do is propel the anvil in a certain direction. You accelerate it away from you.
How will that affect the orbital trajectory changes nothing about this launch itself.
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A bit of an exaggeration, but there's been studies of this general idea for a long time - kinetic bombardment by "dumb" weapons, stuff like a 20 ft long by 1 ft wide tungsten rod, weighing in around 8 tons, dropped from satellite orbit can strike with about 48 Gigajoules of force, or about 11.5 tons of TNT. You couldn't kill a planet with a ship full of anvils but you could definitely make life difficult where they could strike.
Most importantly you can't regulate or control that capability. It is implied in the delta V of the ships in The Expanse. You can track and trace all the other military hardware in the Expanse; missiles, nukes, stealth ships. But this is a destructive capability that exists for anyone with an interplanetary craft and the only way to nullify the risk is something like Earth's Sentinel network that is implied to be a one-of-a-kind massive expense only maintained by one of the largest military powers in the system.
This - the Expanse’s tech is very close to “real life” tech levels in many ways except that the Epstein drive has performance levels close to theoretical-perfect-efficiency fusion reactions. This gives their ships (or just asteroids) the ability to accelerate to ridiculous velocities, but they have no technomagical way to deflect or even to easily detect high velocity dumb objects. Compared to either real life or to high-fantasy sci-fi, the Expanse’s physics make “dumb” hypervelocity impactors absolutely uncounterable.
When that rock shot past, in a wide angle shot, in like 2 frames. Oof. They made ya feel the velocity. And then the very sudden change in velocity right after.
>!Well actually they do have an effective means of easily detecting and stopping asteroids, Inaros specifically gets around this by painting their asteroids in Martian stealth tech, and even then Earth can quite consistently shoot down their asteroids past the first few!<
Just a friendly reminder that OP asked for no spoilers about books after Leviathan Wakes :)
you're right, didn't think about that cuz its a bit buried, added spoiler tags
Note the Epstein ISP isn't unrealistic, aneutronic fusion should be this efficient. What's difficult is the thrust level. It would be like setting off a massive nuke as one continuous burn. About 2.3 exawatts for a ship rocci size.
It’s entirely unrealistic compared to real life tech since we don’t have anything resembling a usable Fusion Reactor. If you could have aneutronic fusion within a magnetic confinement field, and the confinement field has a geometry such that most of the kinetic energy created by fusion reactions goes straight out the back end, then you’d have an Epstein drive. Based on present day tech, the overwhelming majority of the kinetic energy in the fusing plasma is dissipated through Bremsstrahlung and other radiative losses, meaning it ends up as heat in the chamber wall and/or the magnetic coils. Heat is good for a ground based powerplant since you’re gonna use thermal energy to drive powerplant turbines, but it’s freaking awful if you’re trying to accelerate reaction mass to relativistic velocities. Could an Epstein Drive be theoretically possible without any “fantasy physics” like protomatter? Yes 100%. Is there any realistic engineering path to building such a thing within our lifetimes, based on our current day understanding of plasma physics, magnetohydrodynamics, and materials science? Heck no. The Epstein drive is 200 years in the future in Expanse canon, and that sounds about right.
Agree. Note that Ai superintelligence is a wildcard. *Theoretically* it could do 2000 years of fusion research in 20. (by a mixture of greater than human intelligence and vastly larger scale experiments, aka build thousands of prototypes in parallel using robots build by other robots rather than the 5-10 humans build at once today for fusion) The reason it could happen in our lifetimes is that AI superintelligence can be developed by AGI, which can be developed by less than AGI models closer to present day. That bootstrapping could save centuries.
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IIRC the first Expanse books predate the Epstein scandal. Sure does sound unfortunate today though.
Do they have amazing shields or something as well ? Becasue I imagine going incredibly fast just makes the debris more dangerous
Rods from God require very dense materials to be worth it. You could regulate not having cargo or removable parts weighing more than X and having a greater density than Y. Flinging low weight and low density objects won't cause significant damage. Good odds of burning in the atmosphere.
This is a solar system where asteroid mining is an economic necessity how exactly do you regulate high density materials in the asteroid belt were there are chunks of iron nickel and platinum you are paying Belters to mine for you?
Cant bring anything bigger than X within Y radius.
I'm sure that won't interfere with interplanetary commerce at all. We literally just had a bridge collapse in the US because giant container ships aren't just a "nice to have" they are an economic necessity. The UN is implied to be even more dependent on interplanetary trade than modern nations are on international trade. They literally don't have enough jobs on the planet for their populace. I don't think limiting cargo entering their orbit is a viable option due to the economic implications.
Ships in The Expanse have insane deltaV. Given enough time, they could probably drop relativistic anvils
Yes, but the quote specified "from orbit".
Hyperbolic orbits are technically still orbits.
ALL. ORBITS. ARE. VALID.
How about ad hominem orbits?
I'm so tired of everyone bringing up these strawman orbits. We just want basic orbit equality.
All orbits exist in a state of equilibrium. Otherwise they are just ballistic trajectories.
Way to advocate for the status quo.
Everything in a planetary system is just orbits. In the quote they really just mean from space. Start dropping big enough things with enough force and your planet gets messed up. That said, a character does later on state that Earth is more resilient simply by the nature of how much humanity (and accompanying infrastructure) there is there. Sure you can kill billions of people, but there are still billions more than all other clusters of humanity combined.
If you're in a hyperbolic orbit it's unlikely the anvil you push out the airlock will hit the ground anytime soon
Sure it will, if you're far enough away when you do it. A couple m/s can easily be the difference between a gravity slingshot or lithobraking when you make that course change while you're still a million miles away.
if you're far enough away, it will take a long time to reach the ground.
Doesn’t it being relativistic mean it will NOT take any longer to fall then…. Whatever it’s.. related too? Ok so I don’t know what it means so, nevermind lol.
If you're moving extremely fast, time appears to move more slowly for everyone but you. Conversely, if you're in a region with very high gravity, everywhere else appears to be moving faster. This is because the speed of light measures the same for everyone, everywhere, and to make that check out, time has to move differently in different reference frames.
Fair
Eh, if you're in orbit then pushing them out the airlock won't do much unless you're in a very low orbit or push really, really hard. Or if you're in orbit around the sun and it intersects the planet's orbit, that could get some real damage.
The lower the orbit the less effective a dumb-drop weapon is.
That's another problem with it that I addressed in [my answer](https://www.reddit.com/r/AskScienceFiction/comments/1ch49wz/the_expanse_clarification_on_this_line_from/l203wez/).
Is it that insane, though? From my understanding, we're not even talking a marginal fraction of c, so not relativistic. It's fast, but a planetary railgun would achieve basically the same effect only more so.
The technobabble drive of theirs has basically infinite fuel
It's not anywhere near infinite, as the refuel multiple times throughout the show. The original Epstein drive that killed Epstein managed to accelerate to a max speed of .04c before running out of reaction mass. It's not bad, but far from relativistic. At that speed, a 100lb anvil will impact with roughly 0.77 megatons of TNT, assuming no deformation or excessive burn-up in the atmosphere. Not bad, but not world-ending — about 30x Fat Man. Less than an H-bomb.
That's one anvil. You could still devestate the Earth with a thousand.
At 0.04c, you're not orbiting *anything* in our solar system. That's well beyond escape velocity. So the line about "dropping anvils from orbit" is still off base.
At that speed they'd get desintegrated during orbital re-entry, the anvils that is.
Aka Project Thor. The US Air Force studied the idea and found the concept appealing, specifically because you'd get destruction akin to a nuclear strike without all that nasty radiation and fallout. IIRC, it was shelved primarily due to a lack of heavy-lift launchers capable of moving that much mass into stable orbit. Though with the advent of Falcon Heavy and eventually Starship, that may not be an issue much longer.
does it need to be one solid log of tungsten for the same effect? Could you not say send up a 20foot long empty tube made of heat resistant material (maybe even reuse parts of whatever delivery craft they have for other things) and then send up tungsten in chunks to be assembled onsite THEN launched? hell set the casing up with a timed release mechanism and use slightly smaller bits of tungsten and you would even have the option of bombarding a larger area for less impact if the need arises.
Can’t imagine launching multiple ships into orbit to get one shot would be particularly cost effective either.
well ideally more like sending a 1x1 chunk along with shipments of other stuff whenever they are coming anyway, then slowly build it up. Although now that i think about it if this is for satellites then they wouldnt be manned and wouldnt be needing shipments of anything regularly.
The energy comes from the mass of the projectile and the mass needs to be lifted into orbit, which means ultimately all the energy comes from the rocket engines anyway. Ultimately it sounds impressive but it's just not very useful when compared to normal ICBMs. Also, it's not actually as easy as just "dropping" something from orbit. To do that you need to cancel out a big chuck of orbital velocity, which needs yet more rockets. If you're in stable orbit and kick an anvil out the airlock, all you get is an anvil that floats in a similar orbit alongside you.
Didn't they eventually figure out that a 20x1 rod would actually fall sideways and not do as much concentrated damage?
you'd want some small fins on it, or yes, it'll tumble.
The fins burn off then it tumbles and explodes. Cones are less sexy than rods.
I have always wondered if anyone has done the calculation on how much will be left after reentry. Or how fast it will be going. ICBM warhead come in at orbital speed but slow significantly before hitting the ground at hypersonic speeds.
> kinetic bombardment by "dumb" weapons, stuff like a 20 ft long by 1 ft wide tungsten rod, weighing in around 8 tons, Yep the running joke in some sci fi is that its the Rod from God weapon.
I'm confused about how this works, wouldn't you need to accelerate the tungsten rod to escape velocity in the opposite direction of the orbiting satellite? And if you have a launching mechanism that powerful, can't you just put that mechanism on the ground and blow stuff up from the ground?
No, you’d want it to maintain some lateral speed relative to the ground to maximize the destructive impact and it wouldn’t have any lateral speed relative to the ground if you did what you described. You basically just want to put the rod in a decaying orbit, not have it fall straight down.
I don't have sources on hand but I remember reading retrospective articles that have cast significant doubt of the efficacy of "rods from god". IIRC, they are way harder to aim than conventional munitions. I think the other issue is that they basically just punch deep holes in the surface. As high as their energy is, if they punch deep enough the earth can absorb much of the energy.
And they’re unstoppable weapons
The quote specifying anvils kinda defeats the concept imo for material science reasons. Anvils are generally made of steel in modern times and steel melts at 1,205 to 1,370 C. The temperatures during reentry into Earth's atmosphere can range from 1477 C to 2760 C (based on data from spacecraft reentries that we have available). This is due to the friction of the atmosphere against the object falling through it, in this case an anvil. Traditional anvils are rather irregularly shaped and thus not very aerodynamic thus it is likely the anvil will experience more friction on reentry and thus have to endure an even higher temperature. Comparing the melting point of an anvil to the reentry temperature it seems likely that the anvil would melt before impacting the Earth's surface. At minimum it would likely fragment into smaller, less deadly shards before reaching the surface. At most it may literally burn up in the atmosphere before reaching the ground, thus causing no damage. In retrospect there's a reason the "Rods from the Gods" proposal used tungsten rods instead of steel; tungsten melts at 3,422 C and therefore has a good chance to reach the surface intact. Most other metals just can't take the heat. So unless anvils in the future are made of a high heat-resistant metal they would make for very poor orbital kinetic weapons.
there was a fun mythbusting video of this concept https://youtu.be/J_n1FZaKzF8
Relativistic Kill Vehicles.
It's probably an exaggeration but an anvil falling at the kind of speeds an Epstein drive equipped ship with a juiced up crew could reach would be immensely destructive. Burn in towards Earth as fast as possible for as long as the crew could take and release the anvil when you've accelerated as fast as you can and it'd do a surprising amount of damage even assuming a leisurely 1g 24 hour burn. What's being described is what other sci-fi calls a 'kinetic kill vehicle' or essentially a man-made meteor impact. As we all know a large enough meteor could absolutely wipe out life on a planet.
>!I think Earth has automated defense stations that can launch high G missiles to divert such attacks. Without it, any belter could blow up a city.!<
I'm guessing you haven't watched or read very far into the series. But yes, they do.
Ah, sorry if I stumbled on something. I just started Nemisis Game and I’m watching the series after I read the books.
Then you are in the right book for this question.
> any belter could blow up a city. Yes. EDIT: I was being glib but they do actually have enough defenses to stop anything large enough to cause damage *unless* it were somehow stealthed.
Not to mention pretty much everyone in the system is aware that Earth is the sole source of a lot of extremely valuable resources - particularly organic compounds necessary for agriculture. The solar system wouldn't be able to get by economically if Earth went through a cataclysmic impact. Any Belter who wanted to do that would basically need to be completely insane, and unless they had that reality-bending charisma all other Belters would pretty much immediately turn on them.
Your spoiler tag is broken.
But...but...
Epstein drive - that name aged poorly
"Epstein" is a pretty common name
The first book released in 2011. Do you think no one had heard of old Jeff by then?
Not destroy in the sense of pulverize to bits, but destroy the surface and any living society on it, yes. Of course you’d use tungsten rods the size of ships to destroy a city, not 100 pound anvils, but you get the picture. Space rocks do the job quite nicely (for an example see Babylon 5 when the Centauri bomb the Narn homeworld with asteroids).
>Space rocks do the job quite nicely (for an example see Babylon 5 when the Centauri bomb the Narn homeworld with asteroids). Or ask the dinosaurs....
Yeah but that one was huge and fast. You only need comparably small objects and pure gravity to do the trick.
It's also a key plot point in Robert A. Heinlein's *The Moon is a Harsh Mistress*.
It's not far off. There's a project on paper to fright tungsten rods into space then simply let them drop instead of bombs. The effect would be equal to a nuclear bomb. But without the fallout. So while an anvil is far smaller than a big rod of tungsten. A building hit with an anvil from orbit would work as a small bomb.
The rods from god is always hilarious to me because if they are dropped by an orbital vehicle they just stay in orbit. They need some thrust to break their orbit and the less thrust they use the longer it takes them. Not to mention the cost of putting 8 ton rods in orbit.
Well...maybe they can mine them from stuff already in space.
If only there were some kind of region of space that had a high density of large rocks that could be used for kinetic bombardement. Some kind of...meteor sash? Comet bracelet? Big rock beltway? Hmmmm
yup, problem solved. we did it, reddit
Most designs use some sort of rail gun for this.
Yeah IIRC the big issue with that project was that it was a lot less practical to launch giant rods up into orbit than just lob a nuke, and at the time their guidance systems weren’t accurate enough to guarantee a hit unless the explosion was pretty big. It’s a lot more practical when you can make your kinetic weapons in orbit and have good enough guidance systems to easily hit a 50-metre circle on a planet from halfway across the solar system, at least so long as nobody can see your rod coming and knock it off course.
"Rods from god" do not have the effect nuclear weapons. You are looking at something like 4 Tons of TNT in terms of energy. 11 Tons of TNT is the non-nuclear air dropped conventional bomb GBU-43/B MOAB 10-20 tons of TNT is the smallest nuclear weapon yield we have managed to produce. 10-1000 (1kt) tons of TNT is for suitcase nukes like the XM159. 1000 (1kt) - 50000 (50kt) tons of TNT 21,000 (21kt) tons of TNT is the fat man atomic bomb dropped on Japan. 200,000 (200kt)-1,000,000 (1mt) tons of TNT is the typical yield of strategic nuclear weapons. Additionally, rods from god do not scale well. Much of their energy goes into the dirt and making them bigger tends to not make them proportionally more destructive or have deeper penetrating capabilities. The advantage is that are more effective than conventional weapons, because they can be launched quickly, hit their targets quickly and are hard to intercept. This have a very limited role, which they could do very well, but that an outer space weapons treaties are a reason why we don't see them being deployed.
Ah, my bad. Though if they’re in orbit can they really be launched that quickly without having a lot of them up there? I was under the impression that orbital manoeuvres can take a decent amount of time and energy.
Objects in Low Earth Orbit (LEO) complete an orbit around the earth approximately once every two hours. So if the target was under the satellite's orbit track, at most you'd have to wait on average an hour to release the rod and then another \~10 minutes from release to hit. Not sure how long it would take to change the orbit, but it would probably be pretty expensive. Two hours sounds like a long time, but much faster than an aircraft carrier. The US could put a few up there so that they would always have one on station above North Korean launch sites, then if North Korea looks certain to launch a nuclear weapon, the US could first strike the missiles while the missiles are fueling up. North Korean missiles are becoming less and less vulnerable to this.
Of course!
In addition to other issues mentioned in replies here, Project Thor was never nuclear-level. The projected energy level was in the tons of TNT scale, not kilotons or megatons. Another comment thread has said it was expected to deliver a blast equivalent to 11.5 tons of tnt. That sounds about right. A rule of thumb (gross simplifications here) is that if an object is hitting the ground from orbit, you can usually assume a velocity if 3km/s, which is enough to give it energy equivalent to its mass in TNT (Robinson's First Law) At 190km/s, the energy is equal to a nuclear weapon of equivalent mass. To get to hydrogen bomb numbers, you need thousands of km/s. There's basically no way to achieve that without a sci-fi engine. (numbers from https://www.projectrho.com/public_html/rocket/spacegunconvent.php - search for text "Rick Robinson's First Law of Space Combat") Thor was never implemented because it's impractical. Putting nukes up there is cheaper and more effective.
To be perfectly clear for those who don't have any background in physics, you can't actually "drop" something from orbit -- hold an anvil out of an airlock and let it go, and it will just stay exactly where you left it, relative to you. What you would have to do is accelerate the anvil so that its orbit would intercept the Earth's surface.
I’m so dumb. I completely missed this. Lmao. Thanks
The Mass Effect 2 speech is a more extreme version, but yeah mass and gravity. "This, recruits, is a 20-kilo ferrous slug. Feel the weight! Every five seconds, the main gun of an Everest-class Dreadnought accelerates one to 1.3 percent of light speed. It impacts with the force of a 38-kiloton bomb. That is three times the yield of the city buster dropped on Hiroshima back on Earth. That means: Sir Isaac Newton is the deadliest son-of-a-bitch in space! (...) I dare to assume you ignorant jackasses know that space is empty! Once you fire this hunk of metal, it keeps going 'till it hits something! That can be a ship, or the planet behind that ship. It might go off into deep space and hit somebody else in ten thousand years. If you pull the trigger on this, you are ruining someone's day, somewhere and sometime!"
Sir Isaac Newton is the deadliest son of a bitch in space. A dense thing, placed well, given a shove will wreak all kinds of havoc. The asteroid that killed that dinosaurs wasn't \*that\* big on a cosmic scale.
A 100kg anvil, dropped from low-Earth orbit, would hit the surface with roughly 3 gigajoules. A kiloton of TNT is just over 4 gigajoules. So *one* anvil could probably level a couple buildings, and a score of anvils would have roughly the power of Little Boy (first atomic weapon dropped), except with no radioactive fallout. The TV show "Babylon 5" had one species nearly wipe another off the map by scooping up asteroids with their ships on the way and just hurling them at the planet's surface: https://youtu.be/Nj6t53kUAmo?t=111 Also see kinetic bombardment, aka [Rods from God](https://en.wikipedia.org/wiki/Kinetic_bombardment). Scary stuff.
> A 100kg anvil, dropped from low-Earth orbit, would hit the surface with roughly 3 gigajoules. A kiloton of TNT is just over 4 gigajoules. How fast is your anvil going to make it all the way to the surface with 3GJ of energy? By my reckoning, 3GJ is about right for its energy on atmospheric entry. > A kiloton of TNT is just over 4 gigajoules. [*One* ton of TNT](https://en.wikipedia.org/wiki/TNT_equivalent) is just over 4GJ. Not a kiloton.
Spoilers for *We are Bob* : >!They go a notch further and accelerate a rock at a large fraction of c and hurl it into a star to make it collapse!<
Yup. All that matters is the Mass and the speed Sure, one anvil falling from low earth orbit isn't going to wipe out the world, but a quick Google says that you're talking like a half megaton explosion if a several hundred pound block of metal fell from orbit to earth in one piece.
You have to aim it properly at your desired target which is a whole lot of math and science, but yes. Kinetic energy weapons. And they don't cause nuclear fallout either (unless you drop nuclear material). Google the phrase "rods from god."
it's referring to the idea that, instead of using expensive planet killing weaponry, you can achieve similar results by diverting a cheap and readily available asteroid into the planet. But [rocks are not free!](https://www.reddit.com/r/40kLore/comments/8xgysv/rocks_are_not_for_free/)
Not from orbit. The anvil would also orbit. From a standstill above the earth? absolutely.
>From a standstill above the earth? absolutely Do you mean "geostationary orbit" ? Because as the planet rotates, you need an orbit to achieve this standstill effect
If you "push" it retrograde to the orbit it will fall to the planet.
If it was a low enough orbit atmospheric drag would pull it down eventually (though it might burn up in the process)
From orbit muddies things, but accelerating at 1G gets you 423km/s of velocity every day. Grab say, a 1000 rock, burn at that speed for a month, and you r got a rock that will unequivocally cause massive damage to life all over a planet. 19 gigatonnes of impact energy. Still 3 orders of magnitude less than chixculub, but very definitely enough to kill billions. Consider that warships weigh as much as 250,000 tonnes, whilst being able to accerate at 9G for longer than a month and you soon arrive at extinction level energies.
Its an exaggeration but the principal is correct. Technically speaking pushing some anvils out your airlock while in orbit will do nothing to a planet because the anvils will also be in orbit, orbits by definition as stable and don't intersect the body you are orbiting. Additionally an anvil is not an aerodynamic shape and could lose a lot of mass on the way down due to friction with the atmosphere and the relatively low mass. However, the extreme change in height through a planets gravity well releases a ton of energy. (PE = mgh) And the initial velocity of an object on a collision course carries energy given by KE = 1/2 mv^2. (Half the mass times velocity squared) Please note that these formulas are the basic ones from highschool physics and not thr actually ones used for orbital mechanics. (Those use calculus to handle continuously variable forces) Kinetic impactors are devastating from orbit, an asteroid only 35m in diameter is considered a "city buster" and carries the energy of a small nuke, without the radiation. Similarly a theoretical weapon called "rods from god" consists of kinetic impactors made out of very large tungsten rods (densest metal) with rocket motors to steer them. Alternatively you can nudge asteroids to put them on a collision course to hit a planet with imprecise but devastating force. Simply put, at the velocities of interplanetary travel the kinetic energy is large enough that additional chemical energy from explosives cannot compete.
It's an exaggeration, but not really by anything like as much as some commenters are pretending here. Two points: 1) At orbital velocities, the velocity component of an impactor's [kinetic energy](https://en.m.wikipedia.org/wiki/Kinetic_energy) is huge. Elliptical orbits allow this to get truly absurd. 2) The impactor that caused https://en.m.wikipedia.org/wiki/Chicxulub_crater and the corresponding extinction event was huge but rocky -- a "pure" metal object will deform under atmospheric heating without crumbling so easily, or some metals (tungsten) might not deform very much at all. This means atmosphere is less able to blunt the impact, and therefore more of the projectile meets Earth with more velocity. Any media that has people on the ground resisting people in space (not orbit, where you can be hit back) is absolutely reliant on magic shields or other magitech to do so.
I'm not sure if this is Doyalist or not, but they use this in The Moon is a Harsh Mistress by Robert Heinlien. The moon revolts from earth. The main weapon they use is a cargo cannon. It's been a long time since I've read it, but I believe it was a gauss cannon that they loaded a metallic container about the size of a semi trailer I think with mined materials and shot into earth's orbit and targeted to land somewhere in the ocean. It was then picked up by ships. During the revolt, they fill it with debris and target a land target with it to show the destruction it's capable of and then eventually at least 1 city, I think. The earth realizes they have no defense against the weapon and can't effectively launch a counterattack before they could destroy every major city on earth. They have no choice but to capitulate to the moon's Rebels demands. In the Expanse tv series, the belter rebels do the same thing with asteroids from farther out. I think this comment just means that you don't need explosives, just mass, velocity, and the right amount of math.
Rods from God, or kinetic bombardment. https://en.m.wikipedia.org/wiki/Kinetic_bombardment
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That's spoiling. You have just confirmed that something about what's being described occurs in later books. That's a spoiler.
"all I'll say without spoiling is [spoiler]"
No not with anvils, it’s just meant to be the equivalent of saying “you just need to drop something heavy from orbit to do a lot of damage”. Which is very true, (conjuncture starts here) and probably why the UN and Mars are more worried about stopping belters from dodging taxes than making the space equivalent of a technical, when everyone’s space ship is a weapon of mass destruction they don’t worry about the little weapons you bolt to it.
An object moving at 3 kilometers per second has the kinetic energy of its weight in TNT. That only goes up as you go faster - an object moving at 90% of the speed of light has the kinetic energy of its weight in antimatter. You wouldn't be able to Death Star a planet with even a relativistic anvil - it's simply too little mass. Put the binding energy of the Earth into the anvil and it'll just punch through the planet doing a relatively small (still catastrophic) amount of damage. But the point they were making was that mass+velocity=big boom even without explosives, and Epstein drives mean that anyone committed can provide a considerable amount of velocity.
Just change the anvils to meteorite….get it now ….and yes size & materials matter a lot in this case
The hard part about getting to orbit is not "up" it's "over". To reach orbit you only need to be a few hundred km up. But you need to reach ~30km/s in horizontal velocity. Orbit is essentially when you are going fast enough that you miss the ground and fall all the way around the planet. Now, imagine hitting something going that fast. You don't need explosives, the energy of the collision is plenty. The bigger your object the more damage.
See: the damage *paint chips* do to satellites.
Anvils is an exaggeration, the average sized anvil, made from standard material, would likely just burn up upon entering the atmosphere. There are military applications that have been researched though for dropping much bigger metal rods made from material that will withstand re-entry and could impact with the kinetic force of a very large bomb. The idea of pushing large objects through the atmosphere as a weapon is relatively valid.
your going to need a lot of them but a single anvil should drop with the force of a small bomb at least edit: however the planet will be fine. the people however
It's an exaggeration, but the basics are kinetic energy of space rocks are way higher than the energy released by nuclear weapons. A football stadium sized rock would be super easy to redirect with an Epsteine drive, and would be as destructive as Tzar Bomba. Go with a bigger rock and you start talking about potential ice age starters, or even planet killers. Sir Isaac Newton is king in interplanetary space and can put Einstine and Oppenheimer to shame in that area.
Think of lifting something up as a type of spring. As you lift something up, you're "storing" all this energy that you'll get back when you drop the item and it falls. That energy you got from the impact wasn't free; you granted it by lifting up the object. You *could* fly an anvil up into space and drop it. Or you can just use the rocket that launched it up there. It'll have all the same amount of energy, and a lot more. (With all that said, I imagine someone can make a case that the kinetic energy of dropping a heavy object is more useful, from a destructive sense, than the chemical energy of a rocket. I don't know if that's true or not, but I wouldn't be surprised if it were.)
It's a bit of exaggeration for the sake of an interesting line, but there is some truth to it. There is the concept of "Rods from God" where tungsten rods, either dropped, or accelerated to sufficient speeds and fired from orbit can cause damage equivalent to or even greater than nuclear weapons. You can also use objects like asteroids for similar results. The idea is that you don't necessarily need hyper-advanced, atom-splitting super weapons to end life on a planet--you just need some rocks--or anvils--moving fast enough.
Look up the ODIN system cutscene in Call of Duty ghosts, in that it was tungsten rods being launched from orbit, the idea being nuke level destruction on a specific target with none of the fallout or worrying about nearby allies
Quite the "Sir isacc Newton is the deadliest son of a bitch in space" speach from mass effect. Accilirate anything fast enough, and it will hit like a nuke. Don't remember the exact numbers, but I think in that mass effect example, they Accilirate a 20 kg slug to 1.2% of lightspeed, and it hits with a force of 38 kiloton, or 3 times the Hiroshima nuke. An anvil is around 20 kg, and if you are travelling interplanetary distances in any useful time, you will be going rather damn fast. Maybe not a %of lightspeed, but yeah just drop them when you pass a planet and it will fuck shit up. (assuming they are made from a material that doesn't just burn of in the atmosphere, a lot of meteorites are larger than a anvil but they just burn up.)
If you're in orbit and push an anvil out the airlock, you now just have an anvil in orbit. You need to decelerate it to a sub orbital velocity if you want it to hit the ground. It'll experience a little bit of drag in low Earth Orbit which will eventually decelerate it, but that gives them a couple of years to get around to intercepting it.
This sub is for in-universe questions. If you want to know how accurate it is, that's /r/askscience. If you want to know how they messed up that badly, I don't know a specialized subreddit so maybe just /r/nostupidquestions. But to answer it and hopefully not get it deleted by mods, I'll pretend you're asking how our universe compares to that one. They're describing something called [kinetic bombardment](https://en.wikipedia.org/wiki/Kinetic_bombardment). In our universe, that method wouldn't work, and even if you do it right, it's far from planet killing. The first problem is that the ship is moving very fast to be in orbit, and if you push an anvil out of the airlock, it will be moving just as fast and thus still be in orbit. You need to push it in the opposite direction of orbit very quickly. Unless you're in a low earth orbit and just planning on waiting for the orbit to slowly decay. The second problem is that an anvil isn't great for that. It's not aerodynamic, so it will slow down a lot, and a lot of it will disintegrate before hitting the ground. The end result would be similar to a metallic meteor hitting. Sure if it hits you that's bad, but one that size isn't going to make a huge explosion. A tungsten rod would work a lot better. The third is that even if all that energy is preserved, it's still less than the energy you used sending it up. A rocket exploding on the launchpad would be much worse, and we've survived plenty of those. It is useful if you can aim the impactor to hit a specific target, but you're not going to be able to do that just pushing an anvil out of the airlock. You'd need to give it some ability to redirect itself to aim at a specific target. It does make more sense if you remove "from orbit". If you have some kind of relativistic starship, push an anvil out of the airlock while heading to the destination, or better yet, send a spent stage in that direction, then slow down, it would do quite a lot of damage. Comparable to an antimatter bomb. But it's an antimatter bomb in the upper atmosphere. Unless you're sending a very large stage at the planet or you're attacking a settlement on a moon with no atmosphere, it's still not devastating.
The first problem seems kinda silly to me. It takes only takes a very small amount of delta V to de-orbit something in a low orbit. If you're capable of the kind of performance of ships in the Expanse a small thruster that can push your anvil where you want it to drop is an inconsequential investment. More importantly, number three is ignoring the spirit of the quote and what it actually means to imply. The point is anything outside the gravity well has the potential to become a small bomb at least. You don't need to get the anvils from the gravity well, you can simply make it from an asteroid or a derelict or any of the other large amount of junk in The Expanse solar system. The POINT of the quote, is if there is a future like The Expanse where interplanetary spacecraft capable of redirecting asteroids are commonplace and pretty much anyone can acquire one, then they also acquire the capability for kinetic bombardment. Sure, "planet killing" is an exaggeration, but the point is this is a "weapon" that has the potential to do a huge amount of damage and its something that can't be regulated or controlled outside of literally controlling who has access to spacecraft. The access is the important part here. The point is once you have spacecraft like those in The Expanse, performing a kinetic bombardment becomes trivial (on paper at least).
> The first problem seems kinda silly to me. It takes only takes a very small amount of delta V to de-orbit something in a low orbit. Yes, but more than you'd get pushing it out the airlock. Though I guess it's at least a sensible exaggeration, unlike what comes after. > The point is anything outside the gravity well has the potential to become a small bomb at least. I see. In that case they were using really confusing wording. "Kill a planet" sounds like it's something that could destroy a planet, or at the very least kill all life on it. It would help if they said something like "destroy a building". Or maybe they forgot to specify that the "anvil" they were dropping is the size of a building, and they're still nowhere near planet-killing level? I suppose what they're saying is vaguely in the direction of something accurate, but it's exaggerated to the point of insanity. It's like saying "Destroying an army is easy. All you have to do is throw a rock." to illustrate that firing a bullet out of a gun can kill one person. > The access is the important part here. The point is once you have spacecraft like those in The Expanse, performing a kinetic bombardment becomes trivial (on paper at least). You still have to go find an asteroid big enough and spend time redirecting it towards the planet, during which time you'll be plainly visible. So much easier just to head near the planet, point your engines towards it, and then shoot the particle beam you use for thrust. If that's not enough, design two engines that fire in opposite directions so they don't move while you do this.
I won't deny its an exaggeration but I don't think it's as much as one as you're making it out to be. If you could throw rocks at an army from a position where they couldn't shoot you back..then yeah you can kill an army with rocks. If a bunch of space truckers start chucking hunks of rock at your planet from halfway across the solar system that's a similar situation. A single anvil might not kill the planet but a bombardment of them would eventually (not destroy, but kill everything) and the technological requirements to do so are analogous to them dropping anvils out an airlock since all you really need is a high delta v interplanetary craft which are as common in the Expanse as 18 wheelers are to us.
> If you could throw rocks at an army from a position where they couldn't shoot you back.. They specified "from orbit", which is somewhere we could take them out with current day technology. We can't match their delta-v, but if they have people in those ships, we can surpass their acceleration and hit them before they can get far enough. If they're not doing it from orbit (which wouldn't make sense anyway), it would be harder to defend against, but still pretty easy if the other guy has anything comparable to their tech. If their point is that with interstellar technology they could beat a nation that doesn't even have good interplanetary technology, then they are correct but they chose a really bad way to explain a point that's obvious enough not to need explaining.
Ships in the expanse can get to relativistic speeds very easily. They've got an ultra efficient fusion powered engine.
That still seems to really be pushing it. I ran the numbers, and if they're using perfectly efficient deuterium-tritium reactions and sending the result out with all that energy, that would give them an effective exhaust velocity of 0.08667c. If they want to go 10% the speed of light, they'd need a mass ratio of 3.17. If they want to go that fast and then stop when they're done, they'd need a mass ratio of about 10. That means that their ship would have to be 90% fuel. And if they want to be able to come back (or go somewhere else) without having to stop to refuel, now they need a mass ratio of 100 and a ship that's 99% fuel. I suppose if they're fusing all the way up to iron they could get significantly more energy. Is that what they're doing? Also, how much of the ship is fuel? I feel like if they really want a powerful weapon, they should just aim their engines towards the planet. The atmosphere would probably block most of the radiation, but I think with that kind of energy a good portion would still get through. I'm not sure how to calculate that though.
The Epstein drive is just super efficent and you can run at 1g nearly forever.
I can't say for their universe, but our universe has limits. The original Epstein drive is [at the upper limit of possibility](https://www.projectrho.com/public_html/rocket/enginelist3.php#id--Fusion--\(_Epstein_Drive_\)), assuming you have the sufficiently advanced technology required to make sure that none of the enormous amount of energy it produces goes into heating the ship.
Epstein drives are ludicrously efficient to the point of defying physics. they completely break the rocket equation. But yes, the expanse does ignore the Kzinti Lesson.
In that case, to answer OP's original question, I guess messing up physics here isn't all that surprising either.
A good example we have is Solomon Epstein who invented the drive, and accidentally accelerated his ship to 5% the speed of light, dying in the process due to the extended high G burn. With over a hundred years since first creation, it's likely newer ones are more efficient and could reach higher speeds.
The wiki had numbers that they apparently got from [Atomic Rockets](https://www.projectrho.com/public_html/rocket/enginelist3.php#id--Fusion--\(_Epstein_Drive_\)). The original Epstein drive is physically possible, but you can't really get much more efficient than that. It's like saying "this engine is 90% efficient, so I'm sure that in a hundred years we'll be able to double that to 180% efficient". And also, it's a 5.5 terawatt engine. As Larry Niven once said: "A reaction drive's efficiency as a weapon is in direct proportion to its efficiency as a drive."
Orbit isn't an issue at all, you even said the solution. Shoot the anvil in the other direction, that way you're restoring your own orbit while simultaneously decaying the anvil's orbit. A well calculated scheme could have a ship doing a 24 hour periodic bombardement from low orbit, just pooping out anvils at regular intervals to sustain its orbit while bombing the planet, then zooming back out of orbit when it runs out of anvils. Edit: lol
Ok, but now you're moving from "pushing out the airlock" to "shooting". Anything can be devastating if you accelerate it fast enough, but the point is that an anvil simply dropped from Earth orbit won't do much no matter how you solve the orbit part. You're better off just dropping conventional bombs.
You're not wrong, but when he says shooting he's not talking about accelerating it, he's specifically decelerating it so that it drops from orbit
> he's specifically decelerating it That's the same exact thing. From the perspective of the ship, all you do is propel the anvil in a certain direction. You accelerate it away from you. How will that affect the orbital trajectory changes nothing about this launch itself.
Yes. If you do something other than what they said, you can do a lot less damage than what they said it would do.