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I saw that there are many questions about how a lunar colony would defend itself. But in the not so near future the lunar colony might be stronger than Earth. They may have even suffered from attacks and oppression from Earth. They have easy access to space, they have more satellites, they control the heavens.

Why not fight back? Or at least make a power demonstration and declare independence?

Assume both parties have access to a nearly unlimited source of energy, either fusion reactors or large solar arrays orbiting around the Sun, and assume that both parties are capable of assembling spaceships in space, and have permanent bases in space, but the lunar colony dominates space industry. Earth is strong, united and arrogant, and believes strongly in its own superiority.

Mars is already settled, but weak, and depends on the space technology of the Moon, and the terraforming expertise of the Earth, and wants to remain neutral.

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    $\begingroup$ The moon has a huge dependency on Earth to supply it with vital resources like Oxygen and Water. Why would they declare independence when they cannot possible survive without Earths assistance. It would be like Hong Kong declaring independence from China. But there are no external countries at all to assist. $\endgroup$ – Shadowzee Jul 31 at 0:50
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    $\begingroup$ I disagree with Shadowzee's assessment. The moon has plenty of water to make O2 and rocket fuel to-boot. Independence of the glorious Selenite republic is inevitable. I suspect that the question is answerable - if a bit broad and opinion based. $\endgroup$ – We are Monica. Jul 31 at 0:54
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    $\begingroup$ Why would a lunar colony attack Earth? A single missile would destroy the colony, while dozens of missiles hitting Earth would have little significant effect (except of course for the people it landed on). $\endgroup$ – Ray Butterworth Jul 31 at 0:55
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    $\begingroup$ Possible duplicate of How would a lunar colony defend itself against aggression from Earth? $\endgroup$ – StephenG Jul 31 at 2:29
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    $\begingroup$ You might like Heinlein's The Moon is a Harsh Mistress $\endgroup$ – dot_Sp0T Jul 31 at 4:17

11 Answers 11

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The Art of War is about defeating the enemy
The Science of War is about not defeating yourself.

DON'T throw rocks at Earth cities. It's probably counterproductive. Every city you vaporize will harden the Earthies' resolve, make them more willing to sacrifice for the war effort, and more willing support absolutists who want every Loonie dead.

Instead, use Earth's gravity well against it in a very different way: Smash Earth's power in space -- its space fleet. Confine the Earthies to the surface, and make them fight their way up through their own atmosphere to return to space. Then prevent them from building another fleet in orbit. Capture or destroy the supporting orbital industries, platforms, habitats, and bases.

Avoid mass casualties of non-combatants. It makes the Loonies look like jerks...and like evil enemies who are worth fighting. Do not destroy non-combatant outposts, though you can require them to be abandoned and/or mothballed. Do not steal Earthie property.

Use propaganda mercilessly. It's cheap and can be very effective.

Treat prisoners humanely, and allow Martian representatives to inspect their captivity. Do not use prisoners for propaganda purposes (that tends to backfire).

Remember that the end goal should be a signed-and-ratified peace treaty...unless you unwisely intend to exterminate all the Earthies (that doesn't look good in the history books). The military, political, propaganda, economic, and other efforts must be synchronized toward this goal. Each Line of Effort should have metrics to gauge progress toward the goal.

A lasting treaty requires trust and good faith, and should not punish either side. So don't squander good faith by massacring scientists on that space-telescope. Simply have them mothball it, then evict them back to Earth in their own (fully functional) lifeboat.

After peace is signed, expect Earth to return to space with Lunar cooperation, so your officers need to carefully record where they placed all those space-mines because they need to go back and recover each and every one.

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    $\begingroup$ In addition to neutralizing their ability to travel into space, I would also recommend taking control of all orbiting satellites. This would sever their ability to communicate effectively, while also seizing control of most forms of broadcast, which would help you spread your propaganda. $\endgroup$ – R. McMillan Jul 31 at 11:26
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    $\begingroup$ Well said! I'd actually go a step further: Don't go to war at all. Lunar colonies -- any space habitats -- are terribly vulnerable and modern weaponry doesn't miss. Unless the Earth was utterly supine in the years leading up and made no attempt to re-arm itself, the cost to the Earth to cripple the Moon is a tiny, tiny fraction of the cost for the Moon to cripple the Earth. Gravity wells are and very fine, but there won't be a big Lunar enterprise without much, much better access to space than we have now. It's much better to compete peacefully. $\endgroup$ – Mark Olson Jul 31 at 11:43
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    $\begingroup$ The history books always look fine when you're the one writing them. $\endgroup$ – chrylis -on strike- Jul 31 at 17:31
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    $\begingroup$ You make a number of claims which are inconsistent with our own Terran wars' actions and outcomes. Not the least is the claim that making nice after surrender will eliminate Terrans' desire to regroup and fight back 50 or 100 years later. $\endgroup$ – Carl Witthoft Jul 31 at 18:36
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    $\begingroup$ Space mines are stupid. Having a record where you put them just makes the record a point of vulnerability. Don't do mines. Especially over hundred million cubic kilometers of orbit. $\endgroup$ – Mindwin Aug 1 at 12:16
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By throwing rocks at them.

In terms of general war strategy, user535722 is right and you should go vote for his answer because from a strategic perspective it's correct. But, the OP hasn't asked how the Moon might prosecute a war; it's asked how it would attack the earth. From that perspective I still believe this is the right answer. Ultimately it all hinges on your interpretation of the word attack. For those of you who interpret it as striking at an enemy rather than prosecuting a war, I offer you this description of how to do it.

This might sound rather primitive, but from a lunar base it's actually a really good strategy if you want to attack Earth. It's not even a new idea; Robert Heinlein came up with it in The Moon is a Harsh Mistress before we'd even reached the moon.

Put simply, Lunar gravity is sufficiently low that it doesn't take anywhere near the energy to get things out of the Lunar gravity well as it does to get things out of the Earth's gravity well. Just look at the lunar landers of the Apollo missions by comparison to the Saturn V rockets, and you'll see what I mean. On top of that, the Earth's gravity in this instance actually works against itself by attracting the rocks for you. All you have to do is get them off the Lunar surface and headed towards the Earth.

Ultimately, this is a poor colony's mass driver system. You're creating a massive amount of kinetic energy just by launching the rock and pushing it towards the Earth, where the gravity well does your job for you. Rocks the size of a few tens (of thousands) of tonnes should release enough energy on impact that it could easily take out smaller cities, and the impact blast may well be equivalent to a small nuclear strike. Get one that is a few hundred (thousand) tonnes aimed at a major city, and not only will it destroy that city, but a few of them in concert could bring about a non-nuclear winter through dust in the atmosphere.

In theory, you could blow up these rocks if you saw them coming soon enough, but that's a tricky affair. If your pieces are still large enough, you spread the kinetic energy over a larger area and still do at least some damage. Earth would need to think about using its nuclear arsenal of ICBMs as a point defense solution, and that means detonating a large number of nuclear devices above the earth. (I'm pretty sure modern ICBMs can't reach escape velocity to intercept the missiles closer to the Moon.)

As solutions go, it's primitive to be sure but given the cost of getting things out of the Earth's gravity well, the moon is actually in a far more advantageous position than the Earth when it comes to offensive weapons, and therefore can afford to go low tech. Defensively, it would be another matter as the habitats on a lunar colony would be sufficiently fragile that a single glancing hit from the Earth could do a massive amount of damage. All in all, the moon has great DPS1 but is hopeless at tanking.


1. I didn't know what DPS was first time I heard it but it's common enough in gaming parlance so as to have entered my mainstream acronym list. It stands for Damage Per Second, and generally deals with the rate of damage that a specific person can deal within a game. Tanking is another gaming term which relates to the rate at which a specific person an absorb damage before they start losing their own health.

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  • $\begingroup$ Place the colonies on the far side of the moon. Lava tunnels might help hide/ protect the cities also. SDI in lunar orbit to help defense $\endgroup$ – Michael Kutz Jul 31 at 1:25
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    $\begingroup$ "great DPS"?? This means what? When people use acronyms you can use bog-standard acronyms like ICBM which is fine. But when a less common acronym like DPS is used, don't expect everyone to know it. While I could google it, I shouldn't have to, because I've had to do it more often than I care for. Recovering from a bad dose of flu helps one being grumpy. $\endgroup$ – a4android Jul 31 at 2:39
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    $\begingroup$ "A few tens of tons" wouldn't be enough. The Chelyabinsk meteor was around 12,000 tons, and didn't quite flatten a city. $\endgroup$ – Mark Jul 31 at 2:43
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    $\begingroup$ @a4android noted, and updated with a footnote. $\endgroup$ – Tim B II Jul 31 at 3:04
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    $\begingroup$ An important factor not mentioned in the answer: Luna's lack of atmosphere and smaller size makes it comparatively very easy to throw rocks at very high speeds into Earth: any tank-sized railgun can achieve escape velocity of a mere 2.4km/s, while hitting the Moon from Earth bascially requires you to lift the gun into orbit first and then the projectiles will still be slowed down more by gravity. $\endgroup$ – Michael Borgwardt Aug 1 at 12:52
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Weaponized Kessler Syndrome

This is a specific method of denying space to a planet.

If Luna pollutes LEO with enough debris, it would become difficult to impossible for Earth to launch anything into space without Luna's help. Earth would have to successfully run the blockade of debris to reach higher orbit, and then fight through Luna ships that are undamaged and have the kinetic advantage.

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    $\begingroup$ Actually Earth is already doing quite a job pulluting LEO. The simple threat of making things worse, would be enough to keep Earth on check. On the other hand, if Moon would offer to help cleaning LEO, they could avoid war, be the good guys, and get there independence. $\endgroup$ – pintergabor Aug 1 at 12:34
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The Moon is a harsh Mistress.

Luna sits on the top of our gravity well. With a little nudge you can push boulders down that well. But trowing them back is a lot harder. (about 10 times)

But with the levels of tech you are describing, most of the war will be digital and online. And as Luna is depending on live support systems, Earth might have a upper hand there, as more people is likely to have more programmers to disrupt things from afar.

And unless you have faster then light, Mars is to far way to matter as modern wars are very fast.

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  • $\begingroup$ “But with the levels of tech you are describing, most of the war will be digital and online.” Why? Unlike “physical” systems a digital system can be 100% secure (simply because the inputs are limited). $\endgroup$ – Michael Aug 1 at 11:27
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    $\begingroup$ @Michael if you look into what the USA and China expect the next war against a modern and well equipped enemy to be, there is less focus on conventional arms and more on the things you can do online. War is politics by force. If you can disrupt or disable your enemy by online means you are one step ahead in the game. Lastly, you very much over under estimate the vulnerability of digital systems. Please see this: timesofisrael.com/… $\endgroup$ – Flummox - don't be evil SE Aug 1 at 11:50
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    $\begingroup$ The whole cyber war thing seems more like a buzzword than an actual threat. Just don’t connect your power grid or nuclear missiles to the internet. And don’t allow USB drives in your uranium centrifuge facility. $\endgroup$ – Michael Aug 1 at 16:04
  • $\begingroup$ @Flummox that's because it's relatively cheap and China already has the upper hand as the US military and civilian infrastructure depends in large part on electronics supplied by China, with suspected backdoors already built in by the factories. $\endgroup$ – jwenting Aug 2 at 5:10
  • $\begingroup$ @jwenting Enemy backdoors are one thing the USA military will be on the lookout for. We shall see. $\endgroup$ – Flummox - don't be evil SE Aug 2 at 6:59
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How do you want to do things?

There are several ways depending on how aggressive you want to be. If the goal is destruction of entire states or even countries then yes, throwing rocks is probably the most efficient way. If you want targeted elimination, there are many more options. The classic nuclear strike, using a giant lens to focus light in a tight beam, or even use their space fleet to go head to head with whatever space force Earth has(keeping in mind the Earth fleet has probably burned most of their fuel getting to orbit).

Of course, there is one more way - totally impractical, but totally awesome. Send the entire lunar population to orbit in safe space stations or ships. Then, use either a new or existing(but massively upscaled) mass driver to do something like this "big enough rock" story - https://www.reddit.com/r/HFY/comments/8r5v3u/text_a_big_enough_rock/. You use the mass driver with part of the Moon as propellant to deorbit Luna, crashing it into Earth and triggering the extinction of all life. I haven't done the math but pretty sure this could work. Then resettle the Lunar community on NEOs, moons of Mars, and other nearby low gravity worlds. That is probably the most Kerbal, and awesome, solution.

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  • $\begingroup$ I just checked the delta v requirements for deorbiting - canceling out(or not even so if taking an "aeroBREAK" path through the upper atmosphere) all its velocity would take ~1 km/s delta V. This is definitely achievable with an Isp of ~10k seconds and uses only ~1 percent of the mass of the Moon. $\endgroup$ – Lelu Aug 1 at 10:21
  • $\begingroup$ I'm pretty sure that you'd have far easier ways to sterilize the surface of the Earth long before you can harness that much energy. $\endgroup$ – Michael Borgwardt Aug 1 at 12:56
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It's time for the Naturalists / Conservatives / Rusting Earthlings to cede the future of the human race to Spacers

  • Earthlings have long marched about with a regal arrogance, assuming they are the natural leaders of the universe. The Europeans colonized the Aztecs, the Native Americans, the Africans. The French trampled over Vietnam, the English over India. Time and time again, Earthlings have demonstrated a total lack of respect for the natives of established civilizations. Once again they seek to trample all over the culture and rights of a human society, that of the Spacers, with no regard for our traditions or our way of life.

  • Earth was beautiful, and the Earthlings pillaged that beauty (and forced our ancestors into space in the process). Earthlings have proven they don't have the responsibility necessary to handle managing a highly elastic global ecosystem, let alone the highly controlled and vulnerable artificial ecosystem of terraformed Mars or extremely vulnerable artificial dome ecosystem of Luna. How many more planets will we let Earthlings ravage for its resources, destabilizing ecosystems in the process?

  • Earth is a place of anti-intellectualism and radically superstitious people. Our ancestors, all scientists, were forced to flee in the face of persecution for the crime of Speaking Truth. Do we want these Superstitious, Radical Earthlings dictating our social policies? As soon as we left Earth, our technological advances exponentially increased. Should we allow Earth to once again attempt to drag us into the dark ages?

Luna and our ally Mars just want to be left well enough alone. Earth may do as she pleases (and has pleased) to her own scorched planet, why must she always attempt to control all of humanity? It's time for us Spacers to move on, welcoming any Earthlings that wish to join us in our New Vision for Humanity, one free of ecological destruction, anti-intellectual superstition, and cultural hegemony.


If the Moon is truly independent, there is nothing to be gained by out and out war with Earth. The best alternative is to completely shake the specter of Earthling bureaucracy from the Moon and Mars - leave to Spacers the business of Spacers. Initiate a massive propaganda campaign before simply stopping shipment of goods (taxes) back to Earth. Transfer ownership of all space vessels to Lunar command structures, politely and firmly uninviting any Earth-sympathizers off the ships. Continue to disparage Earth as a violent Colonizer type entity, thus confirming for everyone this is true if Earth ever tries to bring the Moon back under control of Earth bureaucracy.

And if the earth does try to take the moon back, detonate a couple hundred thousand tons of moon rock in orbit around Earth, thus trapping Earthlings on the surface for a couple hundred thousand years.

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I guess throwing rocks is the big thing, but it's a little bit... inelegant. For starters it's not very precise and you end up wasting a lot of 'innocent' people without necessarily hitting strategic targets. If you're just after a lot of carnage then I guess that's OK.

The main advantage that the Moon has in this war is the small gravity well. You can get off the Moon a lot easier, and that means you can put much more massive objects into Earth orbit than Earth can. You also don't have to worry about atmospheric pollutants from your rocket exhaust or atmospheric drag, which is nice. And no atmosphere also means you don't have to worry about streamlining your designs.

So what else could we launch from Luna that would be better than rocks?

How about dozens or hundreds of Kinetic Bombardment platforms?

These things are nasty. Take a bunch of tungsten rods, say a hundred kilograms or so each. Load them into firing tubes with carefully calibrated charges to allow you to deorbit them onto a ground target. Put say 50 of them into a smallish satellite and launch it into orbit. Repeat as many times as you like.

The beauty of these little Rods from God is that they hit the ground like tactical nukes, with none of the radiation effects. Aiming is a bit of a problem, what with the messy atmosphere to go through, but when you're firing 10 or 50 of these things into a very small area you can adjust pretty well. And the area is small. These things are tactical as hell, the only thing stopping them from being surgical is the atmosphere being unpredictable.

RfG bombardment could be targeted on very small areas. Like launch facilities. Deny space to your opponents and they're out of the war.

But that's not the worst thing you can do with these nasty little buggers. What happens when you fire all of your RfG payload into LEO and let them orbit? You end up with Kessler Syndrome's big brother. Not only do you scrub LEO free of any functioning satellite system, you have effective screened off the Earth from space. You can't go there, but they can't come out to hurt you anymore. 50,000 or so scattered in various orbits around the Earth would be enough I think.

Of course they aren't going to stay up there forever. Eventually orbital decay is going to bring them down, and there's no way to figure out where. And once they're all down there's not going to be much left of the surface. Perhaps this isn't the nicest approach?

But since we're throwing 'nice' out the window anyway - we're at war, after all, so we can apparently justify any atrocity - why not make a few thousand concrete bombs and use them to wipe out all the military assets you can reach. They're little more than the rocks everyone else wants to throw, but they are steerable so you're more likely to get the target you wanted. Deorbit into the general area, then steer down to the target. Kinetic bombardment with increased accuracy. And you can make them as big as you like, so taking out entire cities... um, I mean military bases will be easy.

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I am quite happy that I have stirred up such a lively discussion. Originally I just wanted to make a contrasting question to the "how the Lunar colony would defend itself" type questions, and make people think differently, and I was really interested in the answers.

Once the Lunar colony reaches energy independence and dominates space, it will be very strong. It may be in position to threaten Earth, or even better, it may be able to demonstrate its power in a peaceful way. Moving dangerous asteroids out of the way, or cleaning up space debris would make it clear to everyone, that if someone is capable of this, it would be capable of the opposite too.

In medieval times the outcome of battles was often decided by who owned the high ground. I think something similar is going to happen in the future. Space is really high up. And the Moon is an excellent place to build a castle. In medieval times sometimes the mere existence of the castle was enough to ensure peace in the surrounding land. I hope it will be the same in the future too.

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An attack serves a (at least imaginary) purpose. Yours is a power demonstration. So maximise that effect while minimizing other outcomes.

You have the superior deep space observatories, you have the superior space tech. Go hunt for an asteroid that will miss earth by X. Covertly send rockpushers up there. On a big public earth event have your diplomats unveil a string of numbers. Those are the ephemera of some big earth space installation, that is blown to bits by the retargeted asteroid the next day. An asteroid, mind, that would have laid a smallish city to waste. That is power. You just demonstrated it.

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Threaten to attack Earth's climate (but please don't actually do it)

The people of the moon would not suffer if the climate on Earth deteriorates, but the people of Earth would.

Terraforming technology may be present, but I suspect that damaging the climate would (still) be much easier than preventing damage to it (how exactly the climate could be attacked, I will leave to you, but feel free to take inspiration from all the experience we already have in ruining the climate); Furthermore to damage the climate the people of the moon would just need to be able to hit the planet -- which is a much bigger target than individual cities -- thus making it very hard for Earth to defend itself (unless they can prevent any lunar spaceships or projectiles from entering the atmosphere, but that would ruin the whole premise of the question.)

So it would likely be possible for the people of the moon to either render earth near uninhabitable or at the very least cause significant damage to the ecosystems on earth -- which, depending on the infrastructure on earth, may also severely damage the agricultural industry on earth.

The threat of mass extinction of the life on Earth -- and possibly a global famine -- will hopefully be enough to cause the people of Earth to surrender on favorable terms.

First, the people of the moon will, however, have to prove their capability to destroy the climate and their intention to do so if their terms arent met. Especially the latter will properly be extremely difficult, as the people of the moon most likely don't want to cause a mass extinction event on Earth, a possible way around this is for the people of the moon to set up some sort of automated "doomsday device" to trigger the attack on earth climate (see for instance https://philosocopter.com/news/2018/11/28/how-to-build-a-doomsday-device).

It should be mentioned that this answer doesn't work if the earth is already uninhabitable, or if the moon is dependent on agricultural imports from the earth.

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The "throwing rocks" meme (popularized by Heinlein) is mentioned here a lot, stating that you just need to exit the moon's gravity well for causing damage. That's misunderstanding the problem. The moon is not hanging by wire from the sky, it is orbiting Earth. So is anything on it. To get something to deorbit Earth, you need a very large change of impulse and the only feasible way to do that is redirection with a slingshot maneuver employing the moon itself. That requires strategically timed changes in impulse so you cannot just use unpowered rocks. It also requires a lot of time.

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    $\begingroup$ Funny thing is, Heinlein actually explained that part. +1 $\endgroup$ – Mad Physicist Jul 31 at 14:08
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    $\begingroup$ There are two major mistakes in this post. First, if you're in orbit around the Moon, you can't perform a gravity slingshot using the Moon -- a slingshot is inherently a gravitationally-unbound three-body maneuver. Second, the delta-V requirements for an Earth impact are only 47% higher than the requirements for getting into Lunar orbit in the first place. If you throw your rocks from the right place in the right direction, they don't need to be powered. $\endgroup$ – Mark Jul 31 at 22:22

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