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Old 10-19-2019, 04:30 PM
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Lunar combat


After watching the scene in Ad Astra, where there’s some combat on the lunar surface, I started wondering what sort of weapons would be better optimized for that environment than the old gun/bullet combination. So imagine you’re in your moon buggy, being chased around the craters by bandits. They are in faster moon buggies (don’t ask me why they’ve resorted to stealing when they can afford space suits, multiple high-performance buggies, and moon lodging). They care not for your life. What hand-carried weapon do you want to keep on the gun rack mounted behind your seat?

What I’ve come up with is just a variation on the gun and bullet. It doesn’t need to be a powerful round, because there’s no atmospheric drag. It would be more like a shotgun shell with dozens of tiny sharp needles instead of pellets, intended to rip multiple holes in a space suit. The gun will need a scope, because these bullets will carry a long ways.

Better ideas? Criticism?
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Old 10-19-2019, 04:42 PM
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You would still need to penetrate the spacesuit and hit the person inside, as a suit rupture wouldn't necessarily immediately incapacitate attackers. A conventional armor-piercing round would still likely be used.
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Old 10-19-2019, 05:17 PM
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Kind of like a miniature shrapnel, loaded with poisoned darts?
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Old 10-19-2019, 05:39 PM
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It occurred to me...if being shot by a firearm in the vaccuum of space becomes more and more of a thing, so will projectile resistant space suits.

Where a bullet could poke a hole in a suit, a layer of thick liquid rubber could suddenly extrude from an intermediate layer within and seal the breach, preventing asphyxiation.

In turn, "bullets" made of white phosphorous could be shot, igniting an unquenchable fire within the oxygen-rich atmosphere inside the suit.
(ouch)
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Old 10-19-2019, 05:41 PM
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What's wrong with regular old gun and bullets? They work fine, they're cheap and light. Hand grenades, too.
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Old 10-19-2019, 05:46 PM
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What's wrong with regular old gun and bullets? They work fine, they're cheap and light. Hand grenades, too.
I agree. It's not because the environment is different that it's sufficiently different to make guns & bullets less than the optimal option. Some minor characteristics like muzzle velocity, caliber, weight might be different but it would likely be quite similar on the whole.

It does bring up the question of what combat would even be like in such a situation, presuming that level of technological advancement. It might be as different from our current way of fighting as the US Civil War was to the present.
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Old 10-19-2019, 06:21 PM
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You do need a gun designed for vacuum. A normal gun might overheat due to there being no air to carry away the heat, or fuse solid due to "vacuum welding".
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Old 10-19-2019, 06:38 PM
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You do need a gun designed for vacuum. A normal gun might overheat due to there being no air to carry away the heat, or fuse solid due to "vacuum welding".
I can't comment vacuum welding but concerning the heat, I've heard many seemingly knowledgeable posters say that a lot of it gets radiated out in the IR spectrum where the absence of air isn't as much of a problem.
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Old 10-19-2019, 06:49 PM
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Originally Posted by Capn Carl View Post
What I’ve come up with is just a variation on the gun and bullet. It doesn’t need to be a powerful round, because there’s no atmospheric drag. It would be more like a shotgun shell with dozens of tiny sharp needles instead of pellets, intended to rip multiple holes in a space suit.
Well, strictly speaking, you haven’t come up with that because flechette shotgun shells are already a thing and have been for at least 50 years.

But flechettes are fin-stabilized by the air through which they fly, which obviously wouldn’t apply on the moon. And I agree with your point that, because there’s no air drag, a shotgun blast at 2000 meters on the moon isn’t very much less energetic than it at 10 meters on earth.

If it were me, I’d probably go with the AA-12 shotgun. Its recoil impulse is very, very low and it’s fully automatic. I’d probably use conventional shotgun shells: 00 buckshot might be a good choice. Even if you could stabilize flechettes on the moon, many tiny needle-holes have no advantage over fewer-but-larger ones.

If I can mount something on my buggy, though, I’d probably install a standard 7.62-mm 6000-rounds-per-minute minigun. It would overheat quickly in a vacuum, but until it did, it would be very effective.

ETA: a shotgun would also need a heck of a choke to work at 2000 meters.

Last edited by EdelweissPirate; 10-19-2019 at 06:51 PM.
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Old 10-19-2019, 06:54 PM
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As for vacuum welding, wouldn't that be a non problem as long as the weapon is manufactured in an enviroment that allows some thin layer of oxidation? My understanding was that for it to happen the sufaces have to be extremely clean or the process can't happen
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Old 10-19-2019, 07:01 PM
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I would want a small signal laser to guide munitions delivered from the an orbital defense station.

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Old 10-19-2019, 07:08 PM
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This is Buck Rogers stuff.

Buck Rogers used a rocket pistol.

Therefore, your weapon of choice is a Gyrojet.

Last edited by mbh; 10-19-2019 at 07:09 PM.
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Old 10-19-2019, 07:41 PM
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Kind of like a miniature shrapnel, loaded with poisoned darts?

The old Sci-Fi standard "needle gun" firing needles at a high rate of speed and usually poisoned. I believe air-powered to be the preferred method.
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Old 10-19-2019, 08:44 PM
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It occurred to me...if being shot by a firearm in the vaccuum of space becomes more and more of a thing, so will projectile resistant space suits.

Where a bullet could poke a hole in a suit, a layer of thick liquid rubber could suddenly extrude from an intermediate layer within and seal the breach, preventing asphyxiation.

In turn, "bullets" made of white phosphorous could be shot, igniting an unquenchable fire within the oxygen-rich atmosphere inside the suit.
(ouch)
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Old 10-19-2019, 09:43 PM
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Originally Posted by Cleophus View Post
You would still need to penetrate the spacesuit and hit the person inside, as a suit rupture wouldn't necessarily immediately incapacitate attackers. A conventional armor-piercing round would still likely be used.
Multiple simultaneous suit penetrations might not immediately kill the occupant, but he/she would have to address the leaks, or die.
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Old 10-20-2019, 02:59 AM
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If you're firing Earth-type projectiles on the moon at Earth-like-projectile velocities, be sure you either hit what you're aiming at or keep dodging and weaving. Shooting yourself in the back might not be absolutely the most embarrassing way to die, but it's probably in the conversation.

Last edited by mjmlabs; 10-20-2019 at 03:03 AM.
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Old 10-20-2019, 07:32 AM
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How much do air-resistance and gravity affect a bullet's destructive power? Would a bullet be much more lethal on the moon than on Earth? Would an artillery shell fired on the moon possess so much kinetic energy that it would circumnavigate the moon and reach the spot it was fired from?
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Old 10-20-2019, 08:14 AM
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If you're firing Earth-type projectiles on the moon at Earth-like-projectile velocities, be sure you either hit what you're aiming at or keep dodging and weaving. Shooting yourself in the back might not be absolutely the most embarrassing way to die, but it's probably in the conversation.
The orbital speed is nearly 4000 mph. The fastest rifle bullet is 2000+ mph. No worries.

Even with a special rifle/bullet the aim would have to be perfect and take into account masscons.

Regarding stability and flechettes: the whole point of being long and narrow with a pointy bit is to keep it aerodynamic. Without air, an equivalent roundish weight with with multiple pointy bits would work the same against a regular space suit. You just need mass and points. (Damaging a human would be a bit different. But like expanding bullets, the goal is to tear up a lot of tissue, not zip right through.)
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Old 10-20-2019, 09:00 AM
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No need to be a dick about it, set phasers to stun.
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Old 10-20-2019, 10:25 AM
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No need to be a dick about it, set phasers to stun.
But might those phasers still burn through or otherwise damage sensitive components of the suit, the consequences of which could be fatal?
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Old 10-20-2019, 10:36 AM
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But might those phasers still burn through or otherwise damage sensitive components of the suit, the consequences of which could be fatal?
Phasers set to stun don't kill people, interstellar travelers kill people.
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Old 10-20-2019, 10:45 AM
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You do need a gun designed for vacuum. A normal gun might overheat due to there being no air to carry away the heat, or fuse solid due to "vacuum welding".
Fairly simple engineering changes could fix those things.

In many ways, guns would work BETTER on the Moon. There is no air to slow the bullet down or change its path, and the bullet will drop far, far less in a lower-G environment. There is never fog of weather or atmospheric blockage of any kind to obscure sighting or laser targeting or rangefinding.
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Old 10-20-2019, 12:59 PM
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The orbital speed is nearly 4000 mph. The fastest rifle bullet is 2000+ mph. No worries.
Googling "orbital speed moon" returns 1.022km/s which is about the muzzle velocity of an M-16.



Moon's lower velocity would allow the use of lower velocity ammo; One of the reasons you want high velocity is to get to your target fast so that gravity has less time to lower the projectile. With less gravity, the bullet will drop less in a given amount of time so you could accurately shoot further (6 times?) with the same setup or use much lower velocity rounds.

Would it be common for the curvature of the moon to make a tactical difference? It already does make a significant difference for air, naval and artillery combat but maybe it would become a factor at smaller scales.

Last edited by MichaelEmouse; 10-20-2019 at 01:00 PM.
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Old 10-20-2019, 01:13 PM
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I'd expect to see a lot more good old fashioned shoulder-fired rockets. They won't overheat, and the lack of gravity/atmosphere would allow them to trade off propellant mass for payload mass, probably a huge mass of suit-piercing shapnel.
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Old 10-20-2019, 01:21 PM
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Multiple simultaneous suit penetrations might not immediately kill the occupant, but he/she would have to address the leaks, or die.
But that doesn’t make them stop fighting you. In real life, people can and do continue to fight even when seriously or mortally wounded.

In any case, a spacesuit is more like body armor than a balloon. Both of them consist of multiple layers designed to absorb high kinetic energy impacts. I would also expect these future raiders to wear suits with hard plates much like modern body armor inserts.

Last edited by Cleophus; 10-20-2019 at 01:21 PM.
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Old 10-20-2019, 01:22 PM
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Really though, suits would be so vulnerable that I'd expect more combat from armored wheeled vehicles. Wheels could get very large if they don't need to be solid or inflatable, just large mesh rover-style wheels.
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Old 10-20-2019, 03:54 PM
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I'd expect to see a lot more good old fashioned shoulder-fired rockets. They won't overheat, and the lack of gravity/atmosphere would allow them to trade off propellant mass for payload mass, probably a huge mass of suit-piercing shapnel.

But ------- recoil in low g? You get the (we hope) bad guys and launch yourself to the dark side.
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Old 10-20-2019, 03:58 PM
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But ------- recoil in low g? You get the (we hope) bad guys and launch yourself to the dark side.
No, rockets don't really have much recoil at all. The tubes are open.

That's why we yell "backblast area clear" before we fire them. The tradeoff of not having recoil is having a large burny gas plume shoot out the back.
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Old 10-20-2019, 04:02 PM
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In any case, a spacesuit is more like body armor than a balloon. Both of them consist of multiple layers designed to absorb high kinetic energy impacts. I would also expect these future raiders to wear suits with hard plates much like modern body armor inserts.
Perhaps not only as armor, but as ballast. I’ve seen designs for more flexible/lighter pressure suits than what the Apollo astronauts used. I could see how between a more flexible suit, but weighed down by by armor plating, one could be much more nimble on the moon.

Last edited by ASL v2.0; 10-20-2019 at 04:02 PM. Reason: Abbreviate quote
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Old 10-20-2019, 04:05 PM
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How about an elegant weapon for a more civilized age?
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Old 10-20-2019, 05:21 PM
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Googling "orbital speed moon" returns 1.022km/s ....
... which is the speed at which the moon travels in its orbit of the Earth, not the speed at which a projectile would need to travel in order to orbit the moon.

The values ftg gave, above, are certainly close enough for idle InterWebz Spitballing. I was vastly overestimating the effect a vacuum would have on muzzle velocity (actual effect of removing air resistance from muzzle velocity: "pretty much negligible, although positive and non-zero if you want to get really sticklerish.") Lunar orbit speed is about 1680 m/s, or 1.680 km/s, or ~3760mph. As noted above, the fastest rifle bullet (Remington .17, I'm guessing) is well below that.

[xkcd]"But ... what if we used more power?"[/xkcd]

Well, 1680 m/s is pretty close to the muzzle velocity of a Paris Gun (1640 m/s). Wouldn't have to tweak that WWI-era technology too much in order to literally fire it around the moon.

Getting something the size of a Paris Gun up to the moon seems uneconomic, but who cares about that when we're InterWebz Sci-Fi Spitballing?

Last edited by mjmlabs; 10-20-2019 at 05:24 PM.
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Old 10-20-2019, 05:31 PM
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Changes from conventional firearms you'd need:

a. Dry lubricants since oils will boil in low pressure
b. Design for a greater temperature range - you might need to use modified propellants so they are stable in 200 Celsius lunar daytime. This also may require fancier alloys.
c. Design for vacuum heat dissipation, or just heavier parts so more rounds can be fired before overheating.
d. Armor piercing rounds or bust. Today's spacesuits have some kevlar in them to protect from micrometeorites, this makes pistol caliber and flechette rounds unlikely to even work. So rifle caliber or nothing.
e. Bigger trigger guards, gun cameras instead of sights mounted on the gun, safety levers that can be operated with heavy gloves on - lots of changes.

All these changes might mean the firearm looks hugely different than anything used on earth. But, fundamentally, it's still just a stick that goes bang and shoots speedy chunks of metal. Also, regular guns will work for a few rounds without any of the above changes, you just might have trouble winning a space gunfight against someone equipped with a weapon designed for the environment.

Also, would you actually have human "infantry" in space? It costs a very large amount of money to put anything into space, and it's really hard to keep a human being alive much less get them home from a mission. Since it costs a fortune anyway, any cost advantages of human infantry versus various missiles and drones might be zilch.
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Old 10-20-2019, 05:55 PM
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e. Bigger trigger guards, gun cameras instead of sights mounted on the gun, safety levers that can be operated with heavy gloves on - lots of changes.
Given the glove/trigger problem, it might be easier to have it remotely controlled. The shooter might say "Alexa, fire a round ... now."
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Old 10-20-2019, 07:11 PM
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No, rockets don't really have much recoil at all. The tubes are open.

That's why we yell "backblast area clear" before we fire them. The tradeoff of not having recoil is having a large burny gas plume shoot out the back.
You're probably, almost certainly, right. I've only done a couple LAWS and ------ I'm still having a problem seeing me shooting one off in lunar g. Wouldn't really want to crack off my M1 either though.
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Old 10-20-2019, 07:30 PM
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All these changes might mean the firearm looks hugely different than anything used on earth. But, fundamentally, it's still just a stick that goes bang and shoots speedy chunks of metal. Also, regular guns will work for a few rounds without any of the above changes, you just might have trouble winning a space gunfight against someone equipped with a weapon designed for the environment.
Good points. The other difference is that anything that can take out a suit at close range is still lethal out to the horizon (and even slightly over the horizon if you get your trajectory right). Probably affects tactics more than the weapons, but you'd want any gun to have long-range targeting ability. So lots of bipods,etc. maybe even fancy auto-stabilizing devices (since the extra weight doesn't matter as much)
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Old 10-20-2019, 07:57 PM
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Good points. The other difference is that anything that can take out a suit at close range is still lethal out to the horizon (and even slightly over the horizon if you get your trajectory right). Probably affects tactics more than the weapons, but you'd want any gun to have long-range targeting ability. So lots of bipods,etc. maybe even fancy auto-stabilizing devices (since the extra weight doesn't matter as much)
That's why I suggest that vehicles are going to be a lot more important than suits. Picture turtle-like vehicles with enormous wire-mesh wheels. They'll be prone to flipping, so they'll be armed and armored to fight upside down.

If we actually need to get troops in the base, then the vehicle will be the armor, the suits will be minimal. It will be motorized infantry tactics; get the troops as close as possible to the enemy base. They will fight hand to hand to avoid breaching the hull, because everybody dies if the hull is breached.

More likely it would be an artillery duel though.
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Old 10-20-2019, 08:21 PM
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More likely it would be an artillery duel though.
That or other smart weapons.

Think about what it means to send a single infantryman. You are sending the mass of the soldier, hundreds of kgs in equipment, life support equipment, you must have some sort of plan to bring them home or medevac them if they get injured.

Or you send 50 small missiles.

On earth, infantry is the thing powers will resort to partly for cost reasons. You can just draft someone, they need in USD about 30k in training and pay to be a basic infantry soldier, with a few thousand dollars of equipment. Equipment that will usually survive the death of the soldier.

Each BMT is 10 million dollars, a modern jet fighter is about 100 million just for the plane. And training is much longer in time and also proportionally more expensive - it costs a lot more to qualify in an Abrams than it costs to qualify with a rifle.

In space, each soldier is far, far more expensive and the same mass can go to a one-way trip robot weapon, whatever is appropriate.

Last edited by SamuelA; 10-20-2019 at 08:22 PM.
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Old 10-20-2019, 08:25 PM
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If we actually need to get troops in the base, then the vehicle will be the armor, the suits will be minimal. It will be motorized infantry tactics; get the troops as close as possible to the enemy base. They will fight hand to hand to avoid breaching the hull, because everybody dies if the hull is breached.

More likely it would be an artillery duel though.
See, I think part of space combat would necessarily include donning pressure suits and depressurizing any structures or vehicles for just that reason. Because giving everyone a pressure suit and oxygen is nothing compared to the cost of getting into space to fight a war to begin with. And if the risk of a hull breach is so obviously catastrophic*, then it stands to reason they’d do more to avoid it, and seek to hobble themselves less, than limit themselves to fighting with spears, particularly when the enemy is probably happy to stand outside and drop a refrigerator on them from orbit before they even know they’re there.

I also think surprise attacks with remotely controlled precision weapons will be the norm. They’re kind of getting that way now.

*As an aside, this kind of "if it would be intuitively obvious to even a casual viewer with a modicum of sense that something can be done a certain way and result in wildly disproportionate damage to the enemy, then there had better be a damned good reason—even if not explicitly stated—why it’s never been done in universe before. If it suddenly is done, that undermines the entire universe" dilemma is why I hate the Holdo maneuver, post-hoc rationalizations in secondary media notwithstanding.

Last edited by ASL v2.0; 10-20-2019 at 08:30 PM.
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Old 10-20-2019, 08:44 PM
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Yeah, I just can't really see people fighting on the moon. What's the military objective?

If country A doesn't like the fact that country B holds certain places on the moon, it would probably be cheaper and easier to bombard it from earth than to maneuver on it from the actual moon.

If country A wants to steal moon stuff from country B, then they would probably maneuver into a position where they could cut power/depressurize/isolate them logistically and wait for them to die.
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Old 10-20-2019, 09:47 PM
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Good points. The other difference is that anything that can take out a suit at close range is still lethal out to the horizon (and even slightly over the horizon if you get your trajectory right). Probably affects tactics more than the weapons, but you'd want any gun to have long-range targeting ability. So lots of bipods,etc. maybe even fancy auto-stabilizing devices (since the extra weight doesn't matter as much)
The weight may be the greatest difference. Normally, soldiers carry about 1/2 to 1/1 of their weight, preferably 1/3. On the moon, a 150lbs soldier who normally has a combat load of 50lbs could use 300lbs. They might end up looking like space marines.


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... which is the speed at which the moon travels in its orbit of the Earth, not the speed at which a projectile would need to travel in order to orbit the moon.

The values ftg gave, above, are certainly close enough for idle InterWebz Spitballing. I was vastly overestimating the effect a vacuum would have on muzzle velocity (actual effect of removing air resistance from muzzle velocity: "pretty much negligible, although positive and non-zero if you want to get really sticklerish.") Lunar orbit speed is about 1680 m/s, or 1.680 km/s, or ~3760mph. As noted above, the fastest rifle bullet (Remington .17, I'm guessing) is well below that.

[xkcd]"But ... what if we used more power?"[/xkcd]

Well, 1680 m/s is pretty close to the muzzle velocity of a Paris Gun (1640 m/s). Wouldn't have to tweak that WWI-era technology too much in order to literally fire it around the moon.

Getting something the size of a Paris Gun up to the moon seems uneconomic, but who cares about that when we're InterWebz Sci-Fi Spitballing?
Thanks for the correction.

In such an environment, would guns or rockets tend to make more sense? One of the things that hampers guns is that their highest velocity tends to occur in a high air density zone which slows them down. In space, you don't have to worry about air resistance or winds messing up your range or accuracy.
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Old 10-20-2019, 10:01 PM
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In such an environment, would guns or rockets tend to make more sense? One of the things that hampers guns is that their highest velocity tends to occur in a high air density zone which slows them down. In space, you don't have to worry about air resistance or winds messing up your range or accuracy.
Rockets. Gyrojet sized bullets, probably with guidance systems. Reason: less heating of the gun barrel (hard to shed the heat in vacuum), less recoil. Also more efficient flight - the bullet could cant over more like a spacecraft and apply it's velocity vector more optimally.

But on the other hand, it just might be easier, for decades, to start with a far better developed form of weapons technology - conventional firearms - and modify them to work in space, than to more or less start over with rocket ammo.

Last edited by SamuelA; 10-20-2019 at 10:02 PM.
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Old 10-20-2019, 10:19 PM
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Originally Posted by HMS Irruncible View Post
Yeah, I just can't really see people fighting on the moon. What's the military objective?

If country A doesn't like the fact that country B holds certain places on the moon, it would probably be cheaper and easier to bombard it from earth than to maneuver on it from the actual moon.

If country A wants to steal moon stuff from country B, then they would probably maneuver into a position where they could cut power/depressurize/isolate them logistically and wait for them to die.
I should think if you want to avoid consequences back on Earth, the trick would be to arrange for some industrial sabotage on the level of a catastrophic "accident" that makes, say, a country or corporation’s base of operations for a mining operation untenable, to the extent that they’d have to dump a whole lot more capital onto the moon to make it profitable again, thereby encouraging them to sell it off to the saboteur (who would presumably already be in a position to exploit said mine at a discount).

Or something like that.

But, yeah, open combat on the moon makes little sense, unless it's coupled to a wider campaign back on Earth. Which, I guess, isn’t completely out sigue realm of possibility.

Last edited by ASL v2.0; 10-20-2019 at 10:20 PM.
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Old 10-21-2019, 07:01 AM
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Originally Posted by HMS Irruncible View Post
Yeah, I just can't really see people fighting on the moon. What's the military objective?
Wars have been fought on earth over oil; on the moon, maybe cheese?
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Old 10-21-2019, 10:08 AM
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Wars have been fought on earth over oil; on the moon, maybe cheese?
You know, I could see a niche market developing for genuine lunar cheese if a lunar economy ever takes hold. I imagine it wouldn’t be anything special, but would be more in line with the branding that comes with, say, Champagne vs. wine that is merely sparkling and produced in other regions of France or, god forbid, Cal-i-for-nay-yay.
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Old 10-21-2019, 10:54 AM
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There was a Cold War-era short story in which US and Soviet troops got into a gun battle on the lunar surface. The rounds which didn't hit anything entered very low orbits, so both countries' bases had to put up walls to stop them. Which, of course, set off a "wall race."

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Originally Posted by ftg View Post
Given the glove/trigger problem, it might be easier to have it remotely controlled. The shooter might say "Alexa, fire a round ... now."
The soldiers in John Scalzi's excellent military sf novel Old Man's War use AI rifles with nanotechnology that can, at a mental order, adapt and create just the right ammo to suit the occasion. Very cool.
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Old 10-21-2019, 12:01 PM
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Another reason orbiting shots are a problem: the Moon rotates (slowly), so you will have moved away some by the time the shot comes back around.

(Remember those old Mercury program, etc., maps that showed the orbits of Glenn and such? Same thing on the Moon only closer together.)

And if you're talking about rotation and artillery, the slower rotation means less correction for it when doing long distance shooting.
  #47  
Old 10-21-2019, 12:03 PM
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There was a Cold War-era short story in which US and Soviet troops got into a gun battle on the lunar surface. The rounds which didn't hit anything entered very low orbits, so both countries' bases had to put up walls to stop them. Which, of course, set off a "wall race."
.
Ben Bova, Men of Good Will. 1965. Very good story!

It wasn't a "wall race", but computers. They needed bigger and better computers to track all the bullets, because every 28th day the perilun of their orbits was right at the base. And every time the bullets hit something, their orbits changed. Everyone was afraid to shoot again because the computers would be overloaded and "they'd have to spend every 28th day sheltered."

But the Americans were secretly building a wall! And then they'd get those Russkies!
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Old 10-21-2019, 03:46 PM
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Ah, thanks. It's been awhile since I read it.
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Old 10-21-2019, 05:26 PM
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Ah, thanks. It's been awhile since I read it.
It holds up well.
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Old 10-22-2019, 07:27 AM
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Ok, why bother with guns? How about a small drone, flown out to the moon pirates before they’re in gun range? Then you fly your drone into the suit of the pirate-buggy driver.
Better yet, the drone could detonate a small charge in the midst of the pirate buggy.

Last edited by Capn Carl; 10-22-2019 at 07:31 AM.
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