Halo's MAC Cannons

[9911MU51C]

I was just wondering, who here thinks the MAC cannons in Halo are pretty cool? Who thinks they would actually work to effect? ( http://halo.wikia.com/wiki/Magnetic_Accelerator_Cannon )

[Tangent]

Provided that you can actually build and power the damn thing there isn't really a good reason why it wouldn't work but it would be a logistical nightmare to have even one of them. Most people think it would just push itself out of orbit but " a pair of thrusters on the bottom side of the station fire for a few seconds to counteract the inertia imparted to the station.". If you were to build a working one you would be carrying the biggest non-nuclear stick anyone would ever need, and with the projectile speed at 4% C (lightspeed) you could hit nearly anything... really really hard.

*edit*

They are also AWESOME!

[drakesdoom]

The only issue I see is keeping it in orbit, best case of ion thrusters of immense size powered by microwave relay still does not look good.

[OtherDalfite]

The only issue I see is keeping it in orbit, best case of ion thrusters of immense size powered by microwave relay still does not look good.

So long as you originally built it in a medium to high orbit, I doubt keeping it up would ever be a problem.

[Drunkrobot]

Assuming the station itself had a huge mass, or the mass of the projectile wasn't that high, then the problem of the recoil wouldn't be that impossible.

[EatThePath]

I've in general soured on mass drivers in sci-fi. .04c? That's impressive, but why not put all that power and tech into a laser? Even in Halo the covenant are described as dodging a noticeable percentage of MAC rounds, increasing your muzzle velocity 25 times seems like it might come in handy. If laser tech is woefully insufficient, then why not a rail launched missile? Get even a little guidance involved in things.

[Tangent]

"Against Covenant shield technology, the rounds possess enough kinetic energy to punch through shields, cut through the ship, and, upon exit, still retain enough energy to destroy a second ship, and cripple a third ship." Thats why. While a laser could potentially deliver the same amount of energy, it would not punch through so much as vaporize the top layers and have the rest of the energy scattered in the vapor.

Accelerating a missile to anything close to 4% C would crush any kind of guidance built in due to extreme g-load, assuming it takes less than a second for the projectile to leave the weapon its 0 m/s to 11991698.32 m/s in an instant. if someone would like to calculate the g-force of such a launch i would be interested in seeing the result.

Edited May 25, 2013 by Tangent

[Kryten]

How could a projectile at anything like that speed hitting anything possibly not simply vapourise on impact?

[Tangent]

I assume large amounts of the projectile would stay in the ship but at that velocity you would have to smack it into a planet to stop it, and even vapor at 4% C would do plenty of damage

[EatThePath]

While a laser could potentially deliver the same amount of energy, it would not punch through so much as vaporize the top layers and have the rest of the energy scattered in the vapor.

Which is why you pulse your lasers. A more pressing concern is probably keeping the spot on target.

Accelerating a missile to anything close to 4% C would crush any kind of guidance built in due to extreme g-load, assuming it takes less than a second for the projectile to leave the weapon its 0 m/s to 11991698.32 m/s in an instant. if someone would like to calculate the g-force of such a launch i would be interested in seeing the result.

Well, we can put a lower bound on it. It's at least 1.2 million g. It's certainly a hurdle, but if you can build rails that survive running that much power through them, or coils that switch that fast, I'm not sure a guidance package that survives the launch is necessarily out of the bounds of sanity. And if you're launching a missile you don't necessarily need to go quite as high on muzzle velocity, because it's a missile.

[drakesdoom]

The issue I think with missile with that much energy on delivery is payload cost. A bullet costs the same no matter how fast you launch it from a magnetic accelerator cannon. To achieve the same kind of energy as a .04c round with an explosive or accelerate a projectile to that speed with even a fusion drive to allow mid flight course corrections is prohibitive. Also their is minimum distance to consider, if your opponent appears in high orbit as they do in the halo series close range engagement become a reality, only a cannon can deliver that 0 distance hit without damaging itself.

As for projectile breakup it really has little effect at those speeds you are firing a kinetic slug. If the slug is not intact you have bits of the ship flying out the back at either a higher speed or more likely a higher mass. At those speeds terminal ballistics break down, you are not shooting them per see, but delivering a blow of kinetic energy that their ship cannot sustain. Any energy after initial impact is maintained in some form either high mass or high speed.

For lasers being better just look at current military projects. The navy is developing rail gun upgrades for their main cannons and the air force is working on anti missile lasers. The navy is almost done but the air force cannot make a laser with enough power without using chemical based lasers that need their chemical components reloaded after a few shots. Whops their goes the whole laser system if you have to fire multiple times.

Recoil in space has no backstop like on earth. A massive station would be able to correct course over a greater time perhaps even entirely after the battle however the energy requirements are the same. It may actually require less energy to keep a lighter station in orbit if you could deliver the thrust fast enough as you are accelerating a smaller mass after a few shots than a large station where the mass change is unnoticeable. Even a light station firing 600 ton projectiles I would imagine would weigh in at 4000 tons or more given only 50 rounds aboard.

[EatThePath]

Well, first off the navy railgun isn't that near ready for deployment yet as far as I'm aware. They may be getting the energies they want, but last I'd heard they were still firing a lot of rail along with each projectile, and that needs fixing. Second off chemical lasers presumably make for a much more portable solution, and I expect when you have fusion power plants in your space ships other options might be available to you. And in space you don't have horizons or atmospheres, which are two things that give the railgun a leg up over lasers.

I do agree that at knife-fight ranges the railgun is probably pretty effective. I just don't think those knife fights are likely to happen often enough to matter in realistic treatments of space combat.

[Rune]

I imagine that with the kind of energy levels we are talking about, a Free Electron Laser is a plausible comparison. It is almost present-day technology, and even if it is theorized to be at least aircraft-carrier size, well, we are comparing with a pretty advanced coilgun. If that is the case, then X-ray lasers are viable in the MW-GW range, and that means an effective range in the order of light seconds. I'm afraid the rationale for using kinetic weapons is poor in those circumstances. At those distances, ships with very low T/W can dodge even stuff coming at 8% of c. So I'd imagine the guy with the sniper rifle always wins against the dude with a shotgun, since the best analogy in space is an open plain with perfect visibility and no chance to sneak up on someone.

Rune. Railguns and coilguns are for low tech levels.

[Volt]

I've been writing some Star Wars fan fiction for a while and I wrote in a faction which used railguns as their main weapons. Then the really geeky part of my brain began to question Newton's Third Law. How the hell do ships counter the opposite, equal reaction of accelerating a piece of metal to a fraction of c? The frigates in Halo look far too small and flimsy to have enough mass to defeat that change of momentum.

[drakesdoom]

Well, first off the navy railgun isn't that near ready for deployment yet as far as I'm aware. They may be getting the energies they want, but last I'd heard they were still firing a lot of rail along with each projectile, and that needs fixing. Second off chemical lasers presumably make for a much more portable solution, and I expect when you have fusion power plants in your space ships other options might be available to you. And in space you don't have horizons or atmospheres, which are two things that give the railgun a leg up over lasers.

I do agree that at knife-fight ranges the railgun is probably pretty effective. I just don't think those knife fights are likely to happen often enough to matter in realistic treatments of space combat.

Chemical lasers do make for a much more portable laser if you only want few shots at most, then all your chemicals are used up and you need a whole new laser for the most part. When considering a combat vessel for deployment if it wins the fight only to return to drydock and need all it's gun replaced is not of much use.

I agree on your assessment of knife fights in real space, however when we are talking about Halo space enemies warp into high orbit similar to a mugger jumping out of the ally you are walking past knife fighting time.

[TheSuperintendnt]

If you are going for realism then you have to realize:

1) you enemy is a LONG way away

2) Lasers need to be powered, focused and aimed - not powerful enough yet

3) rail guns need to be powered and aimed - but the rails need to be replaced after a handful of shots due to plasma damaging them

4) Coil guns need to be powered and aimed - and are simplest option here, longer=faster (generally)

aimed = you can hit a dollar bill from earth and the dollar bill is moving....fast

focused = LOTS of lenses

Powered = like a city level of usage

I'm also just going to point out that people have built coilguns at home that can shoot through cans, where as lasers though a CD case(see the difference).

[EatThePath]

How the hell do ships counter the opposite, equal reaction of accelerating a piece of metal to a fraction of c? The frigates in Halo look far too small and flimsy to have enough mass to defeat that change of momentum.

Well, first off why should they have to? So long as they're sturdy enough to survive the recoil without getting torn apart, a momentum change is just a course change. No big deal really.

But, math. Let us take a UNSC frigate as an example. I don't think they're given a mass anywhere, but they are given some dimensions on the halo fan wiki. The smallest is the Stalwart class, at 478m by 152m by 112m. If I had a model of one handy I could get the true volume, but I don't so I'm just going to eyeball it as a block coefficient of .3, so that is 2.4 million cubic meters of volume.

Material is hard too. My instinct is to assume they're about as dense as a modern naval vessel, but I don't really know that number either. But I know a naval vessel can't be more dense than water, while a space ship doesn't have that restriction. So water might actually be a decent ballpark, and it's neat. 2.4 billion kilograms.

The standard MAC is described as firing a 600 ton slug at 30,000 m/s. Force = mass*acceleration, so it's pretty easy to get our force out of this. 18 billion newtons, though it depends on what ton you use(I hate tons for this reason.). Dividing that by our previously arrived at mass.... gets us an acceleration of 7.5 meters per second. Which is fairly piddling as these things go.

Of course the mass estimate of the frigate could be way off, but probably is good enough to get a rough idea of scale.

Chemical lasers do make for a much more portable laser if you only want few shots at most, then all your chemicals are used up and you need a whole new laser for the most part. When considering a combat vessel for deployment if it wins the fight only to return to drydock and need all it's gun replaced is not of much use.

I agree on your assessment of knife fights in real space, however when we are talking about Halo space enemies warp into high orbit similar to a mugger jumping out of the ally you are walking past knife fighting time.

To the first, yes that's definitely true. That's why I pointed out that to fusion powered space warships other options might be available, such as the free electron laser Rune mentioned.

To the later, that is true, but the MACs were originally built before the covenant showed up with their highly accurate slipspace jumps, and are frequently used at long range in closing engagements.

I'm also just going to point out that people have built coilguns at home that can shoot through cans, where as lasers though a CD case(see the difference).

I've also spoken with engineers who work in related fields who've told me that the powers and switching times for c-fractional coil guns might actually be physically impossible. The ease of building personal scale hand made weapons says nearly nothing about their applicability to space combat.

[TheSuperintendnt]

Yeah the switching speed issue had occurred to me, I'm just going play the game and hope for the future

[Tarrow]

tbh I've always thought that on the smaller ship end of the scale the MAC cannon makes no sense at all as a combat weapon. The energy output of the slug is listed as 64.53 kilotons TNT equivalent, but to get that output you have to accelerate 600 tonnes to 30km/s. 50 years ago we could get 57 Megaton TNT equivalent in a 30,000kg package (the Tsar Bomba half power test detonation in 1961). Throwing that at someone at 30km/s would use 1/20th of the energy of launching a 600 tonne MAC round and be vastly more damaging on target.

[Volt]

Wow, nice job, I guess I've been proved wrong. Also, thank you for putting my mind at ease... my writing is now a little more realistic than I thought. Now, how to address the problem of so-called 'star wars physics'... the complete lack of orbital mechanics. Hmm.

[Flixxbeatz]

The closest we can get in KSP would be Impactors (read: decouplers with horrifyingly large ejection force).

[Comrade Jenkens]

With current technology suh large railguns are certainly not possable. However Halo is set 500 years in the future so advances in thrusters and materials sciences, as well as power storage and generation would probralby make them much more feasable.

As for why arn't the ships sent flying backwards everytime they fire, they are thousands of tons while the projectile is only a few kg meaning its would have a very small effect on the ship.

[Klingon Admiral]

Lets put some science into Halo. Unfortunately, Halo did never run on science.

So we have this so-called super-MACs, propelling a 3000 ton projectile at .04c. We know that the kinetic energy of a mass is E=1/2*3000kg*(11,991,698.32m/s)²=1/2(6000kg*143,800,828,597,890.8224m²/s²) = 2.16*10^17 J. Now we remember that there are 300 of these in orbit. This puts a full salvo of all 300 super MACs at 6.5*10^19 J. To put this in reference, the energy output of the Sun is estimated at around 3.85*10^26 watts or J/s, and the global energy consumption in 2008 were about 143.9 pWh, or 143,900,000,000,000 kWh or 518,040,000,000,000,000 kJ or 518,040,000,000,000,000,000 respectively 5.184*10^20 J. This means every salvo of the EDG equals about 1/8 of the annual global energy consumption. And no, it is never explained where all this power comes from, although you will need a massive network of fusion power plants to keep such a system running. At least it suggests that Halo-humanity is a very solid type 1 on the good old Kardashev scale. I hope you see why the coilguns Halo uses are horrible weapons.

But according to Newton every action triggers a reaction, so according to conservation of momentum the same amount of energy pushes the MAC "backwards". To calculate the resulting delta v we would need the mass of the station ... which we sadly do not have. What we do have, however, is the mass of UNSC warships and the MAC rounds they fire (although it is implied that super-MACs are relatively lightweight). A Marathon-class heavy cruiser has a mass of 100,000 tons (yes, a kilometer-long scifi-warship is lighter than WW2 battleships. ) and fires 600 ton slugs. This would put the mass of a orbital defense station at about 500,000 tons. Now it is a simply matter of rearranging the equation from the beginning.

v²=1/2m/E

v=sqrt(1/2m/e)

v²=(1/2*500,000)/216,000,000,000,000,000=1.157*10^-12

v=sqrt(1.157*10^-12)=1.075*10^-6

This is ... disappointingly low. Probably my math is wrong somewhere. I totally want this things to be violently deorbitted/escaping Earths SOI.