Questions about Halo MAC cannon recoil

[Winston Blake]

Now i haven't played the games or read the books (hopefully that will soon change), but i know enough about the Haloverse from reading forums. Recently i was wondering about how much recoil a MAC cannon would have, and the effect on the firing ship.

Searching around gives me 8,000 tons for an Iroquois-class destroyer, and a MAC round mass of 300 tons. So if we go with "point four tenths" meaning 0.04c, then by CoM such a ship would go flying backwards at over 450 km/s. For 0.4c it's over 4900 km/s. For comparison, an M16 bullet goes about 1 km/s.

Calcs: (copy into google, for some reason the url tags don't like them)
(300e3 kg * 1.2e7 m/s)*(1/sqrt(1-0.04^2))/(8e3 * (1e3 kg))
(300e3 kg * 1.2e8 m/s)*(1/sqrt(1-0.4^2))/(8e3 * (1e3 kg))

Apparently the Iroquois was "almost as massive as two frigates", meaning for 0.4c, a frigate would be kicked back at almost 10 million m/s.

So do UNSC ships get thrown around like this? Are they supposed to have engines which can flare up to such power that this can be cancelled instantly? Or is it all just ignored?

[dacis2]

ignored, mainly. Nylud's math is worse than Weber's.

[Instant Sunrise]

The Halo 2: LE manual states that the Guass cannon on the warthog is "recoil-less". I think it is assumed that the recoil dampening tech used on that could probably have been scaled up for a cap-ship.

But that is just a guess by me.

[Icehawk]

Mac Rounds on the ships in the Haloverse only get thrown around at about 30 or so kilometers per second according to the books. Only the massive orbital Super MAC cannons fire rounds at 0.04c.

[dacis2]

SB's been arguing about this. Because of the Covvie's TT level plasma torpedoes (for glassing planets), MACs must be around the same level of firepower as well. That leads to the 30kps being argued whether its relative to the UNSC ship, the Covvie ship, jokingly, the system primary.

[NecronLord]

SB's been arguing about this. Because of the Covvie's TT level plasma torpedoes (for glassing planets), MACs must be around the same level of firepower as well.

Really. No. Absolutely not.

Please choose between being exposed to the sun by lying outside on a clear day for a second (assuming you have a front profile of aound half a square meter), or being shot with a HK MP7.

Both events are around half a kilojoule. But the physical impactor (the MAC cannon) is vastly more dangerous.

[Winston Blake]

The Halo 2: LE manual states that the Guass cannon on the warthog is "recoil-less". I think it is assumed that the recoil dampening tech used on that could probably have been scaled up for a cap-ship.

But that is just a guess by me.

There's needs to be some kind of reaction mass or CoM gets angry- i suppose they could have been talking about really powerful compensators on the tips, which would need to be independently powered to completely negate a shot's recoil (since i'm pretty sure flames don't blast out the back with every shot). Perhaps in-universe the term is just used a marketing gimmick by some defense contractor for their low-recoil design or something (rocket assisted?).

Mac Rounds on the ships in the Haloverse only get thrown around at about 30 or so kilometers per second according to the books. Only the massive orbital Super MAC cannons fire rounds at 0.04c.

Ah, that would be it then. But i thought Covenant ships were far stronger than that.

SB's been arguing about this. Because of the Covvie's TT level plasma torpedoes (for glassing planets), MACs must be around the same level of firepower as well. That leads to the 30kps being argued whether its relative to the UNSC ship, the Covvie ship, jokingly, the system primary.

Well, to get TT level firepower for a 300 ton projectile you'd need at least 0.5c, relative to the target. If relatively stationary, that means throwing back a frigate at around 3% of c, which is pretty crazy.

[Winston Blake]

SB's been arguing about this. Because of the Covvie's TT level plasma torpedoes (for glassing planets), MACs must be around the same level of firepower as well.

Really. No. Absolutely not.

Please choose between being exposed to the sun by lying outside on a clear day for a second (assuming you have a front profile of aound half a square meter), or being shot with a HK MP7.

Both events are around half a kilojoule. But the physical impactor (the MAC cannon) is vastly more dangerous.

It's true that in general physical impactors can cause more damage due to momentum (especially when considering things like shields which dissipate energy), but i think a better analogy would be if that half square metre of sunlight (a 71cm square) was concentrated into a thin beam 4.7mm across, stored for 1 second and then released in about the same interval that an MP7 round transfers its energy. Knowing what comparatively tiny magnifying glasses do, I wouldn't want something like that pointed at me.

[NecronLord]

The point is to stress the important and often overlooked differences between impactors and energy weapons, not to make an accurate analogy.

[18-Till-I-Die]

SB's been arguing about this. Because of the Covvie's TT level plasma torpedoes (for glassing planets), MACs must be around the same level of firepower as well. That leads to the 30kps being argued whether its relative to the UNSC ship, the Covvie ship, jokingly, the system primary.

Well, to get TT level firepower for a 300 ton projectile you'd need at least 0.5c, relative to the target. If relatively stationary, that means throwing back a frigate at around 3% of c, which is pretty crazy.

May i ask though, why not?

Maybe they have some way of protecting the crew from g forces (they obviously have artificial gravity fields) so they just let the ship get thrown back, then maneuver again to shoot, like those old Civil War cannons that had to be repositioned between each shot. It would mean they have a low rate of fire, like those old cannons, but it would (i guess) explain it all.

[The Grim Squeaker]

Only the massive orbital Super MAC cannons fire rounds at 0.04c.

Are'nt the SMAC's fired at four tenths of light or 0.4c .

Also where are the TT level Covie torpedo's coming from?
I thought they glassed a plnaet as a group action with pin point bombardment until the whole planet has been glassed

[18-Till-I-Die]

Yes as i recall some calcs done here put the Covenant firepower maybe at the low end of the TT scale with a fleet bombardment, but if by TT scale you mean like Star Wars thats just not so, as i understand it.

[Winston Blake]

If relatively stationary, that means throwing back a frigate at around 3% of c, which is pretty crazy.

May i ask though, why not?

Maybe they have some way of protecting the crew from g forces (they obviously have artificial gravity fields) so they just let the ship get thrown back, then maneuver again to shoot, like those old Civil War cannons that had to be repositioned between each shot. It would mean they have a low rate of fire, like those old cannons, but it would (i guess) explain it all.

Even if they have some kind of inertial compensation, i didn't think UNSC tech violated CoM. I haven't seen or read any examples of UNSC ships firing, so i don't know if they do get kicked back (and if so, how far/fast), or if their engines suddenly flare up to high power to compensate for each shot, or whatever.

Those old cannons had friction against the ground to slow them down very quickly after firing, in space you'll just keep flying. To maneuver back for another shot like them, a ship would need to use its engines to cancel out its velocity and move back to its original position (engines that can accelerate 8,000 tons from 0 to 3%c in a few seconds, which could probably be used as weapons themselves).

[dacis2]

clarification: The TT thing on the UNSC side was for SMACs. They reason that the ambiguous "point four tenths" thing has to be 0.4 not 0.04 for parity in firepower.

[JointStrikeFighter]

not nessescarily; Covenant Sheilding tech could be limited in terms of power in comparison to their weapons.

Also, the 0.04c figure still gives a multi GT yeild for the round.

The SMAC is supposedly the UNSC's most powerful non nuclear weapon, so they must have nukes more powerful than this. [Note they have the NOVA planet craking nuke]

Finally, Surely if they had TT level amount sof energy to throw around then surely it would be more efficient to pump it into a different kind of weapons system?

[dacis2]

*scratches head*

act of plot?

anyway, didn't a Covvie ship get hit by a plasma torp and not get blown up? that accounts for pretty powerful shielding dunnit?

[Koolaidkirby]

Maybe they have some way of protecting the crew from g forces (they obviously have artificial gravity fields) so they just let the ship get thrown back, then maneuver again to shoot,

They did not have artificial gravity untill after their contact with the covenent (the first time the spartans boarded a covenant ship they were shocked to see gravity on a ship that DID NOT HAVE a spinning section). As I recall, the Pillar of Autumn was the first ship (or one of the first ships) to use artificial gravity(of the covenant design) as the ship implemented many new "stolen and improved upon" covenent technology.

IIRC the Iriquous did not have artificial gravity(of the covenent type) and seemed to be rocked around quite abit when taking extreme evasive maneuvers.

[Icehawk]

Only the massive orbital Super MAC cannons fire rounds at 0.04c.

Are'nt the SMAC's fired at four tenths of light or 0.4c .

Also where are the TT level Covie torpedo's coming from?
I thought they glassed a plnaet as a group action with pin point bombardment until the whole planet has been glassed

No, this is a common misconception. The quote in the novel Fall of Reach states clearly "point four tenths" of c which equals 0.04c.

[Winston Blake]

OK, so basically the 0.04c/0.4c and TT-level figures apply to SMACs not ship MACs, so MAC recoil is relatively small and not a big issue- but that means Covenant ships get killed using 'only' 32kT shots (300 tons at 30km/s).

Now, i was searching around for quotes, and i got this from Spacebattles:

The first Super MAC shell hit a Covenant destroyer. The ships shield flashed and vanished - the remaining impact momentum transferred to the ship - the hull rippled and shattered into a million fragments.

This might suggest that Covenant shields are like B5 Whitestar shields which supposedly 'absorb all the energy leaving only the physical impact' or something. As NecronLord mentioned, the energy of kinetic impactors can be a misleading indicator of how much damage can be done.

Even if Covenant shields can withstand a bagiliaton of energy, there's got to be a limit to how much force the shield projector mountings can take, and conserving momentum means that stopping a MAC shot in a tiny fraction of a second is going to put an enormous stress on those mountings.

So maybe the reason MAC-weapons are so useful is not because they have a huge yield (ie have parity requiring 0.4c TT-level), but because they have a huge momentum. Using such massive projectiles may be desired because it's easier to rip a Covvie ship's shield projectors right off the spaceframe than it is to overcome their shields' energy-limit (which presumably plasma torpedoes and big nukes do).

Interestingly, this gives a general reason to use bubble shields over conformal shields- the greater distance gives the shield much more time to drop the projectile's momentum to nothing, reducing the reaction force on the projectors. Are Covenant shields bubbles?

[Noble Ire]

Interestingly, this gives a general reason to use bubble shields over conformal shields- the greater distance gives the shield much more time to drop the projectile's momentum to nothing, reducing the reaction force on the projectors. Are Covenant shields bubbles?

As far as I can tell, yes. The destroyer the MC and his team inflitrate and destroy at the beginning of the war has at least enough space under its shields to a allow an armored human under.

[dacis2]

The shield was probably at some distance from the hull, as the Master Chief landed on a shield and waited for the shield to open a hole when firing its pulse laser before dropping in.

Also, standard MACs seem to (after dropping the Covvie Shields) just go right through (they leave a hole). Shouldn't SMACs follow the same principle and also leave a hole if standard MACs already cannot transfer all of their KE?

[Noble Ire]

Also, standard MACs seem to (after dropping the Covvie Shields) just go right through (they leave a hole). Shouldn't SMACs follow the same principle and also leave a hole if standard MACs already cannot transfer all of their KE?

They probably do, hitting something tough or massive enough. However, it seems the KE the SMAC does impart is enough to simply shatter the ship, rather than needing to puncture it.

[apocolypse]

Only the massive orbital Super MAC cannons fire rounds at 0.04c.

Are'nt the SMAC's fired at four tenths of light or 0.4c .

Also where are the TT level Covie torpedo's coming from?
I thought they glassed a plnaet as a group action with pin point bombardment until the whole planet has been glassed

No, this is a common misconception. The quote in the novel Fall of Reach states clearly "point four tenths" of c which equals 0.04c.

It's actually somewhat debateable though, for a couple of reasons. First off is the fraction itself, and secondly is because Archer missiles themselves appear to be capable of at least .1c based on some novel evidence, and Covenant ships can and do evade them. Therefore, if Mark V's weren't even capable of half that speed, then they shouldn't be hitting much at all, if ever, and we know from TFoR that they do.

And dacis, you may be thinking of Chi Ceti 4. One of the Covenant ships was hit by one of it's own plasma torps and the shields failed allowing a MAC round to strike it directly.

[Advocate Walker]

No. A MAC (Mass Acceleration Cannon) is just a more advanced and bigger version of a Railgun. It uses magnets to accelerate a projectile. So, basically the projectile is hovering inside the weapon, and accelerates through magnets. In the videos the Shockwave is the breaking of the sound barrier. And the impact also creates one. However in space there is no such resistance, and it keeps its speed.

Conclusion: There is no recoil.

[Esquire]

No. A MAC (Mass Acceleration Cannon) is just a more advanced and bigger version of a Railgun. It uses magnets to accelerate a projectile. So, basically the projectile is hovering inside the weapon, and accelerates through magnets. In the videos the Shockwave is the breaking of the sound barrier. And the impact also creates one. However in space there is no such resistance, and it keeps its speed.

Conclusion: There is no recoil.

That's not how conservation of momentum works.