Plasma/Fusion weapons recoil

[tjoneslo]

From a discussion occurring on a private list, the question of why would plasma/fusion weapons (first described in Book 4 Mercenary) generate significant recoil. The description of the man portable weapons requires the use of (powered) battledress to manage the recoil.

From several ideas floated by people, and in many different game systems I've found three (semi-plausible) versions of the technology behind the plasma/fusion weapons.

1. Flamer: This is the extreme temperature version of a Flame Thrower. Or, if you prefer, the open nozzle of a fusion m-drive configured to spray plasma (and radiation) around. Getting enough plasma out to melt tank armor would generate significant thrust. Or, as the old saying goes, the more efficient the engine the better a weapon it makes.

2. PAW: A (probably charged) particle accelerator weapon. This is version described by the technical literature and be more familiar to the players knowledgeable with modern weapons research, but less so with the history of Traveller. This weapon won't generate significant thrust or not at the level required for Battle dress.

3. Fusion Spike: This is my vision of what a Plasma/fusion weapon would be based upon the description in Mercenary and Striker. A combination of the Flamer weapon, the PAW, and an explosively formed projectile warhead. Since you don't want the plasma to cool before hitting the target, it gets launched at a significant fraction of light speed. Even a small mass at that velocity generates significant recoil.

Did I miss any good ideas here?

 

[mike wightman]

Only two of the PGMP/FGMP systems require battledress, the PGMP13 and the FGMP14.
The PGMP12, the PGMP14 and the FGMP15 can all be used without BD - the 14 and the 15 require a grav recoil compensation system, while the 12 can only be fired every other turn due to recoil.

They generate a lot of recoil because they are basically a heavy gauss rifle firing plasma rather than a bullet and thus achieving much higher velocity and thus energy, the temperature of the plasma is going to have little effect compared with the 100km/s plasma jet/bolt.

 

[Spinward Flow]

They generate a lot of recoil because they are basically a heavy gauss rifle firing plasma rather than a bullet

This.
PGMP and FGMP would have projectile velocities well in excess of a conventional slug thrower rifle (usually mach 2-3 for man portable chemical round guns). Dial that up to mach 5-6 (or even 8) and suddenly you've got a significant amount of recoil "kick" to deal with, even if you're throwing out puffs of plasma (whether fusing or not). You need to have what amounts to a high(er) muzzle velocity due to the rapid decay/degradation of the plasma over time reducing its effectiveness in damage applications. You don't want to give the plasma time to cool down while in flight (basically) so it has to be launched at extremely high velocities to reach the target at longest range while the plasme/fusion bolt is still "hot" (so to speak) ... and then when it gets there and hits the target it will SPLASH all over everything like a hurled bucket of paint (thrown at multi-mach velocity).

Even a few grams of plasma bolt thrown down range at a high enough velocity will "kick like a mule" against the shooter.

PGMP-12 has insufficient recoil compensation, so ROF is 1 per 2 rounds (shoot/recover/shoot/recover).
PGMP-13 interfaces with Battle Dress to provide some recoil compensation, allowing ROF to increase to 1 per 1 rounds.
PGMP-14 has a gravity compensator built directly into the weapon allowing it to be used with an ROF of 1 and not need Battle Dress.

The FGMP follows a similar development cycle, with the FGMP-15 not requiring Battle Dress to handle the weapon's recoil when fired.

they are basically a heavy gauss rifle firing plasma rather than a bullet

THIS.
The plasma IS THE PROJECTILE thrown downrange.
They're basically gauss guns that don't use slug rounds to throw ... they use superheated plasma instead and throw the plasma.

I would imagine the plasma bolts look something like miniature stars with streamers trailing behind them (in atmosphere, in vacuum they'll fly relatively undisturbed) and because they're "hot" and emitting radiation each shot is basically a tracer round that anyone and everyone can see (even with a Mk I eyeball) so there's no way to NOT give away your position when using these kinds of weapons.

Remember ... tracers work both ways ...

 

[Enoki]

Why would there necessarily be recoil with these weapons at all? As Spinward says, they're really a variant of a gauss gun. I'd think the plasma is formed in a chamber then 'pulled' out of the gun in a magnetic field that hurls it forward much like an open-ended catapult. So long as it isn't pushing against the weapon as it leaves, there'd be no recoil. However, there'd likely be considerable radiation and heat given off and that would require protective clothing for the user. This variant could fire discrete 'blobs' (a highly technical term) or be like a fire hose.

The other possibility is the weapon like a rail gun fires a container with the plasma formed and contained within it (or a tiny fusion device like a miniature nuclear bomb). Upon reaching the target the container disintegrates and WHAM! you get hit with plasma or a fusion explosion. This would require these weapons have a minimum safe use range and the firer wear protection from the resulting explosion at the target.
Containment would only require at most a few seconds, probably less in most cases, in the case of personal weapons. This version would be more like a nuclear grenade launcher.

 

[whulorigan]

Why would there necessarily be recoil with these weapons at all? As Spinward says, they're really a variant of a gauss gun. I'd think the plasma is formed in a chamber then 'pulled' out of the gun in a magnetic field that hurls it forward much like an open-ended catapult. So long as it isn't pushing against the weapon as it leaves, there'd be no recoil. ...

Because momentum is conserved. If the plasma bolt has a positive momentum vector toward the target, it acquired it by applying a negative momentum vector on the firer/firing mechanism. The plasma bolt is interacting with the magnetic field of the barrel and pushing off of it thru the magnetic interaction: the plasma slides forward and the magnetic rails/coils of the barrel are forced backward.

Gauss weapons are not recoilless either.

 

[mike wightman]

Or put another way, Newton's third law...
if you throw plasma out of a gun really fast in one direction the gun has to go the other way.

 

[Enoki]

Because momentum is conserved. If the plasma bolt has a positive momentum vector toward the target, it acquired it by applying a negative momentum vector on the firer/firing mechanism. The plasma bolt is interacting with the magnetic field of the barrel and pushing off of it thru the magnetic interaction: the plasma slides forward and the magnetic rails/coils of the barrel are forced backward.

Gauss weapons are not recoilless either.

Does a garden hose have recoil?

 

[Spinward Flow]

Ladies and gentlemen ... I give you the fantastic example of Discount Thor Kyle Hill from his Because Science days on youtube where he goes through the actual math involved in determining how much energy is needed to overcome the gravitational binding force of a planet (Death Star style) with a laser so as to destroy it.

Answer (3m10s in) for a planet the size of Terra ... is 2.24x10³² joules ... which is as much energy as the star Sol puts out over an entire week.

Light may not have mass, but it does have momentum, which must be conserved.
Note that the conservation of momentum using light is how solar sails work.

So as explained (4m40s in) even a massless laser beam has recoil.
And as Discount Thor Kyle Hill conclusively explains, a laser weapon of the power levels needed by the Death Star is going to have a MASSIVE recoil (5m18s in) of ... deep breath ... 7.5x10²³ kg m/s ... which is ... A LOT.

He then does the math for the recoil force affecting the Death Star (5m51s in) and reaches a conclusion of 44-100 km/s applied to the entire space station in about 5 seconds, thereby accelerating the station away from the direction the laser was fired by about 900-2100G ... which is enough to turn every biological inside of it into a liquified chunky salsa as a result of firing the main weapon (demonstration provided in the video).

Point being that even lasers (yes... lasers!) have recoil.
Momentum must be conserved, after all.

The reason why we don't "feel" the recoil of most lasers is because the recoil is usually below our thresholds of perception.

But a plasma bolt?
You're going to have grams of ionized atomic particles in that plasma bolt, and they have mass ... just like a slug from a slug thrower does.



And yes, electromagnetic guns also have recoil just like chemical propelled rounds guns do.
The difference is that the electromagnetic guns aren't using a gas pressure explosion to propel the rounds, creating a "rocket thruster" effect in zero-G in addition to the recoil of hurling the projectile away from the shooter.

It's probably better to think of plasma and fusion guns as being more like energy shotguns (shooting massive plasma "paint balls" with significant splash on impact) with an enormous kick to them like a shotgun can have.

 

[Enoki]

Given that in Traveller there is anti-gravity technology, what's to stop the designer of such weapons from putting in a grav plate or whatever that exerts equal force in the opposite direction to firing? On the other hand, it's going to be hard to contain all the radiation and heat coming off that plasma or fusion stream.

 

[coliver988]

Does a garden hose have recoil?

having used a fire hose - yes. It is just negligible for a garden hose as the water is not leaving that fast.

 

[whartung]

Given that in Traveller there is anti-gravity technology, what's to stop the designer of such weapons from putting in a grav plate or whatever that exerts equal force in the opposite direction to firing?

That's exactly what the higher TL [FP]GMPs do.

The recoil isn't necessarily from the mass (not sure how much plasma weighs honestly, how much fusing hydrogen do you need to make something owie down range?), but the velocity. The Plasma and Fusion bolts are very high velocity to be effective. Take some very small and accelerate it very fast, and you have a lot of momentum to conserve.

 

[Enoki]

having used a fire hose - yes. It is just negligible for a garden hose as the water is not leaving that fast.

Yes, 1 1/2" and 2" fire hoses in the Navy...

 

[infojunky]

Does a garden hose have recoil?

Yes.

 

[mike wightman]

Does a garden hose have recoil?

Yes.
In that there is a reaction force to the water coming out.
You never made a water rocket?

 

[mike wightman]

Given that in Traveller there is anti-gravity technology, what's to stop the designer of such weapons from putting in a grav plate or whatever that exerts equal force in the opposite direction to firing? On the other hand, it's going to be hard to contain all the radiation and heat coming off that plasma or fusion stream.

That would be the grav compensation they add to the PGMP14 and the FGMP15 - there is an OTU CT adventure where an Impi spook in plain cloths uses an FGMP15 to deal with some underworld types. Argon Gambit IIRC.

 

[whartung]

having used a fire hose - yes. It is just negligible for a garden hose as the water is not leaving that fast.

The interesting thing is that I have my hose coiled on this spool. You turn the handle and it rolls up.

I have one of those generic "push to spray" sprayers on the end.

When you turn the water on, even though no water can actually leave the hose, there's recoil in the system as it fills up.

Speaking of firehoses, I was up in Ouray CO one year on the 4th of July. It's around 7,800 feet elevation.

As part of their celebration, they have the main intersection cordoned off, and two, 3 man teams, each wielding a firehose connected to kitty-korner hydrants. The goal is to pummel the opposition with the water until one team succumbs.

Similarly, there's folks lining the rope off intersection to view all the action.

I think it's the altitude. It's a silly hobby. Typically the person in front is bludgeoned to exhaustion and then, ideally, they rotate back to the 3rd position being replaced by a fresher member of the team.

When I watched it, the teams were face to face. The leader of one was wearing a plastic face shield. Water was spraying everywhere.

In time, one of the leaders apparently got hit under the chin, as he flew backward on to the ground. At this point the hose became uncontrolled and scythed in to the crowd. Several of them went down like wheat.

At that point the contest was finished and they killed the water, and there was much applause and rejoicing.

Like I said, I think its the altitude.

 

[aramis]

Like I said, I think its the altitude.

Nah... Firefighters in Anchorage have been known to do similar... 2.5" lines back a whallop.
Explorers weren't allowed to target each other, but we were given a 6' beach ball to drive with the hoses. Tara accidentally opened up full bore and was lifted clean off the ground... her backup wasn't close enough to her. She was about 120 lbs... (~55kg) At 180 lbs, I was able to be pushed back but not lifted.

It's actually kinda fun... but damn, it hurts getting hit with full bore lines, even through turnouts. Been 33 years and I still remember it.

 

[Magnus von Thornwood]

As per T5 Book 3, pages 98-99 under fusion and plasma it states it is a beam, not a bolt. So more like a hose than people think.

 

[whulorigan]

As per T5 Book 3, pages 98-99 under fusion and plasma it states it is a beam, not a bolt. So more like a hose than people think.

But Pulse Lasers are also classified as "Beams" in the general use of the term in T5. I would think a Plasma Gun is more like a high-power Star Wars "Blaster-Bolt" (including flowing along electromagnetic-field lines on the target after it strikes it (if the target remains intact to some degree)).

 

[Magnus von Thornwood]

But Pulse Lasers are also classified as "Beams" in the general use of the term in T5. I would think a Plasma Gun is more like a high-power Star Wars "Blaster-Bolt" (including flowing along electromagnetic-field lines on the target after it strikes it (if the target remains intact to some degree)).

T5 Book 3, page 98-99. Plasma. The weapon heats hydrogen to a plasma state and fires it as a beam through a magnetically focused field along the barrel. The initial beam is approximately 2cm, but it begins to expand immediately. Plasma weapons have significant recoil. For example, Plasma Gun.