Being all technical and science-like in sci fi

[Ray McCarthy]

The actual slug is launched at hypersonic speed by means of electromagnetic induction, a la railgun.

Yes, theoretically. Ship mounted ones currently have short life so are prototypes. The Slugs can accurately hit over the horizon targets. Hypersonic, so too fast to be intercepted and much cheaper than cruise missiles. US DOD is working on a truck mounted version. Probably needs a 2nd articulated truck as PSU.

If you figure how to have better energy density in a PSU / Battery backpack rather than same weight of chemical propellent / cartridges I see no issue. Maybe LPG and fuel cell, or miniature Fusion reactor backpack. There WAS a backpack atomic warhead that was to be used as munitions, and a version for a man portable recoilless tripod weapon that looked like a bazooka with a calor gas size atomic warhead. That series of weapons, which WAS tested above ground in Nevada is believed to be only a little larger than the theoretical minimum size for fission bomb and the smallest atomic warheads made. Photos on Wikipedia

I thought of pulse rifles in my SF. Issue is weight of cryogenics and PSU. So I didn't explain at all how it worked, except it was more powerful than a carbine / rifle but limited "shots" before the backpack is recharged / refreshed. So they have regular style weapons too with chemical explosive cartridges and slugs (aka bullets ) referred to as carbines or pistols depending on size.
More exotic weapons only used in space and regarded as inferior to "smart" missiles and large kilometre long rail guns.

So the issue with a "rail gun" type rifle is the superconductors (maybe near room temperature ones can be discovered, most need liquid helium, though some materials have worked in lab at liquid nitrogen temperatures) and the electrical power, which obviously has to be generated somehow. Hypersonic will need more power than the supersonic of regular dumb slugs propelled by an explosive. Currently batteries aren't anywhere near that density!

So I see no difficulty. There are only technological hurdles, no breaking laws of physics needed. Plausible, though advantage over existing carbines / rifles for a hand mounted weapon is dubious. Certainly for larger things like ships, a rail gun makes shells obsolete. They use a nuclear reactor for power!

A cast iron slug at hypersonic speed has FAR more energy than same size High Explosive Shell. One ship launched slug is more destructive than a non-nuclear cruise missile (which can take atomic warheads!).

 

[Mirannan]

Ah, energy density problems...

One possible solution to such problems is the idea of using high-energy nuclear isomers as a storage medium. For example (although it didn't pan out) one of the isotopes of hafnium has a high-energy metastable state that stores maybe a twentieth as much energy as would be released by a typical nuclear reaction - which is still vastly higher than anything achievable by chemistry or such things as superconducting loops.

Hafnium didn't work out; but it is at least possible that out of hundreds of nuclides there might be one or two suitable for this sort of use?

 

[Ray McCarthy]

Hafnium didn't work out; but it is at least possible that out of hundreds of nuclides there might be one or two suitable for this sort of use?

A) It would have to be manufactured. Not impossible. Even an "Antimatter" factory is possible.
B) Like anything radioactive, it would have no "off switch" like a battery has (a fuel cell is actually simply a battery that uses externally supplied fuel, advatageous for hydrogen, methane, LPG, alcohol etc which are awkward in a regular battery).
C) Any nuclear isomer source is simply a radioactive material. You need some sort of heat engine (either thermocouples for direct conversion, which is only suitable for low power or liquid cycle to gas to operate a turbine / piston to drive a motor). Plutonium is fine for space probes and rovers on other planets. So not portable unless it's a long life low power continuous consumption device.

Rail guns need very intermittent and very high peak power. This is why for a handheld device the chemical explosive propelled slug is a winner. Even if you figured some miniature fission powered device, (e.g. the nuclear isomer storage), using it as part of an explosive charge rather than to make electricity for a rail gun would be far more controllable and far more efficient.

Large hypersonic rail guns are a good idea. You'd nearly be better off with magic in hard SF than to have a rail gun rifle. It's fine in soft SF and Space Opera as (a) No one expects any given device to be ever feasible (unless they are clueless cinema/TV fans) and (b) You don't explain it, it's only there as it seems cool. We already even have "steerable" bullets that can be fired from handheld weapon, or hand held weapons that can destroy a tank or low flying aircraft, so a personal rail gun is only for "coolness". You have to carry weight of slugs (bullets), cryogenics, coils and power supply!
A back-pack nuclear warhead does exist. It's close to minimum theoretical size and was to be used either as munition, mine or fired from a tripod mounted weapon (second person to carry that!) depending on variant.
An Anti-matter war head needs containment field and vacuum. No real minimum size. It could be fired from a bazooka type weapon or like an RPG, if the cost of making antimatter and problem of safe portable containment was solved. While it sounds less likely than a personal rail gun rifle, it's "proper" SF and theoretically viable, vs the rail gun person rifle which has no advantage over a WWII rifle.

 

[chrispenycate]

I would expect a pulse rifle - well, no, I wouldn't expect anything projecting pulses of energy, of particles or EMP to require rifling to keep the directivity controlled - to be firing discontinuous laser beams, or something other than solid projectiles. I built my first linear accelerator back in the late sixties (that's your railgun, thank you Prof. Laithwaite), and your big problem is going to be energy generation - I ran mine off the local three phase current, none too practical for a portable weapon.

But I'm definitely of the 'hard' school - when I was twelve I conferred with my physics teacher - no, he was my general science teacher then, later to become - and sent a letter to Arthur C. Clarke, explaining he'd made a technical error in 'Earthlight'. He was gracious enough to send a reply agreeing with my analysis, and apologising, which letter I kept for many years. So yes, I enjoy Robert L Forward books, where the technology is worked out and explained to the minor details. But not everybody is this way inclined (indeed, it would be a boringly homogenous universe if we all were), so I'm not suggesting this be laid don as a law as how everything should be done like this, just begging that a few more be published...

 

[Mirannan]

A) It would have to be manufactured. Not impossible. Even an "Antimatter" factory is possible.
B) Like anything radioactive, it would have no "off switch" like a battery has (a fuel cell is actually simply a battery that uses externally supplied fuel, advatageous for hydrogen, methane, LPG, alcohol etc which are awkward in a regular battery).
C) Any nuclear isomer source is simply a radioactive material. You need some sort of heat engine (either thermocouples for direct conversion, which is only suitable for low power or liquid cycle to gas to operate a turbine / piston to drive a motor). Plutonium is fine for space probes and rovers on other planets. So not portable unless it's a long life low power continuous consumption device.

Rail guns need very intermittent and very high peak power. This is why for a handheld device the chemical explosive propelled slug is a winner. Even if you figured some miniature fission powered device, (e.g. the nuclear isomer storage), using it as part of an explosive charge rather than to make electricity for a rail gun would be far more controllable and far more efficient.

Large hypersonic rail guns are a good idea. You'd nearly be better off with magic in hard SF than to have a rail gun rifle. It's fine in soft SF and Space Opera as (a) No one expects any given device to be ever feasible (unless they are clueless cinema/TV fans) and (b) You don't explain it, it's only there as it seems cool. We already even have "steerable" bullets that can be fired from handheld weapon, or hand held weapons that can destroy a tank or low flying aircraft, so a personal rail gun is only for "coolness". You have to carry weight of slugs (bullets), cryogenics, coils and power supply!
A back-pack nuclear warhead does exist. It's close to minimum theoretical size and was to be used either as munition, mine or fired from a tripod mounted weapon (second person to carry that!) depending on variant.
An Anti-matter war head needs containment field and vacuum. No real minimum size. It could be fired from a bazooka type weapon or like an RPG, if the cost of making antimatter and problem of safe portable containment was solved. While it sounds less likely than a personal rail gun rifle, it's "proper" SF and theoretically viable, vs the rail gun person rifle which has no advantage over a WWII rifle.

The whole idea about the nuclear isomer battery concept was that the nuclear isomer could be induced to decay (releasing gamma rays) by irradiating the stuff with gamma or X rays of a much lower energy, thus releasing energy much faster than it would naturally.

 

[Ray McCarthy]

that the nuclear isomer could be induced to decay (releasing gamma rays) by irradiating the stuff with gamma or X rays of a much lower energy

Except that doesn't work on anything, unless the applied radiation is infeasibly high. What does work is irradiation with neutrons. This isn't likely to be portable, ever. However a Tokamak produces sufficient neutrons of sufficiency energy to allow nuclear waste from conventional nuclear power station to decay faster. This increase in heat can be used to make steam and thus electricity. This makes a fusion reactor today a net generator and the radioactive waste safer.

 

[Ray McCarthy]

to be firing discontinuous laser beams, or something other than solid projectiles.

Except smoke and mirrors are counter measures. Plasma is very problematic if it's charged as it will expand rapidly. Laser weapons can be useful in special circumstances. Doesn't bother Space Opera writers, some of which is very good. I have a "Pulse" handheld weapon with backpack in one of my stories, but I carefully never describe it. There are conventional principle carbines too. There are also missiles, spacecraft mounted rail guns, large lasers etc and a magical weapon.

 

[Tim Murray]

Except smoke and mirrors are counter measures. Plasma is very problematic if it's charged as it will expand rapidly. Laser weapons can be useful in special circumstances. Doesn't bother Space Opera writers, some of which is very good. I have a "Pulse" handheld weapon with backpack in one of my stories, but I carefully never describe it. There are conventional principle carbines too. There are also missiles, spacecraft mounted rail guns, large lasers etc and a magical weapon.

I have multi-phasic hand held weapons that use nano-bots. I agree that minimal explanations work to keep the believable mystery going in space operas.

 

[Piousflea84]

The "hafnium battery" has been a controversial nuclear power concept for many years. See wikipedia article at: Hafnium controversy - Wikipedia, the free encyclopedia

The idea of a hafnium battery is that nuclear decay (namely, gamma decay) could be triggered in a controlled fashion (by charged particle bombardment of hafnium). This is completely different from the usual radioisotope thermal generator (RTG) which is continuously decaying at an exponential rate. Right now the physics of "induced gamma emission" are sufficiently unsettled that no one knows if this is plausible, let alone usable in a real device. However, nothing in Standard Model physics precludes the possibility of induced gamma emission.



IMO the most exciting thing about "beyond Standard Model" physics (if it exists) is the possibility of being able to control nuclear reactions. If you could harness nuclear decay in a controlled fashion, you could extract incredible amounts of energy out of common isotopes such as naturally occurring potassium (K-40). This would make "Kardashev-1" scale energy requirements trivially easy to meet.... however, would not produce enough energy to accelerate spacecraft to relativistic velocities or reach "Kardashev-2" levels. (you'd need stellar-scale fusion and/or Fantasy Physics for that)

 

[Nick B]

You Won't Believe This Brilliant Maniac's Homemade Railgun

Homemade railgun. This is possible today, think future, smaller, better.

 

[Ray McCarthy]

Homemade railgun. This is possible today, think future, smaller, better.

If you want the equivalent of a .22

 

[Nick B]

But that is today.

 

[Ray McCarthy]

The energy needed goes up with the cube of speed and linearly with mass in air (in a vacuum, only linearly with mass*). So a slug x4 weight of .22 needs x4 energy. But to get closer to normal bullet speeds needs an additional x9 energy. Even today the demo is less than 1/2 the energy of a .22
A decent slug at hypersonic speed needs 1000x for speed in air and x4 for mass, about 4,000 times the energy per slug.
I'm not saying a such a personal weapon is impossible, but it's more space opera than hard SF. Certainly if you have any non-chemical pulse / slug weapon for hand held use it's for "coolness" rather than something you'd want to describe the operation of.


[* Obviously any projectile weapon is awesome in space with out a nearby planet or atmosphere. Recoil (reaction) is a potential problem, a few aircraft even have that problem!]

 

[Nick B]

Luckily I write space opera! Also, Ray, you have forgotten that in the future we will discover that delerium stuff they use in star trek. Once we have that, and reverse its polarity, we can do anything!

 

[Ray McCarthy]

I think one of the Russian fighters of 1950s or 1960s was fitted with machine gun / cannon of such power it would momentarily go backwards! Could be hoax of course!

 

[Mirannan]

I think one of the Russian fighters of 1950s or 1960s was fitted with machine gun / cannon of such power it would momentarily go backwards! Could be hoax of course!

Probably, but it is a fact that the A-10 slows down considerably when the main gun is fired. I suppose that could cause problems (such as stalling) in some circumstances.

 

[Ray McCarthy]

The USA A10? Fairchild Republic A-10 Thunderbolt II - Wikipedia, the free encyclopedia

I might have been thinking of MiG-27, but it's 21st C. approx. There is a much older piece of nasty I think ...

Gryazev-Shipunov GSh-6-23 six-barreled 23 mm rotary cannon.

The GSh-6-23 has an extremely high rate of fire, with maximum cyclic rates of 9,000 to 10,000 rounds per minute. Compared to the US M61 Vulcan, the GSh-6-23 fires 50-66 percent more rounds per minute, has a heavier projectile, but lower muzzle velocity. The weapon is also lighter and shorter.
A six-barrel version of the GSh-6-23 can also be mounted on the MiG-27 fighter-bomber, even though the plane already carries a 30mm automatic cannon capable of firing 6,000 rounds per minute making it the fastest such weapon around.
The Tula armorers are also famous for their GSh-30-1 automatic aircraft cannon, which, at under 50 kg, is the world’s most lightweight 30 mm automatic cannon.
Another thing that makes it so one-of-a kind is the use of an evaporation cooling system to prevent the detonation of a high explosive round inside a heated barrel. This cooling system consists of a cylindrical water tank around the rear end of the barrel.

About 160 slugs a second! It's a modern Gattling gun. However some of the MiG's only carried a few seconds worth of ammunition.

Gryazev-Shipunov GSh-6-23 - Wikipedia, the free encyclopedia

On the Mikoyan MiG-27 the Gsh-6-30 had to be mounted obliquely to absorb recoil. The gun was noted for its high (often uncomfortable) vibration and extreme noise. The airframe vibration led to fatigue cracks in fuel tanks, numerous radio and avionics failures, the necessity of using runways with floodlights for night flights (as the landing lights would often be destroyed), tearing or jamming of the forward landing gear doors (leading to at least three crash landings), cracking of the reflector gunsight, an accidental jettisoning of the cockpit canopy and at least one case of the instrument panel falling off in flight. The weapons also dealt extensive collateral damage, as the sheer numbers of fragments from detonating shells was sufficient to damage aircraft flying within a 200 meter radius from the impact center, including the aircraft firing.

Gryazev-Shipunov GSh-6-30 - Wikipedia, the free encyclopedia

Nobody Does It Better: Russian Aircraft Cannons Outgun America’s
In space such a weapon could cut an opposing target in half, at ANY range, if the victim didn't notice the hail of slugs coming. A very large space ship may have huge fraction of "c" speed, but speedy dodging like in WWI or WWII dog fights isn't possible in space. c.f. a ship and a hovercraft. Aircraft rely on the atmosphere to change vector quickly, even a Harrier. No drag in space, so if took 3 months acceleration to reach vector, even if you can start moving sideways, you need 3 months of main thrust to kill the forward motion. Laying down various patterns of fire to destroy an incoming craft is easier in space than air, as the gun turret can manoeuvre and the craft is very slow to change vector. Unlike in air, the "shells" don't slow with distance!

Sometimes reality is more scary and unlikely than SF.

You don't want these sort of weapons on Babylon 5 furies or Starwars X and Y craft, but on MASSIVE space craft. The reaction on a small one man "space fighter" would be disastrous. Nor can "space fighters" fight or manouver remotely like WWII aircraft in space.

 

[Piousflea84]

The energy needed goes up with the cube of speed and linearly with mass in air (in a vacuum, only linearly with mass*). So a slug x4 weight of .22 needs x4 energy. But to get closer to normal bullet speeds needs an additional x9 energy. Even today the demo is less than 1/2 the energy of a .22
A decent slug at hypersonic speed needs 1000x for speed in air and x4 for mass, about 4,000 times the energy per slug.
I'm not saying a such a personal weapon is impossible, but it's more space opera than hard SF. Certainly if you have any non-chemical pulse / slug weapon for hand held use it's for "coolness" rather than something you'd want to describe the operation of.


[* Obviously any projectile weapon is awesome in space with out a nearby planet or atmosphere. Recoil (reaction) is a potential problem, a few aircraft even have that problem!]

Wait a second... I don't see any physics reason why gaussgun/railgun technology can't be miniaturized. A "pulse rifle" does not *need* to achieve relativistic velocities. (not least because a very small relativistic projectile hitting Earth-like atmosphere would immediately superheat and explode) It just needs to achieve velocities comparable to or greater than than gunpowder weapons. Existing technology could plausibly produce such a weapon within the next half-century.

If a handgun bullet has 600 J of muzzle energy, and a rifle bullet has 2000 J, a "pulse rifle" (railgun or gaussgun) only needs a small number of kilojoules to fire a AK47-like bullet at an AK47-like velocity. You don't need Lightsaber-class power systems to pack a few kJ of energy into a handheld weapon - an iPhone5 battery has ~19kJ energy capacity, which is worth several pulse rifle shots!

The main barriers to "pulse rifle" adoption are energy storage (batteries+hypercapacitors), electromagnet miniaturization, and rail/barrel materials that don't destroy themselves while shooting. Graphene and other real-world materials could very plausibly overcome all of these deficits. (it's possible that they already have, and DARPA isn't telling anybody) Once all the systems are in place you just need to miniaturize them so they don't weigh too much more than a regular rifle, and ruggedize them so they don't fall apart in combat.

The main advantage of a pulse rifle over an AK-47 would be ammunition efficiency. If you look at a rifle cartridge, the vast majority of it is casing and powder, the bullet is a tiny fraction of the size and mass. A pulse rifle could probably hold 5-10x as many bullets in the same size of magazine. Even if the pulse rifle's muzzle velocity and muzzle energy were exactly the same as an AK-47, it could be a superior weapon if the smaller and lighter ammo compensated for the weight of a pulse rifle's electrical power systems. This advantage becomes even larger if it uses ammunition that is proportionally smaller but higher velocity. (achieving the same recoil but higher muzzle energy and likely higher lethality)

A pulse rifle would also have a much higher theoretical-max accuracy than a gunpowder weapon, as an electromagnetic pulse is very fine-tunable (unlike the detonation of smokeless powder).

 

[Ray McCarthy]

rifle bullet has 2000 J, a "pulse rifle" (railgun or gaussgun) only needs a small number of kilojoules to fire a AK47-like bullet at an AK47-like velocity.

No-one is talking relativistic speeds. Hypersonic isn't that fast.
A "pulse rifle" (railgun or gaussgun) will need more than 2000J to be like an AK-47 if an AK-47 exit energy is 2KJ. You lose energy in the barrel. The electronics is also losing energy.

The main barriers to "pulse rifle" adoption are energy storage

Yes, that's what was discussed. No current battery system or back pack generator can compete with a back pack of chemically powered shots. That's why Hafnium "batteries" were discussed. Forget capacitors except to allow continuous battery discharge to be delivered in peaks (battery internal resistance issues), they actually waste some energy.

Good luck on getting even one rifle power equivalent shot from a phone battery.


The accuracy of a conventional weapon isn't issues with the charge, an electrically powered weapon isn't any better. It's the slug, length of barrel, rifling of it and manufacturing tolerances.

 

[Brian G Turner]

Good luck on getting even one rifle power equivalent shot from a phone battery.

You could throw it really hard at someone. I bet that could hurt.