Portable, practically infinite power sources?

[Sikon]

We've seen them plenty of time, especially in video games. Guns that have their own power source, that for all practise, are unlimited. Any logistics officer dream presumably, as there is no longer the need for ammunition.

A beam weapon with nearly unlimited ammo or the equivalent?

As one option for the peak power demands, have between a fraction of a kilogram and several kilograms of capacitors storing a few joules per gram ... a few kilojoules total. While typical commercial photoflash capacitors today are on the order of 1 to 2 J/gram, at least tens of joules per gram along with millisecond-level discharge time is obtainable. (Actually, the capacitors are relatively the easy part of the weapon compared to the greater technological difficulty of almost everything else in it).

Then a pistol or rifle can discharge energy in the kilojoule range in a timeframe such as a millisecond, if future technology allows a sufficiently miniaturized beam weapon running off that electrical discharge. If the goal is to fire at the rate of one or more shots per second, one to a few kilojoules each, the power supply recharging the capacitors must be in the kilowatt range.

Recharging the capacitors at a rate of up to kilowatts per second with a compact system is a miniaturization challenge for the rifle, requiring specific power for an engine & generator at least on the order of a horsepower per kilogram (plus or minus an order of magnitude, depending on assumptions and design goals). Still, that could be possible. For intuitive perspective to the reader, each kilowatt of power consumption and waste heat is the equivalent of ten 100-watt household light bulbs, half as much as some 2-kW handheld cord-powered electric hairdryers.

Some system using chemical fuel might be a possibility for many shots. For example, if there is ambient air, if 25+% of the energy of a half-kilogram of gasoline (40000 J/gram energy density) generating electricity could be delivered to the target after all inefficiencies, that would be 5000+ kJ in total, like a beam weapon having an ammo capacity up to thousands of shots, one to several kJ each.

That's a lot of potential even with chemical fuel. The 25% efficiency example is arbitrary, albeit plausible.

The preceding for the imaginary future-tech beam weapon running off chemical fuel may seem strange compared to the lesser ammo capacity of today's guns, but, among other differences, a bullet going at 300 m/s to 1000 m/s has a kinetic energy of 45 J/gram to 500 J/gram. With also the mass of gunpowder and brass, current real-world ammunition has still less than the preceding for the ratio of energy delivered to the target versus ammo mass. That compares to the 40000 J/gram energy density for gasoline combusted in air, before inefficiencies.

Alternately, in theory a weapon could have thousands of shots without being a beam weapon, if it fired projectiles fast enough. For example, if a gauss gun could fire bullets at 3 km/s, the mass of the bullets themselves could drop to 0.2 grams per 1 kJ of kinetic energy, like under a kilogram per thousand shots.

Of course, the preceding is obviously rather optimistic, leaving the details to vague future technology, but at least this is relatively tame by sci-fi standards in terms of not breaking the laws of physics.

In contrast, for example, to have a weapon with a micro-fusion reactor not irradiate a human user to death is probably utterly physically impossible, unless it has massive radiation shielding. Arbitrarily small fusion reactors are a common concept in sci-fi but there's a lack of evidence for any plausible means of stopping omnidirectional penetrating gamma and neutron radiation in the real world other than thick mass shielding.

Even aneutronic fusion reactions (D-He3, p-B11, etc.) which do not release neutrons through the primary reaction actually still produce neutrons through secondary reactions (example), lethal quickly enough with a multi-kilowatt reactor unless it has many centimeters of shielding. Without relatively bulky and massive shielding, a weapon with a micro-fusion reactor would be a 360-degree neutron death ray, lethal to humans whether one is in front of or behind the barrel. Maybe, perhaps bulky power armor suits could carry around the equivalent of massive vehicle-mounted weapons with heavy radiation shielding, if actually worthwhile, but weapons with a nuclear reactor wouldn't be anything like an ordinary pistol or rifle in size and weight.

Probably the most practical means of approaching almost unlimited ammo with plausible future technology is just through an advanced chemical fuel system, perhaps like the one previously described.

[Darth Wong]

Some system using chemical fuel might be a possibility for many shots. For example, if there is ambient air, if 25+% of the energy of a half-kilogram of gasoline (40000 J/gram energy density) generating electricity could be delivered to the target after all inefficiencies, that would be 5000+ kJ in total, like a beam weapon having an ammo capacity up to thousands of shots, one to several kJ each.

It's worth pointing out here that this figure is more than an order of magnitude off. Not that your source is incorrect, but your source is assuming that the gasoline is being burned with air, so the actual reactant mass is around 15 times higher once you include the air (and without the air, the power output is zero). Of course, one could pre-suppose that the air is brought in from the environment outside the gun, but now you need an air intake system, an air filter, fans, and an exhaust system. Alternatively, you could have liquid oxygen in a small compressed tank inside the gun, feeding the reaction, but that carries its own problems.

However, your point is valid about how any kind of nuclear power kind of requires Star Trek-style super-shielding on that scale.

An imaginary supercapacitor would be a neat idea, with the caveat that it would explode in a horribly violent way if it was damaged.

[Imperial Overlord]

An imaginary supercapacitor would be a neat idea, with the caveat that it would explode in a horribly violent way if it was damaged.

At least one David Drake book with man portable laser weapons uses super capacitors. As the explosive in grenades.

[Sikon]

Some system using chemical fuel might be a possibility for many shots. For example, if there is ambient air, if 25+% of the energy of a half-kilogram of gasoline (40000 J/gram energy density) generating electricity could be delivered to the target after all inefficiencies, that would be 5000+ kJ in total, like a beam weapon having an ammo capacity up to thousands of shots, one to several kJ each.

It's worth pointing out here that this figure is more than an order of magnitude off. Not that your source is incorrect, but your source is assuming that the gasoline is being burned with air, so the actual reactant mass is around 15 times higher once you include the air (and without the air, the power output is zero). Of course, one could pre-suppose that the air is brought in from the environment outside the gun, but now you need an air intake system, an air filter, fans, and an exhaust system.

As said later:

40000 J/gram energy density for gasoline combusted in air, before inefficiencies

Yes, the figure is for gasoline combusted in ambient air, but that is very much intentional. For this, one doesn't much care about the mass of oxygen consumed from air, just the weight of the fuel carried on the weapon.

After all, almost every combustion engine from those in cars to portable generators to the tiny micro gas turbine engines under research today use air, of course. Indeed, although there is no attempt to be certain about the details of mere hypothetical future technology, such micro turbines may have particular potential for portable power. Fuel may not be literally gasoline, but the slight differences between similar hydrocarbons are unimportant for an order of magnitude illustration.

In event of designing a similar weapon for use in space instead, the performance drops, counting the mass of the stored oxidizer needed in that event. While liquid hydrogen and liquid oxygen is 13 kJ/gram, cryogenic liquids don't tend to be practical for this. Although an extreme situation is the beryllium and oxygen reaction, 24 kJ/g, it requires liquid oxygen storage. A non-cryogenic oxidizer seems more likely in that event, a little like options for rocket oxidizers have included nitric acid, nitrogen tetroxide, hydrogen peroxide, and nitrous oxide. Those storable oxidizers each are hazardous, with there being no perfect choice. The result with such storable oxidizer and fuel can be a figure such as 7 kJ/gram, depending on the particular choices (species data). Indeed, the very highest performance batteries might be comparable performance to an engine & generator system then after adjusting for major efficiency difference (if similar to today), so a space version of the weapon might actually just use batteries rather than an awkward fuel & oxidizer combo.

However, gasoline (with ambient air) is great energy density for operation in atmosphere. Under most circumstances, it is much preferable for performance and even safety advantages to rely on air rather than stored oxidizer.

An imaginary supercapacitor would be a neat idea, with the caveat that it would explode in a horribly violent way if it was damaged.

While this kind of capacitor would need a low enough internal resistance for its high discharge rate as to be capable of rather violent accidental discharge in principle, that's not necessarily a show-stopper. Since the capacitor only stores the energy for one shot at a time, it is more or less the equivalent of the energy of a single bullet, no more than a few kJ, except dispersed over a larger area and not directional. One still wouldn't want the weapon exploding in the soldier's hand, but, if the capacitor is inside a tough casing, the chance of a stray bullet hitting that small object is likely much less than a bullet hitting and killing the soldier himself directly.

Also, if such was actually a really major concern, the energy storage could be an array of capacitors, electrically connected at the moment of firing (e.g. under 1% of the time, for milliseconds each second), not likely at the instant of one getting penetrated by shrapnel with a local short-circuit from the damage. If just a small portion of the total is discharged, like tens or hundreds of joules out of up to a few kilojoules total, that reduces risk. I've personally discharged a capacitor with tens of joules; although the proper method is gradually with a resistor, that much energy on a screwdriver tends to produce a noisy large spark but not lethal shrapnel.

Of course, if the weapon is hit by enemy fire that literally blows the whole gun apart, all capacitors in the array are destroyed with all their electrical energy being discharged, but, in that case, the soldier is likely dead anyway, with or without capacitors in his weapon.

Besides, for perspective, consider that the soldier may also be carrying grenades, which could also explode if hit by a bullet or penetrating shrapnel, yet such release hundreds of kJ to the MJ range.

[Beowulf]

Even if you used other chemical reactants, you still end up with on the order of thousands of shots per kilogram. A nicely self contained fuel example would be Otto Fuel. It's probably not a good gun fuel, given that it makes hydrogen cyanide, however.

As far as high cap supercapacitors go, most SF authors realize that the energy in them has to go somewhere if it's damaged, and that usually means explosively.

[Darth Wong]

After all, almost every combustion engine from those in cars to portable generators to the tiny micro gas turbine engines under research today use air, of course. Indeed, although there is no attempt to be certain about the details of mere hypothetical future technology, such micro turbines may have particular potential for portable power. Fuel may not be literally gasoline, but the slight differences between similar hydrocarbons are unimportant for an order of magnitude illustration.

True, but we're talking about a weapon. If it needs a tiny air intake and filter to operate, knowing the difficulty people have in keeping conventional weapons clean enough to avoid jams in certain designs, you have to wonder how long it will function.

While this kind of capacitor would need a low enough internal resistance for its high discharge rate as to be capable of rather violent accidental discharge in principle, that's not necessarily a show-stopper. Since the capacitor only stores the energy for one shot at a time, it is more or less the equivalent of the energy of a single bullet, no more than a few kJ, except dispersed over a larger area and not directional. One still wouldn't want the weapon exploding in the soldier's hand, but, if the capacitor is inside a tough casing, the chance of a stray bullet hitting that small object is likely much less than a bullet hitting and killing the soldier himself directly.

Actually, I was talking about the idea of using the capacitor as a stand-alone energy storage device, not as an accumulator for the output of some other device inside the gun. Such a cap would produce a really violent explosion.

Also, if such was actually a really major concern, the energy storage could be an array of capacitors, electrically connected at the moment of firing (e.g. under 1% of the time, for milliseconds each second), not likely at the instant of one getting penetrated by shrapnel with a local short-circuit from the damage. If just a small portion of the total is discharged, like tens or hundreds of joules out of up to a few kilojoules total, that reduces risk. I've personally discharged a capacitor with tens of joules; although the proper method is gradually with a resistor, that much energy on a screwdriver tends to produce a noisy large spark but not lethal shrapnel.

Of course, if the weapon is hit by enemy fire that literally blows the whole gun apart, all capacitors in the array are destroyed with all their electrical energy being discharged, but, in that case, the soldier is likely dead anyway, with or without capacitors in his weapon.

I'm thinking more of wear and tear over an extended period of time.

Besides, for perspective, consider that the soldier may also be carrying grenades, which could also explode if hit by a bullet or penetrating shrapnel, yet such release hundreds of kJ to the MJ range.

Grenades undergo no wear and tear until they're actually used.

[Darth Wong]

Has anyone actually done any experiments on lethality of pulse laser shots with regard to power level?

[Sikon]

True, but we're talking about a weapon. If it needs a tiny air intake and filter to operate, knowing the difficulty people have in keeping conventional weapons clean enough to avoid jams in certain designs, you have to wonder how long it will function.

Depending on the details of the future technology, perhaps.

Actually, I was talking about the idea of using the capacitor as a stand-alone energy storage device, not as an accumulator for the output of some other device inside the gun.

Well, I'm talking about using a capacitor with the output of the miniature gasoline generator. The capacitor stores the energy of a single shot, up to a few kJ, discharging it in short timeframe such as a millisecond for up to around megawatt-level momentary power. That works with the gasoline generator recharging the capacitor, which is in the low kW range, e.g. for between one and several shots per second, depending on assumptions and design goals.

Has anyone actually done any experiments on lethality of pulse laser shots with regard to power level?

That's an interesting question, although hard to tell, especially with the usual research focus being so much on other applications like destroying missiles.

[Admiral Valdemar]

I thought Nyrath's site has some calcs on pulse-laser output, but I'd have to check again. They are far more efficient either way that CW types and would be not unlike a projectile weapon in signature and effect if so wished, just without the recoil which in a micro-gee environment, would be ideal.

[Connor MacLeod]

I thought Nyrath's site has some calcs on pulse-laser output, but I'd have to check again. They are far more efficient either way that CW types and would be not unlike a projectile weapon in signature and effect if so wished, just without the recoil which in a micro-gee environment, would be ideal.

Yep. From here - I use this reference alot.

Whether you use lasers or particle beams, you'll need a bit over a kilojoule of output energy to reliably incapacitate a human target. In the case of a laser weapon, that energy would be subdivided into ~1 joule pulses at ~5 microsecond intervals, to achieve penetration in the face of a laser's natural tendency to deposit energy at the target's surface. Particle beams don't have that problem; boost the electrons up to a few hundred MeV, and you can dump the whole kilojoule's worth at once.

The energy output is very small, but it relies as much on the rapid duration and millimeter-scale focus to actually do the damage - its the explosive vaporization that does the damage (as noted, its mechanical, not thermal damage.)

I woudl also note this is for a pistol-sized taget and onyl to "reliably incapacitate" a target. You're probably looking at needing several times the KE of a bullet to do damage, though it could be considerably greater given the differences in damage mechanism (some bullets can put fist sized or larger holes in a target, or even blow off most of a person's head.. that would require much larger explosive effects than to create the 4 cm diameter hole specified for the weapon Atomic Rockets describes.)

It is worth noting that the Atomic Rockets site verifies the "megawatt range" outputs Mike noted as being neccesary - kilojoule level enegies delivered in millisecnods (or rather, a series of microsecond pulses.)

Edit: and of course, as Mike notes, you need to consider extra energy to allow reliable penetration of body armour (which could itself at least double or triple the input at least for some sort of metal or ceramics-based body armour, barring some magic material.)

[Connor MacLeod]

Has anyone actually done any experiments on lethality of pulse laser shots with regard to power level?

I've tried looking, and there appear to be SOME research out there, but most of them appear to be papers and such you have to either purchase or be a member of some journal or organizaton to view (at least online.)

The cloest I have ever been able to find relates to surgical cauterization procedures via lasers (alot of research is done there in order ot perform cauterizations with little or no collateral damage to the body) as well as optical/retinal damage and other safety related hazards to commerical lasers (stuff you find in CD or DVD players for eaxmple.)

I bthink I know someone who might have worked with industrial cutting lasers before. I need to see if I can dig him up and maybe ask him for some stuff.

Industrial safety stuff might also yield some results, but I never really considered looking at safety sites or that kind of thing.

[Cykeisme]

Assuming our fictional power sources generate a lot of waste radiation (like a little fusion generator), we'd need unobtanium shielding surrounding the reactor in the grip.
Could we also assume that personal armor could be composed of the same material, and the weapon beam would have to defeat this?

[Shinova]

I always liked that super-M16 carbine with a double-drum barrel in Metal Gear Solid 3. It had infinite ammo by virtue of the bullets inside the drum magazine forming a Mobius-loop.

Sigint: "That'll give your gun infinite ammunition."

Snake: "Yep, that'll do the trick."

Wait, how the hell is that supposed to work? I know it somehow doesn't, but how?

Mobius loops always confuse me.

[Shroom Man 777]

Wait, how the hell is that supposed to work? I know it somehow doesn't, but how?

Mobius loops always confuse me.

It doesn't. Metal Gear Solid often defies common sense but it doesn't dwell on these facts and doesn't techno-babbulate.

The explanation was just this:
"On the inside, the magazine is shaped like a sideways-8, making it a Mobius Loop and giving it unlimited bullets."

"Yep, that'll work."

That's not even getting to the guy who can control bees, or the guy who spontaneously explodes into one thousand arrows.


I wish we could find more information on Stas' Soviet Space Gun, so calcs can be done and all that. That weapon is the barest and most minimal requirement of a science fiction space gun.