Sci-fi Weapons, Vehicles and Equipment

Even compressed air generates some heat. The more potent the reaction the more thermal energy you are going to have as a byproduct. I can't think of any practical systems that would give you what you want. I think the closest you will get is something akin to the light gas gun.

Compressed air normaly makes the canister itself super cold from my experiance, which is honestly the effect I am looking for, non-scolding cartridges.

The mechanical effect of a compressed gas expanding rapidly is cooling, not heating. Indeed, this is a standard and very common non-exothermic propulsion method used in rocketry and aircraft. It can and is used in projectile weaponry as well.

Now, it's worth noting that the muzzle velocity of a projectile using compressed gas is much lower than you can achieve with explosive propellants: I am not completely sure but as far as I know it cannot be faster than the speed of sound in the propellant.

On the other hand, because you're firing a subsonic projectile, a compressed gas weapon can be a lot quieter.

Edited by Fighteer on Jul 28th 2019 at 9:27:39 AM

Rapidly compressing and releasing air most definitely produces heat to the point it has been used as a means of ignition and you can find examples of such experiments on youtube and an actual ignition system created by Daisy for their very brief and abortive foray into caseless projectiles. Pre-Charged Pneumatic Cartridges or similar systems run a lot cooler than a system using rapid compression because what little compression there is, is happening behind the projectile until the gas reaches a point of maximum expansion behind the projectile. You are still getting the heat just not as much as other systems, you are also getting a lot less acceleration than any system that inevitably generates notably more heat.

Spring and gas ram air guns have heat build-up from the pressure behind the projectile and it is actually possible for an effect called dieseling where various substances in the barrel, usually excessive lubricants and/or solvents are particularized and ignited by the heat when firing leading to a smoking barrel effect. This can damage some models because of how they are made.

The more pressure you put behind that shot the hotter it is going to run. You're not escaping the heat in any form of propulsion just how much you are going produce overall with the system. Gas propulsion runs cooler than other systems in general but its propulsive results are appreciably lesser than any other option you can choose in its place.

Light gas guns are a bit of a hybrid system that uses a propellant to drive a pneumatic piston that rapidly compresses a gas medium to a significant degree. Light Gas Guns have demonstrated an ability to fire hypervelocity projectiles. They don't run quite as hot as pure combustion systems but there is obviously still some heat. They, however, are not very practical as a weapon because of how they work.

Any notable means of propelling anything at notable velocities will result in heat. There is simply no way around it.

Tuffy, I had an air rifle license.

I know first hand, that when you fire a compressed air gun, the thing gets cold as fuck to the point that frost can form on it.

If you mean compressing the air in the first place makes heat, then I don't know, but I do know that firing it makes the gun cold, not warm.

Immy: I have owned, operated, maintained several air rifles only one was a small cartridge PCP gun and it was a cheapy that I ended up throwing away. It was the only one that had any part that cooled when firing and that was air cartridge not the whole weapon by any stretch. They can and do generate heat when you charge and fire them especially the ones that compress their own air for the shot. There is initial heat generated when you fire the round until the pressure drops off and the gas be it air or other gas has enough room to expand and cool. The heat is there your not escaping the basic laws of thermodynamics with gas propelled anything and some of that heat will transfer.

The ones that self-charge, ie the ones you have to pump yourself, can and do have several parts can get quite hot if you keep constantly charging the reservoir from the simple act of compressing the air. Compressing air is not a cooling effect. Especially around the pressure bottle and the seals unless you give them some time to cool off if you rapidly charge the system. Even spring-activated air piston rifles can and do generate heat in the action. The barrels rarely have issues but the actions and any storage parts can and do generate heat when you charge them.

The video below is a very visible example of simple air compression generating sufficient heat to ignite cotton at its flashpoint. I know for fact cotton has a flashpoint of a couple of hundred degrees Fahrenheit. The Daisy V/L's compression system reportedly hit temperatures as hot as 2,000 F before the powder ignited.

That rapid compression is exactly what happens when you fire your air rifle. Yes, there is compression in the chamber behind your projectile otherwise nothing would happen and last I checked nearly every single example of air rifle pushes air from a larger volume to a smaller volume to propel the projectile. That creates compression and therefore heat. There is very little expansion in the chamber until sufficient pressure builds to move the projectile that is compression of air into a new space. But there is still that moment where there is compression and heat is generated. It isn't a lot but it is happening. The more pressure that is behind the round before it moves down the barrel before the gas can fully expand the more heat you will get. The part of the air rifle that gets the coolest is whatever holds the compressed air, if, it holds compressed air and it isn't piston generated pressure which is common in quite a few air guns such as the gas ram or spring ram systems. The spring-type is the most common.

Kids, stop fighting or I'll have to send you to your rooms.

• When a gas is compressed, it heats up.
  • A weapon that mechanically compresses gas in order to use it as propellant would get hot from that action.
• When a gas expands, it cools down.
  • A weapon that uses a reservoir of compressed gas as a propellant would get cold from that action.

Note that gases and fluids always flow from high pressure to low pressure. With both of these mechanisms, you are creating a pressure differential between the chamber and the barrel, such that gas flows into the barrel and pushes a projectile along with it. The main difference between a weapon that is loaded with a cartridge of compressed gas and one that is mechanically pumped is that, in the former, someone did the pumping already.

Edited by Fighteer on Jul 29th 2019 at 7:41:11 AM

Technically it depends upon pressure. Gas that suddenly expands and increases in pressure and temperature is also known as an explosion.

When pressure increases (as often happens in compression or combustion) so too does the temperature. If pressure suddenly decreases relative to ambient pressure, the temperature decreases.

This effect happens on all gaseous materials that can be compressed.

For example when gunpowder is ignited one of the byproducts is gas. The gas suddenly expands and increases the pressure inside the chamber of a firearm. This increase in pressure results in an increase in temperature of the firearm (alongside the friction of the bullet leaving and the conduction/convection of the ambient hot gas).

When you run a propane engine or any engine run on compressed gaseous fuels, if the pressure running out of the tank is too high or too fast (thus rapidly decreasing the pressure of the tank and fuel lines themselves) the tank and/or fuel lines or fuel regulators may freeze up.

Oi. Yes, technically it's the change in pressure that causes the change in temperature, not the act of expanding or contracting.

If you were running an asteroid mining operation, how would you organize it? What stays stationary, what stays mobile? Do you bring the asteroid to the refinery, the refinery to the asteroid, or extract the ore and hurl it towards the refinery? It's ostensibly for a Wild West in Space setting and I'm trying to figure out ways to turn a profit without habitable planets.

Habitable planets would presumably need to enter the equation at some point. I know that some folks have advocated for a completely space-bound civilization but I don't think it's at all realistic with foreseeable technology.

Anyway, what you need to know about asteroids is that (a) they come in all different sizes and compositions, (b) they are very far apart. The average distance between asteroids is something like three times the distance between the Earth and Moon, and the distance between asteroids of significant size is much greater.

One way or another, you're going to them.

As for whether you could do your mining in situ, with giant ships that excavate and process the materials; or at a common point, with ships that capture the asteroids and set them on a course for that facility... I could see arguments for either, and there's not a clear enough winner that it matters. Ergo, you could choose whatever way best suits your world-building.

Heck, you could do both, and have the two methods in economic competition with each other. Either way, the mega-facility or the mining ships would be in the same general orbit as the asteroids themselves, although that's still a staggeringly large volume of space.

Realistically, people wouldn't be involved that much. It would be much more efficient to send robotic facilities to do the bulk of the work, with humans in supervisory and maintenance roles. Of course, that's no fun for sci-fi authors, which is why the trope We Will Use Manual Labor in the Future exists. There's little reason to fight over any particular asteroid, so again authors have to get a bit hand-wavey about this.

Edited by Fighteer on Jul 29th 2019 at 12:48:30 PM

Hmm, send the asteroid and have it shepherd on a sort of cattle drive and have to fend off competing wranglers. At least for story flavor stuff. Profit really depends on where the top dollar sell is and how much it costs for any group to use any method.

Asteroid mining is a very complex question, which depends on the size of the asteroids, the value of the material being mined, and how pure the asteroid is. Also, if the setting is another solar system, then the average distance between asteroids can also be a factor. It also matters whether or not the mined material is being shipped to a planet, or used in deep space. Generally speaking, the ideal case for moving the asteroid to the refinery is if relatively small asteroids contain enough pure material such that it is cheaper to move the entire asteroid than it is to send ships with enough mining and refinery capacity to the asteroid itself. For example, if a small asteroid is relatively pure uranium or something equally valuable, then sending a ship to the location and moving the asteroid to the refinery is no more expensive than sending a ship to the location and returning with just the refined material. To the extent that only a portion of the asteroid is valuable material, that the asteroid is large (so that it might make more economic sense to spread the cost of shipping the material back over a longer period of time), and that the material is less valuable (the material, whatever it is, has to be more expensive than delta v, or mining it makes no sense whatsoever, but the greater the marginal profit, the more sense it makes to move it around).

For a "Wild West" atmosphere, it's usually necessary to depict mining as something the private owner of a single run-down ship can undertake. That tells me that asteroids are small and consist almost entirely of some pure, extremely valuable material, and that the asteroids in question are not too far from their market. The remains of a recently shattered planet might fit that bill.

Also worth noting. The conflict from asteroid mining should be internal, not external. As stated before, anyone who attacks an asteroid with intentions of taking its resources are morons to the nth degree.

Crack open a history book. You'll find plenty of conflicts started over much dumber things than that.

Besides attacking an asteroid to take it over makes perfect sense. Maybe the asteroid in question has built up facilities and thus it could be cheaper to simply take it from your opponent as opposed to finding your own. Or perhaps the asteroid in question has rare minerals or mineral concentrations not commonly found even amongst asteroids. (We have one in our solar system that has an unusually high amount of gold for example.)

That sort of thing is based on the principle of scarcity: that there is a limited amount of resources that someone wants to control. The asteroid belt has more resources than we could mine in a million years. There is literally no reason to fight over them.

If you assume some kind of warfare between major powers exploring and/or exploiting space, then it would be far more efficient to fight over supply routes and/or refineries than remote mining sites. Sending warships millions of kilometers to some asteroids is... insane.

Most of the fighting involves stake claiming. Someone claims a vast swath of asteroids and anyone trying to mine them has to negotiate a percentage. Think of a copyright troll but there's no central authority to arbitrate these claims so the only way to enforce a claim is at gunpoint. It doesn't help that these asteroid trolls tend to "forget" about these claims and not declare them or not notice when someone is mining on their turf and approaches the "claim jumpers" with a shoot first and interrogate the corpses later.

Most of the weapons are macgyvered together industrial equipment or got shipped in from foreign powers wanting to cause chaos.

Edited by Belisaurius on Jul 30th 2019 at 9:59:14 AM

Okay, now you are completely taking the piss, although I concede that it sounds fun in a wacky sort of way. If you want space warfare, go ahead and have space warfare, but the scenario you are postulating is absurd from the point of view of realism.

There is some precedent for the "staked a claim on asteroids" thing, though. Watch this video from Today I Found Out about a man who has made a serious claim to own the Moon and even tried to sell land there.

Edited by Fighteer on Jul 30th 2019 at 10:04:41 AM

Its true that for something to be worth fighting over, it has to be scarce, and raw minerals are anything but scarce. That said, it isnt hard to come up with a list of qualities that might make an asteroid somewhat unique. Size, a population center, a facility of some kind, the presence of a super rare element, and so on.

Hey here's a thought, design a super soldier that can lead a normal life after service, cyborg, drug enhancement, genetic engineering, the end goal is to design a better form of human who can fight better than the rank and file but can still hang up their stars and stripes and live normally.

How would you accomplish this?

I think we've pretty much ruled out the idea of living permanently on an asteroid. They are just not suitable for long-term habitation. Even Ceres, the largest asteroid in the belt, has such low gravity that our physiology would essentially treat it as zero, and humans don't thrive in freefall.

Creating gravity on an asteroid is a non-starter. Rotating them fast enough to provide significant gravity on the inside would cause them to break up. If you have artificial gravity, then you're doing Space Magic and there's no point in discussing physics any further.

It is not unreasonable to assume that some asteroids will have rarer materials than others. We're already pretty sure of this. An asteroid with a high proportion of some highly desirable and rare substance might be worth fighting over were fighting over asteroids even remotely practical to begin with.

An asteroid with a military installation would be a potential target, but we've already discussed this to death.

Edited by Fighteer on Jul 30th 2019 at 1:12:57 PM

I don’t think there would be much point to that. Super soldiers aren’t terribly practical to begin with, and the only people there would actually be any reason to modify are either government service lifers or at least trusted enough to behave after they separate.

You could do what they did in Gundam Unicorn with a colony builder that's made out of an asteroid. Easy access to resources while you make an O'neil cylinder.

Enhancements that could make someone a better soldier, such as improved reflexes, endurance, perception, and cognition, would make them quite capable in civilian life in many occupations. You only run into problems when you start installing armor and weapons into the body, overriding pain, removing remorse, and so on.

If you're turning your super-soldiers into remorseless Black Ops killing machines that can punch through buildings and soak tank rounds, adapting to civilian life afterwards is going to be a bit tricky. Heck, this is true even for non-enhanced soldiers today.

Again, I bring up Deus Ex: Human Revolution, not because of its ham-fisted "augmentation racism" message, but because it presents a serious and even slightly nuanced treatment of many of the psychological issues facing people who have been turned into killing machines when they have to interact with civilian life.

Edited by Fighteer on Jul 30th 2019 at 3:29:42 PM

So quite literally the Captain America formula is the only one where a normal life afterwards is entirely feasible, Cap's issues with not being on duty notwithstanding.