8 ms·

I find the physics of rail guns pretty fascinating. For something nominally invented in world war 1 (1918) which is now "only a few years" away from possible de

I find the physics of rail guns pretty fascinating. For something nominally invented in world war 1 (1918) which is now "only a few years" away from possible deployment. We are talking literally a 100 years later. We went from powered flight to flying in orbit in less time, think about that. Is it a compelling weapons concept? Of course it is, you don't need explosives to shoot things that is pretty huge. Are wars bad? Of course they are. That said, the concept has been around for a hundred years, so people are going to work on making a practical weapon out of it. Which means that at some point its going to be a component of a military action. And not having one of your own, will change the calculus of what you can and cannot do.

derefr 7y ago
It's not like the technology behind railguns hasn't been stable and ready to use for decades now. It's just that, until the more recent invention of ancillary technologies like supercapacitors, it's been so costly to fire them that there was no logical place for them on the battlefield, so we never bothered to operationalize them.
- ChuckMcM 7y ago
  I can't agree with this: "It's not like the technology behind railguns hasn't been stable and ready to use for decades now.", at least not in terms of practicality. I did a bit more research on flight and found a similar comment from Wilbur Wright[1] about George Cayley. It is very different to be able to demonstrate a principle in physics (such as flight, or accelerating a piece of metal with electricity) and building a practical application of that principle. In many ways the time it takes between those two points is likely a good indicator of just how difficult it is to reduce the principle to practice. You yourself mention super capacitors, another comment mentions the rails, then there are the switching devices themselves, the wiring harnesses, the control system. That is why I'm pretty awestruck at the fact that they were able to make it work and get this close to being something they can field test. [1] "About 100 years ago, an Englishman, Sir George Cayley[2], carried the science of flight to a point which it had never reached before and which it scarcely reached again during the last century." -— Wilbur Wright, 1909 --- http://www.ctie.monash.edu.au/hargrave/cayley.html http://www.ctie.monash.edu.au/hargrave/cayley.html [2] https://en.wikipedia.org/wiki/George_Cayley https://en.wikipedia.org/wiki/George_Cayley
- DuskStar 7y ago
  The materials science that goes into making rails that last for more than a handful of shots at useful velocities is pretty advanced, too.
- ijpoijpoihpiuoh 7y ago
  To me, it's not entirely clear why we're bothering. Do we actually envision shore bombardment as a useful combat modality going forward? IIRC the types of ships that can mount this weapon are the same types that are currently vulnerable to hypersonic anti-ship missiles. All our potential equiv-tech adversaries have those, to my understanding. So wouldn't the railgun only be useful against lower tech opponents? And against such opponents, does it fill a substantial gap where we don't already have sufficient other tools?
  - deleted 7y ago
    [deleted]
  - greedo 7y ago
    Railguns have potential for ship defense and missile defense.
  - DuskStar 7y ago
    A large part of the reason that guns fell out of use on warships was that they were outranged by everything - guns that can shoot up to 40km (like those on the Iowa class) aren't enormously useful against destroyers tossing missiles from 200km or strike aircraft from a carrier 400km away. Guns that can shoot down planes and incoming missiles at 100km, though? That's pretty damn useful, even if it doesn't close the distance entirely vs missiles. As for why guns at all - well, guns tend to have magazine depths undreamt of by missiles, and railguns will likely follow that pattern. If moving to railguns for AA defence means you can shoot down 3 or 4 times as many incoming missiles for the same weight, that would be enormous. And in the fog of war... Who's to say that a DD won't be able to close to railgun range of an enemy warship? Life's a lot easier when you can stay below the horizon, after all!
  - nradov 7y ago
    There are no hypersonic antiship cruise missiles deployed today. Some ballistic missiles have limited antiship capability and they do travel at hypersonic speeds but there are reasonably effective defenses against them now.
    - 7y ago
- Animats 7y ago
  I've been wondering when EMALS catapults get converted to ultracapacitors. The current energy storage system on the Ford class carriers is a motor/generator/flywheel setup, and it's a reliability headache. The catapult itself is just a linear induction motor.
- flukus 7y ago
  I'd be interested to know why we haven't seen intermediaries that don't need the advanced tech of a rail gun, like why haven't we seen magnetically driven mortars or artillery? These seem less demanding, is it just a case of existing tech being good enough?
  - killjoywashere 7y ago
    The energy density of batteries is relatively low compared to the liquid hydrocarbons and other chemical accelerants. It goes from being a mortar you can throw in the back of a Jeep, to a mortar you can throw in the back of a Jeep plus a semi truck full of battery capacity. On ships and airplanes, you can replace internal weapons bays which have substantial storage capacity. And the batteries (this is particularly an issue for airplanes) aren't terribly mass-dense either. And you can use the vessel's turbine-powered electric generators to recharge the batteries from fuel (this reduces the range, but hey, tankers).
charlesju 7y ago
I think the interesting use case would be to put things into space for a lot less money. Imagine putting one or many of those new Space X internet satellites into a rail gun that goes straight up. It doesn't need to go all the way into space, it just needs to get pretty high, then the cost to break into orbit can require a lot less fuel and make it a lot more cost effective to do space stuff.
- DuskStar 7y ago
  > Imagine putting one or many of those new Space X internet satellites into a rail gun that goes straight up. Orbit doesn't work like that. Getting 200, 300 miles up is the easy part - the vast majority of the required energy comes from going sideways at 7800m/s.
  - Zelizz 7y ago
    I think they were suggesting that you could save fuel for once you're out of atmosphere, so that you're not fighting air resistance when you start a burn to get into orbit.
    - mikeash 7y ago
      You could save a decent chunk of your fuel this way. Maybe 25% or so. In exchange for that, you have to build your rocket and satellite to withstand 10,000 gees of acceleration and hypersonic flight through the lower atmosphere. And somehow build a rail gun that can fire something the size of an office building.
      - aeneasmackenzie 7y ago
        You use an extremely long track, not high acceleration.
        mikeash 7y ago
        Hard to do if you’re aiming straight up.
mabbo 7y ago
The concept is the same for any projectile weapon: I'm going to convert stored energy into kinetic energy. Bow and arrow? Stored energy in the bow turned into kinetic energy in the arrow. Handgun/cannon/musket? Stored chemical energy in some compound, quickly converted into kinetic energy in the bullet via exploding. A rail gun isn't much different- it's just a different means to store the energy (in electrical storage) and a different means to apply the energy to the projectile (magnets). The real problem is that these two changes require a lot of overhead in terms of gear to make it work. It's only worthwhile to do it if you intend to really, really add a lot of kinetic energy to something. It's the same reason the electric car has taken 100 years to finally be worthwhile- chemical energy is much more dense and easy to convert into kinetic energy. Battery tech is only now catching up to the point that it's worth doing.
- steve19 7y ago
  You put it well. The problem of of putting energy into projectiles caused a move from kenetic to chemical weapons (missiles). But delivering chemicals to a target is expensive and at some point scaling it up becomes politically dangerous (you cannot just lauch even a conventional icbm without all sorts of risks). Scaling up kenetic weapons ended up with huge battleship guns that did almost as much damage to the ship itself as the target (OK, a bit of an overstatement but I doubt any of those sailors left the navy with hearing intact). They were slow to fire, extremely heavy, and required a lot of dangerous chemicals to be stored. One mistake and the ship would blow up. This allows deep penetrating weapons containing huge amounts of energy to pierce bunkers from way over the horizon. This is the kind of weapon the Navy will want if the Korean peninsula ever heats up to a boil. Edit: I suspect I am being downvoted because I am discussing weapon systems. There is a difference between advocating for weapons/war and discussing them. It is better weapons are discussed in the open, than developed in secret where the public cannot weigh in. Truly horrifying things are born in the dark.
  - killjoywashere 7y ago
    Point of order in the definitions here: an explosive projectile is still a kinetic weapon and is not NOT a chemical weapon. A chemical weapon causes chemistry to happen in/on the target: mustard gas, VX nerve gas, etc. This is not my opinion. This is widely accepted and a matter of many international treaties.
mikeash 7y ago
For a more extreme example: it took less than seven years from the discovery of nuclear fission for this discovery to be used obliterate cities.
- saalweachter 7y ago
  On the other hand, consider the time it too to develop gunpowder projectile weapons to the point that they were useful.
  - mikeash 7y ago
    Indeed. I guess a century or so of development isn’t so bad by comparison.
filoleg 7y ago
Reminds me of the electric car tech, in a way. I remember reading somewhere on HN that when the cars were initially gaining traction, electric engines were an option already, even with some prototypes. The issue was that the battery tech wasn't quite there to make it efficient and have any mileage compared to gas powered cars. So we went the gas route. And only within the past 5 years, we got a sign of electric cars coming back as a real alternative to gas cars.
- ChuckMcM 7y ago
  Yes, similar and it was more than batteries, it was also magnets and car materials Etc. Batteries are an important part of that (and still the weak link given relatively long charge times) but it would be a disservice to a Model 3 to say that if you had LiIon batteries in the 70's you could have built one then.

derefr 7y ago

It's not like the technology behind railguns hasn't been stable and ready to use for decades now. It's just that, until the more recent invention of ancillary technologies like supercapacitors, it's been so costly to fire them that there was no logical place for them on the battlefield, so we never bothered to operationalize them.

ChuckMcM 7y ago
I can't agree with this: "It's not like the technology behind railguns hasn't been stable and ready to use for decades now.", at least not in terms of practicality. I did a bit more research on flight and found a similar comment from Wilbur Wright[1] about George Cayley. It is very different to be able to demonstrate a principle in physics (such as flight, or accelerating a piece of metal with electricity) and building a practical application of that principle. In many ways the time it takes between those two points is likely a good indicator of just how difficult it is to reduce the principle to practice. You yourself mention super capacitors, another comment mentions the rails, then there are the switching devices themselves, the wiring harnesses, the control system. That is why I'm pretty awestruck at the fact that they were able to make it work and get this close to being something they can field test. [1] "About 100 years ago, an Englishman, Sir George Cayley[2], carried the science of flight to a point which it had never reached before and which it scarcely reached again during the last century." -— Wilbur Wright, 1909 --- http://www.ctie.monash.edu.au/hargrave/cayley.html http://www.ctie.monash.edu.au/hargrave/cayley.html [2] https://en.wikipedia.org/wiki/George_Cayley https://en.wikipedia.org/wiki/George_Cayley
DuskStar 7y ago
The materials science that goes into making rails that last for more than a handful of shots at useful velocities is pretty advanced, too.
ijpoijpoihpiuoh 7y ago
To me, it's not entirely clear why we're bothering. Do we actually envision shore bombardment as a useful combat modality going forward? IIRC the types of ships that can mount this weapon are the same types that are currently vulnerable to hypersonic anti-ship missiles. All our potential equiv-tech adversaries have those, to my understanding. So wouldn't the railgun only be useful against lower tech opponents? And against such opponents, does it fill a substantial gap where we don't already have sufficient other tools?
- deleted 7y ago
  [deleted]
- greedo 7y ago
  Railguns have potential for ship defense and missile defense.
- DuskStar 7y ago
  A large part of the reason that guns fell out of use on warships was that they were outranged by everything - guns that can shoot up to 40km (like those on the Iowa class) aren't enormously useful against destroyers tossing missiles from 200km or strike aircraft from a carrier 400km away. Guns that can shoot down planes and incoming missiles at 100km, though? That's pretty damn useful, even if it doesn't close the distance entirely vs missiles. As for why guns at all - well, guns tend to have magazine depths undreamt of by missiles, and railguns will likely follow that pattern. If moving to railguns for AA defence means you can shoot down 3 or 4 times as many incoming missiles for the same weight, that would be enormous. And in the fog of war... Who's to say that a DD won't be able to close to railgun range of an enemy warship? Life's a lot easier when you can stay below the horizon, after all!
- nradov 7y ago
  There are no hypersonic antiship cruise missiles deployed today. Some ballistic missiles have limited antiship capability and they do travel at hypersonic speeds but there are reasonably effective defenses against them now.
  - 7y ago
Animats 7y ago
I've been wondering when EMALS catapults get converted to ultracapacitors. The current energy storage system on the Ford class carriers is a motor/generator/flywheel setup, and it's a reliability headache. The catapult itself is just a linear induction motor.
flukus 7y ago
I'd be interested to know why we haven't seen intermediaries that don't need the advanced tech of a rail gun, like why haven't we seen magnetically driven mortars or artillery? These seem less demanding, is it just a case of existing tech being good enough?
- killjoywashere 7y ago
  The energy density of batteries is relatively low compared to the liquid hydrocarbons and other chemical accelerants. It goes from being a mortar you can throw in the back of a Jeep, to a mortar you can throw in the back of a Jeep plus a semi truck full of battery capacity. On ships and airplanes, you can replace internal weapons bays which have substantial storage capacity. And the batteries (this is particularly an issue for airplanes) aren't terribly mass-dense either. And you can use the vessel's turbine-powered electric generators to recharge the batteries from fuel (this reduces the range, but hey, tankers).

charlesju 7y ago

I think the interesting use case would be to put things into space for a lot less money. Imagine putting one or many of those new Space X internet satellites into a rail gun that goes straight up. It doesn't need to go all the way into space, it just needs to get pretty high, then the cost to break into orbit can require a lot less fuel and make it a lot more cost effective to do space stuff.

DuskStar 7y ago
> Imagine putting one or many of those new Space X internet satellites into a rail gun that goes straight up. Orbit doesn't work like that. Getting 200, 300 miles up is the easy part - the vast majority of the required energy comes from going sideways at 7800m/s.
- Zelizz 7y ago
  I think they were suggesting that you could save fuel for once you're out of atmosphere, so that you're not fighting air resistance when you start a burn to get into orbit.
  - mikeash 7y ago
    You could save a decent chunk of your fuel this way. Maybe 25% or so. In exchange for that, you have to build your rocket and satellite to withstand 10,000 gees of acceleration and hypersonic flight through the lower atmosphere. And somehow build a rail gun that can fire something the size of an office building.
    - aeneasmackenzie 7y ago
      You use an extremely long track, not high acceleration.
      - mikeash 7y ago
        Hard to do if you’re aiming straight up.

mabbo 7y ago

The concept is the same for any projectile weapon: I'm going to convert stored energy into kinetic energy. Bow and arrow? Stored energy in the bow turned into kinetic energy in the arrow. Handgun/cannon/musket? Stored chemical energy in some compound, quickly converted into kinetic energy in the bullet via exploding. A rail gun isn't much different- it's just a different means to store the energy (in electrical storage) and a different means to apply the energy to the projectile (magnets). The real problem is that these two changes require a lot of overhead in terms of gear to make it work. It's only worthwhile to do it if you intend to really, really add a lot of kinetic energy to something. It's the same reason the electric car has taken 100 years to finally be worthwhile- chemical energy is much more dense and easy to convert into kinetic energy. Battery tech is only now catching up to the point that it's worth doing.

steve19 7y ago
You put it well. The problem of of putting energy into projectiles caused a move from kenetic to chemical weapons (missiles). But delivering chemicals to a target is expensive and at some point scaling it up becomes politically dangerous (you cannot just lauch even a conventional icbm without all sorts of risks). Scaling up kenetic weapons ended up with huge battleship guns that did almost as much damage to the ship itself as the target (OK, a bit of an overstatement but I doubt any of those sailors left the navy with hearing intact). They were slow to fire, extremely heavy, and required a lot of dangerous chemicals to be stored. One mistake and the ship would blow up. This allows deep penetrating weapons containing huge amounts of energy to pierce bunkers from way over the horizon. This is the kind of weapon the Navy will want if the Korean peninsula ever heats up to a boil. Edit: I suspect I am being downvoted because I am discussing weapon systems. There is a difference between advocating for weapons/war and discussing them. It is better weapons are discussed in the open, than developed in secret where the public cannot weigh in. Truly horrifying things are born in the dark.
- killjoywashere 7y ago
  Point of order in the definitions here: an explosive projectile is still a kinetic weapon and is not NOT a chemical weapon. A chemical weapon causes chemistry to happen in/on the target: mustard gas, VX nerve gas, etc. This is not my opinion. This is widely accepted and a matter of many international treaties.

mikeash 7y ago

For a more extreme example: it took less than seven years from the discovery of nuclear fission for this discovery to be used obliterate cities.

saalweachter 7y ago
On the other hand, consider the time it too to develop gunpowder projectile weapons to the point that they were useful.
- mikeash 7y ago
  Indeed. I guess a century or so of development isn’t so bad by comparison.

filoleg 7y ago

Reminds me of the electric car tech, in a way. I remember reading somewhere on HN that when the cars were initially gaining traction, electric engines were an option already, even with some prototypes. The issue was that the battery tech wasn't quite there to make it efficient and have any mileage compared to gas powered cars. So we went the gas route. And only within the past 5 years, we got a sign of electric cars coming back as a real alternative to gas cars.

ChuckMcM 7y ago
Yes, similar and it was more than batteries, it was also magnets and car materials Etc. Batteries are an important part of that (and still the weak link given relatively long charge times) but it would be a disservice to a Model 3 to say that if you had LiIon batteries in the 70's you could have built one then.