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US Navy's Railgun Now Undergoing Tests in New Mexico

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Re: US Navy's Railgun Now Undergoing Tests in New Mexico

#171
post #49

Earlier quoted context omitted.

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.

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 ag…

The bullets are really cheap.

Re: US Navy's Railgun Now Undergoing Tests in New Mexico

#172

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 ba…

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.

Re: US Navy's Railgun Now Undergoing Tests in New Mexico

#173

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 ba…

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.

This has been discussed before but to summarize, it doesn't work that way.

I realize you didn't say "into orbit" but it is a reasonable place to start. The disadvantage of 'gun' type launch systems are that they only get one shot at putting energy into the system and they have to do that at low altitude where the air is thickest (the biggest impediment to going fast) as a result your space craft leaves the gun and goes into the soup of the atmosphere and burns up[1]. This is a problem with the rail gun as well as hypersonic projectiles that have active payloads have to deal with friction heating and remain functional at the point where they arrive. The secondary problem is the g-force as a function of the acceleration of going from full stop to 7.9 kM/s in say 10 milliseconds. Your basic physics will tell you that is an acceleration of 80 thousand 'Gs'. If you are launching a payload you need a container that can not crush its contents. Of course all that air resistance will bleed off energy/speed so you actually have to start much faster than 7.9 km/s, as much as 10 - 12 km/s to "coast" into orbit. Now you're over 100,000 Gs to start.

[1] This is not unlike shooting a bullet into water (other than water has higher viscosity and the bullet has a lower velocity) but the effect is the same.

Re: US Navy's Railgun Now Undergoing Tests in New Mexico

#174
post #145

Earlier quoted context omitted.

> 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.

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.

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.

Re: US Navy's Railgun Now Undergoing Tests in New Mexico

#175

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 ba…

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.

Re: US Navy's Railgun Now Undergoing Tests in New Mexico

#176
post #112

Earlier quoted context omitted.

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 ag…

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.

> There are no hypersonic antiship cruise missiles deployed today.

https://en.m.wikipedia.org/wiki/3M22_Zircon

Re: US Navy's Railgun Now Undergoing Tests in New Mexico

#177

1) " The system charges for two minutes... " One shot per two minutes is pretty bad; the current 5" gun shoots 16-20 rounds per minute. 2) "...at speeds up to Mach 6." One of the issues with old school, large caliber naval guns was that the blast from the guns would damage or destroy equipment near the muzzle. (I was just reading Pursuit by Ludovic Kennedy, about the British pursuit of the Bismark, and (IIRC) one shi…

No because "chemical" guns accelerate their loads by putting enormously high pressure gases behind them. Obviously, then, once the load is off the gases spew out the end (and make a really, really loud bang noise). Railguns, IIRC, use a chemical charge to get the first couple of mach but then the magnets to pull the load to full speed so it's not followed out the barrel by a mountain of hot gas.

The flames you see coming out the end are chemical charge and/or bits of the sled melting and it travels down the barrel. (people who know better, please feel free to correct me)

Re: US Navy's Railgun Now Undergoing Tests in New Mexico

#178
post #170
post #158

Earlier quoted context omitted.

"shoot satellites out of orbit", not "into orbit"

Same fundamental problem.

Except that in one case they thing you're trying to launch is a tonne of assorted electronics, and in the other case it's two kilos of tungsten.

Re: US Navy's Railgun Now Undergoing Tests in New Mexico

#179
post #70

Earlier quoted context omitted.

A combination of three things: 1) The flash is air in contact with the super-hot rail ionizing instantaneously from the heat, and becoming plasma. 2) Friction (From the projectile against both the rail itself, and air) producing vast amounts of heat, which then a) causes water vapor in the air to flash to steam b) produces smoke from burning metal I am not sure how much of the smoke is from 2)b), because I'm assuming…

Nitpick on 2 a): you can't turn water vapor into steam, water vapor is steam .

No, it's water vapour. Steam is a gas.

Re: US Navy's Railgun Now Undergoing Tests in New Mexico

#180
post #112

Earlier quoted context omitted.

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 ag…

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.

Not cruise missiles, but anti ship missiles are a thing[1]

[1] https://www.zerohedge.com/news/2018-12-25/china-selling-hype...

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