
A First Look at America's Supergun - gist
http://www.wsj.com/articles/a-first-look-at-americas-supergun-1464359194
======
matt-attack
> In conventional guns, a bullet loses velocity from the moment the gunpowder
> ignites and sends it flying. The railgun projectile instead gains speed as
> it travels the length of a 32-foot barrel..

This is incorrect. Most cartridges are design so that the projectile
accelerates for the entire length of the barrel.

~~~
hooloovoo_zoo
Perhaps the author meant the bullet loses acceleration over the length of the
barrel?

~~~
foota
Based on the fact that they state the railgun is different in that it gains
speed over during the time in the barrel, it seems like the author just
doesn't gun physics.

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dredmorbius
Some equivalence values here.

A typical US navy marine propulsion reactor puts out 250 MW. This railgun
would require about 10% the energy output of such a reactor. A large aircraft
carrier might have several cores.

From the 9/11 attack scenario below, impact speed matters (kinetic energy
scales with the _square_ of velocity), but chemical reactions pack a great
deal of energy. The _fuel_ of the airliners crashed into the World Trade
Center towers released some 370x more energy than the impacts themselves,
though as thermal energy delivered over roughly an hour, rather than the
instantaneous impact.

As an alternative to missiles, the railguns would likely allow for increased
firing -- a typical vessel carries fewer than 100 missiles, but could probably
carry far more shells (and be capable of firing them).

I'm wondering at what point increased speed means you're simply punching holes
through things without actually inflicting damage -- it's the _transfer_ of
energy from shell to structure that matters. If you're targeting a deeply
buried concrete bunker, this is appropriate. Residential or commercial
buildings, cars, etc., will to a large extent simply get very well ventilated
(though you might not want to be in the immediate enting area when this
happens). Matching shell structure to target likely matters.

~~~
LNMNMMMC
Never, more speed is good because they can program the projectiles to break
apart before impact with soft targets. The limiting factor is air resistance,
greater initial speeds result in more energy wasted.

Also, I believe they are (were?) looking at the Zumwalt destroyer for this
weapon, which actually only has 78 MW of power output.

~~~
tonmoy
Does power really matter? 25MW instantaneous power vs continuous/average power
are different things. With modern clever power electronics you could get
pretty high instantaneous power from a lower powered source. The exact energy
vs time curve and desired fire rate has to be utilized to make any effective
prediction I think.

~~~
myblake
The article does mention advances in supercapaciter design as one of the
enabling technologies, but I suspect just charging the things requires a ton
of power. Let's do some back of the envelope physics with what we know (and
reasonable ball park guesses when we don't)!

It's traveling 4K mph or about 1800m/s, let's assume since its 24in long and
largely tungsten it has a mass of around 60kg. 1/2 * mass * velocity ^2 means
it needs 97.2 megajoules of power. That's about 4 seconds for a 25MW reactor,
so I guess you're right something smaller could fire it less rapidly, though
the one every 6 seconds they cite as desired would require that much power.

------
dwaltrip
It's a bit fascinating and scary how casually they talk about the weapons of
China and Russia, and what we need to counter them. Do they believe there is a
realistic chance of war with these countries? Or is just about using military
might as a political & diplomatic tool?

~~~
Teever
Let's look at this another way: Do you think that there will never be another
major war? Like never, ever, ever again?

Can you genuinely state with certainty that humanity is over fighting major
wars -- that we've evolved past that?

The answer is simply no, we haven't gotten past that point and likely never
will. So in that context we should be developing weapons to fight and win wars
against the most likely of threats.

The most likely threats happen to be China and Russia.

~~~
tormeh
No, we haven't evolved past major wars, but nuclear weapons have made them
impossible to win. That is something new under the sun.

That's why I don't believe in "a world without nuclear weapons" \- a world
without nuclear weapons is a world in which the next world war is imminent.

That said, _something_ is going to happen in the south China sea. But no
rational actor would ever start a nuclear war. That leaves cold-war style
local dominance battles. Not nice, but not a major war either.

------
stcredzero
_In conventional guns, a bullet loses velocity from the moment the gunpowder
ignites and sends it flying. The railgun projectile instead gains speed as it
travels the length of a 32-foot barrel_

Even the Wall Street Journal has science/engineering illiterate idiots writing
for it? If engineered properly, a conventional naval gun will also continue to
accelerate its projectile all the way down the barrel. Why does this idiot
think there are various guns that have long barrels? It's to give expanding
gasses a longer time to accelerate the projectile.

~~~
edanm
You make good points, but I wish you'd express yourself more nicely. You
really don't need to call the authors idiots (twice!) To make your case.

~~~
stcredzero
This is how I genuinely feel about the level of scientific illiteracy our
society has fallen to. We literally have people at an executive level who are
functionally illiterate in science, making decisions on the basis of their
ignorance. (The editors of the WSJ could be seen as examples of this.) "Solar
Freakin Roadways" got almost $2 million from the public. Are we functioning
with a viable educational system for a complex technological democratic
society? Heck no. Even the people in charge are riddled with ignorance on
basic levels.

Not knowing what you don't know can literally cost untold treasure and many
millions of lives. There are tons of examples of this in history. I'm pretty
sure we're not doing so great a job teaching that either.

And yes, it even goes to examples of basic Computer Science knowledge on HN!

~~~
jessriedel
The sincerity of your feelings is not the point. The point is that calling
people names reduces the quality of the comments.

~~~
TeMPOraL
I think that calling people names here was making the comment much closer to
what 'stcredzero _actually thinks_. I.e. it boosted accuracy and clarity of
the comment.

Also, personally I don't have any other idea how to fix journalism than
calling them out every time, and calling them out _hard_.

~~~
jessriedel
You literally used "accuracy" and "clarity" as synonyms for intensity of
emotion. Under that logic, everything becomes a screaming match, and the
comments devolve into a competition to see who's feelings are the most
virulent.

~~~
TeMPOraL
I meant something else. When you write a comment, you transcribe your thoughts
and feelings into text. That text may or may not be close to what you actually
think - e.g. to the words you use in your internal monologue. In this case I
think the word choice serves to portray the actual thoughts and emotions of
the author more clearly/accurately.

~~~
dwaltrip
High quality comments are written to convey an idea or present an argument
(low quality comments are often written to make the writer feel good about
themselves without conveying any meaningful idea).

Removing words with high emotional charge but low signal (such as "idiot")
will increase the quality and effectiveness of the comment. Others will view
the comment more favorably, and any additional discussion is likely to be more
productive this way.

------
zellyn
"The Navy now believes it has a design that soon will be able to fire 10 times
a minute through a barrel capable of lasting 1,000 rounds."

So the barrel lasts just over an hour and a half?

~~~
m-i-l
Might a bigger challenge be the power source? If each firing requires 25MW,
then 1000 shells would require 25GW, which is equivalent to the output of
several large nuclear power stations.

Edit: Apologies, basic mistake, mixed up power with energy. Thanks for
correcting.

~~~
malisper
> If each firing requires 25Mw, then 1000 shells would require 25Gw

That's not how power works. Power is energy/second, so if one each firing
requires 25Mw, firing every round requires 25Mw.

Edit: Although after doing some calculations, firing 1000 shells would require
22 billion joules of energy, which is about the same as the energy released
during nuclear fission of three grams of uranium.

~~~
madmax96
How plentiful is Uranium? I'm not a nuclear engineer, so the 3 grams metric
isn't meaningful to me -- is that a considerable amount?

~~~
Roboprog
3 grams is between about 1/6 and 1/8 once.

Of course, only a small portion of uranium in a reactor core is converted to
something else. After that, they replace the fuel as its output drops a bit.

Disclaimer: I don't know enough to check the "grandparent" post's math. I'm
assuming the calc is right in that it's the fission energy, and not total
destruction of matter E=mc^2 / matter-antimatter style.

~~~
m-i-l
Thanks. That helps with my original question - how portable will this be? If
it just needs a very small nuclear reactor with a tiny amount of fuel, then
they should be able to have a power source "that generates 25 megawatts" and
can "fire 10 times a minute through a barrel capable of lasting 1,000 rounds"
on a ship. But what about a truck? Having a weapon with a 125 mile range isn't
necessarily all that great if it is too big and heavy to get within 125 miles
of most of the things you want to shoot at.

------
rsp1984
_Missile defense by the railgun is at least a decade away, but Pentagon
officials believe the weapon’s projectiles can be used much sooner. They are
filled with tungsten pellets harder than many kinds of steel, officials said,
and will likely cost between $25,000 and $50,000, a bargain compared with a
$10-million interceptor missile._

Learning about how expensive high-tech weapons are never ceases to blow my
mind. 50k for a single bullet -- equivalent to 1 yearly median US salary. 10m
for a missile -- the price of a luxury mansion or the value of a decently
successful startup.

~~~
wil421
I'm sure it could be a lot cheaper, usually government contracts are inflated.
Seems like everyone increases the actual costs to extract more money from the
government. Not to mention the govt changes requirements constantly (F-35).

But then again I feel like to do deals with the govt it requires jumping
through hoops.

~~~
baddox
> I'm sure it could be a lot cheaper, usually government contracts are
> inflated.

That's a reasonable rule of thumb, but it's kind of funny to apply it to the
weaponry of large scale modern militaries, since those almost certainly
couldn't exist without the very governments that makes their costs inflated.

~~~
TeMPOraL
I think the GP is not saying the problem is with government - it's with the
people who take government contracts and inflate the costs to take more money
for themselves.

------
azinman2
I look forward to the day that the great weapons race is for more weapons like
this that aren't radioactive, biological, or otherwise impact the environment
beyond the war itself.

~~~
Razengan
Tiny automated robot flies that seek out enemy leaders and inject poison?

------
NKCSS
Cool, but also something that makes war even more scary. You'd use to have all
sorts of things to protect you; there isn't anything that can protect you from
this once aimed at you (except a pre-emptive EMP; providing they have no
shielding for it). Feels weird knowing there is nothing that can protect you
from it.

~~~
Artlav
Not exactly. It can be protected from by a multi-layered whipple shield, kind
of like what was proposed to protect spaceships from meteors.

On the other hand, it won't be something you can line a ship or a plane with,
so yeah... Always shoot first.

------
aries1980
How "America's Supergun" is this if it is made by BAE?
[https://i1.wp.com/news.usni.org/wp-
content/uploads/2015/01/1...](https://i1.wp.com/news.usni.org/wp-
content/uploads/2015/01/140708-N-ZK869-010.jpg?ssl=1)

------
forgotAgain
Defense Industry porn.

------
Artlav
I'd love to know how they solved the barrel erosion problem.

A rail gun is as satanically simple in theory as it is satanically hard to
engineer.

A coil gun won't have this problem, but unfortunately the magnetic fields are
harder to get than the electric ones.

------
avodonosov
Gauss rifle :
[https://en.wikipedia.org/wiki/Coilgun](https://en.wikipedia.org/wiki/Coilgun)

~~~
PhasmaFelis
No, railguns and coilguns are different. The second paragraph at your link
explains the distinction.

~~~
avodonosov
Indeed, thanks for the hint. I actually wanted to note, that electromagnetic
guns is an old idea. (Even I came to it once, but of different design; and was
surprised when discovered it to be already studied - in that article though
they said this idea turned out to be impractical).

------
mrep
to put that speed in perspective, thats about 1/6 earth's escape velocity.

------
zaken
A 25-pound projectile traveling at 4500 miles per hour carries as much
momentum as a jumbo jet at cruising speed:
[http://www.wolframalpha.com/input/?i=25+pounds+*+4500+miles+...](http://www.wolframalpha.com/input/?i=25+pounds+*+4500+miles+per+second)

We know the impact a hijacked jumbo jet can have on buildings...now imagine
being able to sustain that level of destruction at a rate of 10 times/minute
with hardly any power or material consumption.

~~~
Someone
That impact wasn't as large as your remark make it appear to be. The twin
towers didn't collapse on impact, they collapsed from the energy released by
burning the fuel in the planes and the burnable stuff present in the planes
and the towers themselves (in what proportions, I don't dare take a stab at)

On the other hand, as another poster already said, you should compute energy.
That goes with velocity squared, so it will be way higher these projectile,
compared with a jumbo jet.

Edit: as another poster said, you also should have said miles/hour. That gives
you
[http://www.wolframalpha.com/input/?i=25+pounds%2F2+*+((4500+...](http://www.wolframalpha.com/input/?i=25+pounds%2F2+*+\(\(4500+miles+per+hour\)+squared)),
apparently about what a Samsung S3 uses in a year (what am I doing wrong?
[http://www.wolframalpha.com/input/?i=25+pounds%2F2+*+((4500+...](http://www.wolframalpha.com/input/?i=25+pounds%2F2+*+\(\(4500+miles+per+hour\)+squared\)+in+kWh)
gives me 6.374 kWh. Seems a tiny amount)

~~~
matt-attack
To reiterate, it's worth reviewing the collisions. You'll see the buildings
don't make the slightest movement upon impact. No discernible affect.

