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from the is-that-a-railgun-or-are-you-just-happy-to-see-me? dept.
The Motley Fool's Rich Smith writes:
For more than three years now, I've been tracking the U.S. Navy's progress toward building a working electromagnetic railgun prototype — a Mach 6 cannon reputedly capable of striking targets 110 miles away with pinpoint accuracy.
Each railgun projectile would cost about $25,000 to produce — and if you're keeping track, then yes, success on the railgun project would yield a weapon boasting nearly twice the 67-mile range of Boeing's (NYSE:BA) Harpoon II missile but costing just 1/48th the Boeing missile's $1.2 million cost.
https://www.fool.com/investing/2017/04/22/navys-new-mach-6-em-railgun-almost-ready-for-prime.aspx
Electromagnetic Railgun - First shot at Dahlgren's new Terminal Range https://youtu.be/Pi-BDIu_umo
(Score: 2, Informative) by qzm on Thursday April 27 2017, @02:41AM (2 children)
So, perhaps you would be so kind as to give YOUR estimate of pinpoint for a passive shell, at mach 6, over a 110 mile range through atmospheric conditions?
My estimate is 'will probably hit the small town it was aimed at', but 'will certainly not hit the large building it was aimed at'
I will back that up with a little maths. IGNORING atmospherics (which would have an order of magnitude more effect at least)
110 miles is just under 180000 meters.
The 'shell' looks to be well under 1/2 meter long.
Its trajectory will be 90% defined by the last 1 meter (2L) of barrel it travels through (actually less, but makes the maths easier)
So, to hit a target of 5m radius, that last 1 meter must have a deviation of less than 5/180000, or around 28um. (0.028mm) from perfect alignment. At these kinds of energy levels? not a chance.
But worse, given a 10 meter barrel (eyeballing that, longer makes it worse), to even aim that accurately means we need a horizontal rotational accuracy significantly better that one part in 2,200,000, including recoil, etc. not a chance.
Vertical alignment is much MUCH more stringent.
So, no, non guided ordinance is never 'pinpoint accurate' at 110 miles.
Atmospherics, of course, make that much Much MUCH worse, and basically make it a joke (and no, the high velocity doesnt make it easier, at mach 6, locally varying atmospherics density will have huge effects).
So, I go back to my claim. At 110 miles It will hit the town it was aimed at, but probably not the building.
(Score: 2) by Runaway1956 on Thursday April 27 2017, @02:27PM (1 child)
In flight correction. The video I watched shows the projectile adjusting it's flight near termination. I have little idea whether that in flight guidance can be triggered earlier, it appeared that guidance took over in the last - ohhh - 5 to 10 miles or so. The antiaircraft projectile surprised me, in that, the main projectile isn't expected to hit the target. Instead, the main projectile opens, and scatters a wad of smaller projectiles, rather like a shotgun. (I watched four videos last evening before work, please don't ask me to retrace my steps for links.)
From what I saw, hitting a large building in a city 100 miles away is only a minor challenge. It is conceivable that a well trained crew can put that shell into the first floor, and they might even be able to choose which window it enters through. Unless I completely misunderstood what I was watching, these projectiles will have guidance only slightly less sophisticated than today's cruise missiles.
And, regarding the size of that crater. Our 5" 54 guns would leave a 5 meter crater in the ground. The USS New Jersey's main guns would carve out a crater about 30 yards, or meters, which are close to each other for "government work". The rail gun probably exceeds the 16" guns in that respect . . . .
Looking for links to compare total energy of the three guns, found this article which echoes some of our comments here: http://www.popularmechanics.com/military/weapons/a21174/navy-electromagnetic-railgun/ [popularmechanics.com]
This is more what I was looking for: http://www.popularmechanics.com/military/weapons/a21174/navy-electromagnetic-railgun/ [popularmechanics.com]
Railgun delivers 64 megajoules on target, while a BGM-109 Tomahawk cruise missile delivers 3000 MJ. The sentence I was looking for is this one: "A MK 8 round fired from the 16-inch guns of an Iowa-class battleship at 2,500 ft/s (762 m/s) has 356 MJ of kinetic energy at the muzzle."
Obviously, my presumption that this railgun projectile would compare to New Jersey's guns was wrong, wrong, wrong. The railgun will maybe deliver a little more destructive energy at the sharp end of the stick than our 5" 54's did.
You make good points, and ask good questions - thank you. You made me look a little harder to make valid comparisons. :^)
(Score: 0) by Anonymous Coward on Friday April 28 2017, @04:14AM
this is an exemplar of why i am displeased when persons disparage eth_funked and runaway1956 in the same sentence. One is 99% troll, the other is a person of occasionally malleable belief and rationale who looks things up for the community sometimes.