# Electromagnetic railgun: why all the smoke and fire? **URL:** \ **Category:** Factual Questions\ **Created:** [February 29, 2012, 4:05pm UTC](https://boards.straightdope.com/t/electromagnetic-railgun-why-all-the-smoke-and-fire/614353 "2012-02-29T16:05:06Z")\ **Posts on this page:** 16\ **Page:** 3
**Author:** ![Francis\_Vaughan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/francis_vaughan/32/3093_2.png) [@Francis\_Vaughan](https://boards.straightdope.com/u/Francis_Vaughan)\ **Post date:** [March 1, 2012, 3:14pm UTC](https://boards.straightdope.com/t/electromagnetic-railgun-why-all-the-smoke-and-fire/614353/41 "2012-03-01T15:14:32Z")
One suspects the shape is derived from a few factors. The rear C shaped part would appear to be designed to contact the rails (it is flat on the outsides) and conduct the driving current through the C. The cylinder to the front of the projectile seems to be there to hold the square top - which, I suspect, is an insulator and is designed to sit within the rails and stabilise the projectile whilst it is being accelerated. They claim the projectile is hypersonic. Aerodynamics get weird at those speeds. The idea that you need a pointy projectile isn’t really the case. No matter what, eventually you have to shift the amount of air covered by your cross section, and whether the nose is pointy of not does not affect this. Indeed a pointy shape simply has more surface area that is seen by the hypersonic flow, and you get worse frictional losses. A blunt nose is actually better. Famously, the Space Shuttle has a blunt nose for just this reason. ---
**Author:** ![Baracus](https://avatars.discourse-cdn.com/v4/letter/b/2bfe46/32.png) [@Baracus](https://boards.straightdope.com/u/Baracus)\ **Post date:** [March 1, 2012, 3:18pm UTC](https://boards.straightdope.com/t/electromagnetic-railgun-why-all-the-smoke-and-fire/614353/42 "2012-03-01T15:18:06Z")
> [@Francis\_Vaughan](#): > > One suspects the shape is derived from a few factors. The rear C shaped part would appear to be designed to contact the rails (it is flat on the outsides) and conduct the driving current through the C. The cylinder to the front of the projectile seems to be there to hold the square top - which, I suspect, is an insulator and is designed to sit within the rails and stabilise the projectile whilst it is being accelerated. > > They claim the projectile is hypersonic. Aerodynamics get weird at those speeds. The idea that you need a pointy projectile isn’t really the case. No matter what, eventually you have to shift the amount of air covered by your cross section, and whether the nose is pointy of not does not affect this. Indeed a pointy shape simply has more surface area that is seen by the hypersonic flow, and you get worse frictional losses. A blunt nose is actually better. Famously, the Space Shuttle has a blunt nose for just this reason. The actual explanation for the shape of the projectile was given back in post 32. ---
**Author:** ![Shodan](https://avatars.discourse-cdn.com/v4/letter/s/9f8e36/32.png) [@Shodan](https://boards.straightdope.com/u/Shodan)\ **Post date:** [March 1, 2012, 3:20pm UTC](https://boards.straightdope.com/t/electromagnetic-railgun-why-all-the-smoke-and-fire/614353/43 "2012-03-01T15:20:23Z")
> [@Leo\_Bloom](#): > > That would be one humdinger of a home defense weapon. No kidding. Not only did I kill the burglar, I cannot be convicted because there is no evidence - he was fucking _vaporized_! Regards, Shodan ---
**Author:** ![carnivorousplant](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/carnivorousplant/32/3563_2.png) [@carnivorousplant](https://boards.straightdope.com/u/carnivorousplant)\ **Post date:** [March 1, 2012, 3:33pm UTC](https://boards.straightdope.com/t/electromagnetic-railgun-why-all-the-smoke-and-fire/614353/44 "2012-03-01T15:33:32Z")
> [@Ravenman](#): > > guided down to the target. I thought the only thing guiding it was Mr. Newton. ---
**Author:** ![Ravenman](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ravenman/32/2929_2.png) [@Ravenman](https://boards.straightdope.com/u/Ravenman)\ **Post date:** [March 1, 2012, 3:41pm UTC](https://boards.straightdope.com/t/electromagnetic-railgun-why-all-the-smoke-and-fire/614353/45 "2012-03-01T15:41:27Z")
> [@carnivorousplant](#): > > I thought the only thing guiding it was Mr. Newton. [Nope.](http://www.navysbir.com/n12_1/N121-102.htm) ---
**Author:** ![Sailboat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/sailboat/32/461_2.png) [@Sailboat](https://boards.straightdope.com/u/Sailboat)\ **Post date:** [March 1, 2012, 3:55pm UTC](https://boards.straightdope.com/t/electromagnetic-railgun-why-all-the-smoke-and-fire/614353/46 "2012-03-01T15:55:53Z")
> [@Baracus](#): > > The actual explanation for the shape of the projectile was given back in post 32. They WERE going to design a more aerodynamic projectile, but the entire thing went off the rails. ---
**Author:** ![carnivorousplant](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/carnivorousplant/32/3563_2.png) [@carnivorousplant](https://boards.straightdope.com/u/carnivorousplant)\ **Post date:** [March 1, 2012, 4:11pm UTC](https://boards.straightdope.com/t/electromagnetic-railgun-why-all-the-smoke-and-fire/614353/47 "2012-03-01T16:11:56Z")
> [@Ravenman](#): > > [Nope.](http://www.navysbir.com/n12_1/N121-102.htm) This is getting better and better. 🙂 ---
**Author:** ![mlees](https://avatars.discourse-cdn.com/v4/letter/m/ba8739/32.png) [@mlees](https://boards.straightdope.com/u/mlees)\ **Post date:** [March 1, 2012, 5:20pm UTC](https://boards.straightdope.com/t/electromagnetic-railgun-why-all-the-smoke-and-fire/614353/48 "2012-03-01T17:20:14Z")
> [@Ravenman](#): > > [Nope.](http://www.navysbir.com/n12_1/N121-102.htm) Must survive twenty to forty thousand G’s of accel? Holy. Crap. > [@from link](#): > > The package must fit within the mass (\< 2 kg), diameter (\< 40 mm outer diameter), and volume (200 cm3) constraints of the projectile and do so without altering the center of gravity. It should also be able to survive accelerations of at least 20,000 g (threshold) / 40,000 g (objective) in all axes, high electromagnetic fields (E \> 5,000 V/m, B \> 2 T), and surface temperatures of \> 800 deg C. The package should be able to operate in the presence of any plasma that may form in the bore or at the muzzle exit and must also be radiation hardened due to exo-atmospheric flight. Total power consumption must be less than 8 watts (threshold) / 5 watts (objective) and the battery life must be at least 5 minutes (from initial launch) to enable operation during the entire engagement. In order to be affordable, the production cost per projectile must be as low as possible, with a goal of less than $1,000 per unit. ---
**Author:** ![August\_West](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/august_west/32/18069_2.png) [@August\_West](https://boards.straightdope.com/u/August_West)\ **Post date:** [March 1, 2012, 8:39pm UTC](https://boards.straightdope.com/t/electromagnetic-railgun-why-all-the-smoke-and-fire/614353/49 "2012-03-01T20:39:22Z")
> [@mlees](#): > > Must survive twenty to forty thousand G’s of accel? > > Holy. > Crap. Yeah, and must be able to withstand “exo-atmospheric flight”? I think they are preparing for a railgun with a range outside of 200 miles if the projectile needs to spend some time in space. Unless I’m reading that completely wrong ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [March 1, 2012, 8:58pm UTC](https://boards.straightdope.com/t/electromagnetic-railgun-why-all-the-smoke-and-fire/614353/50 "2012-03-01T20:58:27Z")
It’d be awfully hard to get that kind of range without leaving the atmosphere. ---
**Author:** ![carnivorousplant](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/carnivorousplant/32/3563_2.png) [@carnivorousplant](https://boards.straightdope.com/u/carnivorousplant)\ **Post date:** [March 1, 2012, 9:40pm UTC](https://boards.straightdope.com/t/electromagnetic-railgun-why-all-the-smoke-and-fire/614353/51 "2012-03-01T21:40:30Z")
How flat a trajectory can you get at Mach seven? That would mess up everybody’s day, going through an aircraft carrier. ---
**Author:** ![mlees](https://avatars.discourse-cdn.com/v4/letter/m/ba8739/32.png) [@mlees](https://boards.straightdope.com/u/mlees)\ **Post date:** [March 1, 2012, 9:46pm UTC](https://boards.straightdope.com/t/electromagnetic-railgun-why-all-the-smoke-and-fire/614353/52 "2012-03-01T21:46:42Z")
I chuckled at the part “all this, and at a price under $1000 each”. ---
**Author:** ![Gray\_Ghost](https://avatars.discourse-cdn.com/v4/letter/g/c0e974/32.png) [@Gray\_Ghost](https://boards.straightdope.com/u/Gray_Ghost)\ **Post date:** [March 1, 2012, 10:20pm UTC](https://boards.straightdope.com/t/electromagnetic-railgun-why-all-the-smoke-and-fire/614353/53 "2012-03-01T22:20:06Z")
The g-loading in the cited spec looks fearsome, but probably isn’t that innovative, considering the Army has had gun-launched electronics for some time, like the Copperhead laser guided 105mm round. This [.pdf](http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA443252) is a brief examination of some of the issues in designing electronics for that environment regime. Further, [this paper](http://books.google.com/books?id=L9oaDntTOvwC&pg=PA1038) from the Ballistics 2011 26th annual international symposium, goes into further criteria for selecting electronics potting materials for gun launch. As a layperson, so completely speaking _ex rectum_, what I see being the real pain to deal with, will be shielding the electronics from the high, drastically changing, magnetic field environment. I would think that properly choosing the potting material would suffice for the temperature and radiation hardening specs. I wonder if they’ll use photonics or some other means of light pulses, instead of traditional solid-state electronics? As far as the height of the trajectory, it’ll make their energy requirements a lot easier if the projectile goes through as little of the lower parts of the atmosphere at possible. Even the big guns on the old battleships, with their comparatively paltry ranges of 20-25 miles, had a maximum trajectory height of 3 miles plus. See this discussion of trajectory heights [here](http://www.kbismarck.org/forum/viewtopic.php?f=36&t=59). I know the range tables for the 16 inchers are floating around the internet somewhere. ---
**Author:** ![Capt.Ridley\_s\_Shooting\_Party](https://avatars.discourse-cdn.com/v4/letter/c/cc9497/32.png) [@Capt.Ridley\_s\_Shooting\_Party](https://boards.straightdope.com/u/Capt.Ridley_s_Shooting_Party)\ **Post date:** [March 1, 2012, 10:38pm UTC](https://boards.straightdope.com/t/electromagnetic-railgun-why-all-the-smoke-and-fire/614353/54 "2012-03-01T22:38:49Z")
Is this likely going to be a US Navy only weapon? One of the prototype are being designed and developed by BAe Systems, using their own money. Are BAe going to be allowed to sell this on to allied nations? ---
**Author:** ![Fubaya](https://avatars.discourse-cdn.com/v4/letter/f/c2a13f/32.png) [@Fubaya](https://boards.straightdope.com/u/Fubaya)\ **Post date:** [March 1, 2012, 10:52pm UTC](https://boards.straightdope.com/t/electromagnetic-railgun-why-all-the-smoke-and-fire/614353/55 "2012-03-01T22:52:08Z")
> [@AaronX](#): > > I think I read that some designs put the projectile on a sled that is vaporised and becomes plasma. Anyone heard of this before? Yes, many have said the projectile is conductive but it’s not. A big chunk of conductive metal tends to get welded to the rails. A conductive armature is placed behind it which the electricity vaporizes into a plasma. In many designs, the armature is little more than aluminum foil, but it’s called a “plasma armature railgun” because vaporizing the foil into plasma is one of the first steps and the plasma is the goal. I think I read that plasma was pumped into the Navy’s gun. I don’t know if that’s inaccurate reporting or what. ---
**Author:** ![Ravenman](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ravenman/32/2929_2.png) [@Ravenman](https://boards.straightdope.com/u/Ravenman)\ **Post date:** [March 1, 2012, 11:19pm UTC](https://boards.straightdope.com/t/electromagnetic-railgun-why-all-the-smoke-and-fire/614353/56 "2012-03-01T23:19:32Z")
> [@Capt.Ridley\_s\_Shooting\_Party](#): > > Is this likely going to be a US Navy only weapon? One of the prototype are being designed and developed by BAe Systems, using their own money. Are BAe going to be allowed to sell this on to allied nations? Anything developed here in the US would be subject to the International Trafficking in Arms regulations, and government licenses would be required to export the articles themselves or technical data about them. [Previous page](https://boards.straightdope.com/t/electromagnetic-railgun-why-all-the-smoke-and-fire/614353.md?page=2)