Mach 7 is ~1.48 miles per second. The escape velocity from the Moon is ~1.47 miles per second [1,2]. (Let's launch stuff from asteroids and from the moon back at Earth (except, let's be sure not to bombard ourselves.))
Not to mention, this is capable accelerating a projectile to Mach 7 within the friction of Earth's atmosphere. Without one, perhaps it would be capable of faster velocities.
This can make a projectile move at mach 7, which is a little more than 20% of the Earth's escape velocity.
Are there physical limits that would prevent us from building a bigger one and using it to launch small things into space? Or "just" engineering problems?
A space railgun is theoretically possible, but you'll still need a rocket to circularize the orbit.
In practice, a rocket goes up (out of most of the atmosphere) before going fast. A projectile fired out of a railgun would be going at its fastest while still in the atmosphere, and would thus be very hot / inefficient at the gun's "muzzle"
Heinlein's "The Moon is a Harsh Mistress" discusses such a solution for sending mined material back from the moon, which seems like a more feasible application.
The whole system is indeed possible, though. See this discussion:
The short answer is that it is a plausible mechanism for g-hardened payloads, but probably not for soft payloads (like human beings). The problem is that accelerating up to orbital velocity at the maximum survivable continuous rate (~4 or 5 g) still takes hundreds of miles, which is probably an infeasible length for a barrel. Additionally, if it's not somehow supported so that it rises above the atmosphere, the de-acceleration from drag at the exist of the barrel is also too extreme.
Elon Musk @elonmusk · Jan 26
Final one: anything launched by a railgun (if you could ever reach ~ Mach 27) would explode upon exiting the barrel in our dense atmosphere
https://twitter.com/elonmusk/status/559629011983147008
Other people have mentioned why you wouldn't want to use a railgun to get a payload into orbit in one go. However, the exponential nature of the rocket equation means that every km/s you can get to start with has a large effect on what fraction of your rocket has to be fuel.
The more likely limitation is the human body. We can only take so much acceleration until we lose consciousness or worse. This would necessitate a much longer "runway" for people to use safely. No comment on unmanned use.
I watched the video with the slow motion shot of the projectile coming out with a large ball of fire behind it. It then goes on while the casing falls away.
But I don't understand, why is there a fireball if it's all electromagnetic?
The projectile has so much kinetic energy that it turns everything it touches into plasma. That includes the air it travels through. At the point of launch there is also very substantial material ablation that feeds a plasma bloom.
In fact, one of the primary engineering challenges in the design of a rail gun is minimizing ablation of the gun itself across firings. Rail guns slowly eat themselves so you want a design where (1) the ablation is slow enough that you can still get many shots off before it is non-functional and (2) the ablation is localized in easily, cheaply, quickly replaceable parts.
Probably from dumping 32 megajoules of energy into the rails/barrel. I wouldn't be surprised if part of it is melting/igniting the actual hardware itself and part of it is due to the friction of the projectile against the air.
Remember that this is still a prototype and one of the big concerns since day one has been lifetime of the system. Essentially, it's probably still melting its own hardware (at least to some degree) every shot.
> One big question this video begs is, what causes the giant fireball? Rail guns are supposed to be powered solely by electricity, and don't use explosives of any kind for propellant. Babb told PopSci the answer: The flames are from pieces of the projectile disintegrating; the 7-pound slug is jammed so firmly between the rails that when it's fired, pieces shear off and ignite in the air.
My first guess was that the explosions are coming from the projectile punching through those walls they put up, or the speed of a projectile superheating the air through which it's travelling to the point of igniting the air around it.
The latter guess seems way off base, but I'd love to learn exactly why!
I wonder what the effective range of this thing actually is because the curvature of the earth is going to come into it when talking about these distances.
The curvature is roughly 8 inches per mile, ~1 meter per 5 miles. Something 6 stories tall (~18 meters), like say a large capital ship would be below the horizon if it was 90 miles away. Granted rail guns don't shoot in a straight line but you aren't going to get much ballistic drop in the time it takes a Mach 7 projectile to get to its destination...
Mounting the gun higher on the ship would help, but then you are dealing with a very large equal-and-opposite force high above your center of gravity...
[EDIT] On second thought, with a velocity of 1.48 miles per second you are talking about 81 seconds of flying time at it maximum range, which is quite long enough for our friend gravity to drop the projectile and "bend" it around the horizon. Holy shit that's pretty incredible.
I'm sure they'll show up on ground-based artillery soon enough, and there will be an arms race in the things, because for many theaters they could give one side an overwhelming advantage. Besides the range, the other benefit is cost: railgun launches cost 1-2% of equivalent missile launches, with fewer risks, eg if the enemy bombs your ammo dump, it's much less of a big deal because it's not full of high explosive. These risks matter a lot; in the history of modern naval warfare, the biggest risk to a warship was having its magazine hit, which would usually tear the ship in two.
Firing something that distance is easier than hitting anything specific once the projectile gets there. Projectiles must have some kinds of internal guidance system (that works at Mach7) or else the Navy is just going to be slamming random meteorites down anywhere within very large swaths of countryside.
I remember hearing about a plan to build a giant rail-gun (or coil, or whatever) into the side of a mountain and try to send stuff into space.
The issue was A) the barrel would be evacuated of air and the piece of glass covering the end would send glass everywhere and B) the resulting sonic booms would destroy the local ecosystem.
Looking for sonic boom energy levels (up to 100 megawatts/sq. meter!) I stumbled across this gem:
> In 1964, NASA and the FAA began the Oklahoma City sonic boom tests, which caused eight sonic booms per day over a period of six months. Valuable data was gathered from the experiment, but 15,000 complaints were generated and ultimately entangled the government in a class action lawsuit, which it lost on appeal in 1969. (http://en.wikibooks.org/wiki/Acoustics/Sonic_Boom#Perception...)
Not that I'm saying killing people or sowing destruction is good, but tons of "good" or productive inventions we use today have their origins or inspirations as weapons of destruction. Who is to say, years later, the work on EM field concentration developed here for the rail gun can't be used to (for example) "tune" people's brains out of seizures.
Isn't the political implications here on Earth the more relevant (though less fun)?
Novel large weapons (I'm thinking lasers, hyper velocity cruise missiles and this and it's ilk) all seem set to unbalance military strategy on a scale we have not seen since the USNavy told a couple of pilots "I bet you can't sink those spare dreadnoughts"
A naval vessel parked thirty miles of the coast of most countries that is able to destroy incoming targets and fire large lumps of metal at seven times the speed of sound at major cities seems like the return of gunboat diplomacy.
Add to which now that lasers seem to be at the 25KW range from a truck, I do wonder what 25 KW will do to a human head. Especially one tracked by facial recognition.
Oh by the way, Washington DC apparently has big zeppelin based radar arrays hanging above it these days - hoping to spot things travelling at Mach 7 before it's too late. So these thoughts have been occurring to folks for quite a while
I'm sure the Navy is really enjoying their new toy and will have lots of fun playing with it, but I honestly don't think it will change politics much.
For most countries in the world, there is little practical difference between a navy ship 30 miles off their coast with a railgun, and a navy ship 30 miles off their coast with cruise missiles. Even if they could shoot down the cruise missile (which most countries couldn't do with much reliability), the fact that the cruise missile was flying through their airspace in the first place implies active military conflict. That's a situation that already escalated beyond diplomacy.
Think of it this way: Which countries would shrug off the US threatening them with stealth bombers and cruise missiles, but wouldn't shrug off the US threatening them with a railgun? Russia or China? Maybe France or the UK? Just about any country that plausibly might be in a position react that way is a nuclear power anyway.
Gunboat diplomacy never went away. When East Timor was reclaimed from the Indonesian cough 'militias' cough, the US parked a fleet in international waters near Jakarta, for example.
UT Austin did a lot research for a tank-caliber railgun; in fact a lot of novel developments for pulsed energy from flywheel storage happened there.
Rifle size is currently a non-starter as a significant issue for rifles is the weight of the ammunition, and any electrical source of energy is likely going to be heavier than modern gunpowder.
The US Navy has a Science and Technology Expo? I wonder what else they showed and how open it is?
"The lack of gunpowder and explosive warheads eliminates some significant safety hazards for Navy crews, officials say." - that's probably an understatement.
Not only that, but because you don't need room for the powder (and all the safety armored bulkheads & systems around it), you can store a lot more of these projectiles on board. So far as warheads are concerned, E=1/2 m v^2 means kinetic energy is probably just as effective, given enough v.
I think I read elsewhere the rate of fire is 5 or 6 a minute. Combine that with the 160km range, and you've got quite a good shore bombardment system. I'm wondering how well it'd do ship vs. ship, over the horizon. Presumably they'd have a drone near the target so they could adjust fire.
A railgun is a direct-fire weapon with no explosives -- it won't be used to carpet-bomb civilian targets or wage drone-like terror campaigns. It's pretty much "a way for a warship to blow up another warship."
That's not to necessarily say we should celebrate any weapons technology, but as far as weapons technology goes, this is one that fits pretty solidly in the role of "militaries fighting other militaries." Sure, I guess that the US Navy could use it to blow up an unarmed civilian vessel, but honestly the US Navy could do that anyway.
Well, it is cool, just on its merits as a machine. The fact that it's designed for killing people doesn't suddenly make it un-cool, nor does it mean we're somehow obligated to ignore it or pretend it isn't interesting.
There's a difference between admiring something because it kills, and admiring something for other reasons, that just happens to kill.
I understand your sentiment, but ultimately I fear that the only way humans will stop doing this is to genetically engineer it out of ourselves. Until then, I'd rather be stronger than weaker, since I cannot control what other humans want to do to me.
I don't like it, but I don't particularly feel like being conquered, either.
[+] [-] politician|11 years ago|reply
[1] http://www.idialstars.com/evmc.htm
[2] http://en.wikipedia.org/wiki/Escape_velocity#List_of_escape_...
[+] [-] dshankar|11 years ago|reply
[+] [-] bduerst|11 years ago|reply
[+] [-] abstractbill|11 years ago|reply
Are there physical limits that would prevent us from building a bigger one and using it to launch small things into space? Or "just" engineering problems?
[+] [-] sparkman55|11 years ago|reply
In practice, a rocket goes up (out of most of the atmosphere) before going fast. A projectile fired out of a railgun would be going at its fastest while still in the atmosphere, and would thus be very hot / inefficient at the gun's "muzzle"
Heinlein's "The Moon is a Harsh Mistress" discusses such a solution for sending mined material back from the moon, which seems like a more feasible application.
The whole system is indeed possible, though. See this discussion:
http://physics.stackexchange.com/questions/35139/what-is-the...
[+] [-] jessriedel|11 years ago|reply
https://www.youtube.com/watch?v=Moo5nuLWtHs
The short answer is that it is a plausible mechanism for g-hardened payloads, but probably not for soft payloads (like human beings). The problem is that accelerating up to orbital velocity at the maximum survivable continuous rate (~4 or 5 g) still takes hundreds of miles, which is probably an infeasible length for a barrel. Additionally, if it's not somehow supported so that it rises above the atmosphere, the de-acceleration from drag at the exist of the barrel is also too extreme.
[+] [-] empy|11 years ago|reply
[+] [-] iblaine|11 years ago|reply
http://www.quora.com/Is-it-possible-to-use-a-big-gun-railgun...
[+] [-] Symmetry|11 years ago|reply
[+] [-] rm_-rf_slash|11 years ago|reply
[+] [-] Yizahi|11 years ago|reply
[+] [-] Dylan16807|11 years ago|reply
[+] [-] loceng|11 years ago|reply
[+] [-] ourmandave|11 years ago|reply
But I don't understand, why is there a fireball if it's all electromagnetic?
[+] [-] jandrewrogers|11 years ago|reply
In fact, one of the primary engineering challenges in the design of a rail gun is minimizing ablation of the gun itself across firings. Rail guns slowly eat themselves so you want a design where (1) the ablation is slow enough that you can still get many shots off before it is non-functional and (2) the ablation is localized in easily, cheaply, quickly replaceable parts.
[+] [-] ethanbond|11 years ago|reply
Remember that this is still a prototype and one of the big concerns since day one has been lifetime of the system. Essentially, it's probably still melting its own hardware (at least to some degree) every shot.
[+] [-] nerfhammer|11 years ago|reply
[+] [-] vilhelm_s|11 years ago|reply
http://www.popsci.com/military-aviation-space/article/2008-0...
[+] [-] bigstumpy|11 years ago|reply
[+] [-] JonLim|11 years ago|reply
My first guess was that the explosions are coming from the projectile punching through those walls they put up, or the speed of a projectile superheating the air through which it's travelling to the point of igniting the air around it.
The latter guess seems way off base, but I'd love to learn exactly why!
[+] [-] lettergram|11 years ago|reply
110 nautical miles = 126.586 miles
That's equivalent to shooting a projectile from:
- Baltimore to Philadelphia (102 miles = 88.6356 nautical)
- San Francisco to Sacramento (87.3 miles = 75.86 nautical)
- Joliet to Champaign (113 miles = 98.1943 nautical)
- (almost) Pittsburgh to Cleveland (132.7 miles = 115.31315 nautical)
- Tampa to Orlando (84.1 miles = 73.0809 nautical)
and so on...
Simply amazing how far these things can fire.
[+] [-] billyhoffman|11 years ago|reply
The curvature is roughly 8 inches per mile, ~1 meter per 5 miles. Something 6 stories tall (~18 meters), like say a large capital ship would be below the horizon if it was 90 miles away. Granted rail guns don't shoot in a straight line but you aren't going to get much ballistic drop in the time it takes a Mach 7 projectile to get to its destination...
Mounting the gun higher on the ship would help, but then you are dealing with a very large equal-and-opposite force high above your center of gravity...
[EDIT] On second thought, with a velocity of 1.48 miles per second you are talking about 81 seconds of flying time at it maximum range, which is quite long enough for our friend gravity to drop the projectile and "bend" it around the horizon. Holy shit that's pretty incredible.
[+] [-] anigbrowl|11 years ago|reply
[+] [-] tpurves|11 years ago|reply
[+] [-] mynameishere|11 years ago|reply
http://en.wikipedia.org/wiki/Paris_Gun
[+] [-] VikingCoder|11 years ago|reply
[+] [-] stolio|11 years ago|reply
The issue was A) the barrel would be evacuated of air and the piece of glass covering the end would send glass everywhere and B) the resulting sonic booms would destroy the local ecosystem.
Looking for sonic boom energy levels (up to 100 megawatts/sq. meter!) I stumbled across this gem:
> In 1964, NASA and the FAA began the Oklahoma City sonic boom tests, which caused eight sonic booms per day over a period of six months. Valuable data was gathered from the experiment, but 15,000 complaints were generated and ultimately entangled the government in a class action lawsuit, which it lost on appeal in 1969. (http://en.wikibooks.org/wiki/Acoustics/Sonic_Boom#Perception...)
[+] [-] Keyframe|11 years ago|reply
[+] [-] ddstanley|11 years ago|reply
[+] [-] ffn|11 years ago|reply
[+] [-] lifeisstillgood|11 years ago|reply
Novel large weapons (I'm thinking lasers, hyper velocity cruise missiles and this and it's ilk) all seem set to unbalance military strategy on a scale we have not seen since the USNavy told a couple of pilots "I bet you can't sink those spare dreadnoughts"
A naval vessel parked thirty miles of the coast of most countries that is able to destroy incoming targets and fire large lumps of metal at seven times the speed of sound at major cities seems like the return of gunboat diplomacy.
Add to which now that lasers seem to be at the 25KW range from a truck, I do wonder what 25 KW will do to a human head. Especially one tracked by facial recognition.
Oh by the way, Washington DC apparently has big zeppelin based radar arrays hanging above it these days - hoping to spot things travelling at Mach 7 before it's too late. So these thoughts have been occurring to folks for quite a while
[+] [-] Crito|11 years ago|reply
For most countries in the world, there is little practical difference between a navy ship 30 miles off their coast with a railgun, and a navy ship 30 miles off their coast with cruise missiles. Even if they could shoot down the cruise missile (which most countries couldn't do with much reliability), the fact that the cruise missile was flying through their airspace in the first place implies active military conflict. That's a situation that already escalated beyond diplomacy.
Think of it this way: Which countries would shrug off the US threatening them with stealth bombers and cruise missiles, but wouldn't shrug off the US threatening them with a railgun? Russia or China? Maybe France or the UK? Just about any country that plausibly might be in a position react that way is a nuclear power anyway.
[+] [-] vacri|11 years ago|reply
[+] [-] zerooneinfinity|11 years ago|reply
[+] [-] desdiv|11 years ago|reply
https://www.youtube.com/watch?v=TWeJsaCiGQ0
The fine print is that they're coilguns, not railguns; their operating principles are entirely different.
[+] [-] aidenn0|11 years ago|reply
Rifle size is currently a non-starter as a significant issue for rifles is the weight of the ammunition, and any electrical source of energy is likely going to be heavier than modern gunpowder.
[+] [-] rnhmjoj|11 years ago|reply
[+] [-] jschulenklopper|11 years ago|reply
[+] [-] protomyth|11 years ago|reply
"The lack of gunpowder and explosive warheads eliminates some significant safety hazards for Navy crews, officials say." - that's probably an understatement.
[+] [-] chiph|11 years ago|reply
I think I read elsewhere the rate of fire is 5 or 6 a minute. Combine that with the 160km range, and you've got quite a good shore bombardment system. I'm wondering how well it'd do ship vs. ship, over the horizon. Presumably they'd have a drone near the target so they could adjust fire.
[+] [-] higherpurpose|11 years ago|reply
[+] [-] aetherson|11 years ago|reply
That's not to necessarily say we should celebrate any weapons technology, but as far as weapons technology goes, this is one that fits pretty solidly in the role of "militaries fighting other militaries." Sure, I guess that the US Navy could use it to blow up an unarmed civilian vessel, but honestly the US Navy could do that anyway.
[+] [-] wyager|11 years ago|reply
[+] [-] mikeash|11 years ago|reply
There's a difference between admiring something because it kills, and admiring something for other reasons, that just happens to kill.
[+] [-] breckinloggins|11 years ago|reply
I don't like it, but I don't particularly feel like being conquered, either.
[+] [-] njharman|11 years ago|reply
[+] [-] enlightenedfool|11 years ago|reply
[+] [-] mhurron|11 years ago|reply