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Magnetic Propulsion Pellet Gun Achieves 20km/s
"Researchers at Sandia National Laboratories have used their Z Accelerator, a magnetic accelerator used in equations of state research, to accelerate pellets to speeds of about 20 km/s (about twenty times faster than a high-powered rifle bullet). Full story is here." Uses projected for this technology include simulating the impact of space junk, and, Yes, as the core of a hyper-velocity weapon.
"A well-regulated Militia being necessary to the security of a free State, the right of the people to keep and bear hyper-veolcity railguns shall not be infringed."
I've seen a detailed proposal for a 15g man rated coilgun capable of launching 1 ton into (very) LEO. It's a 250 mile long fiberglass vacuum tube surrounded by a electromagnets. A launch takes 15GW of electrical power for about 30 seconds. The passenger rides in a crash couch (obviously at 15g) in front of a superconducting coil. For the first 25s, the thrust is forwards. For the next 5s the thrust is upwards, as the end of the gun bends up a convenient mountain. Shortly before the payload reaches them, the muzzle doors open, and the thrust is then backwards (air resistance) for the few seconds it takes to clear most of the atmosphere. Aerodynamic control surfaces on the projectile bend the orbit into an ellipse whose perigee just grazes the atmosphere, with apogee just above. Finally a very small rocket firing 45 minutes later raises the perigee to stabilize the orbit long enough for pickup by an inter-orbital shuttle.
It seemed a completely plausible design, although the failure mode analysis was likely to be tricky.
I can email you the PDF if you like. You can find my email address in my user info.
Sent a day ago, and still waiting. Was it eaten by the 'net daemons?
If necessary, you can find my email address in the Linux Media Labs web-board (http://www.linuxmedialabs.com and hunt around).
Could anyone with closer ties to this project brief me on exactly what the working principles of this are? The article doesn't go into very much detail.
Before I get six different descriptions of how railguns work - I already know how most varieties of magnetic gun work. I want to know *which* this uses.
My best guess is something that uses the same principles as a coilgun (conducting object is repelled by the rapidly changing magnetic field), but the article still doesn't go into enough detail to confirm this.
Earth escape velocity is ~7 MILES/second or ~ 11.3 KILOMETERS/second. But the officials at our national lab says in the article that it is 7 KILOMETERS/second and then goes on to use that to show just how fast this thing is...
Perhaps they meant the velocity required to attain orbit; this is about 8 km/sec.
The current wording if enough. After all, the founding fathers knew that weaponry would change over time.
LK
"Hi. This is my friend, Jack Shit, and you don't know him." - Lord Kano
Because. We're talking about a small pellet here.. to send anything of size this would have to be orders of magnitude larger. See other posters who discuss this.
You've got it. The idea was to decrease the mean airspeed around the nose of the projectile, by setting up a standing pressure wave (sound wave) in the cavity.
They're not so much trying to dump heat as they are decrease the ablative forces on the tip of the projectile, and prevent the tip from heating up so much in the first place. Heat can be dumped into the body of the projectile much more rapidly than it could be dumped back into the air, but they were discovering that the heat built up so quickly in the tip, that they'd have to play some interesting games to keep the thing at a reasonable temperature.
Why yes, I AM a rocket scientist!
How about we consider using this device (or a modified version of it) for sending materials into low Earth orbit? It would be a lot cheaper than sending them up via rocket or space shuttle. Gathering materials in low orbit isn't a major problem (assuming they aren't moving too fast.) People (or anything else living) would have to go conventionally. It'd be like airlines being able to fly your luggage there for pennies on the pound, but you costing quite a bit more.
So long and thanks for all the fish . . . !!!
This would also make a good weapon in a Zero-G environment, again, no chemical reaction required.
No it wouldn't. You ever hear of a guy called Newton? You'd still go backwards with the equivalent force you sent the shell out with.
Newton's third law.
General Relativity: Space-time tells matter where to go; Matter tells space-time what shape to be.
I would imagine that at 20 km/s, anyone with infrared goggles is going to see the superheated column of air in the wake of the projectile.
In fact, I wouldn't be suprised if surface of the projectile got hot enough to boil off and leave a residue of buring gas behind it. I doubt you'd be able to see this in the daytime...
Of course, if I wasn't such a lazy ass I'd do some math, and find out...
Slashdot is jumping the shark. I'm just driving the boat.
Next thing we'll know, this thing's gonna get stolen and we'll be seeing a psycho hanging around night clubs waiting for 50+ people to get in line, then FOOM! 50+ victims in one bullet.. The fallacy of ever-improving weaponry is that the guys holding the trigger (or worse, the funding) just don't get smarter. Now I'm all for research and I can imagine this has plenty of other uses besides railguns (small spacecraft launches perhaps), but people are still people, smart, dumb, genius, psycho, whatever. Some 21st century Saddam Hussein will find a way to make us regret this evolution, it's only a matter of time.
-Billco, Fnarg.com
Earth escape velocity is ~7 MILES/second or ~ 11.3 KILOMETERS/second. But the officials at our national lab says in the article that it is 7 KILOMETERS/second and then goes on to use that to show just how fast this thing is...
Maybe I'm being too picky but it does make them look like idiots when they don't do trivial fact checking.
(I've been forwarded a copy of the research paper, so here's how this thing really works.)
Ok. The Journal of Applied Physics article (Feb. 2001) does not describe this as a "gun" at all.
The device uses the Z-machine current source to send a large amount of current through two concentric pipes that are connected at one end. Current goes up the outer pipe and down the inner one.
This sets up a very strong magnetic field between the pipes, which pushes the two pipes apart (crushing the inner one and pushing outwards on the outer one). This is the same kind of effect that you get in a loop of wire that carries current (motor principle).
Samples on plates are stuck to the sides of the outer pipe. Magnetic forces accelerate these plates outwards rapidly, and the samples deform. This deformation is measured, giving a lot of useful materials information (the purpose of the experiment).
It's unclear from the article whether the plates, the samples, or neither go flying. The velocity quote is probably just the maximum velocity achieved while the pipe is expanding outwards under pressure. Letting the plates fly would give a somewhat better experiment, but would cause practical problems (they'd destroy whatever part of the machine they finally smacked into).
Physics-wise, this works on exactly the same principles as a railgun (motor principle with DC current). It's optimized for pressure experiments, not for firing projectiles; you could probably build a railgun that was more efficient at the second task.
Inductive effects do occur (this is a short current pulse), but are considered a source of error in the experiment, and so presumably aren't the dominant effect.
This or any of a number of other magnetic cannon techniques could work, or even a compressed gas gun (like the "Super Gun" from years ago).
The problems are twofold:
To reach orbit, you need an energy of about 30 MJ/kg (for a velocity of about 8 km/sec). Energy is force (mass times acceleration) times distance, so for a given acceleration, you can calculate the barrel length of the gun required. For a 3g accelerator for humans, you get a gun 1000 km long. If you can overcome the engineering problems and build a gun that accelerates cargo at *3000* gravities... you still have a gun 1 km long (about 0.62 miles, if you were wondering).
This can be built, but it's *expensive*. There would have to be a very strong incentive to build it, and amortizing the cost of the gun will raise your launch costs by quite a bit.
You'll notice that the experiment discussed in the article was done in vacuum.
Your gun will have to have an enclosed barrel (even if it's a magnetic gun). Otherwise, the mach-16 sonic boom will tear the firing coils off their mountings or otherwise harm the gun's structure.
Your gun (and anything near it!) is still going to have a lot of wear from the effects of a hypersonic projectile smacking into the atmosphere on leaving its muzzle.
Lastly, your projectile is going to have to have shielding around it to keep it from burning up while leaving the atmosphere. This will add weight to the projectile, and require a higher muzzle velocity (because the projectile will slow down).
All of these problems are manageable, but they increase the cost of the gun and the cost per kilogram of payload even more.
In summary, yes, we can scale up this and other guns like it; however, they're a royal pain to build and use, and there isn't enough demand at present to make them practical.
OTOH, this is one of the best ways known to get material off the moon. Required energy (and hence barrel length) is much lower, and there's no atmosphere to cause problems.
The range on this thing wouldn't be stupendous, I bet. Particularly with small particles (ones with a low kinetic energy/cross sectional area) aerodynamic drag is going to really kill the velocity quickly. At these velocities, you have to play fun games with the shape of the projectile to cool the thing, so it doesn't just ablate away.
My aerodynamics prof at UT Austin was working on a railgun project for the Army at Balcones a couple years ago. He brought in some videos of the experiments they did with projectile shaping. Basically, the idea was to make a circular indentation in the front of the projectile (think like a hollow-point bullet) whose depth was tuned to the expected velocity of the projectile. (insert obscenely complex mathematics here) The idea was to set up a standing pressure wave in the nose cavity, so the moving air would cool the projectile. The tests I saw were with a plastic blank, but the full-on projectiles were going to be 2" diameter tungsten rods. I can't even really imagine enough heat to ablate a tungsten rod, but damn if that's not just what happens at those velocities.
The computer models I watched of these rods impacting armor plate were amazing. It looks just like those slo-mo milk drop photos, except instead of milk it's molten steel. Wow.
Why yes, I AM a rocket scientist!
About time?!
What percent of the federal budget do you think is spent on 'defense'?
--
Soma: because a gramme is better than a damn.
Now I know why there is an energy crisis in California.
BTW, this DOESN'T sound like a rail gun. A rail gun uses a series of magnets to propel a projectile. This sounds like it uses one rapidly expanding magnetic field.