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Magnetic Ring Could Launch Satellites, Weapons
MattSparkes writes, "A new study funded by the US Air Force has suggested a cheaper method of sending satellites (possibly missile weapons) into orbit. A 2-km-wide ring of superconducting magnets would contain and propel a payload, accelerating it over a period of hours, before suddenly flinging the satellite into space at 23 times the speed of sound. The satellites would be engineered to withstand the g-forces encountered (2,000 g), and be cased in an aerodynamic shell. A two-year study has been commisioned and will begin within a few weeks at LaunchPoint Technologies in Goleta, California." New Scientist points out that if such a launch ring were built, it would instantly become "one of the most important targets on the planet."
No. I thought of the same thing too. Or perhaps the ribbons described in Frederik Pohl's Hechee novels. :-)
Good stuff. Glad to see someone else who enjoys old-school sci-fi.
[C]
http://en.wikipedia.org/wiki/M712_Copperhead
Now you're aware...
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So they are making a longer track.
The reason the payload has to be built to withstand X,000 G's is because at some point or another, it is going to go off the track and run into a wall of air at very high speed.
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o0t!
Your lapse is forgivable, but only because the proliferation of terms like "Gauss gun", "rail gun", and "mass driver" in SF has overwhelmed their usage as technical terminology. But the point is, THIS IS NOT A RAIL GUN.
A rail gun is a parallel, non-touching pair of conductive rails, joined at the back-end by a partial circuit capable of generating an extremely high current flow (amps) of electicity in a very, very short time. A conductive projectile is injected into the gap between the rails (so that it touches both rails at once), which completes the circuit. As current flows from one rail to the other, through the projectile, it generates a powerful magnetic field. The Lorentz force causes the projectile to be pushed toward the far end of the rails--the magnitude of the force depends on the current flow.
Rail guns can achieve extremely high velocities, far higher than conventional explosive-charge guns. The velocity of a firearm projectile is limited by the velocity of the expanding explosive gasses that propel it out of the barrel; the gas velocity is in turn limited by the speed of sound in the gas medium, which has a physical upper limit for any type of explosive. Rail guns don't suffer from this limitation.
I have seen references to a 'Gauss gun' which consists of a series of solenoids stationed along a tube barrel, timed to trigger so that a ferrous metal projectile will be pulled faster and faster down the barrel by each of the solenoids in turn. I don't know how valid this terminology is, though.
You are confusing pressure with acceleration. These are not the same.
Obama likes poor people so much, he wants to make more of them.
Who says they can't? It could just be that a straight-line version would be prohibitively expensive because instead of needing C magnets to span the circumference of the ring, they'd need N * C magnets to span the distance covered by the circumference times the number of revolutions.
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The laser designator for the Copperheads was quite large, the ones I saw were vehicle mounted. I would imagine that in the 20+ years since I saw them that they've gotten smaller and smarter.
cheap labor conservatives - they want to keep you hungry enough to be thankful for minimum wage.
Except that the proposed design accelerates the payload around in a circle -- using magnets arranged inside a torus -- not a long straight runway. I doubt a linear runway would be practical; it would just be too long. The advantage of a torus is you can keep using the same magnets to accelerate the payload, over and over, until you've reached sufficient speed to let it fly.
Unless the circle was ridiculously large (probably the size of a continent or better), you're not going to be able to get up to escape velocity before you'd (as a human being) would be crushed by the effects of the centripetal acceleration.
I'm not going to do the math right now, but I'm pretty confident that of the 6,000 Gs they're quoting, most of them are in the radial direction and not in the tangential, so that even if you brought the payload up to speed slowly, you'd still be crushed. It would be just like being in a centrifuge.
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I think a lot of folks here are confused about the "2000 gs" part of this device. This acceleration is from the centripetal acceleration needed to keep the payload moving in a circular path.
Here's the math:
The acceleration A needed to keep something moving at speed V in a circle of radius R is V^2/R.
A = (8 000 m/s)^2 / (1000 m) = (64 000 m/s/s) = 6 400 gs.
TFA says "More than 2000 gs" - my guess is that this is a mixture of sloppy journalism, and maybe confusion over the minimum acceleration needed to get to escape velocity (about 5.5 km/s). If they did get their wires crossed and report the 8 km/s figure but the g force of getting to escape velocity, the needed A is:
A = (5 500 m/s)^2 / (1000 m) = about (30 000 m/s/s) = 3 000 gs, so they're still wrong.
Incidentally, I love the ring idea, but it could only ever launch pretty specialized cargo due to the g forces needed. What I'd love to see would be a linear accelerator which got a rocket up to about 3-4 km/s, then the rocket would take over. EM launching systems with reasonable length can be built for low speeds, and rockets have high efficiency only when they're already moving fast (otherwise, most kinetic energy goes into making the exhaust, and not the payload, go fast), so a switchover plan seems pretty natural (except that it demands all the infrastructure of a small EM launcher as well as all the problems of a chemical fuel rocket - although some of these problems are less of an issue if you can accelerate the rocket to faster than the fuel's exhaust velocity before it reaches the muzzle of the EM launcher - then your shiny equipmetn doesn't get burned.)
My 2. Enjoy!
Expected time to finish is 1 hour and 60 minutes.
It is not about hypoxia, but rather the fact that you would have your soft tissue torn away from your stronger skeletal tissue. Most of your organs remain in place as long as the connecting tissue is intact.
Remember, You are unique...just like everyone else.
Am I crazy, or did they get the math wrong in the article?
The acceleration equation for circular motion is: a = v^2 / r
We are given:
Velocity: 10 kilometers/s
Width of ring = 2 kilometers, so radius = 1 kilometer
So:
v = 10,000 m/s
r = 1,000 m
a = (10,000 m/s * 10,000 m/s) / (1,000 meters) = 100,000 m/s^2
The acceleration due to gravity is about 10 m/s^2
This gives: (100,000 m/s^2) / (10 m/s^2) = 10,000 g
So it seems that their 2,000 g is way off. Even if we use 2 km for the radius it is still 5,000 g.
Reading code is like reading the dictionary - you have to read half of it before you can go back and understand it.
Cute, but you gotta be kidding. I work with a 3T research MRI magnetic. Both the machine and the facility are heavily shielded, and the field drop-off is very steep. While the isocenter of the bore is at 3 Tesla (30,000 Gauss), the 5 Gauss line is only a few meters (about 5 in the axial direction, 3 in the radial direction) from the isocenter. By comparison, a kitchen magnet is maybe 100-250 Gauss.
How long do you think that straight track would have to be to obviate the need for high-g payloads?
Shorter than a ring with the same g requirements. If you have a ring of radius r and you want to launch a payload at velocity v, then the "g force" on the payload will be at least centrifugal acceleration, v^2/r. If you stretch that out into a straight track of length 2*pi*r and you want to launch a payload at velocity v, then you need acceleration a such that v = a*t and 2*pi*r = a*t^2/2 = v^2/2a, so you need a = v^2 / (4*pi*r), an order of magnitude less force. You can try to cheat by making the straight track length 2*r instead, so it wouldn't just be as long as the ring it would fit inside the ring entirely, and the straight track would still have lower acceleration requirements.
The only reason I can see for using a circular track is to cut the power requirements - that centrifugal acceleration is all perpendicular to your velocity, so it doesn't directly cost you any energy. With a linear track every bit of acceleration costs power, and trying to add 20,000 m/s^2 to an 8,000 m/s payload should cost you at least 160 megawatts per kilogram. It might be nice to add that kinetic energy more gradually.
Of course, maybe I'm just doing my math wrong. v^2/r at v = 7,800 m/s and r = 1,000 m gives you over 6,000 g's, not 2,000. Did I get something wrong or did the article?
Peak for shuttle launch is 3Gs, and for Apollo reentry, exceeded 7Gs (source paper with cited sources). For a launch abort on the Apollo design, stress would have exceeded 16Gs, and this was deemed uncomfortable, but survivable (albeit with an assumed inability to operate controls during the process). (source LBJ Space Center.)
So limiting it to 2Gs of total stress is very arbitrary and unnecessary.
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This ring could fling mass up to a skyhook to recharge its orbit. Imagine a LEO skyhook that catches dozens of dead weight shots from this gun and uses that momentum to promote its orbit to a highly eccentric one. Then the satellite can exchange this orbit potential with a target at its low altitude point through a tether or skyhook style method. The target could be a large satellite in LEO or even a suborbital payload. Once the potential is transfered the target can have its orbit promoted to GEO or other significant altitude.
This method saves a lot of reaction mass in a heavy lifter because you can aim for a high alitutde but a suborbital trajectory. IE it's easier to shoot straight up than curve towards an orbital path at sufficient speed. For instance the X prize is all about sub-orbital. LEO is much harder and GEO is even harder still.
drag resistance in fluid varies as a cube of the velocity, so twice the velocity is 8 times the air resistance: 2.3 times the velocity is 12.167 times the air resistance. It's more than an order of magnitude more air resistance, and building missiles to travel 10 times the speedo of sound is not an easy task.
A Copperhead is fired using the same powder charge as a standard artillery round.
I'm an ex-Artillery NCO.
Consider you're accelerating horizontally until you reach sufficient speed. You'd just have 1g pulling you downwards (or upwards, if you're upside-down) and 2g pulling you sideways (centripetal or lineal acceleration). That adds up to perceived 3g.
I was reminded of Gerald Bull, one of the great "mad scientists" of our day, and Project HARP. :) Check out the plume leaving the barrel of their research gun. That had to be quite something to see in person.
:)
Of modern ballistic launch mechanisms, there are lots of neat options ranging from light gas guns to ram accelerators. I also find the concept of ballistically-launched scramjets to be pretty nifty.
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I don't think that's how it works. Gravity should add like vectors, so 1g down and 2g horizontal should provide sqrt(1^2+2^2) or (sqrt5)g in a down-ish horizontal fashion.
Although the moon is smaller than the earth, it is farther away.
This was a point brought up at the presentation. One of the linear accelerator guys was pretty sure that the struts holding the tracks in place would be transmitting huge amounts of energy, thereby heating the super-conducting magnets and possibly causing the struts to fail. The Launchpoint guy was sure that they had looked at the problem thoroughly though and that there wouldn't be an issue. Time will tell on that one...
Wikipedia has a snippet about an accidental human exposure to near vacuum. "his last conscious memory was of the water on his tongue beginning to boil" ... gnarly.
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