Aviation Week & Space Technology, 07/31/2006, page 533
An electromagnetic rail gun could be the easiest and least costly way of launching small communications satellites by theoretically eliminating the need for the huge quantities of fuel, multistage rockets and redundant systems necessary to lift a payload into space. The rail gun may prove so effective that networks of satellites could be launched at low cost--and if one fails, another would quickly be sent up in its place.
This is the vision of Harry D. Fair, director of the Institute for Advanced Technology at the University of Texas, and an expert on hypervelocity systems and rail guns. Fair believes that "nano satellites" --which would use nanotechnology in electronics and other components and would be a fraction the size of conventional satellites--are ideal candidates for a rail gun launch. "That's a concept we're trying to develop," he says. "It's not a funded program, but it's something that's certainly doable."
In a conventional satellite launch, less than 1% of the mass of a rocket going into orbit is payload. As a result, a launch is virtually a one-shot deal, and the costs and amount of engineering necessary to reduce the chance of failure are exorbitant. Fair estimates it costs at least $10,000/kg. to put a satellite in orbit with the space shuttle. If the size of satellites could be reduced through the use of nanotechnology, and rail guns built that would lift them into orbit, the cost, complexity and complications of rocket launches would be eliminated.
Fair says
it would require long rails and an "embarrassingly little" amount of stored energy--maybe 600-800 megajoules--to launch a satellite with a rail gun. The length of the rails would be computed with fundamental equations based on the force necessary to launch a satellite and the total energy required. A viable rail-launch system could be built on land and even placed on aircraft for use in the upper atmosphere.
There are major engineering challenges to overcome, of course. Chief among these is hardening electronics and other components to resist the force of hypersonic acceleration, and waiting for developments in nanotechnology to yield reliable electronic and other components for satellite operation.
The idea of nano satellites being lifted into orbit by ground-based electromagnetic rails seems fanciful, but it is under scrutiny by scientists around the world. Fair says researchers have published papers on the viability of electromagnetic satellite launches, and
NASA has looked at the concept off and on for 20 years. Predicting a timetable for developing such a capability "depends very much on funding and getting a program together," he notes. Nevertheless, Fair believes the concept has merit. "Buy stock in electric guns," he says. "It's the way to go."
Aviation Week & Space Technology, 07/31/2006, page 529
Pat Toensmeier, New York
U.S. Navy is moving forward with electromagnetic rail gun
The U.S. Navy is ratcheting up development work on a shipboard electromagnetic rail gun, which would use a burst of high-power current to launch kinetic-energy projectiles at hypersonic speeds. Although
at least 15 years from fielding, the futuristic weapon has the potential to substantially improve strategic and tactical strike capabilities, particularly the barrage-type naval surface fire support favored by the U.S. Marine Corps for its forces ashore as well as accurate long-range land-attack capabilities.
The Navy ambitiously plans to demonstrate a rail gun by 2011 and to have a complete system ready by about 2015. The service is targeting an initial operational capability in the fleet between 2020 and 2025.
Though it seems impossibly futuristic, the electromagnetic rail gun is, in theory, a relatively simple device that utilizes straightforward principles of physics to achieve its range and destructive capability.
The gun derives its name from two conductive rails positioned side by side, with an insulating space between them, in a specially designed barrel. The rails are connected to a pulsed-power network that applies a huge amount of stored current to them in a 10-millisecond burst. An assembly consisting of the projectile, sabot and pusher plate (both of which support the projectile) and a conductive armature is loaded between the rails in the breech of the barrel (see illustration). When activated, current from the pulsed-power network runs up one rail and down the other, creating a magnetic field between them and through the armature, which is perpendicular to the rails.
The powerful magnetic fields generated by the current in the rails intersects with the current flowing through the armature. This creates a Lorentz force that causes the armature to accelerate at hypersonic speed along the rails. Immediately after leaving the barrel, the armature, sabot and pusher plate are ejected from the projectile. While the sabot has a structural function, experts say it also lengthens the projectile, increasing velocity.
The science behind an electromagnetic rail gun has been proven in lab experiments since the first model was built in the early 1970s by British, Canadian and Australian researchers. The rail gun is so effective because it puts more energy on target than conventional non-nuclear ordnance, thus yielding greater destructive capabilities while minimizing collateral damage.
Ongoing work by the Office of Naval Research (ONR)--some of it in partnership with the U.S. Army--is part of a plan to transition the rail gun program from a science and technology effort to a research and development phase leading to system acquisition and fielding. The latest step was the recent awarding of 30-month contracts for the preliminary design and technology development of a 32-megajoule rail gun to a pair of teams led by prime contractors General Atomics and BAE Systems.
ONR is directing research in four areas of rail gun technology: projectile, launcher, power sources and ship integration. It awarded the launcher and containment system contracts as part of its Innovative Naval Prototype Rail Gun program.
The General Atomics team includes Boeing, L-3 Communications, Jackson Engineering and materials supplier Sparta Inc. The BAE Systems team comprises SAIC, the Electromagnetic Div. of Curtis Wright Electromechanical Corp. and IAP Research Inc. Once the work is complete, the next contract will be for the design, fabrication and testing of the launcher.
Some of the contractors on these teams will be applying expertise developed in the 1980s and 1990s for the Strategic Defense Initiative (SDI)
and the Army, says Tom Hurn, manager of rail gun launcher systems at General Atomics. Sparta, for example, fabricated components of advanced composites (carbon fiber and epoxy) for a lab-scale Army rail gun in the late 1980s, and used composites for a barrel it delivered to the service in the early 1990s. General Atomics built a composites barrel for the U.S. Air Force in the SDI program. Other areas of work the teams will draw on include techniques for pre-stressing gun components and advances in materials formulation, modeling and simulation tools. "There was a lot of knowledge that was built up in [the San Diego area] during SDI, and we're drawing upon all of it," says Hurn. "It will have an impact on what we're doing."
The rail gun will offer numerous advantages over conventional ordnance, notably in range (extending it to as much as 250 naut. mi.), volume of fire support, area coverage and payload-on-target efficiency.
Rail guns also may have an impact on ship design since the projectiles they launch don't require elaborate explosion-resistant magazines. And they could reduce operational costs because, round for round, they will be less expensive than missiles, rockets and guns, and probably won't require the manpower or degree of training necessary with traditional weapons. "There's never been a weapons system like this," affirms Elizabeth D'Andrea, ONR's program manager for rail guns.
Nevertheless, it will take more than a decade for the weapon to be deployed on the Navy's newest ships, the embryonic DDG-1000-class guided missile destroyers. As Rear Adm. Barry McCullough, the Navy's director of surface warfare, says,
"A rail gun is immature technology. While it has promise, we're looking at a potential initial operational capability . . . in the 2022 time frame."
The Navy has embraced the weapon as a means of extending firepower capabilities beyond those available from conventional munitions, and ONR is evaluating the weapon for use in multiple applications. "We're not attaching the science and technology to any one platform," says D'Andrea.
The Navy's nascent DDG-1000-class ships, however, are logical platforms because their electric propulsion systems will produce sufficient energy to power the weapon. The first ship in this class, the Zumwalt, will be a 78-megawatt plant, "a rather large electric-generation capacity," McCullough says, which is more than adequate to supply the 160 megajoules of energy the Navy believes is necessary to launch a projectile.
The Zumwalt, scheduled for delivery in 2012, will be equipped with two automated 155mm. Advanced Gun System turrets, but could be back-fitted with one or more rail guns when the technology is ready for deployment. DDG-1000 ships, and other surface vessels slated for delivery around 2020, could carry rail guns as standard armament providing they have the onboard power sources necessary for operation.
While no one has yet determined exactly how much space a rail gun requires, the weapon will probably fit anywhere the Navy wants it. "Because of its small footprint, it can be integrated into any platform," D'Andrea says. Moreover, since rail gun projectiles use no energetics, the logistics, storage and manpower needs that might work against installation of a conventional gun in some platforms are not an issue. Risk mitigation is, in fact, one benefit ONR cites for the weapon.
Subsequent development phases will include determining the optimum size and shape of projectiles, and fine-tuning the capacitors used for demonstrations and, eventually, for an initial operational capability. While a number of technical and engineering challenges must be overcome before the rail gun moves out of the laboratory, experts believe it's only a matter of time until the weapon is operational. "There isn't a single technology issue that anybody in the community [of researchers] today has identified as unsolvable," says Joel Drake, General Atomics' project manager for electromagnetic launch development.
As envisioned by ONR, the rail gun will launch projectiles with muzzle velocities of Mach 7 (about 2.4 km./sec. at sea level) and impact targets at a speed of Mach 5 as far off as 250 naut. mi. (Hypersonic speed is generally defined as Mach 5 and above.) It will take about 6 min. for a projectile to hit a target at that distance, ONR calculates.
The rail gun will be able to launch projectiles in a direct-fire mode to destroy threats posed by surface combatants or in
a ballistic trajectory for maximum range. In a ballistic trajectory, the projectile will reach a height of 500,000 ft. before it reenters the atmosphere and homes in on a target. The projectiles also will be capable of guided flight through the use of a built-in GPS satellite receiver and some mechanical guidance techniques. ONR says this work, like much of the technology, is proprietary and declines to reveal details. But it reportedly has study contracts with Boeing and Draper Laboratory to develop projectile concepts, including guidance systems.
What makes a projectile so lethal is the physics of mass and velocity. The energy inherent in an object traveling at hypersonic speed is about the same as the energy in a high-explosive material of equivalent weight, such as HMX, RDX or TNT. One kilogram of chemical explosive contains as much energy as a 1-kg. projectile launched from a rail gun. When the explosive detonates, however, the energy is converted into a blast and transferred to a 360-deg. radius of fragmenting metal pieces, which immediately begin losing velocity.
The projectile, by contrast, directs all of its kinetic energy to the target. When it hits, this creates a far more destructive impact than the chemical reaction of an explosive. "The coupling of the energy of a projectile into a specific target is much greater when all the momentum is along the direction of travel," says Harry D. Fair, director of the Institute for Advanced Technology at the University of Texas (Austin), whose projects include rail gun research for the Army.
The kinetic energy of a projectile launched at hypersonic speed is so great that it melts the armor of a tank on impact in the milliseconds before it causes a blast. One reason the Army likes rail guns is because hypersonic projectiles can defeat reactive armor on tanks and other vehicles. Projectiles launched from rail guns are reportedly 3-5 times more lethal than conventional ordnance.
Projectiles can be fabricated in different sizes, but for initial tests of a prototype, a tungsten version about 1 meter long and weighing 15 kg. will probably be used.
"Notionally, we've been talking about a 20-kg. launch package," says D'Andrea. The extra 5 kg. will comprise the components that eject after leaving the barrel. D'Andrea notes that while up to two-thirds of a standard round is energetics, most of what is launched from a rail gun ends up on target. "This is all tooth; there is no tail," she says of the projectile.
In situations where multiple targets are involved, projectiles can incorporate devices that are released prior to impact, creating an effect similar to that of conventional munitions that eject bomblets, though of course kinetic energy provides the destructive force. "You need to properly couple the lethal mechanism of the projectile to the target," remarks Roger Ellis, ONR's technical director of rail guns. "There will be times when you want a unitary round that penetrates deeply but doesn't create a lot of broad area damage. In other instances, you may want a lethal mechanism that disperses rods or pellets over a greater area coupled to other minor targets."
ONR is considering mounting the rails in a 12-meter-long barrel, two meters longer than the barrel of the Advanced Gun System.
The rails will need to be designed to resist damage from launches. And the barrel must withstand large amounts of stress since the electromagnetic field used to launch projectiles exerts a mutually repulsive force on the rails. Moreover, launching a projectile--which also involves some recoil--will exert a force equivalent to a conventional artillery gun that fires a round with similar energy, notes Amir Chaboki, project manager for the Navy's electromagnetic gun program at BAE Systems. "Bore life is important and will require the use of an advanced material such as composites to contain forces during launch."
Ellis says the goal is to design a barrel that can withstand 5,000 shots.
The barrel could be round, square or some other shape, depending on the degree of magnetic efficiency it yields and other properties, he adds.
Hurn says it's likely that a number of configurations will be considered during development of the launcher and containment system. "What is the right configuration? There are certainly concepts on the board, but those all need to be analyzed and tested at full scale as we go forward."
The rail gun will be able to direct fire more than twice as far as the Advanced Gun Systems, whose 155mm. projectile has a maximum fire-support range of 100 naut. mi. To achieve this, however, it must use special munitions, such as the Long Range Land Attack Projectile, which has rocket motors.
Experts say a key benefit of the rail gun is that it expands projectile range at much less cost than with conventional ordnance.
Standard munitions have virtually reached the limits of their energetics and can be fired no farther than current distances without rocket-assist. While missiles have been put forward as more efficient alternatives to rocket-assisted munitions for ranges of 100 naut. mi. and more, they are expensive. Analysts estimate that it costs at least $1,000 per mile to launch a missile at a target. Rail-gun projectiles, by contrast, use no fuel, no explosives and can destroy targets, including hardened bunkers that now resist artillery and missiles, at a fraction of the cost.
ONR estimates that a rail gun will be able to launch 6-10 projectiles per minute, less than the Advanced Gun Systems, which is designed to fire 12 rounds per minute. The rail gun's ability to hit targets beyond 200 naut. mi., though, can free up other assets for missions besides naval surface fire support. In an analysis published in Proceedings magazine in 2003, the Navy stated that
in the first 8 hr. of a conflict, one rail gun, engaged in fire support against targets 200 naut. mi. away, "could deliver twice the payload, three times the energy, to 10 times as many fixed aim points" as a carrier air wing of F/A-18 fighter jets.
This benefit, if correct, puts the weapon squarely in line with the expanded capabilities the Navy seeks for naval surface fire support and long-range strikes in support of U.S. joint forces ashore. If the gun lives up to the expectations of proponents, it could be a weapons system that helps the Navy redefine its tactics of force projection for years to come.
Interesting. I came very close to actually building a small one in high school--I had about twenty-four car batteries lined up that were from a junk yard buyt in usable condition, and I was in the process of finding copper pipe for busbars. The rails would be made out of stainless steel backed with copper for conductivity, and would have shot a half inch diameter slug made from a bolt with a copper band for conductivity. I estimated that if the gun were to achieve about 45% electrical efficiency, the 70g slug should achieve almost 1.5km/s at the muzzle. At the last minute the administration of the school decided that a rail gun was probably not the safest thing to have one of their Juniors build on campus, so I was denied. (They also denied a previous proposal of mine to rewind an old industrial transformer they had and make a small cyclotron out of it--the word Radiation simply did not sit well them, I guess. But that's a different story... )
Rail guns are fairly simple--they operate by using thousands of amps of current at relatively low voltage to create a very strong magnetic field around the conductors (the rails.) This magnetic field repels the magnetic field created by the current passing around or through the slug. This has the effect of squeezing the slug out of the barrel. Accelerations can be as high as 100,000 gravities, which is about 5 times higher than the acceleration of an artillery shell inside a cannon. They also suffer from a startling effect that, if not engineered for can be catastrophic. Once the slug leaves the barrel, then electrically the circuit is broken. However, because of the strong magnetic fields around the conductors will almost instantly collapse (at the speed of light) this will generate an "ignition coil effect" and the voltage at the end of the barrels will rise until the circuit is completed again. Almost instantly the voltage will rise until the barrels arc together and bleed off the remaining magnetic energy creating quite a spectacular muzzle flash! The only way around this is to create a shunt which crowbars the voltage at about 100v eliminating the arc, but unfornutely this will almost certainly blow the shunt every time you fire the thing!
A hypervelocity rail gun should also make a pretty effective main gun for an all electric tank. Shooting tungsten or depleted uranium rounds with a copper shunted steel sabot (which will also be the pusher) ought to achieve higher velocities than a traditional main gun using chemical propellant. And here's the kicker, such a vehicle will not actually carry propellant, only fuel to be burned in a gas turbine engine.
I don't know about launching satellites with these things--you'd have to package them pretty cleverly to handle not only the crushing launch accelerations, but also the inherent EMP effect from the mega-amp current pulses in close proximity. Packaging high gain antennas, computers, solar cells, and cammeras in a tough aeroshell made to be fired from an electric gun sounds pretty demanding. Just because it is possible to fire something into orbit will not necessarily mean that the result will be useful or practical. Solar cells and antennas would have to be packaged as a solid block--probably encapsulated in solid epoxy resin as proximity fuse electronics are today--and that will make them heavy and hardly effective. Still, it might be cheap enough to try it--it should make for an interesting thesis.
And if satellite launchers don't work, there's always the super long distance guided munitions market!
)
