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The Big Bang: An experimental rail gun, with loads of firepower
(Photo courtesy of Sam
Barros' Powerlabs).
Rail
Gun: Hot Facts
A projected naval rail gun with a 2.5km/sec
muzzle velocity could deliver a guided projectile
with an impact velocity of Mach 5 to
targets at ranges of 250 miles, at
a rate greater than 6 rounds per minute.
A test demonstrated that a rail gun projectile's
kinetic energy could create a 10-foot diameter
crater, 10 feet deep in solid ground, and
achieve projectile penetration to 40 feet
- 3 to 5 times more effective than
current guns.
Rail gun projectiles are smaller and easier
to store: a standard AGS magazine holds 1,500
rounds; a rail gun magazine could hold
10,000 rounds in the same amount of
space.
A gun that accelerates a bullet to a speed of 13,000 miles per
hour in 0.2 seconds? Seems like a science fiction dream, but don't
even blink -- with advances in rail gun technology, a new era of high-speed
military weaponry is coming right at us, faster than a speeding bullet.
In the "more things change, the more they stay the same" category,
we give you basic gun physics. Despite numerous advancements over
the last millennium, all guns, from the blunderbuss to the M-16,
have operated on the "expanding gas" principle, where an expanding
ball of superheated gas is used to force a projectile through a tube.
Well, no longer. Gunpowder, as we know it, may soon become a thing
of the past. Make way for the rail gun, a device that substitutes
electromagnetic (EM) propulsion for gunpowder, with devastating results
in speed and kinetic power. Arnold Schwarzenegger (who took out the
baddies with a similar device in the movie "Eraser") would approve.
Zero to 13,000 MPH in 0.2 Seconds
An EM projector (i.e. rail gun) uses electrical energy to accelerate
projectiles to extreme velocities. How fast? Tests conducted at the
University of Canberra were able to accelerate a 16-gram projectile
down a 5 meter barrel at 250,000 gravities, for a muzzle velocity
of 5,900 meters per second. Loosely translated, that's an acceleration
from 0 to 13,000 miles per hour in the span of 0.2 seconds, not bad
even for Superman. This also translates to an enormous amount of kinetic
energy, at a fraction of the mass needed for a normal bullet. A quick
comparison: an anti-armor projectile shot from a rail gun at 3,000
m/sec (almost twice the speed of current kinetic energy penetrators)
would only need to be roughly one-fifth of the mass of a standard
projectile to deliver the same amount of destructive force. Electromagnetic-power
also has the advantage of stealth: Reduced logistics (rounds can have
a smaller weight and volume), and the lack of chemical propellant
means it will be difficult for opponents to track.
The Principle: A diagram of the rail gun's critical parts.
How are these impressive speeds reached? A rail gun is essentially
two parallel conductive metal plates through which an electrical current
is passed. This electrical current creates opposed linear magnetic
fields along the axis of the rails. The projectile itself is placed
between the rails, and a "driver" (armature) is placed behind the
projectile. The function of the armature is to close the circuit between
the two rails. When the rails are energized, a third magnetic field
is created in the armature which is repulsed by the fields created
in the rails, thus "driving" it down the barrel. The energy required
to drive projectiles at useful velocities is enormous; peak power
outputs are measured in millions of amperes.
Naval Know-How
Logical choice: The Navy's DD(X) destroyer, currently under
construction, could be ideally suited to carry an electromagnetic
rail gun (Lockheed Martin photo).
Obviously, it would be fitting for a weapon with such potential power
to be housed in the most powerful vessel around. The Navy, which has
been at the forefront of rail gun technology since the early 1980s,
plans to incorporate rail gun technology with its next-generation
surface fleet, which will include ships such as the hefty DD(X)
destroyer. Ranges of up to 200 nautical miles for rail
gun projectiles are envisioned, with GPS-guided projectiles traveling
at six times the speed of sound. The fact that rail guns and directed-energy
weapons do not require powders or explosives will free magazine space
for strike and other mission areas (the trade-off is that surface
ships will need to generate massive amounts of electric power to support
them). A proper-sized round could provide missile-like capability.
Take your standard Tomahawk
land-attack cruise missile -- for the same amount of time it takes
a Tomahawk to reach a target, an EM gun can deliver twice the destructive
power to the same target, while operating at about 6-12 rounds per
minute. At a fraction of the cost per round, tremendous volume fires
could be delivered. The DD(X) destroyer, with its all-electric drive
and Integrated Power System (IPS), is the first step towards full
electromagentic weapon capability. The IPS can scale up to provide
additional electrical power as demand grows -- the key to surface
fire support capabilities.
Beans and Bullets: Other EM Applications in Combat and Logistics
The Navy has grabbed the most press with its rail gun experiments
but the Army Research Laboratory (ARL) and Lockheed Martin are developing
an Electromagnetic (EM) Gun System in a two-phase program. The first
phase (scheduled to conclude in 2005) is centered on a medium caliber
gun demonstration, and demonstrating a single rotating power supply.
During Phase II (2005-2007), EM technologies will be integrated into
an armament test-bed, utilizing a large bore gun.
On the drawing board: A sketch of a next-generation Army vehicle
equipped with an EM gun (Lockheed Martin photo).
Fired at hyper velocities (10-100 kilometers/second), projectiles
weighing a fraction of a gram have enormous destructive potential,
and could be fired using the stored energy of a standard armored vehicle
power plant. In addition to combat (especially anti-armor and hard
target applications), EM research is also looking into using rail
gun technology to deliver supplies over long distances. Launched from
a 100m ramp, a 300-pound aerodynamic supply package could be "shot"
over intervening terrain and remotely guided to a designated landing
area. The concept is sound -- it only remains to develop the correct
technology.
Related
Links
Sam
Barros' Powerlabs
EM gadgets aren't just for multi-million dollar
military projects -- a student at Michigan
Technological University has gained attention
for his pioneering experiments with electromagnetic
technology.
The
Next Revolution at Sea
Rail guns are only part of the picture in
the Navy's next-generation warfare plans.
Get a peek at some of the vessels and weapons
on the drawing table.
Continuing on the transportation theme, laboratories utilizing electromagnetic
technology are already working on a Segmented Rail Phased Induction
Motor (SERAPHIM), which opens the door for high-speed ground transportation
systems (i.e., next-generation monorails). Similar linear induction
motors are already being used for airport transit systems, subways,
amusement park rides, and industrial handling systems.
Building It Was the Easy Part…
Although the principles behind rail gun technology have been well
documented and understood for nearly 50 years now, challenges remain
in building a reliable, effective, and efficient EM gun. When an electrical
current is passed through non-super conductive material, a fraction
of that current is converted to heat by the impedance of the conductive
material. Given the huge amounts of energy involved (even when energized
for only milliseconds), the heat generated by a rail gun would be
enough to melt the gun's rails, if used often enough. If EM guns are
going to serve as practical battlefield weapons, a means of cooling
them (cryogenically or otherwise) or of improving the super-conductivity
of the rails must be found.
One naval proposal has suggested using liquid nitrogen to cool the
rails, with a seawater-based heat exchanger to cool the electrical
storage and discharge systems. In addition, to function properly,
the armature must make physical contact between the rails. This requirement
creates some problems: If the current is too great and the armature
has too little mass to absorb the resistant heat energy being transferred
to it by the electric current, the armature may melt or weld itself
to the rails.
Must-Have
Gear
One method of reducing armature "welding" is to make the armature's
rail contact surfaces (brushes) out of a light metal, such as aluminum,
which will vaporize into plasma (ionized gas) when energized. This
process, known as metal vapor arcing (MVA), eliminates physical contact
between the rails while simultaneously closing the circuit (the metal
plasma is conductive.) One of the drawbacks to MVA is the buildup
of metallic residue on the rails, which is formed when the metal vapor
cools inside the barrel. In the same vein, if the rails are placed
too close together, the current between the rails may bypass the armature
(arc) and damage the rails. Given the velocity at which the armature
is driven down the barrel, this friction could further add to heat
build-up, and degrade the driver as it moves down the barrel.
Finally, since the individual magnetic fields created in the rails
are repulsed by one another, a tremendous strain is placed on the
rails as they try to push away from one another. While rail guns do
not suffer from the traditional recoil forces associated with conventional
expanding gas weapons, this repulsive effect can be equally destructive
if not properly compensated for.
The challenges facing the development of rail guns as a practical,
widespread weapon are hefty, but as better super conductive materials
are researched, they come closer and closer to becoming a reality.
And with the speeds that EM power can provide, you can try running,
but you sure can't hide.
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Forum to sound off.]
