Download Unlike conventional naval guns which rely on explosives

Prepared by: Branden Lee
Written on: February 6, 2012
Prepared for: Writ 340 & Illumin Magazine
Article Key Words: Aerospace, Mechanical, Electrical, Security & Defense, Space
Author Contact info: [email protected]
Author Bio: Branden Lee was a sophomore majoring in mechanical engineering at the University
of Southern California. He grew up in San Marino, CA. He enjoys playing basketball during his
free time and is an avid Lakers fan.
Rail Guns: From Sci-Fi to Reality
A rail gun uses magnetic and electric forces to accelerate a projectile. Parallel rails
extend along the length of the firing chamber of the rail gun powered by capacitors.
With the power generated by the magnetic fields contained in rail guns, objects can be
launched at incredible speeds. The result is a destructive force. The rail gun, though,
still has a variety of other applications. Some of these applications are revolutionary and
ground breaking. However, there are still many obstacles to overcome. Advancements
must be made in the area of rail gun technology. By understanding the physical concepts
behind the rail gun, one can grasp the promise that the technology holds.
Introduction
Gunpowder has long been the primary choice of propellant used in firearms since its
invention in ancient China. Conventional weapons have been designed based upon expanding
gases principle to fire projectiles. These weapons have physical limitations though. The
expanding gases can only propel rounds at certain speeds. However, scientists and engineers
have been developing a weapon which utilizes a totally new source of propellant: electricity and
magnetic forces. This weapon is the rail gun. Although the concept of electric-powered
weaponry has been around since the early 20th century, the rail gun has become reality in recent
years.
Figure 1: Rail gun seen in the movie Transformers: Revenge of the Fallen. Rail guns have been long been thought of figments
of the sci-fi genre.
Rail guns have always invoked images of science fiction and the future. The rail gun has
been presented in movies as a futuristic and advanced weapon unlike any other; the pinnacle of
technology. In fact, a rail gun was featured as a prototype weapon in the 2009 blockbuster
movie Transformers: Revenge of Fallen (Figure 1). It was found fixed atop a naval ship, capable
of annihilating a seemingly indestructible extraterrestrial robot. Rail guns have also appeared in
video games. Several games allow players to use rail guns to blast monsters and aliens.
However, today, rail guns are very real. They are not in full scale production yet and are still in
the developmental phases. The potential applications of rail guns, though, extend beyond just
warfare. They range from nuclear fusion to space travel. However, there are still many
obstacles that must be overcome before rail guns become practical.
Design and Theory
A rail gun is essentially an electric circuit
which is comprised of three main parts: a power
source, a pair of rails, and an armature [1]. The
power supply provides the rail gun with the
needed current to produce the required forces to
propel the projectile. Rail guns usually work with
currents in the millions of amps. For perspective,
Figure 2: The basic set-up of a rail gun: a power supply,
parallel rails, and an armament. A rail gun is a large
electric circuit.
the average 60-Watt light bulb only contains 0.5
Amperes of current. The parallel rails and the
armature are made of conductive metals. The armature is used to bridge the circuit between the
two rails to keep current flowing. It also houses the projectile to be fired.
In electricity, current flows from the positive terminal of the battery to the negative
terminal [2]. In Figure 2 of a rail gun circuit, the current flows from the positive terminal of the
power source up the positive rail, across the armature, and back down the negative rail to the
negative terminal of the power source. Current running through a wire has an intrinsic magnetic
field associated with it [2]. In a rail gun, the rails act as the wires of the circuit. Magnetic fields
are created around these rails. The magnetic force lines run in a counterclockwise and clockwise
direction around the positive and negative rails, respectively. Therefore, in between the two
rails, the net magnetic force is vertically up (Figure 3).
The projectile is acted upon the Lorentz
Force (F). The Lorentz force is the product of the
current (i) flowing through the armature and the
magnetic field (B). The Lorentz force is the
driving force which propels the projectile. The
magnitude of the Lorentz Force is determined by
the equation F=i*L*B [2]. As such, the Lorentz
Force can be magnified by increasing the current
or length (L) of the parallel rails. When the
projectile is fired, it exits the ends of the rails. In
Figure 3: The Lorentz Force accelerates the projectile.
The magnitude of this force is calculated by the equation
F=i*L*B. A large current (power supply) will generate a
large Lorentz force and as a result more destructive
power.
doing so, the circuit is broken, and all current flow ends.
Challenges
Power Supply
Rail guns require a large power supply to generate the necessary forces to accelerate the
fired projectile. Capacitors need to store enough electric charge until a large enough current has
built up [1]. These capacitors usually are many cubic meters in size. A problem arises when a
rail gun with a high firing rate (6 rounds/min) requires as much power as needed for ship
propulsion [3]. These power requirements can be met with the all-electric warship with an
integrated power system (IPS). IPS is a highly efficient electric power generation and
distribution system. With this system, a ship will be able to manage its power and switch
between the rail gun and propulsion.
Intense Heat
Electric current that passes through conductive material must deal with resistance.
Materials usually have an internal resistance. The current excites the molecules of the material
which causes heating [1]. This heat is hot enough to melt the rails of the gun. In order for rail
guns to be practical, a solution to this intense heating must be found. Some proposed solutions
offer cryogenic cooling or the improvement of the conductivity of the material in the rails. The
navy proposed the idea of using liquid nitrogen or a saltwater heat exchanger to cool the rails.
The intense heat associated with rail guns not only poses a problem for the rails, but also
the problem of welding. The armature which houses the projectile must be in physical contact
with the rails at all times to keep the electric circuit. Sometimes, the heat dissipated by the rail
gun is hot enough to weld the armature and rails together, leaving the rail gun inoperable. A
possible remedy for this problem is Metal Vapor Arcing (MVA) [4]. In this set-up, a thin metal
foil is placed on the back of a non-conducting projectile. When current flows through the foil,
the foil vaporizes and turns into plasma (ionized gas). The plasma is still conductive which
allows the current to flow through, keeping the circuit intact. However, there are still drawbacks
to MVA. After several shots, metallic residue begins to build up on the rails due to the plasma
cooling back to a solid state. Until a viable cooling option or design is found, intense heating
will be one of the main obstacles in the advancement of rail guns.
Repulsion
The currents in the parallel rails run in opposite directions. The opposing currents give
rise to a repulsive force between the rails [2]. This repulsive force is proportional to the
magnitude of the current (remember we are dealing with currents in the millions of amps). It
attempts to push the rails apart. Wear and tear on rail guns is a serious issue. Many rail guns
break after a few shots which can be disastrous in regards to the amount of money invested in
these guns.
Future Impact and Potential Applications
Naval Defense
The most prominent application of rail guns is in the defense sector. Rail guns may the
way sea battles are fought. The navy is looking at rail guns as a prospective replacement to its
current large artillery. The navy is the logical branch of the armed forces to take on research in
rail gun technology. Rail guns require a large power supply that only new naval battleships and
destroyers can provide. The army and air force do not have the necessary resources to power rail
guns.
Unlike conventional naval guns which rely on explosives, the rail gun delivers damage
via kinetic energy. The rail gun has been measured to deliver 33 megajoules of energy in one
firing [5]. One megajoule is approximately equal to a one ton car traveling at an astounding 100
mph. Now multiply the amount of energy contained in a car traveling that fast by 33 and you
will have an idea of the amount of kinetic energy delivered by a rail gun.
The projectiles fired by rail guns are usually Tungsten (chemical element W-74) missiles
[1]. These missiles are light and easy to transport on naval ships. The navy also is developing
rounds that do not feature warheads. Figure 4 demonstrates one of these rounds being fired.
One benefit of eliminating explosives is safety. Without warheads on board, the threat of selfexplosions when under attack is eliminated. Instead, an enemy’s magazine (ammunitions room)
can be used against themself. By firing the rail gun directly at an enemy ship’s magazine, the
navy can “let his explosives be your explosives" [6].
Figure 4: The firing of a rail gun. The round is traveling at a speed nearly eight times the speed of sound (Mach 8). The rail
gun inflicts damage through kinetic energy. Notice the intense heat that is expelled with the firing of a rail gun.
The warhead-less rounds rely on the high kinetic energy produced from the rail gun [7].
For softer targets such as planes, cars, people, etc., the rounds would have a shotgun-like effect.
Upon being fired, the round would dispense thousands of pellets. The high kinetic energy of
these pellets would be able to penetrate and destroy most targets. For harder targets such as
buildings or bunkers, the round would stay completely intact throughout firing and the kinetic
energy of impact would thereby destroy the target.
Another advantage of rail gun weaponry is the high velocities achieved. Rail guns have
been measured to fire projectiles at nearly Mach 8 (eight times the speed of sound) [7]. The high
velocity projectiles allow for more precise and accurate shots to be made as they are less likely to
be affected by wind speed and other factors. The high speed of rail gun firings also allows it to
hit their intended targets within minutes. Traditional, subsonic missiles take much longer, which
might allow the target to escape before the missile even arrives.
Rail guns also offer the navy the added benefit of a larger firing radius. A ship with a rail
gun on board can hit a target within a 250 mile radius [6]. This would allow naval ships to cover
more area and be more effective in defense. The large firing radius also would allow ships to
fire at targets from a safe distance without having to fear possible retaliation.
Alternative Energy Sources
One of the most innovative ideas in rail gun technology is in the field of nuclear fusion.
Rail guns have been looked at in initiating nuclear fusion reactions. Nuclear fusion occurs when
two small nuclei combine to form a large nucleus. This process causes a large release of energy.
However, the nuclei must be traveling at high speeds for this to occur. Scientists have proposed
using rail guns as a means to achieve these high velocities. The impact of the high velocity
nuclei would create extremely high temperatures and pressures, an environment conducive to
where fusion could occur [1].
Space Travel
NASA has also looked into the possible uses of rail guns. The Applied Physics
Laboratory at Kennedy Space Center is considering the idea of using rail guns to launch shuttles
and satellites into orbit [8]. NASA proposes that a spacecraft with scramjets (jet engine in which
combustion takes place at supersonic speeds) could be launched using a rail gun [9]. It would be
launched horizontally and would use the scramjets to gain lift and reach the upper atmosphere.
In this proposal, the rail gun and aircraft would have a similar capacity to a roller coaster. For
example, roller coasters utilize electric tracks to catapult the carts to speeds in excess of 100
mph. The only difference between a roller coaster and a rail gun-assisted launch is the much
greater speed required to escape Earth’s gravitational field in the latter.
Figure 5: Artist's rendering of shuttle launch by rail gun technology. Scientists and engineers believe that rail guns may
revolutionize space travel, making it more cost efficient.
The rail gun launch system is not meant to replace space shuttles. Instead, it is
designated more for unmanned aircraft and satellites [8]. However, researchers agree that the
system could be adapted to launch manned shuttles once unmanned missions are successful.
The rail gun could revolutionize space launches and the aerospace industry. NASA is
even looking far into the future. The program could potentially be used as the basis for a
commercial launch system. Rail guns would save millions of dollars in propellants and allow for
more frequent trips. Civilians may one day be able to visit outer space realistically because of
rail gun technology.
Conclusion
The rail gun is still in its developmental stages. However, the future looks bright. The
navy plans to have the weapon deployed on one of its ships by 2025. In space travel, the
technology is advanced enough that tests and modeling can take place in the near future. There
are still many hurdles to overcome before rail guns become a viable option. Rail gun technology
is promising though. The design and physical concepts have been already broken ground. Only
a breakthrough needs to occur. One engineer put it best, “We have all the ingredients. Now we
just have to figure out how to bake the cake” [9]. Rail guns are no longer the stuff of sci-fi lore.
They are now reality and will have a substantial impact in the near future.
Annotated Bibliography
[1] W. Harris. How Rail Guns Work [Online]. Available: http://science.howstuffworks.com/railgun.htm
How stuff works is an incredibly useful site for researching the basic ways that a rail gun works.
This site is not as reliable as other online journals or articles since it is not peer reviewed. I
mainly used this source to help outline the ways in which a basic rail gun system is set up. How
stuff works also provided simple diagrams which I used in my article. These diagrams would
help the reader to understand how a rail gun works.
[2] H. Young and R. Freedman, “Magnetic Field and Magnetic Forces” in University Physics,
12th ed. San Francisco, CA: Pearson, 2008, ch. 27, sec. 6, pp. 932-935.
University Physics is a very reliable resource. It was the textbook I used in my Physics 152
E&M course, the most relevant physics to rail guns. I used this book mainly to understand the
underlying physical concepts behind currents, electricity, and magnetic forces commonly
associated with rail guns. This source is not biased because it is peer reviewed and a source of
academic knowledge.
[3] D. A. Adams, “Naval rail guns are revolutionary,” United States Naval Institute.
Proceedings. Vol. 129, iss. 2, pg. 34, Feb. 2003.
This is a periodical that I found on the USC libraries. This periodical was written by a naval
officer who had a deep understanding and technical knowledge of rail guns in the navy. He was
able to discuss specific numbers pertaining to rail guns. I used this periodical to gather
information on the power requirements of rail guns. The periodical as a whole was very
technical and discussed possible advancements in rail gun technology.
[4] (2004). Not Your Grandpa’s Shootin’ Iron: Rail Guns [Online]. Available:
http://www.military.com/soldiertech/0,14632,Soldiertech_RailGuns,,00.html
This source is a useful site for the technical workings of rail guns. This site is managed and
catered toward military members, making it applicable to rail guns because of military
applications. The author seems knowledgeable in the subject of rail guns. I used this source
mainly as research for solutions to intense heating involved with rail guns. This source provided
detailed information about alternative armatures such as plasma.
[5] J. R. Quain. (2010, Dec. 10). Navy Sets World Record With Incredible, Sci-Fi Weapon
[Online]. Available: http://www.foxnews.com/scitech/2010/12/10/navy-railgun-shoots-bulletselectromagnet/
This Fox News source gave me the necessary updated information on the progress of naval
research in rail guns. Fox News has been blamed at times to be too conservative in its delivery
of news. This can cause the source to have an inherent bias when reporting about rail guns.
However, I felt that the reporter delivered the information in a mostly professional and non-bias
manner. This made the article very reliable as I was able to take more facts than opinions away.
[6] D. Gardner. (2010, Dec. 14). The gun that can destroy an enemy 100 miles away and fire
bullets at eight times the speed of sound [Online]. Available:
http://www.dailymail.co.uk/sciencetech/article-1338112/U-S-Navys-supergun--electromagneticrail-gun-obliterates-targets-100miles-away.html
This source is another online news article similar to the above Fox News. However, it is a
British newspaper company. This website covers the navy’s test firings of rail guns and the
results obtained. I felt that this source was reliable much like Fox News. However, some hidden
bias might arise from the website being from Britain and reporting on the technological
advancements of the U.S. Navy. However, that hardly seems to be the fact as the information on
rail guns as well as interviews with U.S. personnel are unbiased. This source also provided a
few pictures from the test firing that I used in my paper.
[7] (2007). Massive Attack [Online]. Available: http://dsc.discovery.com/fansites/futureweapons/episodes/episode-guides-3.html
This source is provided by the discovery channel. The discovery channel is known for its highly
rated documentaries. There is not too much bias in the discovery channel other than the fact that
it might try to deliver info that might have more of an entertainment value. However, I felt that
the documentary on Rail guns was very informative. I used this source to find information about
Rail gun projectiles being developed by the Navy.
[8] N. Atkinson. (2010, Sep. 14). NASA considering rail gun launch system [Online]. Available:
http://www.csmonitor.com/Science/Cool-Astronomy/2010/0914/NASA-considering-rail-gunlaunch-system
This is one of the two sources that I used to write about the space launching applications of rail
guns. This article mainly discussed the research that was being done by NASA. It also provided
some commentary from NASA officials regarding the rail gun projects. The article also focused
heavily on the future of rail gun technology.
[9] R. M. Pacella. (2010, Dec. 17). NASA Engineers Propose Combining a Rail Gun and a
Scramjet to Fire Spacecraft Into Orbit [Online]. Available:
http://www.popsci.com/technology/article/2010-11/nasa-engineers-propose-combining-rail-gunand-scramjet-fire-spacecraft-orbit
This article was published by Popular Science. This is a very relevant source that would be used
in most Illumin papers. The article on Popsci discusses the more technical aspects of rail gun
launchings, compared to the previous source. With this source, I was able to describe how the
launching of the scramjet+rail gun apparatus would work. The source also described the projects
and models that were being made to replicate a full scale model of launching from a rail gun.