Referaat
Railgun
Table of contents
Introduction 3
1.What a railgun basically is 4
1.1History of railguns 4
1.2Theory
behind it 5
1.3How a railgun
works 6
1.4How a railgun would
work on a
military ship in the future 8
3. Research advances so far 9
3.1 A
functional 32 MJ railgun
weapon 9
3.2
Multi -
shot salvos 10
4. Problems with a railgun 11
5.
Different applications 12
5.1
Launch of spacecrafts into
space from Earth 12
5.2 Military weapons 13
5.3
Fusion reaction initiations 14
5.3.1 How inertial confinement fusion should work 15
Conclusion 16
Used materials: 17
Introduction
With the advancement of
technology ideas that used to be futuristic
are
nowadays already being researched with impressive headway made.
One
such research
project is the railgun.
I picked this topic because railguns are a childhood dream of every
kid who
watched sci-fi
movies or something
related to space. I
wanted to learn more about how they’re
supposed to work and it is
important because the research has
done great leaps
since 2009.
Metaphorically it
could be a crowbar used to break into a new
military age in which the use of conventional
guns changes drastically. And as a side effect new uses could be
found in
everyday life, not to
mention the advancement in spacecraft related research.
The
purpose of this
essay is to
explain what a railgun is and how it
works
along with a
little history and the
recent advancements in
railgun related
science .
What a railgun basically is
A railgun is an electrically powered electromagnetic projectile
launcher and a large electric circuit , made up of three parts: a power source, a pair of parallel rails and a moving armature. Along
the pair of parallel conducting rails a sliding armature is
accelerated by the electromagnetic effects of a current that flows
down one rail , into the armature and then back along the other rail.
Railguns have long existed as experimental technology but the mass, size and cost of the required power supplies have prevented railguns
from becoming practical military weapons.
However ,
in recent years , significant efforts have been made towards their development as feasible military technology. For example, in the late 2000s, the U.S. Navy tested a railgun that accelerates a 3.2 kg
projectile to hypersonic velocities of approximately 2.4 kilometres
per second, which is about Mach 7.
In addition to military applications, railguns have been proposed to
launch spacecrafts into orbit ; however, unless the launching track was particularly long, and the acceleration required spread over a
much longer time, such launches would be restricted to unmanned
spacecraft.
History of railguns
The earliest electromagnetic gun developed was the coil gun, the
development of which reportedly started already in 1845. The first patent was awarded to a professor in Oslo when he accelerated a 500g projectile to 50m\s.
The first primitive railgun was created in 1918 when French inventor Louis Octave Fauchon’Villeplee created an electric cannon where two
parallel busbars were connected by the wings of a projectile and the
apparatus surrounded by a magnetic field .When current passes through the busbars and projectile, a force is created which propels the
projectile along the busbars into air.
The
first theoretically viable railgun was proposed in 1944 by Joachim Hänsler of Germany 's Ordnance Office. The gun was never built but a
1947 report concluded that while it was feasible in theory, the
energy consumption for each gun would be enough to illuminate half of Chicago .
While minor successes happened afterward, the most notable one was late
into the first decade of 2000s, when the U.S. Navy tested a railgun
that accelerates a 3.2 kg (7 pound) projectile
to hypersonic velocities of approximately 2.4 kilometres
per second (8,600 km/h), about Mach 7. They gave
the project the motto "Velocitas Eradico", Latin for
"I, speed , eradicate"— or simply, "Speed Kills".
Theory behind it
A railgun consists of two parallel metal rails connected to
an electrical power supply . When a conductive projectile is
inserted between the rails connected to the power supply it completes
the circuit. Electrons flow from the negative terminal of the power
supply up the negative rail, across the projectile, and down the positive rail, back to the power supply.
This
current makes the railgun behave as an electromagnet, creating a
magnetic field inside the loop formed by the length of the rails up
to the position of the armature. In accordance with the right- hand rule , the magnetic field circulates around each conductor. Since the
current is in the opposite direction along each rail, the net
magnetic field between the rails is directed at right angles to the plane formed by the central axes of the rails and the armature. In
combination with the current in the armature, this produces a Lorentz force which accelerates the projectile along the rails, always
out of the loop (regardless of supply polarity) and away from the
power supply. There are also Lorentz forces acting on the rails and
attempting to push them apart, but since the rails are mounted firmly, they cannot move .
By
definition, if a current of one ampere flows in a pair of ideal infinitely long parallel conductors that are separated by a distance of one meter , then the magnitude of the force on each meter of those
conductors will be exactly 0.2 micro-newtons. Furthermore, in
general, the force will be proportional to the square of the
magnitude of the current and inversely proportional to the distance
between the conductors. It also follows that, for railguns with
projectile masses of a few kilograms and barrel lengths of a few
meters, very large currents will be required to accelerate
projectiles to velocities of additions of 1000 m/s.
A
very large power supply, providing on the order of one
million amperes of current, will create a tremendous force
on the projectile, accelerating it to a speed of many kilometers per
second (km/s). Although these speeds are possible, the heat generated
from the propulsion of the object is enough to erode the rails
rapidly. Under high-use conditions , current railguns would require frequent replacement of the rails, or to use a heat-resistant material that would be conductive enough to produce the same effect.
The barrel must withstand these conditions for up to several rounds per minute for thousands of shots without failure or significant
degradation. These parameters are well beyond the state of the art in
materials science for now.
How a railgun works
The power supply is simply a source of electric current. Typically , the current used in medium - to large-caliber railguns is
in the millions of amps .
The rails are lengths of
conductive metal, such as copper . They can range from 1.2 to 9 meters
long.
The armature bridges the gap between the rails.
It can be a solid piece of conductive metal or a conductive sabot --
a carrier that houses a dart or other projectile. Some railguns use
a plasma armature. In this set-up a thin metal foil is
placed on the back of a non-conducting projectile. When power flows
through this foil it vaporizes and becomes a plasma, which carries
the current.
Picture 1. Basic parts in a railgun
Source: http://www.seminarsonly.com/mech%20&%20auto/railgun-seminar-report-ppt.php
The
armature may be an integral part of the projectile, but it may also
be configured to accelerate a separate, electrically isolated or
non-conducting projectile. Solid, metallic sliding conductors are
often the preferred form of railgun armature but "plasma"
or " hybrid " armatures can also be used. A plasma armature
is formed by an arc of ionised gas that is used to push a solid,
non-conducting payload in a similar manner to the propellant gas pressure in a conventional gun. A hybrid armature uses a pair of
"plasma" contacts to interface a metallic armature to the
gun rails.
Picture
2. Forces affecting a railgun
Source: https://science.howstuffworks.com/rail-gun1.ht m
A
railgun consists of two parallel metal rails connected to an
electrical power supply. When a conductive projectile is inserted
between the rails (at the end connected to the power supply), it
completes the circuit. Electrons flow from the negative terminal of
the power supply up the negative rail, across the projectile, and
down the positive rail, back to the power supply. This current makes
the railgun behave as an electromagnet, creating a magnetic field
inside the loop formed by the length of the rails up to the position
of the armature. In accordance with the right-hand rule, the magnetic
field circulates around each conductor.
Since
the current is in the opposite direction along each rail, the net
magnetic field between the rails (B) is directed at right angles to
the plane formed by the central axes of the rails and the armature.
In combination with the current (I) in the armature, this produces a
Lorentz force which accelerates the projectile along the rails, away
from the power supply.
There are also Lorentz forces acting on the rails and attempting to push
them apart, but since the rails are mounted firmly, they cannot move.
A very large power supply, providing on the order of one million
amperes of current, will create a tremendous force on the projectile,
accelerating it to a speed of many kilometres per second (km/s). 20
km/s has been achieved with small projectiles explosively injected into the railgun. Although these speeds are possible, the heat
generated from the propulsion of the object is enough to erode the
rails rapidly. Under high-use conditions, current railguns would
require frequent replacement of the rails, or to use a heat-resistant
material that would be conductive enough to produce the same effect.
Notice that the Lorentz force is parallel to the rails, acting away from the
power supply. The magnitude of the force is determined by the
equation F = (i)(L)(B), where F is the net force, i is the current, L
is the length of the rails and B is the magnetic field. The force can
be boosted by increasing either the length of the rails or the amount of current.
Because
long rails pose design challenges, most rail guns use strong currents
-- on the order of a million amps -- to generate tremendous force.
The projectile, under the influence of the Lorentz force, accelerates
to the end of the rails opposite the power supply and exits through
an aperture . The circuit is broken , which ends the flow of current.
How a railgun would work on a military ship in the future
Rail
guns require tremendous currents to fire projectiles at speeds of
Mach 5 or higher . This presents problems for a traditional battleship
because power cannot be diverted from the ship's propulsion system.
In the Navy's next-generation battleship, the all-electric DD(X),
producing this kind of current will be possible. To launch a rail gun
projectile, power would be diverted from the ship's engine to the gun
turret. The gun would be fired, up to six rounds per minute, for as
long as required. Then power would be shifted back to the engine.
3. Research advances so far
3.1 A functional 32 MJ railgun weapon
In 2009 BAE Systems delivered a functional, 32 megajoule
Electromagnetic Laboratory Rail Gun (32/MJ LRG) to the U.S. Naval Surface Warfare Center .
The
U.S. Navy's experimental railgun is getting new upgrades to make it
fire more powerful shots, and fire them faster. It's the latest bit
of progress on this still -landlocked weapon, but when and where it
actually would be installed on a warship is not clear .
The goal , according to Tom Beutner, head of Naval Air Warfare and Weapons
for the ONR, is ten shots per minute at 32 megajoules. One way of looking at it is that a .22 bullet has 1,000 foot -pounds aka
1356(Nm) of force at the muzzle. A 32 megajoule railgun shot:
23,601,988 foot-pounds aka 3.200000e(plus)7(Nm).
The
existing railgun works by using extremely high electrical currents to
generate magnetic fields capable of accelerating a projectile up to
Mach 6, which is more than twice as fast as any other existing
projectile. The range is 100 miles and it fires projectiles which
destroy targets by smashing into them at hypersonic speeds.
The delay of railguns being added to the Navy is because they’re making
it more durable due to the fact that the raw kinetic power unleashed
in firing the railgun is rough on the weapon’s parts. When the
railgun was delivered to the Navy in 2009 it was said that a few
shots could dislodge the conducting rails or even damage the barrel
of the gun. While previously it wore out after tens of shots, it is
getting closer to firing more than 400 shots.
So
far only the Zumwalt class destroyers, capable of generating 78
megawatts of electricity and built specifically for that purpose can handle the railguns.
Picture
3. Zumwalt class destroyer
Source: http://www.popularmechanics.com/military/research/news/a27455/us-navy-railgun-more-powerful
3.2 Multi-shot salvos
Initial firing repetition rate (rep-rate) of multi-shot salvos have
already been successfully conducted at low muzzle energy. The next
test sequence calls for safely increasing launch energy, firing rates
and salvo size.
Railgun rep-rate testing will be at 20 megajoules by the end of the summer 2017 and at
32 megajoules by 2018 . To put this in perspective; one megajoule is
the equivalent of a one-ton vehicle moving at 160 miles per hour .
The
weapon releases a current on the order of 3 to 5 million ampers which
is about 1,200 volts released in a ten millisecond timeframe. That is
enough to accelerate a mass of approximately 45 pounds from zero to five thousand miles per hour in one one-hundredth of a second.
Due
to its ability to reach speeds of up to 5,600 miles per hour, the
hypervelocity projectile is engineered as a kinetic energy warhead, meaning no explosives are necessary . The hyper velocity projectile
can travel at speeds up to 2,000 meters per second, a speed which is
about three times that of most existing weapons. The rate of fire is
10-rounds per minute.
A
kinetic energy hypervelocity warhead also lowers the cost and the logistics burden of the weapon.
Although
it has the ability to intercept cruise missiles, the hypervelocity
projectile can be stored in large numbers on ships. Unlike other
larger missile systems designed for similar missions, the
hypervelocity projectile costs only $25,000 per round .
The railgun can draw its power from an onboard electrical system or large battery .
The system consists of five parts, including a launcher, energy storage system, a pulse- forming network, hypervelocity projectile
and gun mount .
Currently
the weapon is configured to guide the projectile against fixed or
static targets using GPS technology.
4. Problems with a railgun
In
theory, railguns are supposed to be the perfect solutions for short-
and long-range firepower , but in reality they present several serious problems:
- Power supply: Generating the power necessary to accelerate rail gun projectiles is a real challenge . Capacitors must store electric charge until a sufficiently large current can be accumulated. While capacitors can be small for some applications, the capacitors found in rail guns are many cubic meters in size.
- Resistive heating: When an electric current passes through a conductor, it meets resistance in the conductive material -- in this case , the rails. The current excites the rail's molecules, causing them to heat. In railguns, this effect results in intense heat.
- Melting: The high velocity of the armature and the heat caused by resistive heating damages the surface of the rails.
- Repulsion: The current in each rail of a rail gun runs in opposite directions. This creates a repulsive force, proportional to the current that attempts to push the rails apart. Because the currents in a rail gun are so large, the repulsion between the two rails is significant. Wear and tear on rail guns is a serious problem. Many break after a few uses, and sometimes they can only be used once .
- Railgun durability: To date railgun demonstrations, while impressive, have not demonstrated an ability to fire multiple full power shots from the same set of rails. Tolerating launch accelerations of tens of thousands of g's, extreme pressures and mega ampere currents over this sort of duty cycle is currently beyond the state of the art.
- Projectile guidance: A future capability critical to fielding a real railgun weapon is developing a robust guidance package that will allow the railgun to fire at distant targets or to hit incoming missiles. Developing such a package is a real challenge. According to The Navy's RFP Navy SBIR 2012.1 - Topic N121-102 the following is required:
The package must fit within the mass of less than 2kg, outer diameter
less than 40 mm, and volume 200 cm3 constraints of the
projectile and do so without altering the center of gravity. It
should also be able to survive accelerations of at least 20,000 g
(threshold) / 40,000 g ( objective ) in all axes, high electromagnetic
fields (E > 5,000 V/m, B > 2 T), and surface temperatures of >
800 deg C. The package should be able to operate in the presence of
any plasma that may form in the bore or at the muzzle exit and must
also be radiation hardened due to exo-atmospheric flight. Total power
consumption must be less than 8 watts (threshold)/5 watts (objective)
and the battery life must be at least 5 minutes from initial launch
to enable operation during the entire engagement. In order to be
affordable, the production cost per projectile must be as low as
possible, with a goal of less than $1,000 per unit . ( The Navy's RFP
Navy SBIR 2012.1 - Topic N121-102)
5. Different applications
5.1 Launch of spacecrafts into space from Earth
Railguns can potentially launch satellites or space shuttles into the upper atmosphere, where auxiliary rockets would kick in. On bodies
without an atmosphere, such as the moon , railguns could deliver
projectiles to space without chemical propellant, which requires air
to function .
In 2003, Ian McNab outlined a plan to turn this idea into a realized
technology. The accelerations involved are significantly stronger
than human beings can handle. This system would only be used to
launch sturdy materials, such as food, water, and fuel. Note that
escape velocity under ideal circumstances (equator, mountain, heading east ) is 10.735 km/s. The system would cost $528 a kg, compared with
$20,000 a kg on the space shuttle. The railgun system McNab suggested
would launch 500 tons per year , spread over approximately 2000
launches per year.
Because
the launch track would be 1.6 km, power will be supplied by a
distributed network of 100 rotating machines (compulsator) spread
along the track. Each machine would have a 3.3 ton carbon fibre rotor
spinning at high speeds. A machine can recharge in a matter of hours using 10 MW. This machine could be supplied by a dedicated generator.
The total launch package would weigh almost 1.4 tons. Payload per
launch in these conditions is over 400 kg. There would be a peak operating magnetic field of 5T – Half of this coming from the
rails, and the other half from augmenting magnets. This halves the
required current through the rails, which reduces the power fourfold.
Picture
4. Railgun usage for spacecraft launces from Earth
Source: https://www.nasa.gov/topics/technology/features/horizontallaunch.html
5.2 Military weapons
Railguns are being researched as weapons with projectiles that do not contain explosives or propellants, but are given extremely high
velocities: 3,500 m/s (approximately Mach 10 at sea level) or more
(for comparison , the M16 rifle has a muzzle speed of 930 m/s (3,050
ft/s), and the 16"/50 caliber Mark 7 gun that armed World War II
American battleships has a muzzle speed of 760 m/s (2,490 ft/s)),
which would make their kinetic energy equal or far superior to the
energy yield of an explosive-filled shell of greater mass. This would
decrease ammunition size and weight , allowing more ammunition to be
carried and eliminating the hazards of carrying explosives or
propellants in a tank or naval weapons platform. Also, by firing at
greater velocities, railguns have greater range, less bullet drop ,
less time to target, and less wind drift , bypassing the physical limitations of conventional firearms.
Railguns are of particular interest to the military, as an alternative to current large artillery. Railgun ammunition, in the
form of small tungsten missiles, would be relatively light , easy to
transport and easy to handle. And because of their high velocities,
rail gun missiles would be less susceptible to bullet drop and wind
shift than current artillery shells. Course correction would be
important, but all missiles fired from rail gun artillery would be
guided by satellite.
It
would be more difficult to engineer small arm rail guns, mainly
because of recoil. Recoil is determined by the momentum of the escaping projectile. Multiplying a projectile's mass by its velocity
yields its momentum, which for high-velocity rail gun projectiles
would be considerable . A portable rail gun that fires very small
bullets may be the solution . A small bullet would limit recoil but
still carry enough kinetic energy to inflict serious damage.
Rail
guns have also been proposed as important components of the Strategic Defense Initiative, popularly known as Star Wars . Star Wars is a U.S. government program responsible for the research and development of a
space- based system to defend the nation from attack by strategic
ballistic missiles. Rail guns could fire projectiles to intercept the
incoming missiles. Some scientists argue that rail guns could also protect Earth from rogue asteroids, by firing high-velocity
projectiles from orbit. Upon impact, the projectiles would either
destroy the incoming asteroid or change its trajectory.
5.3 Fusion reaction initiations
Rail guns could also be used to initiate fusion reactions. Fusion
occurs when two small atomic nuclei combine together to form a larger
nucleus, a process that releases large amounts of energy. Atomic
nuclei must be traveling at enormous velocities for this to happen.
On the earth, some scientists propose using rail guns to fire pellets
of fusible material at each other. The impact of the high-velocity
pellets would create immense temperatures and pressures, enabling
fusion to occur . Unfortunately current rail guns do not generate
sufficient energies to enable nuclear fusion to occur.
5.3.1 How inertial confinement fusion should work
Fusion is triggered by very high temperature and pressure at the core . Current technology calls for multiple lasers, usually over 100,
to concurrently strike a fuel pellet, creating a symmetrical
compressive pressure. Railguns may be able to trigger fusion by
firing energetic plasma from multiple directions. The process
developed involves four key steps:
Plasma is pumped into a chamber .
When the pressure is great enough, a diaphragm will rupture, sending
gas down the rail.
Shortly afterwards, a sufficient voltage is applied to the rails,
creating a conduction path of ionized gas.
This plasma accelerated down the rail, eventually being ejected at a
large velocity.
Conclusion
This essay is about what a railgun is and how it works along with
explanations of possible applications which are either in theory or
already being researched and the briefly covers the advancement of
mentioned research.
Railgun testing had picked up pace since 2009. The U.S government had
started to fund the research with more money and since the first
tested and viable 32 MJ railgun had been sent to the Navy,
astonishing progress has been made, getting the shot count from about
10 to over a 100 and closing in on the 400 shot milestone before the
rails give up due to use, which is an important part of introducing
the weapon to basic military use. Unfortunately the Department of
Defense has been moving away from the railgun project, leaning more
towards a mixture of new and existing technologies because the
electromagnetic railgun weapon system as it is now will likely never
see combat in its current form. Although it has been proven that the
railgun works, it hasn’t reached the required 10 rounds a minute,
being able to shoot about 4.8 rounds in one minute. It will probably
take quite a while before research is far enough.
Using a railgun as a railway for spacecrafts is also a long ways from
being brought to fruition as the theory has been set but no practical
headway has been made. Although science hasn’t advanced enough yet
to make full use of the theory behind railguns, the research has been
started and it will only be a matter of time before the full
capabilities of railguns will be exploited both in military and other
aspects.
Used materials:
Adams ,
E. "Electromagnetic railgun," Popular Science. September 7,
2005. http://www.popsci.com/popsci/technology/generaltechnology/64669aa138b84010vgnvcm1000004eecbccdrcrd.html (21.12.2017)
The
Defence Science and Technology Ministry (UK Ministry of Defense) http://www.dstl.gov.uk/pr/science_spot/off_the_rails.ht m(21.12.2017)
Folger,
T. "The guns of Brooklyn," Discover. August 1992.
"Not
your Grandpa's shootin' iron: Rail guns." Military.com, 2004. http://www.military.com/soldiertech/0,14632,Soldiertech_RailGuns,,00.html (21.12.2017)
Office
of Naval Research: Future Naval Capabilities. http://www.onr.navy.mil/fncs/aces/focus_elecweapons_rail.asp (21.12.2017)
PowerLabs
Railgun Research. http://www.powerlabs.org/railgun2.ht m(21.12.2017)
K.
Mizokami. Popular Mechanics. The U.S Navy’s Railgun may never see
combat. http://www.popularmechanics.com/military/research/a14106941/us-navy-railgun-may-be-dead/ (27.12.2017)
K.
Mizokami. U.S Navy’s Railgun is about to get faster and more
powerful. http://www.popularmechanics.com/military/research/news/a27455/us-navy-railgun-more-powerful (27.12.2017)
Rochester
Institute of Technology. http://www.rit.edu/~dih0658/index.html (21.12.2017)
Wise Geek: What is a railgun? http://www.wisegeek.com/what-is-a-rail-gun.ht m(21.12.2017)
S.
Siceloff. Kennedy Space Center. National Aeronautics and Space
Administration. https://www.nasa.gov/topics/technology/features/horizontallaunch.html (27.12.2017)
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