Hot shot

From ultra-violent science fiction to post-apocalyptic video games, the idea of weapons that use electromagnetic force to launch projectiles at devastating speed has been around for some time. But while Hollywood’s take on the concept has been employed to great effect by the likes of Arnold Schwarzenegger, the technology is not without real-world precedents, and many believe that the potential destructive power of EM weapons will put them at the heart of future military strategies.

Now world-leading engineering developments underway in the UK could inspire a revival of interest in a concept that has not received such scrutiny since the US government unsuccessfully ploughed millions of dollars into EM weapons in the 1980s.

The concept behind EM railguns could not be simpler but, as is so often the case, the devil is in the detail. Ever since French scientist Andre Fauchon-Villeplée submitted patent applications for a railgun in 1916 — a project that was subsequently abandoned at the end of World War I — the technology required to make railguns a viable proposition has always lagged behind the theory.

However, in a field outside a sleepy fishing village in rural Scotland, Qinetiq has since 1993 been test-firing an EM gun that demonstrates that the technology may finally be catching up with the daydreams.

Of the two basic EM gun designs — the railgun and the coilgun — the railgun has emerged as the more promising embodiment of an EM weapon.

Coilguns consist of a number of coils along the barrel of the gun. When a large electrical current is pulsed into the first coil, a force is produced that accelerates the projectile towards the next coil, which is excited in turn.

Despite huge investment in coilgun technology in the 1980s, the increasingly high speeds at which the coils had to be switched in sequence made it too complex to launch a projectile much more quickly than 1km/s. It remains an option for lower-velocity applications such as mortars, but in the higher-velocity range it is railgun technology that has attracted most UK research funding.

Railguns use an electromagnetic force known as ‘Lorentz force’ to propel a projectile. They consist of two parallel conductive metal rails connected to a power supply. When a conductive ‘armature’ is introduced between them, it completes the circuit. A projectile can then be introduced in front of the armature.

When the power is switched on, the electrical current runs from the positive terminal up the positive rail, across the armature and down the negative rail. The flow of current creates a magnetic field around each of the rails and a force that moves in the opposite direction to the power supply. This accelerates the armature along the rails, which in turn propels the projectile.

So why are EM guns so sought after, and why have successive governments either side of the Atlantic ploughed millions of pounds and dollars into researching them?

The answer is that an EM gun offers the tantalising prospect of extreme speed, or hypervelocity — with all its attendant benefits. The use of electromagnetic power to propel a missile or round would make traditional gas-fired weapons redundant. Despite huge advances in conventional firearms, all guns still rely on the same theory of expanding gas that they did 1,000 years ago.

In conventional weapons, from the blunderbuss to the AK-47, an expanding ball of heated gas forces the projectile along the length of the gun. These weapons can reach an absolute maximum velocity of around 1.75km/s, for example in an Abrahams tank.

However, the speed of a projectile can never exceed the speed of the molecules pushing it — typically less than 2km/s in conventional firearms. In contrast, a projectile fired from an EM gun is pushed by an electromagnetic field, so in theory there are no upper limits to the velocity that can be created.

Prof Michael Hinton, technical director of Qinetiq’s weapons division, describes moving to electromagnetic weapons in place of conventional firearms as a huge step in the history of warfare.

‘What we are trying to do here is nothing less than revolutionise weapons technology,’ he said. ‘We are trying to change more than 1,000 years of arms history in a single sweep.’

Hinton’s assertion that an EM weapon would change the face of the modern battlefield gains credence when the practical and tactical benefits of railguns are weighed up.

At its purpose-built test site in Kirkcudbright, Qinetiq’s EM gun has already demonstrated muzzle velocities (the speed of the projectile on leaving the gun) in excess of 2.5km/s — the exact speeds remain classified — and experiments in other research centres around the world have conducted small-scale tests reaching speeds of more than 7km/s. An anti-armour projectile travelling at 3km/s would have so much kinetic energy that it would only need to be around one-fifth of the size of a standard projectile to deliver the same amount of destructive force.

In turn, this smaller size allows a significant increase in the number of projectiles that a tank or warship could carry, while the vastly increased muzzle velocity would greatly lengthen the distance that artillery could launch a larger and heavier projectile.

The storage issue is another reason EM guns are so attractive to the military. Without a propellant charge the inert metal projectiles can be carried on-board a ship in complete safety, greatly reducing a ship’s vulnerability.

But no matter how attractive a proposition railguns are — or how much money is thrown at them — there is a reason that the military has been kept waiting for a usable EM gun for the best part of a century. Indeed, the technical challenges that this technology present are so great that many research facilities in the US have been abandoned.

However, in Hinton’s opinion, the UK’s EM test facility, under Qinetiq’s stewardship, is now a world-leader in electromagnetic propulsion technology.

‘We are the only fully functioning EM railgun test site in the western world,’ he claimed.

The most fundamental stumbling block to a successful EM weapon is the huge amount of electrical power needed to fire it. Hinton admitted that the size of the electrical throughput required tests the very limits of both material science and physics. ‘There really are some pretty ferocious challenges to overcome to make this work. The question is not only how can you generate enough power in the first place, but how can you transfer it in a single pulse?’ he said.

Various designs of power generators have been mooted over the years to power an EM gun. The Qinetiq EM gun is powered using an enormous bank of capacitors the size of a small house, but Hinton is quick to point out that this is purely for research purposes. ‘To test the gun we needed a readily available, “easy” technology to provide the power,’ he said. ‘But to get to the stage of producing a weapon that can be operated in the field the use of capacitors just isn’t that practical.’

The most likely candidate for any future electric weapon’s power source is a special type of alternator that uses a rotating drum, spinning at around 20,000rpm, creating a tremendous centrifugal load on the drum’s structure.

To produce enough energy to propel a projectile with sufficient force, the drum has to be able to produce three million amps in five milliseconds, an equation that stretches all aspects of the drum’s manufacture to the limit. To begin with, producing three million amps in such a short interval would melt any conventional wiring, and so researchers have had to investigate the use of advanced composite materials to develop wiring that will stand up to such intense heat.

‘There are few materials that can take that kind of electrical charge,’ said Hinton ‘Fibre composite materials in the drum are already pushing at the very limits of material science.’

Snatching that amount of power also induces massive recoil on the drum, and so a means of keeping it stable has had to be developed that can withstand such forces.

In the US researchers at the University of Texas’ Institute of Advanced Technology have been working on an idea that uses two counter-rotating drums to deal with the recoil problem. The US is particularly strong in this area of the technology, and so both countries have collaborated on many aspects of the research.

However, to produce an EM weapon that could realistically be used on the battlefield would involve a huge improvement in the efficiency of the drum technology. To make a drum small enough to fit in a tank the efficiency would have to improve from its current 1J per gram of structural weight, to 10J per gram.

‘To get to that mstage the materials are going to have to be able to withstand a lot more,’ admitted Hinton.

Obstacles to EM gun technology also extend to the very forces that provide them with their huge firepower potential. The effect of gouging on the rails is a serious problem for EM gun engineers.

For a long time seen as being a significant impediment to the construction of a usable railgun, gouging occurs when teardrop-shaped pieces are pulled from the rails’ surface through contact with the armature at high speeds.

In US tests the gouging by the armature on the rails meant that their EM guns had to be completely rebuilt after every shot, at enormous expense. When an electrical current passes through conductive material some of it is converted to heat. Because of the huge amounts of energy involved, the excess

heat given off can also cause a variety of problems for railgun engineers.

The extremely high temperatures inside the gun’s barrel melt the contact surfaces of the armature, which must remain in contact with the rails on either side. As the surfaces melt they form a liquid film of molten metal which can actually help in preventing the effects of gouging. However, if this liquid film becomes a plasma gas — a change that is known as armature transition — a

discharge is created that can lead to erosion of both the rails and the armature.

Transition does not necessarily render the gun useless, as the plasma gas still conducts electricity, but its higher electrical resistance also reduces its efficiency.

According to Hinton, the UK is leading the way in understanding the physics behind this problem. ‘We have made a lot of progress on this issue,’ he said. ‘It is far from solved but we have been making some real headway on the material science involved.’

The rails also need to be able to withstand massive forces upon firing. The magnetic fields created in the rails repulse one another, putting a tremendous strain on them as they try to force themselves apart.

The apparent advantages of a railgun’s impressive speed also conceal further headaches for engineers. As the velocity at which the projectile leaves the gun edges ever upwards — in excess of 2.5km/s — the effects of aero-thermal damage on the projectile become an issue. Hypervelocity is a challenge for material scientists because as much as 25mm from the projectile’s nose and fins were being lost through heat within two seconds of firing. This is something that Hinton and his team claim to have now solved.

The projectiles themselves involved a large amount of design engineering. The heat generated inside the gun puts so much strain on both the armature and projectile that Hinton and his team have been using sophisticated software to model where heat stresses would cause most damage to the armature’s structure. The projectiles are made from a tungsten alloy with three times the density of steel, similar in design to a standard dart.

A huge amount of research went into developing a system that would allow the maximum transfer of energy to the projectile. This resulted in the design of the four petals of the shell — or ‘sabot’ — which drop away as it leaves the gun’s barrel.

One likely application of railgun technology is on future all-electric warships, as part of an integrated electric weapon and engine system. But despite all the advances in EM gun technology, it is still too early to say for sure when the military may finally get their hands on a usable EM gun, said Hinton.

‘A date of 2025 is a possibility, and a possible late-life variant of FRES (the MoD’s future rapid effect system) is not out of the question. But it is going to take in excess of £1bn of further investment before an EM gun will reach the field. At the moment all this work really is the absolute cutting edge of physics.’

From the earth to the moon

EM launch technology is not just about death and destruction. Engineers around the world are looking at applying the same principles to dramatically bring down the cost of launching vehicles into space.

The idea of projecting a cargo into space using a giant gun has existed since Jules Verne’s Moon Gun, as described in his 1865 novel From the Earth to the Moon.

Advances in EM gun technology have increased the interest in a future EM space launcher, and it is an application that researchers at the University of Texas have been studying for a number of years. Of the many futuristic launch devices mooted to replace conventional rocket launchers — ranging from multi-gigawatt lasers to blast wave accelerators — it’s widely accepted that an EM railgun is the only current viable option.

A civilian launch-to-space railgun system has the advantage that the launch costs would be significantly lower than conventional methods. A large initial outlay of several million dollars on a dedicated power supply for the system could result in launch costs of no more than $1,000 per kilo of payload, said Prof Ian McNabb from the university’s Institute for Advanced Technology. The technology could be used to send packages of food, water or fuel to the International Space Station, cheaply and efficiently.

The major drawback of an EM launcher is that the velocity required to reach space would mean that considerable protection would be required to avoid it burning up as it races out through the Earth’s atmosphere.

Researchers in France and Germany are also currently investigating using EM technology for high-altitude research. Their plans involve equipping a 747 or an A380 with an EM railgun to launch micro-satellites.