AMERICAN FORCES are poised on the border of North Kiran, a rogue state that has built up an arsenal of ballistic missiles.
As the tanks begin to roll, the inevitable happens – North Kiran launches one of its weapons, the telltale vapour trail hanging in the air as it arcs up from the ground.
Meanwhile, 30 miles away, a Boeing 747 circles at high altitude. As the missile breaks through the cloud cover, the jet tracks its flight. Seconds later, a laser beam shoots from a turret on the 747’s nose and locks on to the missile’s fuel tank. It warps under the laser’s focused energy, splits and blows up. The missile falls in fragments to the ground.
Sounds like science fiction? Perhaps not. Above Edwards Air Force Base in California, a highly modified 747 is at the moment performing flight tests in preparation for the installation of a powerful laser later this year.
If more testing and evaluation is successful, it will perform a “lethal demonstration” – defence industry-speak for shooting down a realistic, moving target – some time in 2009.
The 747 flying from Edwards is the flagship of the Airborne Laser (ABL) project, a $3.6 billion (£1.8 billion), American programme that aims to demonstrate the feasibility of using a laser to attack ballistic missiles.
It is probably the most ambitious attempt ever to equip the front line with “directed-energy” systems, as the military refers to weapons that use beams of light, sound or particles rather than old-fashioned projectiles. If it proves successful, the US Air Force could eventually field a squadron of seven laser-carrying 747s.
“It is a pathfinder for these kinds of [direct-ed-energy] weapons,” said Greg Hyslop, ABL programme director.
“You can’t see it, you can’t hear it, and it strikes at the speed of light. It has the potential to revolutionise warfare.”
Military chiefs have long dreamt of having some kind of ray-gun weapon. Two hundred years before the birth of Christ, Archimedes, the Greek mathematician and inventor, came up with a plan to burn enemy ships by focusing the sun’s beams with mirrors. Towards the end of the second world war, Nazi scientists experimented with focused sound, hoping to produce a
Wunderwaffen (wonder weapon). America has also invested heavily in directed-energy research over the past 40 years.
The ABL programme has its roots in the first Gulf war, and a desire to protect coalition troops from Saddam Hussein’s Scud missiles.
The contract to develop the system was given to three of America’s top defence contractors – Boeing (which is the prime contractor), Lockheed Martin and Northrop Grum-man. Hyslop’s team now has 1,000 staff at facilities across America.
The team soon realised that the technology had the potential to do more than merely protect troops. “It was capable against more than just theatre weapons – it could also deal with ballistic missiles,” said Hyslop.
This meant it could play a role in America’s wider plans to protect itself and its allies against ballistic-missile launches, plans that began with the Reagan administration’s Strategic Defence Initiative (SDI), better known as Star Wars.
Having started life as a US Air Force project, ABL now comes under the auspices of the Missile Defence Agency, which looks after the various successor programmes to SDI. Its key programme is a system of ground-based radars and missiles that would track and intercept incoming ballistic missiles. In June 2002, President George Bush withdrew America from a missile treaty signed with the Soviet Union in 1972 that prohibited the development of such a system.
Details of how the ABL works are classified, but it consists of three basic systems – the plane (a version of the Boeing 747-400, a mainstay of commercial airline fleets around the world), targeting and tracking systems, which are in the front section of the aircraft, and a “megawatt-class” laser, which takes up most of the rear. A megawatt is a million watts – roughly enough to power 1,000 homes.
The laser generates intense bursts of light from a chemical reaction.
The machine that ABL will use has already been built and tested, and has been fired three times at maximum power on the ground.
“We know we have a lethal weapon that fits inside a 747 fuselage,” said Hyslop. After the trials, the laser is being taken to pieces and refurbished in preparation for installation in the test plane later this year.
The hard part is to focus the beam on a fast-moving target from a fast-moving platform. Last month, the ABL team made its first test of the tracking system, firing the plane’s tracking laser at an airborne target.
Once a missile is being tracked, the aircraft will then fire a second laser at it, called the “beacon-illuminator laser”. This should allow the systems on board the aircraft to calculate how much the tracking and illuminating beams are being affected by atmospheric turbulence.
This is vital to focus the high-energy laser onto the target. If the focus is wrong, the energy will simply dissipate into the atmosphere rather than strike the missile with enough strength to bring it down.
To get it right, the ABL team is using some of the adaptive-optics techniques used by astronomers on telescopes to look at stars through the Earth’s atmosphere.
“When the laser leaves the aircraft it is like a crumpled piece of paper,” said Hyslop. “We have to make sure that when it arrives it is flat.”
Some experts are sceptical about the ABL’s chances of success. “The adaptive optics required are quite challenging even for observatories looking at stars, never mind focusing lasers on moving targets,” said Professor Roy Taylor of Imperial College. “There is a constant feedback loop involved.”
Taylor said while he thought it was probable the Boeing-led team could mount a successful demonstration under controlled conditions, a laser weapon would struggle in real-life conditions.
“It’s one thing directing a laser onto a missile when you know it’s going to be there. But how can you possibly know when your enemy is going to launch this kind of weapon? I think the best way to bring down a ballistic missile is still by using another missile.”
But Taylor said directed-energy weapons had great potential. “An obvious one is powerful electromagnetic pulses (which can be generated by large transformers or special bombs). If you set one off in the City of London you would shut down all the computers in a second,” said Taylor.
Professor Ian Walmsley at the Department of Physics at Oxford University, said the ABL programme was “a huge challenge” for its developers. “The main problem is keeping the laser focused in turbulent air to reduce the atmospheric scattering that will reduce its power,” he said.
The technical challenges are formidable, but Hyslop is confident of overcoming them. “This programme has not yet hit a technical problem it has not been able to solve,” he said. “It is a bit like the Apollo programme – Apollo 11 got to the moon, and we are working on our Apollo 10.”
