05 Mar 2004
The ballistic missile-killer is almost complete, and the future of the daring billion-dollar ABL project now rests on the tests it is about to undergo. Oliver Graydon reports.
From Opto & Laser Europe March 2004
Thirty years after a high-energy laser first destroyed an aerial drone the Airborne Laser (ABL) project is preparing for what it calls "first light". Later this year, all six modules of the ABL's giant chemical oxygen iodine laser (COIL) will be switched on simultaneously for the first time. Tests will then show whether the COIL is capable of generating the megawatt 1.3 µm beam that is necessary for shooting down ballistic missiles over a range of hundreds of miles. In theory, if these and subsequent trials are successful the ABL could become an active part of the US missile defence system by 2010.
"This last year has been a busy year delivering the hardware. As we enter into 2004 our focus is to take those pieces that we've demonstrated working individually and put them together, with the goal of shooting down our first missile in 2005," a spokesperson for the ABL project told delegates at IQPC's Directed Energy Weapons seminar in London in January. "We are now focused on getting that first light out of those six COIL modules and propagating it through the beam control system."
The theory Assuming that the necessary beam power is demonstrated, how exactly will the ABL kill a missile in a real-life scenario? The answer lies in a series of sophisticated stages that rely on four different lasers and some of the most demanding optics that have ever been built.
Next, the track illuminator laser (TILL), a kilowatt-class pulsed Yb:YAG source, will locate and track the nose of the missile so that the position of its fuel tank can be accurately determined. This is the "sweet spot" at which the high-energy laser will be aimed.
The last step before the COIL is fired is to activate the beacon illuminator laser (BILL), a pulsed Nd:YAG laser. It will bounce an optical beam off the missile so that the atmospheric distortion between the ABL and the missile can be measured and compensated for using an on-board deformable mirror. The COIL will then be fired and the missile, in theory, will be destroyed. All of this must take place in a matter of seconds if the missile is to be shot down during the initial phase of its flight (the boost phase), while it is over enemy territory and open to attack.
The front part of the plane contains the beam-guiding optics and electronics, while the back section contains the laser fuel and the six laser modules that make up the COIL. Each laser module is about the size of a car and weighs 2 tonnes. The two sections of the aeroplane are separated by a sealed bulkhead to protect the flight crew in the case of a chemical leak.
Over the past 12 months, all of the COIL laser modules and 77 tonnes of flight hardware have been installed into the test plane - an old 747-200 fuselage that was rescued from an aircraft junkyard - at the 18 000 ft2 System Integration Laboratory (SIL) at Edwards Air Force Base in California. All of the ground-based laser tests will take place at the specially designed $35 m facilities. After tests inside the SIL are complete, the COIL will be dismantled and reassembled inside the ABL.
Next to the SIL is the ground pressure recovery assembly (GPRA) - a giant airtight sphere that simulates the reduced air pressure at 38 000 ft for tests that will mimic the plane's real-life operating conditions.
One thing is for sure: regardless of whether or not the ABL ever actually goes into active service, just attempting to build it will have advanced the capabilities of US high-tech firms. More than 30 companies across the US specializing in everything from optical coatings to adaptive optics and laser diodes have been paid to push back the frontiers of technology and solve unique problems.
History of the ABL November 1973: The idea of shooting down missiles with a laser is given a credibility boost when a 100 kW CO2 laser destroys a 12 ft long airborne drone during military tests. The event is the first time that a high-energy laser has shot down an aerial target.
November 1996: The US Air Force awards a $1.1 bn contract to Boeing, TRW (now Northrop Grumman) and Lockheed Martin to start developing an airborne laser that could destroy ballistic missiles.
January 2000: A Boeing 747-400 freighter purchased by the US Air Force is flown to the Boeing Modification Center in Wichita, Kansas. Two years of modifications commence.
March 2001: Raytheon conducts a "first light" test of the track illuminator laser (TILL) at its High Energy Laser Center in El Segundo, California. The Yb:YAG laser is used to locate and illuminate the nose of the target missile.
July 2001: The ABL's missile seekers, a set of six infrared search-and-track (IRST) sensors, are delivered to Boeing by Lockheed Martin.
March 2002: The first COIL module (LM-1) made by Northrop Grumman is tested, and generates 118% of its anticipated output power. A total of six such modules are required to generate the megawatt beam that the ABL will use to shoot down ballistic missiles.
July 2002: The modified 747 makes its maiden flight carrying bags of metal balls to simulate the weight of the COIL laser. Since then, 14 test flights have taken place.
December 2002: The plane is taken into a hangar at Edwards Air Force Base and grounded for engineers to install its laser modules and optics.
February 2003: Northrop Grumman finishes making the beacon illuminator laser (BILL) and delivers it to the ABL team. The BILL is a pulsed kilowatt-class Nd:YAG laser that is used to measure the atmospheric distortion between the missile and the aircraft.
2005?: First ballistic missile shoot-down is scheduled to take place over the Pacific Ocean.