Missile-defence aircraft is expected to continue airworthiness trials halted after discovery of sensor wiring fault

The US Air Force's prototype Boeing 747-400-based YAL-1A Airborne Laser (ABL) aircraft was expected to resume flight tests at Edwards AFB, California by 10 December after the first sortie was cut short by a faulty pressurisation warning. The 3 December flight was the first time the aircraft had flown with its integrated battle management and beam-control/fire-control systems installed.

Early in the flight, sensors monitoring the pressure differential across the airtight internal bulkhead between the forward crew section and aft laser section indicated a failure and "flashed red", says the USAF.

After a precautionary landing, the fault was discovered to be a wiring problem in the sensor, rather than a problem with the bulkhead, which is designed to operate with a permanent pressure gradient between the forward and aft sections to prevent potentially dangerous chemical laser gases leaking into the crew compartments.

The aircraft will carry large quantities of chemicals, principally iodine, which will fuel the megawatt-class high-energy chemical oxygen iodine laser (COIL). Initial flight tests will not include the COIL, which will be installed late next year.

After a baseline series of airworthiness tests, the evaluation will focus on the passive beam control system, which "will enable us to measure all the optical systems, and to run the turret [which steers the laser beam] to see if it works properly", says the USAF. A follow-on phase will see installation of two illumination lasers and a surrogate high-energy laser that will "go where the COIL is planned to go".

Ground tests of a full-up six-module COIL began at Edwards AFB on 10 November with a "first light" event.

In early 2005 the surrogate laser will be tested against ground and airborne targets, including the Scaled Composites-built Proteus, which will fly with a target board attached to its fuselage. The evaluations will assess the coherency of the laser beam and the ability of the beam control system to track while compensating for atmospheric disturbances.

Although the ABL is ultimately designed to detect, track and destroy ballistic missiles in the boost phase of flight with the COIL laser, the aircraft is also capable of passing on information about the launch site, target track and predicted impact to other elements of the US global ballistic missile defence system.


Source: Flight International