SEATTLE, June 2 -- Engineers have delivered two prototypes of steering mirrors designed for Lockheed Martin's Airborne Laser (ABL) theater-ballistic-missile defense system. The mirrors are part of Lockheed Martin's overall ABL Beam Control / Fire Control (BC/FC) system that is designed to detect, track and destroy hostile missiles. Engineers for the company can now begin to integrate the steering mirrors with beam-control software.   So far, three kinds of steering mirrors have been developed for the ABL aircraft: the 31-cm slow mirror, the 31-cm fast mirror and the 13-cm mirror. The slow mirror, a lower-bandwidth mirror, provides high-energy laser alignment while the plane is in flight. Its job is to make sure the mega-watt-class laser beam keeps its alignment within the structure of the airplane. The fast mirror, a high-bandwidth design, has to keep the laser on-target while compensating for high-frequency tilt errors caused by turbulence. The 13-centimeter mirror is designed to meet both low- and high-bandwidth applications in the illuminator laser path.   Lockheed Martin's Space Systems BC/FC team, in conjunction with the engineers at Boeing's Laser & Electro Optical Systems organization in West Hills, Calif., were responsible for the development and delivery of the mirrors.