Space Based Laser [SBL]
Megawatt class power levels were first achieved by the Mid-Infrared Advanced Chemical Laser (MIRACL) originally sponsored by the Navy, later by DARPA, and then by BMDO. Because the design was intended for sea level operation, the MIRACL laser does not achieve the optimum efficiency necessary for space-based operation. DARPA launched the Alpha laser program, with the goal of developing a megawatt level SBL that was scaleable to more powerful weapon levels and optimized for space operation. In this design, stacked cylindrical rings of nozzles are used for reactant mixing. The gain generation assembly achieves higher power by simply stacking more rings. SDIO'S primary objective was to develop a chemical laser device that could produce a high-power beam that was scalable to the power needed for laser weapon systems. SDIO planned to complete this ongoing program in 4 years for $162 million. During a series of tests from 1990 to 1992, the laser produced a beam with the megawatt class power and beam quality specified by the 1984 plan. In 1991, the Alpha laser demonstrated megawatt class power levels similar to MIRACL, but in a low pressure, space operation environment. Alpha demonstrates that multi-megawatt, space-compatible lasers can be built and operated. The Alpha design is space compatible and directly scalable to weapon-level power requirements. SD10 spent about $279 million developing and demonstrating the performance of the Alpha beam generator and building the test facility at TRW's San Juan Capistrano, California, test site.
Large Advanced Mirror Program (LAMP)
To demonstrate the ability to fabricate the large mirror required by an SBL, the Large Advanced Mirror Program (LAMP) built a lightweight, segmented 4 m diameter mirror on which testing was completed in 1989. Tests verified that the surface optical figure and quality desired were achieved, and that the mirror was controlled to the required tolerances by adaptive optics adjustments. This mirror consists of a 17 mm thick facesheet bonded to fine figure actuators that are mounted on a graphite epoxy supported reaction structure. To this day, this is the largest mirror completed for use in space. This LAMP segmented design is applicable to 10 m class mirrors, and the Large Optical Segment (LOS) program has since produced a mirror segment sized for an 11 m mirror. The large dimension of this LOS mirror segment approximates the diameter of the LAMP mirror.
The program was completed in 6 years, 2 years behind schedule, for about $28 million. The resulting 4-meter diameter, deformable mirror consists of seven separate segments attached to a common bulkhead; the shape of the mirror can be altered by changing the position of the individual segments. barge space-compatible mirrors are needed to expand and project laser beams on targets. This program demonstrated the technology needed to construct mirrors of M-meter scale, which significantly exceeds the size needed for laser weapons in GPALS missions.
Beam Control- Large Optics Demonstration Experiment (LODE) and ALI
Beam control involves sensing and controlling aberrations in the laser beam that are caused by the laser device and the high-power optical elements; establishing the direction of the beam; focusing the beam on the target; and moving the beam from target to target. The beam control system samples the outgoing laser beam, analyzes the sample to detect aberrations in the beam, and communicates corrections to the deformable mirrors and the fast steering mirrors that operate to control the shape and direction of the laser beam. SDIO planned to complete the beam control system in 4 years for about $59 million. Testing was accomplished in 3 years at a cost of $32 million. To reduce costs, the beam control experiments were conducted with a 60 centimeter diameter, segmented, deformable, primary mirror instead of with the 4-meter diameter mirror. SDIO said the resulting beam control system is scalable to a beam control system utilizing the 4-meter mirror. Testing of the 4-meter mirror and the beam control system at high power will now take place during the ground integration test with the Alpha laser. The ability to control a beam was demonstrated at low power under the Large Optics Demonstration Experiment (LODE) in 1987.
The high power beam control technology was integrated with the Alpha laser and the LAMP mirror in a high power ground demonstration of the entire high energy laser weapon element. This is known as the Alpha-LAMP Integration (ALI) program. The Alpha LAMP Integration (ALI) experiment demonstrated integrated open loop and closed loop fast steering mirror (FSM) and deformable mirror (DM) system operation in 1997. The high power components of an SBL payload were integrated at the Capistrano Test Site (CTS) and successfully achieved project objectives, thereby validating the SBL beam generation and control concepts. The ALI experiment successfully achieved all of its objectives. The integration of the Alpha high power laser with a LODE-derived beam control system and a beam expanded using the LAMP 4 meter mirror. The use of uncooled optics in a high power beam train; and 3) the high power operation of the integrated hardware (LAMP with Holographic Optical Elements (HOEs), Outgoing Wavefront Sensor (OWS) behind the secondary mirror, and FSM and DM control optics). On 20 Feb 1997, the first integrated high power test of SBL technologies was successfully conducted at CTS. The second high power test was completed on 16 Jul 1997, with the OWS controlling the steering of the high power beam through the 4-meter LAMP mirror. The third, and final, high power test of the ALI experiment was completed on 22 October 1997, with the OWS controlling the steering and wavefront error of the high power beam through the 4 meter LAMP mirror. The water-cooled deformable mirror was replaced by an uncooled deformable mirror, and it performed successfully during a high power test on 9 June 1998.
Acquisition, Tracking, Pointing (ATP)
The ATP technologies required (sensors, optics, processors, etc.) have been validated through a series of component and integrated
testing programs over the last decade. In 1985, the Talon Gold brassboard operated sub-scale versions of all the elements needed in the operational ATP system including separate pointing and tracking apertures, an illuminator, an inertial reference gyro system, fire control mode logic, sensors and trackers. Talon Gold achieved performance levels equivalent to that needed for the SBL. In 1991, the space-borne Relay Mirror Experiment (RME), relayed a low-power laser beam from a ground site to low-earth orbit and back down to a scoring target board at another location with greater pointing accuracy and beam stability than needed by SBL. The technology to point and control the large space structures of the SBL was validated in 1993 by the Rapid Retargeting and Precision Pointing (R2P2) program that used a hardware test bed to develop and test the large and small angle spacecraft slewing control laws and algorithms. The Space Pointing Integrated Controls Experiment (SPICE) demonstrated in 1995 near weapon scale disturbance isolation of 60-80 db and a pointing jitter reduction of 75:1.
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