OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): Directed Energy (DE)
OBJECTIVE: This topic will explore the technical challenges critical to significantly reducing the size, weight, and power (SWaP) of directed energy beam control systems through the use of an on-gimbal, bistatic beam director for Laser Weapon Systems (LWS) to replace today’s Common Path-Common Mode (CPCM) monostatic configurations which rely on large optical benches for image and laser management.
DESCRIPTION: CPCM configurations offer the advantage of improved jitter performance and high-fidelity knowledge of the laser aimpoint with respect to the tracking line-of-sight, but are high size, weight, and power (SWaP). Alternatively, a bistatic architecture with modern track camera frame rates and image processing techniques should now be able to achieve comparable accuracy, providing a beam control solution for on-gimbal, phased-array laser sources while significantly reducing the SWaP of the beam control system.
Performers will develop methodologies and tracking algorithms required to perform LWS engagements using a bistatic architecture, where the tracking and imaging path is separate from the outgoing laser path. Performers also will develop jitter mitigation techniques, aimpoint maintenance via electronic beam steering methods, and atmospheric compensation strategies. All traditional functions of a beam control and tracking system are required. These functions include target acquisition, closed loop track, aimpoint selection and maintenance, and atmospheric compensation.
Limitations to an all on-gimbal architecture will be identified by the performer, to include performance limitations as a function of camera aperture size, total system size, and laser power.
Expected deliverables include the following:
- Descriptions of possible physical implementations of on-gimbal beam control systems
- Performance predictions for the performer’s chosen physical architecture
- Including peak and average irradiance for a variety of slant ranges and elevation angles
- Identification of viable algorithms for jitter mitigation, aimpoint maintenance, and atmospheric compensation
- Analysis of the ability to scale the performer’s approach, with respect to effective range and target type, for three laser powers: 12 kW, 50 kW, 150 kW
- Laboratory demonstration of the performer’s on-gimbal LWS design utilizing a performer-chosen low-power phased array
Expected key metrics:
- SWaP comparison between on-gimbal and CPCM LWS of similar laser power and aperture size
- Minimum achievable jitter and aimpoint error
- Atmospheric compensation capability; Strehl, or power-in-the-bucket at the target, as a function of turbulence strength and slant range
PHASE I: During Phase I, the performers will conceptualize a low-power, low-SWaP phased-array Laser Weapon System (LWS) where all hardware and functionalities are located on-gimbal, with the exception of subsystems for power generation/storage and thermal management. The LWS must contain all capabilities of a traditional LWS: acquisition, tracking, pointing (ATP), laser generation, adaptive optics (AO), and system/mission controls. It is assumed that adaptive optics and fine angle beam steering will be performed via the piston phase control capability of the phased array.
To perform the ATP and AO functions without using CPCM, contractors will need to identify viable algorithms and methodologies to establish laser aimpoint relative to tracker line-of-sight, perform aimpoint control, measure instantaneous turbulence distortion, and apply correct wavefront conjugations.
Performers will then design a low-power, on-gimbal, LWS meeting the above requirements. A low-power optical phased array of the performers’ choice, to include fiber-based laser technology, may be used in the LWS design. For this demonstration, the laser source (seed, amplifiers, phase modulators) may be off-gimbal, but the laser array head, or emitting apertures, must be on-gimbal. System size (number of sub-apertures, number of track cameras, etc.) is to be defined by the performer.
Required Phase I deliverables include the following:
- Month 3: A Systems Requirements Review (SRR) for the low-power, on-gimbal LWS, to include a presentation at PI meeting of the requirements.
- Month 5: Report summarizing modelling and simulation software capabilities. Presentation at PI meeting on capabilities.
- Month 9: A Preliminary Design for the low-power, on-gimbal LWS, to include a list of any long lead purchases required, to include a presentation at PI meeting of the design.
Month 10: Phase I final report summarizing Phase I work, to include identification of viable algorithms for beam control, aimpoint maintenance, wavefront measurement/correction, and phase control. Presentation at final PI meeting of accomplishments.
PHASE II: During Phase II, the performers will build the low-power, on-gimbal LWS designed in Phase I, and demonstrate the system under controlled scenarios in a laboratory setting. Contractors will be required to predict the performance of the as-built system, then compare these results to the laboratory tests. Contractors will also be responsible for defining the laboratory test objectives and success criteria; however, the testing must demonstrate all functionalities described above in the Description.
Performers will also conduct modeling and simulation of three on-gimbal LWS variants utilizing a government reference laser source with output powers of 12 kW, 50 kW and 150 kW. Volumes (length x width x height), and masses of the three laser sources, as well as piston phase modulation rates will be based on state-of-the-art laser sources and provided as Government Furnished Information (GFI). System optimization of each variant will be based on achievable Strehl ratios as a function of slant range and engagement angle. Other parameters of interest to the government are achievable slew rates, residual jitter estimates, and system weight and volume reductions when compared to traditional CPCM systems.
Phase II deliverables include the following:
- Month 4: A Critical Design for the low-power, on-gimbal LWS, to include a presentation at PI meeting of the design.
- Month 12: Report containing trade study results for the three laser powers listed above. Presentation at PI meeting of results.
- Month 22: Report containing detailed test and performance results based on laboratory tests. Presentation at PI meeting of results.
- Month 24: Design documents for the low-power, on-gimbal LWS, to include a list of all hardware purchased under contract, as well as a detailed explanation of the algorithms and methods used for ATP and AO, and source code for ATP and AO functions. Phase II Final Report to include a summary of tasks completed during Phase 2, a list of identified changes required to scale the LWS design to higher powers and channel counts, and any recommended system improvements. Presentation at final PI meeting of accomplishments.
PHASE III DUAL USE APPLICATIONS: One potential application of BEAM technology is to marry the laser arrays under development in the DARPA Modular Efficient Laser Technology program (https://www.darpa.mil/program/modular-efficient-laser-technology) with the beam control architectures of BEAM. A high-power, on-gimbal, system could be used on a large variety of ground vehicles for C-UAS and potentially even for counter-mortar missions. Such a low-SWaP system could be used by Special Forces for operational preparation of the battlespace. Finally, airborne applications on smaller UAS might become available depending on the performance results of Phase II.
1. Kenneth W. Billman, Bruce A. Horwitz, Paul L. Shattuck, "Airborne laser system common path/common mode design approach," Proc. SPIE 3706, Airborne Laser Advanced Technology II, (3 August 1999); doi: 10.1117/12.356958
2. Vorontsov, M., Filmonov, G., Ovchinnikov, V., Polnau, E., Lachinova, S., Wyrauch, T., Mangano, J., “Comparative efficiency analysis of fiber-array and conventional beam director systems in volume turbulence,” Applied Optics, Vol. 55, No. 15; http://dx.doi.org/10.1364/AO.55.004170
3. Ahmed Hassebo, Balbina Salas, Yasser Y. Hassebo, "Monostatic and bistatic lidar systems: simulation to improve SNR and attainable range in daytime operations," Proc. SPIE 10094, Frontiers in Ultrafast Optics: Biomedical, Scientific, and Industrial Applications XVII, 1009421 (17 February 2017); doi: 10.1117/12.2253567
KEYWORDS: Beam control systems, Directed energy, Bistatic beam director, Phased-array laser system, On-gimbal laser system, Adaptive Optics (AO), Atmospheric compensation, Acquisition Tracking and Pointing (ATP)