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Multi-Axis Precision Seeker-Laser Pointing Gimbal

Description:

TECHNOLOGY AREA(S): Weapons

The technology within this topic is restricted under the International Traffic in Arms Regulation (ITAR), 22 CFR Parts 120-130, which controls the export and import of defense-related material and services, including export of sensitive technical data, or the Export Administration Regulation (EAR), 15 CFR Parts 730-774, which controls dual use items. Offerors must disclose any proposed use of foreign nationals (FNs), their country(ies) of origin, the type of visa or work permit possessed, and the statement of work (SOW) tasks intended for accomplishment by the FN(s) in accordance with section 5.4.c.(8) of the solicitation and within the AF Component-specific instructions. Offerors are advised foreign nationals proposed to perform on this topic may be restricted due to the technical data under US Export Control Laws. Please direct questions to the AF SBIR/STTR Contracting Officer, Ms. Gail Nyikon, gail.nyikon@us.af.mil.

OBJECTIVE: Develop a line-of-sight stabilized miniature gimbal for a nose-mount application in a small weapon/unmanned air vehicle (UAV) that can precisely point a laser rangefinder, laser jammer or designator beam via Coude’ Path across all three gimbal axes.

DESCRIPTION: The technologies associated with small weapons and small Intelligence, Surveillance, and Reconnaissance (ISR) UAVs and miniaturization of laser radars and laser target markers/designators has progressed rapidly. However, the higher powered versions of these lasers are generally too large to be packaged as a payload component in the small multi-axis gimbals on loitering weapons or small UAVs. This is especially true when considering that the stabilized payload generally contains one or more imaging systems, laser rangefinders, or other components and has severe thermal constraints.

In order to minimize aerodynamic drag and to provide the required field of regard (FOR), the use of a nose-mounted, three-axis gimbal is been determined to be the preferred configuration(roll, pitch, yaw) with a “fourth” or half axis referring to beam stabilization. In this configuration the outer gimbal axis would be aligned with the roll axis of the UAV; the middle gimbal axis would be elevation, with the inner axis being cross-elevation.

This would facilitate a required FOR relative to the air vehicle of at least +30 degree / -135 degree elevation, ± 135 azimuth (larger desired). For the particular class of vehicles, the maximum outside diameter of the gimbal would be about five and one-half inches. To enable laser marking/designation capability from a laser that is too large to fit within the payload, but able to be packaged within a 5-inch cylinder, the beam must be projected through the gimbal crossing all three axes via Coude’ Path. Packaging the laser outside the inner gimbal also facilitates a better thermal management solution which is a critical element for extended operation of these small weapon applications.

The types of lasers used in these applications typically have a center wavelength between 1 and 1.5 micrometer, beam diameters of approximately 4 millimeters, beam divergences of approximately one-half milliradian with pulsed energies in excess of 50 millijoules (mJ) (1/2 megawatt to megawatt peak). Masking of the airframe and wings must be accomplished based on gimbal angle and airspace management for eye-safety of aircrews.

A multifocal or zoom optics approach is desirable but recognized to have performance challenges. Thus, the optical elements used to steer the laser beam must be able to withstand these energy densities, and must be kept free of debris and contaminants and environmental issues (condensation) that would degrade performance. The challenges associated with providing the precise alignments to route the laser path through the gimbal, and providing the electrical power and digital signal paths up to1.5 Gb/s for each video stream across the axes in the tight package is formidable.

In conjunction with these packaging challenges, the payload must be stabilized to less than 100 µrad RMS jitter. This stabilization performance must be achieved on UAVs with operating speeds of 100 KTS (weapons with speeds up to 300 KTS), and angular motion rates in excess of 100 degrees per second in gusty environments, in addition to high frequency vibration from the motor and propeller. As in all small platforms weight, power, and cost are critical elements of consideration for endurance, cost, and platform performance (drag, center of gravity, etc.).

The objective is to incorporate an optical and sensor payload with the 1064 nm or other lasers to acquire, track, and illuminate a specific point on the target at slant ranges over 3 kilometers. The optical payload must acquire and precisely track the target and resolve under 0.5 meter aim-point on moving targets day or night.

The target tracker must hold the laser spot aim-point on a particular point of a target, once operator designated, regardless of target motion, change of orientation, and in the presence of background contrast changes and clutter. The tracker must be predictive so that target transition behind and through structures and trees or clouds will adjust anticipated re-acquire point and open search window to identify target by "memory" of characteristics for scenarios with many movers. Closed loop spot position imaging and management with in band sensors target acquisition with IR and other imaging sensors is envisioned.

System weight of 5 pounds for the larger gimbals and 2 pounds for the small gimbal are design goals, and 80 G launch loads, with 8 to 10 G peak to peak -100 Hz vibration from reciprocating engine propulsion. Air speeds for operation range from 40knots to 250knots with altitudes from sea level to greater than 20,000 feet AGL. Temperature ranges in carriage can exceed -40 degrees C to 70 degrees C.

PHASE I: Design a 3+ axis gimbal concept that can steer a high-energy pulsed or CW laser beam & stabilize it with an on-payload imaging systems to less than 100 µrad RMS jitter for small weapons and UAS environments. Show ability to achieve the stabilization & steer the payload & laser over the required FOR, within a diameter of 3 to 5 inches. Demonstrate critical components in lab/field demonstrations.

PHASE II: Carry the concept from Phase I into a form-fit-function prototype. Design, build, integrate and test the prototype with a suitable laser to demonstrate conformance to requirements. Through hardware in the loop and tower/ surrogate flight testing on SUAS or other fixed wing platforms show the pointing and tracking capability to maintain track on moving targets is sufficient to hold the laser spot on the designated point.

PHASE III DUAL USE APPLICATIONS: Transition into numerous DoD applications and use for laser point to point communications, astronomical, and police applications requiring helicopter and small aircraft precision tracking.

REFERENCES:

    • Brake, N.J., “Control System Development For Small UAV Gimbal”, Thesis, University of California Polytechnic Institute. Http://digitalcommons.calpoly.edu/cgi/viewcontent.cgi?article=1884&context=theses.

 

    • Funk, B.K. et.al., “Enabling Technologies for Small Unmanned Aerial System Engagement of Moving Urban Targets”, JOHNS HOPKINS APL TECHNICAL DIGEST, VOLUME 31, NUMBER 2 (2012) http://www.jhuapl.edu/techdigest/TD/td3102/31_02-Funk.pdf.

 

    • Ewing, L., “Advances in Laser Technology Bring Potent New Capabilities to Small UAS”, Unmanned Systems — February 2011; http://lasermotive.com/wp-content/uploads/2010/04/AUVSI-LaserMotiveUS0211.pdf.

 

  • Otlowski, Daniel, et.al.,“Critical Balancing of Gimbaled Sensor Platforms”, Whtie Paper, Space Electronics LLC, 81 Fuller Way, Berlin, CT 06037-1540. http://www.space-electronics.com/Literature/Balancing_Gimbaled_Sensor_Platforms.pdf.

KEYWORDS: gimbal, laser designator, stabilization, remote piloted vehicle, moving target tracking, shape correlation aimpoint

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