Tech Briefs

Engineers evaluate smaller, lighter, less-expensive guidance components.

AFRL and Boeing engineers conducted successful flight tests of microelectromechanical systems (MEMS) inertial measurement units (IMU) on the Joint Direct Attack Munition (JDAM). They collected flight data and validated the MEMS IMU technology's capability to provide stable navigation performance and accurate weapon guidance, both with and without Global Positioning System (GPS) updates. Researchers will use this flight data to further refine MEMS IMU technology to enhance future capabilities of air-launched munitions.

AFRL and other Department of Defense organizations have explored the use of IMUs for munitions navigation and guidance for many years. MEMS are miniature, electrically driven mechanical structures. Engineers employ standard integrated circuit fabrication techniques to micromachine silicon-based MEMS, enabling mass production of these precision devices. MEMS IMUs can overcome limitations associated with the size, weight, and cost of current spinning mass, fiber-optic, and ring laser gyro IMUs. The performance of MEMS IMU technology is nearing the tactical grade requirements of many current and future miniature munition concepts.

ImageThe increased use and tremendous success of precision-guided munitions (PGM), such as those used by the JDAM during Operation IRAQI FREEDOM, highlight the need for lower-cost, more readily producible PGM components. Boeing currently produces the JDAM GBU-31, a guidance tailkit that, when added to existing "dumb" unitary bombs, provides an all-weather autonomous bombing capability that is highly accurate. The GBU-31 program includes planned product improvements and technology insertions throughout the JDAM delivery schedule. One potential improvement involves the replacement of Honeywell's HG1700 ring laser gyro IMU with a lower-cost, MEMS-based IMU. Honeywell is thus developing a production capacity for such an IMU under AFRL's Affordable MEMS-Based IMUs for Missiles and Munitions program. The focus of Honeywell's effort is to provide—in production quantities—a MEMS-based IMU with performance equitable to that of the state-of-the-art HG1700, but with smaller size, lighter weight, and lower power requirements and costs.

Honeywell's HG1900 device represents the next step in the ongoing evolution of MEMS-based IMU technology (see Figure 1). The unit's size and performance are consistent with tactical missile and smart munitions requirements. Consequently, AFRL and Boeing established a Cooperative Research and Development Agreement for integrating Honeywell's HG1900 Block-B MEMS IMU into JDAM tailkits and conducting a captive carry and guided weapon release flight test. AFRL provided MEMS IMUs to Boeing for integration into JDAM tailkits. AFRL and Boeing performed the planning and preparation for the JDAM flight tests, which were executed by the 46th Test Wing. An F-16 aircraft released two GBU-31 weapons over the Eglin Air Force Base, Florida, test range in early 2005 (see Figure 2).

The flight tests included navigation both with and without GPS updates to the inertial data from the IMU. Test data indicated that guidance performance was stable and much improved compared to previous MEMS IMU versions. Test engineers collected a substantial volume of data to facilitate extensive analysis of IMU characteristics and validation of performance models. Boeing and Honeywell plan to use the flight performance characteristics to devise improvements to future HG1900 versions and meet new requirements of the JDAM and other munitions as they arise.

The MEMS-based HG1900 is also suitable for a variety of commercial guidance and navigation systems. Therefore, an important AFRL goal is to develop a MEMS process that facilitates wider adoption and implementation of the technology through technology transition into the commercial arena and additional military applications.

Mr. Tim Jones, of the Air Force Research Laboratory's Munitions Directorate, and Mr. Lou Concha, of the Air Force Research Laboratory's Materials and Manufacturing Directorate, wrote this article. For more information, contact TECH CONNECT at (800) 203-6451 or place a request at http://www.afrl.af.mil/techconn/index.htm. Reference document MN-H-05-11.