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MEMS and Microstructures in Aerospace Applications - Robert Osiander et al (Eds) Part 10

Tham khảo tài liệu 'mems and microstructures in aerospace applications - robert osiander et al (eds) part 10', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Microsystems in Spacecraft Guidance Navigation and Control 221 Reaction wheels use electric motors to torque against high-inertia rotors or wheels. When the motor exerts a torque on the wheel an equal and opposite reaction torque is applied to the spacecraft. Reaction wheels are typically operated in a bi-directional manner to provide control torque about a single spacecraft axis. The inherently small inertia of a typical MEMS device will make them less efficient as a reaction wheel type actuator and can only be compensated by extremely high speeds which challenges the reliability requirements for such devices. Microwheels for attitude control and energy storage have been suggested and designed by Honeywell.44 They project a performance of a momentum density of 9 N m sec kg and an energy storage of 14 W h kg for a wheel of 100 mm diameter micromachined in a stack of silicon wafers. The advantages of microwheels increase further when the device is incorporated in the satellite s structure. Likewise Draper Laboratory has studied both the adaptation of a wafer spinning mass gyro and an innovative wafer-sized momentum wheel design concept using hemispherical gas bearings as attitude control actuators for a 1 kg nanosatellite application.12 A similar system based on high-temperature superconductor HTS bearings was suggested by E. Lee. It has an energy storage capacity of about 45 W h kg and could provide slewing rates in the order of 250 sec for nanosatellites of 10 kg with 40 cm diameter.45 10.6 ADVANCED GN C APPLICATIONS FOR MEMS TECHNOLOGY It is fair to speculate that the success of future science and exploration missions will be critically dependent on the development validation and infusion of MEMS-based spacecraft GN C avionics that are not only highly integrated power efficient and minimally packaged but also flexible and versatile enough to satisfy multimission requirements. Many low-TRL GN C MEMS R D projects are underway and others are being contemplated. In .