Paul Buchele

Miniature vibration isolation system for space applications

In recent years, there has been a significant interest in, and move towards using highly sensitive, precision payloads on space vehicles. In order to perform tasks such as communicating at extremely high data rates between satellites using laser cross-links, or searching for new planets in distant solar systems using sparse aperture optical elements, a satellite bus and its payload must remain relatively motionless. The ability to hold a precision payload steady is complicated by disturbances from reaction wheels, control moment gyroscopes, solar array drives, stepper motors, and other devices. Because every satellite is essentially unique in its construction, isolating or damping unwanted vibrations usually requires a robust system over a wide bandwidth. The disadvantage of these systems is that they typically are not retrofittable and not tunable to changes in payload size or inertias. Previous work, funded by AFRL, DARPA, BMDO and others, developed technology building blocks that provide new methods to control vibrations of spacecraft. The technology of smart materials enables an unprecedented level of integration of sensors, actuators, and structures; this integration provides the opportunity for new structural designs that can adaptively influence their surrounding environment. To date, several demonstrations have been conducted to mature these technologies. Making use of recent advances in smart materials, microelectronics, Micro-Electro Mechanical Systems (MEMS) sensors, and Multi-Functional Structures (MFS), the Air Force Research Laboratory along with its partner DARPA, have initiated an aggressive program to develop a Miniature Vibration Isolation System (MVIS) (patent pending) for space applications. The MVIS program is a systems-level demonstration of the application of advanced smart materials and structures technology that will enable programmable and retrofittable vibration control of spacecraft precision payloads. The current effort has been awarded to Honeywell Space Systems Operation. AFRL is providing in-house research and testing in support of the program as well. The MVIS program will culminate in a flight demonstration that shows the benefits of applying smart materials for vibration isolation in space and precision payload control.

Heavy load vibration isolation system for airborne payloads

A high-performance vibration isolation system has been developed to isolate large-sensitive payloads from aircraft disturbances. The isolation system senses and adjusts for low frequency aircraft maneuvers and changes in the aircrafts flight angle of attack. Additionally, the isolation system passively filters higher frequency disturbances from aircraft to payload. Six pneumatic struts configured as a hexapod or Stewart Platform make up the primary portion of the isolation system and accomplish vibration isolation and payload support. Each isolator strut is a unique Patented design that takes advantage of gas (the ultimate smart material), because it has a capacity for large energy storage and it possesses a near linear viscosity over a broad temperature range. Any gas that exhibits a somewhat perfect-gas characteristic can be used inside the strut with similar performance results. For our application, gaseous nitrogen (GN2) was used. The pneumatic strut has shown an ideal isolator roll-off quality that is tunable for a variety of payloads and linear over a large dynamic range. Tunability stems from a dual chamber design that allows air-spring-rate changes while maintaining constant support of the load. The strut performance trait combined with the deterministic nature of the hexapod affords predictability and controllability. The system design enables a soft floating support of large payloads with accurate knowledge of their orientation with respect to the aircraft. Another distinctive feature of the isolation system design is a servo-controlled leveling system that senses a set point from an integrally mounted LVDT and fills or exhausts gas, as necessary, maintaining strut position during the rigors of flight. A combination of Commercial Off The Shelf (COTS) and control cards with custom plumbing provides the leveling function. All tolled, the isolation system has functioned flawlessly in service, and has raised the bar for vibration isolator performance. In this paper the isolation system design will be detailed, and its performance measurements will be presented.