Second-generation hybrid D-strut

This paper describes the efforts by Honeywell and MIT to develop a second generation hybrid D-StrutTM (patent pending). The D-Strut is a passive viscous damping and stiffening device used for structural control and isolation. The concept of using an active element synergistically with passive elements was presented in the 1994 SPIE Conference on Smart Structures and Materials paper titled `Actuator with Built-in Viscous Damping for Isolation and Structural Control.' A second generation hybrid D-Strut or active D-Strut with many applications to isolation of spacecraft hardware has been built and tested. The utilization of the device for several system applications is discussed. The primary advantage of the hybrid is that the passive elements are designed for small gravity sag and acceptable mount resonance and the active control is designed to reduce transmissibility over broad or narrow frequency ranges. The payload is then robustly isolated even in the unpowered (active stage off) state. Modeling, dynamic tests, and several single axis isolation experimental results are presented. Also, specific designs for six-axis implementations for microgravity isolation and optical payload isolation, pointing, and suppression are described.