Measurement of Vibrational Damping at Cryogenic Temperatures for Silicon Carbide Foam and Silicon Foam Materials

摘要

The Terrestrial Planet Finder mission requires extreme dynamic stability at cryogenic temperatures in order to carry out its objectives of searching for and observing extraterrestrial planets. As a result, the ability to meet its ambitious science goals will be significantly enhanced by increasing its vibrational damping at cryogenic temperatures. Given the low inherent structural damping at cryogenic temperatures, significant reduction in vibration amplitude could be gained with only modest increases in damping on the structure. To examine the use of vibrational damping options to improve the dynamic stability of cryogenic structures, Jet Propulsion Laboratory has conducted a series of experiments to measure the damping levels of various materials at cryogenic temperatures and to search for the materials with higher cryogenic damping. This paper summarizes our experimental observations on the material damping of silicon foam and silicon carbide foam materials at cryogenic temperatures. These foam materials have been independently developed by Schafer Corporation and have properties that enable their applications in space environments with a range of temperature from 25K to 500K. These materials have been used for mirrors, and uses for foam based structures such as optical mounts and benches are currently in development. As observed from the measured damping, these two foam materials have higher damping than aluminum at cryogenic temperatures, and the damping level is relatively insensitive to temperature change from room to cryogenic temperatures. As a result, these materials may be potential candidates to achieve increased levels of cryogenic damping for the Terrestrial Planet Finder mission.