Low Temperature Characterization of Mechanical Isolators for Cryocoolers

For spacecraft applications requiring active refrigeration, exported vibrations from a cryocooler can be a concern. One approach to minimizing the vibrations transmitted from cryocoolers to the spacecraft is to mount them on mechanical isolators. Many commercial off-theshelf (COTS) mechanical isolators exist and have been characterized at room temperature for ground applications. However, the space environment presents challenges that complicate the selection process. Mechanical isolators in space must be made of materials that can withstand harsh radiation environments. Future instruments, such as the Mapping Imaging Spectrometer for Europa (MISE) on the Europa Clipper mission, are considering operating cryocoolers with low heat rejection temperatures and mounting them on mechanical isolators. However, the performance of many simple, traditional mechanical isolators at low temperatures is unknown. This paper describes the testing and results of various mechanical isolators able to withstand harsh radiation between 200 K and 300 K. The transmissibility of wire rope type isolators showed very little temperature dependence up to ~500 Hz. On the other hand, the transmissibility of silicone gel was strongly dependent on temperature as the material had an abrupt change in stiffness near its solid-solid phase change. Custom titanium flexures showed the most promise with a maximum transmissibility of 0.04 above 500 Hz and no expected temperature dependence.