Reduction of Cooler Induced Vibrations by Means of an Adaptive Add-On System

Kurzfassung

Future space missions' requirements on high precision structures get continuously more challenging with respect to structural accuracy. With classical structural technology coming to its limits, adaptive structure technology offers the potential to solve a variety of quasistatic and dynamic problems. With respect to the dynamic excitation of sensitive equipment, mechanical cryocooler systems, which are often used in aerospace applications to cool specific equipment to their cryogenic working temperatures, represent a typical dynamic disturbance source within a satellite. They either directly excite vibrations at the attached, cryogenic equipment or indirectly by exciting elastic interface structures leading to vibrations of one or multiple remote systems. One approach to compensate for cryocooler vibrations utilizing adaptive structure technologies is presented in the paper. Within a typical small satellite project, two infrared detectors have to be mechanically cooled by two independent miniature Stirling cryocoolers. The induced cooler vibrations critically excite the detectors, leading to a severe reduction of the quality of the scientific results. Opposite alignment of the coolers was impractical due to mission constraints. Within an ESA project, DLR developed an add-on, long life adaptive vibration compensation system that removes critical vibratory energy and works without launch locking devices. The system has been designed and qualified for general space applications on material and system level. Functional demonstration proved a vibration reduction by 53 dB, representing a significant improvement on the general acceptance specifications for residual cryocooler vibration force levels for future missions. Long life testing showed no performance degradation after more than 108 cycles. The system was designed to be easily transferred to other applications.