Design and Verification of Stirling Cooler Interfaces Suitable for Long-Lifetime, Space-Borne Sensor Systems

Abstract

Interfacing a linear Stirling cooler to a spaccborne sensor system poses some unique challenges with regard to achieving high thermal efficiency within the mechanical and integration constraints of the cooler and sensor system. Interface component development and verification activities performed during the X-ray Spectrometer Cryogenic Subsystem (XRS/CSS) Program established a reliable and high-thermal efficiency interface design. In any large, spaceborne sensor system cooled by a cryocooler that provides a point cooling source, the factors limiting achievable interface efficiency stem from the need for mechanical flexibility and the inherent spreading resistances in the interface. Therefore, the overall interface design approach and components developed for the XRS/CSS are applicable to many other sensor cooling applications. The XRS/CSS design uses split, linear, Stirling-cycle coolers (primary and back-up) to remove heat from the outer vapor-cooled shield of the superfluid helium dewar and greatly reduce the helium loss rate. To maximize the benefit of the cooler, the interface between the coldtip and dewar is designed to provide high thermal conductance with minimal parasitic heating. A key element of the interface is a flexible/thermal link having extremely high efficiency. The thermal impedance of this link is small compared to that inherent in the overall interface, and its use can thus provide nearly the same overall interface efficiency regardless of the type of cooler used. To meet requirements for control of vibration to the sensor, the compressor is mounted with mechanical isolation. Prototype verification was performed to prove the designs of the coldtip interface and compressor mount. In this paper we discuss the thermal/mechanical interface requirements, performance drivers, designs and prototype verification activities.