Cryogenic coolers are used in association with sensitive electronics and sensors for military, commercial or scientific space payloads. The general requirements are high reliability and power efficiency, low vibration export and ability to survive launch vibration extremes and long-term exposure to space radiation.A long standing paradigm of using exclusively space heritage derivatives of legendary "Oxford" cryocoolers featuring linear actuators, flexural bearings, contactless seals and active vibration cancellation is so far the best known practice aiming at delivering high reliability components for the critical and usually expensive space missions.The recent tendency of developing mini and micro satellites for the budget constrained missions has spurred attempts to adapt leading-edge tactical cryogenic coolers to meet the space requirements. The authors are disclosing theoretical and practical aspects of a collaborative effort on developing a space qualified cryogenic refrigerator based on the Ricor model K527 tactical cooler and Iris Technology radiation hardened, low cost cryocooler electronics.The initially targeted applications are cost-sensitive flight experiments, but should the results show promise, some long-life "traditional" cryocooler missions may well be satisfied by this approach.
The space-borne infrared instrumentation is known to be inherently susceptible to cryocooler induced vibration, the attenuation of which usually relies on active multi-tonal momentum cancellation under supervision of a dedicated controller. In this approach, the typical single-piston expander is actively counterbalanced by a motorized counterbalancer and the typical dual-piston compressor is counterbalanced by actively synchronizing the motion of the opposing moving piston assembly. The feedback signals are usually provided by external vibration sensors (force transducers or accelerometers). Although compliant with the most stringent space requirements, like 0.2N rms over the frequency range 0-1kHz, such a conservative vibration control approach can result in using outdated, oversized, overweight and overpriced cryogenic coolers for some applications. Such a "space heritage" practice becomes increasingly unacceptable for space agencies now operating within tough monetary and time constraints. The authors are advocating the purely passive approach to a vibration control relying on the combined principle of tuned dynamic absorber and low frequency vibration isolator having a potential to outperform the systems of active vibration cancellation with respect to overall system effectiveness. This approach warrants particularly strong consideration for cost-sensitive missions.
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