Comparison of mechanical cryocoolers versus stored cryogens for balloon-borne observations

Abstract This study examines the relative mass required in the use of stored cryogens and mechanical cryocoolers, for cooling of detectors and optics in stratospheric-balloon—borne observatories. Lofted mass per unit heat removed from a cryogenic instrument is calculated, as a function of temperature, for three cooling approaches: (a) the use of stored cryogens; (b) use of an acoustic-Stirling (“pulse tube”) mechanical cryocooler powered by electric storage batteries; and (c) the same cryocooler with solar-electric energy collection partially or fully replacing storage batteries. For the latter case, the mission duration at which the systems masses are equal is also found. Principal conclusions are (1) stored cryogens can provide cooling for lower mass than storage-battery—operated cryocoolers over most of the temperature range considered, but the difference is not large; (2) solar-conversion systems can be the lower-mass option at higher temperature, but the mission duration for equal mass increases rapidly below ∼30 K.