Test results for a high capacity cryocooler with internal thermal storage.

Ball Aerospace and Redstone Aerospace are developing a space cryocooler for cooling complex optical systems whose loads are intermittent. An example of such a system would be an Earth observation satellite that images for only a fraction of its orbit. If a cooler can store refrigeration during the lull and provide it when the system is active, the cooler can be considerably smaller than one sized to provide the full load continuously. Our cooler provides two stages of refrigeration, a stage of intermittent cooling at 35 K for a focal plane assembly and a stage of continuous cooling at 85 K for the surrounding thermal shields. The cooler provides the intermittent cooling by collecting liquid neon in a unique internal thermal storage tank and forwarding it to the focal plane when the heat loads are high. Our paper presents extensive performance data for neon at 35 K. It carries 2 W at 35 K for 30 minutes plus the 8.5 W of continuous cooling at 85 K for less than 300 W DC power. It is ready to cool again in an hour. For contrast, the same hardware was filled with nitrogen and tested at 82 K. It carries 5 W for 25 minutes plus 15 W of continuous cooling at 130 K for less than 220 W DC power. It is ready to cool again in a little over an hour. The system has many features for space system compatibility. Because the storage is located within an active control loop, the cooler can maintain the 35 K interface temperature to better than ± 0.1 K. Because it circulates liquid it can be located remotely, which solves many compatibility issues. And with careful liquid management, it can work in any orientation and in 0-g. In this paper our flight like equipment will be described, and its continuing evolution to flight will be discussed. [ABSTRACT FROM AUTHOR]