Chapter 13: Cryocooler Integration Considerations

Introduction

The fundamental issue of successfully using cryocoolers in a long-life space application is meeting the integration constraints of both the cryogenic application and the cryocooler itself and its drive electronics. Chapter 11 on cryocooler performance characterization covered what coolers do and how to measure their performance; in contrast, this chapter covers how one deals with the cooler attributes in a real flight application.

Cryogenic Load Estimation and Cryocooler Sizing

Fundamentally, a cryocooler is a thermal device designed to pump heat from one location to another. Thus, load estimation and cryocooler sizing are generally the first requirements to be addressed in the cryocooler integration process. Key estimation and sizing issues include

• accurate estimation of the cryogenic load for a complex assembly where parasitic loads often represent 80% of the total load

• scoping the cooling load variation over the mission's operational and thermal environmental range

• estimation of cooling load growth at mission EOL (end-of-life) resulting from degradation of heat-rejection systems, increase in radiation shield temperatures, or other causes

• estimation of cooling load growth in orbit resulting from contamination of low-emissivity cryogenic thermal control surfaces

• acquisition of cryocooler performance data for the full range of projected cooling powers, cold-tip temperatures, and heat-rejection temperatures

• estimation of cryocooler loss of capacity at EOL resulting from possible degradation

• combining the cryogenic load projections with the cooler performance projections to achieve a successful cooling...