Part 2: Cryogenic Radiators and Radiant Coolers

Chapter List

Overview

A radiant cooler is a passive thermal device used on spacecraft to cool components to cryogenic temperatures via radiative heat exchange to the space environment. The effective temperature of deep space is approximately 3 K, which makes it a very good radiative sink. Radiant coolers can be used on spacecraft instruments because those instruments operate in a high-vacuum environment that eliminates convective heat transfer. A radiant cooler is inherently a long-life device, because it requires no moving parts or stored refrigerants and consumes only the small amount of electrical power needed for maintaining stable temperatures. It can be turned off or warmed up by additional heaters or a cover over the emitting surface that can be closed.

Traditionally "radiant cooler" has referred to a radiator that operates in the temperature range of 60 to 200 K (Fig. 5.1). The lower limit results from the T ⁴ nature of radiative heat transfer. Below 60 K, most instruments cannot afford the volume or mass of the radiant cooler. In simplistic terms, environmental and other parasitic heat loads cannot be minimized enough to allow operating temperatures less than 60 K.

Figure 5.1: (Fig. 1.1, reproduced here for convenience.) Operating temperature and cooling capacity of cryogenic cooling systems.

Generally, radiant cooler designers are provided the temperature or temperature range at which a component must operate for a particular application. The most...