Introduction

Louvers are active thermal-control elements that have been used in different forms on numerous spacecraft. While most commonly placed over external radiators, louvers may also be used to modulate heat transfer between internal spacecraft surfaces, or from internal surfaces directly to space through openings in the spacecraft wall.

In general, a louver in its fully open state can reject six times as much heat as it does in its fully closed state, with no power being required to operate it. Thus louvers find application where internal power dissipation varies rather widely as a result of equipment duty cycles. The most commonly used louver assembly is the bimetallic, spring-actuated, rectangular-blade (venetian-blind) type. Hydraulically activated louvers and pinwheel louvers are used less often today than in the past.

Louver reliability can be improved at the design stage by making each louver blade independently actuated by a bimetallic clock spring. Thus a single-point failure is associated with one blade, not the entire assembly. The spring can be integrated with a heater/controller to decrease the passive closed-to-open temperature range of 10 17 C to as little as 1 C.

Louver radiator assemblies (illustrated in Fig. 9.1) consist of five main elements: baseplate, blades, actuators, sensing elements, and structural elements. The baseplate is a surface of low absorptance-to-emittance ratio that covers the critical set of components whose temperature is being controlled. Blades,...