TABLE OF CONTENTS In most cases, an electronic unit is designed so that the power dissipated within it is transported as heat to the unit's mounting surface (baseplate). This heat is transferred by conduction to a section of the spacecraft structure (here called the mounting plate) and thence by a variety of methods and paths to the space sink. A smaller number of units are cooled partially (sometimes largely) by radiation. Such units are designed so that heat can be radiated from various unit surfaces, but usually not the mounting surface, to the surrounding space-vehicle enclosure or directly to space. The spacecraft's mounting plate is dealt with here, as is the predominant heat-transport method, conduction cooling from the unit's baseplate to the spacecraft's mounting plate.
The temperature rise across the mounting interface should be small; this requirement is important, because each part and device within the unit is subject to this temperature rise. Reliability and, possibly, functional performance are adversely affected by high temperature.
Most space-vehicle electronics boxes have baseplates ranging in size from 100 by 150 mm to 450 by 600 mm, with power levels sometimes exceeding 1000 W. Mounting is typically done by bolts set in a pattern along the baseplate perimeter, as shown schematically in Fig. 8.1. Flange mounting is convenient, because it makes bolts or screws accessible and enables the application of torque from above. When electronics boxes are built up from "slices" or modules (Fig. 8.2), the bolts are arranged along two opposed...
