TABLE OF CONTENTS The thermal control systems of most military spacecraft operating in the year 2001 were designed to meet the thermal test margins defined in MIL-STD-1540A or B. These requirements called for a 25% heat load margin for active thermal control systems. For passive systems, the standard required an 11 C temperature margin for correlated models and suggested 17 C during the design phase, before models have been correlated, unless power or weight penalties are excessive. "Correlation" refers to adjusting the thermal math model such that it agrees with temperature measurements made during a thermal balance test of qualification or flight hardware in a thermal vacuum chamber. Table 19.1 gives examples of what constitute passive and active systems.
| Passive | Active |
|---|---|
| Constant-conductance or diode heat pipes | Variable-conductance heat pipes |
| Hard-wired heaters (either fixed-resistance or variable-resistance, such as auto-trace or positive-temperature coefficient thermistors) | Heat pumps and refrigerators |
| Thermal storage devices (phase-change or sensible heat) | Heaters with commandable, mechanical, or electronic controllers |
| Thermal insulation (MLI, foams, or discrete shields) | Capillary pumped loops |
| Radiators (fixed, articulated, or deployable) with louvers | Pumped fluid loops |
| Surface finishes (coatings, paints, treatments, second surface mirrors) | Thermoelectric coolers |
The thermal margins specified by MIL-STD-1540 were based on statistical analyses of test and flight data for several spacecraft built by three different contractors. This statistical analysis was conducted by Stark [19.1] at The...
