The Thermal Control Subsystem

For the majority of spacecraft in orbit, the thermal control subsystem represents only a small percentage of the spacecraft mass, yet remarkably it generally dominates the overall appearance of a spacecraft. It is what you see! To illustrate the point, Figure 9.15 shows Earth-observation spacecraft SPOT 5 prior to launch (see Table 7.4 in Chapter 4). It looks a bit like a chocolate box wrapped with gold and silver foil, and this "foil" is the multilayered insulation blanket that I have mentioned briefly in previous chapters. There are also other features visible, such as mirror-like surfaces and white-painted areas and antennas, and these are all characteristic of a typical thermal control subsystem design. The same features can be seen in many of the pictures of spacecraft in earlier chapters, with the thermal design dominating their appearance. In this section, we have a look at why this is.

As we recall from Table 7.1, the main job of the thermal control subsystem is to provide an appropriate thermal environment onboard, to ensure reliable operation of payload and subsystem elements.

Figure 9.15: The SPOT 5 Earth-observation satellite. The thermal control subsystem design governs the way the spacecraft looks. (Image copyright © CNES/Patrick Dumas.)
Table 9.3: Approximate temperature range for reliable operation of equipment

Component

Approximate temperature

range (C)

Batteries

0 to 25

Propellant (e.g., Hydrazine)

10 to 50

Electronic equipment (e.g., computer processors)

-5 to 40

Mechanical bearings (e.g., reaction wheels)

0 to 45

0 0

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