Thermal Control
The Thermal Control subsystem keeps spacecraft components within allowable temperature limits across all mission phases.
Core Functions
- Reject internally generated heat to space.
- Maintain components above minimum survival temps.
- Protect instruments and propulsion lines from freezing or overheating.
Key Design Drivers
| Driver | Driven By | Impact |
|---|---|---|
| Power Dissipation | Electronics, payload loads | Radiator sizing |
| External Environment | Orbit geometry, solar flux | Insulation, radiator location |
| Thermal Stability | Sensitive payloads | Material selection, design margins |
| Heater Power | Eclipse & cold survival | Battery capacity, bus voltage |
Methods
-
Passive
- Radiators: Surfaces with high IR emissivity, potentially low solar absorption.
- Multi-Layer Insulation (MLI): Minimizes heat loss or gain.
- Surface Coatings: Tailor solar absorptivity/emissivity.
-
Active
- Heaters: Maintain minimum temps, especially for propulsion lines or sensitive instruments.
- Thermostatic or software control to prevent overheating.
- Heat Pipes or Loops: Transport heat from source to radiator using phase change fluid.
Decontamination Heaters
- Warm optics or surfaces to drive off molecular contamination early in mission or after thruster firings.
Balancing the System
- Adding radiator area helps cool hot conditions but increases heater demands in cold scenarios.
- High-stability structures (e.g., for instruments) may need precise thermal conditioning to avoid alignment drift.
Testing & Verification
- Thermal Vacuum (TVAC) tests replicate on-orbit conditions.
- Cycle tests check survival extremes for components.
Cross-Links
- See Spacecraft Power System for heater power budget.
- See Spacecraft Structure and Mechanisms for conduction paths via structural members.