Computer Thermal Model

Description

The Computer Thermal Model couples a computer’s electrical power consumption to the spacecraft thermal network. It converts electrical power draw into heat generation, allowing the thermal system to model heat rejection from computing hardware. The model also provides optional overtemperature protection that can automatically transition the computer to safe mode or initiate shutdown when temperature limits are exceeded.

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Example Use Cases

• Thermal Analysis: Model heat dissipation from onboard computers during mission phases with varying computational loads.
• Fault Protection: Simulate autonomous thermal safing behavior when computers exceed operational temperature limits.
• Power-Thermal Coupling: Analyze the relationship between computer power states and thermal environment.

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Module Implementation

Heat Dissipation

The thermal model sources its electrical power from the parent computer’s power model. When a power bus solution is available, the model uses the actual absorbed power from the circuit solve. Otherwise, it falls back to the state-based power consumption estimate.

The heat dissipated into the thermal node is computed as:

$$P_{\text{dissipated}}=P_{\text{electrical}}\cdot {\eta }_{\text{dissipation}}$$

where $P_{\text{electrical}}$ is the electrical power consumption and ${\eta }_{\text{dissipation}}$ is the dissipation fraction. For typical computing hardware, nearly all electrical power is converted to heat, so ${\eta }_{\text{dissipation}}\approx 1.0$.

Overtemperature Protection

When thermal protection is enabled, the model monitors the node temperature against configurable thresholds. The overtemperature flag is set using hysteresis to prevent rapid state cycling:

$$\text{Overtemperature}=\{\begin{array}{ll}\text{true}& \text{if }T>T_{\text{warn}}\\ \text{false}& \text{if }T<T_{\text{warn}}-T_{\text{hyst}}\end{array}$$

where $T_{\text{warn}}$ is the overtemperature threshold (default 358.15 K / 85°C) and $T_{\text{hyst}}$ is the hysteresis band (default 10 K).

When the overtemperature condition is active and thermal protection is enabled:

• If $T\ge T_{\text{shutdown}}$, the computer is commanded to shut down.
• Otherwise, the computer is commanded to enter safe mode.

The shutdown threshold $T_{\text{shutdown}}$ defaults to 373.15 K (100°C).

Default Thermal Properties

The model initializes with properties typical of electronics assemblies:

Property	Default Value	Description
Specific Heat Capacity	900 J/(kg·K)	Aluminum/PCB composite
Emissivity	0.85	Typical electronics coating
Surface Area	0.05 m²	Internal bay mounting
Space Radiation	Disabled	Assumes internal mounting

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Assumptions/Limitations

• The model assumes all dissipated electrical power is deposited into a single thermal node.
• Thermal protection actions (safe mode, shutdown) require the parent computer to support these state transitions.
• The dissipation fraction is constant and does not vary with temperature or operating mode.
• Internal component-level thermal gradients within the computer are not modeled.
• Thermal protection is disabled by default to maintain compatibility with existing simulations.