Heater

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Description

The Heater class represents a physical component that converts electrical energy into thermal energy. It extends the Power Sink class and integrates directly with the Thermal Model system to simulate controlled heating of spacecraft components.

The Heater acts as an electrical-to-thermal converter. It draws power from either:

• A connected Power Bus through its associated Power Model, or
• A standalone input using In_ControlPowerMsg.

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Module Implementation

The consumed electrical power is converted into heat that contributes to the parent object’s thermal model.

Power Conversion

Electrical power consumed by the heater is expressed as:

$$P_{\mathrm{elec}}=\min (P_{\mathrm{control}},P_{\mathrm{nominal}})$$

Where:

• $P_{\mathrm{elec}}$​ = electrical power consumed [W]
• $P_{\mathrm{control}}$​ = commanded power input (via control message) [W]
• $P_{\mathrm{nominal}}$ = nominal rated power [W]

The resulting thermal energy added to the system is:

$$P_{\mathrm{thermal}}=P_{\mathrm{elec}}$$

Coupled Thermal Dynamics

The Thermal System subsequently uses this value in the energy balance:

$$\Delta T=\frac{P_{\mathrm{net}}\times \Delta T}{m\cdot c_p}$$

where

• $P_{\mathrm{net}}$​ includes all external fluxes and $P_{\mathrm{thermal}}$​,
• $m$ = object mass [kg],
• $c_p$​ = specific heat capacity [J/kg·K].

Power Input Modes

The heater supports two operational configurations:

1. Independent Mode:
   • Operates autonomously using Power.
   • Directly sets Thermal Model Power Generation to the smaller of Power and NominalPower
2. Bus-Coupled Mode:
   • Retrieves available electrical power from a Power Bus.
   • The Thermal Model Power Generation is capped to the smaller of the nominal heater power and electrical power form the EPS to maintain realistic thermal behaviour. In either configuration, the heater power also considers the Heater Control Message.

Control Message Interaction

The heater can accept a Power Control Message (In_ControlPowerMsg) that dynamically modifies power draw during simulation.
This enables:

• Duty cycling for temperature control loops.
• Power throttling under limited bus conditions.
• Autonomous or script-driven heating events.

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Assumptions/Limitations

• Thermal coupling is instantaneous as Thermal Model updates occur in each simulation step and therefore latency is negligible (depending on time step).
• No radiative or convective losses model within the component as it will handled by its associated thermal model.
• The heater has constant efficiency, and doesn’t model potential efficiency losses.
• The component does not currently account for variable efficiency under different voltage or temperature conditions.
• The heater response is instantaneous; inrush current and switching effects are ignored.
• The heater assumes perfect coupling with its parent’s thermal node resulting in no thermal lag.
• Thermal protection mechanisms must be implemented externally (e.g., through control scripts).

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References

[1] Bergman, Theodore et al. Fundamentals of Heat and Mass Transfer. 8th ed. Wiley, 2017. Web. 29 Oct. 2025.

[2] Howell, J.R., Mengüc, M.P., Daun, K., & Siegel, R. (2020). Thermal Radiation Heat Transfer (7th ed.). CRC Press. https://doi.org/10.1201/9780429327308