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The thermal modules simulate the temperature evolution of spacecraft components under power dissipation and radiative exchange. Both modules integrate the thermal energy balance using simple Euler integration and output a TemperatureMsgPayload message.

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Motor thermal

Computes the temperature of a reaction wheel motor accounting for mechanical power inefficiencies, friction heat generation, and radiative dissipation to the environment.Heat generation modelMechanical power from the motor:
P_mec = Ω × u_s
Power lost as heat (given mechanical efficiency η):
P_loss = P_mec × (1 − η) / η
Friction dissipation:
P_f = Ω × τ_f
Thermal dissipation to environment:
P_dissipation = (T_k − T_ambient) / R_ambient
Temperature update (Euler):
T_{k+1} = T_k + Δt × (|P_loss| + |P_f| − P_dissipation) / C_motor
Messages
MessageTypeDirectionDescription
rwStateInMsgRWConfigLogMsgPayloadInputRW mechanical torque, friction torque, and wheel speed
temperatureOutMsgTemperatureMsgPayloadOutputMotor temperature
Key parameters
ParameterDescription
currentTemperatureInitial motor temperature [°C]
ambientTemperatureAmbient temperature [°C]
efficiencyMechanical efficiency η (0–1)
ambientThermalResistanceThermal resistance to environment [°C/W]
motorHeatCapacityMotor heat capacity C_motor [J/°C]
from Basilisk.simulation import motorThermal

thermalModel = motorThermal.MotorThermal()
thermalModel.ModelTag = 'rwThermals'

thermalModel.currentTemperature = 40.0  # [Celsius] initial temperature
thermalModel.ambientTemperature = 20.0  # [Celsius]
thermalModel.efficiency = 0.7           # mechanical efficiency
thermalModel.ambientThermalResistance = 5.0  # [Celsius/W]
thermalModel.motorHeatCapacity = 50.0   # [J/Celsius]

thermalModel.rwStateInMsg.subscribeTo(rwStateEffector.rwOutMsgs[0])
sim.AddModelToTask(taskName, thermalModel)
Estimating parametersMotor heat capacity from mass and specific heat:
C_motor = m_motor × c_motor
Steel has a specific heat of approximately 466 J·kg⁻¹·°C⁻¹.Ambient thermal resistance from convection:
R_ambient = 1 / (h × A)
For free convection in air, h ≈ 100 W·m⁻²·°C⁻¹.Assumptions
  • Ambient temperature is constant
  • Ambient thermal resistance does not vary with temperature or pressure
  • Motor heat capacity is constant

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Sensor thermal

Models the temperature of a flat-plate sensor accounting for radiative emission, solar absorption, and electrical power dissipation. The sensor is assumed to have an insulated backing (no conduction to the spacecraft).Energy balanceRadiative emission (Stefan–Boltzmann law):
Q_emit = ε × σ × A × T⁴
Solar absorption:
Q_absorb = illuminationFactor × α × S × A_proj
Temperature update (Euler):
T_i = T_{i-1} + (Q_absorb + Q_in − Q_emit) / (ρ × Vol × c_p) × dt
Messages
MessageTypeDirectionDescription
sunInMsgSpicePlanetStateMsgPayloadInputSun state
stateInMsgSCStatesMsgPayloadInputSpacecraft state
sunEclipseInMsgEclipseMsgPayloadInput (optional)Eclipse illumination factor
sensorStatusInMsgDeviceStatusMsgPayloadInput (optional)Sensor power on/off
temperatureOutMsgTemperatureMsgPayloadOutputSensor temperature
Key parameters
ParameterDefaultDescription
nHat_B[0,0,0]Required. Normal vector of sensor face in body frame
sensorArea−1Required. Sensor area [m²]
sensorAbsorptivity−1Required. Solar absorptivity α
sensorEmissivity−1Required. Thermal emissivity ε
sensorMass1.0 kgRequired. Sensor mass [kg]
sensorSpecificHeat890 J/kg/KSpecific heat (aluminum default)
T_00.0 °CInitial temperature [°C]
sensorPowerDraw0.0 WElectrical power dissipated as heat [W]
from Basilisk.simulation import sensorThermal

sensorThermalModel = sensorThermal.SensorThermal()
sensorThermalModel.ModelTag = 'sensorThermal'

sensorThermalModel.nHat_B = [0, 0, 1]       # face normal in body frame
sensorThermalModel.sensorArea = 1.0          # [m^2]
sensorThermalModel.sensorAbsorptivity = 0.25 # [-]
sensorThermalModel.sensorEmissivity = 0.34   # [-]
sensorThermalModel.sensorMass = 2.0          # [kg]
sensorThermalModel.sensorSpecificHeat = 890  # [J/kg/K]
sensorThermalModel.sensorPowerDraw = 30.0    # [W]
sensorThermalModel.T_0 = 0.0                 # [Celsius]

sensorThermalModel.sunInMsg.subscribeTo(sunMsg)
sensorThermalModel.stateInMsg.subscribeTo(scObject.scStateOutMsg)
sensorThermalModel.sunEclipseInMsg.subscribeTo(eclipseObject.eclipseOutMsgs[0])

sim.AddModelToTask(taskName, sensorThermalModel)
shadowFactor is deprecated. Use illuminationFactor in all new code. Support for shadowFactor ends December 31, 2026.
Assumptions
  • Flat plate with insulated backing (no conduction to spacecraft)
  • Earth albedo not included
  • All electrical power converts to heat instantly

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