RADAR Power Model

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Description

The RADAR Power Model extends the Sensor Power Model to couple a RADAR payload to the spacecraft electrical power system. It inherits constant-power load (CPL) quasi-static behaviour from the sensor model, and adds the DC feed a real power amplifier needs to produce the radar’s configured RF output. Capture is refused while the solved node voltage sits below the brownout floor, so an under-voltage receiver cannot report a return.

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Example Use Cases

• Power Budget Analysis: Size the EPS against the DC draw of a radar whose RF output is set independently of the bus load.
• Amplifier Efficiency Studies: Sweep DC-to-RF efficiency to bound how much bus power a given RF output demands.
• Brownout Protection: Confirm that a voltage sag shuts the radar down and holds the last measurement rather than producing a false return.

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Module Implementation

Power Consumption

The model inherits the three sensor operating states from the Sensor Power Model. Standby and shutdown draw only their configured electronics power. While operational, the bus also feeds the transmit amplifier:

$$P_{\text{DC}}=P_{\text{electronics}}+\frac{P_{\text{RF}}}{\eta }$$

where $P_{\text{electronics}}$ is the operational electronics overhead, $P_{\text{RF}}$ is the radar’s configured RF transmit power, and $\eta$ is the DC-to-RF efficiency of the power amplifier (default $0.3$). The RF contribution is present for the whole time the sensor is operational, which matches a radar that is transmitting on every capture tick.

State	DC draw
Operational	$P_{\text{electronics}}+P_{\text{RF}}/\eta$
Standby	$P_{\text{standby}}$
Shutdown	$P_{\text{shutdown}}$

Constant Power Load Model

The radar is modelled as a CPL using the same quasi-static iteration as the Sensor Power Model. Each tick, the resistance is recomputed from the previous tick’s solved voltage:

$$R=\frac{V^2}{P_{\text{DC}}}$$

where $V$ is the voltage from the previous solve (or the nominal voltage $V_n$ on the first tick). The voltage is floored at the minimum operational threshold so a transient brownout cannot collapse the resistance and cause runaway current.

Brownout Detection

The model monitors the same two thresholds as the sensor power model:

Voltage Threshold: The solved voltage must remain above a minimum fraction of the nominal operational voltage (default $V_n=12$ V):

$$|V_{\text{node}}|\ge V_n\times r_V$$

where $r_V$ is the minimum voltage ratio (default $0.8$).

Power Threshold: The absorbed electrical power must remain above a minimum fraction of the expected DC power:

$$P_{\text{absorbed}}\ge P_{\text{DC}}\times r_P$$

where $r_P$ is the minimum power ratio (default $0.13$). Setting $r_P=0$ disables this check.

Falling below either threshold forces the sensor into shutdown.

Capture Gating

Capture is only permitted when both conditions are met:

1. The sensor is in the Operational state
2. The solved voltage meets the brownout floor above

When capture is refused, the radar holds every value from its last successful measurement rather than describing a scene it could not illuminate.

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Assumptions/Limitations

• The RF contribution is applied for the whole operational interval. Pulse duty cycle is not modelled, so the DC draw is a continuous-wave / high-duty-cycle upper bound on the average power of a pulsed radar.
• DC-to-RF efficiency is a single configured scalar. Compression, temperature dependence and frequency dependence of the amplifier are not modelled.
• The model assumes a purely resistive load; reactive power components are not modelled.
• The quasi-static CPL iteration converges over multiple simulation ticks.
• Thermal effects from power dissipation are not coupled to a radar thermal model.