Fuel Pump

Description

The Fuel Pump drives fuel flow between connected fuel sources in a spacecraft propulsion system. It extends the motor electrical model to enable realistic power consumption when connected to the Electrical Power System (EPS). The pump’s flow rate scales with motor speed, rated capacity, and efficiency, allowing simulation of pump performance under varying electrical and mechanical conditions.

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Example Use Cases

• Propellant Transfer: Pump fuel between tanks during orbit maneuvers or station-keeping operations.
• Pressurized Feed Systems: Provide positive displacement flow to thrusters requiring regulated propellant delivery.
• Cross-Spacecraft Refueling: Drive propellant through interconnects during docked transfer operations.
• Degraded Operations: Model reduced flow when electrical power is limited or pump efficiency degrades.

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Module Implementation

Flow Rate Calculation

The pump flow rate depends on motor speed, rated capacity, and efficiency. The effective flow rate is computed as:

$$\dot{m}=\frac{\omega }{{\omega }_{\text{max}}}\cdot {\dot{m}}_{\text{max}}\cdot \eta$$

where $\omega$ is the effective motor speed, ${\omega }_{\text{max}}$ is the maximum motor speed, ${\dot{m}}_{\text{max}}$ is the maximum flow rate, and $\eta$ is the pump efficiency.

When connected to a power bus, the pump uses the actual motor speed from the EPS circuit solve. The motor must draw significant armature current for flow to occur—open switches result in zero flow. When not connected to a power bus, the pump operates in standalone mode using the commanded speed input directly.

Speed Ratio

The speed ratio determines what fraction of rated flow the pump delivers:

$$r=\min \left(1,\frac{|\omega |}{{\omega }_{\text{ref}}}\right)$$

where ${\omega }_{\text{ref}}$ is the maximum speed when defined (${\omega }_{\text{max}}\ge 0$), otherwise the speed input command. This allows both fixed-speed and variable-speed pump configurations.

Network Connections

The pump exposes upstream and downstream ports for connecting to the fuel network:

Port	Direction	Valid Connections
Upstream	Intake	Fuel Source, Valve (Outlet), Interconnect
Downstream	Discharge	Fuel Source, Valve (Inlet), Consumer, Interconnect

Operating Modes

The pump supports several operating configurations:

• Enabled: Flow scales with motor speed as described above.
• Disabled: No flow unless pass-through mode is enabled.
• Pass-through: When enabled, a disabled pump allows passive flow from pressure differential.
• Bidirectional: Allows flow in both directions based on system conditions.

Scheduled Flow Profiles

An optional CSV file can define a time-varying maximum flow rate profile. When loaded, the scheduled value overrides the constant maximum flow rate parameter at each simulation time.

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Assumptions/Limitations

• The pump model assumes incompressible flow; cavitation and compressibility effects are not modeled.
• Efficiency is constant and does not vary with speed, flow rate, or fluid properties.
• When connected to EPS, zero armature current results in zero flow regardless of other conditions.
• The pump does not model priming, startup transients, or thermal effects on performance.
• Bidirectional mode must be explicitly enabled; default operation is unidirectional from upstream to downstream.
• Cumulative transferred mass is tracked from creation and can be reset manually for training scenarios.