Fuel Interconnect

Description

The Fuel Interconnect enables fuel transfer between paired connection points, supporting both internal spacecraft routing and cross-spacecraft propellant transfer during docked operations. Each interconnect bonds to a local fuel component and links to a partner interconnect to form a transfer bridge. When the link is not established or flow cannot pass through (e.g., undocked spacecraft), the interconnect can vent fuel to space, producing thrust in the process.

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Example Use Cases

• On-Orbit Refueling: Transfer propellant from a servicer spacecraft to a client during docked operations.
• Internal Fuel Routing: Bridge fuel between isolated sections of a spacecraft’s propulsion system.
• Emergency Venting: Safely vent propellant overboard when transfer paths are blocked, with predictable thrust effects.

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Module Implementation

Local Bonding

Each interconnect bonds to exactly one local fuel component via its Local port. Supported connections include:

Local Component	Connection
Fuel Source	Local → Tank
Fuel Consumer	Local → Intake
Fuel Valve	Local → Inlet
Fuel Pump	Local → Upstream

Establishing a new local bond automatically clears any existing bond.

Linked Transfer

Two interconnects form a transfer bridge by linking to each other. The link is bidirectional—linking A to B also links B to A. Once linked, fuel can flow between the local components bonded to each interconnect.

For same-spacecraft links, fuel flows whenever the interconnects are linked. For cross-spacecraft links, additional conditions apply:

$$\text{Flow allowed}=\text{IsLinked}\wedge \text{IsDocked}\wedge \text{ValvesOpen}$$

where docking state is determined by the root spacecraft connection status, and valve state is checked if either interconnect has a bonded valve.

Vent-to-Space

When an interconnect has no linked partner or when flow through the link is blocked, fuel can vent to space if enabled. The venting produces thrust based on the configured specific impulse:

$$F=I_{\text{sp}}\cdot \dot{m}\cdot g_0$$

where $I_{\text{sp}}$ is the specific impulse, $\dot{m}$ is the effective flow rate, and $g_0=9.80665$ m/s² is standard gravity. The thrust acts opposite to the exhaust direction along the interconnect’s local axis.

Pressure Differential

An optional mode requires positive pressure differential for transfer between linked interconnects. When enabled, the supply tank’s ullage pressure must exceed the receiver’s ullage pressure for flow to occur. Both tanks must have thermal models attached for pressure comparison.

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Assumptions/Limitations

• Each interconnect can bond to only one local component at a time.
• Cross-spacecraft transfer requires the interconnects to be linked and the root spacecraft to be physically docked.
• Vent thrust assumes cold-gas expansion; no combustion or heating effects are modeled.
• The interconnect does not model flow restrictions, line pressure drops, or quick-disconnect dynamics.
• Bidirectional flow mode must be explicitly enabled; default behavior is unidirectional based on pressure or pump direction.
• Cumulative transferred mass is tracked from creation and is not reset automatically.