Darcy Umbilical Wiki

Purpose

The Darcy Umbilical is the vehicle-side electrical boundary between ground-support equipment and the flight avionics system.

It carries ground power, Ethernet, ESTOP, and RBF/safing signals through a compact connector interface used during integration, testing, and launch operations.

My Responsibility

I was the Design Responsible Engineer and owned the schematic, PCB layout, interface definition, and validation of the vehicle-side board.

System Context

Even though it is electrically simpler than a flight computer or power converter, the umbilical is still a safety-critical integration interface. A connector mistake can prevent communication, defeat a safing function, damage vehicle electronics, or create inconsistent ground-test behavior.

So the design prioritizes clear signal ownership, connector keying, transient protection, and auditable routing over circuit complexity.

Interface Architecture

The board keeps four functional groups separated:

• Vehicle and ground power
• Ethernet
• ESTOP
• RBF and hardware safing

TVS and ESD devices are placed near the connector boundary to prevent externally introduced transient current from propagating into the flight wiring.

Connector orientation, polarity, keying, and labeling reduce the probability of an integration error.

PCB Layout

The power path is routed independently from Ethernet and low-energy safing signals. Ethernet differential pairs preserve pair symmetry and reference-plane continuity through the board.

Safing signals are routed as explicit point-to-point paths that can be traced visually in both the schematic and PCB viewer. Protection-device returns are kept short so surge current is diverted at the interface instead of flowing through the rest of the board.

Validation

Validation should include:

1. Schematic-to-layout pinout audit
2. End-to-end continuity testing
3. Adjacent-pin short inspection
4. Connector polarity and keying verification
5. Ethernet link and packet testing
6. ESTOP continuity and state validation
7. RBF insertion/removal behavior
8. Power-path voltage-drop measurement
9. ESD/TVS orientation inspection
10. Harness-integrated regression test

Engineering Lesson

Small interface boards can get less design attention than central avionics boards, even though they are exposed to frequent handling and integration errors. The main engineering value here is making a complex vehicle-to-ground boundary hard to connect incorrectly and straightforward to validate.