Actuation and Ignition

The Flight SAM is where a software command turns into something physical on the propulsion system. It has to switch real valve/igniter loads from the 48 V environment while still giving us enough feedback to tell the difference between off, disconnected, on, and actually broken.

Powered Vespula Flight SAM in vehicle integration — Rev 4 operating in the propulsion-avionics stack during vehicle integration.

Power Path

The board receives the vehicle's 48 V avionics bus and generates local 24 V and 5 V rails for actuation, compute, and measurement functions.

The high-current regions are intentionally separated from RTD, pressure-transducer, differential-sensor, and ADC circuitry. On a mixed-signal engine controller, the return path is just as important as the outgoing valve current: actuation current should not become part of the analog measurement reference.

Vespula Rev 4 power layer — Dedicated power layer supporting the actuation and local-conversion regions of the six-layer Flight SAM.

Valve Channels

I did not want to call a valve channel 'validated' just because the GPIO toggled. I checked the electrical states we actually care about:

connected and off;
disconnected;
connected and on;
shorted/faulted.

That required checking the switched output together with valve-current and valve-voltage feedback, using the actual solenoid load rather than assuming a bench resistor represented every operating condition.

Igniter Power Problem

The inherited revision also had unstable igniter-power behavior. That could not be treated as a firmware issue because the instability existed in the local power stage itself.

The revision changed the converter/compensation implementation, and then I brought it back up the same way as everything else: rail first, command path second, real output last.

Layout Boundary

The layout separates:

converter switching loops;
solenoid/igniter current paths;
output connectors;
controller GPIO/control signals;
sensor acquisition and ADC references.

This separation prevents the fastest/highest-current loops from sharing unnecessary impedance with the lowest-level measurement paths.

Validation

The actuation side was brought up after the controller and sensor interfaces were already known-good. That sequencing made it possible to distinguish a bad command, bad feedback signal, bad power stage, or actual load fault without debugging all four at once.

By the end of bring-up, the valve and igniter behavior was repeatable enough that the board could be treated like actual propulsion hardware instead of a science project on the bench.

Vespula Flight SAM integrated in engine bay — Flight SAM integrated with the surrounding propulsion hardware and harnessing.