ESL-2 embedded systems, building on Hermès

The embedded systems team covers everything electronic on board ESL-2. The flight computer and telemetry, the recovery sequence, and the onboard control of NAGA, valve actuation and ignition sequencing. There are 9 of us, with forecast spending of EUR 473 to 910.

My role

The project is just starting. For now we are all doing the same thing, finding out what has already been done, and we will split the work into separate tasks soon. As ESL-2 project manager, I also run the project for the team. I provide resources, organize the meetings and handle the budget.

Hermès

Hermès is the avionics that flew on ESL-1. A flight computer built around a Teensy 4.1, its flight software, the recovery timer and a ground station. We are taking it over and extending it for ESL-2, and adapting the hardware to the new recovery system.

The year starts with an inventory of what the society has built in avionics, telemetry, recovery and engine control since 2019. It is sorted by system and separates what flew or was tested from what stayed on paper. In late October 2026, the nine of us go over it together.

What the ESL-1 flight showed

Hermès flew at C'Space 2025. It logs too few measurements to follow the powered phase well, and recovery runs on timers alone, with no apogee detection.

What the test bench showed

The NAGA test bench ran two nitrous oxide firings in April 2026. Its valve control cannot fly as it is, mainly because the valves have no safe position if power is lost.

The ESL-2 requirements written in July 2026 add constraints Hermès was not designed for.

• Two independent recovery chains, one of them an unmodified commercial unit.
• No LiPo batteries.
• Telemetry capped at 200 mW, and 25 mW between 868 and 869.2 MHz.
• Isolated power domains.
• An oxidizer valve that stays closed by default.

As it stands, Hermès can serve at best as the in-house recovery chain and the mission avionics.

Avionics tasks from the initial ESL-2 schedule, with the interfaces they share with structures. This is the plan, not work already done.