Reimplementing the Space Protocol Stack from Scratch

A browser-playable CCSDS stack

It has been reported that Thomas Gazagnaire has reimplemented the CCSDS space‑protocol stack in OCaml and wired up a live demo that runs in the browser. Type a message, watch it get wrapped into a telemetry frame, hover any byte in the hex dump and the page highlights which field you just touched. Nerdy? Absolutely. Delightful? Also yes. This isn’t fluff — it’s a real parser built with a typed binary codec approach so you can poke at real wire formats without firing up a ground station.

Why the stack looks the way it does

CCSDS (the Consultative Committee for Space Data Systems) has been the lingua franca of spacecraft for decades, and for good reason: links are brutal. A spacecraft is a radio blip moving at 7.5 km/s, visible for roughly 10 minutes, talking at kilobits per second. So the protocols are tiny, deterministic and low‑overhead: Space Packets are a 6‑byte header plus payload; TM and TC frames carry those packets; newer AOS and USLP flavors add alternatives for more complex missions. Security and reliability ride on separate layers — SDLS adds AES‑GCM and anti‑replay, while COP‑1 manages retransmissions and the painful reality of missed acknowledgements during a short ground pass.

So what changes?

Most real implementations live as proprietary C libraries inside ground-segment stacks. Reimplementing CCSDS in a high‑level language and exposing it in the browser lowers the bar for learning, testing and tooling. It’s not going to replace flight‑proven stacks overnight, but it makes the stack less of an arcane art and more of a playground for engineers, students and small teams. Want to experiment with delay‑tolerant networking, post‑quantum crypto or simply see which byte does what? Now you can — and that kind of transparency matters when we’re building systems that go from cloud to orbit.

Sources: gazagnaire.org, Lobsters