On 23 April, our pure-OCaml CCSDS protocol stack booted up in low Earth orbit! The project, codename Borealis , is running inside DPhi Space 's ClusterGate-2 payload module on the host satellite, with end-to-end-encrypted command and control and post-quantum key rotation, all implemented in safe OCaml. Why does OCaml matter here? Untrusted code running on a satellite is a huge security risk , and OCaml is an ideal safe language to run in space. In his ICFP 2022 keynote , KC Sivaramakrishnan looked back on the decade-long engineering effort that produced OCaml 5, the release that put safe and performant multi-threading into the OCaml runtime. KC ended his talk speculating that OCaml 5.0 would go to the moon, due to its language features that would deliver C/Rust-like performance on demand while keeping the mathematical rigour of classic ML. Here at Parsimoni, we took his words a bit too literally :-) The host satellite circles the Earth every ninety minutes or so.…