Well, I might have been the first to put OCaml in space, specifically on low-Earth orbit aboard GHGSat-D in 2016. I designed the payload software as a collection of SystemD services talking over DBus, and it included a CCSDS-to-DBus bridge to talk to the platform (the thing that hosts the payload, controls and steers the satellite). The payload also did perform symmetric-key encryption of the resulting data, as per regulations.

I gave a talk about the payload software at the Paris OCaml users group.

The reason for selecting that archicture was that I didn't expect to write the whole payload software by myself, and I assumed that when some other developers join in they would, obviously, not want to use a weird language like OCaml, and so they could write their portion in C/C++/whatever and the system could still work. Of course that didn't happen.

I'd be surprised if the company still uses OCaml, as the standad tendency is to revert to "industry-standard" languages to get industry-standard problems. The whole processing and simulation toolchain was also written in OCaml.

Today there is little reason not to use Rust and it can cover both the processing side and the payload software. But people still insist on using C/C++. I'm OK with that as long as I can invoice them.

EDIT: Found my slides https://lambda-diode.com/static/data/GHGSat_OCaml.pdf