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

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avsm 39 minutes ago | parent [-]

Do you have a link to your talk? I'm also curious if you did any GHG measurements, or it was part of the control stack. We wrote the XenServer stack in OCaml back in 2004, and that made it into orbit in 2017 (I think it did, anyway: https://www.theregister.com/offbeat/2017/05/12/space-upstart...)

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rho_soul_kg_m3 31 minutes ago | parent [-]

Yes see above.

OCaml was very much part of the GHG measurements. On the satellite it was controlling the cameras, acquiring the images, losslessly compressing them, encrypting them and transferring them to the platform controller using a clunky but mandated CSP-based file tranfer protocol. On the ground, OCaml was running almost the entire data processing chain, including spectroscopy, image corrections, retrievals and post-retrieval ad hoc bias corrections, as well as simulations.

I simply used an mmap()'d Bigarrays to do parallel processing (back then OCaml wasn't multi-core.)

At a later stage I replaced a few bits of code (e.g. some sparse matrix routines) with Fortran. The only processing-related part that wasn't OCaml (besides the shells scripts to glue the things together) was the image alignment algorithm which was written by someone else in C++. I even had a job scheduling system written in OCaml.

	▲	avsm 11 minutes ago \| parent [-]
		Nice work! Did you ever open any open source any of it? Looking at your OCaml wishlist from back in 2017, some stuff has improved and some is on its way: - Support for read-only BigArrays (or sections) : we're starting to switch to just using bytes/string in OCaml 5+ now, since the larger allocations go into malloc'ed pools and do not relocate, so they can be used as part of an FFI (without the Bigarray C value overhead) - More support for floating-point numbers (exceptions, representation exploration): OxCaml has some of this now! https://oxcaml.org/documentation/miscellaneous-extensions/sm... - Syntax for extended BigArray indexing: now supported in OCaml https://ocaml.org/manual/5.4/indexops.html#ss:multiindexing - LaCaml remains too low-level (non-functional) and unreadable: still remains the case, but OxCaml's got initial support for SIMD https://oxcaml.org/documentation/simd/intro - BigArray and floating-point I/O remains difficult (we would like: I/O to channels, efficient representation retrieval): much easier now with OCaml effects to build custom fast serialisers (see https://github.com/ocaml-multicore/eio) - Native top-level: ocamlnat is (I think) shipped in OxCaml, but you can also run a wasm toplevel