[bsder]

So, a set of standard software RPCs (remote procedure calls) and APIs (application programming interfaces) and not another electrical signalling standard. Got it.

Thanks for the correction.

So, I guess the next question is what are you folks actually using at the electrical signalling level to talk? (If you are not allowed to say, I understand.)

[oasisaimlessly]

No, not RPCs/APIs either. A satellite bus is a physical object[1], which defines the mechanical standards for mounting payload modules.

[1]: https://en.wikipedia.org/wiki/Satellite_bus