Climb the ladder

A testbed climbs three rungs. Model-in-the-loop runs models of the software, the payload, and the bus. Software-in-the-loop swaps in the flight binary and leaves the payload and the bus as models. Hardware-in-the-loop puts the real flight computer on the real bus.

A payload emulator plugged into that real bus is still the real interface. Mark each cell as a model, the flight binary on a host, or real hardware.