Actually I had another question before this: I just looked at 51-G mission - there were 3 PAM-D + satellites, and fourth active payload is SPARTAN. but seems only 3 active payloads are supported (as suggested by A6U "rotary" payload latch switch "1-MONITOR-2-MONITOR-3").
So, eventually the PAMs will be implemented in SSV (I actually have some things already), and they will talk to the GPCs, and it will be possible to have 3 in a mission (still don't know if that was the actual limit or just what happened to be the maximum flown in the 80s). For now, they will have to be implemented as custom vessels attached to the PLB, and the user will have to control them somehow. As ASEs aren't deployed, they could/should be considered "Passive Payloads".
The "Active Payloads" are the ones that are deployed and/or retrieved, directly from the PLB, with the RMS. Although there were a few "hacks" along the way, 5 should be the maximum number of such payloads, as there are 15 latches and each payloads needs at least 3 of them, so 15 / 3 = 5 payloads. Most payloads actually need 5 latches, so that gives 3 much payloads, and that is why the switch has 3 positions.
P.S. I even imagined optional "scenario" exporter, where shuttle is in "OPF" type position with open payload bay, otherwise it is hard to check payload position. Actually it is how it started, launched, quickly to orbit, and wanted to open PB to see what is right or wrong with payloads...
It is a problem I recognized long ago, but short of implementing Orbiter inside Mission Editor, things have to be checked in Orbiter itself. I don't know the mass, size, orientation, configurations, etc of the payloads, so there isn't much I can do in Mission Editor. This OPF ideia might be interesting....
Thanks, I suspected it's somewhere in MM202, but what is "in SM mode"?
Next to the keyboard there is a Major Function switch, which controls which display is shown in the CRT/MDU.