I remember reading somewhere that the shuttle doesn't open it's bay doors soon after MECO, that it waits a good while first. I know it's vague, but if it's true, why? Wouldn't opening the payload bay doors be one of the first things done on-orbit, to get rid of the system heat of the hydraulics, EPS, APU, OMS and MPS from the climb to orbit and OMS burns?
...Maybe, is it because they want to ensure all systems are working before they open the doors?
Shuttle Reference Manual didn't even mention the opening of the Payload bay doors as one of the post-MECO ops.
The opening of the Payload bay doors happens during the Post-Insertion (PI) checklist. Nominally you begin that task one hour after lift-off, with "CONFIG FOR PLBD OPERATIONS" (PI 1-14) and actually opening the doors at about 01:25 MET.
The PI checklist starts at 00:50 MET and thus directly after OMS-2. before you configure the payload bay doors, you have the following major activities:
- SPECIALIST SEAT EGRESS
- CONFIG GPCS FOR OPS2 (important since the payload bay door control software is in SM OPS2, also this is a very complex task, since it involves 5 computers at once)
- PL BUS ACTIVATION
- PRELIM MIDDECK CONFIG
- AFT STATION CONFIG (so you can also check that the payload bay doors open properly)
Between configuration for payload bay door operations and opening, you have:
- WCS CONFIG/ACT (the toilet, you really need it)
- SWITCH CONFIG/GALLEY ACT (If you get thirsty by now, you might like it)
- DON/CONFIG COMM (It is a bit loud in the Shuttle, so you better get this done soon, so you know what the person right next to you is saying)
- LOAD DAP A5 (configure the autopilot for the next maneuver)
- MNVR TO PLBD OPENING ATT ("maneuver to payload bay door opening attitude"; you can't do this in every orientation, you use "BIASED -ZLV +YVV".*)
- RAD ACT (the radiators are already activated before opening the doors - otherwise you could damage them)
*The exact attitude is defined in UNIV PTG as follows: Body vector is selected as 3 (-Z), Target is 2 (Center of Earth), Omicron angle is 280°. This means the shuttle Z axis is pointed as such that down (-Z) is towards the center of Earth, and Y is in the plane between -Z and orbit antinormal (-h) and then the shuttle is rotated clockwise around the target vector (towards center of Earth) by 280° (Defined in ORB OPS 7-33). Which in this case means: The shuttle flies wings level and with 80° slideslip to the left.
If +/- Y would be selected as reference body vector, the -Z axis of the Shuttle Coordinate System (down) would be used as second vector instead.