Apollo 15 Part 17: Transposition and Docking (A Blender Animation)
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On July 26, 1971, 22 minutes after Translunar Injection (TLI), the Apollo Command Service Module (CSM) separated from the S-IVB stage with explosive devices that swung open the SM/LM adapter (SLA) doors. Separation to hard dock took 11 minutes.
DSKY program and display: Register 1 and 2 show the configuration of the digital autopilot (DAP). Each digit represents a selection from a look up table. Here is what was set.
-R1: 11103 (CSM only config, x translation (fore/aft) using all RCS quads, deadband +/ 0.5 deg, attitude rate 2.0 deg/sec)
--R2: 01111 (use RCS quad B and D for roll, no failed RCS quads)
--R3: Blank
Through this interface, the DAP is configured as to how to use the RCS. For example, the RCS works differently whether the LM is docked or not. For fuel conservation, they may want to operate with a reduced set of RCS quads. Or if one or more quads have failed, the computer can compensate for that. Deadband is the amount of angular tolerance the computer will tolerate before firing the RCS system.
Docking Probe Operation: My prior videos had the blue docking latches in the wrong position. Prior to launch they would have been in the cocked position which is where you see them in the beginning of this video.
--Extension: To extend the probe, ext/rel switch to ext/rel position which barber poles the indicator. Upon full extension, the barber pole goes gray. Then the switch is then placed to the retract position in preparation for docking.
--Capture: When the three small hooks on the tip of the probe engage the drogue, the docking probe indicator will barber pole.
--Retract: Move both retract switches (prim/sec) to either retract 1 or 2. Either switch and either position will work.
After Retraction: Move ext/rel switch to off and return the retract switches to the center position.
CMC mode (command module computer). In auto, the digital autopilot is being used to stabilize the spacecraft attitude while manual translation and rotational control is being used as input. Going to “free” turns off the stabilization. After capture, the switch is placed into free. While my video shows pretty much perfect alignment at capture, this was not reality. The tip of the probe had play in it to get engaged into the drogue hole even with off-axis alignment. A15 had some misalignment. Going to free allowed the SM to not fight the alignment as the drogue retracted. The act of retracting got the CSM into alignment.
EDS Power and Sequence Events Control System are related to the pyrotechnics. In this case for the CSM separation event.
Entry Monitor System (EMS) (above FDAI 1): During setup for docking the EMS display will show opening and closure to the LM. During testing, it was found to not work well around zero, so they biased the setup to 100 ft/sec. So a display of 100.7 is 0.7 ft/sec opening velocity while 99.3 is 0.7 ft/sec closing velocity.
Timing: Pretty much all views with external shots are in real time.
Acronyms:
CM-command module
CMC-command module computer
COAS-crewman optical alignment sight
DAP-digital autopilot
DSKY-display and keyboard
EMS-entry monitor system
FDAI-flight director/attitude indicator
LM-Lunar Module
RCS-reaction control system
SLA-SM/LM adapter
SM-Service Module
T&D-transposition and docking
TLI-translunar injection
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