 |
| Image: NASA |
Apollo Lunar Orbit Rendezvous
During the Apollo moon landings in the 1960s and 1970s, two astronauts landed on the moon in the lunar module (LM). The third astronaut remained in lunar orbit in the command service module (CSM).
After the lunar mission was completed, the two moonwalkers would discard much of their unnecessary equipment (like their life support backpacks) and launch back into orbit.
But what would they do if the LM could not properly re-dock with the CSM?
Spacecraft Design
Both spacecraft had two doors. One was in the roof, and one was in the side.
The roof doors were where the two vehicles docked. The "tunnel" was the connection from the top of the CSM to the top of the LM.
When both craft were correctly docked, astronauts could travel easily between spacecraft using the tunnel.
But each spacecraft also had side doors. On the LM, the side door was where the astronauts came and went on the lunar surface. On the CSM, the side door was only used at launch and landing.
 |
| Image: NASA |
No docking failures were ever encountered in lunar orbit, but astronauts and mission planners gave it considerable thought.
The thinking revolved around two choices:
1. Transfer through the roof doors.
2. Transfer through the side doors.
Technical Debrief Discussion
In 1970, after successfully returning to Earth after a crippling explosion, the Apollo 13 crew discussed their thoughts on these choices with Deke Slayton (Chief of the Astronaut Office) and others.
LOVELL We did the WIF [Water Immersion Facility] exercise, and my feelings were that if we ever were faced with that in reality we were in deep trouble. As a matter of fact, we came up with a new technique.
HAISE We had several ways to go. You go through the tunnel or you could go outside. All we determined was that we couldn't make it through the tunnel.
LOVELL No, but we were trying to determine if we could use the PLSS [Portable Life Support System, backpack] from the lunar surface. Remember we wanted to leave the PLSSs on instead of taking them off.
HAISE We never had a PLSS on, in the water tank.
LOVELL Remember that late in the game we were talking about using a PLSS with John down at the Cape in the one-g mockup. I'm trying to see what the situation was that set us up so we could use that. We said instead of taking the PLSS off and putting the OPS [Oxygen Purge System] on.
HAISE We never did any training for that though. There was some idle conversation about that one day, because the hatch jammed and wouldn't seal. It was stuck in there and we couldn't pressurize the LM.
LOVELL Yes, but the normal thing was to get rid of the PLSS.
HAISE Yes. Do a vacuum mate/demate.
LOVELL I think you would be much better off to leave the PLSS on and do the EVT [Extravehicular Transfer] with the PLSS, because you would have communications and you wouldn't have to do all that vacuum demating and mating and get all that stuff squared away.
HAISE You never get even one-g, on the ascent stage. Why don't you just lift off with the PLSS on your back, and go into orbit that way?
SLAYTON It depends entirely on what your failure mode is. Even in that case, if you get docked, you can get repress from the CSM and get back to normal, anyway.
LOVELL We were looking at the case where we had no LM pressurization, and, we couldn't go to the tunnel. We had to go exterior.
We thought that we could even recharge our PLSS with the LM system under vacuum conditions, better than we could take off the PLSS, put on the OPS, and pressurize.
We were willing to launch with the PLSS on our back and transfer that way, because we would have communications that way. It would take a long time, maybe 4 hours to recharge the PLSS. That was the only change we had on that.
 |
| Diagram from Apollo 10 debriefing transcript showing the EVA that would be route taken to transfer from the LM to the CM should the docking tunnel not be usable. Source: NASA |
Sources:
[1] "Apollo 13 Technical Debrief"; 24 April 1970; PDF by Glen Swanson; https://www.hq.nasa.gov/alsj/a13/a13-techdebrief.pdf
[2] "Apollo Oxygen Purge System (OPS) for the Portable Life Support System (PLSS) & Extravehicular Mobility Unit (EMU)"; Karl Dodenhoff; https://www.hq.nasa.gov/alsj/alsj-OPS.html
[3] "Apollo 10 Day 5, part 17: Snoopy prepares for the main event"; Corrected Transcript and Commentary Copyright © 2012-2021 by W. David Woods, Robin Wheeler and Ian Roberts; https://history.nasa.gov/afj/ap10fj/as10-day5-pt17.html
