How long would it have taken to launch an Apollo contingency flight, if, for example, the lunar lander couldn't have got back up to orbit? Could the lander have held three astronauts?
How long would it take to launch an Apollo contingency flight, if, for example, the lunar lander couldn't get back up to orbit?
There was never a facility for contingency launches on the Apollo lunar missions. The LM's ascent engine simply had to work, or the astronauts on the lunar surface would die there.
All the Apollo launches were months apart. There were periods in which two boosters were at least partially assembled at the same time, but there was never a complete Saturn V ready for flight during another mission.
It might have been feasible to complete preparation for a launch in a matter of weeks instead of months, but the life support capability of the LM was measured in days, not weeks.
The Skylab missions in low Earth orbit did have contingency launch plans. Astronauts on Skylab could survive for months, so the timing wasn't as critical. The Command/Service Module of the rescue mission would have some storage lockers removed and additional couches added, launching with a crew of 2 and returning with 5.
Can the lander hold three astronauts?
The LM could hold three astronauts (and did, for much of the Apollo 13 flight). Getting all three aboard in full pressure suits with two of them using bulky PLSS backpacks would have been a challenge, but probably possible.
Landing the LM with a single crew member for a rescue would have been difficult and somewhat risky, but again, likely possible given the use of the "P65" automated landing program of the LM.
Even if a Saturn would be ready at the launch site, it would have been impossible.
Each mission needed a specific version of the programs for the guidance computers of the LM and CM. Manual manufacture of the core rope memories took several months.
The software version for each mission was an individual design for the specific launch date and landing position of each mission.