Third Period.-This day was filled with activities. Astronauts Stafford and Cernan performed all the maneuvers required to separate the LM from the CSM, flew the LM independently for 8 hours, descended to within eight miles of the lunar surface (while operating the landing radar, cameras, and other equipment), ascended, made rendezvous, and finally docked with the CSM. (Fig. 1-8)

The day began with Stafford and Cernan crawling through the tunnel to the LM, activating the systems, and checking them out. Then a problem arose. Inability to vent the tunnel between the LM and the CSM did not allow the required pressure differential to be maintained between the command module cabin and the tunnel. This in turn permitted the LM to move about 32 degrees out of alignment with the CSM in its docked position. Ground control advised the crew not to undock if the angle exceeded 7 degrees; it was feared that if the angle became larger than that, the locking latches in the docking collar would be damaged and the LM, on its

return, would not be able to make a secure hook-up with the CSM, making it difficult for the astronauts to return to the CSM. (Fig. 1-9)

STANFORD LIBRARIES

As this instruction was acknowledged, the spacecraft passed behind the moon and lost all communications with the ground while it was on the far side. When the LM reestablished communications with the ground, the crew advised that they had separated successfully and were flying formation-"station keeping" some 50 feet apart.

Following a thorough visual inspection of the LM by CMP Young, Stafford and Cernan moved the LM to a point about 2 miles from the CTM. Then, firing the DPS and reducing the velocity of the LM, they descended to within 10 miles of the lunar surface at a point about 15 degrees from the site where the Apollo 11 will land. It is at this point that the powered descent to the lunar landing will be initiated in the Apollo 11 mission.

During this low altitude pass over the lunar landing site, the LM