Landing
Why were the Apollo space craft's preparations started early?
Apollo 11
When Armstrong again looked outside, he saw that the computer's landing target was in a boulder-strewn area just north and east of a diameter crater (later determined to be "West crater," named for its location in the western part of the originally planned landing ellipse). Armstrong took semi-automatic control and, with Aldrin calling out altitude and velocity data, landed at 20:17:40 UTC on July 20 with about 25 seconds of fuel left. Apollo 11 landed with less fuel than other missions, and the astronauts encountered a premature low fuel warning. This was later found to be the result of greater propellant 'slosh' than expected, uncovering a fuel sensor. On subsequent missions, extra anti-slosh baffles were added to the tanks to prevent this. Throughout the descent Aldrin had called out navigation data to Armstrong, who was busy piloting the LM. A few moments before the landing, a light informed Aldrin that at least one of the probes hanging from "Eagle"'s footpads had touched the surface, and he said "Contact light!" Three seconds later, "Eagle" landed and Armstrong said "Shutdown." Aldrin immediately said "Okay, engine stop. ACA - out of detent." Armstrong acknowledged "Out of detent. Auto" and Aldrin continued "Mode control - both auto. Descent engine command override off. Engine arm - off. 413 is in. "Charles Duke, acting as CAPCOM during the landing phase, acknowledged their landing by saying "We copy you down, Eagle. "Armstrong acknowledged Aldrin's completion of the post landing checklist with "Engine arm is off," before responding to Duke with the words, "Houston, Tranquility Base here. The "Eagle" has landed." Armstrong's unrehearsed change of call sign from "Eagle" to "Tranquility Base" emphasized to listeners that landing was complete and successful. Duke mispronounced his reply as he expressed the relief at Mission Control: "Roger, Twan-- Tranquility, we copy you on the ground. You got a bunch of guys about to turn blue. We're breathing again. Thanks a lot. "Two and a half hours after landing, before preparations began for the EVA, Aldrin broadcast that:The schedule for the mission called for the astronauts to follow the landing with a five-hour sleep period, since they had been awake since early morning. However, they elected to forgo the sleep period and begin the preparations for the EVA early, thinking that they would be unable to sleep.