Page 12 - Aerotech News and Review, July 19, 2019

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possible landing site.
Armstrong found a clear patch of
ground and maneuvered the spacecraft towards it. As he got closer, now 250 feet above the surface, he discovered his new landing site had a crater in it. He cleared the crater and found another patch of lev- el ground. They were now 100 feet from the surface, with only 90 seconds of pro- pellant remaining. Lunar dust kicked up by the LM’s engine began to obfuscate his ability to determine the spacecraft’s motion. Some large rocks jutted out of the dust cloud, and Armstrong focused on them during his descent so he could determine the spacecraft’s speed.
A few moments before the landing, a light informed Aldrin that at least one of the 67-inch probes hanging from Eagle’s footpads had touched the surface, and he said: “Contact light!” Armstrong was supposed to immediately shutdown the engine, as the engineers suspected the pressure caused by the engine’s own exhaust reflecting off the lunar surface could make it explode, but he forgot. Three seconds later, Eagle landed and Armstrong shutdown the engine. Al- drin immediately said “Okay, engine stop. ACA — out of detent.” Armstrong acknowledged: “Out of detent. Auto.” Aldrin continued: “Mode control – both auto. Descent engine command override off. Engine arm — off. 413 is in.”
ACA was the attitude control as- sembly, the LM’s control stick. Output went to the LGC to command the reac- tion control system jets to fire. “Out of Detent” meant that the stick had moved away from its centered position; it was
spring-centered like the turn indicator in a car. LGC address 413 contained the variable that indicated that the LM had landed.
Eagle landed at 3:17 p.m., on July 20 with 216 pounds of usable fuel re- maining. Information available to the crew and mission controllers during the landing showed that the LM had enough fuel for another 25 seconds of powered flight before an abort without touchdown would have become unsafe, but post-mission analysis showed that the real figure was probably closer to 50 seconds. Apollo 11 landed with less fuel than most subsequent 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.
Armstrong acknowledged Aldrin’s completion of the post landing check- list with “Engine arm is off”, before responding to the CAPCOM, Charles Duke, with the words, “Houston, Tran- quility 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 mis- pronounced 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 radioed to Earth: “This is the LM pilot. I’d like to take this opportunity to ask every person listening in, whoever and wherever they may be, to pause for a moment and contemplate the events of the past few hours and to give thanks in his or her own way.” He then took com- munion privately. At this time NASA was still fighting a lawsuit brought by atheist Madalyn Murray O’Hair (who had objected to the Apollo 8 crew read- ing from the Book of Genesis) demand- ing that their astronauts refrain from broadcasting religious activities while in space. As such, Aldrin chose to refrain from directly mentioning taking commu- nion on the Moon. Aldrin was an elder at the Webster Presbyterian Church, and his communion kit was prepared by the pas- tor of the church, Dean Woodruff. Web- ster Presbyterian possesses the chalice used on the Moon and commemorates the event each year on the Sunday clos- est to July 20.
The schedule for the mission called for the astronauts to follow the landing with a five-hour sleep period, but they chose to begin the preparations for the EVA early, thinking that they would be unable to sleep.
Lunar surface operations
Preparations for the EV A began at 6:43 p.m. These took longer than ex- pected; three and a half hours instead of two. During training on Earth, everything required had been neatly laid out in ad- vance, but on the Moon the cabin con- tained a large number of other items as
NASA photograph
This photograph of the Lunar Module at Tranquility Base was taken by Neil Armstrong during the Apollo 11 mission, from the rim of Little West Crater on the lunar surface. Armstrong’s shadow and the shadow of the camera are visible in the foreground. This is the furthest distance from the lunar module traveled by either astronaut while on the Moon.
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well, such as checklists, food packets and tools. Once Armstrong and Aldrin were ready to go outside, Eagle was depres- surized. The hatch was opened at 9:39 p.m. Armstrong initially had some diffi-
culties squeezing through the hatch with his portable life support system. Some of the highest heart rates recorded from
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