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| 1 | +Apollo 11 – Lunar Descent and Moonwalk |
| 2 | + |
| 3 | +As the descent began, Armstrong and Aldrin found themselves passing landmarks on the |
| 4 | +surface two or three seconds early, and reported that they were “long”; they would land |
| 5 | +miles west of their target point. Eagle was traveling too fast. The problem could have been |
| 6 | +mascons—concentrations of high mass in a region or regions of the Moon’s crust that |
| 7 | +contains a gravitational anomaly, potentially altering Eagle’s trajectory. |
| 8 | + |
| 9 | +Five minutes into the descent burn, and 6,000 feet (1,800 m) above the surface of the |
| 10 | +Moon, the LM guidance computer (LGC) distracted the crew with the first of several |
| 11 | +unexpected 1201 and 1202 program alarms. Inside Mission Control Center, computer |
| 12 | +engineer Jack Garman told Guidance Officer Steve Bales it was safe to continue the |
| 13 | +descent, and this was relayed to the crew. The program alarms indicated “executive |
| 14 | +overflows”, meaning the guidance computer could not complete all its tasks in real-time and |
| 15 | +had to postpone some of them. Margaret Hamilton, the Director of Apollo Flight Computer |
| 16 | +Programming at the MIT Charles Stark Draper Laboratory later recalled: “To blame the |
| 17 | +computer for the Apollo 11 problems is like blaming the person who spots a fire and calls |
| 18 | +the fire department. Actually, the computer was programmed to do more than recognize |
| 19 | +error conditions. A complete set of recovery programs was incorporated into the software. |
| 20 | +The software’s action, in this case, was to eliminate lower priority tasks and re-establish |
| 21 | +the more important ones. The computer, rather than almost forcing an abort, prevented an |
| 22 | +abort. If the computer hadn’t recognized this problem and taken recovery action, I doubt if |
| 23 | +Apollo 11 would have been the successful Moon landing it was.” |
| 24 | + |
| 25 | +When Armstrong again looked outside, he saw that the computer’s landing target was in a |
| 26 | +boulder-strewn area just north and east of a 300-foot-diameter (91 m) crater, so he took |
| 27 | +semi-automatic control. Throughout the descent, Aldrin called out navigation data to |
| 28 | +Armstrong, who was busy piloting Eagle. Now 107 feet (33 m) above the surface, |
| 29 | +Armstrong knew their propellant supply was dwindling and was determined to land at the |
| 30 | +first possible landing site. |
| 31 | + |
| 32 | +Armstrong found a clear patch of ground and maneuvered the spacecraft towards it. They |
| 33 | +were now 100 feet (30 m) from the surface, with only 90 seconds of propellant remaining. |
| 34 | +Lunar dust kicked up by the LM’s engine began to impair his ability to determine the |
| 35 | +spacecraft’s motion. |
| 36 | + |
| 37 | +A light informed Aldrin that at least one of the 67-inch (170 cm) probes hanging from |
| 38 | +Eagle’s footpads had touched the surface and he said: “Contact light!” Three seconds later, |
| 39 | +Eagle landed and Armstrong shut the engine down. Aldrin immediately said “Okay, engine |
| 40 | +stop.” |
| 41 | + |
| 42 | +Eagle landed at 20:17:40 UTC on Sunday July 20 with 216 pounds (98 kg) of usable fuel |
| 43 | +remaining. Information available to the crew and mission controllers during the landing |
| 44 | +showed the LM had enough fuel for another 25 seconds of powered flight before an abort |
| 45 | +without touchdown would have become unsafe, but post-mission analysis showed that the |
| 46 | +real figure was probably closer to 50 seconds. |
| 47 | + |
| 48 | +Armstrong acknowledged Aldrin’s completion of the post-landing checklist with “Engine |
| 49 | +arm is off”, before responding to the CAPCOM, Charles Duke, with the words, “Houston, |
| 50 | +Tranquility Base here. The Eagle has landed.” Duke expressed the relief at Mission Control: |
| 51 | +“Roger, Twan—Tranquility, we copy you on the ground. You got a bunch of guys about to |
| 52 | +turn blue. We’re breathing again. Thanks a lot.” |
| 53 | + |
| 54 | +Preparations for Neil Armstrong and Buzz Aldrin to walk on the Moon began at 23:43 UTC. |
| 55 | +These took longer than expected; three and a half hours instead of two. Six hours and |
| 56 | +thirty-nine minutes after landing, Armstrong and Aldrin were ready to go outside, and |
| 57 | +Eagle was depressurized. |
| 58 | + |
| 59 | +Eagle’s hatch was opened at 02:39:33. Armstrong initially had some difficulties squeezing |
| 60 | +through the hatch with his portable life support system (PLSS). At 02:51 Armstrong began |
| 61 | +his descent to the lunar surface. Climbing down the nine-rung ladder, Armstrong pulled a |
| 62 | +D-ring to deploy the modular equipment stowage assembly (MESA) folded against Eagle’s |
| 63 | +side and activate the TV camera. |
| 64 | + |
| 65 | +Despite some technical and weather difficulties, black and white images of the first lunar |
| 66 | +EVA were received and broadcast to at least 600 million people on Earth. |
| 67 | + |
| 68 | +After describing the surface dust as “very fine-grained” and “almost like a powder”, at |
| 69 | +02:56:15, six and a half hours after landing, Armstrong stepped off Eagle’s landing pad and |
| 70 | +declared: “That’s one small step for [a] man, one giant leap for mankind.” |
| 71 | + |
| 72 | +Armstrong intended to say “That’s one small step for a man”, but the word “a” is not |
| 73 | +audible in the transmission, and thus was not initially reported by most observers of the live |
| 74 | +broadcast. When later asked about his quote, Armstrong said he believed he said “for a |
| 75 | +man”, and subsequent printed versions of the quote included the “a” in square brackets. |
| 76 | + |
| 77 | +About seven minutes after stepping onto the Moon’s surface, Armstrong collected a |
| 78 | +contingency soil sample using a sample bag on a stick. Twelve minutes after the sample |
| 79 | +was collected, he removed the TV camera from the MESA and made a panoramic sweep, |
| 80 | +then mounted it on a tripod. Aldrin joined Armstrong on the surface. He described the view |
| 81 | +with the simple phrase: “Magnificent desolation.” |
| 82 | + |
| 83 | +Armstrong said moving in the lunar gravity, one-sixth of Earth’s, was “even perhaps easier |
| 84 | +than the simulations … It’s absolutely no trouble to walk around.” Aldrin joined him on the |
| 85 | +surface and tested methods for moving around, including two-footed kangaroo hops. The |
| 86 | +PLSS backpack created a tendency to tip backward, but neither astronaut had serious |
| 87 | +problems maintaining balance. The fine soil was quite slippery. |
| 88 | + |
| 89 | +The astronauts planted the Lunar Flag Assembly containing a flag of the United States on |
| 90 | +the lunar surface, in clear view of the TV camera. Aldrin remembered, “Of all the jobs I had |
| 91 | +to do on the Moon the one I wanted to go the smoothest was the flag raising.” But the |
| 92 | +astronauts struggled with the telescoping rod and could only insert the pole about 2 inches |
| 93 | +(5 cm) into the hard lunar surface. Before Aldrin could take a photo of Armstrong with the |
| 94 | +flag, President Richard Nixon spoke to them through a telephone-radio transmission, which |
| 95 | +Nixon called “the most historic phone call ever made from the White House.” |
| 96 | + |
| 97 | +They deployed the EASEP, which included a Passive Seismic Experiment Package used to |
| 98 | +measure moonquakes and a retroreflector array used for the lunar laser ranging |
| 99 | +experiment. Then Armstrong walked 196 feet (60 m) from the LM to take photographs at |
| 100 | +the rim of Little West Crater while Aldrin collected two core samples. He used the |
| 101 | +geologist’s hammer to pound in the tubes—the only time the hammer was used on Apollo |
| 102 | +11—but was unable to penetrate more than 6 inches (15 cm) deep. |
| 103 | + |
| 104 | +The astronauts then collected rock samples using scoops and tongs on extension handles. |
| 105 | +Many of the surface activities took longer than expected, so they had to stop documenting |
| 106 | +sample collection halfway through the allotted 34 minutes. Aldrin shoveled 6 kilograms |
| 107 | +(13 lb) of soil into the box of rocks to pack them in tightly. Two types of rocks were found in |
| 108 | +the geological samples: basalt and breccia. |
| 109 | + |
| 110 | +While on the surface, Armstrong uncovered a plaque mounted on the LM ladder, bearing |
| 111 | +two drawings of Earth, an inscription, and signatures of the astronauts and President Nixon. |
| 112 | +The inscription read: “Here men from the planet Earth first set foot upon the Moon July |
| 113 | +1969, A. D. We came in peace for all mankind.” |
| 114 | + |
| 115 | +Mission Control used a coded phrase to warn Armstrong his metabolic rates were high, and |
| 116 | +that he should slow down. As metabolic rates remained generally lower than expected for |
| 117 | +both astronauts throughout the walk, Mission Control granted the astronauts a 15-minute |
| 118 | +extension. |
| 119 | + |
| 120 | +Aldrin entered Eagle first. With some difficulty the astronauts lifted film and two sample |
| 121 | +boxes containing 21.55 kilograms (47.5 lb) of lunar surface material to the LM hatch using a |
| 122 | +flat cable pulley device called the Lunar Equipment Conveyor (LEC). Armstrong then |
| 123 | +jumped onto the ladder’s third rung, and climbed into the LM. After transferring to LM life |
| 124 | +support, the explorers lightened the ascent stage for the return to lunar orbit by tossing out |
| 125 | +their PLSS backpacks, lunar overshoes, an empty Hasselblad camera, and other equipment. |
| 126 | +The hatch was closed again at 05:11:13. They then pressurized the LM and settled down to |
| 127 | +sleep. |
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