When the Curiosity rover streaked the Martian atmosphere toward a soft landing in Gale crater in August 2012, NASA officials termed the landing process “Seven Minutes of Hell.” Forty-three years earlier – on July 20, 1969 – a manned spacecraft went through a similar landing sequence. As CBS’s Walter Cronkite reported live that Eagle had fired its descent engine at 102 hours and 33 minutes (102:33) into the mission, the veteran journalist could have termed the ride of astronauts Neil Armstrong and Buzz Aldrin down to the Sea of Tranquility “twelve and one-half minutes of hell.” In a way, I wish he had. It would have perfectly described what I was feeling that afternoon watching the two astronaut heroes make history. At 1:11 p.m., the Eagle undocked and backed away from Columbia, allowing Michael Collins to take a close look at the lunar module and assure Armstrong and Aldrin all was well. At 3:04 p.m., Armstrong fired up the descent engine for the drop to the lunar surface. It would stay lit for 756 seconds; Armstrong would not shut down the engine until Armstrong reported that the contact light had illuminated. That meant that at least one of the probes hanging from three of the footpads had touched the surface. Two problems plagued the Eagle crew during the descent – dropouts in communications with Houston and computer alarms. After the mission, Aldrin discussed the fuzzy communications: “I can’t ever recall having them exercise us in the simulator with the uncertainty of intermittent communications. It was distracting. In simulator training, either things were working normal or there was something going wrong. It would have a degree of polarity to it. It either was or wasn’t. But the uncertainty, particularly in communications, that was exhibited here was frustrating. You didn’t know where you were – whether you were on your own or whether you were still under the close supervision of ground control.” Shortly after the descent engine began firing, Armstrong decided to change the mode of the rendezvous radar from Auto Track to Slew. He didn’t know it at the time, but changing the mode would lead to the program alarms and some hectic moments in Houston as computer experts analyzed the problem. Because the dial was not set at Computer Control, once the astronauts starting getting radar data, the computer was continuously interrupted with useless and false warnings that the radar’s CSM tracking angle was changed. Eagle’s computer became overloaded five times during the descent, but the alarms never put the landing in jeopardy. In the landing’s final moments when Armstrong realized Eagle was headed for a crater and a field of large rocks, he decided not to use the computer for retargeting the landing site. Instead, he manually flew to a safer location. Three minutes into the burn Armstrong analyzed the landing radar data and realized Eagle was going to land long. He told Houston, “Our position checks down range show us to be a little long.” Even as Armstrong and Aldrin deal with the revelation that Eagle will badly overshoot its landing site, they get another program alarm. There’s the slightest tone of urgency in Armstrong’s voice as he says, “Program alarm.” He adds, “It’s a 1202.” A few seconds later, he again quizzes Houston, “Give us a reading on the 1202 program alarm.” The Eagle is at an altitude of 33,500 feet. In the 16mm film record, the lunar surface can be seen in the very bottom of Aldrin’s window. In Houston, Steve Bales, the control room’s expert on lunar module guidance systems, reported that the landing will not be jeopardized by the overflow of unexpected data from the rendezvous radar. The computer recognized the data as low priority and was ignoring it while doing more important landing radar computations. With Eagle at a height of 3,000 feet, astronaut Charlie Duke, Capcom for the mission, told Armstrong and Aldrin, “Eagle, Houston. You’re go for landing. Over.” As Eagle drops to 2,000 feet in height, Armstrong reported a 1201 alarm and Duke responded, “Roger. 1201 alarm. We’re go. Same type. We’re go.” Back on Earth, in the United States, in the state of Ohio, I watched the animation of Eagle’s descent as I listened to the audio including all those alarms. With me were my mom and dad, my sister Jody, and my dad’s sister Emmy, her husband Bill and their three kids, Billy, Kim and Ken. Cronkite and his sidekick, astronaut Wally Schirra, didn’t seem concerned about the alarms and the occasional communications hiccup, so we were calm but hopeful as Eagle flew just 2,000 feet above the lunar surface. Inside Eagle, Armstrong and Aldrin continued to worry about the alarms as Eagle headed for a rock field that could damage the lunar module and make liftoff impossible. After the mission, Armstrong recalled these final seconds, “The concern here was not with the landing area we were going into but rather whether we could continue at all (because of the program alarms. Consequently, our attention was directed toward clearing the program alarms, keeping the machine flying, and assuring ourselves that control was adequate to continue without requiring an abort.” He continued, “It wasn’t until we got below 2,000 feet that we were actually able to look out and view the landing area.” With fuel reserves dwindling, Armstrong reported to mission control, “Pretty rocky area.” Eagle was just 600 feet from the lunar surface. With Armstrong no longer concerned with the program alarms, he could they would land just short of a large rocky crater surrounded by a boulder field of large rocks. He thought that if he could bring Eagle down short of that crater, it would make a good landing area for scientific study. “But it became obvious that I could not stop short enough to find a safe landing area.” Armstrong took manual control and flew over the crater and the rocky area. With fuel nearly spent, he knew he had to set down quickly. Just forty feet above the surface, Aldrin reported “picking up some dust.” Post-flight, Armstrong told NASA officials, “… when we were something less than 100 feet, we were beginning to get a transparent sheet of moving dust that obscured visibility a little bit. As we got lower, the visibility continued to decrease.” Duke, the Capcom, told the Eagle crew only 30 seconds of fuel remained. During his debrief by space agency officials, Armstrong said, “I wanted to make it as easy for myself as I could on that first landing. There’s a lot of concern about coming close to running out of fuel, and I was very cognizant of that. But I did know that if I could have my speed stabilized and attitude stabilized, I could fall from a fairly good height, perhaps maybe forty feet or more in the low lunar gravity, and the gar would absorb that much fall. So I was perhaps less concerned about it than a lot of people watching down here on Earth.” With mission control folks getting nervous, Aldrin reported, “Contact light.” Three seconds later, Armstrong said, “Shutdown.” At 3:17 p.m., on Sunday, July 20, 1969, humankind had landed on another world for the first time. In Houston, Duke radioed, “Roger, Tranquility, we copy you on the ground. You got a bunch of guys about to turn blue. We’re breathing again. Thanks a lot.” Only 30 seconds of fuel remained or 660 pounds of fuel. For comparison, the other five lunar module commanders all landed with roughly 1,100 to 1,200 pounds of fuel remaining. If you want to get a taste of what we felt back on the afternoon of July 20th, 1969, here’s a link to the CBS coverage of the moon landing: https://youtube/watch?v=qj1Rx-w6c6k.
Posted on: Sun, 20 Jul 2014 07:41:05 +0000
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