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| A network of sinuous wrinkle ridges as imaged from lunar orbit during the Apollo 15 mission. The low Sun angle causes the ridges to cast shadows so that they stand out; under high Sun they become be very difficult to see. Image credit: NASA. |
Two weeks after the fire's solemn first anniversary, M. Yates, an engineer with Bellcomm, NASA's Apollo planning contractor, completed a memorandum which demonstrated that renewed confidence. In it, he proposed a surface exploration plan for the third Apollo piloted Moon landing mission.
In keeping with the lunar mission nomenclature proposed in Bellcomm's January 1968 Lunar Exploration Program Plan (see "More Information" below), Yates designated the mission Lunar Landing Mission-3 (LLM-3). An "early Apollo" mission, LLM-3 would include a 35-hour stay on the Moon, three three-hour moonwalks by two astronauts, and surface exploration on foot no farther than one kilometer from the LM.
Critical for detailed geologic traverse planning would be the LLM-3 LM's ability to set down within a 200-meter-diameter circle centered on a preselected landing point. LLM-1 and LLM-2 would be counted as successful if they managed to touch down anywhere on a smooth mare (Latin for "sea") within an ellipse with a total area of 235 square kilometers; LLM-3's landing area would total just 0.25 square kilometers.
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| Artist concept of an early Apollo landing site atop a rugged ridge. Image credit: NASA. |
Mare ridges are common features on the dark-hued lunar maria; some mare ridges are faults, where the mare's basaltic crust has shifted, cracked, and rumpled, while others might indicate magma movement just beneath the lunar surface in the past. Yates expected that the crater on the mare ridge would act as a natural drill hole, enabling the astronauts to collect geologic samples from deep inside the ridge which they could not obtain otherwise.
The first moonwalk of the LLM-3 mission would see the two astronauts, in Yates' plan designated A and B, working together to set up an Apollo Lunar Scientific Experiment Package (ALSEP) north of their LM. The LLM-3 ALSEP would include a hand-held drill for collecting subsurface core samples and heat-flow probes for installation in the resulting empty drill holes.
The astronauts would then move south past the LM to the rim of the fresh crater. During the second moonwalk, astronaut B would descend into the crater while astronaut A monitored his activities from its rim. In addition to keeping an eye on his colleague, astronaut A would relay radio signals from B's space suit backpack radio to the LM for transmission to Earth. This would be necessary, Yates wrote, because the crater rim would block astronaut B's radio signals.
In the third and final LLM-3 moonwalk, astronaut B would move westward down a short canyon to the mare floor, then would walk south along the ridge-mare contact. Astronaut A, meanwhile, would walk along the mare ridge crest to keep B in sight and again relay his radio signals to the LM. The astronauts would then meet up and return to the LM via the east rim of the crater.
No Apollo mission explored a mare ridge, and Yates' proposed radio-relay technique was never used. The second Apollo lunar landing mission, Apollo 12, amply demonstrated the pinpoint landing capability Yates rightly deemed crucial for geologic traverse planning by setting down near the derelict Surveyor III lander in November 1969. Apollo 14 (February 1971), the third successful Apollo lunar landing mission, used this capability to land near Cone Crater, a naturally occurring drill hole that permitted astronauts Alan Shepard and Edgar Mitchell to collect samples from deep within the Fra Mauro Formation.
Source
"A Lunar Landing Mission to a Mare Ridge — Case 340," M. T. Yates, Bellcomm, 14 February 1968.
More Information
"A Continuing Aspect of Human Endeavor": Bellcomm's January 1968 Lunar Exploration Program
Robot Rendezvous at Hadley Rille (1968)
An Apollo Landing Near The Great Ray Crater Tycho (1969)
Dear David, this post raises an important question in my mind. Nowadays, such selection of target for scientific exploration is done by committees of senior scientists and undergoes thorough peer reviews by other scientists specialized in planetary science.
ReplyDeleteI know that the Apollo 11 landing site was selected solely to minimize risks and not for its scientific value. I view of this post, I now wonder who selected the areas actually explored by posterior Apollo missions? Was it just a few consultants working for a private company, as you report here (for a mission which did not happen)? Or were these sites selected after thorough evaluation by specialized scientists working in the academic sector, as done today?
Dear David, thanks for this insight about the preparation of Apollo missions. Nowadays such selection of target for scientific exploration is done by committees of senior scientists and undergoes thorough peer reviews by other scientists specialized in planetary science.
ReplyDeleteIf I rember well, the Apollo 11 landing site was selected solely to minimize risks and not for its scientific value. I wonder who selected the areas actually explored by posterior Apollo missions? Was Bellcomm involved as well? Did this choice also involve the academic sector, as is done today?
I went on too long, so had to break this into two parts. Sorry!
DeleteI've sat in on some modern Mars site-selection meetings - the process is still complicated, there's still a bit of back and forth between the scientists and the engineers, and there's still a lot of behind-the-scenes discussion. The tools and imagery have improved dramatically, so there's much less speculation (not that they don't sometimes get it wrong - we're still talking about exploration). I'm given to understand, after discussions with people involved in Pathfinder and the MERs, that the Phoenix and Curiosity site-selection processes were fairly sedate. In particular, the engineers and scientists understand each other better, so there's less acrimony than once there was.
I urge you to have a look at Wilhelms' book in particular. It's a fun read - he has a dry, sometimes sarcastic wit I appreciate - and he's very frank about what he thinks went right and wrong with the various Apollo sites.
dsfp
Simon:
ReplyDeleteThere are a couple of great books that look into site selection during Apollo. David Compton's WHERE NO MAN HAS GONE BEFORE and Don Wilhelms' TO A ROCKY MOON. Both are available online. The best, in my view, is Wilhelms' book, because he was directly involved in Apollo site selection.
I might garble the details a bit here, but this is how it worked (officially it worked a little differently, but in practice it works the way I'll describe, pretty much). There was a big Apollo science & engineering group, a Group for Exploration Planning (GLEP), and the "Rump GLEP." The big Apollo group involved more people and had fewer meetings. The little "Rump GLEP" had lots of meetings. The GLEP was in the middle. The "Rump GLEP" was made up of the fanatics, the long-time lunar scientists, from all over, including NASA HQ, NASA Centers, Bellcomm, USGS, universities, etc. At various times people like Wilhelms', Farouk El-Baz, James Head, Thomas Gold, Harold Urey, etc. participated. The GLEP screened the "Rump GLEP" proposals before they went to the big Apollo planning group. Then the big Apollo planning group came along and ruined everyone's fun. That's because it involved engineers who nixxed sites if they seemed too risky.
There was a whole lot of back and forth between the various groups, lots of behind-the-scenes communication, and plenty of argument and lobbying. It was kind of chaotic, and site choices could change rapidly - for example, if a Lunar Orbiter or Apollo CSM did not or could not get pictures of a top-rated candidate site for the engineering evaluation, it could be dropped. Truth be told, I don't think the entire tale has ever been written up. No one seems to mention Jim Head's proposal that the crater Lade replace Descartes, for example. At least, I don't recall anyone but Head pitching for that site.
Before all that, there was a rapid buildup as new data came in. A couple of NASA groups proposed an Apollo site list as early as 1962. A really long list of candidate sites was prepared at about the same time. 1965 saw the Falmouth meeting, which assumed an elaborate future sequence of lunar missions. The 1967 was a more refined version of that, but included a foreword that basically said NASA couldn't accomplish all the ambitious stuff it proposed. The 1968 Bellcomm Lunar Exploration Plan - of which the study I describe in this post was a part - was a follow-on to that. More conservative, but still hopeful. And then the GLEP/"Rump GLEP" was established. It drew on the previous studies, but tempered its selections (mostly) with some economic and engineering realities.
Apollo 11's site was one of several that might have been visited. Basically, launch slips would slide the launch target westward across the Sea of Tranquillity, Sinus Medii, and Oceanus Procellarum. If Apollo 11 had slipped and thus landed on Oceanus Procellarum, Apollo 12 would have aimed for the Sea of Tranquillity. There was a scientific side to that plan - Tranquillity and Procellarum had different colors (the difference was very subtle), and the scientists wanted to understand what those different colors meant.
When 11 landed long, 12 was redirected to a Surveyor site to demonstrate pinpoint landing. 13 aimed for a natural drill hole in Fra Mauro, 14 actually got there. Then the J missions went for complex sites. I often wonder, had the scientists know that Apollo would get in only six landings, would the target sites have been different - maybe more complex sooner?
So there you have it - a very, very brief account of a very, very complex process. (cont)
Good post.
ReplyDelete