|Cutaway of the Apollo Lunar Module (LM) showing its ascent stage (top) and descent stage (bottom). A total of six descent stages were left on the lunar surface at six separate sites between July 1969 and December 1972. Image credit: NASA|
NASA then ramped up Apollo exploration by stretching lunar surface stay time to three days, upgrading the Apollo lunar suits to permit moonwalks of about seven hours, and providing the astronauts with a Boeing-built lunar "jeep" - the Lunar Roving Vehicle (LRV) - to extend their exploration range. Apollo 15 (26 July-7 August 1971) exploited these new capabilities to survey Hadley-Apennine, a complex site between mountains and a winding rille (canyon). Apollo 16 (16-27 April 1972) was the only mission to land in the heavily-cratered lunar highlands. Apollo 17 (7-19 December 1972) concluded the Apollo Program with a visit to Taurus-Littrow, where Harrison Schmitt, the only professional geologist to explore the moon, found tiny orange glass beads - remnants of ancient volcanic fire fountains - with his feet.
In addition to intensively exploring the selected site, the astronauts would have performed engineering and life sciences experiments, assessed the lunar environment for radio and optical astronomy, and experimented with resource exploitation. The single site revisit missions would have played the role for a permanent lunar base that Project Gemini played for Apollo; that is, it would have enabled NASA to acquire operational skills needed for its next step forward in space.
The Sub-Group's report began by declaring that a 12-man "International Lunar Scientific Observatory" in 1980 could become a new "Major Agency Goal" for NASA following Apollo. The single site revisit missions, it continued, would pave the way to the new lunar goal by demonstrating the value of a permanent base on the moon. The Sub-Group then examined four options for carrying out its single site revisit program, which it labeled 0, A, B, and C. All would employ spacecraft and standard Saturn V launch vehicles the space agency had already ordered for Apollo.
The first of the four options, Option 0, would employ the basic Apollo Lunar Module (LM), which could support two men on the moon for 24 hours and deliver 300 pounds of cargo to the lunar surface. Three Option 0 missions would visit the single site, where their crews would perform a total of six moonwalks on foot and minimal exploration and technology experimentation. The Sub-Group rejected this option out of hand because it would provide NASA with insufficient experience ahead of the 1980 lunar base.
The first Option A mission, scheduled for the fourth quarter of 1971, would see two astronauts conduct from four to six moonwalks and up to four traverses using a rocket-propelled Lunar Flying Unit (LFU) fueled using residual propellants in the ELM-A descent stage. In addition to exploring the single site's geology, the astronauts would set up a "technology package" to assess the moon's "optical environment" for astronomy. They would also deploy exposure samples to test the effects of the lunar environment on materials and coatings that might be used to build the 1980 moon base. When they left the single site in the ELM-A ascent stage to rejoin their lone comrade on board the orbiting Apollo Command and Service Module (CSM), they would leave behind for the next crew tools, the LFU, the exposure samples, and the optical environment package.
The second Option A mission would take place in the second quarter of 1972. The astronauts would carry out six moonwalks and, after servicing the LFU, up to four flying traverses. The LFU would amount to a exposure experiment; it would need to work reliably after being parked at the single site for six months (that is, through six lunar day-night cycles). The astronauts would also set up an "advanced" Apollo Lunar Scientific Experiment Package (ALSEP) and a technology package to assess the lunar environment's suitability for radio astronomy. Between moonwalks, they would perform unspecified biology experiments in the ELM-A cabin. Finally, they would retrieve for return to Earth some of the exposure samples left behind by the first Option A crew.
The third and final Option A mission would reach the single site in the fourth quarter of 1972, six months after the second. Its crew would perform six moonwalks, fly the LFU three or four times on geologic traverses, and observe the Sun using a small telescope they would bring with them to the site. They would also retrieve for return to Earth the remaining exposure samples left behind by the first Option A crew. If necessary, they would service the advanced ALSEP instruments deployed by the second Option A crew.
Option B mission 1 would last six days, during which time its crew would carry out from six to 10 moonwalks and up to four LFU geologic traverses. In addition to twin LFUs, the ELM-B would deliver an advanced ALSEP, geology tools, unspecified "biological colonies," and environment and technology exposure samples. As with the Option A missions, lunar environment experiments would focus on optics and radio.
Option B mission 2 would land in the fourth quarter of 1972 for a three-day stay. Its crew would perform six moonwalks and up to four LFU traverses. The three-day stay time would mean that the ELM-B could carry 750 pounds of cargo; this would include a solar telescope, plant and animal packages, and bioscience supplies. The crew would also examine the exposure samples left by the first Option B crew and service any equipment at the site that needed it.
The third Option B mission would land in the second quarter of 1973 and last for either three or six days depending on the results obtained during missions 1 and 2. Its crew would perform from six to 10 moonwalks and three or four LFU traverses. In addition to technology and astronomy experiments, the astronauts would retrieve and prepare technology and biology packages and exposure samples for return to Earth.
A 2000-pound cylindrical shelter capable of supporting two men on the lunar surface for from 12 to 14 days would constitute the heaviest LPM cargo item. In addition, the LPM would carry a pair of LFUs, tanks of LFU propellants, a "dual-mode" Lunar Roving Vehicle (LRV) capable of being driven by either astronauts on the moon or flight controllers on Earth, a solar furnace for technology and lunar resource exploitation experiments, a 12-inch reflecting telescope, laboratory equipment, bioscience packages, lunar environment exposure sample packages, and an advanced ALSEP.
While the Single Site Working Sub-Group called their unmanned LM an LPM, in fact it more closely resembled an LM derivative Grumman, the LM prime contractor, called an LM Truck. Grumman proposed two LM Truck types - one would carry only cargo atop a descent stage, while the other would carry cargo and a cylindrical shelter. Grumman's LPM would include an LM ascent stage to house the astronauts on the lunar surface, not a cylindrical shelter. Despite this, I will in this post continue to refer to the Sub-Group's unmanned LM derivative for Option C as an LPM.
The first of four Option C missions would see a piloted CSM deliver the LPM to lunar orbit at the beginning of 1973. The Single Site Working Sub-Group wrote that, in general, little CSM orbital science would occur in the single site revisit program. This was because much CSM orbital science was meant to support selection of multiple Apollo landing sites, which the single site revisit missions would make unnecessary. The LPM-delivery CSM would, however, remain in lunar orbit for some unspecified period after the LPM undocked. During that time, its crew would turn a suite of remote sensors toward the moon's surface and deploy a science subsatellite.
Option C mission 2, launched just one month after the LPM delivery mission, would employ a modified ELM designed to remain "quiescent" on the lunar surface while its crew lived in the LPM shelter. Grumman called the quiescent ELM the LM Taxi. Because most of its systems would be made dormant after landing, it would need fewer expendables than an ELM-B, permitting it to carry up to 750 pounds of cargo despite its 12-to-14-day lunar surface stay time. Cargo would include an LFU for transporting the two-man crew to and from the LPM in the event that navigational error caused them to land beyond walking distance.
The Option C mission 2 crew would perform many tests and experiments over the course of from 12 to 20 moonwalks, up to 14 LFU flights, and up to eight LRV traverses during their 12 to 14 days on the moon. Basically, they would accomplish all of the tasks planned for the three Option B missions and more; they would, for example, not only collect rock samples for return to Earth, they would also analyze them in the manner astronauts would at the 1980 moon base. Before returning to the quiescent ELM and blasting off to rejoin the CSM Pilot in lunar orbit, they would reconfigure the LRV for remote-controlled operation and turn it loose under guidance from controllers on Earth to travel tens or hundreds of miles across the lunar surface in a loop that would end back at the single site.
Option C mission 3, in the third quarter of 1973, would see an ELM-B land near the LPM with 750 pounds of cargo. The astronauts, who would live in the ELM-B would conduct from six to 10 moonwalks, four LFU flights, and up to four LRV traverses. In their most notable experiment, they would attempt to extract water from lunar dust and rocks using the solar furnace; if successful, this could lead to production of life support consumables and rocket propellants on the moon, slashing the cost of lunar base resupply. Before they left the moon, they would reconfigure the dual-mode LRV for remote-control operation.
Option C mission 4, a near-carbon copy of mission 3, would land in the first quarter of 1974. The crew would complete any on-going experiments at the LPM, observe the Sun, and retrieve biological colonies and exposure samples. They would also dispatch the dual-mode LRV on its longest remote-controlled traverse yet; because it would not again be driven by astronauts, it would not need to return to the LPM site and thus might wander for hundreds of miles across the lunar surface under the direction of controllers on Earth.
The Sub-Group then summed up "Major Conclusions" of its brief study. Only a few are noted here. The Sub-Group confided that the single site revisit missions could be portrayed as a part of the Apollo Program, not as a costly new program, thus avoiding possible political roadblocks. It also claimed that the single site revisit program would be "strongly identifiable with the public interest," though it did not specify how. Finally, the Sub-Group explained that the program would meaningfully exploit uniquely human capabilities: these included on-the-spot judgement; skilled observation (for example, rapid recognition of significant geological relations); and complex tool-using skills.
|Shortly after liftoff: the descent stage of the Apollo 17 LM Challenger abandoned in the Taurus-Littrow valley. Image credit: NASA|
They also contemplated where NASA might establish its 1980 moon base; the only specific sites they mentioned, however, were the two lunar poles. This was in keeping with the main body of their report, which provided no candidate sites for the single site revisit program. Finally, they sought guidance as to how they should proceed if the single site revisit option received no funding in NASA's Fiscal Year 1970 budget.
Some small movement toward including the single site revisit concept in NASA's Fiscal Year 1970 budget took place; however, most work on the concept ended with the Sub-Group's 4 June 1968 revised report to the LEWG. In retrospect, it seems likely that the concept would have split the lunar science community between those eager for data from as many landing sites as possible as soon as possible and those prepared to wait (perhaps in vain) for the enhanced exploration capabilities that would become available after the 1980 lunar base was established. In any case, it appears unlikely that an Apollo planning option that laid the groundwork for a costly long-term lunar presence could have gained much traction in Washington in 1968; by the time the Single Site Working Sub-Group began its deliberations, the Congress had already displayed a marked lack of enthusiasm for expansive post-Apollo space goals.
Report of the Lunar Exploration Working Group to the Planning Steering Group, revised 30 April 1968
Report of the Single Site Working Sub-Group to the Lunar Exploration Working Group, 22 May 1968 (revised 4 June 1968)
Memorandum with attachment, MTX/Chairman, Lunar Station Subgroup, to Distribution, "Meeting of the Lunar Station Subgroup," 7 May 1968
Memorandum with attachment, MAL/Director, Apollo Lunar Exploration Office to MTX/Rodney W. Johnson, "Lunar Single Site Working Subgroup," 7 May 1968
Apollo News Reference, Public Affairs Office, Grumman, 1969, pp. LMD-4, LMD-6-8
Conversations with Paul D. Lowman, NASA geophysicist and participant in the Single Site Working Sub-Group, at and around NASA Goddard Space Flight Center, Greenbelt, Maryland, Summer 2000
Early Apollo Mission to a Lunar Wrinkle Ridge (1968)
Robot Rendezvous At Hadley Rille (1968)
"A Continuing Aspect of Human Endeavor": Bellcomm's January 1968 Lunar Exploration Program
Rocket Belts and Rocket Chairs: Lunar Flying Units
An Apollo Landing Near the Great Ray Crater Tycho (1969)