In early 1964, President Lyndon Baines Johnson asked NASA Administrator James Webb to plan a future space program based on Apollo hardware. The primary goal was to squeeze the Apollo investment for all it was worth. NASA began to study options for using Apollo hardware for new missions. Progress in 1964 was minimal in part because the space agency was oversubscribed. In addition to creating Apollo spacecraft, launchers, and infrastructure, NASA was preparing Project Gemini, a series of 10 piloted missions meant to teach American astronauts rendezvous and docking and spacewalk techniques required for Apollo Moon flights and to confirm that astronauts could live in space long enough (up to two weeks) to accomplish a lunar mission.
On 18 February 1965, George Mueller, NASA Associate Administrator for Manned Space Flight, told the U.S. House of Representatives Committee on Science and Astronautics that repurposing Apollo hardware would enable NASA "to perform a number of useful missions. . .in an earlier time-frame than might otherwise be expected" and at a fraction of the cost of developing wholly new spacecraft. He explained that NASA's program for applying Apollo hardware to new missions "would follow the basic Apollo manned lunar landing program and would represent an intermediate step between this important national goal and future manned space flight programs." At the time he testified, the first manned lunar landing attempt was slated for late 1967 or early 1968.
Six months later, in August 1965, Mueller established the Saturn-Apollo Applications (SAA) Office at NASA Headquarters. The new organization quickly began efforts to define the SAA Program's hardware requirements and mission manifest. At about the same time, SAA began to be referred to as the Apollo Applications Program (AAP), the name by which it is best known today.
In late January 1966, Mueller wrote to the directors of the three main NASA facilities dedicated to piloted spaceflight — MSC, the Marshall Space Flight Center (MSFC) in Huntsville, Alabama, and Kennedy Space Center (KSC), Florida — to sum up SAA's evolving objectives. He told Robert Gilruth (MSC), Wernher von Braun (MSFC), and Kurt Debus (KSC) that, in addition to readying NASA for its next Apollo-scale space goal — no one knew what that would be in early 1966, though a large Earth-orbiting space station stood near the top of the list — SAA should provide immediate benefits to the American public in areas as diverse as air pollution control, Earth-resources remote sensing, improved weather forecasting, materials science, and communications satellite repair.
|Apollo spacecraft and rockets in 1966. The "Uprated Saturn I" rocket at lower right, used for Earth-orbital missions, would soon be renamed the Saturn IB. Image credit: NASA.
Apollo Lunar Module (LM) prime contractor Grumman suggested that LMs without legs or ascent engines might serve as Earth-orbital and lunar-orbital scientific instrument carriers and mini-laboratories. The company also proposed manned and unmanned LM variants — respectively the LM Taxi and the LM Shelter — for 14-day lunar surface stays. The LM Shelter design took several forms; most carried surface transportation systems (rovers or flyers).
All of these spacecraft would reach space atop Apollo Saturn IB and Saturn V rockets, some of which might be uprated for increased payload capacity. In its early SAA planning, NASA referred to missions by their launch vehicle designations. The second, third, and fourth Saturn V-launched SAA missions were thus called AS-511, AS-512, and AS-513 because they would use the 11th, 12th, and 13th of 15 Saturn V rockets purchased for Apollo. SAA planners assumed that, the moment Apollo achieved its goal of a man on the Moon, all remaining Apollo hardware would be released to the SAA Program.
AS-512 would see a three-man CSM deliver an uncrewed LM Shelter to near-equatorial lunar orbit. The LM Shelter would undock and descend automatically to a preselected landing site. The three astronauts would then return to Earth.
AS-513, the first SAA piloted lunar landing mission, would launch less than three months after AS-512. Two astronauts would land near the LM Shelter in an LM Taxi while a third astronaut remained in lunar orbit on board an Extended Capability CSM (XCSM) with an independent space endurance of 45 days. The surface astronauts would place their LM Taxi in "hibernation" and use the LM Shelter as their base of operations for 14 days of exploration. A lunar day-night period lasts about 28 days at most sites, so if they landed at local dawn they would leave the lunar surface at local dusk.
The SAA Program Office solicited comment on its plans from Bellcomm, NASA Headquarters' Washington, DC-based Apollo planning contractor. On 4 April 1966, Bellcomm engineer P. W. Conrad (not to be confused with astronaut Charles "Pete" Conrad) wrote a brief memorandum in which he proposed that the AS-511 and AS-512 missions be merged.
Conrad wrote that AS-511 did not need an LM Lab: its CSM could carry the cameras, film, sensors, and magnetic tape it would need for lunar-orbital mapping. He noted also that, in the SAA Program plan, the AS-512 CSM would be a mere "escort" for the LM Shelter, leaving its crew with relatively few meaningful duties. A mission in which a CSM bearing mapping instrumentation carried the LM Shelter to the Moon would keep its crew productively occupied, Conrad argued, and would free up a Saturn V, a CSM, and an LM Lab for other SAA missions.
He examined two possible profiles for the combined mission. In the first, which Conrad called "direct descent," the CSM would release the unmanned LM Shelter immediately following the last SPS course-correction burn en route to the Moon. The LM Shelter would fall toward the Moon's Nearside without entering orbit. Fifty thousand feet above its target landing area, it would automatically ignite its Descent Propulsion System (DPS) engine to decelerate, hover until it found a safe spot, and land.
The piloted CSM, meanwhile, would pass over one of the lunar poles and fire its SPS behind the Moon to perform Lunar Orbit Insertion (LOI); that is, it would slow down so that the Moon's gravity could capture it into polar mapping orbit.
As the CSM orbited, the Moon would revolve beneath it. If it were a Block II CSM with 14-day endurance, it would orbit the Moon for from five to eight days. After about seven days, the CSM would pass over half the Moon's surface and map about one quarter in daylight.
If it were an XCSM, it would orbit for about 28 days. After 14 days, it would pass over the entire lunar surface and map half in daylight. At the end of 28 days, it would pass over the entire lunar surface twice and map the entire surface in daylight. At the planned end of its time in lunar polar orbit — or sooner, if some fault developed that required an early Earth return — the XCSM would ignite its SPS behind the Moon to depart lunar polar orbit for Earth.
Conrad's second combined mission profile would see the LM Shelter remain docked to the CSM until some time after LOI. The CSM would ignite its SPS to slow itself and the LM Shelter so that the Moon's gravity could capture the docked spacecraft into polar orbit, then the crew would turn CSM-mounted cameras and sensors toward the moon.
As the CSM and LM Shelter orbited over the lunar poles, the Moon would revolve beneath them, so that within a few days of LOI the LM Shelter's Nearside target landing site would move into position for descent and landing. The LM Shelter would then undock from the CSM and automatically ignite its DPS to begin descent over the Moon's Farside hemisphere about 180° of longitude from its landing site. It would fire the DPS again close to the landing site to carry out powered descent, hover, and landing. The CSM astronauts, meanwhile, would continue their lunar-orbital mapping mission.
Conrad acknowledged that both scenarios had their advantages and disadvantages. Direct descent would require that the LM Shelter carry extra landing propellants, which might limit the mass of exploration equipment and life support consumables it could place on the Moon. This might in turn limit the scope of the two-week exploration it was meant to support. In addition, the LM Shelter's DPS would not be available as an SPS backup or supplement if an abort were declared before LOI or in lunar orbit.
On the plus side, relieving the CSM of the LM Shelter's mass ahead of LOI would reduce the quantity of propellants the SPS would need to expend to accomplish LOI. The mass freed up by reducing the CSM's propellant load could be applied to additional CSM cameras, film, sensors, magnetic tape, and life support consumables.
Retaining the LM Shelter until after LOI would maximize its payload mass, but would also require that the CSM carry more LOI propellants. This might lead to a reduction in the mass that could be devoted to cameras, film, sensors, tape, and life support consumables on board the CSM. On the other hand, the LM Shelter DPS would remain available as a backup or supplement to the SPS at least through LOI and, in almost all cases, for several days thereafter.
The SAA Program evolved rapidly. Conrad's proposal appears, however, not to have exerted much influence on SAA planners.
More consequential by far was the AS-204/Apollo 1 fire (27 January 1967), which killed astronauts Gus Grissom, Ed White, and Roger Chaffee. The fire, which revealed fundamental flaws in Apollo Program quality-control and contractor oversight, undermined support in Congress for NASA and, along with LM development delays, put off the first piloted lunar landing until July 1969. All six piloted Moon landings took place within the Apollo Program, and neither an Apollo lunar polar orbit mission nor a lunar surface stay longer than about three days was accomplished.
The Saturn V rocket designated AS-511 in Conrad's memo launched the Apollo 16 lunar landing mission in April 1972. By then, NASA had changed its designation to SA-511. The SA-512 Saturn V launched Apollo 17, the final lunar landing mission, in December 1972, and SA-513 launched the Earth-orbital Skylab Orbital Workshop, the sole surviving remnant of what had been the SAA Program, in May 1973.
A lunar polar orbiter would have to wait until 1994, when the Ballistic Missile Defense Organization launched the 424-kilogram Clementine spacecraft (25 January 1994). The U.S. Department of Defense spacecraft followed a circuitous route to the Moon, at last arriving in mapping orbit on 19 February 1994. Though it accomplished a science mission, Clementine was conceived as a test of sensors and other technologies that would be used to detect and intercept nuclear-tipped missiles launched against the United States.
In an experiment using Earth-based radar, Clementine found the first indications of hydrogen concentrations in permanently shadowed craters near the Moon's poles. These were widely interpreted as signs of water ice, though the quantity of ice and its exact location could not be reliably determined. Clementine mapped the Moon until 3 May 1994, when it left lunar polar orbit bound for the near-Earth asteroid 1620 Geographos. A malfunction on 7 May 1994 caused Clementine to expend its propellant, however, scrubbing the asteroid flyby.
|Japan's SELENE/Kaguya lunar polar orbiter with one of its two sub-satellites (center right). The spacecraft orbited the Moon from 3 October 2007 through 10 June 2009. Image credit: JAXA.
Since Lunar Prospector, the United States, Europe, Japan, China, and India have all launched automated spacecraft into lunar polar orbit. As of May 2018, however, only one (NASA's Lunar Reconnaissance Orbiter, launched 18 June 2009) still operates. New lunar polar orbiters are, however, in the planning and development stages: for example, the Republic of Korea (South Korea) plans to launch the Korean Pathfinder Lunar Orbiter in 2020.
"Combining Lunar Polar Orbit Mission with an Unmanned Landing, Case 218," P. W. Conrad, Bellcomm, 4 April 1966.
Living and Working in Space: A History of Skylab, NASA SP-4298, W. David Compton and Charles Benson, NASA, 1983.
Korea Aerospace Research Institute: Lunar Exploration (https://www.kari.re.kr/eng/sub03_04.do - accessed 5 May 2018)
Space Station Resupply: The 1963 Plan to Turn the Apollo Spacecraft into a Space Freighter
"Assuming That Everything Goes Perfectly Well in the Apollo Program. . ." (1967)
"A True Gateway": Robert Gilruth's June 1968 Space Station Presentation