Long before NASA reached the moon, the U.S. civilian space agency's managers and engineers began to look at ways of using Apollo lunar hardware in non-lunar and advanced lunar missions. In April 1963, for example, the Manned Spacecraft Center (MSC) in Houston awarded North American Aviation (NAA), prime contractor for the three-man Apollo Command and Service Module (CSM) spacecraft, a contract to study modifying the CSM to serve as a crew transport and logistics resupply vehicle for a 24-man Earth-orbiting space station.
On February 18, 1965, George Mueller, NASA Associate Administrator for Manned Space Flight, told the U.S. House of Representatives Committee on Science and Astronautics that Apollo-derived 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 MSC, the Marshall Spaceflight Center (MSFC), and Kennedy Space Center, the three main manned space centers, to sum up SAA's evolving objectives. He told them that, in addition to preparing NASA for its next Apollo-scale space goal - whatever that might be - SAA would provide immediate returns in areas as diverse as air pollution control, Earth-resources remote sensing, improved weather forecasting, materials science, and communications satellite repair.
By March 1966, the SAA Program Office had compiled a list of potential new missions for Apollo hardware. From MSC and NAA came proposals for CSM missions in low-Earth orbit (LEO), geosynchronous orbit, and lunar orbit. MSFC, drawing on plans put forward by its director, Wernher von Braun, proposed that spent Saturn IB S-IVB second stages serve double-duty as pressurized "workshops" in LEO. Apollo Lunar Module (LM) prime contractor Grumman suggested that LMs without legs or ascent engines serve as scientific instrument carriers and mini-laboratories. The company also proposed manned and unmanned LM variants - respectively the LM Taxi and the LM Shelter - for two-week lunar surface stays. 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 SAA missions by their launch vehicle designations. The second, third, and fourth Saturn V-launched SAA missions were 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, as soon as Apollo achieved its goal of a man on the moon, all remaining Apollo hardware would be released to the SAA Program.
AS-511 would be a CSM-LM Lab mission to map the moon from lunar polar orbit. Its three-man crew would operate cameras and mapping sensors mounted on the LM Lab.
AS-512 would see a manned CSM deliver an unmanned LM Shelter to near-equatorial lunar orbit. The LM Shelter would undock and descend automatically to a pre-selected landing site. The three astronauts would then ignite their CSM's Service Propulsion System (SPS) main engine to leave lunar orbit and return to Earth.
AS-513, the first SAA manned moon landing mission, would launch less than three months after AS-512. Two astronauts would land in an LM Taxi near the LM Shelter while a third astronaut remained in lunar orbit on board an Extended Capability CSM (XCSM) with a total space endurance of 45 days. The surface astronauts would place the LM Taxi in "hibernation" and use the LM Shelter as their base of operations for 14 days of exploration.
The SAA Program Office solicited inputs on its plans from Bellcomm, the NASA Headquarters advance planning contractor. On April 4, 1966, Bellcomm engineer P. W. Conrad completed a brief memorandum in which he proposed that the AS-511 and AS-512 missions be merged to form a single mission.
Conrad wrote that AS-511 did not in fact 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, CSM, and 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 course-correction burn en route to the moon, which would be carried out by firing the SPS. The LM Shelter would fall toward the moon without entering orbit. Fifty thousand feet above its target landing area, it would automatically ignite its Descent Propulsion System (DPS) to decelerate, hover, and land.
The manned 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, to slow down so that the moon's gravity could capture it into polar mapping orbit. If it were a Block II CSM with 14-day endurance, it would orbit the moon for from five to eight days, permitting it to image up to half the lunar surface. If an XCSM, it would orbit for up to 28 days, allowing it to pass over the entire lunar surface twice.
As the CSM orbited, the moon would slowly revolve beneath it, so that its ground track would not repeat for at least 14 days; that is, until half a lunar day-night period had passed. The mission would be timed so that the CSM and the terrain it mapped would remain in daylight throughout the lunar-orbit portion of the mission. At the planned end of its time in lunar polar orbit - or sooner, if some fault developed that required an early Earth return - the CSM would ignite its SPS behind the moon to begin its journey back to 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, the moon would revolve beneath them, so that within a few days of LOI the LM Shelter's target site would move into position for a landing. The LM Shelter would then undock from the CSM over the moon's Farside hemisphere and automatically ignite its DPS roughly 180° of longitude from its Nearside landing site to begin descent. 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.
Both scenarios had advantages and disadvantages, Conrad acknowledged. 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 demand more LOI propellants for the SPS. 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, and the many changes it underwent have never been fully documented. Conrad's proposal appears, however, not to have exerted much influence on SAA planners.
More consequential by far was the Apollo 1 fire (January 27, 1967), which killed astronauts Gus Grissom, Ed White, and Roger Chaffee. The fire, which revealed fundamental flaws in Apollo management and design, undermined support in Congress for NASA and, along with LM development difficulties, delayed the first manned lunar landing until in July 1969. All six manned moon landings took place within the Apollo Program, and no Apollo lunar polar orbit mission or surface stay longer than about three days was carried out.
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 Skylab Orbital Workshop, the sole surviving remnant of the SAA Program, in May 1973.
References:
Combining Lunar Polar Orbit Mission with an Unmanned Landing, Case 218, P. W. Conrad, Bellcomm, Inc., April 4, 1966.
