|Homeward bound: an Orbital Transfer Vehicle (OTV) bearing a returning lunar base crew aerobrakes in Earth's atmosphere. After aerobraking it will rendezvous with the NASA space station. Image credit: Pat Rawlings/NASA|
SAI explained that its study used a four-step approach. First, the study team judged which science and technology disciplines could best be served by an LEO space station and which by a lunar base. Next, the team developed a lunar base conceptual design capable of serving the disciplines it identified. It then developed a transportation system concept for deploying and maintaining its base. Finally, the team estimated the cost of its lunar base.
The team identified five science and technology disciplines that would be better served by a base on the moon than by a space station. The first was radio astronomy. Bowl-shaped radio telescopes might be built in bowl-shaped lunar craters, SAI wrote. Radio astronomers might take advantage of the moon's Farside (the hemisphere turned permanently away from Earth), where up to 2160 miles of rock would shield their instruments from terrestrial radio interference. The 238,000-mile separation between lunar and terrestrial radio telescopes would permit Very Long Baseline Interferometry observations, enabling astronomers to map minute details of galaxies far beyond the Milky Way.
|A bowl-shaped crater makes an ideal site for a bowl-shaped radio telescope. Visible stars are artist's license; the harsh glare of the Sun in lunar daylight would banish them from view. Image credit: NASA|
Lunar geology (which SAI called "selenology") would obviously be better served by a lunar base than by a space station. SAI noted that, despite 13 successful U.S. robotic lunar missions and six successful Apollo landings, the moon had "barely been sampled and explored." Lunar base selenological exploration would focus on "understanding better the early history and internal structure of the Moon" and "exploring for possible ore and volatile deposits." Selenologists would rove far afield from the base to measure heat flow and magnetic properties, drill deep into the surface, deploy seismographs, and collect and analyze rock samples.
SAI's fourth lunar discipline was resource utilization. The study team noted that samples returned to Earth by the Apollo astronauts contain 40% oxygen by weight, along with silicon, titanium, and other useful chemical elements. Lunar oxygen could be used as oxidizer for chemical-propulsion spacecraft traveling between Earth and moon and from LEO to geosynchronous Earth orbit (GEO). Silicon could be used to make solar cells. (SAI pointed out, however, that the two-week lunar night would make reliance on solar arrays for electricity "somewhat difficult.") Raw lunar dirt - known as regolith - could serve as radiation shielding. If water ice were found at the lunar poles - perhaps by the automated lunar polar orbiter SAI advised should precede the lunar base program - then the moon might supply hydrogen rocket fuel as well as oxidizer.
SAI's fifth and final lunar base science discipline was systems development. The team expected that lunar base technology development would be "devoted to improving the efficiency and capabilities of systems that support the base," such as life support, with the goal of "reduced reliance on supplies sent from Earth." Transport system development might include research aimed at developing a linear electromagnetic launcher of the kind first proposed by Arthur C. Clarke in 1950. Such a device - often called a "mass driver" or "rail gun" - might eventually launch bulk cargoes (for example, lunar regolith, liquid oxygen propellant, and refined ores) to sites all around the Earth-moon system.
The SAI team noted that some disciplines might be served equally well by a lunar base or an Earth-orbiting space station. Large (100-meter) telescopes for optical astronomy, for example, might be equally effective on the moon or in Earth orbit. The moon, however, would offer a solid surface that might enable the "pointing stability and optical system coherence" such a telescope would need to perform adequately.
SAI acknowledged that its report proposed "research and development activities. . .too numerous and often too difficult for a first-generation lunar base." It thus divided activities within the five lunar base disciplines into two categories: those suitable for its first-generation base and those that would need a more elaborate second-generation facility. First-generation radio astronomy, for example, would use two small dish antennas on Nearside (the lunar hemisphere facing Earth). In the second generation, a 100-meter-diameter antenna would operate on Farside.
Having defined its lunar base science program, the SAI team moved on to the second and third steps in its study. The team assumed that NASA's Space Shuttle, which at the time they wrote had just completed its ninth flight (STS-9/Spacelab 1, 28 November-8 December 1983), would form part of the lunar base transportation infrastructure, along with an LEO space station. The Shuttle would cheaply and reliably deliver lunar base crews, spacecraft, and cargo to the station, where they would be brought together for flight to the moon. SAI proposed reapplying hardware developed for the LEO station - for example, pressurized modules - to the lunar base program.
An October 1984 paper by study participants Steve Hoffman and John Niehoff for the first Lunar Bases and Space Activities of the 21st Century symposium provided additional details of SAI's Earth-moon transportation system and surface base design. Where details in the October 1984 paper conflict with those in the December 1983 report, the description that follows defaults to information contained only in the latter (mostly).
SAI's lunar transportation system would include three types of spacecraft. The first, the reusable Orbital Transfer Vehicle (OTV), would be a two-stage vehicle permanently based at the LEO station. SAI assumed that NASA would develop OTVs for moving cargoes between the LEO station and higher orbits (for example, GEO) and that this basic OTV design would then be modified for lunar base use. The OTV, which would operate as a piloted spacecraft through addition of a pressurized "personnel pod," would deliver up to 16,950 kilograms of crew and cargo to lunar orbit.
An OTV-derived four-legged lunar lander would form the basis of two vehicles: the Logistics Lander and the Lunar Excursion Module (LEM). The former would include a removable subsystem module for automated lunar landings. The latter would carry a personnel pod for piloted flight. These were listed as the second and third spacecraft in SAI's lunar transportation system, though one might argue that they were actually tricked-up OTVs.
|SAI's one-way cargo lunar flight mode. Please click to enlarge. Image credit: Science Applications, Inc.|
For two-way crew sorties, the OTV first stage would operate as during a one-way cargo mission. After a three-day flight, the OTV second stage/personnel pod combination would ignite its engines to slow itself so the moon's gravity could capture it into lunar orbit. There it would dock with a waiting LEM carrying lunar base astronauts bound for Earth, who would trade places with the new base crew. In addition to the new crew, 12,750 kilograms of propellants (sufficient for a round trip from lunar orbit to the surface base and back again) and up to 2000 kilograms of cargo would be transferred from the OTV second stage/personnel pod to the LEM.
|SAI's roundtrip crew rotation lunar flight mode. Please click to enlarge. Image credit: Science Applications, Inc.|
SAI's base buildup sequence would begin with a pair of Site Survey Mission flights. The first would see an unpiloted LEM with empty propellant tanks placed into lunar orbit through a variant of the crew sortie mode. An automated OTV second stage bearing the LEM in place of a personnel pod would enter lunar orbit, undock from the LEM, and return to Earth.
The second Site Survey Mission flight would employ another variant of the Crew Sortie mode. Five astronauts would arrive in lunar orbit on board an OTV second stage/personnel pod and dock with the waiting LEM. The four astronauts of the base site survey team would transfer to the LEM along with propellants and supplies. They would then undock and land at the proposed base site, leaving the OTV pilot alone in lunar orbit. After completing their survey of the site, they would return to the OTV second stage/personnel pod, then would undock from the LEM and return to Earth orbit.
Assuming that the base site checked out as acceptable, Flight 3 would see the start of base deployment. A Logistics Lander would employ Direct Descent mode to deliver to the base site an Interface Module and a Power Plant. The Interface Module, which would be based on LEO space station hardware, would include a cylindrical airlock, a top-mounted observation bubble, and a cylindrical tunnel with ports for attaching other base modules. SAI's proposed Power Plant was a nuclear source capable of generating 100 kilowatts of electricity.
Flight 4 would deliver two "mass mover" rovers, two 2000-kilogram mobile laboratory trailers, and a 1000-kilogram lunar resource utilization pilot plant. The rovers would tow the mobile labs up to 200 kilometers from the base on selenologic excursions lasting up to five days. The mobile labs would carry instruments for microscopic imaging, elemental and mineral analysis, and subsurface ice detection, stereo cameras, and a soil auger or core tube for drilling up to two meters deep. The first-generation lunar resource utilization pilot plant would process 10,000 kilograms of regolith per year to yield oxygen, silicon, iron, aluminum, titanium, magnesium, and calcium.
Long-term occupation of the moon would begin with Flight 9, a crew sortie mission that would deliver a four-person construction team. Flight 10 would see three more astronauts join the construction team, bringing the total base population to seven. The OTV pilots for these flights would return to Earth alone after the construction teams undocked and landed at the base in their respective LEMs.
Using the mass mover rovers, the base crew would unload the Logistics Landers and join together the base components. The completed base would provide seven astronauts with 2000 cubic feet of living space per person. They would attach the Lab, Hab, and Resource Modules to the Interface Module, then would link the resource utilization pilot plant to the Lab Module.
Flight 11, the first base crew rotation flight, would see the four-person construction team that arrived on Flight 9 lift off in a LEM and return to lunar orbit, where they would dock with an OTV second stage/personnel pod combination just arrived from Earth. The Flight 9 lunar base team would trade places with them and, following LEM refueling and cargo loading, would descend to a landing at the base. The first construction team and the Flight 11 OTV pilot would then return to the LEO station. On Flight 12, a three-person base team would replace the Flight 10 team.
Lunar base teams of three or four astronauts would rotate every two months. The typical base complement would include a commander/LEM pilot, a LEM pilot/mechanic, a technician/mechanic, a doctor/scientist, a geologist, a chemist, and a biologist/doctor.
|Mass mover rover in the field with advanced power cart and deep drill rig. Image credit: NASA|
Although the OTV would find uses in LEO and GEO, SAI charged all of its development and procurement costs (a total of $7.2 billion) to the lunar base. The expendable Logistics Lander and reusable LEM would cost $6.6 billion and $4.8 billion, respectively. The LEM, though structurally beefier and more complex, would cost less because the Logistics Lander would bear the development cost of systems common to both landers.
Based on optimistic NASA pricing, the SAI team assumed that a Shuttle flight would cost $110 million in 1990. The 89 Shuttle flights in the lunar base program would thus cost a total of $9.8 billion. The LEO station, by contrast, would need only 17 Shuttle flights at a cost of $1.9 billion. SAI placed total LEO station cost plus three years of operations at $14.2 billion. Lunar base cost plus three years of operations came to $54.8 billion.
To conclude its report, SAI noted that both the LEO station and the lunar base could be completed in about a decade. The LEO station would, however, serve a broader science user community and would provide an OTV base in LEO for eventual lunar base use. The SAI team argued that the LEO station was a reasonable near-term (10-year) objective, while the lunar base would yield obvious benefits in a long-term (50 years) space program. It added that the
Space Program will function best if it has both near-term objectives and long-range goals. The near-term objectives assure [sic] that we progress with each year that passes. The long-range goals provide direction for our annual progress. The Space Station and Lunar Base appear to serve these respective roles at the present time.Sources
A Manned Lunar Science Base: An Alternative to Space Station Science? A Brief Comparative Assessment, Report No. SAI-84/1502, Science Applications, Inc., 10 January 1984
"Preliminary Design of a Permanently Manned Lunar Surface Research Base," S. Hoffman and J. Niehoff, Science Applications International Corporation; published in Lunar Bases and Space Activities of the 21st Century, "papers from a NASA sponsored, public symposium hosted by the National Academy of Sciences in Washington, D.C., Oct[ober] 29-31, 1984," W. W. Mendell, editor, Lunar and Planetary Institute, 1985, pp. 69-75
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