A planetary base is sort of like a space station on the surface of a planet or moon. The base has a focus on supporting some particular endeavour, such as a Mars Exploration mission, a military base, a planetary defense fortress, a military observation post, a military picket along the neutral zone, a trading post or "factory", a mining operation, the interstellar equivalent of a lighthouse hazard beacon, or something along those lines.
For whatever reason it makes more sense to locate the facillity on the surface of a planet instead of a space station.
The presence of a base may encourage other bases to be established in the same location (see Boomtown). This can grow to the point where the establishment becomes a full fledged colony. This can occur with both a military outpost and with a civilian commercial trading post.
The main difference between a base and a colony is that the members of a colony do not expect to ever leave.
A new base is established with rugged cargo spacecraft that can handle landing in a wilderness or otherwise undeveloped area. If the base is planned to be expanded, adding a spaceport will be a big help (even if it is just an area that has been bulldozed flat). Trading posts will put up warehouses, even if it is just a shack to hold the local product responsible for the the existence of a post on such a forlorn planet. Warehouses are also useful to store the glass beads, iron kettles, or whatever cheap junk that the ignorant natives think is valuable enough to trade for in exchange for the beforementioned valuable local product.
Like any other living system, the internal operations of a planetary base can be analyzed with Living Systems Theory, to discover sources of interesting plot complications.
Figure 2.4.6-1 summarizes the surface elements identified to support Case Study 4. In addition to those identified in the previous case studies (EMU's, Phobos EVA systems, construction equipment, regolith baggers, unpressurized rovers), the list includes many new elements. The surface habitats involve three major life-enabling components: structure, environmental control and life support system (ECLSS), and thermal control system (TCS). The ECLSS is substantially closed to reduce the logistics strain of continuous occupation. A pressurized rover permits extended traverses. Plants use local resources to produce substantial amounts of rocket propellants. Increased power needs are provided by a megawatt-class nuclear power plant.
Figure 2.4.6-2 depicts a concept for the lunar base layout. Primary power is provided by a nuclear plant whose reactor core is shielded by burying it in regolith allowing some freedom to place it near habitat and laboratory areas. Oxygen plants are located some distance away for safety and to isolate dust and contaminants. The liquid oxygen product is stored in buried tanks to facilitate cooling. A permanent landing/launch pad area lies some kilometers from the base to isolate debris lofted by rocket exhaust. Various navigation aids lie along the lander flight path. Support equipment provides services such as refueling and auxiliary power to landers while at the base. Improved roadways ease access between the major areas.
Inflatable/erectable habitat structures are chosen over modules since they provide more volume for a given mass. The inflatable, depicted in figure 2.4.6-3, consists of a spherical pneumatic envelope around a structural cage that supports floors, walls, and equipment. The cage also supports the envelope if pressure is lost. The design assumes that the habitat is inflated to standard sea-level pressure. A 2-m diameter vertical shaft provides access for crew and equipment. The habitat includes two airlocks, one of which is provided by a construction shack module that is connected to the inflatable by a flexible tunnel. The airlocks have front porches to facilitate cleaning and dusting off extravehicular mobility units (EMU's). The lower half of the habitat is buried below the surface and the top half is covered with bagged regolith for shielding from radiation and micrometeoroids. Burying substantially reduces hazards from external radiation. The envelope is a high-strength multi-ply fabric with an impermeable inner layer and a thermal coating outside. The structural frame is a cage of longitudinal and latitudinal curved beams that surround a combination of radial and concentric beams that support the flooring. A 16-m-diameter configuration has four floors and can house 12 crewmembers with total floorspace of 594 m2. If made of a material similar to Kevlar-29, the envelope would be about 5 mm thick and would weigh about 3.3 t. The remaining mass totals about 16.3t and includes the structural frame (9 t), floor (6 t) and walls (1.3t).
Inflatables require more time to set up than pre-outfitted modules. In the current concept, a construction shack module lands near a hole that has been excavated with explosives. After shaping the hole, the inflatable is laid out, anchored, and erected. Covering with regolith is the most time-consuming task and is a prime candidate for automation.
A regenerative ECLSS is necessary for extended-duration missions to avoid prohibitive resupply logistics. The initial lunar ECLSS uses physical and chemical methods to regenerate oxygen and obtain 97 percent closure of the water cycle. ECLSS technology is assumed to evolve so that the Mars ECLSS is bioregenerative with partial closure of the food loop. The martian system uses local resources to make up water, oxygen, and nitrogen losses.
Total ECLSS closure is not feasible. Even the most optimistic estimates for a lunar base envision a bioregenerative system that recycles about 97 percent of the total mass with resupply of gasses lost through leaks and airlocks. The most important material loops are water, gasses, and food. Water is especially important because of its weight: resupply needs are about 0.93 t/yr per person with 90 percent closure and 0.28 t/yr per person with 97 percent closure. To achieve 97 percent closure involves recycling humidity condensates, wash and hygiene water, and urine. A major trade in designing an ECLSS is the cost of closure versus resupply. It is generally more economical to resupply trace substances than to recycle or reproduce them. With this in mind, the basic goals of regenerative ECLSS can be summarized as follows:
a. Keep material losses to a minimum.
b. Recover useful material from waste.
c. Reduce resupply logistics to a minimum.
The first two goals can be accomplished with physical and chemical means. Achieving the third goal requires post-Space Station Freedom ECLSS and/or biological systems.
The TCS provides for passive protection, acquisition, transport, and rejection of latent and sensible heat. Inside the habitat the major heat sources are metabolism and equipment. Since regolith provides good insulation from the surface environment, the major problem is heat rejection. To handle the drastic temperature variations in a lunar day, a cascaded vapor cycle system is envisioned. Two loops provide adequate heat rejection during the day when temperatures can reach 130°C and a bypass is provided to prevent over rejection at night when temperatures can fall below -150°C The system provides final rejection temperatures of 43°C and 67°C to reject both the metabolic and equipment heat-loads during the day and provides a final rejection temperature of-11 °C to reject the heat loads during the lunar night.
Radiation protection is a major concern for long-term habitation of extraterrestrial surfaces. The major hazards are from solar flares and lengthened exposure to galactic cosmic radiation (GCR). Solar flares occur sporadically and are roughly correlated with the sunspot cycle. GCR contains many more energetic particles man solar flares but at substantially lower fluxes. Solar flares can be lethal over short time periods whereas GCR presents a more long-term hazard. Shields of bagged regolith about 50-100 cm thick have been estimated to achieve a tolerable radiation environment for solar events. The shields also suffice for protection from micrometeoroids which generally penetrate only a few centimeters. Current GCR models are not yet adequate for predicting long-term shielding needs. With such coverings the habitats provide an adequate haven during a solar storm. EVA crew are at risk unless they can retreat to the habitat or some temporary haven. A regolith bagger provides for constructing temporary radiation shelters for crew when far from the base shelter such as during an extended traverse in the pressurized rover. Since the regolith bagging and stacking process can take a significant amount of time, it must be started somewhat before a solar storm.
Currently the ability to predict solar flares is somewhat limited, and warnings are best provided by surveillance of the sun. Warnings of solar storms may be as short as half an hour. Earth-based support can also be limited or nonexistent; for example, when Mars is on the opposite side of the Sun from the Earth. Improved ability to predict solar storms can reduce risks to crew since operations can be restricted during high alert periods. Radiation protection garments provide emergency partial protection when the crew does not have enough time to return to the habitat or construct a haven. The period of maximum flux of a solar storm is often on the order of a few hours. In such situations these garments give enough protection to limit exposure to tolerable levels for short periods of time. Such garments could consist of about 3 inches of multilayered carbon fiber and provide about 8 grams per square centimeter of shielding. This would reduce the dose rate of a solar flare by a factor of five to seven times that of an unshielded suit. During an event like the 6-hour peak of the August 1972 storm, one of the largest on record, they would allow for an emergency dose of about 10-15 rem as compared to 72 rem. However, they could not support an entire flare period but would give crew added time for more appropriate measures.
Including one propellant plant (150 t LOX/yr), base power needs are estimated to be in the 700-900 kWe range. Nuclear plants are favored at higher power levels because of their reduced mass. The lunar design envisions an SP-100-type reactor deployed in a cylindrical excavation with an aluminum bulkhead for protection from dust. This allows freer placement of the reactor relative to habitats and permits crew maintenance of radiator panels. Six high efficiency free piston Stirling engines running at 91.7 percent of capacity and two reserve engines ensure dependable power generation. Vertical spoke-wheel radiator panels and mercury heat pipes provide waste heat rejection. A PV/RFC power systemprovidesfortheearly base and emergency backup. A nuclear power plant concept for Mars will be determined in FY1989 studies.
The pad area is located several kilometers away to minimize blast effects. Analyses indicate that within 400 m, metal objects will experience significant pitting and glass surfaces will experience damage within 2 km. Permanent pads require surface stabilization such as gravel, paving tiles, or compaction. Gravel created as a byproduct of propellant production is a promising option. Pad markings and navigation aids help pilots and automated landers to find the pads and make precision landings. The devices envisioned are lightweight and contain a transponder, a visual marker, and a light. A retroreflec-tor aids the use of a laser rangefinder. Since operation is infrequent and for short duration, power requirements are minimal. A number of specialized vehicles support pad operations. The construction crane is used to load and offload cargo to the truck. A propellant refill vehicle and power carts service the lander with fuel and auxiliary power.
The use of in situ resources offers great potential for bootstrapping and leveraging growth. FY 1988 activities focused on propellant plants for the surfaces of the Moon, Mars, and Phobos. Each is designed as a self-contained unit that includes its own power supply.
The lunar plant is baselined to use the hydrogen reduction of ilmenite process to produce oxygen from lunar regolith. Ilmenite is an iron titanium oxide whose two chief sources are high titanium basalts and mare soils. The ilmenite content of soils varies: about 7 percent by weight represents a typical value for rich deposits. Basalts can contain substantial ilmenite (the richest Apollo mare basalt samples contained about 33 percent by weight). Since the basalts require substantial crushing and grinding to release the ilmenite particles, the mare soil is preferred. Ilmenite reacts endothermically with hydrogen to produce water, iron, and titanium dioxide. Sufficient reaction rates require elevated temperatures. It has been reported that about 70 percent of the oxygen is removed after one hour at 1000°C. In the envisioned design, automated excavator vehicles mine the ore and deposit it into grizzly scalpers. A continuous conveyor carries the feedstock to the beneficiation process where the slightly magnetic ilmenite particles are removed with high intensity magnetic fields. If basalt feedstock is used, it is crushed, ground, and sorted before separation. Soil feedstock requires additional sorting and larger magnetic separators. Processing is done by feeding the ilmenite through low and high pressure hoppers into a three-stage fluidized-bed reactor. Most of the reaction takes place in the middle bed. Residual solids from the last bed are discarded through a solid gas separator after being used to preheat the material in the first bed. A solid state electrolytic cell dissociates the water into oxygen and hydrogen. The oxygen is liquefied for use as rocket propellant and the hydrogen is recycled. A pilot plant producing about 2 t/mo and powered by PV/RFC with a 35 percent duty cycle (daytime operations and hot standby at night) is estimated to weigh about 22.5 t. A 12.5 t/mo plant using nuclear power on a 90 percent duty cycle is estimated to weigh about 47.5 t.
5.1 POWER SYSTEMS
5.1.1 SP-100 Nuclear Power System Conceptual Design for Lunar Base Applications
The objective of this study was to provide a conceptual design of a nuclear power system using an SP-100 reactor and Stirling engine conversion for use on the lunar surface. System configurations were selected for their ability to enable and/or enhance a lunar base mission. Numerous system components and coupling options were examined and recommended options were chosen for safety implications, high performance, low mass, and ease of assembly.
Background. This conceptual design study was performed as a result of a request from the Propulsion, Power, and Energy Division in the Office of Aeronautics and Space Technology (OAST). The design includes system performance and sizing data, as well as layout rationale. An artisf s rendering of the nuclear power system as it applies to a typical mature lunar base was included as part of the study (figure 5.1.1-1). Because of obvious implications to the Office of Exploration (OEXP) case studies, the conceptual design study was extended to provide an evaluation of nuclear power system impacts on an advanced lunar base.
a. Mature lunar base with power requirements in the 700-900 kWe range
b. Presence of rovers for construction and maintenance
c. Advanced technologies, including the SP-100 reactor, free-piston Stirling engines, and mercury heat-pipe radiators
d. Nuclear power system supplies electrical power only; the use of thermal energy from the power system will be examined in future studies
e. Use of lunar-soil shielding designed to meet human safety requirements
This conceptual design was developed using Lewis Research Center (LeRC) experience with the SP-100 reactor and Stirling engines. A critical aspect of the study was to gain an understanding of the lunar environmental conditions and to identify their impacts on the design of the power system. To more fully understand the interactions of a reactor power system with a lunar base, a possible mature lunar base concept was defined with the assistance of the OEXP Surface Systems Integration Agent. The study was a 3-month in-house effort of LeRC's Advanced Space Analysis Office (ASAO) and Power Technology Division (PTD).
Lunar Base Assumptions. The lunar base concept is derived from studies performed at the Johnson Space Center. The central core of the base is comprised of two inflatable, spherical modules for habitation and scientific research. These modules are partially buried and shielded from cosmic radiation. Adjacent to the inflatable structures is a rover storage and recharging facility. The inflatable modules and rover facility can be seen in figure 5.1.1-1 in the upper right corner.
A lunar soil processing plant producing oxygen is located approximately 5 kilometers from this habitation area. Lunar soil is transported to this plant after it has been collected from a nearby mining site. A launch and landing facility is located within a kilometer of the oxygen plant. The proximity of the launch pad to the processing plant enables oxygen for propellant to be delivered quickly to orbit for use in chemically propelled transfer vehicles. The processing plant and landing pad are located in the upper left corner of the figure.
Power Requirements. A solar photovoltaic (PV) power system with regenerative fuel cells is assumed to meet the power requirements of the initial habitat module (25 to 100 kWe). As the base expands to include scientific experimentation, rover recharging, and soil processing, a nuclear power system becomes the most viable means of meeting the higher power requirements.
The processing plant will be the predominant power load. For the purpose of this study, that requirement takes the form of electrical power for electrolysis of water, following a hydrogen reduction of lunar ilmenite. The thermal energy requirements of the processing plant would also be provided by the nuclear power system through electrical resistance heating. For an oxygen production capability of 25 t/m, the plant would require 740 kWe, or 90 percent of the nuclear system output.
The remainder of the electrical power generated by the nuclear system would be distributed to the habitat and science modules for life support, to the science laboratory for experimentation, and to the rover storage and recharging facility.
Nuclear Power System Design. The nuclear power system is designed with an emphasis on safety and reliability. It is shown in the foreground of figure 5.1.1-1. This conceptual design consists of a 2500 kWe SP-100 reactor coupled to eight free-piston Stirling engines. The reactor is identical to the design currently baselined in the SP-100 program, whereas the Stirling engines replace the thermoelectric power conversion system of the present SP-100 design. Two of the Stirling engines are held in reserve to provide engine backup for dependable power generation. The remaining six engines operate at 91.7 percent of their rated capacity of 150 kWe. The design power level for this system is 825 kWe. The system is modular and can be replicated in increments of 825 kWe to meet higher power requirements.
It would also be possible, and perhaps desirable, to replicate this system design and operate the two systems at reduced power levels to meet the 825 kWe power requirement. If one reactor power system needs to be shut down, the other system could compensate for the loss in power. As power requirements increase, the capacity of the systems could be gradually increased to meet the higher power levels.
The Stirling engines are arranged in a spoked-wheel configuration and share a common heat transport manifold with the reactor. Each engine is equipped with a pumped heat-rejection loop connected to a mercury heat-pipe radiator. The radiator panels are arranged in a vertical configuration and extend radially from the Stirling engines. A thermal apron is placed between the panels to reduce the lunar surface temperature and thus reduce the required radiator area. The total mass of the system, including power conditioning and transmission lines, is 20t.
The reactor is located in an excavated cylindrical hole which provides shielding from gamma and neutron radiation. The use of lunar soil eliminates the need to transport heavy terrestrial shielding materials to the lunar surface. A boral bulkhead with a domed cap maintains a dust-free environment for the reactor.
Safe radiation levels are maintained in all directions around the power system. This allows for flexibility in choosing a reactor site. The excavated shield design also allows for periodic maintenance on the system's radiator panels. For this conceptual design, the nuclear power system has been placed 1 km from the habitation area and approximately 4 km from the processing plant.
This is from the US Army's report (Volume I, Volume II) (1959) on Project Horizon about establishing an Army base on Luna by the end of 1966. Apparently the project was not pursued because the US Army could not explain what exactly were the military applications of such a base.
This is from Lunar base synthesis study. Volume 3 - Shelter design Final report, North American Rockwell's study on constructing a lunar base.
Base is composed of eight modules arranged in a closed-loop circular floor plan. Base has 736 cubic meters of space and 232 square meters of floor area. The modules are designed to operate autonomously, but in pairs to improve efficiency. For instance, the three crew modules provide atomospheric and crew services to the lab module, the assembly-recreation module, and the base maintenance module.
The base has an estimated mass of 27,000 kilograms, without supplies.
There are three crew modules. Each houses four crew plus one other major function. Each of the four crew has an individual stateroom with 3.7 square meters of floor. Staterooms have a bunk, desk, chair, and storage closets. The major functions shared in the crew modules are: Command and Control center, Medical facility, Backup galley and backup control center.
The garage module accomodates the prime mover for repair or maintenance. It is also used by the space tug as a shipping container to transport the prime mover (or other mobile unit) to the lunar surface.
The warehouse module is used as a shipping container by the space tug to transport cargo to the base. Then it becomes a general storage module for the base.
The maintenance module provides facilities for the repair and maintenance of all base systems. It has an electronic area, a mechanical area, and a suit area. It also has an EVA port with an airlock large enough to accomodate six spacesuited crew at a time. This inclueds an air shower and multifiltration system to cope with lunar dust. The airlock can connect to the airlock on a prime mover, for shirt-sleeve transfer of crew.
The assembly / recreation module includes the main galley with food preperation and preservation facilities. It also contains a four crew airlock, with dust control. It also can dock to a prime mover for shirt-sleeve transfer.
The base is constructed of lunar base modules. The modules are 9.2 meters long, 4.6 meters in diameter, and have a dry mass of 4,500 kilograms. They have docking ports on each end. Modules are delivered by space tugs and assembled by prime movers.
This is from a Johnson Space Center study focusing on the "wet workshop" concept, re-using the spent fuel tanks as habitat modules. I mean, after all the fuel has been used up, the tanks are not doing anything. Except reducing the payload mass.
Remember that every gram counts, so try to make each gram do double-duty. Every gram you save is an extra gram of payload.