Moon Miners' Manifesto

#108 September 1997

Concept Papers of Seattle Lunar Group Studies

Autonomous Free Flying Robots for Zero-G Space Structures
Another Use for a "Space Elevator"
Magnetic Solar Wind Collector
Using Structural Steel on the Moon
Storing Energy for Lunar Nighttime Use
Sunwatch Satellites
Variety in Biological Life Support Systems
Response to SEI & Stafford Commissions

[A Major Contribution of Seminal Concept Papers to MMM. These are the work of a significant brainstorming group in Seattle which has continued over a span of many years. MMM thanks David Graham and Hugh Kelso for permission to reprint these papers. The first two installment were published in MMM #s 106-107. We will finish republication of these papers in in this issue.]

[Whether the paper was in response to a request for input for the Space Exploration Initiative (SEI) or for the Stafford Commission, is indicated in the byline for each.]

Autonomous Free Flying Robots for Zero-G Space Infrastructures
(Stafford) by Joseph P. Hopkins, Jr.
A series of robots that are autonomous and free flying need to be developed to perform tasks external to zero-g space structures. These robots would be targeted to perform repetitive, hazardous, and simplistic tasks. On manned missions they would also serve as `gofers' and assistants for astronauts performing EVA tasks.

These robots would be comprised of cameras, manipulators, sensors, a communications package, a propulsion/power system, and an on-board expert system computer. The robots will require a software architecture that is a hybrid permitting full autonomy or teleoperation. Computers that are inside the structure or Earthbased would have scheduling, simulation, and teleoperation programs that would support the dispersed robotic systems.

These robot systems would increase crew productivity by reducing the amount of time required for EVA on routine and frequently occurring tasks. The robots can perform tasks that are day-to-day, predictable, well-defined, repetitive housekeeping chores. These tasks, examples which include inspecting the exterior for damage or wear and removing contamination from exterior surfaces, do not represent an optimal use of crew time when performed through EVA. Also they would perform hazardous functions thereby reducing risks to the crew.

Another set of routine tasks within the capability of these robots is experiment support. Many instruments used in space experiments will require routine servicing such as replenishing consumables, replacing focal plane instruments, changing film canisters or optical filters, and placing or retrieving material samples. While similar in required capability to the housekeeping tasks, these tasks are not as basic to robot services because they are not as routine. That is; the task requirements will change from experiment to experiment and the planning and robot programming for the task will probably have to be done on-station. Therefore, savings in crew time is not as great as for automating housekeeping functions. These tasks will also depend on the existence of task-oriented planning software for the robots.

In addition to performing critical and routine tasks, robots may also serve as crew assistants. A mature robot could be used as an assistant to a human crew member in addition to performing tasks autonomously. These capabilities could reduce the frequency or duration of EVA or reduce the number of crew members needed for some EVA tasks. One of the simpler crew support applications possible with a rudimentary robot system, is to use a robot to provide a remote view of a potential EVA site. The Space Shuttle has used a TV camera mounted on the remote manipulator for a similar application.

Development of these robots could be undertaken on low Earth orbit space stations, where when successfully deployed they would go a long way toward contributing to productivity and safety. On Mars bound missions robots would off-load many routine EVA functions. Robot programming languages, sensors, manipulator end-effectors, the operator/ system interface, and autonomous logic systems are among some of the areas in which advances must be made. The resulting technologies would find many Earth bound applications in such diverse fields as: industry, hospitals, the home, agriculture, hazardous materials handling and the military.

Another Use for a "Space Elevator"
(Stafford) by Stan Love
A popular concept for a device that can easily loft great quantities of material from the Earth's surface to orbit is a "space elevator," essentially a cable linking a point in geosynchronous orbit with a point on the Earth's equator. Cargo can be shuttled up and down a space elevator much more simply and safely than by using chemical rockets. Such a system is far beyond current materials and engineering capabilities, but has nonetheless received much attention in popular literature.

In the classic setup, the weight of the cable is counterbalanced by a large mass suspended outward of geosynchronous orbit. This mass, forced to move at greater than orbital velocity, exerts an outward force balancing the inward force of gravity on the parts of the cable that are below geosynchronous orbit. A superior design, however, might be to simply extend the cable outward until its own mass balances on both sides of geosynchronous orbit. The total length of the cable becomes on the order of 145,000 km, and the entire construction can then act as a very large rotating tether. A payload attached to the cable by a ring and pushed outward from geosynch altitude will pick up speed as it slides outward, finally leaving the end of the cable at a velocity of about 11 km/s relative to the center of the Earth. Since escape speed from the Earth is only 2.3 km/s at that distance, packages could be sent anywhere in the inner solar system without the use of propellant, simply by pushing them down the cable at the right time.

Given the technology necessary to build a space elevator, this concept could be realized with little additional effort. Care would have to be taken to let the cable "relax" after each load, since accelerating a payload might cause it to bow backwards, and oscillate for some time after the payload departed. The effects of tides (this cable would reach almost halfway to the Moon, and be in a plane offset by 23 to 30 ° from the Moon's orbital plane) on the cable would also have to be taken into account.

Magnetic Solar Wind Collector
(Stafford) by Stan Love
The idea of using magnetic fields to direct the flow of space plasmas has had considerable attention in popular literature, particularly in connection with the Bussard ramjet, a concept which uses an enormous magnetic field to "scoop" the interstellar medium into a fusion motor to provide a continuous source of fuel for a missions to other stars. A version of this idea could be used to provide a source of hydrogen for use on the Moon. The Moon does not possess a ready supply of this vital element.

The flux of solar wind particles through the Moon's cross-sectional area is roughly 5 grams per second. These particles are primarily (about 80 percent by mass) protons and electrons, but there is also a smaller population of the nuclei of helium, carbon, oxygen, nitrogen, and other elements.

Since all the particles in the solar wind are charged, their flight can be deflected with a magnetic field. A field capable of channeling the solar wind around an area 700 km in diameter is probably within reach of current technology (Andrews, D. G. and Zubrin, R. M., "Progress in Magnetic Sails," AIAA Paper 90-2367,1990). The diameter of the Moon is only a factor of 5 larger than this.

Channeling the solar wind material onto some sort of collector, and recovering it from that collector would be a tough, but probably not insurmountable, problem. If the magnetic field is generated with a superconducting loop, power will be required only to set up the field, but not to maintain it. It may take several smaller magnetic fields to focus the particles trapped in the main field onto the collection surface.

This system, operating at perfect efficiency, could conceivably provide a lunar base with as much as 300 kilograms of hydrogen per day, enough to meet the needs of even a very wasteful colony. Although the efficiency of a real system would doubtless be much lower than unity, hydrogen is so scarce on the Moon and has so many applications in space travel (notably as a fuel cell reactant, a propellant, and for water) that it might well be worth the effort of constructing such a system to capture it.

Using Structural Steel on the Moon
(Stafford) by Hugh Kelso, Bob Lilly, Mike Anderson, David Graham, Robert Taylor, Kent Karnofski, Joe Hopkins, Stan Love
It is widely accepted that large lunar bases will be built using local materials. Aluminum, steel, titanium, concrete (lunarcrete) and glass/glass composites have all been proposed as possible primary structural materials. Steel is the better choice for reasons of superior durability and availability. Steel and aluminum are easier materials to work with than the others and it is much easier to manufacture usable billets. In comparison with aluminum, steel is the better material choice in terms of overall strength, ease of production using well-established technologies, and reduced energy requirements.

Aluminum alloys have received considerable attention in lunar base designs, which may be a carry-over from the orientation aerospace designers have had in designing lightweight spacecraft/aircraft. On the Moon , however, the weight of structures is not a primary design consideration. Other factors, such as abundance of material, durability, and ease of refining, manufacture, erection and construction are more important.

Steel could be made using iron existing in the lunar regolith. In order to create lunar steel, it may be necessary to import certain trace elements, such as carbon and nickel. The quantities required will be only a fraction of the total mass of steel produced: 0.55 percent for ASTM A 36.

Steel is the material of choice for large structures on Earth. The technologies for producing and building with steel are widely known, and the building codes for it are well established. Steel is readily produced in standard structural shapes. By avoiding the expense of creating new materials and learning new technologies, costs can be reduced.

Thermal expansion will play an important role in construction. During the lunar day the temperature reaches 110° C and at night drops to -170° C. Material expansion coefficients must be considered, particularly if different structural materials are to be used in the same structure. At the very minimum, construction must be carried out at a relatively constant temperature, perhaps under some sort of shade awning. The thermal expansion rates of steel and lunarcrete are very close, an important advantage considering the benefits of using lunarcrete in conjunction with metal structural elements.

How the structural material responds to the frequent internal pressure variations must be considered. The operation of air locks and atmosphere recycling systems may cause pressure cycling in the structure. Steel has an excellent fatigue resistance shared by few other metals. Specifically, for strain less than half the yield strength, an infinite number of load cycles may occur without any fatigue effect. The fatigue resistance of steel helps to insure structural integrity for longer periods of time. A lunar base constructed of steel could be expected to last decades longer than one built of aluminum.

The amount of energy required to produce the structural materials must also be considered. Reduction of iron from oxide requires 1/6 the energy per unit mass that is required to reduce aluminum. Also, iron oxide can be reduced using simple heat treatment, whereas the breakdown of aluminum oxide requires a more complicated and less efficient electrolysis process.

Steel can also be used for secondary structural purposes: Partition assemblies, hardware needs, fasteners (screws, bolts, etc.). Once basic processing and mining/refining technologies are set up to produce steel, various tooling machinery can be brought up to expand the variety of items manufactured on the Moon.

Storing Energy for Lunar Nighttime Use
(Stafford) by Dean Calahan
Night phase energy supply is a critical element of Lunar Base design concepts. Two approaches are on-site production and offsite production and transmission (for example, Solar Power Satellite). Of on-site choices, storage of day phase solar heat for power conversion at night has received some attention, but a complete analysis of the opportunities available has not been accomplished. This submission proposes helping to fill that gap in knowledge by examining the opportunities available from storing heat in vaults of regolith or regolith-derived materials. This method will be called DPES for Day Phase Enthalpy Storage.

DESCRIPTION: During Lunar day, focused Solar radiation heats a large mass of high-enthalpy powder contained in an insulated vault. At night, a working gas is pumped through the vault and cycled through a heat engine, generating power for local use. The waste heat must be dumped, either radiatively or into a heat sink of some kind, perhaps a vault of rego-lith cooled radiatively during day phase. Possibly the heat could be dumped into the local regolith environment.

The enthalpy storage mass (regolith or locally manufactured material) and working gas (oxygen) are produced locally. In addition some low-tech parts might also be manufactured at the base. The heat engine and difficult-to-make parts (for example a liquid-drop radiator) might have to be supplied from Earth.

PAYOFF/VALUE: DPES, built primarily from locally available materials, avoids the problem of shipping most of the mass of the energy storage/generation facility from the surface of Earth. For a first- or second- generation base, the nuclear, fuel-cell, and SPS options require most or all of their mass to be supplied from Earth. A power supply system constructed locally increases the self-sufficiency and ease-of-expansion of a Lunar base.

ENABLING TECHNOLOGIES: Lunar construction techniques must be up to the job of building sealed, insulated vaults of regolith. Techniques of radiating or sinking the waste heat must be developed.

SunWatch Satellites
(Stafford) by Stan Love
As manned missions in the solar system become commonplace, it may become necessary to have good and continuous knowledge of the conditions on the surface of the sun, particularly with regard to solar flares. The sun rotates once every 25 days, bringing different areas into view constantly, and violent changes can occur on the surface in minutes or hours. The charged particle emissions of flares and other active regions on the sun can change unpredictably, and missions and installations without superb radiation shielding will benefit greatly from current "weather reports" on solar activity. Each separate crew could obtain this information by training telescopes on the sun and keeping a constant watch on it. A more elegant solution to the problem might be to deploy a small number of solar observatories in orbit about the sun.

A solar "weather satellite" network could be achieved with only two small telescopes, placed in orbit about the sun, 120° ahead of and behind the Earth in its orbit. The change in velocity necessary to emplace them would be on the order of 1 km/s, once escape from Earth is achieved. Since halo orbits of the sort required here are not stable, the observatories would require a small amount of station keeping propellant, and periodic refueling. Every point on the Sun could be monitored by at least one satellite or by telescopes on the Earth, and the Earth would always be in direct line-of-sight communication with each satellite. Adding one more satellite and spacing them by 90° would give redundant coverage of the entire sun by at least two observatories. The current conditions on the sun, or at least warnings of dangerous flares, could be then compiled at Earth and transmitted, either from Earth or from one of the observatories, to spacecraft and space stations anywhere in the inner solar system.

Variety in Biological Life-Support Systems
(Stafford) by Stan Love
A great deal of work has been done recently in the field of biological life-support systems for space applications. Such systems are advantageous in that they almost perfectly recycle their air, water, and solid wastes, producing fresh food at the same time.

An interesting feature of currently-envisioned biological life-support systems is that they contain plant species for producing food and for recycling water, air, and solid wastes which fill the needs of the crew with very little room to spare. A typical design features about a dozen plant species, with just sufficient mass to keep the system functioning. If even one species were to fail in some way, such as via disease, pest, or genetic damage, the entire ecosystem could collapse, perhaps killing the crew if replacements were not readily available.

This danger can be minimized by carefully choosing the species and the seeds used to grow them, but biological systems are notorious for evading even the most careful controls. Worse still, if all biological life-support systems in use in many habitats all use the same species, a plague or pest could infect one, easily spreading to the others and perhaps destroying a large fraction of the life-support systems in use everywhere!

This problem poses an interesting dilemma, and one that will have to be resolved before biological life-support systems can find widespread use in space. A system that barely fulfills the needs of the crew is dangerously unstable against factors even as trivial and commonplace as a bad harvest. On the other hand, stability in biological systems is a function partly of the size of the system and more strongly on the diversity of species in that system.

Adding size, or, more importantly, a variety of species requires additional mass, which is the deciding factor for most space applications. Presumably, the solution to the problem will lie in a sort of compromise. Biological life-support systems could be equipped with a few carefully-chosen standard species as the baseline, to which are added a number of additional species which are capable of performing the job of life-support if the standards fail. This tactic would have the additional advantage of providing a wider variety of food for the astronauts, who may become bored with eating the same dozen plants for years at a time. <SLuGS>

EDITOR: Again, MMM wishes to thank David Graham for permission to reprint these Concept Papers, of great interest to MMM readers.

RESPONSE TO THE SEI & STAFFORD SUBMISSIONS

In January of 1991, the AIAA began mailing out letters of appreciation to contributors. The letters noted that the final assessment report included the best 500 ideas of all the ideas submitted. Most of the SLuGS concepts were included in the final report.

The AIAA report highlighted less than two dozen of the 500 total ideas as having "exceptional merit." Five of the SLuGS concepts were so recognized. We are, of course, very pleased and honored by this recognition.

The concepts granted "exceptional merit" recognition are as follows:

• Magsail Asteroid Survey Missions by Stan Love
• Magsail Stabilization of Lagrange Point Structures by Stan Love
• Magsail Mars Missions by Stan Love
• Lunar Base Construction by Regolith Tunneling by David Graham

For example, the evaluators gave the "Regolith Tunneling" concept exceptional merit status while concluding that the dependent technology, "Sheet Piled Excavations," was not practical on the Moon. The team feels that the sheet pile concepts solve a host of very serious problems that must be overcome before serious construction of permanent lunar bases can begin. Therefore, major papers extolling these and related structural engineering concepts were presented by SLuGS at the International Astronautical Federation congress in the fall of 1991 and the Third International Conference (Denver, 1992) on Engineering, Construction, and Operations in Space sponsored by the American Society of Civil Engineers.

Contents of this issue of Moon Miners' Manifesto