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Bootstrappable Energy
Josh Perry
Student, engineering / plasma physics
Energy is a critical limiting factor in plans to develop a base on Mars into a manufacturing facility that can expand into a self-sufficient colony. It limits how much subsurface ice can be melted and processed, how many structural bricks can be baked, how much iron and glass can be smelted, and critically, how much CO2 and water can be processed into rocket fuel, plastics, and lubricants. The extreme cold also means that many types of equipment left outside will need to be heated to keep them operational. Importing power generation systems from earth would be costly for the organization sponsoring the base, and would limit what the colonists could do in terms of growing their industry during the 18 month periods between launch windows. Additionally, unexpected failure of power generation systems that cannot be replaced on-site would put the colony in danger, or at least drastically slow down its industrial growth.
Using resources that are relatively simple to refine and readily available on Mars, like iron, glass, and polyethylene, what energy generation systems could be mass-produced by martian colonists with minimal use of materials imported from earth?
The book "Mars: Prospective Energy and Material Resources" by Vlorel Badescu, which I read a year or so ago, gives several options, some more realistic than others. Two that stand out from a simplicity of manufacturing perspective are wind turbines and solar-thermal generators. (Yes, wind power is possible on mars, it's because of the higher density of CO2 and the higher wind speeds)
How would you go about designing and manufacturing these systems, or can you think of an alternative?
I'm thinking that this could turn into a project that someone could build in their backyard at fairly low cost, which would demonstrate a piece of space technology that would be very useful to base designers and mission planners.
Mikkel R HAAHEIM
Concepts Development, Organisation, Operations Specialist
There is a third energy resource that is very often overlooked: human power. Mars has a very low gravity, which means that astronauts will need to exercise vigourously and frequently if they wish to maintain sufficient muscle mass for an eventual return to Earth. Exercise equipment can be developed around flywheels that tap device/generator transmission gears to provide resistence... or,in other words, tap resistence settings to provide electrical energy.
Admittedly, you are not going to get a lot of energy from a small crew of three to six astronauts. Instead, this alternative would provide reserve power for small to intermediate sized colonies and production facilities. Also, keep in mind that a human workforce can actually perform most of the tasks routinely supported by automated machinery. In fact, many colonists might welcome the opportunity to practice artisanal production methods to supplement regular production.
Solar thermal and wind power are fairly simple concepts, so the design and manufacture should not be a problem. Most of the effort here would be in determining the designs with optimal efficiencies and/or power production levels. Instead, the issue would be with establishing a suitable infrastructure for producing the energy systems themselves. This would include mining and processing the ores required for production of the components.
Non-electric thermal generators would probably be the easiest to develop. Smaller units would simply require a metallic pad with a blackened surface (preferably blackened throughout the pad itself). This would absorb and conduct the heat from sunlight. Such a generator would be used for passive heating in climate control, as well as for light cooking. It might be necessary to supplement the collector pad with a glass lens to focus more sunlight on the pad. There are literally thousands of designs for this that only require a substrate and a sheet of tinfoil/aluminum foil. More advanced designs would circulate wate to transfer heat, which would require a closed-loop tube. Normally, this would incorporate a clear reserve, allowing the water to flow over the plate; this permits the water to absorb heat conducted from the plate, as well as reflected thermal energy that the plate can not collect.
At larger scales, the heated water would pass through a common electrical generator turbine... but the generator would require a more advanced infrastructure.
The nice thing about wind and solar-thermal power, however, is that they are relatively cheap, and require very small amounts of material mass. A few tonnes of material should easily be sufficient to cover the initial power needs for a production facility... perhaps complemented through good old-fashioned human labour.
Manufacturing with ISRU resources gets a lot more complicated the more you think about it. Wind and solar thermal may sound simple, but there are a lot of added complications if you are trying to make them with Martian materials. The easiest structural material to make is iron because the ore is everywhere in Mars. However, the ductile-to-brittle transition temperature of iron and most steels is above Martian ambient temperature (meaning they would become brittle if not actively warmed). More advanced metallurgy requires a lot of additives, ores for which could probably not be found near the location of a Mars base, and which would add complexity to the manufacturing process.
Polyethylene can be made from carbon dioxide and hydrogen, as a fairly simple extension of the chemistry used to make methane-oxygen rocket fuel on Mars. HDPE is structurally sound at Martian temperatures but a special catalyst is used up in its production.
What I want people to try and find out is: can you make an electric generator with reasonable efficiency just using iron, polyethylene, and basic hydrocarbon lubricants? Could you do the same for a sterling engine or a rankine-cycle turbine? If so, can you make the parts with a combination of 3D printing and artisan labor?
Each of these systems will have an energy cost associated with its production and will have a limited service life. It will need to pay back that energy cost many times to allow the base to grow its industry. I'm not a machinist or mechanical engineer, but I've had just enough experience with both to know how hard these things can be when considering non-ideal materials in extreme conditions. It's going to require a lot of thought and creativity to make this kind of thing work.
I am not so certain that the increased brittleness would be a significant concern. Wind and solar thermal arrays would normally not be subject to high levels of stress, nor impact. Nor would mild levels of cracking much interfere with their function. Furthermore, should more extensive cracking occur, these technologies are rather conducive to repair (cracked edges can normally be heated and rejoined, although this will impact overall efficiency).