New Mars Forums

Previously, we examined building a 200m wide catenary dome from Martian bricks as the site of a town hoysing 3000 - 10,000 people, depending upon the density of construction.  I wonder if a steel structure would be quicker and easier to produce?  Repeatable hexagonal units can be produced in large numbers.  These can be welded into a frame structure that is then covered in loose rocks and regolith.

Duckweed!
https://youtu.be/U_405zhZkbY

This is a small, floating family of plants that is regularly eaten in eastern countries but is considered to be pond scum in the west.  By my calculations, 1kg of wet yield contains 430 calories.  Average productivity is around 20kg/m2/year.  So an 84m2 pond would produce enough calories to feed 1 person indefinitely.  More interesting is that some species are about 40% protein by weight, making this 10x more productive than the equivelent area of soybeans.  What is more, duckweed contains all nine essential amino acids.  This means you can build muscle by eating duckweed without supplementing it with anything else.  It is also a vegetable source of vitamin B12 and omega-3 fatty acid.  Some varieties are high in starch, allowing dried and powdered duckweed to be blended with wheat flour to make bread.  This is more nutritious and healthy than standard bread.

These floating plants are about the size of sand grains.  We could pump floating duckweed through transparent pipes on the Martian surface.  Martian CO2 could be injected into the water and the plants would convert it into biomass.  The water can be warmed using nuclear waste heat.  This allows the wasteheat radiators of Martian nuclear reactors to serve as an abundant food source.  To feed a city of 1million people would need an area of some 84km2.  That is a square about 9km (5.5 miles) aside.  This is more compact than most cities with a population of 1million.  Presumably, water with dissolved acetate salts would grow duckweed without sunlight.  In this case, our food production could take place in a compact facility using nuclear power.  But as nuclear reactors need waste heat radiators anyway, why not use them to grow duckweed in sunlight and then use the electric power for other purposes?

Human waste can be recycled very efficiently in this arrangement.  Waste would first enter an añaerobic digester, producing methane as a fuel.  When fully digested, the waste breaks down into water with dissolved nutrients and an organic sludge which seperates by gravity.  The water can be pumped back into the duckweed farm.  The organic sludge would be added to martian regolith and used to make soil.  Nothing gets wasted in this arrangement.

Duckweed is a photosynthetic plant.  It is therefore a potential source of chloroplasts, which Robert has discussed as a means to produce oxygen and glucose in compact volumes.  The glucose can be added to foods to boost calorie content. It can also be fermented into alcohol.  This will have uses as a fuel, a low temperature working fluid, a screenwash for vehicles, solar panels and greenhouses and for human consumption.  Over time, we may find ways of using alcohol, yeasts and algae to make rum and whisky that we can export to Earth.  This was my original hacienda idea.

The End of China's Rise and the Future of World Order.
https://youtu.be/IL6OHMr21f8

As Chinese economic power declines, it becoming increasingly aggressive.

This video discusses rope drives.
https://youtu.be/C-WxGuZhCuk

One thing I find interesting is that a single pulley can drive several rope drives for different machines.

To make carbon monoxide, carbon must be burned in an atmosphere with limited oxygen.  This releases about 20% of the heat released by complete combustion.  The process that Kbd512 has described produces particles of carbon.  So that is what we start with.  Carbon monoxide has important uses of its own.  One such use is the production of reduced iron.  Making strong engineering bricks is another use we have noted.  But it is a precursor to other more convenient fuels.  For example:

CO + H2O + heat = CO2 + H2
2H2 + CO = CH3OH.

This is methanol.  It is a clean burning liquid fuel that doesn't freeze until -97°C.  We could store it in tanks on Mars with very little pressurisation.  By using the appropriate catalyst, methanol can form dimethyl ether:

2CH3OH = H20 + H3C-O-CH3.

Dimethyl ether has been considered as a diesel substitute.  It would make an energy dense rocket fuel that is less volatile than methane.

SpaceNut, that is excellent research.  To produce actual Earth daylight effect sounds quite energy intensive, given that a sunny day in the northern hemisphere delivers a ground level solar flux of ~400W/m2.  For a 31,000m2 town, that implies 12.4MW of light, requiring ~5x that much power (60MW) in input electricity.  That is a lot of juice and a heavy burden on base power supply.  Averaged over 24 hours, that is 20MW of input power.  It is also a lot of heat that must be removed from the space.  It might be considered acceptable if it proves to have strong benefits for the mental health of residents.  I wonder how much we can compromise in terms of power consumption by eliminating frequencies that are beyond human eyesight?  Lighting for plants tends to be optimised for specific spectra that are most efficiently absorbed for photosynthesis.  How well will humans adapt if the daylight they experience is a different colour, i.e more shifted towards the red spectrum?

It occurs to me that daylight we experience here on Earth has considerable daily fluctuation.  Some days are overcast, others provide full sun and often the weather changes throughout the day.  Lighting in the habitat could be turned into a kind of dump load for excess power.

The pressure-brick method could be used to produce green bricks prior to firing.  A sieve could be used to seperate Martian fines from the regolith.  Fines would then be compacted into moulds producing the green brick.  This avoids the need for water.  Blue Class A engineering bricks must be baked at a temperature of 1200°C in a reduced atmosphere.
https://wordssidekick.com/what-temperat … ering.html

If we are using a lot of bricks, then we could even supply this heat directly using a gas-cooled nuclear reactor.  The reactor would charge the kiln with a mixture of carbon dioxide and carbon monoxide at 1200°C.  Some sort of pebble bed reactor would be ideal here.  These high-temperature reduced iron bricks, would be extremely strong.  Iron rich clay is needed to produce bricks of this type.  Fortunately, Mars is covered in exactly this material.

It would be interesting to know how the 230kWh of electrical energy are consumed.  Is this used in gathering and compressing the CO2?  Is it the motor seperating the carbon flakes?  On Mars, the ambient atmosphere is typically cold - far beneath the CO2 critical point and often beneath the triple point.  CO2 could be gathered as liquid with relatively little compressor work.  Or it could be allowed to accumulate as ice on a cold plate.  What is the energy input creating motion in the nanoparticles?  For particles this small, even brownian motion would generate triboelectric current through friction.  It would be amazing if we could develop a process that could convert low grade heat into chemical energy.  Such energy could be derived from the sun or waste heat from a nuclear reactor.  There is even the potential for geothermal heat to be used in select locations.

From your link, the flow of liquid gallium over silver nanorods, creates triboelectric current.  This breaks the C=O bonds in the CO2.  So this process converts a mixture of mechanical and thermal energy into chemical energy.  The energy consumption of 230kWh/tonne of CO2, is 810kWh per tonne of carbon.  At an electricity cost of $0.1/kWh, that works out at $81/tonne carbon.  That is assuming that the 230kWh is electrical energy.  So this does look promissing.

Here is a similar paper, this time using cerium as the active catalytic surface instead of copper.  Both use liquid metal as conductive carrier for the catalytic surface and dissolved CO2.
https://www.nature.com/articles/s41467-019-08824-8

Correct me if I'm wrong, but they are talking about electrochemical decomposition of CO2 into carbonaceous products.  This is therefore an electrolysis process that needs electric current to work.  The catalyst is essential for reducing the temperature at which this happens.  But the electrical energy is still needed to reduce the carbon.

It would be neat if we found an efficient and rapid process for converting low-grade heat into stored chemical energy.  But the second law of thermodynamics appears to be against it.  Entropy always increases.

How the Inuit survive and thrive at -64°C, without modern technology.
https://youtu.be/gjoNsZlRkSk

Quite inspiring.  As humanity heads out into the solar system and later into interstellar space, we will have to learn how to embrace the cold.  The inuit provide lesson that we can learn from.

Excellent post by GW Johnson.  One addition that I would make is that hoop stress does not necessitate tensile elements in the outer walls.  Provided there is enough overburden over your external walls, the hoop stress can be resisted by entirely compressive structures.  This is how gravity dams work on Earth.  The static friction between the particles in the dam locks them together.  It is quite safe provided that the vector of the centreline resultant force (the resultant vector between outward pressure stress and stress in the wall due to gravity) has a steeper gradient than the taper of the wall.  If the resultant force bisects the surface of the wall before reaching the ground, then the wall will be subject to shear stress.  This might be tolerable within limits for bonded materials like concrete.  But is clearly intolerable for loose soil.  You could build a pressurised structure entirely from regolith materials, but the walls woukd need to be thick and tapered.  That might not fit well with aesthetic requirements for windows.