In the last mini blog-post, we talked about some of the benefits of atmospheric-feedstock ISRU. But that leads to the question, what materials are there in the Venusian atmosphere, particularly in and around the 50km zone? While chemical engineering may limit your ability to rearrange elements from the atmospheric constituents into an end-product, if that element isn’t available in the atmospheric constituents, you’re probably going to have to bring it from earth.
While I’ll go into more detail about the sulphuric acid and water vapor concentration in a future blog post, here are links to two tables (one from wikipedia, and another from a Purdue planetary science lecture). With atmospheric density at 50km being approximately 1atm, and with CO2 being most of the atmosphere, the bulk density is probably just a little under 2kg/m^3. I could get more precise than that, but that’s a decent rule of thumb. So the key atmospheric constituents at 50km, their relative abundance, and their mass density per cubic meter are (assuming I’m doing my math correctly):
- Carbon Dioxide (CO2): 96.5% of the Venusian atmosphere is CO2. I’m not positive if this varies much with altitude in the ranges we’re talking about. But this would be approximately 1.93kg/m^3
- Nitrogen (N2): 3.5% of the Venusian atmosphere is gaseous nitrogen. This works out to about 70g/m^3
- Sulfur Dioxide (SO2): 130-150ppm in the Venusian atmosphere, which works out to 260-300mg/m^3
- Argon (Ar): 65-70ppm, or about 130-140mg/m^3
- Oxygen (O2): 30ppm or about 60mg/m^3 [Note: this one is only listed on the Purdue site]
- Water Vapor (H2O): 20-30ppm or about 40-60mg/m^3. Compared this to the driest place on earth in the Atacama desert near the ALMA observatory in Chile, which had 200ppm water vapor at 5km altitude (.74kg/m^3 atmospheric density), which assuming I didn’t make math mistakes works out to ~145mg/m^3 [Note: I wasn’t able to find anything on how this varies with altitude, so I’m just going with the raw numbers for now, and assuming they still hold at 50km.]
- Carbon Monoxide (CO): ~17-20ppm or about 35-40mg/m^3
- Helium (He): ~12ppm or about 24mg/m^3 [Note: This one was only listed on the Wikipedia site, and I don’t know how much it varies with altitude]
- Carbonyl Sulfide (OCS): 10ppm or about 20mg/m^3 [Note: only shown on the Purdue site]
- Neon (Ne): 7-9ppm or about 15-18mg/m^3
- Sulfuric Acid (H2SO4): I had a hard time finding good numbers for this, but according to Figure 3 on this page, at 50km, the abundance works out to ~14mg/m^3 or about 7ppm. So, between sulfuric acid and water vapor, you have about half as much mass per cubic meter as water vapor in the air near the ALMA observatory in the Atacama desert in Chile. Bone dry by terrestrial standards, but sopping wet compared to say the Moon.
- Hydrogen Chloride (HCl): 0.1-0.6ppm or between 0.2-1.2mg/m^3
- Hydroflouric Acid (HF): 1-5ppb or between 2-10µg/m^3
Of these components three of them (water, sulfuric acid, and hydroflouric acid) have liquid phases at room temperature, which means they can likely be condensed out as liquid phases relatively easily before processing the rest of the gas-phase constituents. Also, the HCl vapors dissolve so readily into liquid water (forming a hydrochloric acid), that they may also be effectively “condenseable.”
So elementally, we have lots of Carbon, Oxygen, Nitrogen, and Sulfur, decent amounts of Argon, Helium, Neon, and Hydrogen, and trace amounts of Chlorine and Fluorine. What can you do with these building blocks, assuming you can make the chemical engineering work to take these feedstocks and convert them to the outputs you want?
- Breathable air
- Drinkable water (from the water vapor and chemically extracted from the sulphuric acid)
- Chemical rocket propellants (LOX, Methane, Hydrogen, and with a lot more work maybe some storables like N2O, N2O4, Hydrazines, H2O2, and storable hydrocarbons and alcohols)
- Most plastics including PE, PP, PC, PET, PVC, Epoxies, Teflon and other flouropolymers (in modest quantities–the Florine’s pretty rare). Just no silicones unless you bring your own Si
- Carbon and aramid fibers
- Graphite, Graphene, and Carbon Nanotubes
- Sulfur “Concrete” (likely using graphite whiskers as the reinforcement)
Anything metal would likely need to be imported, but if the ISRU equipment to get to simple polymers and carbon fibers isn’t prohibitively large, you might actually be able to build most of the structures, the sulfuric-acid resistant outer skin, and the breathable atmosphere, and drinking water all from local materials. Seems promising.
Next Up: Condenseables
Jonathan Goff
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That’s interesting Andrew. Many years ago I came up with an idea of levitating a structure above both poles using tiny satellites in football shaped orbits making an elastic collision with the bottom of the platforms (electromagnetically). Sure enough, Paul Birch had thought of it first in a fairly similar form. ^_^ (Actually, the idea does seem a bit easier than a giant tether because the tether doesn’t have to be nearly so long.)
In the article you linked, he’s transporting heat in large part though a phase transition, as regular heat pipes do, whereas I was concentrating on just using a gas with a very low adiabatic lapse rate. His way is probably better, just given how much he’s studied the problem.
One approach might be to use propane (mwt 44) or 184-proof ethyl alcohol (mwt 43.7) which will both condense at altitude and have lapse rates less than half that of CO2, while having about the same molecular weight to reduce structural issues. Of course, since they’ll be at different temperatures than the surrounding atmosphere their densities will end up differently anyway. Perhaps some kind of fractional distillation setup or varying the gas mix by altitude to help compensate? If you can manage to keep the pressures evenly matched across the column’s sidewalls for its entire length, the sidewall could become little more than a tent structure that resists wind loads and keeps the new gas separate from the overall atmosphere. I’m not sure if that notion is possible, though.
Most of all you can have food from the water, the nitrogen and the CO2. Perhaps you will need to bring in some phosphor and oligoelements to complete that as well as the first seeds of course. You also have sunshine even if you may have to resort to one of those hybrid combination of natural and artificial lighting systems. They are now available off the self here on Earth for bathrooms or other rooms that don’t have direct access to an outside window.
One rocket propellant mix that you forgot to mention is CO+O2, which would be dirt cheap in the clouds of Venus. I suspect it’d be the mix of choice.
Adam,
Maybe. Performance isn’t everything, but it does matter on some level. To get off Venus, you probably want something fully reusable, which likely implies two stages at most. I’m not sure if CO/LOX gives you enough performance to enable that even if you use it only on the first stage.
Might be interesting as a fuel combination for Venusian aircraft though…
~Jon