[Space] Getting Mars to 1% hydrographic coverage

[Michael Thayne]

I hadn't thought of it this way before, but I think a lot of your opinion on the viability of Minimum Viable Mars Terraforming is going to depend on your model of solar mirror costs. If you think that with reasonably advanced technology, the cost of the mirrors will be dominated by launch costs, materials costs, and other things that are a function of mass, such that we can reduce costs a lot by making the mirrors very thin, then the solar mirror array might be a $100 billion or $1 trillion project. That's significant yet very doable for a major nation-state. But if you think we can't get costs below $1 per square foot regardless of thickness, a mirror array with an area of 40 million square miles becomes a quadrillion-dollar project, which is equivalent to the entire US federal government budget for hundreds of years.

[AlexanderHowl]

Any realistic solar mirror is likely to be constructed from materials mined in the Main Belt (probably 8 Flora because of its low relative orbital velocity to Mars). A realistic design will likely be 1 kilogram per square meter, so a 40 million square kilometer design would mass around 40 billion metric tons. You would probably want two of them, one placed in Sol-Mars L4 and one placed in Sol-Mars L5, designed so the light would be reflected and focused to land on the day side of Mars (this avoids a 'no night' scenario), for a total mass of 80 billion metric tons.

Fortunately, 8 Flora has a mass of 6.67 quadrillion metric tons and, even though you would likely process 160 billion metric tons for the required materials, that is less than 0.01% of the mass of 8 Flora. On a side note, precious metals likely account for 100 ppm (mostly palladium and platinum), so you would extract 16 million metric tons of precious metals as a byproduct of mirror construction (including 80,000 metric tons of gold). Even with the resulting 90% reduction in predicted gold prices, this would be still be $320 billion worth of gold.

[Agemegos]

Originally Posted by Michael Thayne

I hadn't thought of it this way before, but I think a lot of your opinion on the viability of Minimum Viable Mars Terraforming is going to depend on your model of solar mirror costs. If you think that with reasonably advanced technology, the cost of the mirrors will be dominated by launch costs, materials costs, and other things that are a function of mass, such that we can reduce costs a lot by making the mirrors very thin

Yeah. It seems reasonable to suppose that such a mirror need consist of little more than a layer of metallised BoPET film stretched over a fibreglass-polymer hoop, with a fibreglass tether for tidal stabilisation. 14 µm of PET and 0.5 µm of aluminium ought to do it, for about 21 grams per square metre. The best plan is obviously to make a bunch of them so that you can replace them as they get damaged. Thus you make a continual maintenance task, but avoid risk of catastrophic failure.

Robert L. Forward proposed some elaborate tricks for using a solar mirror as a lightsail to keep it in a powered stationary orbit, but they look a bit iffy to me. I'd suggest putting a swarm of mirrors into heliosynchronous orbits around Mars.

[DanHoward]

Originally Posted by AlexanderHowl

Now, if Mars was more Earth-like, I would agree that it should be terraformed, but there is a legitimate question of whether that would be a good use of resources.

IMO Venus is a better contender for terraforming if the atmosphere can be brought under control.

[AlexanderHowl]

True, it already has nitrogen (five times as much as the Earth), so you only need to import hydrogen. Of course, you have to trap the carbon dioxide, but genetically designing aerial plant life should not be impossible. Just seed it in the upper atmosphere and let it convert the carbon dioxide into organic rain upon the surface (the heat and pressure, without any oxygen, will turn it into something like asphalt). You will also need to drop ice asteroids into the atmosphere to increase the humidity, but it is not unreasonable.

[Rupert]

Originally Posted by AlexanderHowl

True, it already has nitrogen (five times as much as the Earth), so you only need to import hydrogen.

There's hydrogen in the sulphuric acid.

[AlexanderHowl]

Not enough to make a difference (Venus has more water vapor, 20 ppm, than sulpheric acid, <1 ppm).

[Anthony]

Originally Posted by AlexanderHowl

True, it already has nitrogen (five times as much as the Earth), so you only need to import hydrogen. Of course, you have to trap the carbon dioxide, but genetically designing aerial plant life should not be impossible.

To convert the atmosphere of Venus to Earthlike, you have to get rid of 99% of the oxygen and 99.999% of the carbon, and you have to get them both into a stable storage where they won't just escape or recombine. Unfortunately, Venus doesn't have active subduction zones as far as we know, so your only real choice is probably to send a whole bunch of nickel-iron asteroids at the planet, producing a whole bunch of iron carbonate, and then

We don't know that much about what the surface of Venus is like, but it probably doesn't have a lot of free metals or active subduction zones, so most likely the way you do this is by importing enough nickel-iron asteroids to bind it all in carbonates and cementite (some can be bound as coal, but not too much). That's doable, but, well, it's a lot of mass; probably thousands of times what you'd need for Mars.

[Fred Brackin]

Originally Posted by DanHoward

IMO Venus is a better contender for terraforming if the atmosphere can be brought under control.

The atmosphere is indeed a serious problem and then there's the much greater amount of sunlight but it's the rotation that would be hardest to deal with.

You could cut the insolation and compensate for the lack of rotation with sunshades and a few mirrors to light up the side that isn't pointing at the Sun. Venusian sunshades would probably have to be larger (or more numerous) than Martian mirrors though.

All things considered I don't find Venus to be a very good candiate for terraforming without massive superscience.

[Agemegos]

Originally Posted by Fred Brackin

All things considered I don't find Venus to be a very good candiate for terraforming without massive superscience.

There is no planet B!