A reason to go to Mars

From: Marcel

> 1. On Mars, all you have to do is use a shovel to cover your habitats
> with protective sand for radiation and shielding. Earth moving
> vehicles would of course be much more efficient.

True, about the only legitimate advantage that can be cited for locations on celestial bodies is that the raw material needed is literally underfoot. And yes, transporting the raw material for shielding (or for any other use) is an added expense. But surely operating at the much more distant location of Mars will also be an added expense. So the question becomes, which is the greater expense?

But even if ore transportation costs were significantly greater than the added expenses of operating at the distance of Mars, this may still not affect the outcome. If the habitat in HEO has a product it can profitably sell to Earth (and I think SPS is a defendable proposal), and the Mars surface colony does not, then the entire argument becomes moot. We will set up shop in whatever location provides an economic advantage, and import whatever resources we must to support that operation.

> But in High Earth Orbit, you'd have to import your protective
> shielding material from the surface of the moon either by expensive
> rockets or through enormous capital intensive mass drivers.

Those mass drivers might not be as capital intensive as you're thinking. I know that in more recent years there's been a tendency to talk about lunar mass drivers capable of launching big tanks of liquid oxygen or other finished goods. But Gerard O'Neill was talking about something of far more modest scale. The coil diameter would be about that of a dinner plate. The greater accelerations demonstrated by Model 3 enabled us to talk about a mass driver a mere 160 meters long. In terms of mass, O'Neill once remarked that the parts for the mass driver kit would fit into a single Space Shuttle cargo bay (although the PV power supply would be several more loads.) This is the big advantage of launching ore-only versus finished goods: small bore size and (with greater accelerations being permitted) shorter lengths combine to reduce the size of the initial investment.

> 2. On Mars, carbon dioxide, oxygen and nitrogen can be easily
> extracted from the atmosphere.

Yes, but for this to be any significant advantage, the mass of the carbon dioxide and nitrogen would have to be a significant fraction of the total mass needed. (I exclude oxygen because any operation involving mining of ET materials is going to be producing more oxygen as a by-product that what's needed.)

The only highly-detailed studies we have for this are the NASA Summer Studies (any speculations about Mars settlements for several thousand people have no comparably detailed numbers to go with them). They concluded that the Stanford Torus (or I would think a Mars dome of comparable scale) would require 10 million tons. A lot of that is shielding, and some of it is topsoil. Let's be generous to the calculation and leave that out. The remainder, which we might call "habitat structure and atmosphere" amounts to 500,000 tons. "Gas and hydrogen" (which I think will cover the nitrogen) accounts for 21,100 tons and "Biomass" (which ought to cover the carbon that we could instead get from the Martian atmosphere) amounts to 5,900 tons. So what you're talking about represents less than 18 or 19% of the total mass of what we need. The lion's share of what we need is steel, aluminum, and glass. If it's cheaper to work metals and glass in space than on the surface of Mars, then this advantage might outweigh the advantage of being able to pipe in CO2 or water vapor. Given that phenomenal amounts of solar power can be harnessed in space via low-mass mirrors, I think there's every reason to expect such an advantage for space.

> And water can be extracted from the
> regolith or from the polar caps.

In a similar manner, water can be extracted from the lunar poles. There's not as much there, but it's enough to get us started. Perhaps to the point that we're obtaining water from CC NEAs.

> Oxygen can also be extracted from the
> rocks or through the electrolysis waster on Mars.

The former is the exact method we'll use to create the oxygen for our orbiting habitat. I doubt that much of the latter will be done on Mars, as I think in any operation where ores were being reduced, the water would be far more valuable than the oxygen.

> But in High Earth Orbit, oxygen, nitrogen, carbon dioxide, and water
> would all have to be imported by rocket or by light sail from
> asteroids or from the moons of Mars.

You've left out the lunar mass-driver. This is what brings the idea into the realm of economic plausibility.

> 3. On Mars, you can gradually add small habitat structures or large
> pressurized biodomes which would allow a colony to grow incrementally.
>
> But in High Earth Orbit, you'd either have to build very large
> rotating structures right from the start or build a huge radiation
> protective structure first while incrementally adding small habitat
> modules inside of such protective interior of your shield structure.

Yes, I've encountered this "incremental expansion of living space" argument before. Peter Kohk has some interesting proposals for rotating space structures which could be enlarged incrementally. I don't necessarily know that they defeat your point, though. Your proposal sounds interesting. The shield would be one of the simpler structures to assemble.

Regards,

Mike Combs