Comment by FD3SA | Hacker News Reader

Comment by FD3SA | Hacker News Reader

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They are both extremely difficult to accomplish with current technology. The issue with Mars is that it has no magnetosphere [1], and as such, all habitats will have to be underground and/or shielded with very thick layers of lead, dirt and water.

Man made colonies will have the same problem, in addition to requiring space manufacturing and assembly at a level that is currently impossible.

If SpaceX brings the cost of space flight down to its basic energy costs, we will have solved one problem. The other problem is the power generation required to conduct space manufacturing at a large scale. Solar, although consistent, is low in power density and thus requires large amounts of surface area that is very difficult to maintain in space.

Until we crack compact, high yield fusion, I doubt we will make much progress in realizing our space-faring dreams. This was also the opinion of the late Robert Bussard, inventor of the Bussard ramjet and the polywell fusor.

1. http://www.space.com/24731-mars-radiation-curiosity-rover.ht...

Mars colonies, at least, can rely on Nitrogen and CO2 from the Martian atmosphere. Orbital habitats have to import everything but sunlight.

Having the colonies underground may have an extra advantage, both on Mars and on the Moon, as they may be closer to sources of ice. I remember hearing something about the Moon being much less dry than previously thought. No running water nor blocks of ice, but maybe crunching rocks yields something useful.

Right on. To add to this, early stage terraforming is in the immediate rather than long-term plan for Mars. As soon as we start producing CO2 on Mars, we're on our way.

I'm not against colonizing space itself, but early seagoing explorers didn't attempt to colonize the ocean. We need to establish ourselves in environments that allow easy production of oxygen, water, and food.

In the end, it is about money. It takes a lot of money to get setup on Mars, but after it is setup, it is a HUGE resource, which means much, much more money. The moon could also be a huge resource, but it is expensive to colonize because it can't hold atmosphere easily. Colonizing space itself without mining a resource in a way that eventually will pay off the initial investment is useless and a drain on our society.

> because it can't hold atmosphere easily

But neither can Mars. Most of its early atmosphere was blown away and that will continue. There's nothing we can do about the lack of gravity.

The problem with Mars is that it is cold, terminally. The nuclear furnaces have gone out. I haven't seen a proposal from the terraformers that counteracts that. You might be able to counteract it with CO2, but then that gets blown away by the solar wind. It's crazy hard to fix.

Don't get me wrong, I would love to see us on Mars. Unfortunately, the engineering and science obstacles are huge, enormous.

> Unfortunately, the engineering and science obstacles are huge, enormous.

Yes, I agree we should go to Mars. I don't see the urgency, though. I mean, in terms of the humanity-backup situation, ten years or a hundred, doesn't really make much difference.

We would be better putting the money into energy research, and when we've got that figured out, then we tackle mars.

There is no reason to require the place to hold an atmosphere - you just need to build your colony underground (which you already have to do to protect it from radiation). The Moon may be interesting for magnetic launch systems (no atmosphere, plenty of energy and reduced propellant requirements) and all kinds of metallurgic processes (no atmosphere, low - but not too low - gravity). Mars is also interesting if you can industrialize the manufacture of fuel and oxidiser from the atmosphere - gravity is low enough you can make it into a chemical rocket fueling station (landers and such will still use chemicals for a long time), at least until we develop some icy moons further out.

"No running water nor blocks of ice, but maybe crunching rocks yields something useful"

Space Fracking?

The bright side is you have no ecosystem to worry about.

> Until we crack compact, high yield fusion, I doubt we will make much progress in realizing our space-faring dreams.

What about regular, fission nuclear power?

Not enough fuel.

Projections that there's enough uranium for 200 years[1] are based on levels of present utilization: around 3.7% of global energy use[2]. Bump that to 100% and we'd run through all available reserves in less than a decade (7.4 years, if you're counting).

Solar energy (including solar mediated via plants, wind, or water), hydrogen fusion, possibly geothermal energy, or with really long odds: hydrocarbon prospecting from another body (say, maybe Titan) are the only energy sources which could last a considerable human population for the possible maximum lifetime of the species.

Yes, a small Mars outpost could be powered off of nuclear power for a considerable period, but that would take away from available nuclear fuel supplies on Earth.

The likelihood of managing usable sustainable fusion under terrestrial or other contained circumstances are fairly unlikely IMO.

________________________________

Notes:

1. http://www.scientificamerican.com/article/how-long-will-glob...

2. IEA: http://www.iea.org/Sankey/index.html

I've read that Thorium and Fast Breeder technology pushes that out to somewhere beyond 50,000+ years - http://www.skepticforum.com/viewtopic.php?f=18&t=21247

Looking over that page, there's a critical error materially affecting his supply estimate.

Rob Lister gives global annual energy consumption as 140 TWh.

The true number is 211,782 TWh, for 2011, from IEA (expressed as 18,210 Mtoe -- million tons of oil equivalent)

http://www.iea.org/Sankey/index.html

That's 1512x higher than Lister's value. Dividing his 64,000 year supply by 1512, we get 42 years supply of thorium.

I see a problem.

That's only proven reserves, though. Thorium right now is in basically no demand. Given the extremely high energy density of the fuel, A LOT of ores will become economically extractable.

It might not be 64ky, but >1ky seems to be very realistic.

Edit: See also the Wikipedia section on it: http://en.wikipedia.org/wiki/Thorium#Reserve_estimates

typeof fusion !== typeof fission

Sorry?

I'm not claiming otherwise.

The fuel supply for conventional reactors is limited because they rely on U235, which is 0.7% of uranium. Fast reactors could use the rest of the uranium. That multiplies the supply by more than 100x because it means you can economically retrieve fuel from lower-grade ore, or even from seawater, which would extend the supply to millions of years. Russia has several fast reactors in production right now, and is building more.

Liquid thorium reactors are another option. There's no thorium in seawater, but on land there's several times as much thorium as U238, and it's all the same, useful isotope. China has an aggressive R&D program hoping to get a prototype reactor ready in a decade.

But personally I think it's likely that we will achieve sustainable fusion in the fairly near future.

My understanding of seawater is that uranium concentrations are 0.01 - 0.02%, and that it's not thermodynamically feasible to extract it for energy at those concentrations.

A quick google of "extracting uranium from seawater" gives a different impression. For example: http://spectrum.ieee.org/energy/nuclear/nuclear-fuel-from-th...

...which says that EROI is 22 assuming a conventional reactor. Ie., we'd get 22 times as much energy out as we spent on extraction. With a fast reactor the ratio would be a hundred times better, since we could use all that uranium instead of 0.7% of it.

Also, geological processes bring more uranium to the surface, and rivers are constantly putting more uranium in the oceans, at a rate that would provide 25 times our current electricity usage. If we keep our usage at that level, uranium will last until the sun goes out.

http://www-formal.stanford.edu/jmc/progress/cohen.html

Of course in the context of the current discussion we should also consider the possibility of getting uranium from various other spots in the solar system: http://nextbigfuture.com/2009/08/how-much-uranium-is-in-sola...

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