New Mars Forums

Hey th,

In your proposal for rental heat shields, do you expect that the heat shields will be returned to orbit once used?  Or are you thinking that they will be a one-use deal?

Once we have an adequate manufacturing base on the Moon I believe that it makes more sense for them to be disposed, as it's likely to be cheaper and easier to dispose of them on Earth than to send them back up.

In that case it's not a rental so much as a sale, although I'm sure appropriate organizations will spring up as-needed to provide entry services to those who need them.

I went and had a look at the last time Edward Heisler posted outside of the free chat forum.  It was 7 months ago, in October.  The overwhelming number of his posts within the last year have been political posts in Not So Free Chat.

Everyone is entitled to an opinion, of course, but I've always found that our discussions of space are at a much higher level than our discussions of politics--the former being at a uniquely high level, as far as I can see, with the latter being generally unexceptional.

Hey SpaceNut, Terraformer, and Void,

It's true that the political economy of digging this sort of trench-town is bad if you want to promote terraforming.  Even if it's not flooded, the pressure will always be 50+ times the pressure at the datum down there meaning that if the datum is habitable the trench will not be.

From a political standpoint, if you choose to terraform you will more or less have to tell people that you're filling in their city and they will have to move for the greater good.  Seems tough, but so does terraforming.

Subterranean water would be a big challenge to any project like this.  I don't know how best to deal with it.

Again, I don't know how long Insight will last but decades is probably an overly optimistic estimate

I've got no issue with open pit mining the moon, but even the biggest, deepest open pit mine imaginable wouldn't qualify as the sort of shaft-to-hell that mining the lunar core would be.

A more interesting question might be if it would make more sense to look for meteoric orebodies (meteorebodies?) and do a more traditional type of mining or if it would be better to process the regolith like we were talking about above.

At a high level my take is generally positive, with the usual caveats of ground truth measurement and technological development/investment to actually enable this sort of production.

One point of concern for me is the low concentration of nickel compared to terran ores.  I calculated a concentration of 0.014% above, while 1-3% is more common in terran ores.  Having said that, in Terran ores the material typically exists as an oxide rather than a native metal so it should be substantially easier to separate.  The more I think about it the more I like the electrostatic (or magnetic) tower bulk separation method, probably with some leaching process once the native metals get above a certain level.

I don't think any impactor we could feasibly send to Mars with current launch technology would be able to generate the kind of seismic wave that would provide information about the core.  Might be interesting to aim for somewhere near Insight so you could see how the local material behaves though.  It'd be an interesting complement to spectrographic observations of the dust plume.  Having said that there's reasons not to, too, including the mission timeline (will Insight still be operational? If not, you might choose a site based on areological interest rather than proximity to Insight), risk to Insight (if you're looking to punch through the atmosphere your accuracy should actually be quite good if you incorporate a few stabilizing jets, but I mean still).

As far as whether you'd need a dedicated observation satellite I really am not sure.  You will certainly get better data if you have them, though.

Went back and had a look at what I said last time, and it turns out I'm nothing if not consistent.

You'll find no argument with me about going there to have a look around. 

Having said that, this isn't a matter of counting your chickens before they hatch so much as it is saying that you've got no eggs and shouldn't expect any chickens.  I don't claim certainty.  What I do claim is that even if we couldn't see fossil fuel deposits directly, the environment that could create them would leave behind certain telltale signs which we probably would have seen by now if they were there, as they'd be fairly ubiquitous.  Your post had three sentences:

1. Mars has earthquakes, too, apparently.
2. That means geological processes are still at work and should also be producing very similar types of materials.
3. For all we know, there might be coal on Mars.

I agree wholeheartedly with the first two of the three, while the last one seems unsupported by evidence.

I did some quick research and I was able to provide an estimate for the amount of nickel in the upper level of lunar soil.

This article suggests that iron of meteoric origin is roughly 0.25% of the regolith by mass, and on pdf page 26 (page 252 as marked) of this paper nickel composes roughly 6% of the mass of meteoric metals.  We can therefore surmise that lunar regolith is about 0.014% nickel by mass.  Using an assumed bulk density of 1500 kg/m^3 for the upper layer of regolith (particle density is closer to 2900 kg/m^3 but there are substantial voids caused by micrometeoroid impact, etc.), this means there will be roughly 200 grams of nickel per cubic meter of regolith.  Given the substantial uncertainty in this estimate I consider my estimate of 200 g/m^3 to be generally in agreement with Terraformer's estimate of 300 g/m^3.

I propose that the separation could proceed in two phases: First, separating native metals (Iron and nickel, mostly) from bulk loose regolith.  Second, separating nickel from Iron.

The first paper I linked to notes that the actual size of iron particles (and consequently I would imagine also nickel particles which are probably admixed) is often quite small, substantially less than one micron across, and that they can be physically bonded onto (or inside of) oxide particles.  Ideally you'd be able to use physical methods of separation.  A sieve would be easiest, but I see no reason to believe that the size profile of metal particles (and the oxide particles they bond to) would be different enough from the overall size profile of the regolith to generate a substantial separation using these means.

Next you might look to separate them using the difference in their bulk densities.  This method is often used on Earth and might work, depending how tightly bound the metal microparticles are to the silicate/oxide particles.  You would probably want to agitate the mix using gas flow while spinning it in a centrifuge.  You're going to want to use a low-value gas, because loss rates will probably be quite high compared to the amount of nickel you ultimately recover.  There might be some value, once the metal has become somewhat concentrated, in running this procedure in a basic or acidic (hot?) slurry, which may cause the silicate/oxide particles to break up somewhat and free the metal particles to be separated.

If this is not successful, you could look to exploit the electrical and/or magnetic properties of metals vs. oxides.  Iron and nickel are attracted to electric and magnetic fields, while silicates are generally neutral towards them.  In the hard vacuum and low gravity of the lunar surface (enabling tall structures to be built easily) it's easy to imagine a number of different possibilities for the separation of metal containing particles from non-metal containing particles, not just their different responses to electric/magnetic fields but also their different affinities for static electricity and their ability to become magnetically polarized.

If even this is found to be unsuccessful (for example, if it is typical for oxide minerals to have single atoms or small collections of native metal material distributed throughout) you need to look to more aggressive techniques: Separating out metals with the rock in the liquid state, for example, or trying to use a carbonyl process (which will certainly result in the loss of tons and tons of carbon monoxide, given the low proportion of metal materials, the ability of finely ground dust to physically and chemically absorb volatiles, and the impossibility of pumping anything down to perfect vacuum).

It will likely be the case that some mixture of the above procedures is used (in many different stages) to enrich metal levels to a usable concentration (75% would be 300x).

Once you have obtained the nickel/iron mixture in relatively pure form, I propose that the nickel be separated from the iron by a process of selective oxidation.  This is a tried-and-true method (although perhaps not often used specifically for these two metals) and here's how it works: In a bath of liquid metal, introduce some oxygen.  The more reactive element will oxidize while the less reactive will not.  Being less dense than the metal mixture and insoluble, the oxide will float to the top as slag where it can be removed using various physical means.  This process is very widely used to pull the carbon out of smelter iron to make usable steel, but I believe similar chemistry applies to the iron/nickel system.  Solidus/liquidus behavior in the nickel/iron system may also allow you to concentrate it further, I'm not sure.

Launch methods are a topic for another thread.  As far as entry vehicles, I favor woven basalt fiber as a thermal protective material.

Louis,

I won't mince words: Chernobyl was a catastrophe on the scale of 9/11.  Estimates for the number of deaths range wildly, from a few dozen (certainly too low) to the number you have provided.  Wikipedia suggests a good estimate is 4,000.  It can be difficult to say.  For example, let's say a woman who lived in Chernobyl at the time and is a lifelong smoker was exposed to some radiation as a result of the event and ultimately dies of cancer in 2025 at the age of 79 years old.  Did the radiation cause the cancer? Might she have lived longer? Life expectancy for a woman in Ukraine is 77.  Even if the radiation did cause her death, how much longer might she have lived otherwise?

I'm not trying to minimize Chernobyl, merely to point out that a simple count of fatalities perhaps overstates the size of the public health impacts of released radiation by a bit. 

Chernobyl is a bit of a worst-case scenario, both from a risk standpoint and an outcomes standpoint.  To briefly recap the conditions that caused the accident and the release of radiation:

• The Chernobyl reactors had what is known as a "positive void coefficient", meaning that they are dynamically unstable and not self-regulating

• The Chernobyl reactors had no "Scram" mechanism to kill the nuclear reaction in the event of nuclear runaway

• The Chernobyl reactors were being operated by engineers transferred from a coal plant with very little training in nuclear-specific concerns

• The Chernobyl reactors had no containment building that would prevent the release of radiation in the event of a meltdown

• The Soviet system treated failure as being akin to sabotage and therefore dis-incentivized engineers from speaking up about potential issues.  While this can be a problem in any system (Ask the engineers who spoke up about the O-rings on Challenger in that same year) the risk of a life sentence in Siberia is a lot worse than the risk of being ignored, yelled at, or fired.

• The Soviet government tried to cover up the accident at first, rather than admitting to it and taking steps to protect people

Taken together, these amount to "worst practices" for a nuclear reactor.  If you compare to the Three Mile Island accident in the US (no radiation was released despite a nuclear meltdown*) or the Fukushima disaster in Japan (in which an earthquake/tsunami that killed 20,000 people also caused a reactor meltdown which itself caused one single fatality) you'll see that nuclear power mishaps needn't end that badly.

The question of terrorism seems a bit more like a red herring--short of actually bombing the reactor it doesn't seem like there's much a terrorist could really do without causing the reactor to shut down or scram.  While a bombing on US soil is certainly a big deal the threat is not limited to reactors.  We don't have a military brigade protecting individual skyscrapers or sports stadiums after all, but rather one centralized military which protects the whole country.

Finally, I would like to point out that estimates suggest that the US nuclear bombings of Hiroshima and Nagasaki caused 150,000 to 200,000 fatalities each.  Unless you'd also contest those figures I would say it's not credible to suggest that Chernobyl--a disaster much smaller in size and scope--killed the same number.

As I said above, I do not and cannot deny that operating a nuclear reactor comes with an inherent risk of the release of radiation, even if this risk is egregiously overestimated in the popular imagination.  I will close by reiterating 2 of kbd's points:

1. The average coal plant releases more radiation into the environment per joule of electricity than the average nuclear plant.  While coal plants have many issues this is rarely if ever cited as one of them.
2. Cheap, reliable energy also has a value which can be measured not just in dollars but also in lives, as economic development increases life expectancies and decreases mortality.

*CORRECTED: A small amount of radiation was released with no known consequences to human health

Hey kbd512,

I don't think we have any disagreement on the desirability of nuclear power or the extent to which the public overestimates the danger.  However, I do try to see this one from the other side.  A Chernobyl-style release of radiation, no matter how unlikely (and I bet the average person would overestimate the probability by a factor of 100 or 1000 or more), can never be made impossible.  It's true that a nuclear reactor that is being run by the book with adequate reinvestment in maintenance should never melt down.  It's also true that no system works perfectly forever.  You're probably right that opposition to nuclear power probably stems more from environmentalism as an ideology than anyone's objective self interest (if such a thing exists).

There's an interesting, vaguely related factoid that I heard somewhere or other about vegans.  People are vegan for lots of reasons, but I would say the big three reasons are personal health, environmental footprint reductions, and animal cruelty concerns.  Vegans, in general, don't expect people to quit meat cold turkey (so to speak) and often advocate for incremental steps.  This is where there is the potential for conflict: If you believe that people ought to be vegan for personal health or environmental reasons, you might tell them to eat less beef and more poultry; If you believe people ought to be vegan for animal cruelty reasons, you might tell them to eat less poultry and more beef.  Instead, they present a simpler message to the world: Eat Less Meat, something all vegans can agree on.  There's a lesson somewhere in there about compromise and coalition building.

I may have gotten ahead of myself in thinking about a global power grid.  I stand by it as a good idea, and if we do see a global boom in solar energy it will likely happen whether it's done intentionally or not.

On intermittency: Vox has a good article about how scheduled solar intermittency affects the energy grid.  The tl;dr is that with the current mix of power sources it's not a problem until you hit 10-15% of total generation.  That's far above where we are now but solar is growing very rapidly and could reach this level in the next few years.  In California solar is already 12% of electrical generation, with wind contributing another 6%.  Turbines using natural gas are much more flexible in their output, but people are concerned about the economics of building new ones: Once you've built electrical generating infrastructure there are strong incentives to keep it running as long as you can to get the most out of your sunk costs.  Hydro is also fairly flexible.  It's not crazy to overgenerate by a bit during peak solar hours, storing the power if you have the infrastructure but letting it go to waste if you can't use it.

Anyway, there will come a time, perhaps at 10% solar penetration or perhaps at 50%, when (Assuming a global grid does not get built at the same time) you have no way to deal with its intermittency without grid-scale electricity storage.  The US uses about 500 GW of electricity on average, so if your grid is 100% solar you will need to store and release about 2.5e16 J every day.  To the extent that other forms of generation can compensate during off hours you will need proportionally less.

I can't say I have any new ideas on the storage front.  At the moment, we have a bunch of imperfect battery technologies that we can start trying to deploy.  No technology is perfect but there are lots of avenues for potential research and development.  Terraformer brought up sodium ion batteries, an idea which I think is good.  GW brought up flow batteries for their ease of use and that seems like a good idea.  Louis brings up hydro storage, which has questionable economics in that you need to move massive amounts of water but which is in use now and likely will continue to be.  I have brought up the idea of a global power grid as an ultimate solution, which has its own challenges but also, to my mind, the potential to be way cheaper than any of the solutions brought up thus far.  I don't believe it requires room temperature superconductors, although without a doubt they would help.

I would like to introduce flywheels as a possibility for nighttime power storage. Perhaps it's my bias as a mechanical engineer to like technologies which are fundamentally mechanical, but a well-balanced steel flywheel on a low-friction central bearing (magnetic, perhaps?) and in a low-pressure environment could be a simple, robust way to store power overnight.