You are not logged in.
The main consequence of low-grade ore is that you have to process much higher volumes of material for more effort and energy expended, and you use a lot more resources to do it. I suspect the first steel plant on Mars will have to be located near the South polar cap, where both ice and dry ice can be mined easily to support the direct reduction process. It'll need a big nuclear power plant. That makes it a major base to be established.
It would be nice if there were usable iron ore deposits nearby, too, but I doubt we can count on that. Being the smallest volume component of the process, it would be the ore we would have to ship to the otherwise-sited plant. That makes the entire problem a chicken-and-egg problem, seeing as how we need the steel to build the surface transportation necessary to make the steel.
This stuff is too heavy to transport by flying/rocket ballistics in any practical sense, even at 0.38 gee. At 6-7 mbar pressure, the "air" is too thin for practical winged flight, with such heavy loads. So, it's surface transportation that makes the most sense.
That situation makes it a gilt-edged priority to look for a suitable place on Mars to build a steel plant with the next generation of exploration probes, be they manned or unmanned. Ice seems fairly ubiquitous, dry ice not so very much. Iron ore? Who yet really knows? We need some prospectors on the ground all over the planet, be they robot or human. It would be nice to find all 3 within a few miles of each other.
As for the effects of lower gravity on direct-reduction reactors or electric furnaces, that's not so very much of a problem. Fortunately. You just need enough to hold the puddles in place in the furnace, and 0.38 gee is plenty. The hot gas reactor is all gas with no separations. It would likely work even in zero gee.
It's the other combustion-driven processes, like the blast furnace, that require something closer to 1 gee to hold processing times to something reasonable, due to the inherent "drag" affecting separations in the column. Since these require enormous masses of oxygen, not widely available on Mars directly, I doubt those processes would be preferred anyway.
Building from scratch the infrastructure for an industrial civilization is hell. It took many centuries to do it here at home, and it was still hell in an environment benficial to our form of life. Mars is lethal to us.
This kind of thing is not something you do with a half a dozen "flag-and-footprints" landings on Mars. And you can't just count on the transplanted locals to invent it all out of nothing for themselves, because it's not the environment we evolved to live in. Done that way, we'd never survive the Martian "stone age", much less progress beyond it.
GW
Steel-Making
I’m an old man, and memory fades, so I went and looked up iron and steel-making in my old college manufacturing processes textbook (yep, I still have it). It’s basically two stages: you have to make pig iron, then you refine the pig iron into the product you want.
Pig Iron: variable composition, many “pollutants” in it, but it is mostly iron
There are two processes that create the pig iron. They are the blast furnace and the direct-reduction process. The direct reduction process actually creates “sponge iron”, but you can refine it the same way as pig iron.
Blast Furnace (98% of production)
The one used here on Earth commercially today is the blast furnace. It is a vertical tubular structure packed with layers of iron ore, limestone, and coke (a hot pure carbon derived from charcoal or coal). This structure is already burning, because of the coke. You blast air under pressure into the bottom to intensify the combustion and raise the temperatures near the injection point above the meltpoint for iron (and the slag).
The iron and the slag both liquefy and percolate down through the bed to puddle at the bottom (so gravity is very important!!). The slag floats on top of the heavier iron. You periodically decant both separately. Most modern mills transport the molten pig iron directly to the refiner, but you can cast pig iron ingots, if you wish (you will have to re-melt them later, though).
The charge ratios for the blast furnace are for every ton of pig iron produced, you need 2 tons of ore, 0.8 tons coke, 0.5 tons limestone, and 4 tons of hot air. (Yep, that’s tons mass of heated air at Earthly pressures, and is that ever an incredible volume!) The usual production lot size ca. 1960 was 1000 tons of pig iron from a furnace around 25 feet in diameter and around 200 feet tall.
Direct Reduction (under 2% of production)
The direct reduction process is an extension of the old campfire process. You crush the ore and react it at elevated temperature with a reducing agent. There is (at least, was, ca. 1960) a plant in Mexico that made pig iron this way in 500 ton batches. That plant used a mixture of carbon monoxide and hydrogen derived from natural gas and water as the reducing agent. There were two reactors in operation: the reducing-gas former, and the iron reactor. The gas feed to the iron reactor was hot, and the ore well-crushed. The product was something called sponge iron, a spongy, granular, clinker-like material. This is rather similar to the product from the old campfire process of 3+ millennia ago. (That process required a lot of manual stirring to agglomerate the iron into little balls that could be recovered after the fire was out.)
This direct reduction process is probably the basis of any process we would use on Mars. Carbon monoxide can be derived from the local atmosphere, although compression from 6-7 mbar to 1000’s of mbar will be difficult and expensive. Perhaps direct mining of dry ice from the polar caps would be better, since closed vessel vaporization automatically compresses the gas to usable pressures. The hydrogen can be derived from ice deposits by mining.
It sure would be nice if we knew where some iron ores were on Mars, no? That’s what exploration (manned or unmanned) is all about: “what all is there?”, and “where exactly is it?” My old book says they liked to use hematite at 70% iron, magnetite at 72% iron, siderite at 48% iron, limonite at 60+% iron. These are all high-quality ores.
Products (wrought iron, steel, cast irons)
What you do with the pig (or sponge) iron depends upon the product you wish to make. Wrought iron is under 0.1% carbon, but has 1-3% finely divided slag particles dispersed within it. It is very resistant to corrosion, easily welded, and able to take a variety of finish coats. It’s very ductile at 30-35%, and tests at 35-47 ksi tensile, with Brinnell hardness 90-110. Here on Earth, it is produced by the puddling process, or by a sequence of the Bessemer process and the Ashton process. These are all air-fired combustion processes. Something new would have to be developed for Mars
Steel is a crystalline alloy of iron and carbon, and perhaps other alloying additives. It contains no slag at all. Carbon content ranges from 0.1% to at most about 1.4%. Low carbon plain steel ranges from 0.1% to 0.3% carbon. A medium carbon plain steel ranges from 0.3% to 0.7% carbon. A high-carbon plain steel ranges from 0.7% to 1.4% carbon. Alloy steels classify by the type and quantity of the principal alloying additive. Low-alloy steels are up to 8% alloy additive total. High-alloy steels exceed 8% alloy additive total. Alloying elements include manganese, nickel, molybdenum, and chromium. Steels can be made by the Bessemer process, the open-hearth process or the electric process. Bessemer and open-hearth processes are air-fired and air/oxygen injected. The electric process holds potential for Mars, as it requires either vacuum or an inert atmosphere.
Cast iron is a general term for iron-carbon-silicon alloys exceeding 2% carbon. These are not malleable, unless converted by appropriate processes involving heat to a different internal structure involving carbon or carbide nodules. Gray cast iron is around 3-3.5% carbon, and 1-2.75% silicon. White cast iron is around 1.75-2.3% carbon, and 0.85-1.2% silicon. The malleable and nodular iron materials are made from white cast iron. Only these last have any ductility. Gray iron is manufactured by the cupola process, and malleable irons by the air furnace process. Both of these are air-fired combustion processes. Something new would have to be developed for Mars. Tensile strengths range from 16 ksi to around 40 ksi. Ductility is 0-2% except for malleable iron, which can run as high as 20%. Brinnell hardnesses range from 100 to 150.
Electric Furnace Processes
This is a big closed room lined with refractory materials, into which gigantic carbon electrodes are extended. There are acid and basic linings. Composition control of the phosphorus and sulfur is far easier with the basic lining, so that’s what is most commonly used. This is a magnesite lining on structure and walls of magnesite and alumina brick. They usually use alumina brick for the roof of a basic-lined furnace. The electrodes are nearly a meter-diameter graphite, and over 25 meters long, and are consumed slowly in the process. The best way seems to be immersion in the melt puddle, which implies charging with molten pig iron (or re-melted sponge iron). You can add recycled scrap to the melt puddle, quite easily. Just watch your composition.
Voltage potential is only around 40 volts, but currents are in the 12,000 amps range, or more. This is for heats ranging from ½ to 20 tons of product. It’s a batch process. On Mars, this will require a substantial nuclear power plant, well over 500 KW. I doubt you can easily generate electricity like that from photovoltaics or even concentrated solar power. (Tons here was really the American 2000 lb ton, but the metric ton is quite comparable at 2205 lb.)
The big advantage on Mars is a furnace atmosphere of vacuum or inert gas. 6-7 mbar CO2 is essentially a vacuum, as far as this process is concerned. The fact that it’s CO2 should not really matter.
Converting Raw Steel to Final Product
You can cast the steel directly to shape, but the properties are not so great, so most steel is cast into ingots (from a few hundred pounds up to 25 tons in size), and sent to a steel mill, where it is re-heated and forged, pressed, and/or rolled to final shape. This would be plate, bar stock, pipe, beams, etc. You’ve all seen movie or video footage of this. The ingot is reheated to forming temperature (yellow-orange heat, almost but not quite welding temperature), and hammered or pressed or rolled into a thinner, more elongated shape. There’s a whole sequence of forming operations for each shape and each ingot size. Rolls are the most common forming equipment for making plate, bar stock, structural shapes, even pipe. Reheat is required between forming operations.
Plain and non-stainless alloy steels emerge from this process more-or-less annealed. Further heat treat / quench operations will harden the steel to high tensile strength, at the expense of ductility. Stainless does not heat-treat (nor is it magnetic, too much nickel). The final stages of forming the structural shape with stainless need to be cold-working, if a hard, high-strength product is desired. Otherwise the material is weak but ductile.
Finished commercial steels can range anywhere from 40 to 300 ksi tensile strength, at 15-22% ductility (I’ve seen stronger at less ductility in military-grade alloy materials). Brinnell hardness can be anywhere from about 110 to 500. All this is specific alloy-dependent.
Okay, that’s the broad highlights of steelmaking. There’s a lot (and I do mean a lot!!) more detail to it, of course. The book included nonferrous materials, too. It was 754 pages. I used it about 44 years ago in a freshman introduction to engineering class. I kept it, because it had so much “good stuff” in it.
Looks like my only failure of memory was the carbon content in wrought iron. I misremembered it as high, like cast iron, when it actually is very low.
GW
Josh -
It's possible we ought to start a steel-making thread. I know how it's done here, and posted that in another thread here in this topic (I forget which one). I dunno how it would have to be done on Mars in 6-7 mbar CO2 atmosphere. But, ultimately it would have to be done, and on a significant scale, if we are ever to plant multiple bases there.
This would be to support general construction of buildings and facilities, and any steel-rail railroads. The scale of it would resemble late 19th-century steel-making plants. That's the scale of construction we're talking about: big buildings and hundreds of miles of track, plus railcars and locomotives.
GW
Here's a silly idea that would not require centuries of time. Just use a nuclear implosion wave to ignite and blast most of the massive atmosphere off the planet Venus. The residuals, plus what outgasses from the surface, plus what you could bring in by crashing icy NEO's, would make an atmosphere you could actually seed with organisms, and fairly quickly turn into something like our own here on Earth. Time scale: under 100 years. Maybe just a few decades. Most of that is the biology.
If we can solve the asteroid defense deflection problem, we can certainly target Venus (or Mars, or the moon) with icy NEO's. Nothing "Star Trek" about that. Although it does assume we are willing to travel outside LEO, and solve the associated problems.
As for the nuclear implosion wave, it was often said to be a very small (but finite!!!) risk during a major (WW3) nuclear exchange here on Earth. It just takes a particular hemispheric detonation pattern of a sufficient number of thermonuclear warheads, to cause fusion of the local atmosphere gases. Nothing "Star Trek" about that, either. A sort of scale-up how the Fat Man bomb was detonated, into the fusion range.
If you blow the atmosphere mostly off of Venus, you no longer have the high-density greenhouse to worry about. You might have some lava that will take a little while to cool. But I don't think all that much. Then, you can tailor the atmosphere you want, just like we have often discussed for Mars.
Because of the slow rotation, an orbiting sunshade system might well make sense, just to ensure no repeat of the massive greenhouse. That's the closest thing to a "Star Trek" technology in the whole plan.
Fusion bombs we can build. Organisms we can engineer. But lightweight space structures thousands of miles in extent? That's "Star Trek". So far, anyway.
GW
Well, steelmaking is a little more complicated than just a hot fire. Although that is exactly how one makes small wrought iron nodules: in a campfire with decent ore and a positive air blast.
Once made, these nuggets can be forged together into a useful-sized ingot, for fashioning various items, but it's still wrought iron. Very high in both carbon content (like cast iron) and slag inclusions (which make it easily formable, hence the name "wrought").
To make real steel, you have to remelt a big pot of this stuff (about 3000 F, 1650 C), then blow oxygen through the puddle, to burn out the carbon to just the right trace amount for steel. The slag floats to the top as a thick layer, rather like the scum floating on overheated hot chocolate. Then, you decant the steel through the bottom, out from under the slag layer, and cast it into ingots (usually about half the size of a diesel submarine battery cell).
Cast steel still has lousy properties, variable all through the ingot. You have to reheat it to just below melting (about 2800 F, 1540 C), and forge it, usually with repeated hammer blows and roller-forming operations, both measured in multiple tons for a typical ingot. This operation produces the typical shapes coming from the steel mill as product, and these shapes have the structural properties we are used to (for mild steel around 36 ksi yield, 80-100 ksi ultimate, in tensile, with a Young's modulus near 30,000 ksi, and a Poisson's ratio near 0.3).
The alloy steels are made similarly, they just add things like nickel and vanadium in the initial melt after carbon burnout. Some of these are heat-treatable after manufacture to very high strengths, others (like 300-series stainless) are not.
To make these materials in industrial quantities requires a pretty big plant. It did in a relative sense, even 300 years ago, when railroads were first attempted here on Earth. Cast irons and wrought irons were usually just not suitable for rails and boilers. It took real steel, just like that used in sword- and gun-making, only just a whopping lot of it. Ship-building did a lot better by the beginning of the 20th century, once steel became available in 10,000 ton+ quantities.
How one would do all this on Mars, I dunno. Certainly not in some analog to a campfire, or even in an analog to a 17th century puddling furnace. But it certainly needs to be done, especially once we start planting bases.
GW
For a stake here, there is a force normal to the stake, some fraction of which (via the friction coefficient) becomes friction parallel to the stake. This also acts in other directions, complicated by the other forces involved in deflecting material out of the way as the stake rotates through the ground. All of the forces are generated by the overburden pressure: the weight of material above any particular plane you want to analyze. A very crude approximation is density times depth, although solids really do not behave like liquids. There is no overburden pressure at the surface, and no friction or lateral resistance to "plowing". Deeper, there is overburden pressure, friction, and plowing resistance, because of gravity.
So, what happens if there is virtually no gravity? There is virtually no overburden pressure, thus no normal force to derive friction or plowing forces from. Hmmmm....
Thought experiment: what happens if you jump off a tall building with a bag of sand and push on the sand bag while in free fall? Now, what happens if there is no bag around the sand? Two completely different outcomes. The difference is the tensile forces of the bag containing the sand, not anything to do with the sand itself.
What I learned at the asteroid defense meeting in Spain in 2009 is that a lot of these small bodies are very unconsolidated piles of rock dust, sand, gravel, cobbles, and boulders, all very angular in shape. The dry ones seem to have zero cohesiveness, like the bag of sand without the bag. The wet ones (the "icy" bodies") seem to have some structural cohesiveness, most likely due to the ice content. Basically, these wet ones are a natural form of the "icecrete" we have been discussing in another thread. (There's been another asteroid defense conference this last year in Budapest, but I didn't go.)
That last about cohesion brings up one more thought experiment: jump off that building with a wet, frozen sand bag. Bag or not, you really can push on it in free fall. What holds it together is not friction, but it is a force that resists very effectively. Cohesion. Also known as structural strength (the names tension, compression, shear, and bending come to mind).
Last few thought experiments: can you drive a stake into a sandbag while in free fall, and will it hold any force if you can? Hmmmm..... Do this with dry sand in a bag, and with dry sand not in a bag, then with frozen wet sand in a bag, and with frozen wet sand not in a bag. Hmmmm. Very interesting. Cohesion is necessary to exert any significant forces on these bodies.
So, how to we get some cohesion on the dry ones?
Use a hollow stake, drive it in with rocket thrust perhaps, then flood the body with water (perhaps as steam) and let that freeze the constituents "in place". Could that hold any significant force? Maybe. If so, then we just dreamed up our first application for the "icecrete" concept on NEO's: a way to touch down and actually stay there for a while, hanging on for dear life, as it were.
Good questions, no?
Hmmmm, rope around the NEO. Interesting. If the body is cohesive to begin with, it might work. Pull tension on the rope, it presses on the surface, thus generating friction, which resists slipping around the body.
But what if the NEO is one of the dry, unconsolidated (zero cohesion) rubble piles. If you pull tension on the rope, wouldn't it just cut into the body? What happens in the thought experiment, if you try to lasso a falling dry sand bag, without the bag?
Now wet the surface down and let it freeze where you want to place the rope. Hmmm. It just might work, unless the rope pressure forces exceed the crushing strength of the "icecrete" you laid down. Very interesting indeed!
I like thought experiments. Very intriguing thing to try. They often raise more questions than answers, though.
GW
One other idea to consider: you have to be able to drill to blast. It's done in "shot holes", not necessarily large ones, although ANFO requires a 9-inch hole. Major construction (as in a real base) always requires blasting to be truly inexpensive. It has for centuries here.
So, we simply have to learn how to drill in low gravity environments. Anything we could get working on the moon would work on Mars at over twice the gravity. Nice to have it so close by, as a playground where we can learn how to do such things, ain't it?
The real trouble will be drilling in essentially zero-gee on the NEO's, later on asteroids and comets.
I'm not even sure a stake would hold in unconsolidated rubble piles like that. Stakes hold by friction as much as anything. Friction develops from the normal overburden "pressure" (weight above per unit area below). On an NEO, that's negligible.
So, is there any friction on an NEO to hold a stake? That (surprisingly enough) is actually a very good question.
GW
BTW, payloads on a Falcon-9 or Falcon-heavy do not necessarily have to fit within the standard payload shroud. They can ride "naked" on top of the rocket, if the form factor is right, and there is sufficient resistance to ascent heating and air loads. We've done that for decades with all the other rockets.
GW
Last I heard, Spacex was already building a Falcon-Heavy pad at Vandenburg. That would be for the huge military payloads.
I knew they needed a big pad to fly from Canaveral as well. 39A makes good sense. I hope they do it.
NASA's SLS might be bigger, if it ever really flies. But I doubt it will be cheaper. It will be hard for anyone to beat the price posted on Spacex's web site for 53 metric tons to LEO from Canaveral. Around $1000/lb ($2000/kg). You just don't do that with a giant government agency and a giant complex of contractors and vendors. We've already been there and done that. Giant logistical tails are just inherently supremely expensive (as the weapons guys like me knew long ago).
Given orbital assembly (as proved by the ISS), you care a whole lot less about having a giant rocket, and a whole lot more about simple cost per unit mass. Once you hit about 25+ metric tons to LEO (the shuttle payload size), the simple unit cost is just more important than any max payload size limitations.
We can build anything of any size now, from docked modules in the 30+ to 53 metric ton class. Kinda makes 100-ton modules less important, don't it?
GW
Just to let y'all know, Spacex has been testing Merlin engines frequently at its McGregor facility, just a few miles from my front porch. I've been listening to the tests the last several days. They did a full Falcon-9 first stage just a day or so ago.
That stuff then goes to Canaveral. It'll be the next launch, which I see is now scheduled for April 30. This is the final COTS mission, condensed from two in the original plan. Actual docking and token (test) delivery of material to the ISS.
The rendezvous is automatic. The docking is done by the ISS crew, using its remote manipulator arm.
Looks to me like the Falcon-9/Dragon system is coming right along, and very smartly.
I know they're testing the super-Dracos out at McGregor, but I can't hear those from 8 miles away. Not loud enough. That'll be the landing thrusters for Dragon-as-planetary-probe, and the launch escape system for manned-Dragon.
I also know they're building a new test stand out there for Falcon-Heavy. Last I heard, it's supposed to be down in a hole, with water-curtain noise attenuation.
Just an update.
GW
Railroads of one type or another would make very good sense for hauling large loads to specific destinations on Mars, just like they do here. It was rail that opened up the American west, not wagon roads. (Bit of history.)
Railroad construction as we know it here uses "gravel" as the roadbed, yes, but not the gravel you are thinking of (the rounded stuff we also use in concrete). It's an angular crushed stone, sieved to size. There's layers of this stuff in different sizes, capped by the half-inch stuff you typically see. The cross-ties are embedded in this stuff, those being (here on Earth) timbers almost a foot square in section.
Some railroads have used concrete ties (the high-speed 150 mph+ ones), but timbers are far cheaper and more cost-effective here on Earth, even considering periodic replacement for ordinary freight at ordinary speeds. (And don't kid yourself about speeds, I've seen freights moving 60-80 mph right here in Texas. All it takes is well-maintained track to make that safe.)
The rails are spiked to the ties with "nails" that are about 10 inches long, and about an inch thick steel, not round, either. These days, rails are welded, and about 6 or 7 inches tall. That's to hold the steady upward growth in railcar weights I've seen the last several years. I've seen hopper cars labeled as 245,000 lb loaded going by at crossings. A lot of these are using aluminum in their structure now, as evidenced by unloaded weights creeping down from around 62,000 lb to about 41,000 lb.
Not sure what a railroad might look like on Mars, given that steel will not be generally available for a long time after the first bases are established, except as an expensive import. Could be a guideway-modified roadway with pneumatic tires at first, although the rolling friction with that is orders of magnitude higher than steel wheel on steel rail. I'm afraid maglev will always be too expensive for routine freight, even here. It's just hard to beat that low-friction rail transport, even after 3 centuries.
The power source for the locomotive needs some serious thought, since the only "fuel" I know of that burns with carbon dioxide is magnesium. Nuclear? Electric? There's several possibilities. The electric train with a central power plant supply might make the most sense.
GW
I quite agree that the experiments need to be run: that high aggregate content eliminates, or at least reduces, the creep behavior of "icecrete". And, that high Young's modulus reinforcement does exactly the same thing. Does anybody have a specific contact at NASA, ESA, or JAXA for proposing such experiments as a small business initiative? I think I could actually run these experiments here on the farm.
As for melting problems, I suggest you do not use this material inside actual human habitations. Outside the heated environs, it would be fine for building construction. That is, assuming my contentions about creep limitations are true. There are few, if any, places on Mars, the moon, or the NEO's, that a shaded location at ambient pressure (or the lack thereof) would not be below 0 degrees C.
Assuming creep is not an issue, I see no reason that pre-stressed "icecrete" beams cannot be used in conjunction with "icecrete" slabs to form the pressure shell of a habitat. Burial under regolith is even better, but I see the freedom not to rely on burial, given a proper coating. The trick is to stay outside the insulation for the heated spaces, not necessarily the pressure shell! Those are two completely different issues.
For roads, scraping the rocks aside from the sand-like fine regolith might do, up to a point, but what happens when your vehicles start to fall in the 100,000 lb local weight class? And what happens when you have a wash to cross (don't kid yourself, these exist on Mars)? In either case, you need a tough substrate underlying your regolith-fines surface, and, you need a "real bridge" to cross the gulley. That's the same pre-stressed "icecrete" bridge beam technology, as the pre-stressed concrete bridge beam technology here on Earth.
Concrete in the sense of Portland cement-bonded aggregate and reinforcement structures, are going to be rare on Mars (or the moon, or the NEO's). Yet the substitution of ice for Portland cement, makes sense on all of these bodies, since rocks, regolith fines, and ice, are present on nearly all of them. And, temperatures in the shade are very cold.
Given the experiments regarding creep and anti-sublimation coatings, I think we're onto something here. This is every bit as important as the mechanical-counterpressure spacesuit idea, and that idea is absolutely critical!
GW
I posted an article with illustrations on "icecrete", over at http://exrocketman.blogspot.com, dated 3-11-12. There are still serious questions, but I was able to pose a list of credible experiments needing to be done. I am still very enthusiastic about such a material.
GW
Well, following Spacenut's links, it appears that water-based paints can be applied to ice, at least here on Earth. Hmmmmm.
Maybe the experiment is really to see what happens to a bucket of (water-based) wet paint in vacuum. If there is no bubble formation, then we can paint poured "icecrete" structures once they are frozen, in vacuo.
The second test is to see if that coat of paint stops the sublimation.
If both tests are successful, then we have a way to create structurally-useful materials and construction parts on Mars, on the moon, or on any other celestial object that has both ice and regolith.
As to color, I'd suggest a highly-reflective white or aluminum pigment, to reduce the absorption of solar energy that could melt the ice. Or, just keep the stuff in the shade. The paint might have to be an imported item, but the paint on a pre-stressed "icecrete" beam weighs a lot less than the beam.
GW
Thanks, Midoshi. I had forgotten the distinction between the vapor pressure above the ice vs the "air" pressure above the ice. Had been thinking vacuum-only, as for spacesuit compression issues so long, I got stuck in that rut.
BTW, "hi". Long time no see, crash and all that.
So, since Mars's atmosphere is generally very dry, the water vapor pressure in that atmosphere would be pretty near zero, regardless of the atmospheric pressure. Summer temperatures in the equatorial regions will get close to the standard freezepoint (triple point), so we can't count on very-cold-ice vapor-pressure reduction. Yep, "icecrete" will need a tough sublimation coating. That material will not know Mars from the vacuum of the moon or space.
I was hoping for some sort of paint coating we could spray on and "cure" right in place on the dirty-but-not-wet cold ice surface. Maybe an evaporating solvent cure with linking residuals like some oil-based paints here on earth.
Hmmm, some sort of water-based latex paint might even work, if it could be kept from boiling before it dries.
Does any body have a bell jar and a vacuum pump? Two ice cubes, one painted at below-freezing conditions with latex house paint, the other not. Maybe three: try an oil-base hardware paint, too. (Maybe even Krylon clear sealer spray - ha ha.) Paints will take a long time to set-up in the kitchen freezer on a not-wet icecube surface, but that's what we need.
Here in central Texas it's never cold enough to do the painting successfully outside, although I have a couple of good freezers. Maybe somebody in snow country?
GW
If Gingrich does get the nomination, which I doubt, he would still have to beat Obama, which the polls indicate as a lower probability, at best.
But, if Gingrich did become president, why should anyone believe he would make good on his promises as regards space (or anything else)? His decades of history in Congress, and as an influence peddler/lobbyist advisor, indicate pretty strongly that he typically tells people what they want to hear, then just does whatever he thinks is best for him personally.
Of course, that kind of misbehavior is no different from all the rest. But, Gingrich is the only one talking bases on the moon while in Florida, but nowhere else. See the pattern? Again?
GW
If you have something from which to build the mirrors, a solar concentrating furnace makes a lot of sense for melting things. I know the ones here are made using mirrors of silvered glass, and with a big-enough field of actively-steered mirrors, can melt steel.
Where do we get silvered glass, or an effective substitute, on Mars? Where do we get the materials from which to fabricate mirror towers than can be steered? Where do we get the electronic/electric controls? We're talking substantial-horsepower electric motors here, and gears to boot.
Looks to me like, initially at least, a lot of this gear has to come from Earth. Chicken-and-egg problem.
GW
I'm still thinking about a coating for "icecrete" to prevent sublimation. If the local pressure is 6+ mbar, then a coating is not needed. But, if it is, then I am not sure PVA (polyvinyl acetate?) or any other organic plastic will be easily obtainable on Mars or the moon.
Re: Mars atmospheric pressure: I have my doubts as to northern lowland pressures really being 6-7 mbar per Viking 1 & 2. Why? Because the recent northern polar lander (Phoenix) saw ice that it exposed while digging sublimate, and fairly quickly. If the pressure really were 6+ mbar in the polar lowlands, that would not have happened. Basic physics.
So, I really think we need an anti-sublimation coating. I'd like the coating to be local materials, and I'd like to avoid the energy expenditure of melting local rock or dirt. This is going to be some sort of chemistry thing. If we find one, it would work at 0.00 mbar on the moon, too. "Icecrete" is a pretty nice thing to have, so the anti-sublimation coating for "icecrete" is really a very important item.
For reinforced "icecrete", any material with tensile strength would do for the rebar substitute. Basalt (or any other rock) fiber would do, braided into a coarse-textured rope. I dislike the energy expenditure of melting the rocks to do it, but it seems unavoidable, since no one has ever spotted an active volcano on Mars or the moon. Ideas?
Does anyone know the elastic modulus of a braided basalt-fiber rope? (It would not the same as the individual fibers, not by a long shot, no real composite material ever has the properties of the individual fibers.) If the rope's effective modulus is near that of steel (30 million psi = 207 MPa), such a rope might in some way be tensioned very hard, thus serving as the pre-stress member in a pre-stressed "icecrete" beam. Not worth dreaming up, if the modulus is too low, though.
Having pre-stressed beams available is nice for bridges and buildings. Good for resisting bending, such as in pressurized habitats. Very important.
GW
A dark horse nobody is talking about is XCOR. Their Lynx should be flying for the first time by year's end. Suborbital flights, single stage, HTO/L on simple tricycle gear at very ordinary lightplane speeds, with a simple delta-wing rocket plane. Ground crew of 3 or 4 to refuel and fly again, multiple times a day. Stick and rudder flying, like a piper cub, just very fast straight up and back down. I've sat in their mockup. Even I could fly the thing.
Mark my words, it's people like that who will solve the practical space plane-to-orbit problem. Extremely tiny logistical tail, just like Spacex. Combined with true reusability, just like Spacex is trying to do. Very impressive. In some ways, they're ahead of Spacex, as regards designed-in reusability and long life airframes.
That kind of thinking did not (I repeat, did not) come out of a government lab. The real smarts is out there in the innovative companies. And it's not all science, either. I'm fond of saying "rocket science" ain't just science, it's about 40% science, 50% engineering art, and 10% blind dumb luck. Because it's true. The government labs have the science, but little or none of the art.
GW
That 6 mbar vapor pressure at 0C is a very nice result. I calculate about 3.8 inches or 10 cm dirt cover will stop all sublimation once the water freezes, and that's in total vacuum. If we use liquid water very near the freezepoint, the vapor pressure is not much higher, so a maybe a foot or 30 cm of dirt cover over a plastic tarp would do nicely while the ice concrete "sets up". That's figured at 0.38 gee, too. It's only 1.5 inches of dirt at 6 mbar here on Earth, inside a hard vacuum chamber.
That means casting ice concrete and getting it solidified without evaporation loss will be relatively easy. Simple backhoe work. Nice. We're going to need an electric backhoe.
My understanding of Mars's atmosphere is that the surface pressure is 2-4 mbar over most of the planet. The 6 mbar is down in the bottom of a very deep hole: Valles Marineris. That's pretty close to vacuum conditions in any practical sense for most of the settlement locations.
You're quite right, some foundations need no forms, only a shaped hole. It depends upon whether you want the top of slab above grade or not. For the rest, sheet metal and maybe rods or tubes as stakes will likely do. Be nice if it was scrap needing re-use. Any sort of building is going to need a foundation to be stable. Unsupported walls sink into and tip over if just set upon dirt. Slow, but fatal to the structure. Takes less than a year here to tear up a loose cement block wall in the garden.
Still thinking about preventing sublimation from exposed ice. Sure would be nice to build bridge beams from water, dirt, rocks, cheap plastic pipe, a few steel rods, and some nuts and washers. Your idea of some sort of plastic paint is very interesting.
GW
The electric furnaces they use for steel-making are using scrap steel as an input. That just a remelting thing.
Making steel directly from pig iron and coke is an enormously power-hungry combustion-driven process. There is a hollow furnace stack fed compressed air and fuel at the bottom, which burn to create heat at the bottom, percolating up through the stack with lots more air injection. There are alternating layers of pig iron, coke, and limestone filling the stack. The coke and the added air burn, the 3000+F temperature melts the pig iron and the limestone, and the molten limestone is a liquid slag coating the puddles of iron so that it does not oxidize.
That's the slow, relatively "energy-efficient" way (LOL). For the fast, not-so-efficient way, look at a Bessemer converter. It's really quite spectacular when they turn on the oxygen lance to burn out the excess carbon. Those processes don't sound very amenable to solar PV to me. It'd be hard to make that kind of chemistry happen at 1200 MWe direct from a nuclear plant here on earth.
What's needed on Mars is a different set of chemistries reflecting the availability of atmospheric CO2 instead of O2. No one knows what that is yet. Maybe we'll be lucky and the yet-to-be-defined process won't be such an energy hog. I wouldn't hold my breath about that, though.
Do we yet know if Mars has both uranium and thorium reserves in deposits accessible on the surface? If there are deposits like that, the entire thorium breeder cycle could be bootstrapped into operation locally with HEU as the starter. The machinery to refine the materials would either have to be imported or built from parts and supplies locally. The smarts to do it is intellectual property shipped electronically from earth. The whole thing is dependent upon supplies of alloy steels locally.
Sort of a chicken-and-egg thing. Those situations always require a kick-start of some kind.
GW
Now there's an idea I hadn't thought of: solar PV with the panels on the freight cars. Neat.
Heat engines on Mars should use something that will react with a CO2 atmosphere. If you have to carry both reactants, that's like rocket vs airbreather: a real disadvantage. Magnesium will, but it's awfully smoky. Raw soot carbon plus solid mag oxide for the "exhaust".
Batteries? Not very energy-dense compared to chemistry of liquid reactants generally, but lithium ion seems to work the best.
GW
If it's unmanned, slow is OK. Use fuel cell electric, water and sunlight are all over Mars. Just load enough H2 and O2 bottles to make the trip.
GW
Why not think some sort of paved roadway, and a rubber-tired truck-trailer-trailer-***-trailer rig? Extremely simple.
We've been talking about concrete substitutes in some of the other threads. We just need a minimally-paved fairly-smooth surface for rubber tires.
The tractor/locomotive unit could be electric, steam, chemical fuels, whatever turns out to be best. It's train, just no tracks. They run 3 and 4 trailer trucks on the highways in Australia, as I understand it.
GW
Is Paul Webb's elasticspacesuit.com site still in operation? He had some good stuff up there, when I was last there months ago, including video clips from old movie footage. That was 1969-vintage stuff that they demonstrated with 6 or 7 layers of the then-new-technology pantyhose material.
Part of the problem MIT is having is the NASA requirement for 1/3 of an atmosphere counterpressure. That's coming from the 1/3 atm they customarily use in the O2 gas suits. Been standard for years like that. That's just about 253 mmHg, or 338 mbar.
But it's more oxygen than we get here on Earth at sea level, which is 159 mmHg or 212 mbar. You don't really need 1/3 atm pressure on pure O2. You don't really even need sea level oxygen. Most of us do fine up to 10,000 foot altitudes. Some higher.
One has to account for the displacement of oxygen by water vapor inside the wet lungs, and should account for exhalation CO2 displacement of O2, but that's a minor effect. I did numbers like that and posted them over on http://exrocketman.blogspot.com, as an article dated 1-21-2011.
The upshot is that 20-25% of an atm's compression will do. That's 152-190 mmHg, or 203-253 mbar. 190 mmHg (253 mbar) is what Paul Webb used in 1969, so he and I got the same answers decades apart.
MIT's suit design can already supply compression like that. What is holding back immediate success is the unnecessary higher compression requirement. How stupid is that?
GW