New Mars Forums

Falcon-heavy will launch 50-53 ton payloads to LEO from Canaveral.  We built the ISS with 15-25 ton payloads in the Shuttle.  Assembly is not a problem.  Cost will be,  once the payload size threshold for practical assembly (25 ton) is crossed.  Falcon-heavy is projected at $800-1000/pound of delivered payload. 

Do you really think a government heavy-lifter will ever be that cheap?  (I don't.)

If so,  please tell me why,  when shuttle was $1.5 billion for 25 tons.  And Delta-4 is way above the competition curve between Atlas-5 and the Falcon family.  Falcon is the better choice,  by the way.  I posted that data on "exrocketman" a little while back.  It's a strong function of payload size,  but flattens some as you get into the 20 ton + range. 

If not,  then why do we need an expensive 100-ton lifter when 2 cheap 50-ton lifters will do the same job?

GW

Rails,  like any beam gravity-loaded on top,  typically resist the worst heavy bending loads between the crossties,  and the worst shear as low-to-moderate shear forces at the ties.  The support case is continuous span across many ties,  not the "simply-supported beam" case. 

Bending is tension in the "fibers" away from the loaded side (on the bottom),  and compression in the "fibers" close to the load (on the top).  Up to the elastic limit,  the stress distribution is linear between the tension and compression extrema,  and zero at the "neutral axis" somewhere in between.  Once you exceed the elastic limit,  another more complicated model applies,  plus you permanently bend the beam. 

You're going to need a shape that takes advantage of tension resistance (the bottom flange) and a stable compressive column (another flange in most I beams,  the rail cap in RR rail),  and a thin web continuously-connecting them that resists the shear.  Rails are just modified I-beam shapes,  configured to match up with flanged tapered wheels. 

For use this way,  the material requires considerable tensile strength.  That's why we like hardened alloy steel for RR rails (nope,  it's not just plain carbon steel,  it's extremely tough to withstand the heavy pounding and the wear).  In metals,  shear strength is usually around 60+% of tensile test strength.  In other materials like rock fiber and crystals,  nope.  The compressive strength comes from the stable column geometry,  not the true material compressive strength. 

Concrete (and similar) materials are strong in material compression strength,  and have some strength in shear,  but are very weak in tension.  That's why we add reinforcement of good tensile strength,  and high stiffness (!!!),  to make concretes that can take some bending.  These reinforced concrete materials get used mainly in compression columns and foundations with compressive loads,  and maybe a little bending and shear, but only if reinforced for it,  like erectable wall panels.  The extreme case is the pre-stressed concrete bridge beam.  Very complicated reinforcement. 

In a composite like a reinforced concrete,  you have to pay very careful attention to how much of each material is present,  and how stiff each material is (Young's modulus and some geometry).  The stiffer one wants to pick up more than its share of load first,  and may fail before the other component can even load up.  The details of actually doing that kind of design analysis are neither simple nor easy. 

With metals like steel and aluminum,  you also have to consider how many times the structure gets loaded ("fatigue").  On a log-log plot,  the load level vs cycles-to-failure is a descending linear line,  down to a fatigue limit stress,  where the line is horizontal,  no matter how many cycles.  That fatigue limit stress is way below the tensile yield stress,  and way-to-hell-and-gone far below the ultimate tensile stress for the material. 

The fatigue limit for steel is typically a bit higher relative to its yield than with aluminum.   That's why we build things that don't have to fly out of steel way more often than we do with aluminum.  Things that fly,  the higher strength/weight of aluminum is better,  unless it gets too hot.

Concrete and organic composites (and wood) are quite different from the metals.  Concrete life is limited by weathering of the surface and corrosion of the internal steel reinforcement.  Shrinkage and weathering cracks are inevitable;  that's how water gets in to do its evil corrosion work.  Organic composite life is limited mainly by UV damage or simple impact damage.  Wood life is limited by wet or dry rot. 

All suffer nuclear radiation damage,  but it really does take quite a lot. 

GW

Elysium 0 lat 155-160 long sounds like a pretty good site for the first manned exploration trip.  Need a geologist-type to go prospecting for the ice,  the lava rocks,  the iron ores,  etc.  He'll need a real drill rig,  too. 

I'd bet you've got a least a dozen similar such sites you could make very good arguments for.  Maybe a lot more than that. 

A smart first manned mission would visit all of them,  and leave transponders.  It's a lot of trouble to send men that far.  Why just make one landing?

GW

Man,  I dunno about all the thermonuclear fusion reaction stuff.  I'm a aero/mechanical engineer,  not nuclear. 

But,  I do recall from reading the old writings of the Los Alamos team that setting off atmospheric fusion was initially of concern for the Trinity test in New Mexico 1945.  They figured out it was of no risk (with dissenters),  so they went ahead with the test,  and the attacks on Japan. 

In the late 1960's,  I remember reading published accounts from the likes of the fusion weapon physics folks,  and some USAF generals,  about the slim chance of an implosion wave detonation pattern setting off fusion burning in Earth's atmosphere during a WW3 extinction-event-size exchange of around 3000 warheads or so. 

As I said,  I dunno myself,  and those fears back then don't seem to square with the reaction data I see posted above,  but I do very clearly remember that those fears were very real at the time.  There must have been some plausible reason for it,  those were very knowledgeable folks.  The specifics are very probably still classified data,  perhaps rightly so. 

Assuming those 60's experts weren't wrong,  then it seems to me that there might be a way to do it on Venus,  and "blow off" that thick blanket in one bright piece of fireworks.  If so,  I'd be less concerned about the fallout,  since the solar wind is a far larger source of nuclear pollution than any puny fireworks we can dream up for some centuries yet.  Sort of a matter of perspective,  I guess. 

GW

For the Earth,  I don't know if it was O-O or N-N fusion.  Given enough density,  all are possible.  The density is created by the implosion wave.  The propagation or quench depends upon the mass that you "implode". 

On Venus at high density,  you have the prospects of both O-O fusion and C-C fusion.  None of these involve the hydrogen species we are used to thinking about.  All are involved in creating the heavier elements in the cores of stars. 

GW

You need not "melt the iron twice" if your reduction reaction produced molten pig/sponge iron instead of solid.  I am not familiar with the Mond process,  but the net effect should be similar to that old plant in Mexico,  I suspect in solid form.  Once you get this stuff,  you have to convert its composition to that of steel,  and that is a melt process,  no way around it.    That's what the electric furnace would do,  at essentially local ambient conditions as a substitute for vacuum on Mars.  You may need to blow or bubble oxygen through the puddle. 

Once you have molten steel,  you cast the ingots,  but you need not let them cool all the way.  Temperature distributions will be necessarily very,  very nonuniform during cooling,  but once solidified,  you bring the ingot to a uniform forming temperature.  Then you can forge,  roll,  and hammer to your heart's content.  It is hard to describe just how useful,  plate,  flat,  bar stock,  pipe,  angle,  tubing,  and I-beams are. 

GW

Venus is a tough nut to crack,  for sure.  If we learn something from terraforming places like Mars and some outer moons,  it would certainly apply,  after the thick atmosphere has been thinned. 

By the time we can go way out there "in force",  we will be wielding a lot more power than we do now.  That power will provide some way to reduce the CO2 blanket about Venus.  Have faith. 

I just suggested the fusion blast as a way to do it "right now" with the power we currently wield.  We just don't really have a compelling reason to do that "right now",  but if we did,  that'd be the way.

Fusion ignition of atmospheric gases is accomplished by hemispheric-inward shock compression of a significant mass of atmosphere against the solid surface at a single point.  It takes a really big wave,  created by the properly-sequenced detonation of an awfully lot of really big bombs.  But it is possible. 

You have to compress a big enough mass to self-sustain a spreading fusion wave outward without quenching.  That's easier on Venus because of the higher density,  but it was possible here.  That's what had some folks scared about a major nuclear exchange at the height of the cold war.  Not enough,  but some. 

Of course,  if you do it (thin Venus's atmosphere) that way (with a fusion wave),  most of the mass of the atmosphere is lost to space.  Destructive,  but effective.  And quick. 

GW

It is certainly possible to live under an ice-covered artificial lake on Mars.  That requires building the lake (earthmoving,  and ice-mining activities,  plus energy to liquify the ice).  Then you live inside the equivalent of a submarine hull,  able to venture outside with a wetsuit and scuba gear.  But,  you are restricted to the lake,  unless you dress for what amounts to vacuum as far as the body is concerned. 

Why not just build the equivalent of the submarine hull on the dry surface and bury it with dirt for insulation and radiation shielding?  It's less total construction activity,  and less earthmoving in particular.  To go outside,  dressing for vacuum does not necessarily require a gas-balloon-type suit.  Mechanical counterpressure garments with a gas breathing helmet rig have existed since the late 1960's. 

These do not need to be one piece garments.  You could doff the compression gloves for up to about 10 minutes at a time,  if barehanded work could be done without mechanical or thermal injury risks.  Depends on how sharp and how cold the dirt and rocks are. 

Although,  for recreational and agricultural purposes,  being able to go outside down in a lake would be very nice.  And,  would that be a good environment in which to grow food?  That's the easiest way I can imagine to pressurize and wet-down very large areas:  under an ice-covered lake.  It takes large areas to grow food for people. 

Hmmmm.  Intriguing idea. 

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

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

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

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