New Mars Forums

Calliban,

CO2 bubbled through a Gallium-Indium-Copper catalyst will produce pure O2 and flakes of pure Carbon that float to the top of the liquid metal column, very near room temperature.  There will be plenty of other losses associated with obtaining CO2, compressing the O2 oxidizer, and possibly liquefying it to further reduce storage volume, but CO2 will always be plentiful on Mars and can be extracted at night and stored as LCO2 using minimal energy input.  The Carbon powder can be pumped by fluidizing it with LCO2.  Storing large amounts of O2, even somewhere pretty cold like Mars, is the most challenging issue.  The exhaust effluent from a gas turbine burning pure Carbon and O2 is nearly pure CO2, which can be recaptured using appropriate cooling and recompression equipment.

The Allam-Fetvedt cycle uses a SCO2 power turbine and recaptures most of the CO2 effluent from combustion for heat re-injection.  Approximately 95% of the "atmosphere" fed into the combustor is actually recycled hot CO2.  The remainder is coal dust or natural gas and pure or O2-enriched "air".  Re-heating of a larger volume of "cold combustible mixture" is not required.  Here on Earth, this cycle is paired with an energy-robbing ASU to produce pure or enriched O2.  Using the Gallium-Indium-Copper catalyst to produce coal dust and O2 would mean the major energy losses are limited to O2 compression and CO2 recompression.

We're going to start operating a 300MWe power plant in Odessa, Texas, starting in 2026.  It was built by NetPower on land owned by Occidental Petroleum, who is presumably supplying the gas.  A 50MWth demo plant has already been built and tested in La Porte, Texas.  The utility scale plant will burn natural gas instead of coal powder, but that's because we have so much natural gas here.  Another similar plant being built in one of the other midwest states will supposedly be rigged to burn coal brought in from the Powder River Basin.  Plant construction for the Odessa facility is nearing completion.  Certification to get connected to our grid is on track to begin next year.

An overhead shot of the La Porte, Texas demo facility:

I can't swear to it, but I believe the Odessa facility is merely a rework of part of an existing 1GWe natural gas fired power plant that's been in operation for some time now.

NET Power Consolidates Business to Gear Up for Allam Cycle Power Plant Deployment

Assuming all goes well in Odessa, and the engineers seem reasonably confident that it will, they're talking about converting 1,000 power plants here in the US and about 15,000 globally.

tahanson43206,

Aircraft propellers are balanced using a method similar to what you described.  The prop is mounted on a level jig using a pin or pipe through its center.  The individual blades are checked for balance by moving them to the vertical and horizontal positions, letting go to determine whether or not the blade falls / moves out of position due to gravity, and then sanding individual blades or adding small weights to the prop.  It's a "trial-and-error" type of process, but those experienced in building propellers become good at determining where material should be removed to achieve balance.  When you can position each blade in the vertical and horizontal positions by hand and let go of the propeller without further movement, static balance has been achieved.  This test is almost always performed by the manufacturer of propeller / rotor blade assemblies.

Achieving dynamic propeller / rotor assembly balance requires some rather sophisticated and expensive accelerometer equipment to evaluate assembly acceleration during operation, but this is frequently done anyway for aircraft propellers and helicopter rotor blades to reduce the vibration generated during flight.  This test cannot be performed by the manufacturer, only the operator of the aircraft, because engine / motor balance in an actual installation is part of achieving dynamic balance for the connected propeller / rotor.  The same would be true of a wind turbine's rotating assembly.  Every installation will be slightly different.  Dynamic balance is typically achieved by inserting a washer or two under the bolts going through the prop hub.  The vibration reduction is physically noticeable by most people, meaning your body can actually feel and your ears hear the difference while seated in the aircraft while the prop or rotor is turning at cruise rpm.

The prop / rotor is effectively a high-inertia flywheel, so if it's out-of-balance while turning, it's pretty noticeable.  The same is true of flywheels and crankshaft balance weights attached to engines in motor vehicles like cars / trucks / trains / boats, but there's typically a lot more vehicle and drive train component mass to help absorb those engine vibrations than there is in aircraft.  Regardless, a perfectly balanced engine / motor, propeller / rotor for vehicles that use them, and drive train will be smoother and quieter in operation.  Excessive vibration is ultimately damaging to the propeller assembly, engine / motor, drive train, and the airframe or vehicle chassis itself, so the less you have, the better.  Engineers who design engines for motor vehicles typically devote quite a bit of time to "Noise / Vibration / Harshness" (NVH) reduction.  Race engine builders will devote even more time than a production plant to perfectly balancing all the components in the rotating assembly of an engine- crankshaft / connecting rods / pistons always, sometimes even the camshafts and other valve train components of very high-revving engines.  Using CNC machines to make parts doesn't automatically guarantee that they're balanced correctly due to "stacking tolerances".  Every mass produced part is made to a tolerance range, however fine.  When money is no object, additional measurement, touch labor, and machining is used to minimize those "stacking tolerances".

tahanson43206,

Are we still on for our 1PM CST / 2PM EST Sunday install of phpBB3 for user-generated image storage?

Suppose we did simply create an open pit "mine" of the kind shown by SpaceNut in Post #30.  The "Superdome" that Calliban want to build is merely a means to an end- pressurized living space, presumably appropriately "greened" using seeds brought from Earth.  Apart from holding in the pressure, I presume the most important secondary reason for piling on so much regolith over the structure is to block-out space-based radiation, primarily the highly penetrating and damaging (slowly but surely) Galactic Cosmic Rays (GCR).  All available literature from NASA indicates that using approximately 2m of regolith shielding is sufficient to absorb enough of the dose to remain below lifetime limits.  GCR is not like SPE / CME radiation, in that it consists of ionized nuclei, ranging in weight from Hydrogen to Iron, although it's over 90% Hydrogen in practice, traveling through space near the speed of light.  There's no practical passive shielding material for an interplanetary spacecraft due to shielding mass, but once the settlers arrive on Mars we're obligated to provide appropriate protective measures incorporated into the engineering of habitable spaces.

Here's a question I'd like the AI to answer for us:
By constructing Calliban's Superdome at the bottom of the open pit mine shown in Post #30, how much Solar Particle Event (SPE) / Coronal Mass Ejection (CME) / Galatic Cosmic Ray (GCR) radiation will the open pit mine block by erecting the dome at the bottom of the pit?

If the protection provided is still insufficient for humans, is it enough for the plants to survive all or most SPE / CME / GCR?

Maybe the humans will still need to temporarily seek more substantial shelter during a SPE / CME, presumably by evacuating to tunnels carved into the rock underneath the dome or into the walls of the pit.  I'm thinking of the open pit mine as being somewhat akin to "castle walls", used to protect the people inside from powerful space-based radiation rather than invaders, but a castle nonetheless.  The Superdome at the bottom is the castle's "keep"- for keeping the people inside warm / fed / clothed.

Erecting a giant dome is supposed to be a significant quality of life improvement for the settlers, so if it still gets sufficient sunlight to grow plants using fiber optics and/or mirrors arrayed around the pit, then perhaps the effort to dig the pit and erect the Superdome at the bottom of the pit still represents an acceptable energy trade for the long term security and psychological support of a miniature Earth-like environment.

I looked into Airloom because their tech is potentially easier to implement at a scale that would actually matter.  The wind turbine industry now consumes more composite and plastic materials than the entire aviation industry.  Similarly, the data center / super computing industry now consumes more barrels of oil than the aviation industry.

INL removed the linked document in Post #370 from their website, or moved it, so here's an alternative link to the same document:

Conceptual design of a CERMET NTR fission core using multiphysics modeling techniques

Edit (in response to tahanson43206's question about the total number of coolant channels):

37 coolant channels per fuel element * 151 fuel elements = 5,587 coolant channels

The Left's Macro-Cult: Recruited to Fight a Make-Believe War

Cast basalt's tensile strength is 30-40MPa, roughly half that of any variety of oak wood.  While it doesn't absorb water at all and is highly resistant to most acids and bases, which is great for chemical processing and brine transport, it's not particularly fond of large thermal shocks or very cold temperatures or impact loading.  Those drawbacks may mean very little for this application or they might become stumbling blocks on Mars since we're operating outside of the normal environmental extremes encountered on Earth.  Here on Earth steel mills frequently use cast basalt as a liner for chemical processing piping and waste stream removal.  Some sewers and runoff systems also use basalt liners.

Basalt can be cast or carved into plates / bowls / coffee mugs, too:

Mexico makes their traditional molcajetes from hand-carved basalt.

I've seen sinks / wash basins, bathtubs, and various decorative pieces carved from basalt as well.  Presumably, all tile flooring, sinks / tubs / toilets / shower stalls / drain pipes for bathrooms and kitchens, and most types of ceramic kitchenware could be made from cast basalt.

For structural applications, are there examples where cast basalt was selected for use here on Earth, just to show that it can be done and has been done before?

How might we improve upon basalt's tensile strength and other mechanical properties to something approaching a plain Carbon steel, if that's possible to do?

Could we add small amounts of Carbon Fiber to greatly enhance tensile strength?

We'd be processing the materials in an Oxygen-free near-vacuum atmosphere.

If that's not possible, can internally pressurized structures be kept in near-uniform compression using externally-applied loads, and how difficult is this to do in practice?

It seems as if that requires very careful engineering and construction, like weighing-out the overburden used to bury a basalt structure to guarantee the applied load matches the engineering calculations.  How generous are the "fudge factors"?  Maybe we can carve tunnels into bedrock and then use cast basalt tiles as abrasion and chemically resistant liners?  That would mimic how we already use cast basalt as pipe liners here on Earth.

You have to heat up the basalt, and presumably the mold, to around 1,300C to pour it like liquid Iron.  I don't know how fast you can cool molded basalt without cracking.  Pure Iron melts at 1,538C.  Inconel and stainless start to melt at temperatures remarkably similar to basalt.  They retain much more of their room temperature strength at higher temperatures than plain Carbon steels, but their alloy content, which reduces high temperature oxidation, actually depresses their melting points.  That's not a major difference in melting temperature between basalt and Iron, even though you also have to source coking coal or Hydrogen to make steel.  I can see how sourcing other materials to make steel would easily consume a huge amount of energy, though.  Steelmaking on Mars could end up being far more energy-intensive than it is here on Earth, so there's sound engineering and economic logic behind choosing a construction material with fewer processing steps and energy inputs.  The actual energy savings may be more modest than Earth-based energy input averages would suggest, though, and it's likely to be the case that making any bulk construction material on Mars is energy intensive.

If we have to make cast basalt structures thicker and therefore heavier to approximate the tensile strength values of steels, then how much energy do we save?

Is the entire logistical tail required to make cast basalt easier to acquire and use for structural applications?

Either way, we're starting from scratch here.  We obviously wouldn't be welding or cutting as much, nor splitting water to source Hydrogen to make steel, but we might need quite a few molds for all the castings (standardization is obviously key here), grinding and polishing to exact dimensions, adhesives with special properties to work in extreme cold to seal the structure, and specialized construction techniques to support above-ground structures before internal pressure can be applied.

Steel has been a staple of construction for the past two centuries, but that's because we have easy access to the energy inputs to mass produce it here on Earth.  Perhaps a modern Mars civilization will be built with stone instead of steel.

tahanson43206,

This document from Idaho National Laboratory describes XNR-2000's conceptual design:
Conceptual Design of a CERMET NTR Fission Core Using Multiphysics Modeling Techniques

It describes materials that were actually tested and proven to survive 3,000K temperatures while exposed to hot flowing Hydrogen.  The total Hydrogen mass flow rate required to achieve a 25,000lbf thrust level, with an Isp of 950s using 512MWth of reactor power output, was 12.05kg/s.  At the exhaust temperature / velocity associated with a 950s Isp, we'd therefore need 45,150,618Wth of input power per 1,000kg-f.

Edit:

This idea that the core heating length needs to be kilometers long is completely bogus.  I have no clue where it comes from.

Let's tally the total coolant flow channel volume.

0.1778cm^2 * pi * 90.69cm = 9.006847cm^3
9.006847cm^3 * 37 channels per fuel element = 333.253339cm^3
333.253339cm^3 * 151 fuel elements = 50,321.254189cm^3 (about 0.05m^3)
50,321.254189cm^3 / 12.05kg/s = 4,176.037692cm^3 per 1kg/s
The above is not exact since there's a power density difference in different core regions, but it's close enough.

50,321.254189cm^3 / 512MWth = 98.2837cm^3 to transfer 1MWth

1kg/s produces 941.064kg-f, so 1.063kg/s produces 1,000kg-f at 950s.

Let's say we did use a singular tube to transfer core thermal power, for whatever good that would do for us:
151 fuel rods * 37 coolant channels per fuel rod * 90.69cm core length = 506,685.03cm
506,685.03cm / 12 = 42,223.7525cm = 422.237525m

If we had a mere 37 individual coolant channels to mimic a single fuel rod, then the length of each heat transfer tube is 11.412m.  Presumably, we can manage a heat transfer tube length of 1m with 422 heat transfer tubes.  If each tube was "touching", then the width of a planar heat transfer device is only 150cm across.  Obviously we'd need spacing between tubes to contain the pressurized Hydrogen, but it's pretty easy to determine that a planar device with 422X 1m length heat transfer tubes is far less than 1m in width.  If the thickness of this "hot plate" was 2X that of the tube diameter, then it's only 7.112mm thick.  The device could be made from Tungsten and its total mass still wouldn't matter all that much to the performance of this low-thrust vehicle.

If we had a "hollow cylinder" (aka, "a pipe") device with a bunch of heat transfer pipes drilled through the pipe wall, with a gas manifold on each end, somewhat similar in external appearance to a NTR reactor core, but with a big empty space where the reactor fuel would normally go, then we ought to arrive at a mass / volume / length remarkably similar to an "empty" NTR reactor core (since our heat is being applied externally by concentrated sunlight, rather than generated internally through fissioning Uranium).

tahanson43206,

Assuming I did this correctly, which I may not have since it's been about 20 years since I took trig...

For a 200:1 expansion ratio, given Athroat = 2.5cm^2 Athroat, then Aexit = 500cm^2.

r = sqrt(A/pi)
sqrt(2.5cm^2/pi) = ~1.772cm
sqrt(500cm^2/pi) = ~12.616cm

GW said keep the nozzle wall angle between 12 and 15 degrees to minimize erosion, so I'm going with 15 degrees:
base * tan(90-15) = height
12.616 * tan(75) = 47.084cm
1.772 * tan(75) = 6.613cm
47.084cm - 6.613cm = 40.471cm = height of the frustum (nozzle length)

Anyone who wants to analyze a nozzle design can do so using the 3 software packages from the links I provided in my prior post in this thread, but you will need to know some design fundamentals- terminology, the basic equations involved in nozzle design, some gas and combustion kinetic fundamentals applicable to chemical rocket engines, etc.

I realize that our particular design problem only involves Hydrogen as a monopropellant used to produce NTR-like Isp using photonic power from the Sun, yet nearly all of the fundamentals still apply.  Combustion kinetics won't apply since this engine does not use combustion to generate heat, but still useful for general understanding of liquid rocket engine nozzle design.  GW can tell you if there are any major differences in solid vs liquid nozzle design considerations, but I think combustion kinetics would affect the design differently since combustion begins inside a rather lengthy motor casing and propellant grain geometry differences greatly affect reaction rates and thrust.

As a monopropellant, Hydrogen has some unique thermal properties and at the temperatures involved, hot flowing Hydrogen would cause a severe chemical attack against certain kinds of materials, especially metals, but the materials I specified are known to be resistant to that attack from the work NASA performed for the ROVER / NERVA Nuclear Thermal Rocket engine programs.  Specifically, Hydrogen has the highest heat capacity of any element, a bit over 14.3kJ/kgK at or near room temperature.  That's another way of saying it requires an enormous amount of heat energy input to raise the temperature of 2kg of H2 (the mass flow rate we previously agreed was necessary to achieve our thrust target) from 20K to 3,000K.

The radiation plume would've been a significant problem, but I feel like the overpressure effects from supersonic flight are a bit exaggerated.  Back when the Air Force was still studying this, researchers were uninjured by a 144psf overpressure produced by a supersonic F-4 flying 100ft overhead.

Roughly speaking, Project Pluto envisioned a F-4 mass vehicle (61,000lbs), albeit with significantly improved aerodynamics, moving at Mach 3 at low-level only for the penetration run into Soviet airspace, using its 513MWth / 35,000lbf engine.  However, this nuclear ramjet powered "cruise missile" would've flown at much greater altitudes while loitering and cruising into the target area.  Its onboard autopilot would direct the weapon to descend to treetop level only upon entering enemy airspace.  As far as "unlimited range" is concerned, that should be heavily qualified.  Range was estimated to be around 113,000 miles, so this thing could "only" fly around at Mach 3 for two days or so before the reactor core suffered too much thermal damage and/or the fuel was depleted to the point of no longer able to maintain Mach 3 flight speeds.  Perhaps the weapon could fly over longer distances at reduced speeds and temperatures, but the notion of it staying aloft for a month or more was mostly fantasy.

How or why this weapon would ever be more useful or more lethal than a conventional ICBM equipped with a dozen MIRV warheads is beyond my understanding.   ICBMs reach their targets in less than 20 minutes, regardless of where they're launched from, and travel at speeds far beyond Mach 3.  To this day, there are very few known-effective defenses against ICBMs.  Successful interceptor weapons typically cost more than the nuclear warheads / ICBMs they're being fired at.  There have been many successful interceptions of much smaller sea-skimming supersonic (Mach 2-3) anti-ship cruise missiles and target drones.