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Mark Friedenbach:
Thanks, Mark. I didn't know myself that anybody had seriously been looking at this NEO resource production cost issue. I'm an old guy (very old now), and I've not kept up very well with what's been going on in much detail. Old guys are like that, we're getting tired.
Be careful, though: I would say this about guys who "built their careers" on some technological item. We started "seriously looking" at scramjet propulsion ca. 1960, and many famous folks that I knew personally "built their careers" looking at it, without any significant success (and I do mean zero) until the USAF X-51 test very recently. That is over 50 years. (The NASA X-43A tests in 2004 do not count, being only 1-second burns after rocket boost to full speed, with no thermal energy balance, and no acceleration under airbreathing power.)
Point is, guys who "build careers" on a difficult problem actually have a vested interest in not solving said problem. I can say that with a lot of believability, because I'm just about the US's last living all-around expert in (subsonic-combustion) ramjet propulsion, and scramjet is something I kept up with long ago as a possible second specialty. This vested interest problem in scramjet is not any different in any of the other technology niches. Never has been. Never will be. Human nature.
I'm not so sanguine as you are about rare-earth ore concentrations in stony or metallic asteroids. This is all based on remote observation and (most significantly) inferred numbers. The actual history is that "ground truth" has always been vastly different than any of the remote observations ever led us to believe, for well over a century now.
There is also subsurface versus surface to consider. Few coal mines show high carbon concentrations on the surface for any kind of remote sensing to pick up. Same for oil. It really does take a deep drill rig or some equivalent thereof. And it will out in space, too. That’s also been the history of things. So, be very skeptical of anybody’s claims to “know” what’s really out there.
But, yes, it's well worth going to find out. It always has been, for well over half a millennium now. That’s another lesson from history. Knowing that, and actually believing in it, is a source of faith, I suppose.
Keep the faith....
GW
As I said earlier, for some decades yet, the whole thing about space resources centers around LEO. What is the price of a gallon of clean water in LEO? (Or the price of any other commodity in LEO.) I gave some data in an earlier post for the delivery cost of water to LEO.
That brings up total cost: there are two components to it. One is the delivery or transportation cost, for which we have pretty good figures Earth to LEO. Figures for transport from the moon or other places are more speculative, but are at least estimatable in ways we can at least debate. The other major cost item is processing/recovery costs on-site at the resource location. For water on Earth, in the industrialized countries, this cost is almost trivial at pennies per 1000 gallons, plus or minus. (Not so in the third world, lamentably, I might add.)
Here is where we have no data at all: what will it cost per unit of product to produce that product on the moon, Mars, an NEO, or anywhere else? Not only do we have no data, but also we don't yet even know how it can be done at all. Nor do we have a clue what the set-up costs will be, that have to be amortized over the (also still-unknown) life of the system. And, it's probably a completely different system at each different site, even on a single planet like Mars. Every site is different: you don't mine coal the same way in Wyoming that you do in West Virginia, for example.
That being said, it is still fruitful to dream up ways this task could be done. The ones that are simplest, with the smallest energy and effort inputs, and the smallest waste factors, are likely to be the least expensive ones. At least, that's been the history down here at home, so it's a good place to start.
Accordingly, I am concerned by proposals that might require enclosures of very large size that also have to input very large amounts of energy, as in capturing and "cooking" or "grinding" small asteroids. Enclosures like that are expensive to build, to launch, and to send to remote bodies. The power supplies for the proposed operations are even worse. Example: shuttle's 25 KW solar array was 65 feet long, several feet wide, heavy, and expensive. We might get 50 KW for the same costs today, but that's a far cry from the 10's to 100's of MW for melting rocks.
That's why I recommend looking first for really high-grade "ores", such as nearly-pure water ice, that would require very little quantity of nothing but low-grade heat at low temperatures to process the resource, at worst a bulldozer or backhoe to recover it (as on the moon or Mars), and a lightweight/low-pressure or otherwise "negligible" container for processing and transport. For example, ice can be shipped almost but not quite naked through space, and supplies its own structural strength to do so. This is highly to be desired. You just need a few millibars worth of containment pressure of water vapor to stop sublimation.
I looked first at ice because it is a source of water, oxygen, and hydrogen, things any human presence in space must have to survive. The two gases are propulsion energy even for a robotic presence. But, minerals and metals you have to look at in the very same way. Picking up iron meteorites on Mars might be a good way to accumulate that commodity. So would deflecting a nickel-iron asteroid into a suitable orbit.
The asteroids and comet cores will have some variable amount of volatiles (ice, ammonia, and CO2, largely), and a lot of stony solids. I doubt if most of these would be very rich in real metals of interest, like iron. As limited as we are for the next few decades, it's the very small ones we might process for products, limited primarily by launch of equipment from Earth (as we are). Very-thinly spread metals imbedded as part of the stony materials are not (yet) of much interest, as the yield is just too low for the processing effort, just like low-grade ores here on Earth.
I would look in some way inside these bodies for high ice content in an otherwise undifferentiated structure, in sizes under 50 meters. You enclose the thing gas-tight in a thin shell, apply solar heat, and melt the ice. The initial spin of the body becomes your enclosure's spin (how to practically achieve that I'm not yet sure). The atmosphere inside your enclosure becomes some fraction of an atmosphere's worth of ammonia and CO2 as the volatiles sublime. Inside the spinning enclosure, the ice liquifies to water and separates centrifugally from the stony particulate content. Your enclosure does need to be strong enough to take the "whacks" as the asteroid breaks up and its pieces fall radially outward under centrifugal force. No plastic films here!
You pump the now-clean layer of water to lightweight "tanks" and let it refreeze there. Compress, separate (not sure how), and store the ammonia and CO2 in gas bottles. Then bag up the stony particulates for shipment, if they represent something you can use. If there were iron, I doubt you could separate it magnetically, because nickel-iron isn't magnetic.
Done automated or by remote control from a practical distance without an hour's time delay 2-way, a rig like this could move from NEO to NEO and process them into usable products for several years. That's the kind of thing that just might be able to supply water to LEO for under $7500 per gallon. If we're lucky and we're good at designing this, the price might be well under $7500 per gallon in LEO.
The smarts for doing this does not lie within a government lab anywhere in the world, not NASA, nor any of the others, it lies within a visionary private group. The smarts for everything we ever did never lay within government labs, it was in the contractors and vendors they hired to do the job. Many of those have grown too large and stultified to qualify as visionary anymore. Truly visionary private groups are rare indeed. Spacex is one. The new asteroid mining venture (PRI) is another. The tourist space companies are some others. That's the fertile field you cultivate to get anything revolutionary done.
Ammonia and CO2 might not have much value in LEO. But for a colony or base on Mars, ammonia is a good fertilizer for crops, however they are grown. And compressed CO2 from an NEO might be cheaper and easier than trying to compress atmospheric CO2 from 7 mbar to 2000 psi. It's a different place; you have to think differently. As in a multi-way trade network among the several colonies we would like to plant eventually.
GW
My idea about Saturn was to take advantage of mostly-pure water (as compared to very thinly-spread water on the moon and most NEO's), not much processing required if the "ore" is very rich. The capture and processing, as I described the very-slightly elliptical or inclined orbit, could be done automated. Even the shipment from Saturn could be done automated or by remote control.
Without men aboard, what difference does it make if the one way transit time is 5 years? Just ship a load out every few months, and a while later, start seeing shipments arrive every few months.
I know Saturn has a gravity well, so does Mars, the only other known source of high-purity ice off Earth.
What we're addressing here is the price of a gallon of clean water in LEO. With the shuttle, at $1.5B per launch to a max of 25 metric tons, and 8.34 pounds in a gallon, that was about $227,000/gallon from Earth. With Atlas-V 551/552 or Falcon-9 at about $2400-2500/pound, that's about $20,000/gallon from Earth. Projected with Falcon-Heavy at $800-1000/pound, it's about $7500/gallon from Earth.
Water from the moon, Mars, NEO's, or Saturn should be under about $7500/gallon "turnkey" delivered to LEO to be competitive, once Falcon-Heavy enters service the next year or so. I'd think that could be done in an automated fashion from any of those destinations, but I don't yet really know.
GW
I was just thinking of very little objects, a few meters or smaller. Things to enclose objects like that we can build, right now.
The Saturn rings idea: last I heard these particles were very small objects, like snowballs and snowflakes. It occurred to me that a very slightly elongated or inclined orbit might allow my "craft" to move into one of the rings and then out for a while, with a very slow relative velocity while in the ring: maybe 5-10 mph.
While in the ring, you scoop up material, and while outside the ring, you close the opening and process the captured material for the products, especially water. After you accumulate a bunch of water, it might be worth shipping inward toward, maybe, Mars. I was looking at the rings for a high yield of water, and very little of the solids.
Just a screwy idea.
GW
Metals I understand. Some stony minerals might also prove useful, who knows yet? Water (and other volatiles like ammonia and CO2) I think vary very greatly from object to object, and are likely the "matrix" that sticks the sand, gravel, cobbles, and boulders together, sort of a natural "icecrete".
What we have been calling "asteroids" have lesser volatiles, what we have been calling "comets" have more, but I'd bet real money these are really just a spectrum of volatile content, not two distinct classes of objects. The drier ones are the really loose rubble piles.
I would think enclosing a small asteroid/comet object inside a pressure "shell" of some sort, rated in a dozen or so millibar pressure capability, and heating the body to the ice-melting point 0 deg C, would separate the metals and minerals as solids, and the volatiles as liquid water and gases. Spin the vessel a little to separate these materials centrifugally, and then pump the gases and liquids where you want them.
I'm wondering if the rings of Saturn might not be a happier hunting ground for volatiles, especially water. Does anybody know if we have a composition, and particle density, for any of those rings yet?
GW
Peroxide can be handled OK, but not at full strength. 50% peroxide in water is the max accepted strength for safe long-term storage. You distill it up to 90+%, use it, then dilute what you didn't use back down under 50%. At 90%, you've only got 3-5 days before it spontaneously decomposes, and very violently, too. That's why the scheme never really caught on for the submarines. But, ignition of peroxide with hydrocarbon is hypergolic.
I think what RobS is proposing with exhaust gas dilution is fuel+oxygen, diluted by combustion gases. It can be made to work, but you have to cool the gases before you can feed them back. Since heat transfer is intrinsically slow compared to chemistry, that'll be the limiting factor on any design.
As for making hydrogen peroxide, I dunno. Never looked into it before. But I know it's done in very large quantities industrially. I've seen tank car trains of under-50% going by at RR crossings.
GW
I ran a crude ideal chemistry balance that assumed a "hydrocarbon" at an empirical H to C ratio of 2:1, and ideal conversion to nothing but CO2 and H2O. It balanced out as: CH2 + 3H2O2 = CO2 + 4H2O. By mass, the required peroxide to fuel ratio is about 7.3. The steam to fuel mass ratio is about 5.1, and the CO2/fuel mass ratio is 3.1. It might balance a bit different with methane fuel, but crudely in the same ballpark, I think.
That's a lot of steam to dilute the fuel-oxygen 6000F reaction down to something cooled steel can contain. Burning fuel and air, the nitrogen in the air fulfills the same dilution role, so that fuel air reactions at stoichiometry are in the 4000 F neighborhood, not 6000 F. Air/fuel by mass is typically near 14-15 with hydrocarbons.
The diesel-peroxide submarine propulsion scheme was not as efficient as sucking air on the surface or through a snorkel, but it did allow short bursts at high power while very deeply submerged. They did it in the same diesel engine as ran diesel and air normally. But I know little of the details. Normally, diesels run very lean of stoichiometry, and control power by mixture ratio, there being no air throttle at all.
Exhaust gas feedback in cars is a very small percentage, and is done mainly to finish burning fuel-like pollutants that couldn't get burned completely before the exhaust valve opened. It's a hot enough feed that your EGR valve will fail from corrosion, sooner or later. Mine certainly did, just not long ago. It upsets air/fuel mixture just a tad when that happens, knocking about a mpg off of about 30 mpg.
GW
The longer form of what I posted just above is now posted for all to see at http://exrocketman.blogspot.com, in the article dated 4-23-12. The details and all the rationale are there. I included no illustrations.
GW
I didn't say it in my long post just above, but yeah, by all means take some experimental ISRU gear on the first mission and try it out. It's just not smart to count on it for crew survival on that first mission, because the probability is, it won't quite work right. Maybe not at all. That's just the nature of engineering development.
If the first mission really does get done right (and I think that is a low probability, given NASA's track record since 1972), then the second mission really could be based on the surface at one, at most two, sites, instead of LMO. Some better ISRU machinery prototypes could really get "wrung out" on a mission like that, but it's still just plain stupid to count on them for crew survival. My experience with engineering development (19 straight years) is that "second time up" still does not work well enough to serve. Doesn't matter what you are attempting, that's just pretty much a "given" in the real world.
That's why I'd like to see two properly-sequenced government missions before a corporate visionary takes over, like Musk. (Boeing and Lockheed-Martin = ULA sure as hell won't.) By that time, he will have both the lander and the ISRU technology, to really succeed at planting a proper base, one that might actually become a nascent colony.
Do it wrong or out of sequence, that colony just plain will not happen in the next century, at least. It'll take that base/colony a significant while (measured in years) to become self-supporting. That's been the history of things. That's also why ULA won't plant it: no short/near-term profit in doing it, unless the government pays them to do it. And I can pretty much guarantee you that it won't.
GW
I rather think that if we're lucky, there will be two government-funded "exploration" missions to Mars in the next 20 years. If we're really lucky, it'll be a coordinated and sequenced pair of mission objectives from the same government or consortium of governments.
If we're not so lucky, it'll be a duplicated first landing "exploration" by different governments. If we're not very lucky at all, there'll only be one government mission. Most likely, there won't be any. Not the way things have been going since 1972.
A government "exploration" mission is the enabling prerequisite for a privately-funded trip, generally speaking from 500 years' worth of history. The exception today is Musk/Spacex. But, he lacks a manned landing vehicle. His Falcon-9, Falcon-heavy, and manned Dragon, plus an inflatable spacehab module (perhaps from Bigelow), is pretty much all we need to get men to Mars orbit. But to the surface? Hmmmm.....
I consider it possible but rather unlikely that Musk might beat a government mission to put men on Mars, precisely because of the lander problem. One-way suicide missions are not the answer, although a Dragon might just be able to pull one of those off.
With chemical propulsion, and the rockets I named, it is fairly easy to stack up enough propellant modules, some engines, a spacehab module(s), some crew return Dragons, and maybe a lander or two in LEO. You end up throwing away all the propellant modules and perhaps all but the crew return capsules. But you don't need a gigantic rocket to do this. That gigantic rocket development development is why NASA is starved for money everywhere else, and it's just not necessary. Once you're at or above 25-ton shuttle payload sizes, only cost per unit payload to LEO matters anymore. We're there already, with Falcon-heavy and the Atlas-5 551 configuration.
With solid core nuke propulsion, you can do exactly the same slowboat job, except that you can keep most or all of your ship, and use it again for the second mission. If you can do that, then why not? Why launch all that stuff twice, and throw it all away both times? That's utterly stupid. Resurrecting NERVA for the Mars mission(s) is way to hell-and-gone far more important than developing another gigantic moon rocket from shuttle technology. Mars transit propulsion is what NERVA was originally for.
Radiation: two different types. Cosmic background 22-60 REM/year, astronauts currently allowed 50 REM/year, with an accumulated career limitation. Close enough even at worst I'd say we can get them there and back without killing them. But, one 2- or 3-year round trip is pretty much a career limit. No second trips. Solar flare: just requires some water and wastewater tanks around the crew as a suitable storm shelter. I'd make it the vehicle's flight deck, myself.
Microgravity disease: just build your vehicle as a long stack, put the hab on one end and the engines on the other. Spin it end-over-end. 4 rpm at 56m "radius" is one full gee. The ship should stack up way longer than 112 m long anyway. Also solves a world of problems cooking, bathing, toilet, etc. Just de-spin for maneuvers or docking operations, then re-spin for coasting cruise.
Consider sending the landers and landing supplies, and all the landing propellants, as separate vehicles assembled out of modules in LEO. Just send it/them one-way. Have it all waiting in LMO for the crew when they get there. Send the men with enough propellant to get home, in case rendezvous fails in LMO. Suspenders-and-belt. Dead crews are more expensive than anything else at all. Just ask NASA.
Myself, I'd solve the lander problem before I designed anything else. Those are dead-head payload. The more landings you make, the more landers you send, the more you have to launch from Earth, the more it all costs, and the less likely it'll ever get done. But, exploration is not "flag-and-footprints". What we did in Apollo with one trip-one landing was not really exploration at all. Don’t think like that. Too many still do.
If there were a single-stage re-usable lander, you don't have to send very many, yet you could still make a lot of landings all over Mars on that first mission. Chemical can't do that job. NERVA could. And push all the landing stuff to Mars, too.
Just some ideas to consider.
GW
Need rails? Use dirt path?
Sure, it's done all the time, especially in Australia. The only difference between a train of truck-trailers and a train on rails is friction. Any sort of wheels (pneumatic or solid) on roads, especially dirt roads, is very high friction. Rail friction is (2-3 order-of-magnitude) 100-1000 times lower.
If manufacture of the engine propellants is tough, then that's a serious issue to consider, since fuel use is proportional to the friction.
GW
It would be very hard to build a Bessemer converter that worked in a near-vacuum CO2 atmosphere. Direct reduction would be much better. Easier to do, because it's all closed reactor vessels that don't care what's outside.
You'll have to melt the sponge iron in an electric furnace, adding just the right amount of carbon and alloying elements. The electrical demand to power that is enormous.
We do it all the time here with our electric grid, but on Mars with no grid at all, that's going to take dedicated atomic power of large capacity. I would suggest a big water electrolysis plant powered by a big reactor. The electrolysis goes offline in favor of the furnace when making steel. That way the reactor itself runs a constant power.
GW
I knew of paper designs based around the NB-36 airframe for a test nuclear turbojet, but to my knowledge it was never actually flown. They did fly a test of a reactor in the NB-36, as a sort of safety prerequisite for the nuke turbojet test. That's the flight with the 500-mph-impact containment vessel. But to my knowledge, there was no heat transfer loop flown.
The turbojet test bed for the B-52 wasn't anything to do with the B-36. The initial B-52 designs (Boeing) were for a turboprop similar to the Tupolev Bear. That turboprop was tested on one or two old B-17's, replacing the bombardier/nose gunner compartment, making it a 5-engine airplane. When they (Boeing) decided to go turbojet, the engines were based on those powering the 6-engine all-turbojet B-47 (also a Boeing airplane). Not exactly the same engines, but a later model. GE's I think it was, but I could be wrong about details like that.
Convair/General Dynamics had a competitor (the B-60) to the B-52 that was based on its B-36. They swept the wings and tails, pointed the nose a bit, and put 8 turbojets under the wings, very similar to Boeing's final B-52 jet design. Convair's entry was the YB-60, Boeing's was the YB-52. As it turns out, Boeing won. The two aircraft were quite similar in characteristics, as it turns out.
Convair's "last gasp" in the strategic bomber business was the B-58 Hustler. Impressive aircraft in many ways, but a one-way suicide trip on its design mission, and no hold-at-a-failsafe-point capability. Compared to the B-36 and B-52, its practical range was way too limited, precisely because it flew so fast. Supersonic is very expensive in terms of fuel.
As General Dynamics, they (Convair) did a pretty good job, and made a lot of money selling, the F-111. Turned out to be a very good attack bomber. Not a fighter at all, in spite of the "F" designation. And there's the F-16, one of the finest fighters of all time. General Dynamic's other big division was/still is the Electric Boat Company, which builds most of the Navy's submarines, even today.
GW
ps - sorry, we seem to have wandered very far afield from the topic of terraforming Vesta.
You know, if this fuel-peroxide diesel thing were to work, then that makes possible locomotives on Mars not too dissimilar to what we have here. Not the same, but the same basic idea: IC/electric series hybrid.
That makes railroading possible big-time on Mars, once a set of bases (nascent colony) get planted. And that makes possible bringing together resources from different regions to one place to do manufacturing. It's a real bootstrap/chicken-and-egg process, but we've already done it here.
That's a major piece of technology that needs to be nailed down. It's not a prerequisite for a first mission, but it sure would be an enabler for a real settlement.
GW
There was something about nuclear jet propulsion, NERVA, and Timberwind, earlier in this thread. NERVA was an enriched-uranium solid-core nuclear thermal rocket that received a lot of ground test and development work in preparation for a flight application that got cancelled right before it flew. The gross characteristics of NERVA as tested were Isp 750-900 sec, engine thrust/weight 3.6, and a longest-demonstrated single "burn" of 47 minutes (yep, that's minutes!). NERVA and its predecessors like Phoebus and Kiwi, were part of AEC/NASA "Project Rover" for nuclear rocket propulsion.
Timberwind was a fluidized-bed improved design concept that never got much ground testing. There were others as well, such as an alternate-geometry solid-core design called Dumbo, which I think actually had more potential than Timberwind. The consensus potential of solid-core nuclear thermal rocketry based on 1970's experience was Isp 1000 sec, at engine thrust/weight 4, and several hours of restarts and accumulated burns, based mainly on Kiwi/Phoebus/NERVA.
The entire program was prematurely cancelled in 1973 before it could fly. The intended initial application was a replacement third stage on the Saturn-5 for the S-IVB third stage. It would have at least doubled the payload capacity of the Saturn-5 to the moon.
There were two gas core designs (generically "Lightbulb" and "Open-Cycle"), and several fluidized-bed (like Timberwind) or liquid-core ideas. None got tested beyond the level of academic university bench tests. All were part of "Project Rover", but none ever made it to any sort of real engine tests. Of these, the "Open-Cycle" idea was probably the closest to reality, being limited more by its waste heat radiator design than by anything associated with gas phase nuclear reaction controllability or by its degree of gaseous (actually plasma) uranium containment.
The B-36 "nuclear airplane" thing was most definitely not a nuclear jet engine. There was one NB-36 built and flown that had a working nuclear reactor aboard. The containment vessel for it had been crash-tested on the rocket sled at Holloman AFB, NM, to 500 mph impacts into solid stone without leaks. But it was no engine, just an ordinary reactor for a power plant, inside an extraordinarily-tough containment. Just the reactor, no steam loop, no generator turbine. They did generate thermal power in flight, but no electricity. I do not remember the government project name under which this was done, but it was 1950's vintage.
The nuclear jet engine was done under "Project Pluto", which I believe was AEC/USAF, nothing to do with NACA/NASA. It was 1950's-1960's vintage stuff. There were a lot of concepts investigated, but the only one actually tested was the nuclear ramjet. There used to be a facility for it at Jackass Flats, NV, on the government nuclear test site, alongside that for "Rover" and NERVA. A little of that stuff is still there, most has been disposed of.
The government supplied the reactor core, and LTV Aerospace was the airframe prime, for a nuclear ramjet cruise missile application. It was to cruise "forever" at low altitude and Mach 3, and divert to Russia and explode if war ever broke out. There was a separate megaton-range warhead for that. The engine was tested in direct-connect ramjet test mode at Jackass Flats in full scale and at full power, but the vehicle never flew, fortunately. It was superseded by rocket ICBM's in 1962. The nuclear ramjet spewed enough radiation, and more importantly its trailing shock waves and noise were so lethally loud, it would have killed more people on the ground as it cruised, than its warhead could ever have killed by exploding.
The only other nuclear propulsion effort was USAF "Project Orion" from about 1959 to 1965, when all military space was cancelled and diverted to NASA, excepting MOL, which wasn't cancelled until 1969. This was the nuclear explosion drive, based on in-company research by General Atomics in San Diego, from about 1950-ish up to 1959. It wasn't supposed to be anything but paper studies, but General Atomics couldn't resist, and flight-tested explosion propulsion with ordinary high explosives in a 1-meter long test article. It worked great, and just as predicted.
Nuclear explosion propulsion as it was understood ca. 1960 requires a shaped-charge fission device (that we could actually build) that is actually rather unsuitable as a blast weapon. It is very peculiar: working more efficiently in very large vehicles (10,000+ tons) and not very efficiently at all in small vehicles (few hundreds to 1000 tons). In 1959 the baseline paper design vehicle for "Orion" was 185 feet in diameter and 280 feet long, weighing 10,000 tons at surface launch. It spun for artificial gravity, and was designed for several dozen crew for a 2 year round trip to Saturn and back, single stage, stopping off at the moon and Mars along the way.
I wish we'd built that one. We still could. "Orion" was viewed by NASA as a competitor to "Rover", so they "cancelled" it by lack of funding in 1965.
GW
I rather think Zubrin is wrong claiming atmospheric CO2 can be used on Mars as the dilution gas for fuel-oxygen combustion inside engines. The compression required is simply technologically infeasible on Mars. Thermodynamics requires engine cycle pressures similar to those here on Earth for decent output. Here on Earth, the source to be compressed is at 1 atm, on Mars it is at about 0.006 to 0.007 atm. We do not have compressors capable of compression ratios that high, in a physical form that could be part of a practical engine.
That's why I suggested the diesel/hydrogen peroxide scheme with the steam dilution gas "built-in" to the already-pressurized propellants. There's a reason they tried this (and not hydrazine decomposition) as submarine propulsion from late in WW2 until atomic power came along in the mid and late 1950's. It actually worked at practical levels of power, and with practical amounts of liquid storage. Peroxide storage stability is the only real hitch.
I don't know the details, but the steam torpedo power plant is a cousin of this system, and versions of it have been around since WW1. It's suitable for a one-way weapon, but not really suitable for the sub itself, or else they would have done it already.
My intuition suggests that liquid methane could be burned with hydrogen peroxide the same as diesel or kerosene can. Not sure whether compression or spark ignition might be better suited with methane (high vs low octane number) in piston engines (turbine doesn't care). But I'd think you could build a piston or turbine engine for shaft power around this combination that would work even in vacuum.
GW
Once you have the frozen CO2 from your freezer, just be sure there's very little free volume in your canister. The sublimating dry ice will pressurize the canister quite nicely, to perhaps multiple atm.
GW
RobS:
This is an excerpt from my last post from the "airbreathing engines" thread under this same topic:
"The closest thing I know to a practical piston engine system independent of atmospheric oxygen was attempted for submarines decades ago. Diesel fuel plus hydrogen peroxide actually did work from storable liquids while submerged. It's somewhat similar to the propulsion of the torpedoes, but more suited to a reusable vehicle. There were great difficulties with it, and it was superseded by atomic power in submarines, then forgotten.
Given some sort of fuel that could replace the diesel, and some way to make hydrogen peroxide on Mars, that technology might lead to practical internal combustion or gas turbine power plants on Mars. The storable liquids are pressurized at around 1 atm, like here. Hydrogen peroxide decomposes to oxygen and steam. Steam is the diluent gas that reduces stream temperatures to something you can confine with cooled steel.
It can be done, but needs some development before we take it to Mars and count on it at the risk of lives."
Given a tad of development to make fuel-peroxide really work well, the same piston-engine "Gator" could be run with stored liquids pre-pressurized to around 1 atm in their storage tanks. This shouldn't take more than a couple of years to check out and debug pretty thoroughly, if done by a Spacex-type of outfit. (A ULA-type would milk this for lots of gov't $ for about a decade.)
Rubber tires in the cold are a problem with brittle failure. But it can be done. Already was done for the Antarctic bases in the late 1950's.
GW
My engineering intuition suggests the instability of the rocket plume fired into an oncoming supersonic/hypersonic stream derives from it's being fired straight ahead into the stream: the shock layer doesn't know which way to jump, so it buzzes around.
What if you have multiple thrusters and cant them all, at least a little. Now the shock layers know exactly which way to bend things. My intuition suggests this will be fluid dynamically stable. It would make rocket braking feasible during re-entry.
Guess what! The super Draco's on the Spacex Dragon are canted about 45 degrees. It's supposed to be rated for trips to Mars.
Others seem to have the same intuition regarding rocket braking in re-entry. I bet Spacex has already tested this, too.
GW
RobertDyck:
I quite agree with you about NASA. I am pleased with what happened in Canada with the RadarSat. Sounds like Canada's space agency has not stultified with "bureaucratic disease" the way the US agency did.
Part of our problem here in the US is that we allowed Congress to make pork-barrel political footballs out of every little project NASA does, which means NASA does nothing Congress cannot play for politics. That is precisely why American astronauts have not left Earth orbit for 4 decades now.
I hope Canada can avoid that mistake - it is fatal.
As for gas turbine or any other combustion engines on Mars, if they suck the local "air", they have to compress it to useful pressures inside the engines. Those are cycle pressures measured in tens of atm. Here, the source is 1 atm, for a compression ratio of tens. On Mars, the source is 0.0068 atm (at 7 mbar), for a required compression ratio in the thousands. The most extreme gas turbine ratios are around 30-something with known technology.
The most extreme recip compressors are in submarines, which for the high pressure air banks are around 480 atm and around 480 compression ratio. Those are not exactly the transportable-weight devices you could make a part of an engine, either.
You could in a vehicle carry both a fuel and liquid oxygen, and operate a turbine or a piston engine with it. The problem is the around-6000 F (3300 C) stoichiometric flame temperatures with just about any fuel and straight oxygen, again at tens of atm cycle pressure. Except for rockets, you'll need huge volumes of colder diluent gas to bring the stream temperatures down to something the hardware can withstand. Gas turbines do this with excess air, here on Earth. Due to the difficulties of compressing on Mars, that's not really an option.
The closest thing I know to a practical piston engine system independent of atmospheric oxygen was attempted for submarines decades ago. Diesel fuel plus hydrogen peroxide actually did work from storable liquids while submerged. It's somewhat similar to the propulsion of the torpedoes, but more suited to a reusable vehicle. There were great difficulties with it, and it was superseded by atomic power in submarines, then forgotten.
Given some sort of fuel that could replace the diesel, and some way to make hydrogen peroxide on Mars, that technology might lead to practical internal combustion or gas turbine power plants on Mars. The storable liquids are pressurized at around 1 atm, like here. Hydrogen peroxide decomposes to oxygen and steam. Steam is the diluent gas that reduces stream temperatures to something you can confine with cooled steel.
It can be done, but needs some development before we take it to Mars and count on it at the risk of lives.
GW
Turbojet? That gets us right back to the question of how to build such a thing. How to build a gas turbine that thinks CO2 is an oxidizer, and can generate a useful cycle pressure level in a 6-7 mbar atmosphere.
Like I said, that will be a really tough thing to do.
I really do have to wonder whether rocket-powered vehicles augmented a tad by aerodynamic lift while cruising supersonically wouldn't be just about as practical. But I sure would like to see some sort of "air"-breathing engine developed. We'll need a lot better compressors than we know how to build right now, of that I'm sure.
GW
The high-altitude NASA craft was very subsonic. Not compatible with supersonic flight with ramjets, so the propulsion would have to be something very subsonic, like propellers. There might be a way to do that with a combination of solar PV and chemical or battery storage of electricity. I have no idea what takeoff might look like in "air" that thin. Probably JATO-assist would be required.
GW
If for your transfer vehicles you are considering propellant modules in the 30 ton class assembled by simple docking in LEO, I think that is the right approach. Unmanned supplies and equipment can go "slowboat" this way on min energy trajectories for capture into Mars orbit, and the basic transfer vehicle could be reused, but only if you do not jettison the empty modules.
Myself, I would use the NERVA design that almost flew for this, not Timberwind, which never got that far through test. Later, as better nuke engines become available, you could replace the NERVA's. But why throw away hardware if you don't have too?
That sort of transfer begs the question of propellant supply at both ends, so that the vehicle may return for reuse. For nuke rockets, hydrogen is usually considered, which is fairly easily made from water using solar PV, if the rate of production required is not too high. Both Mars and Earth have lots of water, as ice on Mars, both liquid and ice here.
Why not shoot ice payloads almost naked into LEO and LMO with light gas gun technology? That technology is powerful enough now to work on Mars, and almost ready to do that job with small payloads to LEO. So the payloads are small? So what? Use solar thermal to melt, and solar PV to electrolyze, in both LEO and LMO. As long as the individual transfer flights are many months apart, you don't care that the batch process is small scale and slow. Your propellant reserves build up over that time interval. It can be automated. Product is both hydrogen and oxygen, items very valuable.
Single stage one-way nuke transfer by min energy trajectories, with fully reusable vehicles, means you build them and launch the fueled modules from Earth only once. After that, resupply is very cheap, once the light gas guns and solar propellant satellites are in place. This is not "battlestar galactica" stuff, either. The biggest one-way payload to ship to establish this capability is the light gas gun equipment to be landed piecemeal on Mars.
Now, this does also beg the question of equipment transfer from LMO to the surface at Mars. If piecemeal components can fit inside one-way Dragons rigged as landers, that's the start. But, if you have NERVA engine technology resurrected, that also supports one-stage fully reusable lander technology, using nothing more sophisticated than direct rocket-braking descent. These things could carry a big load fueled for a two-way trip from LMO. Check it out yourself at Isp near 1000 sec, engine T/W around 4, vehicle structural fraction 20% to be tough as an old boot, and 70% propellant fraction to be fueled for up to 30 degrees out of plane, full rocket delta-vee two-ways. I got a 10% payload fraction.
If you make hydrogen both in LMO and on the surface, you could carry far heavier payloads fueled only one-way like that.
The more desirable follow-on to NERVA would be one of the gas core concepts, but that's future stuff. We could do the NERVA thing right now, but we need to pick the brains of those who did it for their engineering art. There are very few of those guys left. That was 4 decades ago they did that.
If it turns out there's significant ice inside Phobos, so much the better. No light gas on Mars is necessary.
It takes a while to bootstrap into a setup like that, but if you plan for it from the outset, the right choices can be made along the path. There's a real sustainable transport system to Mars. Simple, direct, and launch things only once (keep on using hardware once launched).
GW
Bamboo is actually a decent structural material. Good strength/weight, and rather easy to work. Joining seems best done with lashings, actually.
You will have to have a place with air and water to grow it in. There's osmotic pressures of transpiration to consider, among many things.
I doubt we'll bio-engineer anything that could live outside until Mars is terraformed. The water vapor pressure problem is insoluble at 7 mbar dry CO2.
GW
Sure. They're a good idea too.
GW