Yet another Mars architecture

louis · 2013-08-04 06:46:32

Russel wrote:

JoshNH4H wrote:
Reliable, lightweight aeroentry is a vital technology for the colonization of the inner solar system. Why develop it later rather than sooner? This is the question that you need to answer (I am after all defending the Mars Direct plan). This is the question that I don't think you have an acceptable answer to.
*Yes, the US Congress and the American public. What other country could go to Mars any time soon?
Reliable lightweight aeroentry is vital to landing large masses on Mars. And I'm not suggesting it be developed later rather than sooner. Seriously, I'm not. It just doesn't matter as far as the crew goes. It will always be safer to land the crew separately (And indeed that is what you're suggesting if you have the kind of mission where the crew arrive 2 weeks later).
I will differ on one issue and that's I think you don't need to land anything on Mars larger than about 15 tonnes. Practically anything you can think of can be built up from that scale. I see Mars drive as a response to the "big lander problem" but I believe they're going a bit too far in the other direction. In any case they don't really make the landing problem go away either.
You're defending Mars direct. Fortunately I'm not
What I do see though is a lot of frustration people have with NASA coming up with ridiculously large mission mass. And thus a lot of architectures that are attacking the problem from particular directions. Mars direct is largely a response to the NASA overkill. I kinda like it in some ways. Its got a certain minimalism. But, for me the solution ultimately lies in something a bit more considered, a bit more conservative, but still not wasteful either.
However we get to Mars, its going to take a decade or two. And that's time enough to for everyone to sit around and bang heads together and not get too wedded to their particular approach.
NASA isn't the only body that theoretically could do this. I think ESA has the resources to do this eventually. Japan, China could all play the part.
The thing about the US is that if you've got a great architecture, whose going to build it. If its NASA then you've got to get through its strange meld of hard core rationality, plain old fashioned bureaucracy, and US style corporate welfare. Not that the ESA doesn't have its own politics at play.
Point is, even the most spartan Mars architectures are not pocket money. Eventually the big space agencies will have to be won over. And if that's the case they're going to be won over with with architectural proposals that don't just save launch costs, but also simplify development effort and most of all don't make them look like they're taking unnecessary risk with their crew.
And that's about as far into politics as I dare venture. I'm interested in this as a problem worth solving that hasn't been solved well by anyone, yet.
We do have time to get the technology right, to scrutinize what we're doing in unprecedented detail and do it safely, and I might add, in style.

For a safe mission, I think we need lots of pre-landings by robot craft guided in by transponders into the landing area. I think maybe up something like 6-8 separate missions over maybe 8 years bringing in the bulk of supplies and the initial surface hab.

The landing should be in a small, Apollo mission sized lander. They can they then decamp from the lander to the hab within the first 40 hours or so.

JoshNH4H · 2013-08-04 15:51:39

Russel wrote:

Without going into chapter and verse about the process engineering involved (I'm not a chemical engineer, but I do know my way around materials) what I can say is that no presently proposed process is ready for Mars. And every process that involves the use of Martian CO2 requires development of technology for efficient compression. The sabatier process is not by any means simple. And it involves working with electrolysis to boot. The point of the paper I presented is that there is ample room for improvement in electrolysis of CO2 using lower temperatures and more reliable materials. Now we can debate this back and forth but my original claims about conversion of hydrogen to methane, versus simple oxygen extraction being likely to be more energy intensive and involve more mass of equipment still stand. There is no free lunch. And nor did I claim that oxygen was "free". I said that its wrong of Zubrin to include the mass of oxygen in his leverage ratios. He simply hasn't considered importing methane or doing the comparison on that basis.

Actually, Zubrin has already demonstrated a low-mass, small scale sabatier reactor. While there was plenty of room for improvement on top of the design that he came up with, given that his budget was something like $50,000 I think it has been sufficiently demonstrated that it would not be difficult to construct a reliable and efficient machine that would produce Methane from the martian atmosphere and hydrogen feedstock.

What I fear going on is a chicken and egg situation, where people refuse to fly to Mars unless they've actually committed to a development program that is actually about settlement. And I suspect that this way of thinking is what I'm dealing with here. I don't necessarily subscribe to colonisation. I do subscribe to exploration. But the problem is this. At the very least we need to extract oxygen from the Martian atmosphere. We need to do that in order to breathe. So we need to get that technology right independently of making fuel. If we settle for the less ambitious goal of importing methane we get to land successfully, leave safely, and have the time to then experiment with sabatier technology for the sake of future missions. If we insist we do it the Zubrin way we're just going to have to trust robotic precursor missions to get the technology right, and my instinct tells me that will inevitably delay the point at which we can safely set foot on the planet.

Robotic precursors are a good idea anyway, and they need not be expensive. Most of the costs in robotic missions are in development as opposed to construction. The cost to build, launch, and operate (for their rated lifetime) Spirit and Opportunity was $800 million. It wouldn't be $400 million for just Spirit, and it wouldn't be $4 billion to send 10 of them. The point here is that the technology required to scope out a launch site robotically is a good investment and not that large of one, relative to mission costs.

Yes, colonization is the goal. Exploration for its own sake is great, but knowledge for its own sake isn't enough to justify a program with costs running as high as tens of billions. The idea is to design the initial sortie missions such that they segue naturally into a robust and inexpensive colonization effort that results in easily measurable gains both to the new Martians and to the Terrans who have funded the effort.

Now about hydrogen. You've either got hard cryo cooling, or you don't. If you don't, then you can use all the insulation you want but in your process plant there will be gaseous hydrogen, and in that state there is no known material that can contain it. It will leak. That's an accepted fact of Earthly process engineering. Either you've got hard cryo cooling, or you lose some hydrogen. Its as simple as that.

All told, Hydrogen and Helium have a lot in common when it comes to diffusing through materials and escaping into the atmosphere. However, the average person is much more familiar with Helium from Balloons. What any child can tell you (perhaps not in these words) is that aluminized mylar is far superior to polyethylene at retaining Helium. While Polyethylene will slowly leak all of its Helium out in a day or two, Aluminized Mylar will retain it for up to a month. The point here is that some materials are better at retaining low molecular mass gases than others, and that proper design can minimize or eliminate Hydrogen loss. Your claims are really a red herring, because Hydrogen leakage will occur mostly on the trip from Earth to Mars, and I have already shown that the leakage in that situation is far less than you suggest it will be.

We're clearly both in the same place, convinced that the other is being illogical and not accepting the arguments proffered. But I would like to point out that much, if not all of those who are thinking in terms of ISRU for a Mars mission stand with me.

GW Johnson · 2013-08-05 08:52:50

In my ignorance, I would guess the most practical source of oxygen on Mars to be mined water. One would use the vapor pressure rise upon heating to self-compress a batch of confined ice to usable pressures (near 1 atm). Then just do solar PV electrolysis. It's a whole lot easier to compress the hydrogen and oxygen from 1 atm into 2000 psig bottles than it is from 6 mbar.

What one does with the hydrogen is not well understood by me. It should be possible to make methane from it and the CO2, but the source of the CO2 makes a big difference to practicality. Compression from 6 mbar is a real practical problem, while dry ice can only be mined at the poles (same self-compression mechanism as water ice).

GW

JoshNH4H · 2013-08-06 15:07:37

GW- That's absolutely true, but Zubrin makes the point that there's a big difference between proving water resources and proving atmospheric CO2 resources. The difference is that we know what the composition of the atmosphere is, and thanks to diffusion and the tendency of pressures to equalize we can expect it to be the same anywhere on the planet: 95% CO2, and between 5 and 10 millibars, depending on the exact landing site. Water, on the other hand, can be present in all sorts of different forms-- from water vapor dispersed through the atmosphere at ppm quantities, to small ice crystals, to hydrates, to adsorbed water. It's the kind of thing you need to do some real advance prospecting to figure out.

By the way, a copy of Zubrin's paper that covers his experimentation with the Sabatier Reaction can be found here.

Regarding compression-- it sounds to me that the issue isn't technological so much as how much energy we're willing to put into it. I personally have played with air compressors capable of compressing air to 10 atm. Two in series would result in .6 atm, with further compression needs being slight. Alternatively, one could use an equivalent of the snowmaking machines that we have on Earth to condense the CO2 down to a solid, which from that point would be rather simple to pressurize.

We do pressurize things on Earth all the time, after all. I don't see why being on Mars represents an inherently greater problem.

GW Johnson · 2013-08-07 08:18:43

Hi Josh:

Pressure ratio is not much of a compression problem. You just stack up enough stages, like you said. The problem is the mass throughput that you're compressing, which depends upon the first stage inlet density, which on Mars is about 0.7% of what we are used to. This is a governing factor for sizing machinery. Any air compressor on Mars will be physically enormous and very heavy in comparison to the total mass it processes in any one run.

Avoiding that dilemma takes innovation, which is why I suggested the self compression effect of phase change with heated, confined solid resources. There's a lot of large ice deposits all over Mars, usually from +/- 40 latitude to the poles, as I understand it. And, there's lots of ice and dry ice deposits at the poles. That tells me where the first ISRU-dependent landings ought to be made.

But, not every site will have the water. It's not evenly distributed in minable quantities. Based on mining experiences over the centuries here, no one should expect water on Mars to be evenly distributed. You have to locate the buried glacier, and land your base or colony next to it. No different than here.

See you and all the guys next week.

GW

GW Johnson · 2013-08-07 08:32:53

Update:

I looked at Zubrin's Sabatier paper. Very intriguing process. I did notice that the pressures in the system used gas feeds at 50 to 75 psi (3+ to 5+ bars), and the reactor was at 0.8 bar (Denver ambient). How to compress on Mars was unaddressed, something very worrisome considering that compressor weight is proportional to inlet density and something like 10 stages will be needed at minimum.

And, I rather suspect the conversion in the Sabatier reactor works better and better as reactor pressure increases. Chemistry is usually density dependent (another word for mass/volume concentrations in your Arrhenius-type overall reaction rate equations or empirical models). This atmospheric gas compression issue is a critical design issue for using technologies like this on Mars. That near-vacuum of an atmosphere is a real impediment, for a lot of things.

GW

Terraformer · 2013-08-07 09:35:48

I recall he suggested using a Zeolite bed to adsorb the CO2, and then drive it off to pressurize it.

How cold does it get at night? Enough that it wouldn't be too taxing to create dry ice from the atmosphere?

RobertDyck · 2013-08-07 13:42:51

It gets cold. Temperature is available for Mars Pathfinder. It was recorded by the rovers as well, but that data is harder to find. Pathfinder recorded temperature over 3 days: the "typical" daily high was -10°C, although it got to -8°C once. And the "typical" daily low was -76°C, although it got to -77°C once.

http://mars.jpl.nasa.gov/MPF/science/atmospheric.html

Carbon dioxide freezes at -79°C in one atmosphere pressure. It has to get a bit colder in the thinner atmosphere of Mars, but it does get close every night. Overall Mars atmospheric pressure is the equilibrium between CO2 gas and dry ice at the winter pole. So yea, it only takes a few degrees to cause dry ice to freeze at night.

Ps. I did look at the entire temperature dataset for the Viking 2 lander. It recorded temperature for more than a Martian year. Its absolute low was -111°C. At the time I was looking at synthetic rubber for soles of boots. Found one that doesn't become brittle until -112°C; so use that. But this also demonstrates at moderate latitudes outside the tropics (equivalent to temperate on Earth), at night in winter, it can get very very cold. Below freezing for dry ice?

RGClark · 2013-08-07 13:54:13

Russel wrote:

...
What I do see though is a lot of frustration people have with NASA coming up with ridiculously large mission mass. And thus a lot of architectures that are attacking the problem from particular directions. Mars direct is largely a response to the NASA overkill. I kinda like it in some ways. Its got a certain minimalism. But, for me the solution ultimately lies in something a bit more considered, a bit more conservative, but still not wasteful either...

Very interesting and informative discussion here guys. Reminds me of the good old days of NewMars!
I share your frustration Russel with NASA always wanting to go overlarge with their manned missions. In my opinion it was the decision to make the Altair lunar lander three times the size of the Apollo lander, 45 metric tons, that forced the Constellation system to be so large and ultimately doomed it on cost grounds. Imagine my surprise when I found by running the numbers that if instead you used a single capsule of 2 mT size and all-hydrogen in-space stages, that the entire mission could be launched on a single Delta IV Heavy!

I'm also frustrated with NASA's always bloated costs for their programs. For instance I could not grasp why in the world it would take according to NASA $10 billion to do a Mars sample return mission. Here's a nice informative article about NASA's plans for such a mission:

TECH | 8/02/2013 @ 6:12PM |
NASA Is Still Dreaming About Tomorrow: The Fantastic Mars Ascent Vehicle.
Michael Venables, Contributor.

http://www.forbes.com/sites/michaelvena … t-vehicle/

I had thought perhaps it was because of some expensive one off propulsion system they had to design for the return flight, but from the article it's just off the shelf, and small, solid rockets! Where is the $10 billion coming from?!? Seriously, we could have done this years ago, and for well less than the cost of MSL.

Bob Clark

Last edited by RGClark (2013-08-07 13:59:00)

RGClark · 2013-08-07 14:06:13

RobertDyck wrote:

It gets cold. Temperature is available for Mars Pathfinder. It was recorded by the rovers as well, but that data is harder to find. Pathfinder recorded temperature over 3 days: the "typical" daily high was -10°C, although it got to -8°C once. And the "typical" daily low was -76°C, although it got to -77°C once.
http://mars.jpl.nasa.gov/MPF/science/atmospheric.html

Ah, Mars Pathfinder, one of my all time fave's. I read alot about its climate measurements. It is important to note that the temperature actually on the ground on Mars can be significantly above the air temperatures, even for just a few feet above the ground. Indeed temperature sensors on Sojourners wheels were frequently well above freezing during the daytime.
In fact orbital measurements show daytime temperatures actually on the ground at near equatorial sites can exceed 20°C(!)

Bob Clark

louis · 2013-08-07 14:51:02

JoshNH4H wrote:

GW- That's absolutely true, but Zubrin makes the point that there's a big difference between proving water resources and proving atmospheric CO2 resources. The difference is that we know what the composition of the atmosphere is, and thanks to diffusion and the tendency of pressures to equalize we can expect it to be the same anywhere on the planet: 95% CO2, and between 5 and 10 millibars, depending on the exact landing site. Water, on the other hand, can be present in all sorts of different forms-- from water vapor dispersed through the atmosphere at ppm quantities, to small ice crystals, to hydrates, to adsorbed water. It's the kind of thing you need to do some real advance prospecting to figure out.
By the way, a copy of Zubrin's paper that covers his experimentation with the Sabatier Reaction can be found here.
Regarding compression-- it sounds to me that the issue isn't technological so much as how much energy we're willing to put into it. I personally have played with air compressors capable of compressing air to 10 atm. Two in series would result in .6 atm, with further compression needs being slight. Alternatively, one could use an equivalent of the snowmaking machines that we have on Earth to condense the CO2 down to a solid, which from that point would be rather simple to pressurize.
We do pressurize things on Earth all the time, after all. I don't see why being on Mars represents an inherently greater problem.

That's one of the reasons I favour robot pre-landers to prove the water resources.

louis · 2013-08-07 14:52:41

GW Johnson wrote:

Update:
I looked at Zubrin's Sabatier paper. Very intriguing process. I did notice that the pressures in the system used gas feeds at 50 to 75 psi (3+ to 5+ bars), and the reactor was at 0.8 bar (Denver ambient). How to compress on Mars was unaddressed, something very worrisome considering that compressor weight is proportional to inlet density and something like 10 stages will be needed at minimum.
And, I rather suspect the conversion in the Sabatier reactor works better and better as reactor pressure increases. Chemistry is usually density dependent (another word for mass/volume concentrations in your Arrhenius-type overall reaction rate equations or empirical models). This atmospheric gas compression issue is a critical design issue for using technologies like this on Mars. That near-vacuum of an atmosphere is a real impediment, for a lot of things.
GW

Wouldn't you use solar energy to power compression?

RobertDyck · 2013-08-09 13:12:08

I presented a paper at a past Mars Society convention, about producing other gasses from Mars atmosphere. My design used 10 bar pressure, and -100°C to freeze out CO2. The idea was to collect everything else. It wasn't intended to be optimal for CO2, it was designed for the other stuff. With a plantinum or rhodium catalyst to break down ozone, and combine CO with O2 to produce CO2. Turns out there's more than enough O2 in Mars atmosphere to react all CO. The catalyst would have to be warmed, but doing it in the same vessel as the freezer to remove CO2, so the CO2 produced by this reaction would be removed as well. The result was primarilly N2 and Ar, with traces of other stuff. This could be used directly as diluent gas for a habitat, just add oxygen. Or further process to produce Ar to fill sealed casement windows, or N2 for production of nitrogen fertilizer. Although heating and freezing in the same chamber would consume energy, it's really necessary for the application. A catalyst at +24°C at the top of a chamber, while freezer operates at -100°C. But power for the pump would rival the temperature stuff.

So I've looked at this. But Dr. Zubrin's design has an elegant way of avoiding that. He freezes dry ice at Mars ambient, then puts that dry ice in a sealed canister before sublimating. The result is pressure from phase change. He doesn't need a pump, CO2 will pressurize when it becomes gas. It could be done with some sort of a condenser in a canister, with vents that open for collection, then close before sublimation.

GW Johnson · 2013-08-09 22:19:51

Self-compressing by phase change makes a lot of sense to me, for both CO2 and H2O resources. I think the machinery would be a lot smaller, lighter, and less energy-consumptive. Your biggest expenditure would be the heat for the phase change.

Only one trouble, these solid resources (ice and dry ice) are not evenly-distributed the way the atmosphere is. Problem with that atmosphere is it's too bloody thin to use in any efficient way. It means you need to know where the buried glacier is before you land and try to use it. Same for any other local resource.

That's part of what exploration is really all about. It necessarily precedes successful colonization. As history teaches us.

GW

JoshNH4H · 2013-08-10 00:55:11

The downside to freezing is the energy consumption: To go from gaseous to solid CO2 requires the removal of approximately 600 kJ/kg of energy from the CO2. Fortunately, because the Martian ambient temperature is so cold to begin with, this can be done with the input of as little as 100 kJ/kg of mechanical energy. More realistically we're probably looking at 150-200 kJ/kg, which really isn't very bad. If we want to pressurize to 10 atm, there's even a nice little trick that we can use: Instead of transferring the heat from the air that we seek to solidify to the outside air or a radiator, we can actually transfer it to the dry ice that we want to sublimate. There will be a temperature differential between the two chambers because the sublimation temperature of CO2 is slightly higher at 10 atm than at .006 atm. The difference isn't that much, though, and thanks to the magic of thermodynamics isothermal compression can be accomplished at an energy cost perhaps as low as 50 kJ/kg of CO2. While this does represent an addition to the energy cost of fuel production, it's not really that much in comparison to the electrolysis (performed later in the fuel production cycle), and has very good results.

As a matter of fact, these results appear to be so good that I can't help but wonder if I'm doing something wrong. I don't have my thermodynamics textbook on me, but I suppose that because the product PV (pressure times volume) is staying constant, as it does for isothermal compression, the only energy input is ultimately the energy used to heat the CO2 from its temperature right before it solidifies at Martian ambient pressure to its final temperature at 10 atm. The downsides here are that this is a batch process, unlike the Sabatier and Reverse Water Gas Shift reactions, which are continuous, but that seems to be a trifle in comparison to an effective, low-energy way to pressurize CO2. In fact, the energy costs here are so low that I suspect this will form the basis of the method of choice to pressurize anything on Mars. It should come as no surprise that the energy costs get higher as the pressure gets higher, but it still seems to be a strong candidate to me.

RobertDyck · 2013-08-10 10:57:53

GW Johnson, your arguments are contrary to what I've been saying for a long time. I want to go, not waste more time. Robert Zubrin and Dr. Baker wrote Mars Direct in 1989. Their design did not rely on prior robotic exploration. So they use atmosphere only. Freezing dry ice out of atmosphere only requires a couple degrees at night, so do that for maximum energy efficiency. A Sabatier Reactor requires gasses to be heated, so you'll have to heat anyway. And it only requires 1 atmosphere pressure, not 10. My design requires 10, but that also requires -100°C in the same chamber. That's to produce argon and nitrogen, not fuel. To produce fuel, you need a Sabatier, so 1 atmosphere.

Furthermore, Dr. Zubrin argued for human exploration. He argued in 1989 and 1990 that humans could be on Mars by 1999. We could have, but it wasn't done. NASA argued for robotic exploration. So I argue that robotic exploration is now done. There has been so much that we don't need any further robotic stuff. Pick a location and start the permanent base with the first human mission. If you wanted human explorers first, then it should have been done in the 1990s.

And NASA wanted a life support system with 95% recycling efficiency. Robert Zubrin argued to go with what we had at that time. He said if we waited for 95% efficient life support, it would be the 21st century before we could go. Oh wait! It is the 21st century now! We've pissed away so much time that the 21st century has caught up with us. I've been saying that since 2001.

Dr. Zubrin also argued to not build a space station. Instead go directly to Mars; do not pass "GO", do not collect $200. The reference is deliberate, because military contractors have been gouging NASA and the American taxpayer since the beginning of the Shuttle era. But my argument is that we have ISS now, so let's use it. And this ties with the previous argument. ISS has recycling life support, it only requires a couple small additions for Mars. So again, we're ready to go. Go now!

RobS · 2013-08-10 20:09:01

I can see that one more robotic landing is justified: to explore the intended landing spot for the first manned exedition, especially where subsurface water is concerned. It seems to me that's the priority resource for a landing site. The lander could also test ISRU, perhaps methane/oxygan manufacture from imported hydrogen and local CO2. It would also be useful to characterize Martian dust better, as it may be the most serious hazard astronauts will face. That may require sample return, though.

RobertDyck · 2013-08-10 20:52:52

Well, yea. Apollo tested every technology as they went. Not everything worked. In fact, something went wrong with every Apollo mission, except the last one. Only Apollo 17 went smoothly without a hitch. There's a story that when Nixon cancelled Apollo, one Manager said "We finally got it right, and now they cancel it!" This demonstrates we have to test as well.

We need to test/demonstrate ISPP before committing human lives. That means a sample return mission. At one Mars conference I got Robert Zubrin to say he would accept sample return only if it was a technology demonstrator. I had argued to designate it so. Besides, every past attempt at sample return has started with ISPP to make it affordable. Then someone said "you aren't putting untried technology on MY mission!" So ISPP was removed, causing the budget to skyrocket. When politicians saw the new extreme budget, they cancelled it. This cycle repeated 3 times that I'm aware of, and probably more. Anyone in favour of unmanned missions should learn from this: use ISPP or it won't happen. Unfortunately some people just don't learn. The only way to ensure ISPP doesn't get removed this time, is to designate the entire mission "technology demonstrator", with the Mars soil sample secondary only. That way the mission will actually happen. Of course my motivation is to see ISPP demonstrated: preparation for the human mission. But still, anyone who supports unmanned should learn from this. Make ISPP primary, or it won't happen at all.

The other technology we need to demonstrate is aerocapture. MGS demonstrated aerobraking, but Mars Climate Orbiter was supposed to demonstrate aerocapture. They made a US to metric conversion error, dipping too deep into the atmosphere. There's a new crater somewhere. I think I know what that error was. I noticed before this that NASA tended to report the altitude of ISS in miles. But when I checked, the numbers didn't make sense. It turned out to be nautical miles, not statue miles. But anyone other than NAVY who hears "miles" will think statue miles. After all, that's what cars use. Ok, so we know what the problem was, and it's been fixed. Since then NASA has official policy to use metric exclusively. Ok, so now send an orbiter to demonstrate aerocapture. Ideal would be to do this with MAVEN, but it's way too late. MAVEN arrived at KSC last week: Friday, August 2nd. "InSight" is a lander, scheduled for 2016. Landers use direct entry, not aerocapture. They're both important, and I look forward to their data, but they can't do aerocapture.

There is a Mars mission for 2020, but it's not clearly specified. The JPL website shows another rover. I would prefer the two technology demonstrators that I just mentioned.

Last edited by RobertDyck (2013-08-12 23:07:42)

GW Johnson · 2013-08-12 10:49:18

This is for RobertDyck, Bob Clark, Louis, and several others in this thread:

RobertDyck: I think you and I are not arguing for things poles apart, which I seem to have given you the impression that I am. I am sorry that I was not clearer. Like you, I think the typical NASA mission proposal is bloated, cost-wise and mass-wise, by around a factor of 10, if not more. NASA also suffers from a very bad case of NIH (not-invented-here) attitude, and has since around 1960-or-so. (No one else on these forums seems to have noticed that.)

All: I am not suggesting that ISRU/ISPP won’t work, I am suggesting that it is not ready yet to bet lives upon it, and for reasons that have less to do with the technology than what we know about exactly where all the resources are, underground, on Mars. I detect from your (plural) comments that all (or at least most) of you feel the same way I do.

All: RobertDyck is exactly correct in pointing out that without ISRU/ISPP, the “typical” mission costs are simply too high to be feasible for a manned mission yet, because of politics. USA, Europe, doesn’t matter. Yet, if the mission is not led by NASA (or ESA, or any other governmental agency), those same costs might actually become quite feasible!

Louis: of course, I am proposing solar PV or solar thermal for powering any compression scheme, whatever it might be. Why not use the energy that is already there, why ship it from Earth when that is so very bloody heavy?

All: that last being said, there is great ease, simplicity, low mass, and low cost associated with the notion of trapping mined water (or dry ice) inside a container barely larger than the mined solid volume, and heating it with simple solar thermal, as a batch process. As the solid vaporizes, its vapor pressure very rapidly builds into the 1-2 atm range, making further compression by more-or-less standard electro-mechanical means simple, small, and lightweight (and very little different from here at home).

All: Once in that 1 atm range, then all of the Sabatier reaction (and many other proposals) start to look for Mars exactly like their experimental counterparts here at home. But, until you get vapor near 1 atm to compress, nothing about those processes looks anything at all like their experimental counterparts here at home. It’s vapor compression, not the specific process we are discussing, that is the show-stopper/crew-killer, for an ISRU/ISPP technology we can bet astronauts’ lives upon. That’s because the size, mass, cost, energy demand, and complexity of the compression machine (whatever it is) depend more upon inlet density than any other variable. Simple fact-of-life.

All: So, to avoid both super-high mission costs and the very high probability of a dead crew (which NASA has correctly identified as the highest-cost item associated with spaceflight), we need to do reliable ISRU/ISPP on the first manned mission to Mars, as RobertDyck has so eloquently pointed out. Yet, this has to be done at a site with solid minable ice, as I have pointed out more than once, or we will most likely kill that crew!

All: So, we need a site where we already know there is massive buried ice for that first manned mission. Otherwise, nothing we do will reliably succeed, or save mission costs. Absolutely none of the probes and rovers we have sent so far have the capability to answer the question “where is massive buried ice?”, not even Curiosity. None of these can drill or dig more than a few centimeters beneath the surface, when the answer to the critical question requires (at the very least) drilling MULTIPLE METERS beneath the surface.

All: There is maybe the opportunity to send one or two more probes to Mars before we try to send men. If you believe NASA, we will try to send men somewhere in the 2030’s, but I believe this to be “code” for “never”. None of the probe proposals I have seen has drilling capability to 10’s, maybe 100’s, of meters, yet that is EXACTLY what we need.

All: NASA’s typical manned Mars mission “design” falls in the $500B class. I think that someone like a Musk/Spacex (not ULA or “the usual gang”) could do the same job for around $50B or so. Add in reliable ISRU/ISPP, and you might get this down to around $5-10B (or $50-100B if done by NASA/ESA/etc). THAT is where we are. Now, how do we get out of this quandary? I honestly don’t know.

GW

RobS · 2013-08-12 11:08:10

I'm not sure it's that complicated, GW Johnson. Zubrin wanted to haul the hydrogen along, and the technology to do that seems to be pretty well advanced. The alternative is to haul methane along, which has four times the mass of hydrogen alone, but it's much more storable and is still less than a quarter the total fuel mass (you need 3.5 times as much oxygen as methane for optional specific impulse).

You still need oxygen, but we know how to get it from the air. If a system to crack CO2 seems too heavy and energy intensive, haul just a few kilos of oxygen along and use it to burn a little methane. One byproduct is water; take that, electrolyze it, store the oxygen in your big oxygen tank, then take the hydrogen and use the Sabatier process with carbon dioxide to make more carbon monoxide and water, repeat the electrolysis, etc. You can get your oxygen that way.

And as Robert Dyck said, we need to test all this with a robotic probe before we send it with people, anyway.

JoshNH4H · 2013-08-12 16:08:15

I would like to emphasize (As RobS just said, but it's very important) that it's not necessary to have proven reserves of groundwater to make ISPP (In Situ Propellant Production) work.

Just as Zubrin suggested, by bringing Hydrogen one can produce 100 tonnes of propellant with 5.4 tonnes of Hydrogen delivered to the surface. Of course I can't say for sure, but I would imagine that the equipment required to mine the water and pressurize it would be nearly this much, plus would represent a significant addition to mission unreliability: Digging things up tends to be difficult work, after all.

By the way, this is what Zubrin has to say in The Case For Mars on pressurization of the Martian atmosphere:

In The Case For Mars, Zubrin wrote:

Pumps that can acquire gas at this pressure [of 5-10 millibars] and compress it to a workable pressure of 1 bar or more were first demonstrated by the English physicist Francis Hawksbee in 1709. Even better pumps are available today. However, you don't even need a pump to compress carbon dioxide. Instead, you can use a sorbant bed that will act like a sponge, soaking up carbon dioxide. All you need to do is take ajar and fill it with either activated carbon or zeolite, and then expose it to the Martian atmosphere at night. Given the chill (-90°C) nighttime temperatures, the material bed will soak up to 20 percent of its weight in carbon dioxide. Then when day comes, you warm the bed up to 10°C or so, and the carbon dioxide will outgas. You can generate very high pressure carbon dioxide gas this way, with essentially no moving pans and very little power expenditure. In fact, you can even use the waste heat generated by other components on your propellant maker to drive the outgassing process. At my lab at Martin Marietta we built such a system and it worked quite well.

RobS · 2013-08-12 17:10:21

Once you have a crew on the surface that can prospect for water, you can import drilling equipment and get your own. You can even extract it from the Martian soil; the Case For Mars says you can erect a tent over a piece of ground and heat it up and it'll outgas a certain amount of water. But the first mission will need to bring its hydrogen or methane, unless it lands in a polar zone.

RGClark · 2013-08-13 00:38:52

GW Johnson wrote:

In my ignorance, I would guess the most practical source of oxygen on Mars to be mined water. One would use the vapor pressure rise upon heating to self-compress a batch of confined ice to usable pressures (near 1 atm). Then just do solar PV electrolysis. It's a whole lot easier to compress the hydrogen and oxygen from 1 atm into 2000 psig bottles than it is from 6 mbar.
What one does with the hydrogen is not well understood by me. It should be possible to make methane from it and the CO2, but the source of the CO2 makes a big difference to practicality. Compression from 6 mbar is a real practical problem, while dry ice can only be mined at the poles (same self-compression mechanism as water ice).
GW

Yes, this gives an alternative to getting propellant for the return trip from the Martian air. Mars Odyssey showed there were large swaths containing hydrogen-rich material near surface even in mid latitude regions on Mars, such as at the Viking 2 landing spot. The Mars Odyssey scientists because of the large amounts believe it more likely to be ice rather than hydrated minerals:

Odyssey's Homer: Hints of water near both poles of Mars.
From Science News, Volume 161, No. 23, June 8, 2002, p. 355.

DEEP BLUE ICE? The Martian regions depicted in dark blue may hold buried deposits that are up to 50 percent water ice. Light blue regions may hold lesser amounts. White arrows at left and right denote the approximate landing sites (red dots) of Viking 1 and Viking 2, respectively.

Feldman and Boynton note that the discovery of hydrogen-rich material on Mars needn't have waited until the 21st century. The lander on each of the Viking missions, which arrived at Mars in the mid-1970s, scraped trenches 10 to 20 cm deep to sample the arid soil. The new data from Odyssey suggest that Viking 1 dropped into an area on Mars with little if any buried ice. Viking 2, however, descended in a region apparently endowed with some buried, hydrogen-rich material. After a trip of more than 100 million kilometers, the lander may have stopped digging just a few centimeters shy of striking ice.

http://www.phschool.com/science/science … _mars.html

Further landers need to be sent to determine if this hydrated material really is ice in these mid latitude regions on Mars.

Bob Clark

Last edited by RGClark (2013-08-13 05:45:02)

RGClark · 2013-08-13 05:43:47

See you and all the guys next week.
GW

I couldn't swing the finances, but good luck with your presentation.

Bob Clark

RobertDyck · 2013-08-13 06:37:10

The neutron spectrometer on Mars Odyssey detected hydrogen in the surface of Mars. It was estimated that space radiation (solar and GCR) that is the basis of this instrument had penetrated up to 1 metre. The Gamma Ray Spectrometer detected large chunks of ice. These instruments found a great deal of ice at or near the poles. However, there's practically none at or near the equator. There is a little at the bottom of ancient river channels, but you don't want to land in the bottom of a canyon. You want to land somewhere flat and smooth. You also want to send a human mission to some place relatively warm (not so cold). Ideal is near the equator, or at least between the lines of latitude that is the tropics. It feels odd talking about tropics on Mars, but it's the line of latitude that equals the axial tilt. Only one location has subsurface water, and flat/smooth, and tropical latitude. Unfortunately it's a high plateau, so relatively little atmosphere to protect against radiation. That's Meridiani Planum, where Opportunity landed. Opportunity examined the ground, and did not find obvious ice like Mars Phoenix did. Subsurface ice is not EVER going to be easy, so designing a mission to rely upon it is foolish.

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