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Raw data is deceptive, as I said. US population grew by about 50% between 1975 and 2010, from near 200 million to over 300 million. Normalize your park visit numbers by population to get a percentage of the population visiting the parks. You will see the recent dip with the great recession.
Our only hope to stop exporting ever-larger amounts of cash for foreign oil is a two-pronged strategy. We need higher-mileage vehicles, as you say. We also need more domestic production of fuels. The problem with domestic production of oil is price: we don't set it, OPEC does. Even if we went to all-North American sources and bought nothing from OPEC (Mexico is OPEC, B.T.W.), that would not affect its market price by any material amount. The way out of that dilemma is fuels made from something other than oil. We've been screwing around instead of doing that, for over 40 years now. It's a bit late to be starting. But better late than never, I guess.
I know about the Prius, we have one. We have some far older vehicles, too. Everything I drive on the street (and all my lawn and garden equipment) runs totally unmodified on an E-30 to E-35 blend, made from the E-10 that is today's regular, and E-85 where it is available, splash-blended in the tank at the pump. That's about a 1/3 reduction in petroleum fuel usage by this family. I've been doing this for 7 years now, ever since E-85 first became available in this area.
The 220,000-original-miles-on-it catalytic converter in my '98 Sentra shows a check-engine / cat-converter-not-working code whenever I have to drive that vehicle on plain gasoline. That light goes out about a week after I use E-30+ blend again. It takes about that long for the solvent action of the alcohol to clean the accumulated soot off the cat converter bed. It's soot buildup that kills cat converters, you know.
My 1944 Farmall-H tractor has run on straight E-85 for 7 years now. I did the conversions myself, they were very simple. That old corroded steel gas tank is now sparkling clean inside, something the "corrosive ethanol" was not supposed to do. All I know is that it runs cleaner, more powerfully, and with less degradation in its lube oil, than it ever did on gasoline. And its petroleum use has been reduced by 85%.
That being said, we need ethanol not-from-food crops. Food vs fuel is a stupid thing to perpetuate, although we had to start with what we knew how to do. I have great hopes for cellulosic ethanol, although it's "not there yet". There is also ethanol fermented directly from spoiled grocery store produce, something that should be about as easy and efficient as sugar cane. Nobody seems to be doing that yet. In fact, Texas has a law against using spoiled produce that way. How stupid is that?
We need the other alternatives too. Things like "grassoline", etc. Biodiesel can play a role in both trucks and turbine aircraft, too. You just have to get away from the food-vs-fuel dilemma, which is where we had to start.
GW
I have never understood how or why people will read more into what is written, than what is actually written.
I never, never, never said that cheap fuel is mentioned in any work by Adam Smith himself, or in any other person's works. I said that our western economies were "designed" by the "dead hand of Adam Smith". That's a colorful way of saying nobody "designed" anything, it was simply unconsciously "worked out" more-or-less at random, under prevailing market forces. All of our fuels for over 2 centuries have been cheap, relative to even poor family incomes, until shortly after 1973. Nothing has been cheap since for very long, and we had good times during the short interval that it was once again cheap. We have had bad times otherwise, ever since.
I didn't say "oil prices", I said fuel prices, specifically gasoline prices, and I did say "inflation-adjusted prices". Raw (unadjusted) data tells you very little. Average people don't buy crude oil. Most of them buy gasoline. A very few buy diesel. Whatever it is, it is a finished fuel, ready to use. Everything about our economies depends upon transport of goods, in turn dependent upon finished fuels. I chose to look at gasoline prices over time, because that's what most folks have to buy. Plain common sense. Nothing else is implied.
There is a second more recent problem with US diesel, which is now around 30% more expensive than gasoline, when it used to be about 10% cheaper. This is also quite important for family budgets (especially poor folks), because about 40% of the price of your box of corn flake cereal is diesel used in the transport of corn and finished product, when the corn itself is only around 2-3%. The food price spikes blamed on ethanol production were really caused by diesel fuel price hikes. Sad, but true.
To see the inflation-adjusted regular-grade gasoline price plot, you can go to zfacts.com, and get one for yourself. It will not have the set of current events added to it that I used. The most recent form of the version I used is posted at http://exrocketman.blogspot.com, in an article dated 8 March 2012, and titled "Iran, Oil, and Economies". Go there, scroll or navigate down, and see for yourself what actually happened, the same as I did. All the political ideologies about what government policies might and might not do relative to economic good times versus depression turn out to be lies (surprise, surprise!!!!). Finished fuel prices has been the real driver since 1973. OPEC formed as a price-fixing cartel in 1963. US oil production peaked about 1970, ceding “control” over prices to OPEC thereafter. Simple as that.
Consumer fuel demand is "very inelastic", by-and-large. You'll find that term in a lot of business school and management textbooks. Except for upper middle class to rich, there is not a lot of “by-choice” driving going on out there in the US anymore. Most folks just go to work, to school, and to the grocery store. They go occasionally to the doctor when they can afford it. Almost nobody drives all over the country for vacations anymore; ask the national parks, they'll confirm what I say.
There still is no viable alternative product available to the public, to gasoline made from oil. Doesn't really matter why. Effectively, gasoline fuel is a monopoly cartel product, whose price depends upon three things. There is a base supply-and-demand signal, which until around 2004, was about $1.80-$2.00/gal of gasoline, I am pretty certain (from examining the graph), as expressed in early 2012 dollars. Superposed upon top of that since the beginning have been various speculator "bubbles" that spike and crash, usually around 50 cents a gallon or less, in 2012 dollars. Also superposed on top of all those effects are the two OPEC punitive pricing spikes, which are quite large, and which were intended to crash our economies (they did). One was from 1979 to 1986, the other since 2003. These are trivially easy to see from the graph, once you “spot” the right current events upon it.
The thing that bothers me is the distinct possibility that OPEC supply (the largest remaining on the planet) is peaking just as Chinese and Indian demand is spiking up for the next few decades. That puts us western civilization folks into a supply-shortfall-at-any-price situation for the very first time in history. Dangerous territory indeed, for economies "designed" to run on cheap fuel.
THAT was my point.
GW
Hi Bob:
The answer depends upon the ballistic coefficient of what you are trying to land, which in turn depends on the mass you are trying to land. That answer also depends very strongly on whether you do a direct entry from "deep space" vs an entry from low Mars orbit. The detailed "critical variables" are velocity and trajectory angle (relative to horizontal) at the entry interface altitude. I've been using Justus & Braun's interface altitude of 135 km, entered from a 200 km circular orbit, for which the entry angle is about 1.6 degrees and the de-orbit burn delta-vee is about 50 m/s maximum. The Mach at end-of-hypersonics (with severe heating) is about 3 (local). The M3 altitude ranges from near 30 km at around 100 kg/sq.m to around 5 km at around 1000 kg/sq.m.
If you come out of hypersonics below about 20 km, there's not time to deploy a chute, much less have the time for it to do any good. So, I was looking at direct rocket braking to touchdown from the M3 altitude. No chutes at all. It actually seems to be feasible. There's about 3 km/s delta vee required to touchdown from that M3 point, by the time you get all the speed killed, do the final slow approach with some hover, and throw in a kitty for contingencies. It varies from scenario to scenario, but you are moving around 2 km/s more or less horizontally at that M3 point. That puts a sort of lower bound on it.
Hope that helps.
GW
Glandu:
I think you and I actually agree on point 3 above. My point is that the correlation between economic troubles and fuel prices is not random. From 1973, decreasing toward 1978, then even more strongly from 1979 to 1986, fuel prices were well above the inflation-adjusted supply-and-demand level of 1.80 to $2.00 per gallon (American, which is a different tax structure than Europe). After 2001, prices once again skyrocketed and have stayed above $3.00/gallon (American) since then, except for a dip during the 2009 crash.
The numbers are different in Europe, but the trends are the same. These two big price spikes are OPEC punitive pricing for the US and/or NATO getting crosswise with onbe or more OPEC members. Remember, all westerners are "infidels", so it only takes one of us getting all of us hurt.
The other smaller spikes are speculator bubbles.
The different shape of the trends post-2001 relatrive to 1973-1986 suggests there might be an upward trend in supply-demand pricing buried underneath the punitive pricing spikes.
Note that there was no punitive pricing spike after the Soviet (1980) or US (2002) invasions of Afghanistan. Not an OPEC country, no oil to speak of, OPEC didn't care. Note also that there was no spike-up (other than a small speculator bubble) after the 1991 US invasion of Iraq: OPEC begged NATO to do that. But the 2003 invasion of Iraq prompted a big one. Most of OPEC and the rest of the world was against that one.
You can get an inflation-adjusted price history of US regular-grade gasoline from about 1970 to the present at zfacts.com. They will have some historical events on their graph, but you have to spot most of these in this discussion on their graph yourself. Again, the numbers in Europe are different, but the trends are identical. European prices reflect the environmental and health costs of oil in product prices, in the US we fund those out of taxes not collected in fuel prices.
GW
Vincent:
There is no good way to dry carpet except streams of heated dry air. Even then, the pad underneath (which most homes and apartments generally have) will mildew before you can get it to dry. If you have carpet over pad, I'd strongly recommend pulling them up and drying them. It is possible to reuse them, but there may be staining or shrinkage distortion.
A lot depends upon how deep the water got, in order to wet your carpet. It will infiltrate the walls and wet your sheetrock, your insulation, and your framing. If the sheetrock shows no signs of disintegration above the baseboards, you do not have to remove it. Mold will develop in the wet materials inside the wall, but then will die once the water is dried up.
You generally do not need to rip out walls barely wetted somewhere hidden down inside the baseboards. I know the remediation guys say you need to rip it all out, but that's how they make more money. Mold does not live in the dry.
GW
The Saturn-V boosters that might have supported these "Apollo 19 and 20" missions are pretty well accounted for at other sites on the internet. Most of the components (stages) have been on public display since the 1970's Apollo-Soyuz mission (supposedly "Apollo 18"). You still cannot launch to the moon without an adequate rocket today, and you certainly could not, back then. So, I think this stuff referenced here as "Apollo 19/20" is a fake, as is so much that I see posted on the internet.
Myself, I do not post fake stuff. Whatever you see that I put up there, is real. That would be on http://www.txideafarm.com, and http://exrocketman.blogspot.com. There's a bunch of how-to stuff for manned landings on Mars posted there on "exrocketman" in recent months. 60-ton-class manned Mars landers are very easily feasible, as long as you break out of the "rut" of prior hardware practices.
In particular, you must dispense with aero decelerators on Mars, and go straight to rocket braking for your landing, once you "pop out" of the high-heating hypersonics at about Mach 3 (local). There's no point to chutes or ballutes or any other aero-decelerator concepts: you "pop out" too low to use a chute at high ballistic coefficient, even at very shallow entry angles.
GW
The two largest oil finds in history were North America and the Middle East. All the other finds since have been far smaller. Even the things speculated about (like the Arctic) are figured as far smaller. That's just an unpleasant fact. Even the new oil boom in the US Williston Basin is only about the size of the Alaska North Slope find, and that peaked in 15 short years, although it is still in production.
Another unpleasant fact: he who has the most oil to sell has the greatest influence on its price. That's been OPEC since US production peaked about 1970. OPEC formed in 1963 specifically to be a price-fixing cartel. That's what they do. I watch what they do, rather than listening to what they say. Truth really is not a premium item in most Middle Eastern countries in recent centuries.
A third unpleasant fact: western civilization was "designed" by the dead hand of Adam Smith to run on cheap fuel. Fuel is no longer cheap, so things don't "work right" anymore. Since 1973, every major economic downturn has correlated to inflation-adjusted fuel prices at or above 150% of what appears to be the long-constant supply-and-demand value in a market not limited by supply (on top of which speculator "bubbles" and cartel punitive-pricing events get superposed). Good times are associated with the lower supply-and-demand-driven prices. Government policies seem to have had very little to do with any of this (bad news for you political activists and ideologues out there).
A fourth unpleasant opinion: the Middle Eastern fields may be peaking in production the way US peaked in 1970. This is a suspicion, not a confirmed fact. It is based on the observation that Saudi production levels in recent years have been lower, but have never exceeded, their 2004 levels. That's a bad sign in a world where demand is skyrocketing as China and India industrialize. If the speculation is true, then from this point forward we live in a world where supply always falls short of demand, so that prices spiral rapidly upward, even without the effects of speculator "bubbles" and cartel punitive pricing.
A fifth unpleasant observation: it seems to take about 40 years for one industry to fully replace another, looking at history, such as petroleum vs whale oil. There are many examples. You just don't do this in a handful of years.
Substantive conclusions: We should have earnestly started finding a replacement for oil about 40 years ago, instead of screwing around making scads of short term profits on something we knew was ultimately finite. Now it looks like we face about 40 years of chaos, war, and economic depression. That's the price we are going to pay for allowing money to influence public policies (no matter whose or what form of government) to the exclusion of ordinary common sense, or any notion of the public good.
GW
The Italians are not known for a justice system that produces rational or fair results.
GW
Those are some very odd-looking rocks in post 181 just above. I'd swear they look like lakebottom black mudstone that's been broken up and eroded in some fashion. Wind erosion produces really odd patterns and textures like that.
I see that kind of black lakebottom ooze in farm tanks and small lakes here. It is definitely organic life-produced detritus here. There's usually too much algae in those bodies. That black ooze bottom material really stinks. A lot of (but not all) the organics came from the rear ends of cows.
GW
I'm not entirely sure, but I think this is based on breeding U-233 from Th-232. They spent the last decade or so working on this. You have to start by using the U-238/Pu-239 cycle to breed your U-233 from Th-232, until you can stockpile enough U-233 to shut the U-Pu cycle down. The Indians have been working the final reactor design and the U-233 issues in parallel. Looks like they're just about "there".
BTW, nearly everybody has a lot more thorium than uranium. This is not the first time somebody proposed to do this. The Canadians proposed this unsuccessfully in the 1950's. It was no-go because the militaries of the time needed weapons materials, which this cycle really does not produce very well. U-233 can make a bomb yes, but you use a lot more, and it's bigger and heaver.
GW
News story seen today on NBC news "space" topic: Krunichev in Russia is pushing ahead with a reusable flyback booster strap-on. This is for vertical launch rockets. The booster strap-on is a liquid rocket (LOX and kerosene or methane) unit with tail fins and tricycle landing gear. One version has a swivel straight wing. It stages off about 30 km up at around M7, and falls back to winged lifting flight at about 12 km (if memory serves). Then it cruises back on turbojet propulsion to the launch site, and lands horizontally as an airplane.
This is a concept seen at airshows as a mockup for some years now. It was also a topic of conversation in multiple threads here before the last server crash. One of the variants of this that I have explored is an integral rocket-ramjet strapon that stages around 70,000-80,000 feet and M2.5-toM3, based on simple pitot-inlet ramjet technology. Such a thing would integrate well with current acceleration practices for vertical launch rockets.
The article said NASA had looked at similar ideas, using the rocket engines to cruise back, instead of a turbojet package.
The fallback does require proper treatment of nose shape and construction for hypersonic but well-suborbital re-entry. And perhaps several other surfaces as well, but that was not mentioned.
If sufficiently simplified so as to require a small logistical tail on the order of a battlefield weapon, this could lead to significant launch cost reductions. We already know small logistical tail has a huge effect. Here is a chance to see if lower manufacturing cost could provide similar benefit.
GW
The eskimos dealt with the old age problem by pushing them outside to die in the cold. On Mars, this is pushing them out the airlock without a suit. It is a problem that must be dealt with, somehow.
This problem is precisely why I do not think a one-way mission is wise anytime soon.
GW
It is very clear viewing RobertDyck's powerpoint that he knows his chemistry and his chemical engineering. If he says we can get aluminum from bytownite on Mars, I believe it! Great news, Robert. Aluminum metal is one very useful material. (What about iron and steel?)
I am no chemist or chemical engineer, the bulk of my training and experience is mechanical/aeronautical. But, in an environmental clean-up situation, I once used ammonia solution (at about 5% strength) to neutralize battery acid (sulphuric acid) that had flowed to inaccessible locations in building wall and truck trailer structures, in a battery acid spill incident. I kept it very dilute, because I was afraid of steam explosions, pouring this stuff directly onto spilled battery acid.
It worked, and far better than the "standard" treatment of spreading powder lime. Plus, the reacted product was just very-slightly-salty water, which we could dilute further and just send down the storm sewer. That clean-up effort was actually far easier and less labor-intensive that way. Spreading lime makes a horrible mess. Plus, we couldn't effectively get lime into the building wall internal structures where the battery acid had flowed, or down through the truck trailer structures where it got to.
We bought industrial ammonia solution concentrate at 10% strength, and cut it half-and-half with water on the job site. I saw bubble formation, but no violence. Sure were a lot of poison fumes inside that truck trailer, though. Time inside was basically limited to breath-hold times. But we got it cleaned it up. The building was better ventilated.
That was an interesting day.
GW
Question: Does it really matter in the long term, if some Earth bacteria got to Mars on these probes? Because, in the long term, men are going to go, and maybe even stay. That will introduce Earth organisms to Mars, even if nothing else before did.
GW
I'm no geologist, but sure looks like some kind of mudstone to me. It's had some kind of history with water post-deposition, for sure.
GW
I was very pleased to see a successful Dragon flight in spite of an engine out. In the absence of details, I do not understand the NASA safety rule forbidding second stage restart after a first stage problem. That caused the loss of the piggyback Orbcomm satellite, not anything to do with the Falcon-9. Bureaucracies, bah, humbug! That's why Spacex is looking for its own launch site. I hope they pick south Texas.
On the other hand, Spacex will have to get to the bottom of the engine out, even if NASA were not breathing down their neck. Something leaked somewhere upstream of the throat, that's how you get a pressure drop. Leaks get catastrophic in a tiny fraction of a second, that's why you need an automatic way to detect them and shut down, at way-faster-than-human speed. Looks like the controls on the Falcon-9 do exactly that. Bravo and kudos to Spacex for getting the safety/failsafe things right!
Leaks ahead of the throat show more pressure loss than thrust loss, at least initially on the transient while the hole is still small. Leaks downstream of the throat will show as thrust loss with no chamber pressure loss at all. You'll have to be monitoring thrust, as well as pressure, to detect leaks in the bell downstream of the throat. I would hope they know to do that. I would guess they are doing it, based on how well they have done the rest.
Leaks in either place cause errant hot gas plumes and shedding debris that very quickly damage adjacent engines or other structures. You have to worry about both phenomena.
BTW, what I said about engine and nozzle leaks applies to all rockets, not just liquids. Solids and hybrids, too.
GW
Typical Texas. Wore a coat (not a jacket, and actual coat) yesterday. Today, short shirt sleeves. It's been like that all my life.
That conflict between hot and cold air masses is why the US Great Plains has the absolute most violent weather on Earth. Texas is at the south end of that. It's called Tornado Alley.
I'm no meteorologist, but I do understand a few things about the weather here. Unlike the TV weathermen, I actually look out of the window (sound of laughter). They say we might get rain later in the week with another front. The little weak one tonight brought clouds but little else. Still quite warm out there.
I'll believe rain when I see it. Around these parts, a "six inch rain" is raindrop splatters 6 inches apart on your windshield. (More muffled laughter. I'm trying to be funny. Apparently unsuccessfully.)
GW
Yep, we got a norther. It didn't look like the stereotypical blue norther here, because the approach speed was so slow, but we sure did cool off nicely. It was almost 90 F here during the afternoon before the front hit. That front came through sometime after midnight. It was nice and cool Sat, even a bit cooler today (Sun). They say we're headed back to near-90 F by week's end. Typical Texas.
GW
I have no idea what a "magnetic plasma ramjet" is in Sark0y's post 47 just above, but you can use chemical ramjet, chemical turbojet, and chemical rocket propulsion together, if you wish, in one vehicle. I have less faith in combined-cycle engines, and more faith in just using two or even three separate types of well-developed engines run in parallel.
For a skip-glider limited to Mach 3, turbojet/ramjet is good enough to get the job done. I am not at all sure about the economics, but I am sure they would be better than sustained Mach 3 cruise in the atmosphere. Both engines burn the same kerosene or kerosene-like fuel (even liquid methane or biodiesel). You get to reject air friction heat while exoatmospheric on the glide. At Mach 3, you can do the skip atmospherics with a metal airframe. Stainless and titanium skins seem adequate, based on prior experience. You could up that to Mach 5+, but no more than Mach 6, using Inconel skins, as in X-15, but those are pretty heavy.
For the single-stage rocketplane ballistic vehicle, the velocity requirements are just too high for large payload fraction and a large structural fraction at the same time, which is required for economics and safety-of-flight. That speaks to nuclear Isp levels. The final form of NERVA ca 1973 was pretty well free of core erosion, which means it was pretty well free of exhaust plume radioactivity. That's quite an improvement over the earlier Phoebus and Kiwi experiments.
The problem is reentry at destination. Is the reactor turned off? That's a little safer, but you still must deal with core containment in the event of a crash. If it is off, you're deadstick, so how do you handle emergency needs to divert to another runway or to go-around? This is a big heavily-loaded airliner full of people, remember? While an intriguing and promising technological approach, there are some serious design and safety issues here.
The solution might be a gas-core reactor concept, something not out of the academic lab demo stage. But it could be. I'd suggest the open-cycle approach as the lighter of the two (the other being the "nuclear light bulb"), which also automatically has no core to contain when you shut it down. But, you have to accept a radioactive exhaust at the launch site if open cycle. How bad? No real data, but consider LH2/uranium (-235 or -233) mass flow ratio 30:1 is "perfect" containment at the nuclear burn-up rates needed. There's an upper bound estimate of the daughter-product "fallout" you spew. Those are much more benign if you use Thorium-bred U-233. Or so I hear.
If you go with "nuclear light bulb" instead, the exhaust is clean, and you dump the core at burnout in space, retaining nothing on board. Unfortunately, that core dump takes place at suborbital speed, so it comes down very quickly. Just on a different target. Or, you land with a retained core, just like the solid core engine. Take your choice.
GW
If your greenhouse is a tall structure anyway, why not rack your hydroponics vessels above your soil-based agricultural activity. Racks should be easy to build on lower-gravity Mars from most anything. Even lashed bamboo would work, which could be grown there. Including bamboo fiber-based rope for the lashings. A rope-making machine is a very old, very simple technology. You do need to know your knots and your lashings. Not in the usual astronaut training, but maybe it should be.
Think a round foundation in the middle of a small crater or depression, a mushroom-shaped building with a regolith-covered cap for a radiation shield, and clear walls around the "mushroom stem". Surround the thing to the poleward and sunrise-sunset sides with reflectors made of aluminum foil bonded to any convenient substrate (including even permafrosted regolith) as a 3/4 ring solar reflector bringing light inside the building laterally. You can mount your solar thermal and solar PV stuff up on the roof.
Over on the equator-ward side, that's where you set your very large water tanks. They are both your supply and a huge thermal mass. Paint them flat black, and let them be passive solar to the extent possible. It works in my greenhouse here. The other 1/4 ring of reflector surface on the equator-ward side would help amplify the water tank passive solar effect, but also blocks surface access to the building. If you need a roadway in, put it there.
I'm not sure what to make the transparent walls of, but eventually some sort of glass should be possible there, if the right silica sand can be found. I'd recommend a double or even triple wall for the insulative heat trap effect, and for decompression safety.
Comments?
GW
That's a very unusual-looking rock depicted in Vincent's post 162 just above. I swear I've seen rocks with dissolution pockets like that in limestone caves. Any idea what it's made of? That sure resembles water-based dissolution as seen here. But, limestone ???? There? What a good target for the laser and spectrometer!
GW
Vincent is correct about the likelihood of transient liquid water on today's Mars. In context, "transient" could refer to a time constant ranging from minutes to centuries, depending upon circumstances. I have seen lots of evidence for liquid water in photos from several sources, for some time now. It is quite obvious that there are transient outflow streams occurring on Mars today. The source is likely melting of subsurface ice in warm conditions. But no one yet knows for sure.
One should remember that in an atmosphere that tenuous (unlike here), there will be a very wide disparity between surface and atmospheric temperatures. Surface temperatures will lead the air temperatures in timewise variation, because of solar heating of a near-gray-body surface, while the "air" is a mere narrow-band absorber of relatively very-low effective absorptivity, even though it is CO2, the greenhouse gas. In the limit of zero "air", behavior is very much like that on our moon: very hot exposed surfaces in daylight, while there are very cold surfaces in darkness. "Air" temperatures in the boundary layer close to the surface will be somewhat closer to solid surface temperatures. The rate of surface temperature variation hot-to-cold and back is only limited by surface layer thermal mass relative to achievable heat transfer rates air-to-surface.
That being said, these water outflows are truly transient at today's air pressure on Mars. To be "stable" on time constants longer than a century, Mars's atmosphere would have to be dense enough that the partial-saturation (less than 100% relative humidity) partial pressure of water vapor would exceed the equilibrium vapor pressure of water at the local liquid pool temperature. For a liquid pool at 0 C, that is 6.1 mbar. For a warmer pool, that partial pressure is higher still, being the value shown in the standard steam tables. I have a psychrometric chart for Earth air that gives relative and absolute humidities. I don't have one for the nearly-all CO2 atmosphere that Mars has. But, in a crude sense, it would still be similar. It's still basically what an ideal gas can hold, at any given gas temperature. Hotter holds more water vapor.
All thermodynamics books and air conditioning handbooks have such charts for Earth air. I'm sure there's one in any edition of the CRC Handbook of Chemistry and Physics, if anybody wants to go look. (Try section F.) My best guess is that we wouldn't be more than half an order of magnitude wrong applying such an Earth air chart to Mars "air". But, somebody somewhere at NASA JPL has the corresponding psychrometric chart for Mars "air", or they would not be reporting a typical relative humidity of 0.3% on Mars.
All that really doesn't matter. The partial pressure of water vapor on Mars today is somewhere around a very tiny fraction of a single mbar. There would be wide geographic variations, including localized transients far higher around the outflow streams. But for "average" conditions, not only will small pools of exposed liquid water evaporate, they will do so quickly and rather violently. They'll approximate an adiabatic system and freeze in the act of boiling, in most locations on Mars under "typical" conditions. Local temperatures above 0 C only make the evaporation rate higher.
Yet in the past, conditions on Mars were far more Earthlike. The semi-fossilized gravel bar that Curiosity photographed is startling proof of that. Obviously, there were streams. That by itself implies lakes, perhaps even oceans. And, I suspect, microscopic life. Those microbes might still be there, underground. We found microbes like that deep down in the rocks here, only a few years ago. I'm not so sure about multicellular forms, as that took over 3 billion years here, and Mars only had about 1-2 billion years before it dessicated, froze, and lost its atmosphere. As best we know, anyway.
Dang, I wish that rover had a real microscope. Bacterial fossils here are very tiny, those odd little traces in the Allan Hills meteorite were even smaller. But, still crudely comparable. And the shapes were startlingly similar.
GW
Louis:
Very interesting study. Hydroponics is possible, for sure. I did notice that the microflora were acknowledged, but not really understood, based on what I read in that report. The focus of the study was obviously inorganic nutrients in the water and air. The bacteria and fungi counts they did almost seemed like an afterthought.
That actually sort-of makes my point in my previous post. There's a lot more to real farming than just nutrient chemistry. It's the symbiotic stuff that's the real make-or-break item. Always has been. The biologists know vastly more about that issue than I do, but I think they would agree with my assessment: we know a lot less about symbiotic ecology than we like to admit.
That being said, there are millennia of accumulated human experience with growing crops here on Earth. The bulk of it long pre-dates modern science, and still lacks a rigorous and truly-detailed scientific basis. The bulk of that long experience would suggest that our modern "green revolution", which is based on the heavy use of inorganic fertilizers, is a transient phenomenon, that it is not sustainable over multi-century timescales. I tend to agree, based on what little experience I personally have out here on this little ranch.
That's why I suggest we take the less-intensive, demonstrably-sustainable, "traditional" agriculture practices (that date back to the stone age) with us to Mars.
Why screw it up twice?
GW
There's more to fertile soil than just rock dust, water, and ammonium nitrate (AN). (BTW, AN is a class 1.3 mono-propellant explosive, even in fertilizer grade (a purity standard). Adding fuel oil just increases the yield. It is friction-sensitive, shock-sensitive, and can be induced to decompose (deflagrate) by heat; which in large-enough piles, can propagate into full detonation. Try justifying the shipping of THAT in interplanetary supply.) Any AN you use in agriculture on Mars needs to be locally produced. We know there's perchlorate salts there; there are probably nitrate salts as well. These are all evaporites.
You also need "organic matter", which is primarily animal/human feces, to mix with the rock dust, which feces contains both carbon-hydrogen-oxygen-nitrogen compounds plus real, live organisms (some microscopic, some macroscopic-especially in the third world). You don't have to ship the feces, any people on Mars, and any animals they bring, will supply more than can be initially used. Later on, we'll see. But in Asian rice culture, it seems to balance out pretty well.
Urine is another useful soil component, although it might prove useful to remove some of the salt first. The ammonia in it is fixed nitrogen, the very thing plants need most. Ammonia is actually better than AN in that respect, or else the mass of AN fertilizer bags would exceed the mass of tanked ammonia at rural ag-supply places; it does not.
On Mars, you are living in an environment that pressure-wise is very little different at 0.7% of an atmosphere from the vacuum of space. It should be very easy to build a vacuum flash still rig that could separate the most of the water and nearly all of the ammonia from urine, and so isolating the leftover brine as something to be disposed of by evaporation, preferably not in contact with the soil. Same thing might work in deep space travel. Not a closed ecology, but maximized recycling of what we can use.
The "clean" all-hydroponic thing as most seem to conceive it may well prove to be a technological dead end. Most of the useful plants we have are more symbiotic with the organisms in the feces than most folks want to admit. We are not yet capable of engineering plants that do not need such symbiosis long-term.
By the way, although I most definitely do not claim to be an agricultural expert, I have personally seen this process in action. It is quite real. I really do live on a cattle ranch in the midst of farm and ranch country. My wife is a trained composter. This is most definitely not theoretical knowledge from some school or some book. It is the real McCoy.
GW
The geologists tell us that the fossil record here on Earth is a very skewed sampling, and for a wide variety of reasons. Yet, what it seems to show is that life here was one-cell microbial for about 3 billion years, and may have begun almost as soon as liquid oceans formed, very shortly after the planet cooled enough to have a solid crust at all. How all of that life evolution interacts with changing climate and chemistry, and a slowly-dimming sun, is not well understood. But there it is.
This microbial sort of thing left only microscopic fossils, of similar size and form to the odd traces found in the Allan Hills meteorite, which rock came from Mars. Only in the last 660 million years or so does there seem to be evidence of multicellular life here. This is not conclusive, of course, but it does suggest that microbial life sprouts up quickly and easily in a liquid water environment, while multi-cellular forms may require a time constant on the order of 3 billion years, of benign conditions, to evolve. I could be wrong about that, but that's what the record here seems to say.
We have no reason to believe that the fossil record on Mars would not be as skewed as that on Earth, and probably for the all same reasons. There, like here, the geological record will be hard to interpret, especially any fossil record. What does seem very clear is that early Mars was much warmer and wetter, with similar conditions and chemistry to the earlier Earth. I'd bet real money it had microbial life, just like here. Maybe even the very same sort of life, if the panspermia hypothesis was a factor: the late heavy bombardment event could have spread microbes, or perhaps just their chemistry, between the two planets.
The problem is, from what we can tell, is that Mars too-quickly dried out (acidifying along the way), and froze up, as it lost its atmosphere. (For whatever reasons.) Apparently this was a couple of billion years ago. There might have been short warmer, wetter events since then, but that is not clear. My hypothesized 3-billion-year time constant for evolving multicellular forms didn't happen on Mars, as best we know. Accordingly, I would not bet real money on our finding macroscopic fossils. But, then, it's only a bet. No one yet knows.
I view putative macro fossils with a jaundiced eye, meaning I have a strong "show-me" attitude about that. There are so many ways for inanimate geology to create forms that look like life fossils, as we know. Putative microfossils on Mars I find much easier to accept, since the climate seems to have been hospitable to Earth-like life for a billion or two years, perhaps. I do think the NASA scientists who claimed microfossils in the Allan Hills meteorite were very badly mistreated by the scientific establishment. That would be one of Carl Sagan's few mistakes, reacting the way he did.
Here is what I predict: we may find microfossils of microbial life in sites scattered all over Mars. If we drill deep enough, we may, (I repeat "may") even find living microbes far under the surface, similar to deep-rock microbes found here recently. If we ever terraform Mars, that life may re-invade the surface and re-colonize it. I rather doubt Martian microbes could sicken us, or that our microbes present a threat to Martian microbes. The chemistry should be different enough after 2-3 billion years' isolation, to prevent any such compatibility, even if they had the same original panspermia source just after planetary formation.
All of that is just my speculation, of course. Enjoy.
GW