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Thank you for these marvelous references!
-- RobS
The Case for Mars also argues for a Skylab type atmosphere. Nitrogen tends to suppress fires, apparently, so it is safer than pure oxygen. Also, a large colony will need a hospital and the hospital will need to give patients oxygen. That is much easier to do if there is nitrogen or argon in the air, which an oxygen system replaces with oxygen.
Any hapitations on Mars will need multiple escape routes in case of depressurization or fire. This is the same principle as in fire protection on Earth; no building should have only one way out, lest a fire block the only escape route. The earliest outpost, before any large domes are erected, could accomplish this by connecting habitats and greenhouses together in squares or rectangles; that way each unit has an exit at each end to the rest of the outpost. When domes are built, much housing can be put under the circumferential skirt, with windows facing the greenery and the regolith holding the dome down overhead to protect the housing from cosmic rays. If apartment buildings are built inside the dome, they should have underground escape tunnels (which might also serve as utility tunnels) in case of depressurization. Many universities already have such utility tunnels on Earth.
When a Mars settlement grows to village and town size, it probably should have multiple domes, so the loss of one would not jeopardize most of the living space. The best way to do that would be to start making domes of small or intermediate size (say, 50 meters across) and make a dozen or so, then graduate to 100-meter domes, make a dozen or so of them, then 250-meter sized domes, etc. At each stage the colony gains experience with construction at that size, and lays the foundation for larger and more complex domes. Connecting the domes together would be underground utility tunnels and "streets" on which robotic vehicles would transport inhabitants the length of the settlement. When the settlement promises to grow to thousands, one could envision the municipal government laying out an underground "street" with sidewalks, utility lines, and mass produced airlocks every fifty meters or so, and then selling the lots along the street to private developers, who would build something behind each airlock and connect to the municipal oxygen, hydrogen, sewer, and electrical lines. Some developments might be expensive private homes; others might be apartments; others might be agricultural units. Some will have open domes, some "partially open" (you can see the sky, but not the landscape outside because of the housing around the central space) and some might just be pressurized buildings with no domes at all.
-- RobS
I dearly hope that Mars exploration can serve as an international symbol of cooperation, collaboration, and efforts to create a peaceful and better Earth. For Mars to symbolize that, it will have to be explored by an international team. And it unlikely any one nation will try to go it alone, anyway.
-- RobS
Oh yes, I forgot about aluminized skylights; I have one in my kitchen, and it works very well! But I am not sure it can work well enough to reflect concentrated sunlight into a cave; otherwise you'll need one square meter of skylight for every square meter of plants. You might need big mirrors on the surface to concentrate sunlight onto the skylight.
-- RobS
Thank you, this is very interesting. I will look forward to anything your geologist friend says. I never knew that much geochemistry, and the little I know makes me worrisome about all the assumptions. The problem we have is that the Viking and other elemental analyses can tell us the elements, but not their combinations. Sometimes combinatins can be guessed, but even then we are not sure. And the existing combinations make a huge difference in terms of releasing the oxygen. If the Martian regolith basically formed in an aqueous environment millions of years ago and the only modifications that have occurred since are dessication and exposure to intense ultraviolet light (which made the superoxides and peroxides), then wetting the soil now will not release oxygen at all, except from breakdown of the superoxides and peroxides. The other chemical breakdowns to release oxygen upon wetting would have already happened millions of years ago when the sample was wet then. As far as I know, Na2O and K2O almost never exist in nature; they are part of complex molecules, feldspars originally, probably clays now(smectite and montmorillonite have been mentioned as possibilities on Mars).
Even the existence of superoxides and peroxides are now disputed. I remember when the gas release experiment was first performed and the strange results had everyone scratching their heads. Then someone remembered Bob Hugenin's work where he had theorized the existence of superoxides and peroxides. He was flown out to JPL and gave some talks to the scientists and was a hero; he had solved the problems. This is as I remember the events, as a lowly graduate student at the time. I remember looking at Hugenin's papers and being utterly baffled by the chemical equations, pages and pages of them. I even wondered whether the biology experiment guys understood 20% of what he was saying! It was pretty specialized research. Since then the idea of peroxides and superoxides has been disputed, but I haven't read those papers because they were published between 1980 and 2000, when I wasn't paying much attention to Martian geology.
At any rate, we know when you wet the Martian regolith, it releases oxygen; Viking proved that. The mechanism is in dispute, but not the result. I suspect 20 tonnes of reg should degas at least 20 kilos of oxygen; that's only 1/10 of 1% of the mass. It might degass 10 times that; I don't know. I wonder whether 20 tonnes of regolith needs something like 5 tonnes of water to release it, though? I suppose that's not a problem, since it has to be wetted for the plants anyway!
-- RobS
You wouldn't use batteries for back up power; you'd use fuel cells. Reversible fuel cells will also do your electrolysis for you. A kilogram of hydrogen-oxygen provides something like five kilowatt hours of electricity. A four-person base needs about ten kilowatts of continuous power to operate life support systems; probably less at night. So fuel cells would need twenty-four kilograms of hydrogen-oxygen (a bit more methane and oxygen; maybe thirty six kilos, there are now methane/oxygen fuel cells) to keep the lights on at night. That amount can be regenerated during the day. Even during a dust storm, the sort of array I described on the first page of the Mars 24 postings would put out ten kilowatts.
If you don't want to use fuel cells, a pressurized rover has an internal combustion engine able to produce far more than ten kilowatts of power. A spare engine would weigh what?; a hundred kilos? How much does a ten kilowatt natural gas electric generator weigh; maybe thirty kilos or fifty kilos? Methane burned in oxygen is, basically, natural gas.
-- RobS
Have you ever walked in a lava tube before? There are some on the southern flank of Mt St Helens that are open to the public. They are God-awful places. The lava is often very sharp and can cut through shoes. They are also incredibly untidy; there are huge solidified, sharp blobs of lava all over the floor, scattered boulders that have collapsed off the roof, and hanging stuff that can fall. So a lava tube will require a jack hammer to clean it up and will be dangerous (because the roof will have to plucked of the loose stuff).
As for "piping in" light using glass fiber, that's pretty complicated. You need huge reflectors able to track the sun and collect the light.
Kevlar inflatables are much easier to make than that.
-- RobS
The moons are chondrite, which is usually something like 5-10% water by mass (much of which is chemically bound, so heat is needed to drive it off). The ill-fated Phobos 1 spacecraft the Russians launched detected hydrogen ions near Phobos before it failed, suggesting the regolith has bound water in it. You probably need to drill into the moon and heat the "bedrock" directly to extract the water; the regolith itself has been bombarded by micrometeorites and cosmic rays and would be depleted in water.
-- RobS
A More Efficient Way to Obtain Solar Energy
Last night I was researching Mars balloons and solar-powered aircraft on the Web. There is an incredible amount of information available. In the process, it occurred to me that there is a better way to concentrate solar energy for use as electricity and heat on the Martian surface.
Imagine a cylinder of plastic 100 meters long and 30 meters in diameter. Such a cylinder has a surface area of about 10,000 square meters and an interior volume of 70,000 cubic meters. In spite of the cylinder?s huge size, its mass is actually fairly reasonable. The recent ?Mars balloon? that flew in Colorado this summer had a volume of 0.6 cubic meters and a mass of 60 grams. Its surface area would have been about 3 square meters, so the mass (if all of it were the balloon?s skin) is about 20 grams per square meter. A 10,000 square meter cylinder would therefore mass about 200 kilograms.
The plastic cylinder is inflated with Martian air to keep it rigid. It is silvered on its bottom half and transparent on its top half, except for a stripe of silver along the very top. Covering the very bottom of the cylinder, inside, is a strip of solar panels 100 meters long and 1 meter wide. Their mass is 300 kilograms; this number is derived from the Helios solar-powered aircraft, which has a total mass of 600 kilograms and a wing surface (which is completely covered by solar panels) of 186.6 square meters (3 kilos per square meter, if you assume that propellers, batteries, etc., have some mass. Probably the solar panels? mass a bit less than 3 kg/m2, but let?s be conservative).
The silvering permits all the sunlight falling on the cylinder to be reflected onto the panels if the cylinder is always oriented toward the sun. It is not difficult to orient it, I think. If the cylinder is aligned with its axis north-south, the cylinder need only to be rolled across the ground to point the silvered surface first toward the east at dawn, then overhead, then to the west at dusk. This could be done by attaching cables every few meters along the ?top? running to anchor points with electric powered winches east and west of the cylinder. If the eastern winches pull while the western winches play out the cable, the cylinder will roll toward the east. To make the rolling smooth, the ground around the cylinder has to be smoothed and a plastic membrane put down, so the cylinder?s plastic surface doesn?t snag on anything or get punctured. This would even allow the winches to ?pivot? the cylinder?to pull the southern end of the axis more than the northern end in order to track a sun that rises in the northeast and sets in the northwest in summer.
How much power can the cylinder make? The surface area reflecting sunlight is 30 meters wide and 100 meters long, a total area of 3,000 square meters. Mars receives an average of half a kilowatt of solar energy per square meter, so the cylinder receives 1,500 kilowatts of it. If the panels are 30% efficient, they can make 450 kilowatts of electricity! The panels will be exposed to solar energy about 12 times as intense as on the Earth?s surface, but the new panels now being made can function efficiently at twice that intensity (I read that on the web somewhere). And consider that this entire solar concentrator has a mass of 500 kg! If one makes the cylinder tougher and more durable, includes the mass of the plastic underskirt, beefs up the panels to make them able to handle more intense ultraviolet light, and adds cables and winches, maybe the mass will be 1,000 kilograms, or even 2,000 kilograms. But that?s still only half the mass of the 100-kilowatt nuclear reactor of Mars Direct.
But there?s a bit more. The panels, exposed to such intense light, will get hot. I don?t know how hot, but my guess is that they will quickly heat to at least 100 Centigrade, maybe 200. (Does anyone know how to figure out there equilibrium temperature?). Hence one could run a network of plastic tubes under the panels and blow pressurized Martian air through them to extract the heat. If one extracted half the ?wasted? solar energy as heat, that would be another 450 kilowatts of energy. Thus the ?solar energy cylinder? would give a Mars base a total of 900 kilowatts of useable energy, which is VERY good. The Mars Direct reactor makes 2,000 kilowatts of energy (100 kw of electricity and 1,900 kw of heat), or twice as much as the solar cylinder for twice the mass. But I?m pretty sure the solar power cylinder could not be deployed without people.
There is one problem to remember: dust storms. They will reduce or eliminate the gain from the silvered surface. The 100 square meters of panels can only make 15 kilowatts of energy if pointed directly at the sun, and probably very little heat. Most of the time during dust storms, one can probably see the disk of the sun at least a little, so the silvering will help somewhat. So solar energy will have to be stored in the form of oxygen and methane for the dust storm season, and efforts requiring a lot of energy?such as making and working metal?would have to be rescheduled.
Dust storms will also require that the cylinder be anchored very carefully; the cables will have to be strong. The cylinder will also get covered with dust, which will have to be blown or brushed off.
There?s another version of this: the solar powered dirigible. A cylinder with a volume of 70,000 cubic meters, I think, can lift about 2,000 kilograms if filled with hydrogen, and as we have already seen its mass, with solar panels, is 500 kg. Trying to point the silvered area toward the sun may be impossible, so there may be no reason to silver part of the cylinder at all; the panels will make 15 kilowatts at high noon if they lie on the bottom of the cylinder (which they will tend to do, since they are the heaviest part of the vehicle). Such a dirigible could have a pod on its bottom with propellers; it would be able to transport over a tonne of cargo (or cargo plus people). It could probably move only slowly under its own power; maybe 30 kilometers per hour. But that speed would be sufficient to circumnavigate the Martian equator in 29 days. If one utilized prevailing winds, one could circle Mars much faster. This would be quite adequate for cargo transport, especially if the vehicle were scaled up somewhat (perhaps doubled, so that it could carry two tonnes of cargo).
Cool, eh?
I see that in *Case for Mars,* page 156, Zubrin says ISPP for a sample return mission, requiring 400 kilograms of fuel, would take 20 kilograms of equipment (sabatier reactor and such) and 300 watts of power. On page 190 he refers to a "standard RTG" putting out 300 watts, so I infer he was thinking that an RTG would power the ISPP. The possible problems NASA has identified are (1) maybe they need a bigger sample return vehicle and thus more than 400 kg of fuel; (2) maybe there are no RTGs available any more. I think the latter is true.
-- RobS
Bob Dyck noted that we could easily make an atmosphere with these components:
<<<if you pressurize a greenhouse and use a sorbent to remove 95% of the carbon dioxide and 80% carbon monoxide, and then extract oxygen from the soil by soaking with water to release the super oxides, that should leave you with 45.3% nitrogen, 26.8% argon, 22.3% oxygen, 2.26% carbon dioxide, 0.23% carbon monoxide.>>>
Bob, if you're still reading this thread, how much regolith did you have to soak to release that much oxygen? I ask because it occurs to me that if oxygen is fairly readily available in the regolith, that simplifies Mars exploration greatly. An expedition crossing the surface in pressurized rovers would have to bring along methane fuel for their engines, but not oxygen; and since a kilo of methane requires 3.5 kilos of oxygen to burn completely, that's pretty important! A tonne of "fuel" would take you 4.5 times as far if you don't need to bring the oxygen. But what we don't know is how much reg we have to wet to release the needed oxygen, or how much water we need to release it. Any ideas?
-- RobS
Ah hah! I found it using Google!
"The second class of orbits considered are quasi-periodic orbits near the Earth-Moon triangular libration points. Transfer costs from geostationary transfer orbit amount to 880-1060 m/s plus 50 m/s for mid-course corrections. Annual costs for station-keeping are about 3- 5 m/s. Eclipses will occur only very occasionally. They can be avoided through orbit changes. Data transmission distance is about 350 000 to 400 000 km. Two groundstations will provide about 80-90 per cent time coverage."
This comes from http://216.239.37.100/search?....e=UTF-8
By comparison, geostationary transfer orbit to escape is 700 meters per second. Conclusion: getting to L1 costs
180 to 360 meters per second "extra."
Advantages of L1:
1. Can be used to stage missions to moon as well as Mars
2. Delta-vee requirements to Earth/sun L1 and Earth/sun L2 are only 50 meters per second. Hence Earth/moon L1 can be used as a repair area for telescopes and other equipment destined for Earth/sun L2. The next generation space telescope to replace Hubble may be put at the Earth/sun L2. If it needs repair, a 50 m/sec deltavee can take it to earth/moon L1.
3. From earth/moon L1, one can use gravity assist manuevers with both the Moon and the Earth to go to Mars. This makes up for the extra delta-vee to get to L1 or allows a wider range of launch times (because the moon can be used as an extra stage to perform plane changes).
--RobS
I am not sure why the scientists keep talking about L1 and L2. This is a good question and maybe a Google search will reveal the answer. The only thing I can think of is that L1 and L2 are useful for both the Moon and Mars, whereas L4 and L5 are useful only for Mars. If one has an ion engine--even a small one--it is probably very easy to stay at L1 or L2.
-- RobS
Zubrin's book *Entering Space,* pages 28-30, tells a sad story: that three plans for the International Space Station were drawn up, the most capable and cheapest of which proposed building a Shuttle C and launching the space station 70 tonnes at a time. But this plan was rejected because (1) launching the station 16 tonnes at a time would keep the shuttle busy and thereby "justify" creating it, and (2) it enabled a modular approach that meant the Europeans and Canadians could be involved building their own modules. But the result was an immensely expensive space station. A shuttle C could have launched it in 1 or 2 flights and it would be finished, and we'd have a heavy lifter as well!
-- RobS
I agree that any plan for settling Mars needs to have plenty of spares and margin, with a machine shop of some sort among the early cargo flights. Any plan also needs backups; I think a spare hab is always a good idea (i.e., if a hab accommodates 4 and you have 4 people on Mars, you need to have space for 8; when your crew expands to 8, you make sure you have a third hab and room for 12; etc.). This is another argument in favor of settling one spot on Mars, rather than landing at a different spot every two years. In fact, I think it is an argument that the first mission ought to involve two vehicles capable of accommodating four each, but flying only three each; that way if a hab or shuttle breaks, everyone can squeeze into the other one. Once confidence in the equipment builds, one could then fly four in each vehicle.
Multiple possible use of equipment is also wise. For example, a greenhouse might be able to serve as temporary housing if a hab has a problem. Same with machine shops and garages. If one has two habs and two greenhouses, it might be wise to connect them in the form of a square, so every module has escape routes at either end. As more modules are added, they should always be connected, if possible, so that they always connect to other modules at each end.
Someone stressed the value of nuclear power. I quite agree. I put together Mars-24 without it to see whether it is possible. It appears to be possible. But I agree, nuclear is easier. It may not prove politically practical.
Robert Dyck again stressed the problem of using L1 because it requires circularization. If it requires orbital circularization, I agree a highly elliptical orbit is better. But I have not yet seen anything suggesting it requires circularization. It seems like it should, but L1 is not a real orbit; it is a point where gravity cancels out. It may also be easier to get to it by flying to the moon and circularizing into a high orbit around the moon just short of L1, then raising the orbit to L1. And L1 is a popular idea among the experts; as we recently saw in Space.com, there is a big proposal from NeXT to build an L1 station as a staging point for lunar and Mars exploration. I am assuming they know something we don't, but I wish I knew what it was! Objects often do not stay "at" Lagrange points, but wander in complicated orbits around the point.
-- RobS
Thank you for the web page about advanced propulsion concepts. I did not use anything of this sort because (1) I didn't know much about it, and (2) I was concentrating on shorter term technologies. So far, the largest function ion engine in space uses only 2 kilowatts and the ones being designed are in the 10s of kws range, not even 100s, which is what Mars-24 would need. The more advanded propulsion systems you are suggesting are probably farther down the time line. Of course, if it takes 40 years to send people to Mars, we will probably be using the more advanced systems!
-- RobS
I think I read somewhere that a Sabatier reactor can be used to make ammonia, just like it can make methane. Ammonia is a key ingredient in making nitrogen fertilizer.
I would guess that even if we bring hydroponics to Mars, we would want to start experimenting with making Martian soil for plants, if for no other reason than growing potted trees (which would be pretty). One would start by bringing hydroponic "miracle grow" and steadily add to it nutrients derived from human waste, Martian air, and even Martian soil (such as phosphorus), but eventually it would be easier to make soil. Once your "starter soil" from Earth has expanded to a couple of cubic meters of soil that is functioning, you can probably add 10% of inorganic regolith to it every couple months, add more fertilizing nurtients, and add dead plant matter. It would steadily increase in mass and after a few years you'd have enough to grow the base's vegetable supply. Then a few years more and you'd be able to support chickens and rabbits. In a decade or two, you could have a pretty complex ecology. Assuming, of course, you have a full time person or two watching the ecosystem and preventing collapses.
-- RobS
Why salt water?
-- RobS
I think the plan for avoiding a ravine is to land the hab in a place where there aren't any. But the unexpected can still happen.
I don't think any of us know the answer to your question, since we weren't involved in designing the hab. But here would be my guesses:
1. Covering the roof of the hab with sandbags is adequate in terms of radiation protection (*Case for Mars* does not envision doing anything else).
2. Designing a hab that can be swung around and deployed without a crane is complicated and prone to failure. The thing will weigh several tonnes even in Martian gravity, after all.
3. The floor area in the "tuna can" design is probably the same as in a quonset hut, or nearly the same.
Therefore on the principle of keep it simple, the idea was not considered.
-- RobS
You may be right that a quasi-Gregorian calendar is neither fish nor fowl, and thus may not work well.
I agree, the weekdays simply can't be made the same. Martian Christians and Jews will have to decide how they will solve that problem themselves. It may very well be that the First Martian Church of Christ willend up celebrating Easter on a different day than the Martian Methodist Church, too. But we already have that with Eastern Orthodox Easter different from Catholic and Protestant Easter.
I am not worried that Monsol, September 1, doesn't perfectly line up with Thursday, September 1. I have called New Zealand before and have already had the strange pleasure of asking people how tomorrow looks over on the other side of the planet. This Bulletin Board operates on a different time zone than my home in Indiana by seven hours. Wouldn't it be interesting or cool to get emails from Mars that are current but are dated one day ago or one day in the future? Sometimes it might even be off by two days. At least it would be reasonably familiar to someone unfamiliar with the 56th of Scorpio or some such dating system.
-- RobS
The current hab isn't split into two quonset-shaped halves because the hab is spun to produce artifical gravity on the way out, and that would put the floor "standing up" ninety degrees in the wrong orientation for artificial gravity.
-- RobS
That's a fascinating idea, but alas, I flunked calculus, so I can't help. I think ion engine are always assumed to work continuously and to raise perigee and apogee constantly, wastefully spiralling out of low orbit.
One possibility would be adding a tonne of energy storage system, probably fuel cells, storing up your solar power and using it all to thrust the ion engines at maximum only at perigee. That might work reasonably well when the apogee isn't too high. But as the orbit gets more and more elliptical the percentage of time away from perigee gets longer and longer and you'd have to store a bigger percentage of your total energy.
I am not sure why people aren't thinking of deploying big mirrors to put more light on their solar arrays. The high efficiency gallium arsenide cells operate very well at high temperatures and insolations; I think I saw 25 times normal insolation is okay for them. A mirror deployed in earth orbit could be a hectare in size (100 meters square) and weigh almost nothing. It seems to me with mirrors one could easily create megawatt solar arrays that are small. One could even operate such arrays half decently at Saturnian distances from the sun; the mirrors would just have to be bigger. This would give you so much power, you could just turn the ion engine on and off to make the orbit elliptical, and you'd still have a reasonably short acceleration time.
-- RobS
I'm not sure the O'Neal colony described in the posting above will ever come about. There is no need to treat people like worker bees or worker ants.
As for the ethics of the situation, an important ethical principle to consider is that people must be treated as ends, not as means. When you treat people as means, then they become pawns and their rights are stripped away. But if they are ends, then they have to be given freedom to achieve their potential.
All significant ethical systems on Earth treat people as ends, not means. I suppose the biggest exception is the military, but even there the goal is to minimize the loss of humanity. I do not see how exploration of space will cause the elininatin of this basic ethical principle.
There's a long history of agricultural people making pets out of the animals they eat. Rabbit pets, anyone? They may be the first non-human mammals going to Mars.
As for non-food animals, I'd favor some canaries; they sing beautifully, and people will miss bird songs.
-- RobS
I had trouble following your calculations because I wasn't sure your starting mass (I guess 24 tonnes; it's a nice round number, isn't it?) or how much cargo you were pushing. The overall masses for the panels and thrusters look similar to the assumptions of Michael Duke's "Lunar Reference Strategy" paper that I used as a baseline for developing Mars-24.
Regarding the total delta-vee necessary; I have heard that ion engines generally require about twice the delta-vee of chemical rockets because of all the gravity loss caused by leaving a planet slowly. I suspect launching to near-escape requires at least 50% more energy because one is circularizing ones orbit constantly as one moves upward. Among other things, that means one briefly travels through a circular geosynchronous orbit, and it requires a delta-vee of 4.1 km/sec to achieve (2.5 km/sec to go from low earth orbit to a geosynchronous transfer orbit, then 1.6 km/sec to circularize). I arbitrarily assumed that L1 (near-escape) required 4.5 km/sec to achieve rather than 3.2 km/sec.
Robert, we have similar background in some ways. I was raised on a farm and was just the second member of my family on my father's side to go to college. My father built aircraft engines but not as an engineer; he was the foreman of an assembly line. Then he quit that work to go from part-time farming to full time. I should add that my mother's father homesteaded in Manitoba, probably in the 1890s, before settling in New England and becoming an insurance executive.
-- RobS