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I have to agree with GCN. It's not that the issues are talking about don't exists (viscosity, ect...) it's just that when you are dealing with gasses at this high a temperature, it becomes a negligable factor. The energy lose due to expansion, friction, whatever, is minescule in comparison to the energy the gasses already posses. In fact, I highly doubt you would be able to find a measurable diffrence if you were to test for them some how. Definetly not worth the extra mass you would introduce in trying to compinsate for these factors some how.
No, no, no.
On either side of the tube, there is only enough force to push the water up 10 meters. 10 meters, that is it. The water level can never rise above 10 meters. That still leaves 35,999.990km to go. In order for a siphon to work, the water would have to be able to rise all that distance. It's not going to hapen.
On Mars, you would also have to carry around the oxidizer for the chemical fuels, so their advantage in energy density would not be as large.
Already accounted for, most likely fuel-oxidiser combinations have energy densities ~10MJ/kg.
As for flywheels, there energy densities are on-par to supperior to batteries <400kJ/kg, and since all they need is transmition equipment there power-to-weight ratios are excelent. But safety would be even more of a concurn than with compressed air. If a rotor was to get loose at 20,000rpm, the effect would be disaterous. Also, wouldn't a large rotating weight cause issue with manuverability.
I still tend to think that batteries would be the way to go, if you decided to exclude chemical options.
Hmmm... after some more research I found some figures for a possible pneumatic engine.
The compressed air in the tank was expected to give some 25 Whr/kg or 90kJ/kg. Which is not to impressive, chemical fuel sources generaly have >10MJ/kg. So they are about 100 times more energy dense. Even assuming 100% efficency for the pneumatic engine and say 25% for a chemical (perhaps combustion), you would come way ahead chemicaly. Even conventional batteries have supperior energy densities, greater than 300kJ/kg. And batteries have efficency (40-50%) on their side as well.
They do better on power-weight ratios however, with the figures I saw claiming 500W/kg. This is on par with combustion engines, and better then batteries and fuel cells clock in at about 100W/kg.
As for the more etherial issues, I do not see an great advantage in compressed air over the other alternatives. All pneumatic engine relies on the expansion of gases, so is probably going to have as many moving parts as any combustion engine would, giving it no advantage in reliability. While refuling an air tank might be simpler than refuling a chemical vehicle, it is certianly less easily done than a battery powered vehicle.
OTOH, for a short range utility vehicle the power-weight ratio is much more important that fuel efficency/energy density. Which is a point in favor for the pneumatic engine.
However for my money if you do not want to use chemical power for your short-range utility truck (because of complexity of refuling or whatever), then batteries are probably the way to go. Their energy density is 10 times greater, and there power density is only 5 times less. And they should be if anything easier to fuel and more reliable.
I don't see any reason you couldn't build a air-powered 4-wheeler or something, but I guess the question then would be, how does an CA engine stack up against other options (particularly electrical, ICE, and fuel-cell). What would be the typical power-weight ratio and fuel efficency of such a vehicle? I've done a quick search but I haven't been able to find any data.
No you don't understand.
I think Shaun had the right way of explaining it. Vacume doesn't "suck" anything. What happens is the rest of the atmosphere pushes back.
Think of this, ever put your finger on top of a straw and pull liquid out of a cup that way? Gravity should pull the liquid out of the straw and onto the floor, but it doesn't because the rest of the atmosphere has enough force (pressure) to keep (some) of it inside the straw.
The problem is comparitivly the force of our atmosphere is small and the force of gravity is very large. There is only enough force (pressure) in our atmospehre to push up ~10 meters of water agains't earth's gravity. That is all the force there is. If the diffrence in the two sides of these tubes is greater than this 10 meters, there is no possible way the water can siphon from one side to the other.
It's like a car trying to climb a hill to cost down the side. Sure, there may be potentialy greater energy for the car if it can climb all the way over the top of the hill, but if the hill is to tall, the car cannot climb it, no matter how much energy it might get on the other side.
None. There are no elements you can burn on the moon to get carbon.
In fact, there are no elements ANYWHERE you can burn to get some-other element. That is the nature of an element. Chemical reactions (like burning something) do not change what elements are present. They do not transmute say Titanium or Oxygen into Neon or Carbon.
That said, there is apparently very, very little carbon on the moon.
Engineeris got to eat to ya know?
But seriously, the last launch vehicle of that size, the Saturn V cost over 7 billion to develope, in 1967 dollars. That would be nearly 40 billion to day. Comparitivly, it's a bargin.
First off the topic of this post is realy messed up for me, symbouls numbers, whats up with all that? Anyone else seeing something similar?
Obviously there are serious diffrences in the method of opertaion of a ICE or a Gas Turbine engine.
Performance wise there are alot of diffrences. Turbines tend to have both much higher power to weight ratios and tend to be generaly more efficent. Turbines also generaly have fewer moving pecies than ICE engines. Also, nearly all the motion is rotary as opposed to the reciprocating motion in a ICE engine. All this generaly translates to more reliability.
The problem with turbines is that they are generaly very big. We have little expirence with building them to smaller scales. So it is uncertian if the benifits associated with them will scale down to the 2-10kW size that a mars rover would need. I am not aware of any turbine engines currently produced in this size. Progress is being made on these issues however, and turbines probably hold the potential to beat both ICE and Fuel Cells in terms of efficency and power-weight ratios.
Another point to consider, why did air-liners change over to turbine engines. Simple they had vastly higher power to weight ratios than piston engines of the time and were far more reliable than the piston engines as well. When first introduced that were less efficent, but modern turbines do considerably better than ICE.
I imagnine a rendivous with a spacecraft in a high eliptical orbit would be fairly difficult. It would be moving considerably faster than any craft that would want to dock with it.
Errorist, you obviously have no idea what you are talking about. A quick talk with any science teacher, or about 30 secounds on goggle should prove all this to you. You are seriously mistaken about how and why a siphon works.
You see a siphon works due to diffrences in air-pressure on the two sides, which I guess is indirectly due to gravity. And while you are semi-correct in that there is more pressure on the low-side, in this case it still doesn't matter. As that diffrence in pressure in no where NEAR great enough to draw the water up several thousand kilometers. There is a limit to the power of vacume, it's not some magical force.
And again, even if it did work, what the heck is the point in sending water up to orbit and back? Why, oh why would you want to do that?
It's physics man, physics. And to answer your question while I have personaly never done it, I have seen it demonstrated on Mr. Wizard when I was younger.
Aghh... you are making me want to pull my hair out.
When you are dealing with such large distances and amounts there are more factors to deal with than simple PV=nRT.
I think GCN tried to point this out to you before, but I'll try and beat it into your head again.
Space is a vacume, correct? And earth has an atmosphere at (comparitivly) high pressure. So why then does not all our atmosphere run-off to space, a region of low pressure? Because of gravity of course. Earth has heck of alot of gravity which keeps out atmosphere from flying off. Which is convient, because I like to breathe.
That is the same reason you can't have a "manometer" that goes all the way up to oribt. It simply wont work. And even if it did, you would have achived nothing for it. A 50,000km trip, up and down, for no point.
Here are a couple expirment you can do at home to prove it. First find a short length of tube and two containers for water. Fill one up with water and place it about a foot above the other one. Now suck through the tube until water comes out and place it in the other container, viola! A siphon.
Now, after staring in amazment for a while, lift the lower container up above the level of the higher container... and look, the siphon has stoped. Repeat the expirment all you want with any variation you care, the results will always be the same.
For a secound expirment you would require a garden hose, and a roof. Place your two bucket as before (they should probably be bigger this time), and suck on the hose to start the siphon. Now, climb up on the roof and then drag the middle of the hose up with you. After you have rasied the middle up 10meters (hmm, maybe a two-story house), the siphon will stop. Anyway you repate this the results will be the same. Your plan will NEVER work.
This is realy getting quite looney.
There is no way a siphon could lift water up to orbit. First off it be incredibly impracticle to try and prime such a huge siphon. Even a perfect vacume can only lift water like 10m against Earth's gravity.
Secoundly, even after you have primed the siphon, it doesn't get the water into orbit. A siphon cannot raise water higher than when it started, only lower. So all you might manage to achive is sending the liquid on several thousand kilometer trip, for no pupouse. Congradulations.
Thirdly, it still won't work. Gravity will counteract the force of atmospheric pressure after only about 10 METERS! Much less the many kilometers you need to get up into orbit. The entire idea is incredibly stupid.
As for pumping anything to oribt, while it might be possible, it is incredibly impracticle. The mass of the pipes, and the water would be incredible. Halling the water up in elevator cars is SO much simpler and more practicle. The idea of a pipline to orbit is just looney. (Well on Earth at least, it might make sense elseware, but that's another story).
Also, people need to just face it, you can't cheat your way to oribt. Not via capilary action, not via siphons, gravity wheels, or whatever other loony idea you might come up with. It takes alot of energy to get up there, and you have to spend that energy to get there. period.
Lastly, these topics rightly belong in Interplanetary transportation I think, not here.
It all depends upon the size and nature of the tube. You've got the formula there, look up some of the constants and do the math yourself, it's not realy hard.
Yes dook, we have been over your calculations, and your method for arriving at them is simply wrong. ICE engines (rotary or otherwise) are less efficent than fuel cells (only about 40% efficent), but still a workable alternative. And as mars dog points out they can generate nearly 5 times more energy per unit of engine weight than a fuel cell can.
You are also incorrect about the gasous byproducts of a martian closed cycle engine. Without nitrogen in the combustion atmosphere, no energy is wasted in the formation of nitrogen oxides, and in a closed cycle engine the formation of other products of incomplete combustion is very small.
I won't go back over all my arguments in favor of them again, but you can see them http://www.newmars.com/forums/viewtopic.php?t=3495]here
All of this stuff relies upon lifting a continuous colum of water up to orbit. I think this is impracticle due to the mass involved. Assuming a tube of about 1cm^2 in cross section, the first 300 kilometers alone would mass 30 metric tons, and the entire colum up to geosynchronous orbit would weigh more than 3000 metric tons. Clearly to much for any reasonable elevator to support, regardless of what crazy system of pumps you develop to try and bring it up.
Here is a stab at what kind of tube would be required to lift water to low-orbit via-capillar action. Re-working the equation I showed you earlier you get
r = 2T/Hdg
r = radius
T = Surface tension = 7.29e-2 J/m^2
H = height = 300km
d = density = 1.0 g/ml
g = gravity = 9.8m/s^2
Solving this, you find that you would need a tube an impossible 50pm. Water molecules are about 300pm in diameter. I don't think I need to repeat the excersize for geosyncronus orbit, do I, that's some 34,000km up...
Now while water has just about the highest surface tension of any liquid due to the strong hydrogen bonds bettwen the molecules, the intermetalic bonds in mercury are about an order of magnitude higher (in fact, this is why mercury has a reverse meniscus) 4.6 x 10-1 J/m2. But in anycase, the idea is still impossible.
Also, none of this addresses the problem of how do you get the water out once it has risen to the top. If you just drill in a whole in the tube, the water level just drops down lower. Tree's remove the water via various methods of cellular filtration, I guess you could do something similar, but it's not an easy problem either.
Hmm... I'm not exatly sure what you are trying to say, the cohesive forces bettwen water molecules and the forces bettwen them and the walls of the tube are EXACTLY what capillary action is. The website you use assumes a figure of 5nm for a minimum size to get that figure of 2.8km, which is not a bad assumtion for a minimum tube diameter. But in any case this figure is far, far short of the some 300km you need just to achive low-obit, much less the 35,785km you need for geosynchronous orbit. Even for the low-orbit tube your tube would have to be an impossible 50pm in diameter, this is smaller than most atoms, and much smaller than a water molecules, clearly not possible.
Capillary action is not infinate, there is a limit as to how high it will alow a liquid to rise. You can caluclate that distance via the following equasion:
H = 2T/drg
H is the distance the liquid will rise
T is the surface tension bettwen the liquid and the tube
d is the liquid's density
r is the radius of the tube
g is acceleration due to gravity
I am unsure what the surface tension would be bettwen carbon nano-tubes and any given liquid, but if you knew that you could calculate the height. However, this all may be misleading because at such small distance (nano-meters) the action of surface tension may break down.
In any case the liquid is not going to rise far enough to help with space travel, and it is not going to make this loony "gravity wheel" work either.
There are three ways to get rid of heat, convection, radiation, and conduction. I'll go over each of them in term.
Convection is the difusion of hot molecules from a hot area to cooler areas, primarily in liquid or gasses. On Earth this is the primary method of getting rid of heat, as it is the most efficent. You move cold air/water by something that is hot, and you cool it. The problem is in space, there are no large quantities of air or water to dilute your high temperatures with, and bringing such quantities up with you is very inefficent. Sometimes convection is used as a means to transfer heat from a region that has a lot of it (like a laser or a reactor), to an area that can get rid of it (like a radiator), because convection is the most efficent means to transport heat, but in any case, it is not an effective means of heat disposal in space at least.
The secound method of heat transfer in radiation. And it is the primary means by which heat is delt with in space. Excited molecules emit photons, which take the heat energy away with them. However, this method of heat transfer is fairly small scale, and you often need very big radiators to get rid of the vast amounts of heat you have.
The thrid method of heat transfer is conduction, which is the movment of heat by moleculor action. Exited (hot) molecules bump into other molecules, giving away some of there heat energy in the process. This method is most prevelant within crystline solids, like most metals. Now, while conduction can transport the heat away from it source, or give it to a gas in order to be rid of it via convection, all it realy does is spread your heat around your spacecraft, not get rid of it.
So you see, just because space is realy cold, doesn't mean it is the best enviroment for cooling things off. In fact, vacume is the best insulator in existance.
Well frozen ammonia would be far supperior to water ice anyways. Oxygen is easy to find, and the moon has pleanty of it, but nitrogen is fairly rare out in the solar system (little to none on the moon, mars, and most asteriods), so finding a source of it on the moon would be excelent. Luckily, nitrogen is recycled fairly effiecently by natural systems. We don't even touch the N2 in our air, and plants and animals fairly efficently recycle the nitrogen in there systems, and without any mechanical help from us. Compare this to carbon, which is recycled not nearly as efficently in the ground (although it makes up a much smaller part of the cycle there), and less than optimaly in the air, where it usualy has to be recycled by mechanical means anyways.
In anycase finding ammonia or methane ice on the moon would be great, and the dissasociation of ammonia and methane of there hydrogen should pose little problem. However, water ice is still the most likely prospect. Nitrogen, carbon, and practicly every other element you could consider are just plain more rare in the universe than oxygen. Also in craters sheltered from solar wind and radiation, there is still cosmic radiation to consider. It comes from just about every angle imagniable, and the moon (lacking an atmosphere and magnetic field), suffers more strongly from it than earth. It could cause dissasociation and loss of hydrogen atoms as well.
I agree with GCN on this one. Domes aren't a bad idea on mars, where there is an atmosphere to speak and the water concentration is much greater. You wouldn't have to dome huge sections, just move the dome after you have collected a good amount.
On the moon things are diffrent. A soil oven is a much better choice, and would necessarily have to be extreamly complicated. For example, you could dumb you water bearing soil into some sort of transparent container, then just focus a series of mirrors on into heat it greatly and collect the vapor. With the moons extreamly long days, there is no reason you couldn't do this in very large quantities at once (maybe put a stirrer in it to shake it up every now and then), and get a good amount of water without to much trouble, that is if you could find good water bearing soil.
As for what the hydrogen readings on the moon actualy are, I think water is the realy the most serious option, if the readings are correct and they actualy are detecting hydrogen. The O-H bond in water is like the secound strongest bond possible for hydrogen (only H-F is stronger IIRC). So water tends to be pretty stable and resistant to cosmic radiation. Not that there are not other possibilities but water (possible trapped up in a mineral) is the strongest one. The only other possiblities I could think of is HF, but hydroflouric acid does not form strong hydrogen bonds like water does and so whole molecules of it could wind up lost out into space. Most covalent compounds are even more unlikley as the hydrogen would simply be ionized off even easier then a crystal of HF would be.
I don't know about fagile, but it would seem you would need a fairly large plate to achive a signifigant amount of thrust per blast.
How do you fill the wells back up with hydrogen after you blast it off, or is it a one shot only kind of deal?
Liquified CO2 would be neat, because it would evaporate quickly fairly quickly at typical martian temps and pressures. The liquied would hopefully quickly wash off the dust, and then evaporate taking any remaining particles with it.
One of the problems with this is that liquid CO2 is obvioulsy fairly cold.
I would simply use an "air-currtain" or a blown wall of higher pressure air to block enviromental dust from getting into the airlock and to help clean the dust off of the suit. I would then have use an "air-pick" to detail the suit, and blow off any remaining dust. Of course, filtered CO2 would be used for the "air" in the system.
One of the problems with this setup is that it would be fairly bulky, since you would need an air-lock big enough to clean the suit off in. It would probably be easy enough to do at the base, but more difficult on the rovers where space is a premium.
As for filtering CO2, that should be pretty easy. Liquify it, the dust should settle to the bottow, and the evaporate CO2 off of the top. Presto, filtered CO2.