China plans manned moon mission

Discussion in 'World Events' started by cosmictraveler, Jan 3, 2012.

  1. KilljoyKlown Whatever Valued Senior Member

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    Maybe if that was the purpose of mining the moon or asteroids. I'd like to think it will mean we can get the materials we need to live off world without having those materials expensively shipped from earth. Also, there might be some materials that are easier to find on the moon or in some asteroids that would make it cost effective to ship back to earth.
     
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  3. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

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    There is nothing worth the cost of bringing it back as many times cheaper to get it from Earth. The only possible exception is He3, which may be economical if and when the SECOND geneation of fusion energy is possible and economical.

    Many "mine the moon" nuts have suggested that He3 MAY be found in the upper layers of the moon dust as it definitely is a very tiny fraction of what streams out of the sun in the solar wind. I am 99.9% sure that this is just wishful thinking effort to justify spending money on their favorate space projects.

    Helium, all isotopes, is very very mobile. It finds its way thru the smallest of holes. Why it is used to detect tiny leaks in vacuum systems. And that is at room temperature. The moon surface is under full sun heating for 14 days with no nights and gets very hot. If there were any He3 there it would very rapidly evaporate into space.

    Summary: there ain´t nothing on the moon that is not at least 100 times cheaper on earth than bringing it back from the moon.

    The moon is not even useful "high ground" from which to attack an enemy on Earth. Your attack craft will need 4 or 5 days after launch to do so, and can be watched by targets´s radars, etc. for optimum counter launch time to blow it up; but with a launch from Earth at your target, the max time from launch to target is only ~45 minutes.
     
    Last edited by a moderator: Apr 9, 2012
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  5. KilljoyKlown Whatever Valued Senior Member

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    For the most part your probably right as far as high ground goes. If I was going to use a weapon from the moon I'd like to build a very large rail gun, something that would shoot telephone pole sized projectiles. At rail gun velocities those projectiles could reach earth in less than a day and I'd hate to be on the receiving end of all that kinetic energy. However it might also be used to deflect asteroids heading our way or if they can be accurately placed it could also send back mined metals cheaply.
     
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  7. garbonzo Registered Senior Member

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    Oooo lala. Likey likey!
     
  8. KilljoyKlown Whatever Valued Senior Member

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    True, but when you ask for the moon. You might as well think big.

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  9. billvon Valued Senior Member

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    Not for any sane amount of mining.

    Of course, outside of some very rare and unlikely materials (i.e. a source of pure U235.)
     
  10. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

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    I´m correct on all of it.

    Surface to surface moon / earth separation is about 380,000 miles. To do that in 24 hours implies your dense rod leaves the rail gun at 15,600 mph. Assuming there is a constant, probably magnetic, force acting on the Rod as it accelerates on the rail gun, the average speed on the rails is 7,800 mph.

    The duration of the acceleration, T, is related to the length, L of the rail gun in miles by: L = 7800 T but T is in hours. Let’s convert to t in seconds. Then L = 7800x(t/3600) or approximately L =2t but L is still in Miles.

    Actually your rod may need to leave the rails going faster as moon´s gravity will be slowing it down until Earth gravity begins to speed it up. I am too lazy to look up escape velocity from the moon or do the trans time with varring gravity forces correctly, so just ignoring all this to get first order estimates. I also assume you are not firing tangentially from the side of the moon, but straight up to have a shorter linear path, with no tendancy to orbit the moon.

    You could not support on the surface, even in the moon´s weak gravity a 10 mile long vertical rail gun structure pointed up at the Earth when every foot of it has huge heavy magnetic accelerating coils, so I will assume a well 10 miles deep has some how been dug in the moon to house the rail gun. I.e. L=10 miles (or 16093 meters) and hence we accelerate for 5 seconds.

    The velocity V leaving the rail gun in meters per second is 15,600x 0.4470 = 6972m/s = V. Now in general, V =At where A is the constant acceleration applied to object initially at rest. Thus the acceleration required, even with a 10 mile long rail gun is:

    A = V/t = 6972/ 5 = 1,394.4 m/ (sec^2). To give you some understanding of that I note the acceleration of gravity at Earth´s surface is 9.8 m/ (sec^2). Or you need more than 142 times stronger acceleration than gravity. Few 10 mile long vertical structures could widthstand that effective weight. I.e. everything so accelerated is like it weighs 142 times more than it would on Earth. This huge force applied magnetically to your rod is also acting on the rail gun, so to prevent it from collapsing it must be very strong if the rod mass is large enough to not just harmlessly burn up in the atmosphere.

    SUMMARY: It is totally impossible to send enough mass from moon to Earth, even with a 10 mile long rail gun launcher, in only 24 hours and have any of the mass reach the surface of the Earth. Also the cost of all those heavy magnetic coils and rail gun construction steel taken to the moon would be more than the US could afford, not to mention the mining equipment that could dig a 10 mile deep well in the moons surface. It is easy to dream up nonsense, but more realistic to compute, even crudely, a little first.
     
    Last edited by a moderator: Apr 9, 2012
  11. KilljoyKlown Whatever Valued Senior Member

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    Couple of things, I don't like the word impossible, implausible works better for me. I don't think it will ever happen. But sense the moon faces the earth without rotating on an axis, it would be possible to build the whole thing on the surface with the business end always pointing at earth. I was hoping for a more flexible system that might be possible with more power and something smaller than a ten mile long rail. I don't see us generating that kind of power on earth for quite some time let alone on the moon. Even if it was possible I don't think it would be built for many other reasons.
     
  12. ElectricFetus Sanity going, going, gone Valued Senior Member

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    Mining the moon is a weak argument, for anything other then rocket fuel produced from lunar ice getting out off even the moon gravity well is to much of a cost. Asteroids are far better targets, rich in valuable minerals and many like the C class asteroids likely have large reserves of volatiles that can be used for fuel. The very low gravity makes very high specific impulse engines viable from the asteroids surface all the way to earth, heck many asteroids have escape velocities of less than a meter a second, no mass driver required simple hydraulics could get you into solar orbit!
     
  13. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

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    All you say is correct, but not said strongly enough, so I will again say:

    THERE IS NOTHING IN ORBIT ABOUT THE SUN, WHICH IS WORTH THE ENERGY COST TO DELIVER IT TO THE EARTH SURFACE (at low impact velocity - not burn up it the atmosphere etc.). Someday, if and when second generation fusion reactors are economical, then if there is any He3 in the first meters of moon dust it might be economically attractive to bring it to the earth. I am 99.9% sure there is not enough He3 in the moon to economically collect due to helium´s very very high mobility and 14 days of 24 hour continuous solar baking of the surface - out gassing any that might have been absorbed from the solar wind, back into space.

    I.e. much cheaper to simply get it from the earth.

    True it costs essentially nothing to leave the gravity of almost all asteroids - I could throw many pounds (mass) off more than half of them every minute; but getting those kilograms into a quite different orbit about the sun (such as the Earth´s orbit), is an entirely different story. That is where the energy cost per pound (mass) makes it too costly.

    Just to be clear, avoid arguments, etc. the Earth and Moon are both in solar orbit. Their joint center of mass (barricenter) is in nearly circular but slightly elliptical orbit about the sun. When viewed for the earth, the moon appears to orbit the earth, but the sun gravity is stronger on the moon than the earth´s gravity is.

    Point is, "nothing in orbit about the sun" includes the moon.

    The moon is however the most economical non-terrestrial source of material as it is already essentially in an identical orbit about the sun as earth is. (No significant "orbit transfer energy" cost as from an asteroid.) If you were to accurately plot earth and moon´s orbit on an 8.5 by 11 inch sheet of paper they would be the same ellipse to the width of a fine pencil line.

    PS, I suspect it is cheaper to make He3 on earth in a first generation fusion reactor (if that is ever an economically feasible energy source) than bring it back from the moon (if any is there). I.e. Instead of the "normal" D +T -> He4 +n try for D + D -> He3 + n.

    I´m not sure but think you will always get the n as you need two "products" to conserve both energy and momentum but the D+D reaction does require higher temperatures.
     
    Last edited by a moderator: Apr 23, 2012
  14. ElectricFetus Sanity going, going, gone Valued Senior Member

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    No that is untrue, since the cost of energy in space or particularly NEO is very low. Getting back from an asteroids can be as low as a few hundred m/s and the asteroids provide all the materials and a continues supply of solar energy at least 1000 watts/meter^2 to build and power mines and return ships. The only limiting factor is how much we must expend to get up there, not get back, how much that cost is dependent on how automated the mining system is.

    That like saying no meteor ever survives to the earths surface. Building heat shields is as simply as sinstering the right kind of Regolith.

     
  15. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

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    You must be claiming that there exist interesting to mine asteroids than are in nearly circular orbit about the sun with Earth´s velocity about the sun, plus or minus a "few hundred meters."

    I doubt that, but you can try to name one.

    Reason I doubt that is that Earth is a planet, but Pluto is not. I.e. the definition of planet was changed a few years ago to exclude Pluto after several larger than Pluto objects orbiting the sun were discovered. The new definition´s main requirement is that a Planet clears its orbit and all nearby similar orbits of ALL other bodies.* I.e. If Earth is a planet there are no asteroids, comets etc. with nearly same orbit as earth.

    If one happened to get scattered into NEO, then the periodic interaction with much more massive Earth would drive it out of NEO trajectory. Earth dominates quite a band of NEOs and allows no tiny competitors to dwell in that band of similar orbits - only the moon is allowed in earth´s NEO. Earth moon is really one planet, clearing the NEOs.

    Almost all theories of the moon´s origin predict many smaller bodies (than the moon) would have been produces too. If they did not quickly merge with the moon, or get captured by the Earth, then they were driven into quite different solar orbits.

    Find the easiest asteroid to mine, then compute how much energy (per kg of mass separated from it) is required to change the orbit of that kg from that of the asteroid to that of the earth.

    * Jupiter is a planet even though it has Trojans in the same orbit as definition excludes requirement that Trojans be cleared from the orbit. AFAIK earth dose not have any Trojans as big as a marble.
     
    Last edited by a moderator: Apr 23, 2012
  16. quadraphonics Bloodthirsty Barbarian Valued Senior Member

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    Anything like that you tried to build on the moon would get destroyed by a nuclear attack launched by a rival on Earth long before you ever got it operational. Plus a railgun system like that would require a massive power plant, which what is that going to use as fuel? Not to mention upkeep - you can only fire a railgun a handfull of times before you need to rip the thing apart and refurbish it - one big enough to shoot telephone poles from the moon would be a one-shot device.

    The SDI pipedreams about geosynchronous satellites that could drop tungsten rods on targets on Earth was more realistic, but even that is still stupid (because you're either stuck with a long firing latency due to the time required for the rod to de-orbit, or you have to stock a prohibitive quantity of fuel to de-orbit the rods quicker).

    At the end of the day, none of these pie-in-the-sky weapons even offer much advantage of existing nuclear ICBM systems in the first place. Do we really need better weapons than that?
     
  17. ElectricFetus Sanity going, going, gone Valued Senior Member

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    Read "Mining the Sky" by John S. Lewis, he actually has a table of NEA with very low delta V to and from, unfortunately I can't quote the book directly because I don't have it with me, Africa, etc, etc.

    Also the NEA are replenished by being sent into Near Earth Orbits by a variety of presently active forces, if not there would be far fewer NEA.[1]

    The total mass of NEA is microscopic compare to the earth so I think the earth still counts as having "cleaned it orbit..." If not then none of the other planets are planets as they all have a small population of objects that have similar-crossing orbits (even if you don't want to count Lagrangian squatters)

    [1]http://www.boulder.swri.edu/~bottke/Reprints/Morbidelli-etal_2002_AstIII_NEOs.pdf
     
  18. KilljoyKlown Whatever Valued Senior Member

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    Yes not a possibility anytime soon. It was just a wishful response to using the moon as the high ground. As you say not very likely.
     
  19. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

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    I´ll wait for you to chose one to mine - telling its orbit, then I´ll try to calculate the energy cost per kg of changing that orbit to Earth´s orbit. (Not even worry about cost of getting mining and chemical refining equipment and their power/energy system to it, if orbit transfer costs alone kill the idea, as I think they will.)

    Yes, I said that objects can scatter into NEO and it may take many decades before they are cleared out of NEO by the periodic driving forces of their gravitational interaction with the Earthmoon system. The new definition of what is a planet does not require that nothing can be scattered into NEO, only that it can not stay there.


    You may find the following interest (and my comments after it?):

    “…At least two start-up companies are putting money and impressive names in science, business and even entertainment behind the theory that platinum and other precious metals can be mined out of this world and brought back to Earth to become parts of our cell phones and other important electronic devices. …” From: http://www.channel3000.com/news/Com...-metals-in-space/-/1648/11776726/-/m840u5z/-/

    I repeat:
    There is nothing in orbit about the sun that can not be much more cheaply gotten from the earth compared to bringing it back to earth.

    There are always scams trying to make a fast buck on those ignorant of space dynamics (or the fundamental limitations of NH3 production, - GreenGas.com who posts here every few months telling they need funds to commercialize their new cheap "in your back yard" ammonia production system etc.)

    When their IPOs comes out, the principles will get their profits out and the IPO buyers will soon realize they have been had.

    One of the two new venture capital firms is at least not obviously a scam as they speak of using comet H2O as refueling station for space ships that do not try to return to Earth. (It’s not clear what those ships are doing routinely cruising around in space.) Making fuel in space may be feasible; however an electrolysis plant and the electric power from solar cells for it requirements makes think that too is just a better disguised scam.
     
    Last edited by a moderator: Apr 24, 2012
  20. KilljoyKlown Whatever Valued Senior Member

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    6,493
    You might enjoy the article I posted about some very rich people investing in asteroid mining.

    http://www.sciforums.com/showpost.php?p=2929174&postcount=3
     
  21. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

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    Yes now that NASA has quit, dozen or so venture capital groups have stepped up to the plate, often getting famous persons to be part of their eventual IPO efforts.


    This is the caption under illustration at your link but photo did not copy for me:
    “Small, water-rich near-Earth asteroids can be captured by spacecraft, allowing their resources to be extracted, officials with the new company Planetary Resources say.”
    Later by edit: found same photo at another site:

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    “Bucket” that will capture the asteroid falsely shown as less massive. In reality the capture vehicle will be much more massive than the very small asteroid. Getting that “bucket” into almost the same orbit as the asteroid is half of the cost problem – moving it to some other desired orbit is the larger “half,” but I think either alone kills the economics of the idea.

    Quite possible they will soon be telling that by separating the capture from the chemical processing (Plant presumbly on larger NEO asteroid) they have great economy as their chemical processing plant and its power sources can process many different asteroids that are brought to it, etc.
     
    Last edited by a moderator: Apr 25, 2012
  22. KilljoyKlown Whatever Valued Senior Member

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    6,493
    Yeah, I hear that and if I was a billionaire I'm sure I'd be reluctant to invest my fortune into that business, but never the less I'm very interested in the story and what might happen because of it. I'm sure everyone's heard the saying "No guts, no glory".
     
  23. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

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    To Electricfetus

    As you don´t have your reference, here you can find a list of NEOs asteroids: It even will sort them various ways for you. For example with eccentricity roughly same as Earth´s and willl show graphically the orbits.

    http://neo.jpl.nasa.gov/

    You may need to find other source to check if it is an iron nickle type. I can´t promise, but once you chose one, I will try to calculate the energy required to place a kg of it into Earth orbit from its current orbit.

    Lets initially focus on just that - I.e. not include cost to process the nickle from the iron or worry about how we cut a piece of it off the asteroid, etc. There is plenty of data on the typical percentage of nickle and iron from the meteors that made it to earth.
     
    Last edited by a moderator: Apr 24, 2012

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