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I often wondered if it was practical to catch a payload from a mass driver. Clearly for this to be efficient it is necessary to have a vehicle that can maneuver is space craht without using too much fuel. This suggests the use of an ion drive. With such a system it will take months to get to the moon. Reading the minimum energy trajectory stuff there is a wide range of possible trajectories that can be reached from the LaGrange point with use of a small amount of energy. Perhaps for instance the payload could be launched on the mass drive around the moon and pass on the side of the LaGrange point that is ahead of the moon in terms of angle and proceed to orbit around the earth. The ion craft will be in an earth orbit at a radius bellow but near the Lagrange point and meat up with the payload by the proper use of timing and with a minimum expenditure of fuel. The draw back is each craft will take months to move its payload and an economical use of a mass drive will probably require a frequency firing rate. This would mean having over 30 tugs in a high earth orbit. I also wonder how the trajectories would look if there was a space elevator in the way that they have to try to miss. I suspect that the trajectories would no longer lie strictly in the earth moon plane.
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Try to find yourself a copy of *Space Settlements; A Design Study* a 1977 NASA publication (SP-413). It describes a mass driver on the moon firing 10 kilogram bags of sintered regolith 0.2 meters in diameter at the Earth-moon L2 point. A catcher shaped like an icecream cone waits there, its big, open front covered by a kevlar lattice shaped like the center of a tennis racket. The bags fly in, hit the kevlar, and break; the regolith sprays into the icecream cone shaped catcher, which is rotating; the debris settles onto the rotating sides. Smaller mass drivers attached to the catcher grab rocks from the interior and toss them at high speed to steer the catcher and eventually to move the accumulated stuff to L4 or L3, where it is used to make space colonies and solar power stations. The delta-v between lagrange points is only 50 m/sec or so.
This SP is filled with lots of neat details. it's where I got the data on the number of square meters of housing and work space and agricultural space a colony needs. Of course, the report is now 27 years old and may be out of date. But a lot of the ideas are useful.
-- RobS
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The bags fly in, hit the kevlar, and break; the regolith sprays into the icecream cone shaped catcher,
That approach would require processing in orbit. I think it would be easier to build processing facilities on the moon. But then again I could be wrong.
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I think catching regloth at L1 is worth some study. It would have the same capacity to expand as a large industrialization of the moon but maybe it could help get some infrastructure in place that could be used for a large industrialization of the moon. I am concerned about flying dirt damaging an L1 space elevator but the space elevator could be put at L2 instead. I am also concerned about the firing accuracy. Perhaps though instead dirt bullets could be made by gluing dirt to gather with glass. Perhaps they could be fired out of a large gun kind of like the Missouri. I suggest a large gun because they are smaller and lighter then electromagnetic propulsion and perhaps even more accurate. Maybe the bullets could be caught in a large plane made by alternating Kevlar with foam. I’m not sure how you would remove the bullets and patch up the holes.
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I think that it would be easier to use asteroid material than it would be to use lunar regolith.
I am concerned about flying dirt damaging an L1 space elevator but the space elevator could be put at L2 instead.
If you have a space elevator, then I don't think that the mass drivers would be necessary.
Perhaps they could be fired out of a large gun kind of like the Missouri. I suggest a large gun because they are smaller and lighter then electromagnetic propulsion and perhaps even more accurate.
You also have to consider that there is no air on the moon. That would make it easier to build a mass driver, but harder to build a gun.
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If you have a space elevator, then I don't think that the mass drivers would be necessary.
I'll forget the word necessary. The goal is to get the greatest output for the least cost. I think a mass driver would deliver mass to orbit at a faster rate per mass of the mass driver then a space elevator would deliver mass to orbit per mass of the space elevator.
You also have to consider that there is no air on the moon. That would make it easier to build a mass driver, but harder to build a gun.
Can you explain this. I think a spin of the built might create some lift in air although I am not necessarily sure of the physics but for a small gun wouldn’t the velocity of the payload leaving the gun be greater then the velocity of they payload leaving a mass driver of the same size or am I missing something.
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Mass drivers as Naval weapons are pretty much going to be the Standard on surface combatants in western navies in the next 20 years. Both the US and Great Britain have done a lot of research into using this technology. Actually the Mass driver is a much more accurate weapon than the use of conventional weapons and it lends itself to in flight correction and reduces barrel wear to a fraction of a normal artillery piece. Another side benefit is the reduced risk of ammunition explosion either through enemy fire or accident as the main round of a mass driver being purely kinetic requires no explosives as propellant.
I think you will find that a mass driver on the Moon will make a better proposition than one located on an asteroid certainly at first. The Moon unlike most asteroids has an abundance of the most important ingredient that a Mass driver requires in this case, power. Of course we could use Mass drivers to redirect an asteroid into a better orbit for us to use its materials. But then we have the potential for serious political problems and a security nightmare.
Chan eil mi aig a bheil ùidh ann an gleidheadh an status quo; Tha mi airson cur às e.
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Can you explain this. I think a spin of the built might create some lift in air although I am not necessarily sure of the physics but for a small gun wouldn’t the velocity of the payload leaving the gun be greater then the velocity of they payload leaving a mass driver of the same size or am I missing something.
One of the main problems with mass drivers in the atmosphere is that the projectile creates a shockwave that damages the inside of the mass driver. That is why mass drivers would be more effective in a vacuum. The reason why a gun would be less effective in a vacuum is that normal gunpowder burns rather than detonates. If there is no atmospheric oxygen, then it can't burn. This problem can be overcome, but there is another concern with a gun on the moon: where will you get your gunpowder? It would not be economical to import it from Earth, and I suspect that it would be difficult to produce large quantities of an acceptable propellant on the Moon.
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The Moon unlike most asteroids has an abundance of the most important ingredient that a Mass driver requires in this case, power. Of course we could use Mass drivers to redirect an asteroid into a better orbit for us to use its materials. But then we have the potential for serious political problems and a security nightmare.
What power source does the moon have that asteroids lack?
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The main asteroid belt is between Mars and Jupiter. At that distance the effectiveness of solar power is much reduced. This is not the case on the Moon where it is possible to make easily made solar cells which though only about 5% minimum effectiveness provide a lot of power.
This constant power is the lifeblood of Mass drivers and it makes them cheap, especially as the solar cells made on the Moon come from easily collectable silicon and are radiation hardened naturally and easy to make.
Chan eil mi aig a bheil ùidh ann an gleidheadh an status quo; Tha mi airson cur às e.
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The main asteroid belt is between Mars and Jupiter. At that distance the effectiveness of solar power is much reduced. This is not the case on the Moon where it is possible to make easily made solar cells which though only about 5% minimum effectiveness provide a lot of power.
This constant power is the lifeblood of Mass drivers and it makes them cheap, especially as the solar cells made on the Moon come from easily collectable silicon and are radiation hardened naturally and easy to make.
The main belt asteroids probably won't be exploited for a long time. Near Earth Asteroids are another story. Most of them enjoy much more sunlight than the main belt. Strategically place photovoltaics could provide an asteroid with power 24/7.
Sunlight is less available on the moon because of the 14 day night.
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Sunlight is available somewhere on the moon all the time and a simple circumfrential power grid will allow power to be deployed anywhere its required.
NEO asteroids are easier to get to than the Moon and Mars and it makes sense to get rid of these just so they no longer pose a threat to the Earth. The problem is though its these asteroids composition that makes them less valuable tending to be stony rather than the metal rich or carbaceous chondrites we really would prefer.
But pholtovoltaics will only power as long as they point to there power source the sun. This is not really a quarantee as they roll. Unlike the easy computations that tell us where lunar mass driver material will go to.
Chan eil mi aig a bheil ùidh ann an gleidheadh an status quo; Tha mi airson cur às e.
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Sunlight is available somewhere on the moon all the time and a simple circumfrential power grid will allow power to be deployed anywhere its required.
NEO asteroids are easier to get to than the Moon and Mars and it makes sense to get rid of these just so they no longer pose a threat to the Earth. The problem is though its these asteroids composition that makes them less valuable tending to be stony rather than the metal rich or carbaceous chondrites we really would prefer.
But pholtovoltaics will only power as long as they point to there power source the sun. This is not really a quarantee as they roll. Unlike the easy computations that tell us where lunar mass driver material will go to.
A simple circumfrential power grid would be a huge structure especially about the equator and lower latitudes. And, unless your lines are superconductors, you wouldn't be able to send power much past the terminator. Line loss is a pain in the butt for power providers.
The composition of most NEOs remains unknown. It is thought most are recent arrivals from the Main belt or the Kuiper Belt thrown down into the inner system by perturbations from Jupiter or Neptune. One asteroid, 1979 VA is an extinct comet. 1979 VA is actually a rediscovery of the Wilson-Harrington comet. As comets outgas, it's believed their surface becomes a thicker and thicker mantle of insulating dust. So the extinct comets are thought to have volatile ices beneath their insulating mantles.
An example of a carbonaceous NEO is 1998 KY26
http://antwrp.gsfc.nasa.gov/apod/ap0209 … 20919.html
Since their composition remains largely unknown, I advocate a series of Discovery missions to the most easily accessible NEOs. If the probes are mass produced and miniaturized (like SMART-1), the unit cost per asteroid prospector probe might be quite low. Gathering an inventory of available NEO resources would be well worth the investment, in my opinion.
Some NEOs tumble chaoticly (Toutatis for example) Putting Photovoltaics (or even landing) on such may be a problem. But many may spin about a single axis (like the earth or moon). In such cases it'd be possible to put a rotating photovoltaic array on ball bearings on the north and south poles of the asteroid. You could also put arrays in close orbit about the asteroid and send power to rectennas on the asteroid's surface.
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