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I am interested in the feasibility of shipping carbon to GEO as opposed to launching it from earth. How fast would the ship have to move between the earth and the asteroid? How much cargo would it need to be able to hull? How much power would it consume? How light would the power system need to be? How close is current technology to these requirements? As far as the mining goes, for now that is secondary. I am primarily interested in the transportation methods. If this can’t be done there is no hope for the mining.
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I was thinking of nuclear electric transportation and I remember GCNRevenger saying that the reactor doesn’t way much but the other equipment would like the radiators. Couldn’t you use the radiators to support the ion grid. If the grid was big enough the flow of the gas to be ionized past the reactor could act as the coolant. Since this will preheat the gas it should be easier to ionize.
http://sci.esa.int/science-e/www/object … d=1537]Ion Propulsion
In gridded electrostatic ion accelerators, also known as ion engines, ions are produced in a magnetically contained ionisation chamber by a direct current discharge, radio frequency energy or tuned electron cyclotron resonance. The exit from the ionisation chamber is covered by a double-grid structure with a space between the grids of around half to one millimetre, across which the ion acceleration potential is applied. Ions that move near to the inner (screen) grid are extracted from the chamber and accelerated by the field between the grids.
Ion thrusters suffer from low thrust density (available thrust per unit exhaust area) because the maximum ion current density that can be sustained is limited by space-charge distortions of the applied electric field.
So my solution is just build a really big area. Since the array is not delivering much thrust per area it can be pretty light and flimsy Support by some truss on the back. The area will provide one big heat sink for the nuclear reactor and if it is big enough will provide considerable trust.
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In Mining the Sky John S. Lewis actually proposed solar "steam rockets" for this kind of freight, at least as far as NEO's are concerned. The spaceships would use solar power to heat water which would be used as propellant. The water would be extracted from the asteroids themselves, the main benefit being the low rate of secondary refinement needed for this sort of propellant, whereas if you used oxygen/hydrogen rockets, the water to produce the fuel would first have to be electrolyzed etc.
From the Main Belt, where solar power is relatively low, other forms of propulsion would probably be used. The other type of steam rocket is one powered by a nuclear reactor, basically a NTR, but with water as working fluid instead of hydrogen. Maybe such freighters could be used in that setting?
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From the Main Belt, where solar power is relatively low, other forms of propulsion would probably be used. The other type of steam rocket is one powered by a nuclear reactor, basically a NTR, but with water as working fluid instead of hydrogen. Maybe such freighters could be used in that setting?
There are two questions we need to ask. We need to know how much of our fuel we need to conserve this will dictate the ISP and its thrust. The vehicle must be able to transport as a minimum 10% of its launch mass per year to be economical. I suspect the vehicle will need to be either nuclear powered or laser powered unless solar arrays can be made very light and very large. I would consider NEO those that lie within mars and Venus. Lets consider the worst in terms of distance for the NEO's.
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Plotting the Trust, Specific Impulse Economic Viability Boundary
Consider the worse case of having to deliver the delta V to go from LEO to mars and back with one tank of fuel. Lets plot a curve have one axis the specific impulse and the other axis the average thrust per wet mass of the ship full of cargo. The average thrust is the equivalent amount it of thrust it would take if a ship of the same fully loaded wet mass delivered that thrust constantly over the trip and did not loose any mass. Because the ship looses mass as it travels the effective thrust will be higher then the actual thrust. Also if the ship delivers most of the thrust early in the journey the effective thrust will be higher. The fully loaded ship will be the optimal in terms of minimum thrust that will allow the ship to deliver 10% of its wet mass per year over the trip described above. Thus we plot this curve of effective thrust vs specific impulse and all systems with more thrust or more specific impulse then shown on the curve will be suitable propulsion systems.
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Depending upon how much you mine when you're on the asteroid the mass of the outgoing vessel could well be similar to the mass of the returning vessel. When you consider the equipment you'd have to carry on the way out, which can be replaced by carbon for the return journey may well have to use the same cargo area. So if this was the case the outgoing leg would need to use less that 50% of the total fuel to allow some for maintaining orbit around the asteroid (unless you are landing the vessel, in which case you'd need to have some fuel remaining for taking off again). This all depends of course on the position of the asteroid in relation to the Earth.
Graeme
There was a young lady named Bright.
Whose speed was far faster than light;
She set out one day
in a relative way
And returned on the previous night.
--Arthur Buller--
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Depending upon how much you mine when you're on the asteroid the mass of the outgoing vessel could well be similar to the mass of the returning vessel. When you consider the equipment you'd have to carry on the way out, which can be replaced by carbon for the return journey may well have to use the same cargo area. So if this was the case the outgoing leg would need to use less that 50% of the total fuel to allow some for maintaining orbit around the asteroid (unless you are landing the vessel, in which case you'd need to have some fuel remaining for taking off again). This all depends of course on the position of the asteroid in relation to the Earth.
Graeme
Clearly we want the highest possible heating of the working fluid. Clearly we want to keep the reactor mass small. That says nothing about what architecture is used to take the heat from the reactor and transfer it into kinetic energy.
I say plan for the worst. Consider an asteroid with an orbit similar to mars. There are not very many C type asteroids as NEO's so the ship must be able to travel to a large percentage of them.
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