h a l f b a k e r yNot so much a thought experiment as a single neuron misfire.
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Digging tunnels through rocks is a slow and expensive process. Either you have to inch you way forward with a boring machine or remove the rock in batches using explosives. That's why long tunnels often take decades to build.
A new method:
Set up a very large array of solar mirrors. Concentrate
the sunlight into a single powerful parallel beam with a 6 m diameter. Direct the beam into the mountain where you want to have the tunnel. Sit back and wait for a month. Voila. Tunnel is ready.
OK, it's probably not quite as simple as that. The design is similar to solar furnaces, which can easily reach 5000 degrees C. This should be more than enough to vaporise the rock. But you probably still need some kind of ventilation system to get the vaporised rock out (suggestions welcome). Also, the method will only be suitable for load-bearing rocks, otherwise the tunnel would keep collapsing.
Still, it should be faster and cheaper than the traditional methods, because it's less complex, it requires less human labour, and energy costs are zero. The initial investment is higher, but the solar reflectors can easily be dismantled and moved to new sites, and can be expected to last for decades.
[link]
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Won't it be tough to keep the beam
coherent beyond a few dozen meters?
This would be good only for short
tunnels. Obviously, a more powerful
beam could compensate for less beam
coherence. One would therefore need
more and more powerful beams as one
cut further. The tunnel would flare out
larger and larger as it went. |
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It is not just temperature you need. How much energy does it take to vaporize a ton of rock? A few months will not be enough to drill a tunnel. |
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>>How much energy does it take to vaporize a ton of rock?<< |
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Heat of vaporization of SiO2 (silica) ~ 20 MJ/kg |
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For a 50 km tunnel volume of rock extracted is 3^2 * 3.14 * 50000 = 1.5 M m^3 |
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density of silica = 2200 kg/m^3 |
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1.5e6 m^3 * 2200 = 3.3e9 kg of silica |
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3.3e9 kg * 2e7 J/kg = 6.6e16 J (total energy needed) |
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Let's say we want to burn the tunnel in a month. |
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there are 60*60*24*30 = 2600000 seconds in a month |
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6.6e16 J / 2.6e6 s = 2.5e10 W (minimum power output of solar furnace) |
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So the solar furnace would need a power of at least 25 GW |
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...Assuming it's sunny all the time. |
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Psst, [kinemojo], the sun doesn't shine at night. |
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Could you get some usable energy from the stream of lava pouring out of the tunnel? |
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[Edit] and why vaporis(z)ed? that seems like overcooking it to me. |
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... imagines condensation problems in the ventilation system for removing vaporized rock... |
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perhaps you can get it to condense into a fine dust. |
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The last mirror bringing all the 60GW (extrapolated from the night-ignoring calculation) into its final parallel form could use some good cooling methinks.
And most modern tunnels have a slight bend, an endeavour for which most optic solutions are most unsuited. |
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One place this might makes sense is on the Moon's Mt. Malapert. |
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Mt. Malapert is just near the South Pole and its 5,000m high summit is lit for over 90% of the time. All that unfiltered sunlight is handy for power generation. |
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Once you had dropped in your giant solar panel your rock-vaporizer could get going blasting out a base inside the mountain. This moon-cave might be ready in a few years for humans to move in to, safe from the cold, radiation and meteorites. I am guessing that the 1/6 gravity and vacuum would help out with the blasting too. |
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(Malapert is close to a possible ice cap and his direct line of sight to the earth all year, so its THE spot for a base.) |
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Okay, [aide], that last was just confusing. Turns out that you are talking about the Moon and a mountain near its southern pole. You coulda said so right away. |
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Ok [baconbrain] fair point - fixed now I hope. |
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The sun is half a degree wide. Anything done with mirrors directly has to account for that. With 6 meter diameter hole at about 500 meters into the mountain the mirror optics will start to spread wider than the hole. (about 89.5 x 6 as a first guess) |
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Instead of mirrors you power rock cutting lasers with sunlight maybe through solar cells. |
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Carve a rock doughnut 6 meters in diameter and whatever depth seems to work.. Remove a doughnut hole the size of a explosive charge. Blast so as to shear off the doughnut. Remove doughnut. |
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Carve a rock doughnut 6 meters in diameter and whatever depth seems to work.. Remove a doughnut hole the size of a explosive charge. Blast so as to shear off the doughnut. Remove doughnut. |
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With lasers you can go as deep as you wish and turn corners if need be. |
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(But we can't go to the sun, it too hot. Sure we can you dummy, We just go at night. ) |
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An ancient Roman method of tunnel boring involved
building a fire against the rock face, letting it get the
rocks hot, and then using water to cool/shatter the
rocks. Of course that also put the fire out, making it
take longer to get the fire going again for the repeat
performance, but the shattered rock needed to be
removed, anyway.... |
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Here the solar heater could take the place of the fire --
no need for such heat as to cause melting. Water is still
generally available for rapid cooling/shattering of the
rock. And modern machinery would make quick work of
removing shattered rock. If the machinery was
automated, it might even be able to do it while the
rock face was getting heated up again. |
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[Vernon], I like that. (I recall that Hannibal's crossing of the Alps
involved heating rocks and dashing vinegar on them.) |
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