Now, of course, there could be "hotspots" where it comes closer to the surface, but still, Mars is the last place I'd want to focus on geothermal power...Heck, now that I think about it, how would you even work with drilling fluids on Mars? They're going to be constantly trying to boil off and freeze your well. And as they boil off they'll be depositing the suspended slurry - on everything that they touch.
[...] I would rather invest in a deep tunnel where a thick air column, perhaps 10-15 km below Hellas can grow crops without needing to pressurize mechanically or warm them, than only surface greenhouses. [...]
Are you guys discussing things that can be accomplished this century, or just in some distant future?Sorry for the hyperbole, but 15 km deep shafts are not something I think we'd be looking at in the near future, and certainly not in a near-term colony plan. The deepest borehole on earth, with all of our local resources, is a little over 12 km deep, and about 20 cm across. I like reading KSR as much as the next sci-fi fanatic, but we are probably not quite ready to start boring man- or -vehicle sized boreholes on another planet to 15 km. YMMV
If you're already signed up to ship a tunnel boring machine to mars (as this thread has done) there's nothing futuristic about running your tunnels deep instead of horizontal. It's merely a planning decision.
I don't think you are going to be able to build a 15km elevator even in Mars gravity, so you have to do a gradient. You would not want much beyond a 10% grade. Now you have a 150km tunnel. Not impossible, but not fun or easy either. That is a long way to remove rock. But I think the radiation protection would be sufficient. If Mars is not susceptible to Radon leaks anyway.
Are you guys discussing things that can be accomplished this century, or just in some distant future? The deepest borehole on earth, with all of our local resources, is a little over 12 km deep, and about 20 cm across.
Will Harriet the tunnel-boring machine go to SpaceX now that her work on Crenshaw/LAX Metro line is done?
SpaceX submitted tunnel-digging plans to Hawthorne city officials just a few days after Harriet’s work on the LAX/Crenshaw Line finished on April 6.The vertical tunnel shaft is complete. The next step is to dig the 500-foot-long horizontal pedestrian tunnel.“This tunneling will be conducted by excavating a large bore pit almost 20 feet by 150 feet and 13.5-foot diameter,” said Arnie Shadbehr, Hawthorne’s interim city manager. “Currently, plans are being reviewed by the city as well as the Fire Department.”
Geothermal Gradients: For a given heat flux, geothermal gradients depend on thermal conductivity. On Earth, typical geotherms are around 30-35 K/km. Everything on Earth is water saturated, and water is actually a relatively poor conductor of heat (although in convecting systems it is an excellent advector). In the upper layers, at least, of Mars we expect water to be frozen. Ice is a much better conductor of heat, especially at lower temperatures, so for ice-filled porosity on Mars we expect conductivity ~ 25% better than on Earth. For dry but compacted regolith, we expect conductivities ~25% worse than on Earth. Consequently in dry regions of Mars we might find geothermal gradients of ~ 10.6 K/km, while in ice-saturated zones we would expect values of a mere 6.4 K/km....Equator: For equatorial mean surface temperatures of ~ 220K...Temperate Mars: A typical mean annual temperature of 200-210 K...Polar regions: below the permanent polecaps, year-round temperatures are buffered to ~150 K by subliming CO2 ice.
The ice cap in the north is of a lower altitude (base at -5000 m, top at -2000 m) than the one in the south (base at 1000 m, top at 3500 m)
According to theory and observation, the temperature, pressure and density of undisturbed air at 3.5 km depth in the Western Deep should be 330 K, 1.48 P0and 1.3 ρ0, respectively. It is understood that after the introduction of refrigerated air, the temperature is brought down to 28°C or 301 K and the pressure rises to 2P0 as a result. One can verify that0.52 moles of refrigerated air at 220 K and 1.48 moles of ambient air at 330 K can account for the working condition temperature and pressure of 301 K and 2P0, respectively. One should point out that atmospheric pressure at the surface of the mine (elevation 1740 m) is only about 82% that at sea level 17. However that does not affect the results, which are expressed in terms of surface pressure and density.
To meet schedule requirements, the mine opted for the use of a Tunnel Boring Machine (TBM), marking the first use of TBM technology in a mine on the continent. Due to the geological and mine conditions, the TBM was highly customized. The Robbins Company, the world’s first and foremost TBM manufacturer, supplied the Dual Mode Crossover TBM that could excavate in both hard rock and mixed ground, and in the presence of potentially hazardous methane gas.
A 1:6 grade decline tunnel to 28km depth would be 168km long. About 17 years at 200m/wk (about the same length of time as the Gotthard Base Tunnel took).A 1:5 grade decline tunnel to 28km depth would be 140km long. About 14 years at 200m/wk, down to less than 4 years at theoretical maximum of 800m/wk.
Quote from: Dao Angkan on 04/22/2017 07:09 AMA 1:6 grade decline tunnel to 28km depth would be 168km long. About 17 years at 200m/wk (about the same length of time as the Gotthard Base Tunnel took).A 1:5 grade decline tunnel to 28km depth would be 140km long. About 14 years at 200m/wk, down to less than 4 years at theoretical maximum of 800m/wk.Living 28km down is one thing. A drive of 140km or 200km to get out is another. Doesn't sound good to me. If this is done it needs a vertical shaft. Building climbing elevators instead of elevators hanging on a rope should not be the issue. But then you may want to balance two elevators, one going up, one going down.