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Yes you could cap the top of the shaft. My starting assumption was that we would be introducing flourocarbons into the atmosphere for terraforming. So we would want the gas to escape at a certain rate. But if the gas is expensive, then a cover on top is easy to do. If the top of the shaft can be pressurised, then the required depth can be reduced. If the the top of the shaft is pressurised to 12.2mbar (vs 6.1mbar ambient) then depth can be shortened by 1.8km to 6.2km. If the top is pressurised to 24.4mbar, then depth can be reduced by another 1.8km, such that the shaft only has to be 4.4km deep. With 48.8mbar at the top, required depth drops to 2.6km. Note that 48.8mbar is <0.05 bar. It is likely to be much cheaper to pressure rate the top of the shaft to 50mbar than to dig it 5.4km deeper.
This has clear implications for terraforming. If Mars can be warmed to the point that an 80mbar ambient atmospheric pressure is created, then a crater 1 mile deep, filled with this gas will experience a 200mbar pressure at the bottom. That is sufficient for people to walk around on the surface with an oxygen mask.
Regarding the reason for trying to build a habitat in a deep mine. The reasoning seems to be that a habitat needs constant mechanical power to achieve pressurisation. That doesn't make any sense to me unless you assume that the hab is full of holes. If it is built under several metres of soil, leakage rate will be extremely slow.
Last edited by Calliban (2025-02-03 09:58:05)
"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."
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For Calliban re #26
Thanks for pointing out that the needs for constant pumping is forced in part by leaks, so avoidance of leaks will reduce the amount of pumping needed for resupply. However, if we assume there are living creatures (of various kinds perhaps) in the habitat (any habitat on Mars or away from Earth), then the pumps will be running constantly to resupply oxygen that is consumed, and to drive pressure to force CO2 through collection devices.
However, I think you might be missing the benefit of PhotonBytes original idea....
All habitats on Mars are going to need pumps to maintain the .5 bar atmosphere.
Your point seems well placed, that the pumps need not operate continuously if there are no leaks, and if there are no humans consuming oxygen.
A submarine on Earth seems to me to demonstrate the technology that will be needed on Mars, with a significant difference being that the exterior is an ocean instead of a vacuum, but I'll bet that if we had anyone in the group who knew anything about submarines, they would be able to confirm or falsify my theory that pumps and fans have to be operating constantly every moment that a submarine is in service.
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Taking a larger view ... I think it should be possible to create a computer model that reflects the flows that will occur inside a habitat on Mars.
My guess is that such models must exist for the ISS and perhaps for the Tiangong as well.
In the case of the ISS we ** know ** there are leaks, because we know (from reports) that the Russian docking port module is leaking from the tunnel between the port and the main body of the station. Therefore, there ** must ** be pumps in action to resupply gasses that are lost.
There ** must ** be machines in operation to monitor proportions of various gases, and to make adjustments as needed as time progresses.
I believe that ** all ** that machinery needs to be present and in operation in ** every ** habitat on Mars.
Since we are still in PhotonByte's 55 km topic, I will offer the thought that the water air lock might handily solve the problem that a regular two door air lock has.
** Every ** two door airlock has a waiting room between the two doors. In this room, humans wait for pressure or gas mixture to change to match the environment on the other side of the door towards which they are moving.
The ocean habitat run by NASA illustrates the water air lock idea.
The pressure inside the habitat under the surface of the ocean is maintained at a level such that the ocean is kept out of the habitat.
Something similar would apply on Mars, except that the water column on the Mars side would be taller than on the habitat side. If a leak were to occur inside the habitat, it would fill with water.
It is possible someone already posted the numbers for this kind of air lock.
(th)
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