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Mars atmosphere pressure on surface equals the stratospheric value on earth. To increase it one have to add more air as in the most terraforming projects or somehow to lower the solid surface with 50 km. Somewhere I met a proposal on Mars to be dig out a pit - by collision with quite big asteroid or strip-minning alike method -- several tens of km deep and with bottom tens of thousands km2 in area. The thin martian atmosphere would settle down at the bottom of the pit resulting in 0.3 to 1 bar ambient pressure in there ( depending on the depth according to the conventional zero altitude ), leaving the rest of the globe in near vacuum.
Without to be necesarry putting a roof or doming the artificial crater. You end up with something like the Larry Niven`s planet Canyon.
But indeed you don`t need to dig out millions of km3 in order to localise horizontally the terrestrial pressure of the introduced or compressed atmosphere.
And you don`t need to cover the pocket of air with dome or other kind of roof.
If it is possible walls high enough to be constructed, than thay like the wall of a cup will hold the terrestrial atmosphere apart from the original non-brethable one.
Paul Birch ( again!!! :-) - http://www.paulbirch.net]www.paulbirch.net "Supramundane planets") proposes two rows of sealed to eachother columns made of arranged on top one another gas-bags, filled with cheap locally gases ( H2 for the gas giants, CO2 for Venus or Mars..., He, etc.), each gas-bag with hexagonal base and linear dimesions in hight and wight of ~20 km... the final wall about 200 km high and about 40 km thick... ... ... for separating the terraformed area on supramundane habitat or in a huge rotating tube, from the vacuum outside. The 200 km hight seems enough to prevent the spill of the terraformed 1 bar (25%-O2, 75%-N2) air asside in respect of the gravity direction toward the unterraformed yet zones. The gas-bags in the base of the wall should have about 2 metters thick plastic membranes, at the top gradually diminishing to film thin plastic sheets of ~100 g/m2. The presure in the gas-bags is ~2bars to effectivelly separate vacuum from 1 bar brethable gas mixture.
On Mars or mars-like planet with several times lower gravity and hundreds of times thinner air the terraforming could begin with fencing a plot of land of, for example 10 000 km2 -- comparable with the area of many little but prosperous countries with such gas-bags` wall 200-300 km high -- forming a huge cup. Fill the cup with compressed breathable air ( one could begin with compressed original CO2 atmosphere drawn in through the walls, and to use the air cupfill to aerobrake shippings of artficial NH3-iceteroides to use it for processing the CO2 in water, O2 and N2...). Move the outer gas-bag wall`s layer to enclose further part of the terrain. Fill it. Remove the inner layer to enclose further... Use the old gas-bags, produce new ones on demand...Such way gradually the whole surface could be terraformed. Such way some of the terrain could be preserved in natural original state to satisfy the eventual 'Reds' or rather for the needs of the touristic business... Such way you begin with little investments and effort to terraform part of the planetary surface, even as little amount of money -- within the range of the private investments, incrementaly terraform the planet without to cut the open air in multiple small domes, and you can stop the terraform according to your will and ecinomy growth parameters.
Such schemes could be also used on planets where the external pressure is bigger than the terraformed cup inner one -- say decrease the pressure of Venus twice and you have many thousands of km2 -- the higghest mountains -- under just several bars of innitial atmosphere. Build gas-bag walls - terraform the fenced area, and even use the presure gradient to work... Such way -- you have walled 'continents' + lots of floating huge rafts 'islands' and 'archipelagos' out of the fence, and big part of the natural conditions are preserved -- something very usefull if really some local venusian life is present and should be preserved...
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Interesting would be to flatten a large surface area, near the equator, and have the atmosphere collect at the center. How large of an area could be flattened on Mars before the rock would start to cave back in ?
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People could live in the center, and conveniently launch to space at the boundary of the flat area.
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Interesting would be to flatten a large surface area, near the equator, and have the atmosphere collect at the center. How large of an area could be flattened on Mars before the rock would start to cave back in ?
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People could live in the center, and conveniently launch to space at the boundary of the flat area.
I don`t have idea from which point the rocks would begin to cave back in the hole, but I think such 'flattening ' will be much more expensive than gasbag walls.
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