Dome Over the Valles Marineris?

 

 

In development of a Martian human presence, there will be immense challenges. It would seem a good way to obtain sizable gains in as short as time period as possible, it behoove the settlers to make a large as possible Earth-like space on the planet as possible. One possibility is to cap a portion of the Valles Marineris under a glass envelope.  As pressure of the habitat inside would be much more than normal Martian atmospheric conditions, the pressure differential would hold up the glass structure. The weight of the glass would also keep the pressure at human-habitable levels. In addition, as the whole structure would act as a greenhouse, the temperature inside the habitat would also be more Earth-like.  It also helps that the VM is roughly equitorial and thus gets lots of sunlight relative to other parts of Mars.  Water in the form of lakes inside the habitat would act as thermal mass and prevent wide temperature fluctuations during the day-night cycle. The glass could also have additives such as lead or other materials to protect against radiation, but having a lot of air above one's head helps a lot with that.  Essentially, the whole habitat would work much like Biosphere 2, but at a much larger scale and with all the ecologies worked out, which may be as or more challenging than building the dome itself.      

As an illustration, a 200km length segment of the VM would be capped with glass gathered from minerals in situ. An example width of the VM is also 200km. The depth of the segment could be around 5km. To calculate a rough-order glass thickness, I would compare the pressure of earth's atmosphere at 5km height. There is a difference based on gravity on the air column but that may be neglected for now. On Earth at 5km high, the air pressure is approximately half what it is at the surface or 50kPa. On Mars the average surface pressure is 0.6kPa so the gauge difference can be calculated as 49.4kPa. Using the density of silicon dioxide (2.6grams/cm³) as a representative density of the envelope, one may calculate the thickness required to counterbalance the gauge upward pressure. First I convert the gauge force into equivalent mass on Mars. 49.4kPa for a one square meter area amounts to 13.3kg/m² mass density of the glass given Martian gravity of 3.71m/sec². Dividing this mass density by the density of glass yields 5.1mm thickness required to keep the pressure within the habitat.  So not too bad as far as feasibility goes.  In future posts, I will explore the technical aspects of this concept.