I am going to cut and paste some discussion from other threads and more it to a new topic so it is easier for others to find. Please feel free to add your own comments.
The power consumption of various oxygen production schemes.
Oxygen concentrator direct from Mars atmosphere. The current medical oxygen concentrators use roughly 300W to produce 5 liters per minute. On Mars the over atmosphere must be compressed 15 times to get to 1 barr, then would also need to be an absorbent CO2 to minimize that first, exposing the used absorbent to the outside near vacuum and concentrated should refresh it for the next cycle. That should add little extra power but should not more than double to power consumption. Worst case 3KWh for 25 liters of O2.
Water extraction from soil. Using the microwave extractor, 10KW for maybe half an hour, for 5KWh plus rover power, to produce 60 liters. From that, 0.008KWh per mole which is small addition. So 5KWh plus for 22.4 liters of O2.
So it looks like they are much closer than I thought, but the concentrator still looks a little better.
Mike, you've mentioned this oxygen concentrator idea before but it won't work. I'm sure medical oxygen generators work great but they also have the advantage of operating in an environment that already has 20 kPa partial pressure of O2. On Mars, O2 makes up just 0.14% of the atmosphere (not the 0.6% figure you gave in a different thread). Also, the average atmospheric pressure is just 0.6 kPa which means the partial pressure of O2 is 0.6 kPa * 0.0014 = 0.00084 kPa. To get the 20 kPa partial pressure of O2 that humans need to live you'd have to concentrate the available oxygen almost 24,000 times! It's just not practical.
It's much more practical to get O2 from electrolysis of water. And yes, for the skepticals, there are large quantities of water on Mars, in the form of ice just beneath a thin regolith layer in many places. Phoenix only had to remove a few millimeters of regolith to find water ice underneath.
Each time there's a meteorite crashing on Mars the splashes expose large quantities of ice: http://news.nationalgeographic.com/n...e-picture.html
The method to extract water from the ground without drilling has already been explained.
Starfarer42, you are quite correct. I was talking on the phone while trying to write this up and left out the compression step. You are correct that neither step will work well without first reaching near Earth normal pressures. Also I have been seeing different partial pressures on Mars for nitrogen and oxygen. I did find to reputable (better than wikipedia, which is where I probably got the .6% number), I tend now to agree. The oxygen will be 0.0063 time lowered overall pressure of 0.007, it will need concentrating and compressing of over 20,000 times its initial pressure. But it does take MUCH less energy to compress a near vacuum than air that is already dense or under high pressure. I still think it will be less power, and mechanically easier and more reliable to compress Mars are, absorb out the CO2 (to be added to the garden to enhance growth rates) then of the remaining Argon, Nitrogen, Oxygen atmosphere, run the concentrator a little higher in the cycle to get better purity oxygen from 20 to 1 instead of 3 to 1 Nitrogen. I am not sure if the zeolite would capture the Argon as well. And the argon might be useful for TIG welding, industrial processes, and maybe even Mars Suit mixtures to avoid nitrogen narcosis problems in the outside suit run at substantially lower pressure than inside the habitat.
I realise that the rovers must still be sent out to get water, and currently it looks like electrolyses to make oxygen once the water has been collected in a small price to pay in the power budget, and it also produces hydrogen, which can be used to converting CO2 back to O2 and methane, but I still like the greater mechanical simplicity of a stationary oxygen generator instead of driving a rover all over the place to get to fresh regions where the water has not be all 'exploited; already.
But if both systems or so close in power budget, then maybe they should each be the redundant backup for the other.