In The Martian, Mark creates a source of water through a complicated chemical process that involves, in part, an open flame. Flames use oxygen as fuel, and a lot of it. Since this flame seemed to be running non-stop, how did Mark produce enough oxygen to keep himself alive? Was the process described in these answer enough?
asked Jan 21, 2016 at 22:53
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2Are there numbers to suggest that such a flame would use too much oxygen for Mark to keep himself alive?– Misha RCommented Jan 22, 2016 at 3:27
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2 Answers
From the book:
I did a little EVA today to check. The MDV has 292 liters of juice left in the tanks. Enough to make almost 600 liters of water! Way more than I need! There’s just one catch: Liberating hydrogen from hydrazine is…well…it’s how rockets work. It’s really, really hot. And dangerous. If I do it in an oxygen atmosphere, the hot and newly liberated hydrogen will explode. There’ll be a lot of H2O at the end, but I’ll be too dead to appreciate it. At its root, hydrazine is pretty simple. The Germans used it as far back as World War II for rocket-assisted fighter fuel (and occasionally blew themselves up with it).
So the most he's going to make is 600L of water. I could try and do the math, but he explains where he gets the oxygen a bit later on:
So I ran into a bunch of problems with my water plan. My idea is to make 600 liters of water (limited by the hydrogen I can get from the hydrazine). That means I’ll need 300 liters of liquid O2. I can create the O2 easily enough. It takes twenty hours for the MAV fuel plant to fill its 10-liter tank with CO2. The oxygenator can turn it into O2, then the atmospheric regulator will see the O2 content in the Hab is high, and pull it out of the air, storing it in the main O2 tanks. They’ll fill up, so I’ll have to transfer O2 over to the rovers’ tanks and even the space suit tanks as necessary.
He brings 10L of CO2 from the hab each day and lets the oxygenator turn it into O2. He explicitly says that the rate limiting step in his production of water is his ability to produce enough oxygen.
Yes I think the responses to that question are sufficient. The answer with the highest number of votes seems particularly helpful.
That answer notes that CO2 extraction isn't limited just to the oxygenator:
My crewmates took the MAV away weeks ago. But the bottom half of it stayed behind. NASA is not in the habit of putting unnecessary shit in to orbit. It left the landing gear, ingress ramp, and fuel plant behind. Remember how the MAV made its own fuel with help from the Martian atmosphere? Step one of that is to collect CO2 and store it in a high pressure vessel. Once I get that hooked up to the Hab’s power, it’ll give me half a liter of liquid CO2 per hour, indefinitely. After 5 days it’ll have made 125L of CO2, which will make 125L of O2 after I feed it through the Oxygenator.
Also notice how he is able to feed gallons of liquid CO2 through the oxygenator on top of the normal daily load of the oxygenator. This implies that the oxygenator can process a tremendous amount of CO2 efficiently.
I can't imagine that the small flame for water creation purposes would overwhelm a system with so much overhead, plus the additional unplanned overhead of only having one person in the Hab.
