So MOXIE is using solid oxide electrolysis to produce Oxygen.
I assume the amount of oxygen MOXIE can produce is limited so how much can it produce before the solid oxide electrolyzer cell stops working?
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1$\begingroup$ Do you mean per day, or before it wears out? Do you mean given an unlimited amount of electrical power? Do you mean the MOXIE demonstration experimental unit on the rover, or the technology that MOXIE demonstrates? $\endgroup$– uhohApr 24, 2021 at 12:57
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1$\begingroup$ @utoh - before it wears out. I've updated my question. Thanks! $\endgroup$– neubertApr 24, 2021 at 13:50
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$\begingroup$ Thanks for the clarification! I've left a comment under the existing answer in case they want to make small adjustments to it. $\endgroup$– uhohApr 24, 2021 at 13:52
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2 Answers
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The answer is up to around 10g/hour. The experiment will be run multiple times throughout the lifetime of the rover and each run will be for about an hour. A full scale version for use on a human mission would need to be many times larger. NASA suggests two orders of magnitude larger, but if Starship is used probably three orders of magnitude bigger.
Alternatively MOXIE might just be used in conjunction with electrolysis in order to tailor the net oxygen production. This is because Raptors burn fuel rich and because oxygen will also be needed by the crew and wasted by leakage during airlock cycling etc., so MOXIE could be used just on a small scale to balance the oxygen demand to prevent dumping excess hydrogen from electrolysis and provide an immediate source of additional breathing oxygen on Mars from day 1.
https://mars.nasa.gov/mars2020/spacecraft/instruments/moxie/
Edit: the ultimate limiting factor on MOXIE is an open question. There are a number of constraints that might cause problems such as electrode degradation, dust blocking the HEPA filters, damage caused by repeated temperature cycling (MOXIE runs at 800 degrees C) as well as the potential to over heat and the need to use the 300 W consumed by MOXIE for other things. Perseverance itself only uses 110W so MOXIE will drain the battery if used for an extended period. https://www.hou.usra.edu/meetings/ipm2016/pdf/4130.pdf
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$\begingroup$ I'd asked the OP for a clarification and it may affect your answer slightly, but since it's a technology demonstrator and not designed for long-term use I don't think the answer really changes much. $\endgroup$– uhohApr 24, 2021 at 13:52
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2$\begingroup$ You might want to point out that 300W is about 3 times the total power of the RTG, i.e. long term operation is no option at all. $\endgroup$– asdfexApr 24, 2021 at 15:54
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$\begingroup$ A man at rest consumes 0.25 l/min of pure oxygen. The density of oxygen is 1.43 g/l, so the 0.25 l/min are 0.36 g/min or 21.4 g/hour. But at hard work the consumption is more then 10 times higher. $\endgroup$– UweApr 26, 2021 at 22:08
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$\begingroup$ Yes good reason you might want to have MOXIE as well as electrolysis $\endgroup$– SlartyApr 26, 2021 at 23:01
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since the question was answered properly, I wanted to add a tidbit I learned at a JPL event. MOXIE produces enough oxygen to keep a small dog alive.
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$\begingroup$ But not a Jack Russell :-) (for those who don't know, that's an extremely active breed) $\endgroup$ Apr 26, 2021 at 12:56
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$\begingroup$ Then, we can send a Chihuahua to Mars on the Starship before we send people! $\endgroup$ Apr 26, 2021 at 13:46
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$\begingroup$ But only had enough power to run MOXIE for about 20% of the time, so the doggy will have to timeshare its breathing. 300w for MOXIE alone, and the whole rover's power source is just 110w-ish, of which it needs about half just the keep itself defrosted. $\endgroup$ Apr 26, 2021 at 21:10