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How long can you store LOX-LCH4 on Mars equatorial latitude?
Depends. If you actively refrigerate, indefinitely. One idea that I suggested was to place one tank inside the other, instead of stacked. LOX at 1 atmosphere boils at -182.96°C, LCH4 boils at -161.48°C. So you could place the LOX tank (colder one) inside the LCH4 tank, then you only need a refrigeration pump to re-liquefy LOX. The chill from LOX will keep LCH4 liquid.
At Mars pressure the boiling temperature drops, so if you don't pressurize, you have to keep it colder. Nesting tanks also means only the outer tank has to maintain pressure.
Mars atmospheric pressure is very low. That means it doesn't transport heat quickly. That reduces the rate of boil-off. But if you don't let the boil-off escape, but capture and run through a refrigeration pump, then no loss. Rate of boil-off can be further reduced with insulation. (Obvious) So there are a lot of factors.
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An interesting article here:
http://voices.yahoo.com/nasa-develops-t … 67000.html
It would seem that Mars is in fact the perfect place to keep rocket fuel in terms of boil off - I presume it would be stored in a shaded spot.
Let's Go to Mars...Google on: Fast Track to Mars blogspot.com
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I'd say it's at least 50% better than Earth Seal level when it comes to limiting boiloff. I would even say that the much thinner air is more important in this context than the cooler temperatures, although both are great.
-Josh
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