4 ms·

> So if this is about total human consumed water, on 2% loss, per unit time, without replenishment its 100 units to rundown. Can you elaborate on how you came

by clipsy 3y ago

> So if this is about total human consumed water, on 2% loss, per unit time, without replenishment its 100 units to rundown. Can you elaborate on how you came to this conclusion? How do you define rundown and how much water (outside of their own bodies) are they bringing with in this scenario?

ggm 3y ago
I assumed this was the main issue around water in their closed system. I assumed even if there are other water cycles, this one would be a limit. But there is no necessary need of that. Every day they lose all but 2% of this water into the system. So its the approximation of linear decline, assuming a constant 1-2% loss rate per day. I mean sure. Maybe it's 50 days because 2% per day loss not 1 % but I assume they have good and bad days. And that astronauts tolerate some level of uncomfortableness e.g. by reducing the humidity. I assumed that it's a closed system, and that all water not retained inside somebody is exhaled, sweated or peed out. Presumably quite a lot of water is in fact incorporated into them as something. ?glycogen? alongside the carbs they eat? inside Fat cells? It's certainly false accounting because this water isn't the only water in the system. fuel cells, fishtanks, wet wipes, cleaning things. They will have other water cycles, and this specific loss rate isn't going to be the limiting factor.
- clipsy 3y ago
  I agree that there are other water cycles involved that should be treated independently. I guess, from my view, this seems like a fairly straightforward evaluation (under ideal conditions): if the ship (or space station, or colony, or whatever) has N gallons of water per astronaut, astronauts require 1 gallon of water per day (according to the article), and 98% of water used by astronauts can be recovered, then the rundown time would be d days, where d satisfies: 0.98^d == 1/N Past that point, you have less than 1 gallon of water per astronaut, which entails rationing and sub-optimal performance etc. Rearranging the equation we can solve for d as: d = -Log2(N)/Log2(0.98) = 34.31 Log2(N) If you bring 2 gallons of potable water per astronaut, for example, after ~34 days you will be down to slightly more than 1 gallon, and after 35 days you will be in suboptimal conditions as you will have less than 1 gallon of potable water remaining from this system alone. In order for d to be 100 you would need a bit less than 8 gallons of potable water per astronaut at mission outset under this model. Edit: I suppose the much briefer way of putting this is that you can't count time until the water runs out; you have to count time until the water is insufficient to meet requirements (in this case, 1gal/day/astronaut).

by clipsy 3y ago

ggm 3y ago

I assumed this was the main issue around water in their closed system. I assumed even if there are other water cycles, this one would be a limit. But there is no necessary need of that. Every day they lose all but 2% of this water into the system. So its the approximation of linear decline, assuming a constant 1-2% loss rate per day. I mean sure. Maybe it's 50 days because 2% per day loss not 1 % but I assume they have good and bad days. And that astronauts tolerate some level of uncomfortableness e.g. by reducing the humidity. I assumed that it's a closed system, and that all water not retained inside somebody is exhaled, sweated or peed out. Presumably quite a lot of water is in fact incorporated into them as something. ?glycogen? alongside the carbs they eat? inside Fat cells? It's certainly false accounting because this water isn't the only water in the system. fuel cells, fishtanks, wet wipes, cleaning things. They will have other water cycles, and this specific loss rate isn't going to be the limiting factor.

clipsy 3y ago
I agree that there are other water cycles involved that should be treated independently. I guess, from my view, this seems like a fairly straightforward evaluation (under ideal conditions): if the ship (or space station, or colony, or whatever) has N gallons of water per astronaut, astronauts require 1 gallon of water per day (according to the article), and 98% of water used by astronauts can be recovered, then the rundown time would be d days, where d satisfies: 0.98^d == 1/N Past that point, you have less than 1 gallon of water per astronaut, which entails rationing and sub-optimal performance etc. Rearranging the equation we can solve for d as: d = -Log2(N)/Log2(0.98) = 34.31 Log2(N) If you bring 2 gallons of potable water per astronaut, for example, after ~34 days you will be down to slightly more than 1 gallon, and after 35 days you will be in suboptimal conditions as you will have less than 1 gallon of potable water remaining from this system alone. In order for d to be 100 you would need a bit less than 8 gallons of potable water per astronaut at mission outset under this model. Edit: I suppose the much briefer way of putting this is that you can't count time until the water runs out; you have to count time until the water is insufficient to meet requirements (in this case, 1gal/day/astronaut).