Water reserve for astronauts?

How much water reserve for 4 astronauts on a 1 year mission. Educated guesses are fine here. I am guessing about 1/2 pt per day per astronaut at best but really have no idea.

IDK. I’d need to have more than a 1/2 pint. That’s a tiny ammt. I going to at least a litre or more a day per astronaut.

Bulk storage tank for one use or a filter / recycle system?

so plan on about 2.5-3 liters per person per day for just water. Unless they eat mostly soup and watermelons.:wink:

I think the OP needs to clarify. He asked for a “reserve” which, to my ears, means how much they need to have on hand in case their water generator breaks down.
I don’t know about shuttles, but the ISS runs dehumidifiers and does water treatment to provide water for the astronauts. They’re drinking their own urine and sweat over and over.
If that stops working, then they’d need to have a backup supply until they can get it running again.

Also, from what I recall, it’s not a centralized system. They have humidifiers and purifiers all over the ISS. I assume they’re not tied together in a way that a single even would take down all of them.

I wondered that and missed the edit. You could do with a lot less in an emergency situation. But for everyday working adults 1/2 pint in miniscule. Unless like you say it’s kept in reserves or some such. I don’t know why they would do that. It would be wiser to make water from waste and make it a reliable system with backups. IMO

I should have been more clear. I was assuming a water treatment and recycle would be operating so the question is over and above recycling their own wastes. On the imes I have monitored my own intake I tend to take in about 1 quart a day plus the liquid in the food I eat at about 75 degree temps and 50% humidity.

This says a sailor needs a gallon of small beer per day, so say a gallon of something, though “the Ships Company shou’d never be reduced to Water-Drinking, so long as any other Liquor was to be had for Credit or Money.”

Astronauts probably get less sweaty, so perhaps 3 litres is reasonable. But how much in reserves is needed when surrounded by multiple redundant recyclers?

When Das Boot came out I saw it with the girlfriend I had then and, being familiar with the Battle of the Atlantic, was mentioning some of the authentic details that were shown. When the clean-shaven ‘No. 1’ showed up I mumbled, “What a prat.”


“He gets a two liter ration of fresh water a day and is spending part of it to shave.”

For the record, a trip from the Earth to Mars will take 6 months. The return trip takes another 6 months. AND it takes 12 months for the 2 planets to come around to position for the briefest trip.

So, if you’re wondering how much water will be needed for a Mars mission, you need to wonder about how much water will be needed for 24 months per crew member. I guess they’re practicing water recycling on the ISS now.

NASA says the ISS is recycling the equivalent of 10,000 lbs. of water per astronaut per year. Water weighs 8.34 lbs/gal, so that’s roughly 1,200 gallons. That works out nicely to 100 gallons per month or around 3.3 gallons per day.

I’m guessing that’s water for all uses, include cooking, showering and maintaining the humidity in the ISS atmosphere. But even if we’re talking only water necessary to sustain the crewmembers’ lives, I can’t see getting by on less than a gallon per day.

My question is how much reserve water they need to take on board allowing for recycling. Would it be 1000 gallons or a hundred gallons??

This says, “a reserve of a minimum of 697 ℓ of potable water is stored on ISS in Iodinated Contingency Water Containers (ICWCs) and Potable Water Reservoirs (PWRs) to maintain ISS operations in response to contingency scenarios”.

It looks to me like it boils down to how big a buffer you want to carry. The numbers hover around 3 liters per day per person. In a pinch, for a week you could probably ration out 1 liter per day. Starting at the 3.5 liter per day recycling level, knock out whatever reuse ability you want and then see how long you have to survive on the water aboard, at a somewhat reduced daily allotment Every pound of water you lift into orbit or for the mission is one pound less of fuel, food, scientific instruments. If it were me I’d recommend 42 gallons per person.

The actual transport times using a pseudo-Hohmann minimum energy trajectory are actually between 7.5 and 8.5 months, with the opposition-class stay at Mars being around 40 days and the longer conjunction-class mission profile as having a stay of over 18 months. Faster transits and more flexible mission profiles are possible only with much more capable propulsion systems that exist today only in concept. See ”Trades Between Opposition and Conjunction Class Trajectories for Early Human Missions to Mars”, B. Mattfeldand, C. Stromgren, et al for an assessment using the Multi-Purpose Crew Vehicle (MPCV) (which is kind of ridiculous but whatever). Six months is a commonly stated error that seems to come from cycler trajectories (which have higher injection energies) and Elon Musk, who appears to know about as much about interplanetary trajectory analysis as he does about running an automotive company.

The International Space Station (ISS) uses the Environmental Control and Life Support System (ECLSS) which includes the Water Recovery System (WRS) which extracts water from not only wastewater but the cabin environment. Note that the study above, which used the Human Exploration Logistics Model (HELM) to assess consumables, assumes a volume of 612 m[SUP]3[/SUP] of “ECLSS fluids” (presumably primarily water) for an opposition-class mission and 682 m[SUP]3[/SUP] for a conjunction-class mission. From that you can see that the longer duration doesn’t add that large an increase in water because reclamation is a crucial technology for human habitation in space. We also cannot assume any ability to obtain water on Mars using In-Situ Resource Utilization (ISRU), because even though we know that there is water on Mars it is not anywhere near a safe equatorial landing site and what water exists near the surface is locked up in a thick brine and contaminated with toxic perchlorates, and may be nearly impossible to extract without expending far too much energy.

There is no ‘reserve’ per se; if a water recovery system (and preumed backup) stops working there is no practical way to carry enough water or extract it from the surroundings (see above) to complete the mission and safely return the crew. However, water does make excellent radiation shielding, and carrying “extra” water in external tankage might be done for that purpoise, although at one metric ton per cubic meter it is very heavy, which is prohibitive in terms of propulsion requirements.