Ways to reduce ECLSS water requirements on a human Mars mission

[Slarty1080]

I have just been reading a technology article: Mars 2, 72-82, 2006; doi:10.1555/mars.2006.0005 that discusses ECLSS for a human Mars mission, which I found on one of the threads here.
 
This suggests that the vast majority of water used on a human Mars mission is for hygiene purposes with half of all water being used for “laundry” at 12.5 out of 22.1kg/CM/day. (reference Hanford 2004/2005 for this figure).

This seems quite fantastical to me. Granted this is an old report (2006) but was/is this even a remotely accurate? If so has anyone carried out any work to see if this amount could be reduced?

Regardless of the accuracy of this report, has anyone considered using supercritical CO2 as a washing medium to reduce the water required - whatever amount it is?

http://e3tnw.org/ItemDetail.aspx?id=512
Even if the laundry water requirement was much less it might still be useful.

[speedevil]

This suggests that the vast majority of water used on a human Mars mission is for hygiene purposes with half of all water being used for “laundry” at 12.5 out of 22.1kg/CM/day. (reference Hanford 2004/2005 for this figure).

This seems quite fantastical to me. Granted this is an old report (2006) but was/is this even a remotely accurate? If so has anyone carried out any work to see if this amount could be reduced?

Perhaps by not doing that?
This is a 'quite high' figure - I'm pretty sure I'm beating that on laundry use with no special effort at all, just purchasing a moderately efficient washing machine. Examine the assumptions in the original references, and see if they're even slightly plausible.
(I am not doing manual labour).

You need quite a large amount if you're assuming daily 'normal' showers, as I suspect that may be.
You need remarkably less if more water efficient techniques are used.

[john smith 19]

This suggests that the vast majority of water used on a human Mars mission is for hygiene purposes with half of all water being used for “laundry” at 12.5 out of 22.1kg/CM/day. (reference Hanford 2004/2005 for this figure).

This seems quite fantastical to me. Granted this is an old report (2006) but was/is this even a remotely accurate? If so has anyone carried out any work to see if this amount could be reduced?

Perhaps by not doing that?
This is a 'quite high' figure - I'm pretty sure I'm beating that on laundry use with no special effort at all, just purchasing a moderately efficient washing machine. Examine the assumptions in the original references, and see if they're even slightly plausible.
(I am not doing manual labour).

You need quite a large amount if you're assuming daily 'normal' showers, as I suspect that may be.
You need remarkably less if more water efficient techniques are used.

Keep in mind the "laundry" method for ISS is "Change to new set of clothes" 

This is one of those things that's going to need to addressed if we want human presence to be anything but a base in space (any part of space). 

[Slarty1080]

Good point, although at 12.5kg of clothes per day they could probably wear disposable duffel coats? I think that the report is badly flawed and makes some unrealistic assumptions about water consumption.

So is there a more recent report available which uses realistic water quantities? Seems it’s a critical point to get right as even allowing for recycling of water this 12.5kg would equate to many tons of extra water.

In early mission planning who or how do they keep track of issues like this? I’m sure this is just scratching the surface. I didn’t look at all the other figures in detail.

[guckyfan]

If I remember correctly at the NASA workshop for selecting landing sites they set the requirement of available 80-120t of ISRU water. That was for 2 or 3 expeditions to the same site and camp.

[AnalogMan]

Good point, although at 12.5kg of clothes per day they could probably wear disposable duffel coats? I think that the report is badly flawed and makes some unrealistic assumptions about water consumption.

So is there a more recent report available which uses realistic water quantities? Seems it’s a critical point to get right as even allowing for recycling of water this 12.5kg would equate to many tons of extra water.

In early mission planning who or how do they keep track of issues like this? I’m sure this is just scratching the surface. I didn’t look at all the other figures in detail.

This document may contain the info you need, but it will take some work to dig it out!

Life Support Baseline Values and Assumptions Document
NASA/TP-2015–218570/REV1 - January 1, 2018  234 pages

Abstract
The Baseline Values and Assumptions Document (BVAD) provides analysts, modelers, and other life support researchers with a common set of values and assumptions which can be used as a baseline in their studies. This baseline, in turn, provides a common point of origin from which many studies in the community may depart, making research results easier to compare and providing researchers with reasonable values to assume for areas outside their experience. This document identifies many specific physical quantities that define life support systems, serving as a general reference for spacecraft life support system technology developers.

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20180001338.pdf

Copy also attached.

[speedevil]

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20180001338.pdf

Copy also attached.

Which disagrees with the above 12l/day - page 91, giving for those scenarios listed, 2l/day.
The total water usage for a couple of the scenarios is approaching 12l/day, but only a very small fraction of that is for laundry.
Dishwashing is very, very high to an implausible amount, at 3.5kg/day/crewmember in both those scenarios.
I can hit that number in a sink, without much effort. (scrape off food, one pass soapy water, spray off).

[Slarty1080]

Thanks - that confirms it the 12.5 figure is unrealistic. Great resource BTW

[philw1776]

IF half is being used for laundry, use CO2 washing machines.  Those plus ultrasound cleaners to vibrate out dirt & dust particles should reduce the Earthside "soak it in water & spin & rinse it" paradigm.

[Russel]

You know this discussion begs the following question: In a climate controlled environment, is clothing actually needed?

[Nomadd]

You know this discussion begs the following question: In a climate controlled environment, is clothing actually needed?

All that stuff you're laundering out of the clothes isn't going to disappear. You'll still have to clean it out of or off of something. Not that I or Robert Heinlein would object to mandatory nudism for good reason. Or halfassed reason.

[CuddlyRocket]

You know this discussion begs the following question: In a climate controlled environment, is clothing actually needed?

I once started a thread posing this question which was deleted by Chris shortly thereafter - apparently because posters soon veered off into non-family-friendly territory. Might be wise not to continue such discussion further!

[Russel]

Being naked is only one option. Point being that underwear requires a lot less water/energy to clean than full uniforms.

I also take the point that humans shed a lot of gunge and this has to go somewhere. But let me explain my full context.

Suppose that instead of very minimal body cleaning we instead encouraged regular full showers. The problem then transfers to one of filtration rather than the harder problem of cleaning fabrics.

Even wider context. Firstly I believe in modest spin gravity - about 0.4g. That not only solves other problems but it makes regular showers and drainage a lot easier. Secondly the water that escapes into the cabin air is an easier problem. I don't even see a problem with regular towels being used since they can be reused for long periods with suitable sanitizing (UV/ozone).

So what you're left with is cleaner and happier space travellers and this is good since there is then less need for laundry - even if you do wear more than underwear.

Edit: Perhaps I should have started with this perspective. For me the issue isn't the quantity of water. Its the complexity/cost/reliability and energy usage involved in recycling the water. Its also worth noting that humans create water metabolically so in a well sealed spacecraft you could actually end up with more water than you started.

Reclaiming water from cabin air is relatively easy and well understood. That's why you'd prefer as much water as possible to go via that path and why (in the presence of modest g) its not really necessary to go to great lengths to dry people after they leave the shower.

Reclaiming water from showering means essentially three things. One is coarse contaminants. Dead skin and other organics. Filtering is well understood technology. Another is biologically hazardous contaminants. Which means you need both micro filtration and sterilisation. Again this is not very energy or resource intensive so its not a barrier to using decent quantities of water. Finally there is removal of various soluble chemical components. This is where you don't need an absolutely perfect processing back to pure water at every use. You can instead gradually process/remove such contaminants. Again it doesn't bother me and the cost/complexity is mainly related to what is being used besides water, not the actual water volume.

Reclaiming water from clothes. This is where minimising soiling in the first place makes all the difference. I have to wonder about things like super critical CO2, but again that requires some fairly heavy duty equipment. One point I will make though is that to some extent you can make do with sanitisation rather than actual washing. Again, I'm not that keen on clothes where they don't serve much purpose, but I will admit that in one of my other posts I've written about personal radiation protection vests (which add mass and increase workload for muscles in modest g environments as well as providing another layer of radiation protection). Again, you'd need some degree of cleaning/sanitising.

Finally.. keep the plumbing simple and the number of bits of machinery minimal. Sooner or later someone is going to have to take a spanner to it.

[Nomadd]

 The whole laundry/shower thing loses me anyhow. Why would you lose any water? Using the right detergents, grey water is easy to recycle for anything but drinking. You can use it almost directly for growing things.

[IRobot]

The best way to overall reduce water consumption on a Mars transit is just to reduce transit time. At some point, it pays off the extra fuel to make it in 3-4 months instead of 6-9 months, considering you can lower the mass of water, food, radiation shielding, etc. Not to mention reduction of zero g issues when arriving on Mars.

Also the R&D money for more efficient ECLSS, shielding, etc can be diverted to more up-mass or more R&D on other topics.

IMHO, there might be an initial mission with transit above 4 months, but quickly it will be changed to 3-4 months.

[Russel]

The best way to overall reduce water consumption on a Mars transit is just to reduce transit time. At some point, it pays off the extra fuel to make it in 3-4 months instead of 6-9 months, considering you can lower the mass of water, food, radiation shielding, etc. Not to mention reduction of zero g issues when arriving on Mars.

Also the R&D money for more efficient ECLSS, shielding, etc can be diverted to more up-mass or more R&D on other topics.

IMHO, there might be an initial mission with transit above 4 months, but quickly it will be changed to 3-4 months.

I tend to agree with you that the optimum is closer to 4 months. However whilst shorter flight times might imply less mass of consumables, other things don't scale as well such as the vehicle itself and radiation shielding. Plus no matter how short the trip you still have to carry consumables for contingencies.

Back to subject. I tend to think that the mass of water isn't as big an issue as some think. Its relatively easy to continually recycle. Human solid waste is the really fun part. And I suspect even on a shorter transit it will be a good idea to actually grow stuff. Anyhow that's off topic too.

[RonM]

Another consideration is the design of the spacecraft being used. Mars Direct or NASA concepts are mass limited. Even gram counts and extremely efficient ECLSS are needed. Using a SpaceX BFS with a 150 tonne payload makes like easier. Carrying more water because of using ISS grade ECLSS is not a problem.

[IRobot]

My point is that we keep discussing so many optimizations, like this one or using astronauts without legs to save weight or other nonsense. If we go this path, we will never go to Mars.

Optimizations cost money,  time and probably some limitations.
Either there is a large up mass capability or we will never go there.

[Russel]

My point is that we keep discussing so many optimizations, like this one or using astronauts without legs to save weight or other nonsense. If we go this path, we will never go to Mars.

Optimizations cost money,  time and probably some limitations.
Either there is a large up mass capability or we will never go there.

We may as well continue to refine technology whilst the big problem is being solved (big problem = who is going to pay for it all anyhow).

[Slarty1080]

The whole laundry/shower thing loses me anyhow. Why would you lose any water? Using the right detergents, grey water is easy to recycle for anything but drinking. You can use it almost directly for growing things.

No process is 100% efficient and processing grey water will lose perhaps 5% to brine waste – the more effort you put into reducing this loss the more weight and complexity you add.

There might well be some element of “growing things” on a Mars mission but it would be experimental / supplemental. The vast majority of a Mars mission’s food will be ISS style so there will be limited need for water to grow things. This will change over time, but will be true for the first few missions and probably for a lot more after that.

My main point (see the start of this thread) was to draw attention to the huge amount of water forecast to be used for “hygiene” especially laundry and one potential solution to that problem. A crew of 4 using 12.5kg of water every day and a 95% recycle efficiency results in 2.5kg of waste brine every day. 12.5 x 4 * 0.05. On a 3-6 months transfer to Mars this equates to 225-450kg.

Subsequently it became clear that the report I had cited (Hanford 2004/2005) must have been seriously flawed with respect to water usage (hygiene water usage will be << 12.5kg/CM/day), as it conflicts significantly from other reports.

This only goes to show how important it is to check and recheck the basic assumptions made in these studies to ensure they are as accurate as possible.

All suggestions for how to reduce water consumption are of interest. And a prime example here is to correct the hygiene water usage from 12.5kg/CM/day to perhaps half of that or even less saving hundreds of kg in payload.