Author Topic: Ways to reduce ECLSS water requirements on a human Mars mission  (Read 6437 times)

Offline Bananas_on_Mars

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I think that a lot of aspects of waste water processing need to be covered anyhow even if you want to do ISRU for fuel only. I think on the ground a system based on vacuum destillation (directly solar powered?) can be set up with not to much trouble, something that doesn't work in microgravity. Next thing is
 chemicals in grey water - if you're using pure water, you need a lot less detergents than with your average tap water. Then get rid of the stuff in detergents you don't really need for cleaning, and you can use the grey water for plant growth. Use your rinse water for the next wash.
For solid human waste - sterilize it and add it to your vacuum destillation, or to your greenhouse.

I think for Mars there's a middle ground between the way we do things here on earth and inventing completely new processes - do things effectively and don't waste water and process the rest.

Offline Nomadd

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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.


It sounds like you're talking about a desalination system. All you need to do to recover water from "brine waste" is dry it out. It's disposed of in terrestrial systems because it's not worth the energy and added equipment to recover. You're not going to dump it overboad on your spaceship. Even water from the hydrates you make can be recovered.
 The main issue would be when the extra equipment and energy requirements for a certain voyage weren't worth their weight in saved water. That's a point that should move as the technology develops.
 Even if the payoff is sketchy for a Mars mission, they'd be good chances to test tech for the years long missions to the outer system.
« Last Edit: 04/02/2018 12:23 AM by Nomadd »

Offline Slarty1080

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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.


It sounds like you're talking about a desalination system. All you need to do to recover water from "brine waste" is dry it out. It's disposed of in terrestrial systems because it's not worth the energy and added equipment to recover. You're not going to dump it overboad on your spaceship. Even water from the hydrates you make can be recovered.
 The main issue would be when the extra equipment and energy requirements for a certain voyage weren't worth their weight in saved water. That's a point that should move as the technology develops.
 Even if the payoff is sketchy for a Mars mission, they'd be good chances to test tech for the years long missions to the outer system.

It is not as easy as you think to recover water from waste brines especially when they are contaminated with a range of impurities such as Butyric acid, ammonium salts, soap and other organic materials as well as salts (which they will be). If it were easy to recover 100% of the water from brine they would do it on the ISS, but they don't. They aimed to recover 80% of the water from urine, but only managed to recover 75% in the end and there were significat issues with the equipment even then:
https://en.wikipedia.org/wiki/ISS_ECLSS#Water_recovery_systems

I think recovering 95% of grey waste water would be good. The remaining 5% would end up as contaminated brine waste with volatile components that are not easily remove by "drying it out". Not to say it can't be done, but to do so would involve a lot more complexity and weight and with life support it is better to have 95% recovery and 99.9% reliability than have 99.9% recovery and 95% reliability.
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Offline Russel

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I agree. If you can wash more efficiently that's a good thing. Avoiding having to wash  is better. However we can do better than 95% recycling.

Offline john smith 19

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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.
Wasn't Musks average travel listed as something like "127" days?
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Offline A_M_Swallow

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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.
Wasn't Musks average travel listed as something like "127" days?

Try and avoid getting hung up on travel time because the astronauts will have similar ECLSS problems when they get to Mars.

Offline Slarty1080

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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.
Wasn't Musks average travel listed as something like "127" days?

Try and avoid getting hung up on travel time because the astronauts will have similar ECLSS problems when they get to Mars.

True, although there will be significant differences such as gravity, the availability of localy produced water and increased difficulty in disposing of waste brine. Not sure planetary protection restrictions will let them dump it outside, although there's probably an easy way to vent the volatiles into the atmosphere whilst avoiding bacterial contamination. In the long run they will be able to expand the recycling capability to recover more from the brines as a permenant base will have less weight restriction issues than the BFS.
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Offline speedevil

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Try and avoid getting hung up on travel time because the astronauts will have similar ECLSS problems when they get to Mars.
If you're doing ISRU, they really won't for water.
If you're digging up (or extracting through some other method) water from the surface to do electrolysis on, they can make up moderate losses without issue.
And also run their black water probably through the same process into methane at the same time.

Offline Russel

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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.
Wasn't Musks average travel listed as something like "127" days?

Try and avoid getting hung up on travel time because the astronauts will have similar ECLSS problems when they get to Mars.

A transit vehicle and a Mars hab probably have different constraints.

For one thing, while on Mars itsrlf, environmental water is limited but its still there. In transit you've only got the water you took with you, plus the water that comes from metabolism.

Plus a surface hab is less limited in space and probably power. Plus servicing more extensive/complex equipment is easier on Mars. So you can afford more complex processes. Plus you get more freedom to use plants.

So  I believe the transit phase is a harder problem (not that either is easy).

Offline A_M_Swallow

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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.
Wasn't Musks average travel listed as something like "127" days?

Try and avoid getting hung up on travel time because the astronauts will have similar ECLSS problems when they get to Mars.

A transit vehicle and a Mars hab probably have different constraints.

For one thing, while on Mars itsrlf, environmental water is limited but its still there. In transit you've only got the water you took with you, plus the water that comes from metabolism.

Plus a surface hab is less limited in space and probably power. Plus servicing more extensive/complex equipment is easier on Mars. So you can afford more complex processes. Plus you get more freedom to use plants.

So  I believe the transit phase is a harder problem (not that either is easy).

After 4 or 5 landing with a working mining operation many things are possible. Until then the water processing system has to be cargo on the transit vehicle or the same machine.

Offline john smith 19

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After 4 or 5 landing with a working mining operation many things are possible. Until then the water processing system has to be cargo on the transit vehicle or the same machine.
I find this conversation quite strange.

On orbit these are problems due to a)Limited power b)Limited ability to dump heat c) Limited space to build the plant.

On Mars you've got a whole planet to work with, including a huge lump of cold rock and even (sort of) an atmosphere.

So  you do what you do on Earth and build a sewage plant.  My instinct is for a reed bed design lit by light pipes but various other designs are possible.
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Offline A_M_Swallow

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After 4 or 5 landing with a working mining operation many things are possible. Until then the water processing system has to be cargo on the transit vehicle or the same machine.
I find this conversation quite strange.

On orbit these are problems due to a)Limited power b)Limited ability to dump heat c) Limited space to build the plant.

On Mars you've got a whole planet to work with, including a huge lump of cold rock and even (sort of) an atmosphere.

So  you do what you do on Earth and build a sewage plant.  My instinct is for a reed bed design lit by light pipes but various other designs are possible.

What do you drink and how do you get rid of your sewage whilst you are building your sewage plant?

Offline spacenut

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People in water shortage areas of America can use gray water (washing machine and shower water) for flushing toilets.  Then the water goes to sewage eating bacteria and plants that can produce CH4 and O2.  Then it can be used to water crops, eventually filtering back to fresh water used to grow fish and around we go again.  Water on Mars will have to be recycled, no questions about it.  Otherwise what there is will be used up quickly and if released back into Martian atmosphere will eventually leave the planet.  So it will have to be recycled. 

Offline speedevil

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Water on Mars will have to be recycled, no questions about it.  Otherwise what there is will be used up quickly and if released back into Martian atmosphere will eventually leave the planet.  So it will have to be recycled.

'quickly'.

There is at the moment between 1-3km^3 of water in the atmosphere of Mars.
To even increase this by 10% takes somewhere of the order of a hundred million tons a year of water evaporation.

As context, current loss rates of water from Mars are around 100g/s - 3000 tons a year.

Might this be relevant in the case of a wholly terraformed Mars - sure. But not any time soon.

Offline Dean47

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I have been a lurker on the NSF for a long time.  It is refreshing to visit a site where intelligent people are having thoughtful discussions about challenging technical topics.  There isn't much of that around any more.

I'm jumping in here because I recently attended a lecture held by two university professors on the topic of developing ECLSS's that are efficient and as close as possible to being closed-loop.  Their comment was that the only stable closed-loop ECLSS for human use that has been demonstrated is the Earth.  It seems like a more reasonably sized, efficient, nearly closed-loop system would be possible and would be very useful for nearly every space destination that you have been discussing.   Otherwise, any moon base, Mars colony, etc. will always be closely tethered to Earth by some sort of logistics system to supply the things the ECLSS cannot recycle.

I know of multiple projects working on parts and pieces of a more efficient ECLSS.  NASA has a project called CUBES that involves multiple researchers working on different parts of the process.  Japan is working on parts and pieces.  Does anyone know of a group that is working on a complete closed-loop ECLSS for use in space?

Offline Slarty1080

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I have been a lurker on the NSF for a long time.  It is refreshing to visit a site where intelligent people are having thoughtful discussions about challenging technical topics.  There isn't much of that around any more.

I'm jumping in here because I recently attended a lecture held by two university professors on the topic of developing ECLSS's that are efficient and as close as possible to being closed-loop.  Their comment was that the only stable closed-loop ECLSS for human use that has been demonstrated is the Earth.  It seems like a more reasonably sized, efficient, nearly closed-loop system would be possible and would be very useful for nearly every space destination that you have been discussing.   Otherwise, any moon base, Mars colony, etc. will always be closely tethered to Earth by some sort of logistics system to supply the things the ECLSS cannot recycle.

I know of multiple projects working on parts and pieces of a more efficient ECLSS.  NASA has a project called CUBES that involves multiple researchers working on different parts of the process.  Japan is working on parts and pieces.  Does anyone know of a group that is working on a complete closed-loop ECLSS for use in space?

I would have thought that a fully closed ECLSS is some way off due to the complexity of the task and especially as 99% or even 95% closure should be fine for most missions in the foreseeable future as you note.

Any Moon or Mars base will be closely tethered to Earth for a very considerable time for many needs. For example complex manufactured goods such as computer chips might not be manufactured on Mars for centuries.

But the presence of local resources means that ECLSS non closure does not necessarily mean resupply from Earth. Locally acquired water, oxygen and nitrogen are likely to meet all needs within a fairly short period.

Production of plastics and food might also ramp up after a few years and no longer need to be resupplied from Earth.
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Offline Bananas_on_Mars

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To add to what Slarty1080 wrote:

The last few percent of to bring something to 100% are often the hardest. This often adds a lot of complexity, and weight. Going with the 95% solution might reduce weight far more than bringing the 5% with you will cost you. Then there's complexity versus reliability to be considered. Same goes for energy requirements.

Next thing to be considered: There's a lot of extra stuff to be brought for emergencies, for example to survive some kind of depressurisation event. You might need enough gases to fill a spacecraft several times over. You might need water for emergency purposes where ECLSS doesn't work. The further you are into the mission, the less supplies might be needed  for emergencies. So you can use part of the stuff allocated for emergencies to replenish those 5%.

So fully closed ECLSS in my opinion might be needed when mankind really populates the solar system, but for near term missions might not even be a reasonable choice when looking at the big picture.

Offline Dean47

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I agree that the moon and Mars offer some on-site resources that can be used to balance an ECLSS.  However, it seems to me that if a moon base, for instance, had a fully closed ECLSS, then any oxygen or water generated locally could be used for critical needs such as propulsion.  Therefore, the goal should be to use local resources as a backup for a closed ECLSS.  Of course, we expect much more CO2 and water to be available on Mars, so there should be less of a concern about using a system that is only - say - 95% closed for those resources.  However, there should be a lot more emphasis on growing food on Mars and that part of the ECLSS could be closer to 100% closed.  Everything not recycled will need to be shipped in for a space station, so in that case a fully closed ECLSS would have advantages.

As Slarty1080 said, there will be a vital supply/resupply link between earth and our space bases for a long time.  However, the bases can devote a lot more resources to expansion if the resupply is focused just on things that cannot be produced or used locally.

I agree that extra stuff must be available for emergencies, and that an out-of-balance ECLSS would certainly qualify as an emergency.  I also agree that a 95-99% closed ECLSS may be a much more cost- and maintenance-intensive solution than a fully closed system, at least in the near term.  However, my point is that no one seems to be taking all the components of an ECLSS and integrating them to determine if a 95-99% (overall) efficient ECLSS is possible at a reasonable cost, size, and complexity to be useful for space exploration.  It's as if there are a lot of people at work on engines, tires, brakes, and steering wheels, but no one is looking at how to put it all together to make a car.

Offline speedevil

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Their comment was that the only stable closed-loop ECLSS for human use that has been demonstrated is the Earth.

The earth is not stable closed loop.
Energy is supplied from the decaying sources of solar, gravitational collapse of the core, radioactive decay of the core, with additional energy removed by the moon.

If human civilisation lasts a billion years, with a billion people, each of them gets half a ton of crustal resources a year equivalent, without getting into reuse.

Also, earths environment is quasi-stable, not stable. It is in a region of stability that has only been moderately stable over the past 500 million years in a mostly unchanging environment.
Additional stressors taking the 'control loops' out of their 'designed' range may mean it's unstable, and we for example go back to no oxygen in the atmosphere.

This neglects the more important arguments around stability of the earths life support at the moment due to nonrenewable resource use.

Most earthly communities or projects are very, very far from closed loop.

Offline Russel

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I agree that you can do a lot better than 12.5Kg per day.

I also think you can do a lot better than 95% recovery. It all boils down to energy.

My approach would be to keep the humans clean (more showers) so their clothes can be used for longer between washes. That and using sanitisation in preferrence to actual cleaning.

The less chemicals you use the easier the water reclamation.

Tags: ECLSS water Mars