Author Topic: Ways to reduce ECLSS water requirements on a human Mars mission  (Read 6409 times)

Offline Dean47

  • Member
  • Posts: 10
  • Utah, United States
  • Liked: 11
  • Likes Given: 5
I apologize to speedevil if I seemed to be advocating a system that violates the laws of thermodynamics.  Of course a fully closed ECLSS needs enough input energy to function.  I also completely agree that no human system on earth is fully closed.  We always throw away some (usually substantial) amount of the resources we use.  Also, I agree that even the earth will not be a stable closed-loop ECLSS forever, or even that the universe will be stable forever.  However, I still think we can talk about something that would be beneficial for our expansion into space.

Successful fully closed ECLSS can be demonstrated at small scales.  You can buy one at https://eco-sphere.com/ .  However, since humans are not shrimp, the system must become much more complicated and self-correcting to support human activities.  NASA and others are working on the pieces of such a system.  I also see a lot of great ideas in various forums here at NSF.  I just became interested during the lecture I attended because no one seems to be looking at integrating all the systems into a complete closed (or mostly closed) ECLSS, taking into account the feedback loops, buffers, and emergency provisions.  The only hint the scientists gave was that some theorists believe a fully closed ECLSS capable of supporting humans becomes progressively unstable as the systems scale down from planetary size.  They theorize there even may be some ecological equivalent of a Reynolds number that predicts the conditions under which an ECLSS of a certain size/complexity transitions from stable to unstable.  However, that is all theory, with little research data to support it.

I am getting off my soapbox now. 

Online speedevil

  • Senior Member
  • *****
  • Posts: 2149
  • Fife
  • Liked: 1057
  • Likes Given: 1184
They theorize there even may be some ecological equivalent of a Reynolds number that predicts the conditions under which an ECLSS of a certain size/complexity transitions from stable to unstable.
This is relevant if you have a natural ecosystem, where you are largely not regulating it systematically. You need to be careful about what particular specialties say - their statements may be true in their realm of interest, but false for more limited systems.

For example, with very simple systems if in fact you can control all the inputs and make up for any lacks chemically.
A system with just potatos, vegetables, pigs, humans, and a compost pile may be very unstable if you do not actively manage it, to the point of chaos.

With adequate control and storage and seed, and the possible ability to completely sterilise your growing system if something goes wrong, it may be stable over long periods.

Care needs to be taken you're not too dogmatic at minimising things that are not important.
For example, if your near-term workers are all going to be in a place where they have access to ISRU oxygen, for propellant production, and you'll be evacuating them if that fails as the colony isn't sustainable, there isn't much point in closing the oxygen loop too well.
Similarly - if your colonists are eating better than the workers in your control center, you may have gone too far.

I wasn't trying to raise in the prior message thermodynamics, but that you need to be careful about what you're thinking about as the boundaries of your system, and if they matter in the timescales of interest to you.

Remembering the details!
For example, adding an extra fifty tons of water onto tanks on BFS that you use on the trip may be very cheap, if you have good and reliable tankers, as long as you use it up before aerobraking.

Stuff gets more expensive as fuel is multiplied by the rocket equation and the cost of rockets to hold it.


Offline Russel

  • Full Member
  • ****
  • Posts: 966
  • Liked: 84
  • Likes Given: 1
Let me elaborate on what I've ssid before.

Humans produce water through metabolism. About 0.4Kg per day. That's enough to make up for losses in an imperfect system.

The mass of course come from food. Unless you're proposing to produce food in transit (beyond a few greens) you've got the irreducible mass of food. Some of that gets metabolised to water and that makes up water lost to an imperfect recycle.

So unless you really want to grow food there is a limit to how perfect you need the system to be or how much mass/energy you throw at increasingly fancy chemistry.

Growing food (beyond on a small scale in part to keep people amused/happy) is likely to increase total system mass a lot.

Having said this, there's no room for waste. So if there are good ways to reduce water usage, go for it. I just think that there are bigger problems:

Consumables for contingencies (fly by etc)
Radiation shielding.

All likely to present a bigger headache than water.


 
« Last Edit: 04/10/2018 08:23 AM by Russel »

Offline Slarty1080

  • Full Member
  • *
  • Posts: 113
  • UK
  • Liked: 26
  • Likes Given: 4
Let me elaborate on what I've ssid before.

Humans produce water through metabolism. About 0.4Kg per day. That's enough to make up for losses in an imperfect system.

The mass of course come from food. Unless you're proposing to produce food in transit (beyond a few greens) you've got the irreducible mass of food. Some of that gets metabolised to water and that makes up water lost to an imperfect recycle.

So unless you really want to grow food there is a limit to how perfect you need the system to be or how much mass/energy you throw at increasingly fancy chemistry.

Growing food (beyond on a small scale in part to keep people amused/happy) is likely to increase total system mass a lot.

Having said this, there's no room for waste. So if there are good ways to reduce water usage, go for it. I just think that there are bigger problems:

Consumables for contingencies (fly by etc)
Radiation shielding.

All likely to present a bigger headache than water.

Valid points, but we are discussing minimising water use on this thread. There is obviously a trade off between adding new equipment to deal with ever decreasing amounts of different waste types and I believe 90-95% water recycling would be the best we could expect. Both water and waste brine could both be used as radiation shielding

As an aside it might be benificial to bring a range of fresh fruit an veg (to be consumed in the first few weeks) instead of part of the water requirement as the water content from the fresh fruit and veg would find its way into the water cycle.
The first words spoken on Mars: "Humans have been wondering if there was any life on the planet Mars for many decades … well ... there is now!"

Offline Russel

  • Full Member
  • ****
  • Posts: 966
  • Liked: 84
  • Likes Given: 1
Let me elaborate on what I've ssid before.

Humans produce water through metabolism. About 0.4Kg per day. That's enough to make up for losses in an imperfect system.

The mass of course come from food. Unless you're proposing to produce food in transit (beyond a few greens) you've got the irreducible mass of food. Some of that gets metabolised to water and that makes up water lost to an imperfect recycle.

So unless you really want to grow food there is a limit to how perfect you need the system to be or how much mass/energy you throw at increasingly fancy chemistry.

Growing food (beyond on a small scale in part to keep people amused/happy) is likely to increase total system mass a lot.

Having said this, there's no room for waste. Ith the same contaminants and thus the ssme lost water.So if there are good ways to reduce water usage, go for it. I just think that there are bigger problems:

Consumables for contingencies (fly by etc)
Radiation shielding.

All likely to present a bigger headache than water.

Valid points, but we are discussing minimising water use on this thread. There is obviously a trade off between adding new equipment to deal with ever decreasing amounts of different waste types and I believe 90-95% water recycling would be the best we could expect. Both water and waste brine could both be used as radiation shielding

As an aside it might be benificial to bring a range of fresh fruit an veg (to be consumed in the first few weeks) instead of part of the water requirement as the water content from the fresh fruit and veg would find its way into the water cycle.

Agreed that part of the water stored should come in the form of fruit and veg. I wonder if its possible to stretch that time beyond a few weeks.

Back to the basic problem though. The basic problem is mass. That has dimensions of usage and recycling efficiency. There are two things I don't necessarily agree with.

The first is the exact limit of recycling efficiency before the process becomes "heroic". I'm not an expert but I'm inclined to believe we can go beyond 95%.

The second and more subtle point is I don't accept that water lost as brine etc scales with water use.  The reason being that the quantity if water bound into a non recoverable form presumably scales with how much salts, organics and other chemicals go into it - rather than the actual quantity of water used.

To be conceete. Suppose you step into a shower. You use 5L of water. Out of that 5L there is 250mL of water lost (unrecoverable). Now suppose you used 20L. Will that result in in four times (1L) of lost water? I very much doubt this. You're dealing with the same quantity of contaminants. Yes your filters have to process more water, but when its boiled down you should end up with the same loss (in this exsmple 250mL).

This is why I said two things. First I'd actually propose generous showers. On the basis that more wster used simply means more water recovered. Secondly if you have clean crew you have less of an issue with laundry. The underlying assumption there is that washing people requires less chemicals than washing textiles. In other words you should get higher recycling efficiency from a shower than a washing machine.

And I'll also repeat that if you can keep your crew clean you can be pretty conservative with the laundry - using UV/ozone rather than actual washing.  Or even just accepting that your "intimate apparel" is disposable. Possibly less mass than actual cleaning. If this is the case you may find that you can survive a 4 month trip without any normally scheduled washing of clothes.
« Last Edit: 04/11/2018 01:11 AM by Russel »

Offline Slarty1080

  • Full Member
  • *
  • Posts: 113
  • UK
  • Liked: 26
  • Likes Given: 4
Agreed that part of the water stored should come in the form of fruit and veg. I wonder if its possible to stretch that time beyond a few weeks.

Back to the basic problem though. The basic problem is mass. That has dimensions of usage and recycling efficiency. There are two things I don't necessarily agree with.

The first is the exact limit of recycling efficiency before the process becomes "heroic". I'm not an expert but I'm inclined to believe we can go beyond 95%.

The second and more subtle point is I don't accept that water lost as brine etc scales with water use.  The reason being that the quantity if water bound into a non recoverable form presumably scales with how much salts, organics and other chemicals go into it - rather than the actual quantity of water used.

To be conceete. Suppose you step into a shower. You use 5L of water. Out of that 5L there is 250mL of water lost (unrecoverable). Now suppose you used 20L. Will that result in in four times (1L) of lost water? I very much doubt this. You're dealing with the same quantity of contaminants. Yes your filters have to process more water, but when its boiled down you should end up with the same loss (in this exsmple 250mL).

This is why I said two things. First I'd actually propose generous showers. On the basis that more wster used simply means more water recovered. Secondly if you have clean crew you have less of an issue with laundry. The underlying assumption there is that washing people requires less chemicals than washing textiles. In other words you should get higher recycling efficiency from a shower than a washing machine.

And I'll also repeat that if you can keep your crew clean you can be pretty conservative with the laundry - using UV/ozone rather than actual washing.  Or even just accepting that your "intimate apparel" is disposable. Possibly less mass than actual cleaning. If this is the case you may find that you can survive a 4 month trip without any normally scheduled washing of clothes.

You may be right with improvements beyond 95%, but I don't think they achieve that on the ISS at the moment. Another issue is how robust it is. As I think I mentioned up thread, better to have 99.5% reliability and 95% recycle efficiency than 99.5% recycle efficiency and 95% reliability.

I agree with you on the water scaling issue in terms of water recovery, but another problem arises in that the larger quantity of water will require a lot more power to recover. So from a water efficiency perspective it’s not an issue but from a power perspective it might be.

I also agree that that they won't be taking any washing machine as it would probably not be weight effective. For the weight of a watering machine and plumbing, how many light weight garments can you pack?

Regardless of the method chosen, I would assume someone has or will investigate in some detail how best to produce the cleanest human from the least water producing waste that is easiest to recycle.
The first words spoken on Mars: "Humans have been wondering if there was any life on the planet Mars for many decades … well ... there is now!"

Offline Russel

  • Full Member
  • ****
  • Posts: 966
  • Liked: 84
  • Likes Given: 1
That's a very good point about robustness. I guess the point I'd make is that 99%+ isn't really necessary because humans produce water through metabolism. In other words, beyond a certain percentage of reclamation efficiency, a sealed spacecraft would actually accumulate water.

I suspect that the level of processing for showers isn't very energy intensive. Micro filtration and UV/ozone treatment would render the water safe for reuse. Then you'd have a slower background process continuously removing other contaminants. In other words manageable in terms of energy.

The most interesting thing for me is bodily wastes. There's enough volume in that to make the energy budget an issue. I wish I knew more.

I guess the ultimate last resort is plasma decomposition. Making that simple and robust would be interesting..


Offline Slarty1080

  • Full Member
  • *
  • Posts: 113
  • UK
  • Liked: 26
  • Likes Given: 4
That's a very good point about robustness. I guess the point I'd make is that 99%+ isn't really necessary because humans produce water through metabolism. In other words, beyond a certain percentage of reclamation efficiency, a sealed spacecraft would actually accumulate water.

I suspect that the level of processing for showers isn't very energy intensive. Micro filtration and UV/ozone treatment would render the water safe for reuse. Then you'd have a slower background process continuously removing other contaminants. In other words manageable in terms of energy.

The most interesting thing for me is bodily wastes. There's enough volume in that to make the energy budget an issue. I wish I knew more.

I guess the ultimate last resort is plasma decomposition. Making that simple and robust would be interesting..

Of course like everything else with rocketry, it is not easy. In fact trying to land a rocket vertically is particularly challenging so there was much scope for explosions

Re humans producing water through metabolism, very true, although it just means that a certain amount of the mission’s water budget is actually initially carried as oxygen and food. I think the recycling efficiency of all water wastes would have to be very high before human metabolism started to build a surplus.

Not sure about the showers through. substances like butyric acid and salt from sweat, surfactants from soaps and some other decomposition product would dissolve in the water and would not be be easily removed by filtration.

Plasma decomposition would be the ultimate leveller, perhaps might be needed on very long many year missions to the outer planets or beyond but sourcing the power would be difficult.
The first words spoken on Mars: "Humans have been wondering if there was any life on the planet Mars for many decades … well ... there is now!"

Offline Russel

  • Full Member
  • ****
  • Posts: 966
  • Liked: 84
  • Likes Given: 1
That's a very good point about robustness. I guess the point I'd make is that 99%+ isn't really necessary because humans produce water through metabolism. In other words, beyond a certain percentage of reclamation efficiency, a sealed spacecraft would actually accumulate water.

I suspect that the level of processing for showers isn't very energy intensive. Micro filtration and UV/ozone treatment would render the water safe for reuse. Then you'd have a slower background process continuously removing other contaminants. In other words manageable in terms of energy.

The most interesting thing for me is bodily wastes. There's enough volume in that to make the energy budget an issue. I wish I knew more.

I guess the ultimate last resort is plasma decomposition. Making that simple and robust would be interesting..

Of course like everything else with rocketry, it is not easy. In fact trying to land a rocket vertically is particularly challenging so there was much scope for explosions

Re humans producing water through metabolism, very true, although it just means that a certain amount of the mission’s water budget is actually initially carried as oxygen and food. I think the recycling efficiency of all water wastes would have to be very high before human metabolism started to build a surplus.

Not sure about the showers through. substances like butyric acid and salt from sweat, surfactants from soaps and some other decomposition product would dissolve in the water and would not be be easily removed by filtration.

Plasma decomposition would be the ultimate leveller, perhaps might be needed on very long many year missions to the outer planets or beyond but sourcing the power would be difficult.

The figure I have stuck in my head is 0.4Kg/person/day for metabolic water production.

So a 95% efficiency would allow 8L/day and 98% would allow 20L/day.

I'd guess that the majority of what you get off humans is organic (dead skin etc) and also wouldn't pass microfiltration. Surfactants, salts and other contaminants  require more processing. But.. you don't have to remove all of these at every reuse. All you need is for the water to be reasonably sterile. So this can happen at a slower rate.

I'm a bit more optimistic about plasma decompositon. Provided the mass rate is low (by using other means first) I think its worth considering. Plasma isn't actually all that complex. Its the recovery of  elements from the gas stream that poses a challenge if volume/mass is at a premium

Offline Slarty1080

  • Full Member
  • *
  • Posts: 113
  • UK
  • Liked: 26
  • Likes Given: 4

The figure I have stuck in my head is 0.4Kg/person/day for metabolic water production.

So a 95% efficiency would allow 8L/day and 98% would allow 20L/day.

I'd guess that the majority of what you get off humans is organic (dead skin etc) and also wouldn't pass microfiltration. Surfactants, salts and other contaminants  require more processing. But.. you don't have to remove all of these at every reuse. All you need is for the water to be reasonably sterile. So this can happen at a slower rate.

I'm a bit more optimistic about plasma decompositon. Provided the mass rate is low (by using other means first) I think its worth considering. Plasma isn't actually all that complex. Its the recovery of  elements from the gas stream that poses a challenge if volume/mass is at a premium

"0.4Kg/person/day for metabolic water production. So a 95% efficiency would allow 8L/day and 98% would allow 20L/day."

Not sure I quite follow you there?

General point  - I think there should be different qualities of water such as drinking water and washing water as well as different waste streams - dehumidified water condensate to be purified for drinking and urine purified for washing etc.
The first words spoken on Mars: "Humans have been wondering if there was any life on the planet Mars for many decades … well ... there is now!"

Offline Patchouli

  • Senior Member
  • *****
  • Posts: 4370
  • Liked: 170
  • Likes Given: 295

The figure I have stuck in my head is 0.4Kg/person/day for metabolic water production.

So a 95% efficiency would allow 8L/day and 98% would allow 20L/day.

I'd guess that the majority of what you get off humans is organic (dead skin etc) and also wouldn't pass microfiltration. Surfactants, salts and other contaminants  require more processing. But.. you don't have to remove all of these at every reuse. All you need is for the water to be reasonably sterile. So this can happen at a slower rate.

I'm a bit more optimistic about plasma decompositon. Provided the mass rate is low (by using other means first) I think its worth considering. Plasma isn't actually all that complex. Its the recovery of  elements from the gas stream that poses a challenge if volume/mass is at a premium

"0.4Kg/person/day for metabolic water production. So a 95% efficiency would allow 8L/day and 98% would allow 20L/day."

Not sure I quite follow you there?

General point  - I think there should be different qualities of water such as drinking water and washing water as well as different waste streams - dehumidified water condensate to be purified for drinking and urine purified for washing etc.


I think plants should be included as part of a recycling system as grey water can be put to use for watering them with only minimal processing.
« Last Edit: 04/19/2018 07:06 PM by Patchouli »

Offline johnfwhitesell

  • Full Member
  • ***
  • Posts: 306
  • Liked: 96
  • Likes Given: 193
It's possible to only send a mission after you know there is water in the area, but what about soap?  Everyone on the planet would need to be exercising daily, getting sweat on not just themselves but also their clothes and their surroundings.  How much soap do they go through on the ISS keeping that place bearable?

Online guckyfan

  • Senior Member
  • *****
  • Posts: 6674
  • Germany
  • Liked: 1732
  • Likes Given: 1693
Washing  clothes can be done with CO2, without water and detergents. There are even a few CO2 machines operational on earth right now.

For people soap will be needed.

Offline A_M_Swallow

  • Elite Veteran
  • Senior Member
  • *****
  • Posts: 8396
  • South coast of England
  • Liked: 313
  • Likes Given: 135
Washing  clothes can be done with CO2, without water and detergents. There are even a few CO2 machines operational on earth right now.

For people soap will be needed.

Question for chemists. Can they devise a cleaning material (soap) using materials easily available on Mars? Same for the Moon?

Offline Coastal Ron

  • Senior Member
  • *****
  • Posts: 3913
  • I live... along the coast
  • Liked: 2603
  • Likes Given: 3337
Washing  clothes can be done with CO2, without water and detergents. There are even a few CO2 machines operational on earth right now.

For people soap will be needed.

Question for chemists. Can they devise a cleaning material (soap) using materials easily available on Mars? Same for the Moon?

I think at the beginning they will only be able to rely on gasses from the atmosphere. And then, as the do soil analysis around their landing area, they can decide what chemicals the would want to extract, and have machinery built on Earth for future extraction.

Otherwise just building up mounds of dirt is as much solid extraction that they will be likely to do. And I'm not assuming they will be landing near the poles, so ice initially probably won't be available either.

First couple of missions will have to subsist on just what they bring...
If we don't continuously lower the cost to access space, how are we ever going to afford to expand humanity out into space?

Offline Bananas_on_Mars

  • Full Member
  • *
  • Posts: 121
  • Liked: 61
  • Likes Given: 12
Washing  clothes can be done with CO2, without water and detergents. There are even a few CO2 machines operational on earth right now.

For people soap will be needed.

Question for chemists. Can they devise a cleaning material (soap) using materials easily available on Mars? Same for the Moon?
Soap is just fat (animal fat or fatty oils) cooked with lye. No fancy chemistry, something you can make with household stuff. But this is a little overblown, for centuries past a lot of people just had one set of clothes, on mars they will need to wash some, but there won't be a new set of underwear every sol for a long time i guess. Synthetic fabrics (silver ions) can counter some of the smell that comes from microbial activities, and that might be sufficient to have fresh underwear maybe every 2 weeks or so?

Another interesting bit i found, there's a company marketing a spray that allows you to forgo showering for years if necessary, AO Biome.
It's even available on Amazon, i'm not sure wether to put a direct link, the products name is "Mother Dirt AO mist spray".
What it does is reintroduce ammonia oxidising bacteria to the skins biome.

Here's , the inventor who hasn't showered for a dozen years or so.
« Last Edit: 06/15/2018 06:48 AM by Bananas_on_Mars »

Offline A_M_Swallow

  • Elite Veteran
  • Senior Member
  • *****
  • Posts: 8396
  • South coast of England
  • Liked: 313
  • Likes Given: 135
Washing  clothes can be done with CO2, without water and detergents. There are even a few CO2 machines operational on earth right now.

For people soap will be needed.

Question for chemists. Can they devise a cleaning material (soap) using materials easily available on Mars? Same for the Moon?
Soap is just fat (animal fat or fatty oils) cooked with lye. No fancy chemistry, something you can make with household stuff. But this is a little overblown, for centuries past a lot of people just had one set of clothes, on mars they will need to wash some, but there won't be a new set of underwear every sol for a long time i guess. Synthetic fabrics (silver ions) can counter some of the smell that comes from microbial activities, and that might be sufficient to have fresh underwear maybe every 2 weeks or so?
{snip}

Animal fats are complex chemicals. Lacking grass fields the Mars base probably will not have the self propelled devices (animals) to produce the fat. A totally man made chemical with one end that likes grease and whose other end likes water may be needed.
https://en.wikipedia.org/wiki/Martian_soil

Offline Bob Shaw

  • Full Member
  • ****
  • Posts: 1049
  • Liked: 423
  • Likes Given: 371
I wonder what would happen to dirty clothes if you simply left them at ambient Mars pressures and temperatures for a couple of weeks, then gave them a good shake?

Offline Bob Shaw

  • Full Member
  • ****
  • Posts: 1049
  • Liked: 423
  • Likes Given: 371

Otherwise just building up mounds of dirt is as much solid extraction that they will be likely to do. And I'm not assuming they will be landing near the poles, so ice initially probably won't be available either.

First couple of missions will have to subsist on just what they bring...

Just land in the northern hemisphere near a recent (say, a year old)  small impact crater and you'll find lots of nice lumps of ice. Dozens have been imaged from MRO.

Offline zhangmdev

  • Full Member
  • *
  • Posts: 111
  • Liked: 46
  • Likes Given: 0
I wonder what would happen to dirty clothes if you simply left them at ambient Mars pressures and temperatures for a couple of weeks, then gave them a good shake?

Giving vacuum cleaning and freeze drying a new meaning? But percholerate on Mars is a serious hazard to human

https://www.researchgate.net/publication/242525435_Perchlorate_on_Mars_A_chemical_hazard_and_a_resource_for_humans

The up side is percholerate is a source of oxygen.

Tags: ECLSS water Mars