Author Topic: MCT and ECLSS and a SpaceXy approach to bootstrapping a colony  (Read 49819 times)

Offline guckyfan

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As Jim argued above there will be plenty of time until MCT will transport 100 people. That is because the station/colony cannot accept that many. So there will be plenty of time to optimize the system and make it reliable. Maybe 4 systems are needed but there will be 5 providing failsafe. Closed loop may well be worth it even if it only recovers all the oxygen and discards the methane like in the ISS.

Online meekGee

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As Jim argued above there will be plenty of time until MCT will transport 100 people. That is because the station/colony cannot accept that many. So there will be plenty of time to optimize the system and make it reliable. Maybe 4 systems are needed but there will be 5 providing failsafe. Closed loop may well be worth it even if it only recovers all the oxygen and discards the methane like in the ISS.

The argument is pretty much independent of the number of people.  I'm counting 2 kg/person-day, or 200 kg/person, all inclusive.

I don't think there's any fully closed system that can approach that, all included.  Not even close, from what I'm reading.  The people objecting to MCTs design based on the grounds of "show me the closed-system ECLSS" had a point, to a certain degree.

So not in the hypothetical, but in reality - what technology do you propose for a closed loop ECLSS for MCT?   Even for a crew of 10-20. 
« Last Edit: 10/04/2015 05:06 am by meekGee »
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Offline llanitedave

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While you're recovering metabolic products, you also need to figure out a way of dealing with the accumulating sodium, calcium, magnesium, chlorine, potassium, phosphorus, and nitrogen that you need to separate out from the waste stream.
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Offline docmordrid

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Closed space composting, which gives you good fertilizer for crops at the settlement. In one test using stored solid human waste it took about a year to get nice, fluffy and pathogen free uber-fertilizer. Food waste is faster. Urine is relatively pathogen free, and after 30 days of 'ripening'  pathogen free. Careful design, of course.
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Offline guckyfan

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So not in the hypothetical, but in reality - what technology do you propose for a closed loop ECLSS for MCT?   Even for a crew of 10-20.

First, water recycling. There is a lot of water in human waste that needs to be recovered plus water from controlling humidity of the air. That includes water metabolized from hydrogen in the food but also the water already in the food.

Second, a mix of oxygen production from electrolyzing water plus at least the hydrogen produced in the process can be used to process CO2 to methane and oxygen. If it is worth liquefying the methane and add it to the fuel or just dump it over board like on the ISS is an engineering exercise I don't want to do.

Early flights could have experimental setups that don't endanger the mission if they fail somewhere on the way, only maybe cause some inconvenience. Evolve them until they are reliable enough to use on a 100 person MCT.

Offline guckyfan

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Closed space composting, which gives you good fertilizer for crops at the settlement. In one test using stored solid human waste it took about a year to get nice, fluffy and pathogen free uber-fertilizer. Food waste is faster. Urine is relatively pathogen free, and after 30 days of 'ripening'  pathogen free. Careful design, of course.

There is the melissa advanced life support project of ESA. It includes anaerobic processes to break down waste, aerobic processes to make nutrients available for plants again and bacteria/algae and higher plants for food production.

http://ecls.esa.int/ecls/?p=melissa



Edit: added schematic
« Last Edit: 10/04/2015 07:35 am by guckyfan »

Offline MP99



The talk of this for 100 person MCT is needless.  Any life support systems will have been proven out on early vehicles before they get to colonization. There will be smaller 4-8 person vehicles for the initial explorations.  Then there will be larger vehicles for the initial settlements that will handle 2 digits worth of passengers.  It will be years before infrastructure on Mars can handle an increment of 100 people.  Until then, there will be smaller vehicles with less passengers making the rounds

Agree completely - which makes that 100 comment pretty pointless.

Cheers. The

Offline MP99



While you're recovering metabolic products, you also need to figure out a way of dealing with the accumulating sodium, calcium, magnesium, chlorine, potassium, phosphorus, and nitrogen that you need to separate out from the waste stream.

Just do the minimum to extract water and store this stuff. It has no use on the flight, but is a valuable part of the cargo after you've landed.

Cheers, Martin

Offline MP99



While you're recovering metabolic products, you also need to figure out a way of dealing with the accumulating sodium, calcium, magnesium, chlorine, potassium, phosphorus, and nitrogen that you need to separate out from the waste stream.

Just do the minimum to extract water and then store this stuff. It has no use on the flight, but is a valuable part of the cargo after you've landed.

Cheers, Martin

Offline guckyfan

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Agree completely - which makes that 100 comment pretty pointless.

My understanding was that the discussion on major problems for 100 person ECLSS is needless at this point. It will be ready when needed which is not now.

Offline MP99



While you're recovering metabolic products, you also need to figure out a way of dealing with the accumulating sodium, calcium, magnesium, chlorine, potassium, phosphorus, and nitrogen that you need to separate out from the waste stream.

Just do the minimum to extract water and then store this stuff. It has no use on the flight, but is a valuable part of the cargo after you've landed.

Cheers, Martin

Offline MP99



Metabolic processes produce CO2 but also a lot of H2O. The necessary hydrogen to process CO2 would be produced by electrolysis of H2O. The endresult of the reaction food +O2 will be methane CH4 plus O2. This process would not be closed though because the ratio of C and H would be closer to CH2 than CH4 because of longer chaín carbohydrates. To close that gap you would need more H2O to electrolyze. With enough energy from the solar panels the system could produce not only CH4 methane but also O2 that could be added to the LOX in the tanks. That way most of the food and water consumed during the flight would end up in the propellant tanks.

I am not sure though if that would be the optimum solution overall. It really depends on availabel energy from the solar panels.

Solar panels have a low efficiency of conversion of sunlight to electricity, and electrolysis also has a low efficiency of use of electrical energy.

Consider a solar concentrator to make direct use of heat energy, which can also take advantage of the UV component of light:-

https://en.m.wikipedia.org/wiki/Water_splitting#High-temperature_electrolysis

"When the energy supply is in the form of heat (solar thermal, or nuclear), the best path to hydrogen is through high-temperature electrolysis (HTE). In contrast with low-temperature electrolysis, HTE of water converts more of the initial heat energy into chemical energy (hydrogen), potentially doubling efficiency to about 50%. Because some of the energy in HTE is supplied in the form of heat, less of the energy must be converted twice (from heat to electricity, and then to chemical form), and so less energy is lost."


https://en.m.wikipedia.org/wiki/Water_splitting#Solar-thermal

"The high temperatures necessary to split water can be achieved through the use of concentrating solar power. Hydrosol-2 is a 100-kilowatt pilot plant at the Plataforma Solar de Almería in Spain which uses sunlight to obtain the required 800 to 1,200 °C to split water. Hydrosol II has been in operation since 2008. The design of this 100-kilowatt pilot plant is based on a modular concept. As a result, it may be possible that this technology could be readily scaled up to megawatt range by multiplying the available reactor units and by connecting the plant to heliostat fields (fields of sun-tracking mirrors) of a suitable size.[18]

An interesting approach to solar thermal hydrogen production is proposed by H2 Power Systems.[19] Material constraints due to the required high temperatures above 2200 °C are reduced by the design of a membrane reactor with simultaneous extraction of hydrogen and oxygen that exploits a defined thermal gradient and the fast diffusion of hydrogen. With concentrated sunlight as heat source and only water in the reaction chamber, the produced gases are very clean with the only possible contaminant being water. A "Solar Water Cracker" with a concentrator of about 100 m² can produce almost one kilogram of hydrogen per sunshine hour."

If you assume 20 kg of H2 over 24 hours, that's 180 kg of water reduced, and 160 kg of O2 produced.



This will clearly give you another issue with waste heat.

100 square metres is approximately a 12 metre diameter reflector. If MCT is orientated to point towards the Sun with the concentrator mounted on the tip, then the capsule will be shaded. The waste heat can be used to actively heat the living spaces. Pointing like this may also simplify the solar panel pointing system.

(I think this would require EVAs to install in orbit, and stow before MOI.)

Of course, this also ensures that the prop tanks are at the cold end of the stack.

I had another thought about this. The Raptors will be in permanent shade. They will get extremely cold. They are designed with cooling channels built into the thrust chamber walls, and the vacuum nozzles provide a large surface area for heat rejection.

Perfect for dumping waste heat out of MCT, with LCH4 as the working fluid.

Cheers, Martin

Offline MP99



Metabolic processes produce CO2 but also a lot of H2O. The necessary hydrogen to process CO2 would be produced by electrolysis of H2O. The endresult of the reaction food +O2 will be methane CH4 plus O2. This process would not be closed though because the ratio of C and H would be closer to CH2 than CH4 because of longer chaín carbohydrates. To close that gap you would need more H2O to electrolyze. With enough energy from the solar panels the system could produce not only CH4 methane but also O2 that could be added to the LOX in the tanks. That way most of the food and water consumed during the flight would end up in the propellant tanks.

This brings up two related issues:-

The ratio of carbon, hydrogen and oxygen molecules in the food, compared to an O:F of ~3.8.

Food quality.

As you point out, dried food will give you something closer to CH2 than CH4.

We are used to dehydrating food to reduce its weight, which also affects food quality. But if you leave the food hydrated, that tips the molecular balance more towards CH4.

Cheers, Martin

Offline MP99

Plastic packaging - can you burn it and also recover water and CO2 to be cycled into propellant?

My initial thought is no - too likely to introduce contaminants into the system?

Cheers, Martin

Offline guckyfan

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Solar panels have a low efficiency of conversion of sunlight to electricity, and electrolysis also has a low efficiency of use of electrical energy.

Consider a solar concentrator to make direct use of heat energy, which can also take advantage of the UV component of light:-

https://en.m.wikipedia.org/wiki/Water_splitting#High-temperature_electrolysis


Sounds like a very complex machinery to have on a spaceship. Maybe more suited for operation on the martian surface. However on the surface there is one very big obstacle to using concentrators. Function of concentrators breaks down during duststorms. They also need to be quite clean to be efficent so constant cleaning is required. Non concentrating solar panels work just fine during duststorms or covered with some dust as the Spirit and Opportunity rovers prove though with reduced output.

But we have other threads in the Mars section for this kind of discussion. Like this:

Planning for Power on Mars - Options

http://forum.nasaspaceflight.com/index.php?topic=37518.0

Offline MP99

Solar panels have a low efficiency of conversion of sunlight to electricity, and electrolysis also has a low efficiency of use of electrical energy.

Consider a solar concentrator to make direct use of heat energy, which can also take advantage of the UV component of light:-

https://en.m.wikipedia.org/wiki/Water_splitting#High-temperature_electrolysis


Sounds like a very complex machinery to have on a spaceship.

I am not sure though if that would be the optimum solution overall. It really depends on availabel energy from the solar panels.

It sounds like this is a version of the standard electrolysis that you'd use anyway, but just at the focus of a fairly simple reflector.

On the basis that electrolysis is part of the sizing of the solar panels, this reduces their size by more than the surface area of the reflector. (Assumes that electrolysis runs close to 24x7.)

As an external system, I think this also reduces the radiator / heat rejection required from inside the hab.

Cheers, Martin

Offline RonM

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The ECLSS on MCT should be as simple as possible. The flight time is short, the crew will be small until much later, and there will be plenty of mass available for supplies.

It's the base/colony on Mars that will need a sophisticated ECLSS and recycling capability.

Offline guckyfan

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The ECLSS on MCT should be as simple as possible. The flight time is short, the crew will be small until much later, and there will be plenty of mass available for supplies.

Especially early on most people will go back sooner or later. The return trip is much longer and needs to be taken into consideration, too. Mass is more restricted on the return leg but no cargo needed beyond supplies.

What can be made easy? No oxygen recirculation and no electrolysis. There is a huge tank full of LOX nearby. Draw the oxygen from there. That reduces the task to CO2 scrubbing. Plus regulating temperature and moisture.

But the biggest position in supplies is the water requirement. Especially for the return leg I think recycling water will be a big mass saver. Unfortunately it is probably the part of a closed loop ECLSS that is most likely to fail.

Offline guckyfan

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It sounds like this is a version of the standard electrolysis that you'd use anyway, but just at the focus of a fairly simple reflector.

On the basis that electrolysis is part of the sizing of the solar panels, this reduces their size by more than the surface area of the reflector. (Assumes that electrolysis runs close to 24x7.)

As an external system, I think this also reduces the radiator / heat rejection required from inside the hab.

Cheers, Martin

It is a whole subsystem that would need to be placed outside the vehicle and so cannot be serviced if necessary. High temperature processes also tend to have long term reliability issues. That is what I think makes it complex.

Normal electrolysis and solar panels may be less efficient but they are straight forward. It really depends on how large the panels can practically be. When the power is needed for 100 people panels will be much better than they are now, they are getting better all the time.

Many trades to be made and probably nobody can determine today which the best solution will be in 20 or 30 years. I do hope that catalytic processes will get also much better making the systems less energy hungry and more reliable.


Online meekGee

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So not in the hypothetical, but in reality - what technology do you propose for a closed loop ECLSS for MCT?   Even for a crew of 10-20.

First, water recycling. There is a lot of water in human waste that needs to be recovered plus water from controlling humidity of the air. That includes water metabolized from hydrogen in the food but also the water already in the food.

Second, a mix of oxygen production from electrolyzing water plus at least the hydrogen produced in the process can be used to process CO2 to methane and oxygen. If it is worth liquefying the methane and add it to the fuel or just dump it over board like on the ISS is an engineering exercise I don't want to do.

Early flights could have experimental setups that don't endanger the mission if they fail somewhere on the way, only maybe cause some inconvenience. Evolve them until they are reliable enough to use on a 100 person MCT.

Sure... I didn't say "throw away everything"...  I said:  "MCT's life support will rely heavily on stored consumables.", and in particular, use stored O2 for sure, and probably also chemical scrubbing of CO2.   There's plenty opportunity to extract humidity with pretty minimal equipment, so why not.

Regarding the other much more complex processes you describe - of course they exist, but the equipment is very complex, some of them are very energy intensive, and MCT doesn't have infinite space.  For the colony, sure.  For a 100-day trip, why bother?

When you talk about a return trip, do you mean a free-return turn-around, or just a regular back trip?
« Last Edit: 10/04/2015 04:40 pm by meekGee »
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