Author Topic: Indefinite duration ECLSS general thread  (Read 7083 times)

Online speedevil

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Re: Indefinite duration ECLSS general thread
« Reply #20 on: 06/12/2018 07:23 PM »
There are several firms working on ECLSS equipment. Have they produced a CO2 scrubber for say 12 people that can work for at least 6 months?
At what $/kg/year tradeoff?
As one example, 50 tons of lime will do it for $500K, if your lift is $10/kg.

If you have to fit it in 10kg, then it's going to get expensive/impossible.
« Last Edit: 06/12/2018 07:24 PM by speedevil »

Online testguy

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Re: Indefinite duration ECLSS general thread
« Reply #21 on: 06/13/2018 12:51 AM »
I'm reading Scott Kelly's book "Endurance" about his year on ISS.  The most troublesome piece of equipment they had on board was the CO2 scrubber, referred to as a CDRA ("Sidra").  There were actually two of these and they were constantly breaking down and Houston only would power up one of them at a time.   Each was about the size of a car engine.

Kelly thought that NASA was allowing the CO2 levels to get too high most of the time.  One CDRA could theoretically deal with the CO2 produced by 6 residents (if it kept running that is).  Having more than 6 people on board would require both CDRA's working.   BFS with its much larger potential passenger count is going to need something more efficient and more reliable.

There are several firms working on ECLSS equipment. Have they produced a CO2 scrubber for say 12 people that can work for at least 6 months?

Arenít there Co2 scrubbers on subs that will clear the air for large crews?  Do we really need to reinvent the wheel here?

Offline QuantumG

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Re: Indefinite duration ECLSS general thread
« Reply #22 on: 06/13/2018 12:58 AM »
Arenít there Co2 scrubbers on subs that will clear the air for large crews?  Do we really need to reinvent the wheel here?

Little thing called mass.
I hear those things are awfully loud. It glides as softly as a cloud. What's it called? Monowhale!

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Re: Indefinite duration ECLSS general thread
« Reply #23 on: 06/13/2018 01:16 AM »
Arenít there Co2 scrubbers on subs that will clear the air for large crews?  Do we really need to reinvent the wheel here?

Little thing called mass.

A company I used to work for manufactured them as a side line.  If my memory is correct they werenít very large.  That was 30 Yearís ago.

Offline QuantumG

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Re: Indefinite duration ECLSS general thread
« Reply #24 on: 06/13/2018 01:36 AM »
A company I used to work for manufactured them as a side line.  If my memory is correct they werenít very large.  That was 30 Yearís ago.

Do tell.
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Online hop

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Re: Indefinite duration ECLSS general thread
« Reply #25 on: 06/13/2018 02:02 AM »
Arenít there Co2 scrubbers on subs that will clear the air for large crews?  Do we really need to reinvent the wheel here?
I'm going to go out on a limb and assume the people who built CDRA and Vozdukh for ISS were aware of the existence of submarines. If they re-invented the wheel, they almost certainly had a good reason.

Offline Lar

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Re: Indefinite duration ECLSS general thread
« Reply #26 on: 06/13/2018 02:14 AM »
Yeah, the cost of lifting things. Reduce that by 100x and all of a sudden a submarine scrubber might not be so bad. That's the point being made by some, the crazy save every gram solutions may not be the best if you have a fuel rich architecture.
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Offline A_M_Swallow

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Re: Indefinite duration ECLSS general thread
« Reply #27 on: 06/13/2018 03:17 AM »
On Earth CO2 scrubbers tend to pump gasses though liquids and use gravity to separate them. This may work on submarines and could work on the Moon but will fail in microgravity.

Offline pathfinder_01

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Re: Indefinite duration ECLSS general thread
« Reply #28 on: 06/13/2018 04:15 AM »
There are several firms working on ECLSS equipment. Have they produced a CO2 scrubber for say 12 people that can work for at least 6 months?
At what $/kg/year tradeoff?
As one example, 50 tons of lime will do it for $500K, if your lift is $10/kg.

If you have to fit it in 10kg, then it's going to get expensive/impossible.

While cost is important, lime will not do for any CO2 scrubber used for a long duration spaceflight. The problem isn't cost but mass, redundancy, and volume.  More mass equals needing more propellant for the trip perhaps bigger engines for more thrust, larger tanks to hold more propellant and so on.   It even means larger thrusters and more mass for a landing system to cope with basically it complicates things. Then there is the problem of redundancy, you need a system that is able to recharge or at least not run out on a long flight because you canít count on the supply ship reaching there .  Also in any spacecraft or base volume is limited. Cheap lift is nice but it doesnít solve all problems.

Online speedevil

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Re: Indefinite duration ECLSS general thread
« Reply #29 on: 06/13/2018 08:59 AM »
Cheap lift is nice but it doesnít solve all problems.

Cheap lift is nice, but if it solves a particular problem, it sets a hard backstop as to what prices for subsystems are reasonable.
Clearly lime is unlikely to be OK, for most situations, but if you're in an orbiting station near earth - and it forms part of the shielding, it is useful as context.

Similarly, if you don't actually care about microgravity on your spacecraft, and the extra costs of spin are not particularly high, submarine type units (of several different models), with large excess capacity are another important backstop on price.

'Cheap lift doesn't solve all problems' needs to be set against 'expensive designs cause problems of their own'.

If your ECLSS is expensive enough(counting direct costs, and savings due to lighter launch weight)  that it is the long pole, compared to 'dumb' life support, you have not won.
Especially if you can augment the dumb life support with ECLSS that only has to work 90% of the time.

(And of course, you can heat lime to 800C and regenerate it, though there are clearly more sane systems).

Offline AncientU

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Re: Indefinite duration ECLSS general thread
« Reply #30 on: 06/13/2018 11:07 AM »
On Earth CO2 scrubbers tend to pump gasses though liquids and use gravity to separate them. This may work on submarines and could work on the Moon but will fail in microgravity.

The submarine CO2 scrubber was designed assuming gravity -- a space system would assume none in the design.  There are several flows and pressure gradients in the system that could be used instead of gravity if so designed.  Basic chemical process would obviously work; CO2 removed would probably be converted via Sabatier process instead of being compressed and sent overboard as on a sub.

One interesting complication is that the BFS system would have to be designed for 0-1g since it would be used on planetary surfaces as well as in space.  Still believe this is fairly straightforward design-wise.
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Offline Coastal Ron

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Re: Indefinite duration ECLSS general thread
« Reply #31 on: 06/13/2018 02:34 PM »
On Earth CO2 scrubbers tend to pump gasses though liquids and use gravity to separate them. This may work on submarines and could work on the Moon but will fail in microgravity.

The submarine CO2 scrubber was designed assuming gravity -- a space system would assume none in the design.  There are several flows and pressure gradients in the system that could be used instead of gravity if so designed.  Basic chemical process would obviously work; CO2 removed would probably be converted via Sabatier process instead of being compressed and sent overboard as on a sub.

One interesting complication is that the BFS system would have to be designed for 0-1g since it would be used on planetary surfaces as well as in space.  Still believe this is fairly straightforward design-wise.

I wonder if one of the potential zero G solutions could use a vortex action - spinning the water volume and then injecting the air in the center so that it is forced to migrate out to the edges. Which maybe would work, but due to the volume of water needed, and the centripetal forces created, that it was going to be "non-optimal" for the ISS?
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Offline ThereIWas3

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Re: Indefinite duration ECLSS general thread
« Reply #32 on: 06/13/2018 03:45 PM »
The CDRA on ISS actually does more than just remove CO2 (most of which goes overboard).  It also recycles some through a Sabatier reactor to produce drinking water.  I do not recall where they get the Hydrogen, and this may have just been an experiment that was running during the period Kelly was on board.    The CDRA has to dry the air, which as a side effect heats it a bit.  So then the air has to be cooled again because the CO2 removal process requires cool dry air to work.

The US segment has two of these.  The Russian segment has one machine that works along the same principle.  Each one can handle about 6 people, but they are rarely all running at once.

The actual CO2 absorbant is Zeolite, which is an aluminosilicate.  From Kelly's report, this stuff often gums up the working seals inside the unit.   The Zeolite is perodically exposed to space vaccuum, which sucks the trapped CO2 out.   They also had one of the air recirculating fans inside the unit fail.  (They have lots of spare parts)

Here is a picture of Kelly and another astronaut working on a CDRA unit which they have slid out of its mounting rack. That process is very labor intensive due to all the hoses and cables that are connected to it.  Houston is also involved in the repair because the CDRA is actually remotely managed from the ground.  Anything on the way to Mars had better be able to be operated locally.


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Re: Indefinite duration ECLSS general thread
« Reply #33 on: 06/13/2018 05:01 PM »
A company I used to work for manufactured them as a side line.  If my memory is correct they werenít very large.  That was 30 Yearís ago.

Do tell.

Atlantic Research Corporation built them in the 70's and early 80's for nuclear submarines.  The market was limited because the number of subs was also limited.  I think there was more of a profit potential in service contracts rather than production.  The scrubbers were not high tech and could be built by many manufactures.  The company got out of the business since it really wasn't worth the effort.

Just Google nuclear submarine C02 scrubbers  and you will find a wealth of information.

BTW I did not think about 0 G operation and have no feel for that impact.  I didn't work on the scrubbers, just occasionally sent some of my personnel to far off places around the world to service them.

Offline envy887

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Re: Indefinite duration ECLSS general thread
« Reply #34 on: 06/13/2018 11:15 PM »
Centrifuges on Earth routinely create artificial gravity fields in order to separate fractional fluids. That's not a showstopper, particularly in an environment that doesn't require high quality microgravity for research.

Online hop

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Re: Indefinite duration ECLSS general thread
« Reply #35 on: 06/14/2018 01:42 AM »
BTW I did not think about 0 G operation and have no feel for that impact.
Power, thermal and consumables trades are likely quite different too. That doesn't mean submarine heritage is necessarily irrelevant, trades for moon and Mars bases will be different from ISS too.

There is a good amount of information on the ISS systems and their development on NTRS.

Offline deruch

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Re: Indefinite duration ECLSS general thread
« Reply #36 on: 06/14/2018 04:27 AM »
Centrifuges on Earth routinely create artificial gravity fields in order to separate fractional fluids. That's not a showstopper, particularly in an environment that doesn't require high quality microgravity for research.

There's a company testing something similar, without the centrifuging or artificial gravity, for separation of immiscible liquids in microgravity on ISS right now.  Their device was part of the OA-9 cargo that just went up to station last month.  It was discussed in the pre-launch science briefing (start at 5:48): 

https://www.youtube.com/watch?v=SxyvE5ryT0k?t=001
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Offline pathfinder_01

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Re: Indefinite duration ECLSS general thread
« Reply #37 on: 06/14/2018 04:36 AM »
The CDRA on ISS actually does more than just remove CO2 (most of which goes overboard).  It also recycles some through a Sabatier reactor to produce drinking water.  I do not recall where they get the Hydrogen, and this may have just been an experiment that was running during the period Kelly was on board.    The CDRA has to dry the air, which as a side effect heats it a bit.  So then the air has to be cooled again because the CO2 removal process requires cool dry air to work.


The Hydrogen comes from the Oxygen generation system. Due to mass and the danger of leakage\explosion the ISS limits the number of Oxygen gas canisters onboard. It has them but uses them for back up and space walking. The Russians also have Oxygen generating candles in case of emergency or in case the Oxygen generation system can't keep up with demand.

Instead of using gas canisters, the ISS electrolyzes water to produce Oxygen and it used to dump the Hydrogen. The Sabatier allows the ISS to recover some of the Oxygen that would have been dumped overboard with the CO2 as water dumping methane instead.

The life support system also recovers water from Air to reduce the amount of water that needs to be sent to the ISS.  The American system attempts to recover water from Urine.
« Last Edit: 06/14/2018 04:47 AM by pathfinder_01 »

Offline pathfinder_01

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Re: Indefinite duration ECLSS general thread
« Reply #38 on: 06/14/2018 05:15 AM »
Cheap lift is nice but it doesnít solve all problems.

Cheap lift is nice, but if it solves a particular problem, it sets a hard backstop as to what prices for subsystems are reasonable.
Clearly lime is unlikely to be OK, for most situations, but if you're in an orbiting station near earth - and it forms part of the shielding, it is useful as context.

Similarly, if you don't actually care about microgravity on your spacecraft, and the extra costs of spin are not particularly high, submarine type units (of several different models), with large excess capacity are another important backstop on price.

'Cheap lift doesn't solve all problems' needs to be set against 'expensive designs cause problems of their own'.

If your ECLSS is expensive enough(counting direct costs, and savings due to lighter launch weight)  that it is the long pole, compared to 'dumb' life support, you have not won.
Especially if you can augment the dumb life support with ECLSS that only has to work 90% of the time.

(And of course, you can heat lime to 800C and regenerate it, though there are clearly more sane systems).

 It isn't launch costs that drive costs here. The Problem here is that it takes a lot of money to design and test systems but you have very few units to spread the costs over so it tends to get expensive. Anyway what you are describing is an open life support system vs. a closed one and longer missions favor more closed life support systems.  Open life support systems like the Shuttle are simpler but they can have draw backs as mission time increases.

For instance, Apollo and Shuttle used LIOH canisters for CO2 scrubbing. Skylab didn't. When Endeavor was built they wanted to add 2 days to the mission but found and they could not use LIOH canisters because there wasnít enough space to store the additional canisters and additional supplies, so they built system similar to the ISS one to Augment the original system. Likewise Orion wanted to use the canister but with a 21 day mission there was no space for enough of them and due to size and power constraints they could not use the ISSís system and so a new CO2 scrubbing system had to be developed for Orion(ESA was planning to install a similar type of system in the ISS there have been proposals to upgrade the ISS life support system with that type of scrubber).

Bigloew was planning a system similar to the ISS but wouldnít attempt to recover water from crew waste. Anyway what you donít need is an indefinite life support system. You just need one with enough reliability and spare parts to be practical. Just as you donít need to have 100% closed loop, you just need enough closure to control costs as well as make the system practical.  Also ISRU can be used to top off what gets lost.


Online speedevil

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Re: Indefinite duration ECLSS general thread
« Reply #39 on: 06/14/2018 07:51 AM »
It isn't launch costs that drive costs here. The Problem here is that it takes a lot of money to design and test systems but you have very few units to spread the costs over so it tends to get expensive. Anyway what you are describing is an open life support system vs. a closed one and longer missions favor more closed life support systems.  Open life support systems like the Shuttle are simpler but they can have draw backs as mission time increases.
<snip>
Bigloew was planning a system similar to the ISS but wouldnít attempt to recover water from crew waste. Anyway what you donít need is an indefinite life support system. You just need one with enough reliability and spare parts to be practical. Just as you donít need to have 100% closed loop, you just need enough closure to control costs as well as make the system practical.  Also ISRU can be used to top off what gets lost.

If, in a specific case, launch costs are such as to make it plausible to have open loop as a backup, and to have multiple simple systems that will probably work, and to have that cheaper than engineering a proper system to a 'reasonable' weight, the unreasonable solution may be reasonable.

Launch costs are important as if your life support vendor (or department) is proposing a solution that will never get cheaper than just doing it the heavy way, you should probably start looking at other routes.

Be that trying lots of hacked together stuff that will probably work and you can test on orbit, with the only criteria for design being 'can't emit toxics'.

If your CO2 scrubber has been rigorously tested in orbit for 3 months, is made of serviceable parts, is ten times heavier than the normal class of solution, and you can carry 24 of them and have 3 months open loop reserve, that puts you in a very different part of the solution space than if you have one (or two) which have to work 99.9% of the time, or everyone dies.


Tags: ECLSS life support