MOXIE payload

[MickQ]

I’m wondering if this technology can be used to supplement or even replace lithium hydroxide use in space suits and specifically Mars surface suits.

[Hobbes-22]

In a closed-cycle breathing system you need both. Lithium hydroxide removes CO₂ from the exhaled gases. You have to do this regardless of the oxygen content. At 1000 ppm, CO₂ already starts to reduce brain function.

The Shuttle replaced lithium hydroxide scrubbers with a system that does not use consumables.

The regenerative carbon dioxide removal system (RCRS) on the Space Shuttle orbiter used a two-bed system that provided continuous removal of carbon dioxide without expendable products.

[ccdengr]

MOXIE weighed 17.1 kg, used 300 watts of power, and produced enough oxygen for a mouse, maybe.  The basic tech might be useful one day, but I question if it's feasible for portable use barring some now-magical way to produce power.

https://mars.nasa.gov/mars2020/spacecraft/instruments/moxie/ talks about a "big MOXIE" for ISRU that would weigh 1000 kg and use 25 kW.

[MickQ]

MOXIE weighed 17.1 kg, used 300 watts of power, and produced enough oxygen for a mouse, maybe.  The basic tech might be useful one day, but I question if it's feasible for portable use barring some now-magical way to produce power.

https://mars.nasa.gov/mars2020/spacecraft/instruments/moxie/ talks about a "big MOXIE" for ISRU that would weigh 1000 kg and use 25 kW.

As I understand it 2/3 of the power consumption was used to heat the SOXE from around -40C ambient to 800C operating temperature before each one hour experiment run.  This obviously would not be the case for an operational unit so watts per gram O2 produced would be much lower.

Also, MOXIE is an experiment so I expect that there is much optimisation to come. 

I also wonder if combining this system with rebreather technology would allow suits that used buffer gas and a higher internal pressure to maybe eliminate, or at least significantly reduce the need to pre-breathe prior to stepping outside.

[Slarty1080]

I think it would be very useful to have multiple means of producing oxygen on Mars beyond water electrolysis as the demands for it will be varied (crew breathing, airlock and other losses, and non stochiometric propellant requirements. So electrolysis and MOXIE could both be used to optimise production even if the final propellant combo is methalox.

[Robotbeat]

I think it’s funny that people seem to not understand the idea of scaling something bigger. “It was only enough for a mouse!”
Oh come on. It’s a tech demo. It’s not necessary to make it any bigger just to prove it works.

If we want to build one big enough to fill a Starship or provide oxygen for a Mars city, we now can.

[Twark_Main]

"Why did NASA waste so much mass making it big enough for a person??  A mouse would have been enough to prove the tech!"  -- people in the other Universe

[MickQ]

OK.  Now we know that the technology works, can it be used in a suit backpack ? 

Should I start a new thread ??

[Twark_Main]

OK.  Now we know that the technology works, can it be used in a suit backpack ? 

Should I start a new thread ??

First, I suggest doing the math on how high a battery density you need to beat simply carrying an oxygen tank...   

Carrying the oxygen itself is a surprisingly mass efficient "battery" to store chemical energy (no need to cover the MOXIE conversion losses either!), and it eliminates a lot of failure modes. Simpler is better, especially on a space suit.

[Zed_Noir]

OK.  Now we know that the technology works, can it be used in a suit backpack ? 

Should I start a new thread ??

Why put it in a spacesuit. Much easier to slightly scaled up the MOXIE apparatus and put it on something like a golf bag cart that also have a deployable solar array parasol and large battery pack. Fill up an oxygen reservoir unit and switch it with an depleted unit in the spacesuit. Think the reservoir unit placement on the spacesuit have to be at locations that are easily reachable by the suit wearer like the front torso.

[MickQ]

In that case don’t swap cylinders but have a gas inlet in a convenient accessible spot on the suit and recharge from a hose on the cart.  Less wear on seals and fewer points of possible failure.

[Robotbeat]

Having MOXIE built into the suit if the suit is battery powered doesn’t make sense at the energy density that batteries are. To make O2 from CO2 takes like 18-19MJ/kg of O2 assuming 100% efficiency (50% is more likely, but less than that at MOXIE scale), and batteries are only 1MJ/kg, maybe up to 2MJ/kg for state of the art lithium metal or lithium sulfur batteries.

It’d be better to focus on better storage of oxygen and a regenerative CO2 scrubber.

[Robotbeat]

Actually, it’d be kind of neat to make a suit that can extract oxygen from peroxide in the regolith, if high enough concentrations can be found.

Peroxides are already often used for chemical oxygen generators (usually lithium peroxide as lithium is the lightest metal).