Revised : 7 Jun 2022

In NASA’s Journey to Mars: Pioneering Next Steps in Space Exploration, the stated goal for the agency is to “extend human presence deeper into the solar system and to the surface of Mars”.

As also stated therein, “It is time for the next steps, and the agency is actively developing the capabilities that will enable humans to thrive beyond Earth for extended periods of time, leading to a sustainable presence in deep space.”

The three phases required to reach these goals are defined as

In the first and current phase, Phase 0, Earth Reliant exploration is focused on research aboard the International Space Station (ISS).

Space agencies are are currently testing technologies in space stations as they are advancing human health and performance research that will enable deep-space, long-duration missions.

In order to go beyond Phase 0, one of those technologies listed to be fully developed is Environmental Control and Life Support Systems (ECLSS).

Aboard ISS, various iterations of flight demonstrations for long-term ECLSS testing are ongoing. They help validate, evaluate and certify various technology candidates for future system.

In overall, many research and developmental work on sorbents and systems have been identified at various Technology Readiness Levels (TRLs).

And these development efforts have the potential to be applied as upgrades to existing systems, as merited, or to future surface habitats on the Moon or Mars.

As we know, CO2 buildup can lead to death of the settlers in a Mars settlement.

In mars-sim, we have not established a detail model for scrubbing or removing CO2 in the life support system.

What we do currently have is simply pumping away these excess CO2 under the resource-processing function called Carbon Dioxide Pump process as found in various buildings such as 'Lander Hab', 'Inflatable Greenhouse', 'Large Greenhouse', 'Fish Farm', and 'Inground Greenhouse' in buildings.xml.

We could first introduce the idea of scrubbing CO2 in EVA Suit. To do so, we need to build up our understanding in removing CO2 chemically.

There are several technology candidates available. The old way has been the use of Lithium Hydroxide (LiOH) canisters.

The Portable Life Support System (PLSS) used by NASA's space suit uses LiOH to scrub CO2 metabolic waste from the suit's air supply. However, this process is non-regenerative, in which the canisters get saturated with each use and are limited to around 8 hours.

There are regenerative processes available such as the Pressure Swing Adsorption (PSA).

For instance, the Amine Swingbed is an open-loop CO2 removal technology currently being well-tested on-orbit.

It operates in a PSA cycle and uses Rapid Amine Cycle (RAC) beds that use amine sorbents to temporarily capture CO2 and a small amount of water at atmospheric pressure, and then regenerate at reduced pressure by venting the excess to the vacuum of space.

The Amine Swingbed has already achieved its experimental objectives of 1000 hours of operation. It has been used to augment the primary CO2 removal systems, the U.S. Carbon Dioxide Removal Assembly (CDRA) and Russian Vozdukh systems.

However, due to the water loss to space during vacuum regeneration of the amine absorbent, this system is currently used only when required due to a large ISS crew or during repair of the primary CO2 removal systems.

We may relocate this process from being under resource-processing function to life-support function in a building if it's more appropriate to do so.