Capillary structures could provide lower risk water recycling

Rows of small structures

Capillary Evaporator prototype with transparent capillary structures filled with test fluids. Credits: IRPI LLC

Human use a lot of water for drinking and hygiene. Recycling is a key strategy to make the water that is launched into space last longer. Existing water recycling methods in space use harmful chemicals or considerable energy, and do not recycle 100% of the water. Reliability is crucial as well. So the search continues for new approaches to improve the water recycling process.

NASA is considering capillary structures for water recycling. Capillary action involves electrostatic forces literally pulling water through small tubes, similar to how drops of water will hang on objects despite the force of gravity pulling them away. NASA’s capillary structures investigation studies “a new method of water recycling and carbon dioxide removal using structures designed in specific shapes to manage fluid and gas mixtures in microgravity.” The capillary structures equipment is made up of small, 3-D printed geometric shapes and sizes sizes (see above image).

This investigation also involved evaporation. “If you could do controllable evaporation in space, you could do all kinds of things” said Mark Weislogel, one of the project’s principal investigators.  “You could evaporate urine and recover all of the water. All of it. If you had a way of holding the liquid in a passive, no-moving-parts way like a puddle does on earth, but in space, then you could do a lot of unique processing, safely and with no maintenance.”

Just as with the capillary investigations, the evaporation “structures are set up to have different geometries, different angles, different heights, all these different parameters that we are varying across these structures to get quantitative data of evaporation in low gravity,” according to Kyle Viestenz, co-investigator for the project.

“If you could do controllable evaporation in space, you could do all kinds of things” said Mark Weislogel, one of the project’s principal investigators.  “You could evaporate urine and recover all of the water. All of it. If you had a way of holding the liquid in a passive, no-moving-parts way like a puddle does on earth, but in space, then you could do a lot of unique processing, safely and with no maintenance.”

Contractor held in hand.

Capillary Sorbent contactor with channels to expose liquid to ambient air. Credits: IRPI LLC

Another part of the investigation demonstrates the use of fluids in a carbon dioxide removal system, called the Carbon Dioxide Liquid Sorbent System. This system uses a network of “water falls” to bring a material used to absorb gases, into contact with air, allowing the carbon dioxide to be carried away by the liquid. In a microgravity environment, the liquid does not “fall,” but is driven by surface tension forces generated passively by the unique surface geometry of the capillary structures.

It is unknown if or when this technology would be deployed.

Further Information:

tanks and components mounted on three racks

NASA ISS water recovery equipment at Marshall Space Flight Center. Credit: SustainSpace.

Airbus ESA Advanced Closed Loop System (ACLS)

Two technicians point to large instrument box.

ACLS technology demonstrator generates oxygen and water in a closed system

The Advanced Closed Loop System (ACLS) is an advanced life support system that has been developed by Airbus for the European Space Agency (ESA) to be used as a technology demonstrator on the ISS, in the Destiny module, from summer 2018. The ACLS will be installed in the HTV-7 space transporter at the Tanegashima Space Center in Japan and is due to be transported to the ISS in August 2018. It is set to be operated for a period of one year.

The ACLS will purify air and produce oxygen for the International Space Station (ISS). Specifically, the ACLS extracts a portion of the carbon dioxide in the cabin atmosphere. Then, using hydrogen obtained from splitting water molecules, it will convert the carbon dioxide into methane and water in what is known as the Sabatier process. Oxygen is then produced from this water using electrolysis. Airbus asserts that this will increase overall system efficiency and hence reduce the need for supplies from Earth.

The main advantage claimed for the ACLS is the use of the adsorbent Astrine, a solid amine resin, which has a high adsorption capacity even at the carbon dioxide levels in the cabin air. The ACLS will be contained in an International Standard Payload Rack (ISPR).

A future use for the ACLS may be for the Deep Space Gateway / Lunar Outpost. NASA is reported to be looking to the ESA for part of the habitat.

Sources:

Clearing the Air with inXitu

Mars Science Laboratory rover

Mars Science Laboratory

inXitu develops clean-tech air purifiers and portable material analyzers. The technology used in inXitu’s portable rock and mineral analyzer was chosen to fly on the Mars Science Laboratory rover (upper left). inXitu has been developing a low-power, passively-cooled, grounded-anode miniature x-ray source to be deployed in miniaturized instruments for surface and subsurface exploration of the solar system. inXitu is also developing solutions targeted for identification and analysis in the areas of explosives, pharmaceuticals, forensics, art and archaeological materials.

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