Using forward and reverse osmosis to enable astronauts’ suits to produce fresh water from urine

The uncomfortable reality of spacesuits used for extravehicular activities (EVAs)—commonly referred to as spacewalks—is that astronauts spend hours in them, during which time normal bodily functions such as urination and defecation continue. The current record for EVAs on the International Space Station is just under nine hours, which necessitates a new approach. Now, a team of researchers has put forward the idea of ​​a water recovery system inside the suit in a paper published in [Sofia Etlin] And colleagues As published in Horizons in Space Technology.

For the current EVA spacesuit for the Extravehicular Mobility Unit (EMU), the current solution is the so-called magazine:Ultra-absorbent clothing, which is actually a luxury adult diaper that contains sodium polyacrylate as an absorbent for up to 2 liters of fluid. It replaced the urine collection device (UCD) that was used until female astronauts joined the astronaut corps in the 1970s. In general, astronauts aim not to defecate until they are done with their spacewalk, leaving urination and rehydration activities as spacesuits hold only 0.95 liters of water that should last for the duration of a spacewalk.

Creating a prototype of the system circuits. (Copyright: Sophia Etlin et al., 2024, Front. Space Technol.)

By filtering urine and recycling it into drinkable water, we would avoid all the drawbacks of diapers and give astronauts more water to drink during extravehicular flights. Although media reports about this paper have often been Referred to Still photography suits Sand dunesThis device is significantly less advanced and bulky, with the filtration equipment being packed into a backpack and weighing around 8kg. The wastewater is filtered using a dual Forward Osmosis – Reverse Osmosis (FO-RO) system, with forward osmosis being used as a primary filter to prevent membrane fouling common with reverse osmosis.

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Urine is collected by a UCD device much like pre-MAG systems, with a silicone cup that conforms to the male or female astronaut’s genitalia. When urinating, the cup’s inner lining will detect moisture and activate a vacuum pump to remove the urine and deliver it to the FO-RO system as quickly as possible. Salts are added to the filtered water before it is available for consumption.

It’s worth noting that this is still a prototype, but considering that similar technology is already being used on the International Space Station to filter wastewater, it seems like it’s only a matter of time before a miniature version of this model is added to the new EVA spacesuits. It should make long, confined spaceflights less uncomfortable, with obvious benefits for astronauts during extravehicular excursions.

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