L'Affaire Siloxane

2 days ago

Water recycling on the ISS began in 2008 with the Urine Processing Assembly, aiming to increase water reuse from 45% to 80%, but in 2010, elevated levels of total organic carbon appeared in drinking water, threatening to exceed safety limits and potentially forcing evacuation.
The mystery contaminant was identified as dimethylsilanediol (DMSD), a siloxane from personal care products like antiperspirants and lotions, which evaporates, decomposes due to space radiation, and enters the water supply, causing periodic spikes in organic carbon.
NASA faced challenges analyzing DMSD because it contaminated lab equipment and wasn't in reference libraries; siloxanes are inert, hard to filter, and damage systems like heat exchangers and filtration beds, costing significant resources for replacements.
Efforts to filter siloxanes from cabin air led to mold outbreaks, forcing a hybrid charcoal-HEPA filter solution; the problem highlights the complexity of life support, where interactions between radiation, contaminants, and equipment create compounding issues.
The siloxane issue serves as a template for future Mars missions, illustrating risks from unknown unknowns, the difficulty of simulating space conditions on Earth, and how mundane problems can escalate in high-stakes environments with low error margins.

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