GoKawiilIn the early years of the International Space Station, water needed to keep the crew alive had to be delivered by Space Shuttle at a cost several times its weight in gold. By 2005, over 9,000 kilograms of the stuff had been flown up from Earth to keep astronauts hydrated, while a further 7,000 kilograms of treated urine were sitting in orbital storage tanks, waiting to be processed.
In November 2008, the Water Processing Assembly arrived on the ISS to realize the great dream of space exploration: boiling astronaut pee. The 800 kilogram Urine Processing Assembly would help take the station from a 45% to 80% water reuse rate. For the first time in the history of space flight, astronauts would be substantially recycling their water in an orbiting habitat.
In June 2010, thirteen months after the Water Processing Assembly went online, excessive levels of total organic carbon began to show up in the astronauts’ drinking water. Total organic carbon is a non-specific measurement that warns the crew about a contaminant being present, but gives them no clue to its identity.
Graph of total organic carbon in reprocessed ISS water, 2010-11. The red arrow points to the safety limit of 3ppm.
When the space station was being designed, NASA had set the safety limit for total organic carbon at 3 parts per million, based on a worst-case scenario where formaldehyde got into the drinking water. By summer, the weekly trend in organic carbon was rising steadily and on track to exceed this threshold in December. At that point, NASA would either have to send up fresh drinking water or bring the crew back home.
There is no provision, then or now, for doing analytical chemistry on the space station. If you have a mystery substance, you need to put it into a returning Dragon or Soyuz capsule and wait for a lab on Earth to identify it. Astronauts and cosmonauts collect regular environmental samples, but whatever is in those samples only gets analyzed when that archive is brought down to Earth. So it wasn’t until September that a Soyuz capsule finally landed with the summer’s trove of water samples, which were quickly sent to the Food and Water Analysis lab in Houston.
There chemists confirmed the total organic carbon reading, but to everyone’s surprise couldn’t identify a specific contaminant in the samples. Whatever was in the water was not on the watchlist of several hundred chemicals that ISS engineers had anticipated might find their way into the station’s water system. In fact, the mystery substance wasn’t even in the lab’s vast reference library of mass spectra.
It took colleagues at Boeing, working from a newer reference library, to identify the mystery contaminant as dimethylsilanediol, or DMSD.
Dimethylsilanediol (C 2 H 8 O 2 Si), first of its name, destroyer of life support systems.
DMSD belongs to a family of compounds called siloxanes, molecules that contain a silicon-carbon-oxygen bond and occupy a kind of middle ground between organic chemistry and beach sand. Siloxanes (also called silicones) are common ingredients in cosmetics, contact lenses, fake boobs, caulks, packaging, and all kinds of personal hygiene products, where they’re used to make things feel smooth and slippery. It’s siloxanes that give deodorant and hair conditioner their slick texture, and the same property makes them a popular industrial lubricant.
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