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| Recycling air and water |
Before 2009, the ISS could only recycle the small
amount of moisture that was condensed from
astronaut breath and sweat. Urine and waste
water from washing were dumped overboard
and replaced with water that was hauled into
orbit in 41-kilogram (90-pound) bags during
resupply missions. For a space station orbiting 370
kilometres (230 miles) up, that’s expensive, but
for a long-duration mission to another planet, it’s
simply out of the question.
Today’s ISS uses a rack-mounted water treatment
system that filters and distils water on demand. In
microgravity, steam doesn’t rise, so the keg-sized
distillation drum is spun to separate the steam by
centrifugal force. The processed water is cleaner
than tap water on Earth but there’s still a small
amount of water lost from the system each day.
Once efficiency improves from 93 to 95 per cent,
the ISS will be able to obtain all the remaining
water from the moisture present in food supplies.
Oxygen on long-duration missions is actually
less of a problem. The Apollo and Shuttle missions
generated the oxygen they needed as a by-product
of the hydrogen fuel cells that generate electricity.
Oxygen can also be produced by splitting water
and venting the hydrogen into space.
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