How Does The ISS Get Oxy­gen And Wa­ter?

How do as­tro­nauts make re­sources such as oxy­gen and wa­ter last un­til the next sup­ply mis­sion?

Science Illustrated - - ASK US -

At reg­u­lar in­ter­vals, sup­ply mod­ules are launched to the In­ter­na­tional Space Sta­tion (ISS). They bring ev­ery­thing that the as­tro­nauts need, in­clud­ing wa­ter and oxy­gen. How­ever, the ISS's six in­hab­i­tants would die of oxy­gen deficit be­tween two sup­ply mis­sions, if re­cy­cling sys­tems did not uti­lize the wa­ter and oxy­gen aboard as ef­fi­ciently as pos­si­ble.

As­tro­naut urine is col­lected and sent through a sys­tem, in which it is fil­tered and chem­i­cally pu­ri­fied, so it can be reused as drink­ing wa­ter. And all the wa­ter vapour pro­duced in the air of the space sta­tion is re­trieved, pu­ri­fied, and reused. Vapour from wet tow­els, sweat from the gym, and moist from as­tro­naut ex­ha­la­tion air also end up in a plant, in which the wa­ter vapour of the air is con­densed and pu­ri­fied. The sys­tem makes sure that about 93 % of the wa­ter flown to the space sta­tion is reused.

Wa­ter is par­tic­u­larly valu­able, as it is also used to pro­duce oxy­gen, which the as­tro­nauts in­hale. In elec­trol­y­sis, wa­ter mol­e­cules are split and con­verted into oxy­gen and hy­dro­gen. The oxy­gen is used in cabin air, whereas the hy­dro­gen can­not be used, so it is lost in space.

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