Breathing Easy on the Space Station
Breathing with Machines
The oxygen that humans and animals breathe on Earth is produced
by plants and other photosynthetic organisms such as algae.
Hydrogen that's leftover from splitting water will be vented into space,
at least at first. NASA engineers have left room in the ECLSS
hardware racks for a machine that combines the hydrogen with excess
carbon dioxide from the air in a chemical reaction that produces
water and methane. The water would help replace the water used
to make oxygen, and the methane would be vented to space.
"We're looking to close the loop completely, where everything will be (re)used,"
Roman said. Various uses for the methane are being considered,
including expelling it to help provide the thrust necessary to
maintain the Space Station's orbit.
At present, "all of the venting that goes overboard is designed to be non-propulsive,"
The ISS will also have large tanks of compressed oxygen mounted on the outside
of the airlock module. These tanks will be the primary supply
of oxygen for the U.S. segment of the ISS until the main life
support systems arrive with Node 3 in 2005. After
that, the tanks will serve as a backup oxygen supply.
Last week, while the crew were waiting for activation of a water electrolysis
machine on the Zvezda Service Module, they breathed oxygen from
"perchlorate candles," which produce O2 via chemical
reactions inside a metal canister.
"You've got a metallic canister with this material (perchlorate) packed inside
it," Perry explained. "They shove this canister into a reactor
and then pull an igniter pin. Once the reaction starts, it continues
to burn until it's all used." Each canister releases enough oxygen
for one person for one day."
"It's really the same technology that's used in commercial aircraft," he continued.
"When the oxygen mask drops down, they say to yank on it, which
actuates the igniter pin. That's why you have to give it a tug to
begin the flow of oxygen."