How Is Breathable Air Replenished on the ISS?

Since 2000, there’s been not less than one human dwelling and respiration exterior of the earth’s decrease ambiance orbiting aboard the Worldwide House Station (ISS).

The house station, is provided with every thing that astronauts and cosmonauts want for all times: meals, water, and air. The meals is delivered recurrently on resupply missions. Nevertheless, in the case of water and air, the house station is totally self-sufficient. 

Whereas we have now the luxurious of photosynthesizing crops that provide us oxygen, these aboard the ISS should rely on different means to remain alive and respiration.

So the place does all the oxygen come from?

How does the house station produce oxygen?

Earlier than the Worldwide House Station was launched, we had already perfected the strategies of making oxygen inside a vacuum for prolonged durations of time. Nicely, not tons of of miles above the earth to be actual, it was deep beneath the floor of the ocean as an alternative – inside submarines. 

Submarines haven’t got to come back as much as the floor to replenish their supplies of oxygen. Usually they can not as a result of they’re underneath ice, as a result of surfacing would compromise their in any other case covert operation. This has meant that submarines have needed to lengthy create their very own provides of inner oxygen. Nicely, not precisely “create” however quite “recycle”. 

The first programs utilized aboard the ISS are nearly an identical to these present in submarines. 

The house station’s oxygen and water system consists of two foremost components: the Water Reclamation System, or WRS, and the Oxygen Technology System, or OGS. Every of which relies upon on the different to operate correctly. 

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The WRS collects water from urine, humidity, and condensation, which is then purified to potable requirements. However this makes up solely a portion of the water aboard the ISS. Some water can be regularly shipped from earth to the station to make sure that there’s sufficient “fresh” water being blended in for the crew.

The remaining water is used to create oxygen aboard the house station. The OGS, a system designed by NASA, and its accompanying Russian Elektron system make the most of the means of electrolysis to separate water into its elemental parts:hydrogen and oxygen

Electrolysis includes passing an electrical present via water from an anode to a cathode, which generates sufficient vitality to separate the atoms. The result’s the formation of hydrogen gasoline, H2, and oxygen gasoline, O2

How Is Breathable Air Replenished on the ISS?
A simplified diagram of the electrolysis response in water. Supply: Jsquish/Wikimedia

The electrical energy for this chemical response and most of the electrical energy used aboard the ISS comes from photo voltaic panels on the station’s exterior.

Chemically, electrolysis is just like the photosynthesis response in crops.

Now, you could be questioning, what occurs to all that hydrogen gasoline created by the water-splitting response? Nicely, it is fed again into one thing known as the Sabatier System aboard the ISS. This method combines waste hydrogen with waste carbon dioxide derived from the respiration of the crew to create water and methane via an exothermic response. The system seems to be one thing like this:

CO2 + 4H2 → CH4 + 2H2O + warmth

The following query you could be asking your self is what occurs to the methane and the warmth now that we’ve generated water? Nicely, the methane is vented out into house, and the warmth is managed via warmth exchangers.

So let’s recap. The steps wanted for producing and sustaining oxygen in house are as follows:

  1. Water is reclaimed from the house station utilizing the Water Reclamation System.
  2. A part of that water is utilized to create hydrogen gasoline and oxygen gasoline via the means of electrolysis.
  3. The hydrogen gasoline is then fed into the Sabatier System, which converts it again into water utilizing extra CO2 generated in the station.
  4. The by-products of the Sabatier system are vented into house.

Whereas oxygen era may look easy on paper, it requires some quite subtle expertise to drag off tons of of miles above the earth.

How Is Breathable Air Replenished on the ISS?
Marshall-managed Environmental Management and Life Assist System’s Oxygen Technology System rack delivered to the Worldwide House Station. Supply: NASA

The ISS and its oxygen era programs have been designed to have the ability to deal with a crew of 7 at most. Though, the station is never ever staffed as much as that degree. 

The backup strategies for producing oxygen

Excessive-tech house programs are nothing if not redundant. So simply in case the foremost processes that the ISS makes use of to generate oxygen fail, there’s loads of backup programs. Simply in case. 

The ISS receives common shipments of oxygen from the earth in pressurized tanks mounted exterior the airlock of the station. These aren’t sufficient to produce the station for an prolonged interval, however they’re sufficient to constantly high off the tank, as there are occasional leaks.

The opposite backup is a solid-fuel oxygen generator (SFOG) developed by the Russian House Company, initially for the Mir house station, which is not operational. (Historic aspect notice: Mir’s decommissioning was a quite theatrical affair. The house station was intentionally crashed right into a extremely distant place in the Pacific.

However again to the Worldwide House Station. 

This Russian system is named the Vika System or SFOG, and the crew usually tries to keep away from utilizing it. 

The Vika system works by leveraging canisters of powdered sodium chlorate and powdered iron. The canisters are ignited and attain temperatures of as much as 600 levels Celsius (1,112 levels Fahrenheit), which is sizzling sufficient for the sodium chlorate to interrupt down into sodium chloride and oxygen gasoline.

Woo, gaseous oxygen, mission completed! Nevertheless, having excessive temperatures, hearth, and an enormous provide of gaseous oxygen in house proper subsequent to one another is not excellent in house – or wherever for that matter. 

In 1997, one in all the canisters really caught hearth aboard the Mir station and unfold hearth onto the bulkhead. Not excellent. The opposite draw back to the Vika System is that it would not really produce that a lot oxygen.

One kilogram of fabric produces 6.5 crew-hours of oxygen. That is not rather a lot, and principally signifies that the Vika system is reserved for absolute emergencies and as a backup in the occasion of another catastrophic failure aboard the ISS.

How Is Breathable Air Replenished on the ISS?
A flowchart diagram exhibiting the interactions between the totally different segments of the Worldwide House Station’s Environmental Management and Life Assist System. Supply: NASA/Wikimedia

The house station has a leak

Now that we’ve coated how the house station produces and maintains a gradual provide of oxygen, let’s discuss the ISS actually leaking.

Leaks aboard the ISS aren’t unusual. There’s usually at all times some small leak aboard contemplating it is a big stress vessel in the vacuum of house. Just lately, nonetheless, the leaks have gotten barely extra severe. As of August 2020, the time of this writing, the leaks have gotten so dangerous that the ISS’s crew of three has needed to cordon themselves off in an escape capsule in order that floor crews may attempt to examine the place the leak is coming from. 

Notably, NASA crews have harassed that the leak poses no severe risk to the astronauts, however the scenario, regardless, is a little bit scary. 

Floor crews are intently monitoring all of the compartments of the house station to find out the place precisely the leak is coming from.

Discovering leaks in a large stress vessel with a lot of exterior connections and hatches is not straightforward. Small leaks have been identified about for a while now, however their actual areas have but to be decided. The supply may very well be a tiny hose connection tucked away in a small compartment, or it may very well be an O-ring on a hatch. The chances are mind-boggling. 

For now, the scenario seems to be hopeful as NASA and crews work to gather more data on the challenge. That is to not say, although, that extra leaks will not spring up in the future. Conserving the ISS in clear air is a tricky job. However collectively, NASA and the Russian Space Agency are doing all they will to make sure that their crews keep protected and breathe straightforward as they orbit the earth for months on finish.

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