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The interactions between the components of the ISS Environmental Control and

Life Sup port System (ECLSS)

ISS ECLSSFrom Wikipedia, the free encyclopedia

The International Space

Station Environmental

Control and Life

Support System

(ECLSS) is a life

support system that

provides or controls

atmospheric pressure,

fire detection and

suppression, oxygen

levels, waste

management and water

supply. The highest

priority for the ECLSSis the ISS atmosphere,

but the system also

collects, processes, and

stores waste and water

produced and used by

the crew—a process that

recycles fluid from the sink, shower, toilet, and condensation from the air. The Elektron system aboard

Zvezda and a similar system in Destiny generate oxygen aboard the station.[1] The crew has a backup

option in the form of bottled oxygen and Solid Fuel Oxygen Generation (SFOG) canisters.[2] Carbon

dioxide is removed from the air by the Vozdukh system in Zvezda. Other by-products of humanmetabolism, such as methane from the intestines and ammonia from sweat, are removed by activated

charcoal filters.[2]

Contents

1 Water recovery systems

2 Atmosphere2.1 Air revitalisation system

2.2 Oxygen generating system

2.3 Elektron

2.4 Vika

2.5 Vozdukh

3 Temperature and Humidity Control

4 Fire Detection and Suppression

5 References

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Water recovery systems

The ISS has two water recovery systems. Zvezda contains a water recovery system that processes waste

water from showers, sinks, and other crew systems and water vapor from the atmosphere that could be

used for drinking in an emergency but is normally fed to the Elektron system to produce oxygen. The

American segment has a Water Recovery System installed during STS-126[3] that can process water

vapour collected from the atmosphere, waste water from showers, sinks, and other crew systems, and

also urine into water that is intended for drinking. The Water Recovery System was installed initially in

Destiny on a temporary basis in November 2008[3] and moved into Tranquility (Node 3) in February

2010.[4]

The Water Recovery System consists of a Urine Processor Assembly and a Water Processor Assembly,

housed in two of the three ECLSS racks.[5]

The Urine Processor Assembly uses a low pressure vacuum distillation process that uses a centrifuge to

compensate for the lack of gravity and thus aid in separating liquids and gasses. [6] The Urine Processor

Assembly is designed to handle a load of 9 kg/day, corresponding to the needs of a 6-person crew. [3]

Although the design called for recovery of 85% of the water content, subsequent experience with

calcium sulfate precipitation[4] (in the free-fall conditions present on the ISS, calcium levels in urine are

elevated due to bone density loss) has led to a revised operational level of recovering 70% of the water

content.

Water from the Urine Processor Assembly and from waste water sources are combined to feed the Water

Processor Assembly that filters out gasses and solid materials before passing through filter beds and then

a high-temperature catalytic reactor assembly. The water is then tested by onboard sensors and

unacceptable water is cycled back through the water processor assembly.[5][6]

The Volatile Removal Assembly flew on STS-89 in January 1998 to demonstrate the Water Processor

Assembly's catalytic reactor in microgravity. A Vapour Compression Distillation Flight Experiment

flew, but was destroyed, in STS-107.[6]

The distillation assembly of the Urine Processor Assembly failed on November 21, 2008, one day after

the initial installation.[3] One of the three centrifuge speed sensors was reporting anomalous speeds, and

high centrifuge motor current was observed. This was corrected by re-mounting the distillation assembly

without several rubber vibration isolators. The distillation assembly failed again on December 28, 2008

due to high motor current and was replaced on March 20, 2009. Ultimately, during post-failure testing,

one centrifuge speed sensor was found to be out of alignment and a compressor bearing had failed. [4]

Atmosphere

Several systems are currently used on board the ISS to maintain the spacecraft's atmosphere, which is

similar to the Earth's.[7] Normal air pressure on the ISS is 101.3 kPa (14.7 psi);[8] the same as at sea level

on Earth. An Earth-like atmosphere offers benefits for crew comfort, and is much safer than the

alternative, a pure oxygen atmosphere, because of the increased risk of a fire such as that responsible for

the deaths of the Apollo 1 crew.[9]

Air revitalisation system

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Elektron units in the Zvezda service module.

Carbon dioxide and trace contaminants are removed by the Air Revitalisation System. This is a NASA

rack, to be placed in Tranquility, designed to provide a Carbon Dioxide Removal Assembly (CDRA), a

Trace Contaminant Control Subassembly (TCCS) to remove hazardous trace contamination from the

atmosphere and a Major Constituent Analyser (MCA) to monitor nitrogen, oxygen, carbon dioxide,

methane, hydrogen, and water vapour. The Air Revitalization System was flown to the station aboard

STS-128 and was temporarily installed in the Japanese Experiment Module pressurised module. The

system is scheduled to be transferred to Tranquility now that the module has arrived and was installed

during Space Shuttle Endeavour mission STS-130.[10]

Oxygen generating system

The Oxygen Generating System (OGS) is a NASA rack designed to electrolyse water from the Water

Recovery System to produce oxygen and hydrogen. The oxygen is delivered to the cabin atmosphere and

the hydrogen is vented overboard.[6] The unit is installed in the Destiny module. During one of the

spacewalks conducted by STS-117 astronauts, a hydrogen vent valve required to begin using the system

was installed.[11] The system was delivered in 2006 by STS-121, and became operational on 12 July

2007.[12]

This was the first time Americans had reprocessed the atmosphere of any spacecraft. From2001, the US orbital segment had used oxygen in a pressurized storage tank on the Quest airlock

module, or from the Russian service module.

In 2011, American news outlet CBS news and news magazine spaceflightnow reported "The OGA over

the past six months has not been running well because the water that's been fed to it is just slightly too

acidic," said station Flight Director Chris Edelen. "For the past several months, the station crew has been

using oxygen brought up aboard visiting Progress supply ships, a European cargo craft and the Russian

Elektron oxygen generator while awaiting delivery of the OGA repair equipment. The OGA, like the

Elektron, uses electricity to split water molecules into hydrogen and oxygen. " [13]

Elektron

Elektron is a Russian oxygen generator, which was

also used on Mir, that uses electrolysis to produce

oxygen. This process splits water molecules

reclaimed from other uses on board the station into

oxygen and hydrogen via electrolysis. The oxygen is

vented into the cabin and the hydrogen is vented into

space. NASA claims the three Elektron oxygen

generators on board the International Space Station

have been 'plagued with problems', sometimes

forcing the crew to use backup sources (either

bottled oxygen or the Vika system discussed below).

To support a crew of six, NASA added the oxygen

generating system discussed above.

In 2004, the Elektron unit shut down due to (initially) unknown causes. Two weeks of troubleshooting

resulted in the unit starting up again, then immediately shutting down. The cause was eventually traced

to gas bubbles in the unit, which remained non-functional until a Progress resupply mission in October

2004.[14] In 2005 ISS personnel tapped into the oxygen supply of the recently arrived Progress resupply

ship, when the Elektron unit failed.[15] In 2006 fumes from a malfunctioning Elektron unit prompted

NASA flight engineers to declare a "spacecraft emergency". A burning smell led the ISS crew to suspect

another Elektron fire, but the unit was only "very hot". A leak of corrosive, odorless potassium

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September 17, 2014.

6. ^ a b c d "International Space Station Environmental Control and Life Support System"

(http://www.nasa.gov/centers/marshall/pdf/104840main_eclss.pdf) (PDF). NASA. Retrieved 25 January 2010.

7. ^ Craig Freudenrich (20 November 2000). "How Space Stations Work"

(http://science.howstuffworks.com/space-station2.htm). Howstuffworks. Retrieved 23 November 2008.

8. ^ "5–8: The Air Up There"

(http://web.archive.org/web/20061114010931/http://www.nasaexplores.com/show2_5_8a.php?id=04-032&gl=58). NASAexplores. NASA. Archived from the original (http://nasaexplores.com/show2_5_8a.php?

id=04-032&gl=58) on 14 November 2006. Retrieved 31 October 2008.

9. ^ Clinton Anderson; et al. (30 January 1968). Report of the Committee on Aeronautical and Space Sciences,

United States Senate—Apollo 204 Accident (http://klabs.org/richcontent/Reports/Failure_Reports/as-

204/senate_956/as204_senate_956.pdf). Washington, DC: US Government Printing Office. p. 8.

10. ^ "STS-128 Press Kit" (http://www.nasa.gov/pdf/379392main_STS-128_Press_Kit.pdf) (PDF). NASA. 18

August 2009. Retrieved 1 September 2009.

11. ^ "International Space Station Status Report: SS07-01"

(http://www.nasa.gov/home/hqnews/2007/jan/HQ_SS0701_station_status.html). NASA. 5 January 2007.

Retrieved 25 January 2010.

12. ^ Chris Bergin (12 July 2007). "Oxygen Generating System activated onboard ISS"

(http://www.nasaspaceflight.com/2007/07/oxygen-generating-system-activated-onboard-iss/).

NASASpaceflight.com. Retrieved 25 January 2010.

13. ^ http://spaceflightnow.com/shuttle/sts133/110305fd10/index2.html

14. ^ Amit Asaravala (20 September 2004). "Space O2 Generator Fails Again"

(http://www.wired.com/science/space/news/2004/09/65026). Wired News. Retrieved 25 January 2010.

15. ^ Tariq Malik (4 January 2005). "Repaired Oxygen Generator Fails Again Aboard ISS"(http://www.space.com/missionlaunches/exp10_elektron_050104.html). Space.com. Retrieved 25 January

2010.

16. ^ William Harwood (18 September 2006). "Oxygen generator problem triggers station alarm"

(http://www.spaceflightnow.com/station/exp13/060918elektron.html). Spaceflight Now. Retrieved 25 January

2010.

17. ^ "International Space Station Status Report #48"

(http://www.nasa.gov/home/hqnews/2006/nov/HQ_SS06048_station_status.html). NASA. 3 November 2006.

Retrieved 25 January 2010.

18. ^ a b Kerry Ellis - International Life Support - Ask Magazine

(http://www.nasa.gov/offices/oce/appel/ask/issues/44/44s_international_life_support.html)

19. ^ "In-Flight Carbon Dioxide Exposures and Related Symptoms: Association, Susceptibility, and Operational

Implications" (http://ston.jsc.nasa.gov/collections/TRS/_techrep/TP-2010-216126.pdf) (see page 6), NASA,

June 2010.

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Categories: Components of the International Space Station Medical technologySpacecraft life support systems

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