Life support system

Life support system

In human spaceflight, a life support system is a group of devices that allow a human being to survive in space. US government space agency NASA,[1] and private spaceflight companies use the term environmental control and life support system or the acronym ECLSS when describing these systems for their human spaceflight missions.[2] The life support system may supply air, water and food. It must also maintain the correct body temperature, an acceptable pressure on the body and deal with the body's waste products. Shielding against harmful external influences such as radiation and micro-meteorites may also be necessary. Components of the life support system are life-critical, and are designed and constructed using safety engineering techniques.

Contents

Human physiological and metabolic needs

A crewmember of typical size requires approximately 5 kg (total) of food, water, and oxygen per day to perform the standard activities on a space mission, and outputs a similar amount in the form of waste solids, waste liquids, and carbon dioxide.[3] The mass breakdown of these metabolic parameters is as follows: 0.84 kg of oxygen, 0.62 kg of food, and 3.52 kg of water consumed, converted through the body's physiological processes to 0.11 kg of solid wastes, 3.87 kg of liquid wastes, and 1.00 kg of carbon dioxide produced. These levels can vary due to activity level, specific to mission assignment, but will correlate to the principles of mass balance. Actual water use during space missions is typically double the specified values mainly due to non-biological use (i.e. personal cleanliness). Additionally, the volume and variety of waste products varies with mission duration to include hair, finger nails, skin flaking, and other biological wastes in missions exceeding one week in length. Other environmental considerations such as radiation, gravity, noise, vibration, and lighting also factor into human physiological response in space, though not with the more immediate effect that the metabolic parameters have.

Atmosphere

Space life support systems maintain atmospheres composed, at a minimum, of oxygen, water vapor and carbon dioxide. The partial pressure of each component gas adds to the overall barometric pressure.

By reducing or omitting diluents (constituents other than oxygen, e.g., nitrogen and argon) the total pressure can be lowered to a minimum of 21 kPa, the partial pressure of oxygen in the Earth's atmosphere at sea level. This can lighten spacecraft structures, reduce leaks and simplify the life support system.

However, the elimination of diluent gases substantially increases fire risks, especially in ground operations when for structural reasons the total cabin pressure must exceed the external atmospheric pressure; see Apollo 1. For this reason, most modern crewed spacecraft use conventional air (nitrogen/oxygen) atmospheres and use pure oxygen only in pressure suits during extravehicular activity where acceptable suit flexibility mandates the lowest inflation pressure possible.

Water

Water is consumed by crew members through drinking, cleaning activities, EVA thermal control, and emergency uses. It must be stored, used, and reclaimed (from waste water) efficiently since no in-situ sources currently exist for the environments reached in the course of human space exploration.

Food

Life support systems often include an indoor plant cultivation system which allows food to be grown within buildings and/or vessels. Often, the system is designed so that it reuses all (otherwise lost) nutrients. This is done, for example, by composting toilets which reintegrate waste material (excrement) back into the system, allowing the nutrients to be taken up by the food crops. The food coming from the crops is then consumed again by the system's users and the cycle continues.

Microbe detection and control

The NASA LOCAD (Lab-on-a-Chip Applications Development) project is working on systems to help detect bacterial and fungal growths in spacecraft used for long-duration spaceflight.[4]

Space vehicle systems

Gemini, Mercury, & Apollo

American Mercury, Gemini and Apollo spacecraft contained 100% oxygen atmospheres, suitable for short duration missions, to minimize weight and complexity.[5]

Space Shuttle

The Space Shuttle was the first American spacecraft to have an Earth-like atmospheric mixture, 22% and 78%.[5] For the Space Shuttle, NASA includes in the ECLSS category systems that provide both life support for the crew and environmental control for payloads. The Shuttle Reference Manual contains ECLSS sections on: Crew Compartment Cabin Pressurization, Cabin Air Revitalization, Water Coolant Loop System, Active Thermal Control System, Supply and Waste Water, Waste Collection System, Waste Water Tank, Airlock Support, Extravehicular Mobility Units, Crew Altitude Protection System, and Radioisotope Thermoelectric Generator Cooling and Gaseous Nitrogen Purge for Payloads.[6]

Orion crew module

The Orion crew module life support system is being designed by Lockheed Martin in Houston, Texas.[citation needed]

Soyuz

The life support system on the Soyuz spacecraft is called the Kompleks Sredstv Obespecheniya Zhiznideyatelnosti (KSOZh).[citation needed] Vostok, Voshkod and Soyuz contained air-like mixtures at approx 101kPa (14.7 psi).[5]

Plug and play

The Paragon Space Development Corporation is developing a plug and play ECLSS called commercial crew transport-air revitalization system (CCT-ARS)[7] for future spacecraft partially paid for using NASA's Commercial Crew Development (CCDev) money.[8]

Space station systems

Skylab

Because of fire risk and potential physiologic effects, Skylab used 28% Oxygen and 72% Nitrogen.[5]

Spacelab

Mir

The Mir and Salyut space stations contained an air-like Oxygen and Nitrogen mixture at approximately sea-level pressures 93.1 kPa (13.5psi) to 129 kPa (18.8 psi) with an Oxygen content of 21% to 40%.[5]

International Space Station

Bigelow commercial space station

The life support system for the Bigelow Commercial Space Station is being designed by Bigelow Aerospace in Las Vegas, Nevada. The space station will be constructed of habitable Sundancer and BA 330 expandable spacecraft modules. As of October 2010, "human-in-the-loop testing of the environmental control and life support system (ECLSS)" for Sundancer has begun.[9]

EVA systems

Extra-vehicular activity (EVA) systems primarily consist of the traditional space suit, but can also include self-contained individual spacecraft.[citation needed]

Space suits

Both space suit models currently in use, the U.S. EMU and the Russian Orlan, include Primary Life Support Systems (PLSSs) allowing the user to work independently without an umbilical connection from a spacecraft. A space suit must provide life support, either through an umbilical connection or an independent PLSS.[citation needed]

See also

References

  1. ^ "International Space Station Environmental Control and Life Support System" (PDF). NASA. http://www.nasa.gov/centers/marshall/pdf/104840main_eclss.pdf. Retrieved 11 December 2010. 
  2. ^ "Breathing Easy on the Space Station". NASA. http://science.nasa.gov/headlines/y2000/ast13nov_1.htm. 
  3. ^ F.M. Sulzman & A.M. Genin (1994), Space, Biology, and Medicine, vol. II: Life Support and Habitability, American Institute of Aeronautics and Astronautics 
  4. ^ "Preventing "Sick" Spaceships". NASA. http://science.nasa.gov/headlines/y2007/11may_locad3.htm?list994055. 
  5. ^ a b c d e Davis, Jeffrey R.; Johnson, Robert & Stepanek, Jan (2008), Fundamentals of Aerospace Medicine, XII, Philadelphia PA, USA: Lippincott Williams & Wilkins, pp. 261-264 
  6. ^ "HSF – The Shuttle: Environmental Control and Life Support System". NASA. http://spaceflight.nasa.gov/shuttle/reference/shutref/orbiter/eclss/. 
  7. ^ "Paragon Projects". Paragon. January 2011. http://www.paragonsdc.com/paragon_projects_09.php. 
  8. ^ "Commercial Crew and Cargo Paragon CCDev". NASA. November 30, 2010. http://www.nasa.gov/offices/c3po/partners/paragon/index.html. 
  9. ^ Volunteers Test Bigelow Life-Support Gear, Aviation Week, 2010-10-22, accessed 2010-10-23.

Further reading

  • Eckart, Peter. Spaceflight Life Support and Biospherics. Torrance, CA: Microcosm Press; 1996. ISBN 1881883043.
  • Larson, Wiley J. and Pranke, Linda K., eds. Human Spaceflight: Mission Analysis and Design. New York: McGraw Hill; 1999. ISBN 007236811X.
  • Reed, Ronald D. and Coulter, Gary R. Physiology of Spaceflight – Chapter 5: 103–132.
  • Eckart, Peter and Doll, Susan. Environmental Control and Life Support System (ECLSS) – Chapter 17: 539–572.
  • Griffin, Brand N., Spampinato, Phil, and Wilde, Richard C. Extravehicular Activity Systems – Chapter 22: 707–738.
  • Wieland, Paul O., Designing for Human Presence in Space: An Introduction to Environmental Control and Life Support Systems. National Aeronautics and Space Administration, NASA Reference Publication RP-1324, 1994

External links


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