Primary Life Support System
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A Primary (or Portable) Life Support System/Subsystem, or PLSS, is the "backpack" of a spacesuit. It provides most of the functions of a spacecraft life support system, in a smaller package. The functions performed by the PLSS include:
- regulating suit pressure
- providing breathable oxygen
- removing carbon dioxide, humidity, odors, and contaminants from breathing oxygen
- cooling and recirculating oxygen and water through the Liquid Cooling and Ventilation Garment, or LCVG.
- sensing and reporting suit parameters
- providing communications for the suit occupant
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[edit] Space Shuttle/International Space Station PLSS
The PLSS for the EMU suit currently used on the Space Shuttle and International Space Station is manufactured by Hamilton Sundstrand. It is mounted to the back of the Hard Upper Torso (HUT) assembly.
Oxygen (O2), carbon dioxide (CO2) and water vapor are drawn from the extremities of the suit by the LCVG, which sends the gas to the PLSS. When gas enters the PLSS, activated charcoal removes odors and lithium hydroxide (LiOH) removes carbon dioxide. Next, the gas passes through a fan which maintains a flow rate of about six cubic feet per minute. A sublimator then condenses water vapor, which is removed by a "slurper" and a rotary separator. The removed water is stored and used to supplement the water supply used in the LCVG. The sublimator also cools the remaining oxygen to about 55 °F (~12.8 °C). A flow sensor monitors the flow rate.
Extra oxygen is added to the flow from a storage tank as necessary, downstream of the flow sensor. The oxygen is then returned to the suit at the back of the head, where it flows down over the astronaut's face. By delivering oxygen to the helmet and drawing gas from the extremities, the suit is designed to ensure that the suit occupant breathes the freshest oxygen possible.
The operating pressure of the suit is maintained at 4.3 psi during extravehicular operations, and 0.7 psi relative to external pressure while in intravehicular mode, i.e., before and after extra-vehicular activity (EVA).
[edit] Developing technology
Technologies being considered for application in future PLSSs include Pressure Swing Adsorption (PSA), a process by which CO2 can be separated from gas more efficiently, and through a repeatable process, as opposed to the current LiOH canisters, which become saturated with each use, and are limited to around 8 hours.[1] By regenenerating the sorbent during EVA, the size and weight of the sorbent canister can greatly reduced. PSA accomplishes this by venting CO2 and water vapor into space.[2]
[edit] See also
[edit] References
- ^ Alptekin, Gokhan (08-01-05). An Advanced Rapid Cycling CO2 and H2O Control System for PLSS. NASA. Retrieved on 2007-02-24.
- ^ Heather, Paul; Alptekin, Goekhan; Cates, Matthew; Bernal, Casey; Dubovik, Margarita; Gershanovich, Yevgenia (2007). "Development of a Rapid Cycling CO2 and H2O Removal Sorbent". 37th International Conference on Environmental Systems, Chicago: NASA. Retrieved on 2007-02-24.
- Primary Life Support Subsystem (PLSS). Hamilton Sundstrand. Retrieved on 2006-11-03.
- Jones, Eric M. (January 3, 2006). PLSS Technical Information. Apollo Lunar Surface Journal. NASA. Retrieved on 2006-11-03.
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