Primary Life Support System
From Wikipedia, the free encyclopedia
A Primary (or Portable) Life Support System, or PLSS, is the "backpack" of a spacesuit. The functions performed by the PLSS include:
- regulating suit pressure
- providing breathable oxygen
- cooling and recirculating oxygen and water through the Liquid Cooling and Ventilation Garment, or LCVG.
- removing carbon dioxide, humidity, odors and contaminants from breathing oxygen
- providing communications for the suit occupant
- sensing and reporting suit parameters
[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.
Oxygen, carbon dioxide and water vapor are drawn from the extremeties of the suit by the LCVG, which sends the gas to the PLSS. When gas enters the PLSS, activated charcoal and lithium hydroxide remove odors and 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 some of it is added to the water supply used in the LCVG. The sublimator also cools the oxygen to about 55 °F. 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 psid during extravehicular operations, and 0.7 psid while in intravehicular mode.
[edit] References
- Primary Life Support Subsystem (PLSS). Hamilton Sundstrand. Retrieved on November 3, 2006.
- Jones, Eric M. (January 3, 2006). PLSS Technical Information. Apollo Lunar Surface Journal. NASA. Retrieved on November 3, 2006.
