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A Primary (or Portable or Personal) Life Support System (or /Subsystem) (PLSS), is a device connected to an astronaut or cosmonaut's spacesuit, which allows extra-vehicular activity with maximum freedom, independent of a spacecraft's life support system. The PLSS is generally worn like a backpack. 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 through the pressure garment, and water through a Liquid Cooling and Ventilation Garment or Liquid Cooling Garment. *two-way voice communication *display and/or telemetry of suit health parameters *telemetry of an indicator of the wearer's immediate health (e.g. heart rate) The air handling function of a PLSS is similar to that of a diving rebreather, in that exhaled gases are recycled into the breathing gas in a closed loop. When used in a microgravity environment, a separate propulsion system is generally needed for safety and control, since there is no physical connection to a spacecraft. ==Apollo PLSS== The Portable Life Support System used in the Apollo lunar landing missions used lithium hydroxide to remove the carbon dioxide from the breathing air, and circulated water in an open loop through a Liquid Cooled Garment, expelling the water into space, where it turned to ice crystals. Some of the water was also used to remove excess heat from the astronaut's breathing air, and collected for dumping into the spacecraft's wastewater tank after an EVA. The PLSS also contained a radio transceiver and antenna for communications, which were relayed through the spacecraft's communication system to Earth. PLSS controls were provided in the Remote Control Unit (RCU) mounted on the astronaut's chest. Oxygen and water were rechargeable for multiple EVA's from the spacraft's environmental control system. Lunar surface EVA times for the first four missions (Apollo 11 through 14) were limited to 4 hours, with oxygen stored at , of lithium hydroxide, 8.5 pounds (3.9 liters) of cooling water, and a 279 watt-hour battery. For the extended missions of Apollo 15 through 17, the EVA stay time was doubled to 8 hours by increasing oxygen to , lithium hydroxide to , cooling water to 11.5 pounds (5.2 liters), and battery capacity to 390 watt-hours.〔 An emergency backup was provided in case the main system failed, by a separate unit called the Oxygen Purge System (OPS), mounted on top of the PLSS, immediately behind the astronaut's helmet. The OPS maintained suit pressure and removed carbon dioxide, heat and water vapor through a continuous, one-way air flow vented to space. When activated, the OPS provided oxygen to a separate inlet on the pressure suit, once a vent valve on a separate suit outlet was manually opened. The OPS provided a maximum of about 30 minutes of emergency oxygen for breathing and cooling. This could be extended to 75 to 90 minutes with a "buddy system" hose that used the other astronaut's functional PLSS for cooling (only). This allowed the vent valve to be partly closed to decrease the oxygen flow rate. The PLSS was high, wide, and deep. It was tested in space for the first time by Russell Schweickart in a stand-up EVA in Earth orbit on Apollo 9. His PLSS weighed on Earth, which translated to a weight of only 14 lb (equivalent to the Earth weight of ) on the Moon. The OPS weighed on Earth (6.8 lb (equivalent to the Earth weight of ) on the Moon).〔 〕 The OPS was also used as a backup on tethered in-space EVAs where a spacecraft provided oxygen to the astronaut through an umbilical hose. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Primary Life Support System」の詳細全文を読む スポンサード リンク
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