Apollo Portable Life Support System (PLSS)

The "backpack" worn by Apollo crewmen while performing extravehicular activities was called the "Portable Life Support System" or PLSS.

The PLSS was a compact assembly of various environmental control devices which supplied breathing oxygen; controlled suit pressure; recirculated oxygen after removing CO₂, odors, moisture, and trace contaminant gases; controlled temperature; provided warnings of certain system malfunctions; and provided voice communications and data telemetry.

The PLSS was ordinarily topped with an "Oxygen Purge System", or OPS. The OPS was an emergency backup system for the PLSS, providing oxygen in case the PLSS should fail. The OPS consisted of two interconnected, spherical, high-pressure oxygen bottles (each containing approximately 2 pounds of usable oxygen at 5880±500 psi), an automatic temperature control module, a pressure regulator, a battery, an oxygen connector, and the necessary checkout instrumentation. The OPS also provided the hard mount for the PLSS VHF antenna.

Unlike the PLSS, which was jettisoned shortly after the mission's final EVA, the OPS was retained, should it become necessary to perform an emergency LM-to-CM EVA transfer. On Apollo 15 through Apollo 17, the OPS was also used by the Command Module Pilot when he performed the trans-Earth EVA to retrieve the film cassette from the lunar mapping camera located in the SIM bay located in Sector 1 of the Service Module.

The PLSS, along with the suit itself, essentially formed a wearable spaceship for the astronaut.

The interior components of the PLSS were protected by a hardcover which was then wrapped in layers of Betacloth, making it look rather plain and ordinary, but as seen here, the PLSS was a complex device.