Portable Life Support System (PLSS) oxygen recharge safety cap, measuring 1.25″ in diameter and 1″ tall, used on the lunar surface by Dave Scott for a total of 18 hours and 35 minutes during his three lunar EVAs. The metal cap, engraved with part numbers, “SNC 4599-17, Ser No 2,” was used to cover the PLSS oxygen port while conducting the moonwalks to prevent the port from contamination; this was critical as the port was was used to recharge the oxygen supply after each EVA. In fine condition.
Accompanied by a signed letter of provenance from Scott, in part: “I hereby certify that the Apollo 15 PLSS-LM Oxygen Recharge Safety Cap included with this letter was an integral part of the PLSS that I used during the three periods of Extra Vehicular Activity (EVA) on the surface of the Moon during the first extended scientific exploration of the Moon, July 26–August 7, 1971…This cap provided two vital safety functions: (1) preventing a leak from the PLSS O2 supply; and (2) protecting the PLSS O2 connection from contamination due to lunar dust during the EVA. After each EVA, the primary oxygen subsystem of the PLSS is refilled (recharged) from the Lunar Module (LM) oxygen (O2) system through a leak-proof, self-sealing, quick-disconnect till connector. As shown in the diagram and photos below, the recharge port is located on the lower right side of the PLSS beneath a beta cloth flap that was opened to expose the port. After EVA reentry into the LM, the cap is removed, the LM O2 supply is connected for recharge after which the cap was replaced…This safety cap was attached to my PLSS during our three EVAs for a total of 18 hours and 35 minutes outside on the surface of the Moon…This PLSS Oxygen Recharge Safety Cap has been in my personal collection since returning to Earth.”
