Sheck Exley tests the Cis-Lunar MK1 prototype rebreather, December 11, 1987. Weighing a whopping 205 pounds (93 kg) the unit was not considered "portable" and had to be wheeled into the spring on a dolly, yet underwater it was neutrally buoyant. The unit had outrageous "range" and was also fully redundant, meaning it contained two complete rebreathers within the one backpack. Shortly before this dive Bill Stone used the rig to conduct a 24 hour dive in Wakulla Basin. Only one half of the rig was used for this dive, meaning that a 2-day underwater mission could have been carried out. This was the first rebreather to utilize multiple, redundant computer systems for electronic control of the life support backpack. It was also the first rebreather to use lithium hydroxide to remove carbon dioxide from the breathing loop and contained novel concepts to permit the safe use of that material [photo ©1998 Wes Skiles].
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