Stone Aerospace has developed several generations of real-time partial pressure oxygen control systems for PLSS backpacks. These form the heart of any PLSS and ECLSS system for both spacesuits and spacecraft as well as underwater breathing apparatus. Our embedded firmware runs on triply redundant processors, any one of which can independently run the control system. The system generally runs in open-loop mode (oxygen addition only) since there are only a small number of abort scenarios that exist where ascending PO2 would be of concern -- and those only occur underwater where very specific, alternate remedial actions are required to be executed by the user (as opposed to a fully closed control system wasting precious diluent gas in a futile effort to remedy a situation where O2 was free-flowing into the system e.g.).

That said, the control system is sophisticated and employs a fuzzy logic approach to adaptive oxygen control that will maintain a tight deadband on PO2 regardless of metabolic workload. Our system is programmable on-the-fly during a mission and the real-time PO2 level is ported to the onboard decompression engine, which can be used for both underwater as well as spacecraft EVA applications where the suit pressure is operating at less than cabin pressure. We will develop on-spec systems for customers, including fully-closed designs.

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