This paper describes a novel integrated optic spacesuit atmospheric quality sensor to enhance astronaut safety by monitoring the spacesuit's closed environment. The integrated optic sensor (IOS) is made of self-calibrating miniaturized channel waveguide elements that monitor oxygen concentration in real time. Fabrication employs direct photolithographic writing of channel waveguides onto a photoactive porous glass matrix. The active channel waveguide is doped with an oxygen-sensitive fluorescent indicator. A compact phase fluorometer measures relative fluorescence lifetime -- a direct function of the oxygen partial pressure. In testing, the IOS chip demonstrated a response time of 5 seconds from 0% to 100% oxygen at STP.