One of the primary causes of material degradation in low Earth orbit (LEO) is exposure to atomic oxygen. When atomic oxygen molecules collide with an orbiting spacecraft, the relative velocity is 7 to 8 km/sec and the collision energy is 4 to 5 eV per atom. Under these conditions, atomic oxygen may initiate a number of chemical and physical reactions with exposed materials. These reactions contribute to material degradation, surface erosion, and contamination. Interpretation of these effects on materials and the design of space hardware to withstand on-orbit conditions requires quantitative knowledge of the atomic oxygen exposure environment. Atomic oxygen flux is a function of orbit altitude, the orientation of the orbit plan to the Sun, solar and geomagnetic activity, and the angle between exposed surfaces and the spacecraft heading. We have developed a computer model to predict the atomic oxygen exposure of spacecraft in low Earth orbit. The application of this computer model is discussed. Bourassa, R. J. and Gruenbaum, P. E. and Gillis, J. R. and Hargraves, C. R. Unspecified Center APPLICATIONS PROGRAMS (COMPUTERS); ATOMIC COLLISIONS; EARTH ORBITAL ENVIRONMENTS; EXPOSURE; LOW EARTH ORBITS; OXYGEN ATOMS; USER MANUALS (COMPUTER PROGRAMS); COMPUTERIZED SIMULATION; DEGRADATION; EROSION; FLUENCE; SPACECRAFT CONTAMINATION; SPACECRAFT ORBITS...