The objective of this study was to characterize the effects of the space environment on the engineering properties and chemistry of a chemically modified T300/934 graphite-epoxy composite system. The material was subjected to 1.0 x 10¹⁰ rads of 1.0 MeV electron irradiation under vacuum to simulate 30 years in geosynchronous earth orbit. Monotonic tension tests were performed at room temperature (75° F /24° C) and elevated temperature (250° F/121° C) on 4-ply unidirectional laminates. From these tests, in-plane engineering and strength properties (E₁, E₂, ν₁₂, G₁₂, X_T, Y_T) were determined. Cyclic tests were also performed to characterize energy dissipation changes due to irradiation and elevated temperature. Large diameter graphite fibers were tested to determine the effects of radiation on the stiffness and strength of graphite fibers. No significant changes were observed. Dynamic-mechanical analysis demonstrated that the glass transition temperature was lowered by 50° F (28° C) after irradiation. Thermomechanical analysis showed the occurrence of volatile products generated upon heating of the irradiated material. The chemical modification of the epoxy did not aid in producing a material which was more “radiation resistant" than the standard T300/934 graphite-epoxy system. Irradiation was found to cause crosslinking and chain scission in the polymer. The latter produced low molecular weight products which plasticize the material at elevated temperatures and cause apparent material stiffening at low stresses at room temperature. / M.S.