A detailed, two-dimensional, laminar, flame spread model over a thin solid is solved in both a normal gravity downward spread configuration and in a microgravity quiescent atmosphere configuration. The radiation transfer equation is solved using discrete ordinates methods. While flame radiation plays only a secondary role in normal gravity spread, it is crucial in microgravity. By using the solid fuel total emittance and total absorptance as parameters, systematic computations have been performed to isolate the roles of flame radiative loss to the ambient, absorption of flame radiation by the solid and solid emission. Computations show that depending on the values of the solid radiation parameters, trend reversals in spread rate and extinction limits between flames in normal gravity and in microgravity can occur.