Multiple-bit upsets were observed in two types of memories operating in the radiation environment of space. They have been categorized according to their orbital location, amount of shielding and upset multiplicity. The mechanisms responsible have been identified from ground testing of identical memories using both energetic ions and pulsed laser light. With the aid of bit-maps (generated with the pulsed laser) multiple-bit upsets could, in most cases, be attributed to one of three mechanisms, i.e., charge diffusion away from an ion strike, an ion strike to control circuitry, and an ion track intersecting a number of memory cells. Heavy-ion strikes to peripheral circuits on the memory chip generated multiple-bit upsets involving as many as twenty-one cells. Proton-induced multiple-bit upset rates have been calculated for the spacecraft orbit, and the results show good agreement with measured rates.