As part of the NASA Planetary Science Summer School 2010, the Ganymede Interior, Surface and Magnetosphere Observer (GISMO) team developed a robotic mission to Ganymede, one of Jupiter's icy moons. This process included the formulation of the science objectives and the selection of a payload tailored to meet these goals. The team then designed a mission architecture aimed toward achieving the science objectives. Using a sequence of 14 flybys of Ganymede, the vehicle would use a simple, staged operation of the science payload. This timeline allows for a simplified design, with relatively low risk and cost. Principle challenges included the finite power available to the vehicle, along with a limited data downlink rate. Otherwise, this preliminary design would meet all mission requirements, as determined by the science goals, and within the allocated cost cap.