To enable new science opportunities and measurements on future planetary missions, the combination of high-power active science instruments and high-power electric propulsion was investigated. Combining high-power science instruments and high-power electric propulsion on a single spacecraft has very significant benefits for planetary missions. As an example, a comet rendezvous mission was considered for combined science and propulsion. Significant mass reductions were enabled with electric propulsion systems over the current state-of-the-art chemical propulsion system. Two types of electric propulsion systems, Electron Cyclotron Resonance and ion propulsion, were considered. With electric propulsion, the launch mass of the comet spacecraft could be reduced by 2930-3270 kg or by 61-68 percent over the chemical propulsion baseline mission. In addition to enabling the mass reductions with electric propulsion, this high power spacecraft was able to deliver a significant high power radar science payload to the comet. After the high power from the solar array is used to propel the spacecraft to the comet, its power is then used for the high-power science radars. These radars were designed to detect hazardous dust and particles during the comet approach, to map the comet nucleus and to determine the nucleus' internal structure. These science experiments are currently impossible with the low power available on baseline chemical propulsion mission. Other issues that were considered in the study were the use of high power for telecommunications, on-board processing, and thermal control. An assessment of the desirability of directly integrating the hardware for the science instruments and the propulsion system was also conducted.