Ridgetop will demonstrate the feasibility of developing a radiation-hardened analog-to-digital converter (ADC) suitable for the Jupiter Europa Orbiter mission. This proposal responds to topic S1.09, In-Situ Sensors and Sensor Systems for Planetary Science. With this innovation, the ADC will be hardened to significantly higher levels of radiation (5 Mrads) than currently existing ADCs, and its performance will still clearly exceed the performance of ADCs used previously on NASA planetary missions. The ADC will have 12-bit resolution, 125 MSPS sampling speed, and low 150 mW power consumption. The ADC will be designed on the IBM 8HP 130 nm silicon germanium (SiGe) fabrication process, which has been shown to be tolerant to very high levels of total ionizing dose (TID) radiation and suitable for wide temperature range operation. At the end of Phase 1, the proven mixed-signal circuits will provide momentum to create an radiation-hardened, transistor-level ADC design in a follow-on SBIR Phase 2 Program, in which the ADC will be fabricated in the IBM 8HP 130 nm BiCMOS SiGe process and tested.