A 95 GHz Doppler radar prototype has been developed with a design guided by requirements for potential space flight missions to comets or icy moons of the outer planets in order to probe ice- and dust-filled jets and plumes. The radar operates in a frequency-modulated continuous-wave (FMCW) mode with a bandwidth, pulse repetition interval, and coherent integration time chosen to achieve better than 10 m range resolution, 0.1 m/s velocity resolution, 5.1 km maximum unambiguous range, and 46 m/s maximum unambiguous velocity span. With an ultra-high transmit/receive isolation exceeding 85 dB, the radar operates with thermal-noise-limited sensitivity even with 1 Watt of continuous transmit power and a 540 K noise-temperature receiver sharing a single, 15 cm diameter monostatic aperture. Experimental testing has verified the radar's range-Doppler remote sensing capabilities using a developing rain shower as a dynamic and distributed target.