Precision of Radio Science Instrumentation for Planetary Exploration

Radio Science techniques have been used for planetary exploration, space physics, and experiments addressing aspects of relativity on many deep space missions. Various Radio Science experiments are also planned for many future missions. This paper presents the noise processes in the Radio Science data acquired by the Deep Space Network and provides a detailed noise model for Doppler radio science experiments. The most sensitive instrumentation and experiments to date achieve fractional frequency fluctuation noise of 3E-15 at an integration time of 1000 seconds, corresponding to better than 1 micron per second velocity noise. Our noise model focuses on the Fourier range in the millihertz to 1 Hz, but we briefly discuss noise in lower frequency observations. We identify phenomena limiting current Doppler sensitivity and discuss prospects for significant sensitivity improvements.