Survey of capabilities and applications of accurate clocks: directions for planetary science

For planetary science, accurate clocks are mainly used as part of an onboard radioscience transponder. In the case of two-way radio data, the dominating data type for planetary radioscience, an accurate spacecraft clock is not necessary since the measurements can be calibrated using high-precision clocks on Earth. In the case of one-way radio data, however, an accurate clock can make the precision of one-way radio data be comparable to the two-way data, and possibly better since only one leg of radio path would be affected by the media. This article addresses several ways to improve observations for planetary science, either by improving the onboard clock or by using further variants of the classical radioscience methods, e.g., Same Beam Interferometry (SBI). For a clock to be useful for planetary science, we conclude that it must have at least a short-time stability (< 1,000 s) better than 10^−13 and its size be substantially miniaturized. A special case of using laser ranging to the Moon and the implication of having an accurate clock is shown as an example.