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Loading contentMeasuring a spacecraft's distance and velocity from its radio signal — range from the round-trip signal time, and line-of-sight velocity from the Doppler shift. Combined over time from the ground stations, these fix a spacecraft's trajectory across the Solar System.
Facts on this topic will be cited from these primary and reference sources.
Mission data, planetary science, space telescopes, and public-domain imagery.
Most NASA-produced imagery is in the public domain; individual items are checked for usage terms before publication.
Orbital data, ephemerides, and small-body parameters for planets, asteroids, and comets.