The spaceflight technique that uses Doppler shifts in radio signals to determine a spacecraft’s velocity is Doppler tracking.
A spacecraft transmits, or coherently retransmits, a radio carrier that is received by a ground station. If the craft is moving toward the station, the received frequency is shifted upward; if it is moving away, the frequency is shifted downward. Measuring that change gives the spacecraft’s line-of-sight, or radial, velocity relative to Earth.
Doppler tracking is a core part of radiometric navigation. NASA’s Deep Space Network combines Doppler data with ranging, which measures signal travel time, and angular measurements that indicate where the spacecraft appears in the sky. Doppler alone does not directly reveal every component of three-dimensional motion, so flight teams collect measurements over time and fit them to an orbit model. The technique has guided probes across the Solar System and also supports radio-science experiments involving planetary atmospheres, rings, and gravity fields. It is distinct from photometry, triangulation, and radar ranging, although those methods may complement it.