How NASA Uses Gravity and Radio Waves to Study Planets and Moons

The Deep Space Network, NASA’s international collection of giant radio antennas used to communicate with spacecraft at the Moon and beyond, helps scientists and engineers use gravity and radio science experiments to learn more about our planetary neighborhood.

After reaching a spacecraft reaches its destination, it uses radio antennas to communicate with the Deep Space Network, which in turn transmits radio signals back to the spacecraft. Every spacecraft travels in a predetermined path emitting radio signals as it orbits around its target. Scientists and engineers can infer the spacecraft's location and how fast it's going by measuring changes in the spacecraft's radio signal frequency. This is made possible by the Doppler effect, the same phenomenon that causes a siren to sound different as it travels towards and away from you.

The Doppler phenomenon is observed here when the spacecraft and the Deep Space Network antenna move in relation to each other. Differences between the frequency of radio signals sent by the spacecraft as it orbits and signals received on Earth give us details about the gravitational field of a planetary body. For example, if the gravity is slightly stronger, the spacecraft will accelerate slightly more. If gravity is slightly weaker, the spacecraft will accelerate slightly less. By developing a model of the planetary body's gravitational field, which can be mapped as a gravitational shape, scientists and researchers can deduce information about its internal structure.