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 asa
gravitational shape, scientists and researchers can
deduce information about its internal structure.
The Deep Space Network was developed by and is
managed by NASA's Jet Propulsion Laboratory
(JPL) in Southern California. The antennas of the
Deep Space Network are the indispensable link to
robotic explorers venturing beyond Earth. They
provide the crucial connection for commanding
our spacecraft and receiving never-before-seen
images and scientific information on Earth,
propelling our understanding of the universe, our
solar system and ultimately, our place within it.
JPL manages the Deep Space Network for the
Space Communications and Navigation (SCaN)
Program, based at NASA Headquarters within the
Space Operations Mission Directorate.