Tracking the spacecraft can be a repetitive, tedious job, and demands constant precision and accuracy.

First, the Cassini navigators release predictions (called "predicts") that determine at which angles the DSN antenna should be pointed and which radio frequencies to use for uplink and downlink. These predicts are based on past tracking experience. The navigators then gather data for several hours, tracking the spacecraft using Ranging to measure the distance to the spacecraft, and the Doppler effect to measure its speed toward or away from Earth.

Many thousands of these Ranging and Doppler data points are processed routinely to update and maintain a computer model of the spacecraft's trajectory (planned orbit to Saturn). That model is used again to provide predicts for the next tracking period, to continually acquire more data. The process repeats itself again and again, as the Cassini spacecraft made its way to Saturn and the planet's vast surrounding region.

Deep Space Station 14, a 70-meter radio telescope at the DSN's Goldstone Deep Space Communication Complex

There are occurrences when some of the tracking data is lost during specific DSN tracking periods. Fortunately however, the computer model of the spacecraft's trajectory is never compromised, and it can always be used to locate the spacecraft in the sky at the proper radio communication frequency for the next tracking period. Tracking data are sometimes lost in real time due to bad weather, since X-band radio signals from the spacecraft cannot be received through heavy rain.

Sometimes one of the many computers in the system has a glitch and causes some data loss. Equipment hardware, such as mechanical systems, hydraulic systems, cooling systems, and electrical systems can malfunction from time to time as well. Several years ago, an unfortunate desert rat caused an electrical short, disabling the DSN antenna for hours.

Most of the time tracking data serves as a beneficial statistical commodity: the more data that is received by the DSN, the the better the solution will converge. Not all data points will always converge, and there are sometimes outlying points that need to be deleted from the process.

Sometimes, a short period of tracking data can be crucial to the navigators, during maneuvers that use the spacecraft's active propulsion system. For example, during the Saturn Orbit Injection maneuver (SOI) that was scheduled to occur in July 2004, to lose even a few minutes of a critical period might have been extremely problematic for the navigators. For that reason, important maneuvers were planned so that the chance of data loss was minimized, for example by using DSN stations on two continents to track the spacecraft for a given period.

To make sense of where the spacecraft is and how fast it's moving with relation to the Sun, it is imperative to know where the Earth is, where the DSN station is, and how fast both are moving in relation to the Sun, because DSN tracking stations are of course located on a moving Earth. Nowadays, one can calculate almost precisely these measurements because of observations that the astronomical community has been refining over the course of many decades, and even centuries. They include precise longitude and latitude coordinates of each DSN station, the exact rate at which the Earth is rotating on its axis, and its speed in orbit as it revolves around the Sun. Even the tiny, slow motions of the Earth's poles caused by precession and nutation are factored in. Add precise astronomical knowledge of Saturn's motions, as well as Titan and the other Saturnian satellites, and the equation can be solved for reaching the specific targets involved in the Cassini-Huygens mission.