"Ace" is the call sign used on the voice-net for the Mission Controller. The Ace's main responsibility is to monitor the ground data system and the spacecraft during the periods when the Deep Space Network is tracking the spacecraft. The Ace is also responsible for correcting problems that sometimes occur with the hundreds of computers, programs, data files and processes that enable the flight team to communicate with the Cassini spacecraft.

The Ace also verifies that the ground data system is obtaining the important information needed by the navigation team to determine the spacecraft's speed and trajectory. This data type is known as tracking data.

The Ace actually sends the commands to the spacecraft, but the determination of what commands to send is made in processes involving other teams long before the commands are actually sent.

Typically, the Ace sends the spacecraft one quick command to make sure the two-way communications link is operating properly. When the spacecraft receives this command, it resets a timer on board. If this timer, called the Command Loss Timer, ever reaches a predetermined value, it will cause the spacecraft to make the assumption that something is wrong since it hasn't heard from Earth for a long time. At this point, the spacecraft will begin taking corrective actions such as swapping radio receivers.

Commands that the Ace sends have been arranged into files known as command sequences. It is the Ace's job to make sure these sequences are radioed to the spacecraft, and to make sure the spacecraft has received literally every one of the commands in perfect order. In the rare instances when the spacecraft misses a command or a part of a command, the Ace will re-send the missing part(s) and then verify that the whole sequence is properly installed aboard the spacecraft.