The spacecraft is being ditched in the atmosphere of Saturn on Friday, bringing to an end 13 amazing years of discovery at the ringed planet.
The team hopes to receive a signal for as long as possible while the satellite plummets into the giant world.
But the radio will likely go dead at about 6 seconds after 04:55 local time here at mission control in California.
That is 11:55:06 GMT (12:55:06 BST). This is the time that antennas on Earth lose contact.
Because of the finite speed of light and the 1.4 billion km distance to Saturn, the event in space will actually have occurred 83 minutes earlier.
"The spacecraft's final signal will be like an echo. It will radiate across the Solar System for nearly an hour and a half after Cassini itself has gone," said Earl Maize, the US space agency's (Nasa) project manager.
"Even though we'll know that, at Saturn, Cassini has already met its fate, its mission isn't truly over for us on Earth as long as we're still receiving its signal."