We’re mere days away from the end of NASA’s Cassini mission. The spacecraft has been exploring Saturn and its entourage of moons for more than a decade, but the time has come to execute the “Grand Finale.” In the early morning on Friday (September 15th), the final signals will be sent by Cassini as it falls into Saturn’s atmosphere. All the pieces are in place to track Cassini during its final maneuver, including a giant communication facility in Australia, which will receive Cassini’s data in real time.
NASA began the Grand Finale back in April with a course correction that sent Cassini spiraling in toward the gas giant. It was able to observe the rings and upper atmosphere during these orbits, which were deemed too dangerous when the probe wasn’t nearing the end of its life. Of course, Cassini could continue to operate for years, but it’s nearly out of fuel. With no way to control the craft, it may eventually crash on one of Saturn’s moons, and NASA wants to avoid contaminating those environments.
There is a handy “end of mission” timeline on the NASA JPL website, which includes the expected time of various events over the coming days. It has a live countdown to Cassini’s final plunge into Saturn. The exact times may change as contact with Saturn’s atmosphere slows the probe down, but the current target for loss of signal is 4:55 AM PDT on Friday. NASA has three ground stations for its Deep Space Network, one each in California, Spain, and Australia. Only the Australian station will be pointed the right way, so that’s where Cassini’s last message will be received.
The Canberra Deep Space Communication Complex (CDSCC) is located on the outskirts of Canberra, and is operated by Australia’s Commonwealth Scientific and Industrial Research Organisation (CSIRO). The complex has four massive antenna dishes, the largest measuring 70 meters (229 feet). The CDSCC provides two-way communication with dozens of active NASA missions, including Cassini.
One of the CDSCC antennas.
Cassini usually stores its data and sends it back to Earth in bursts to save power. However, the Grand Finale will be a little different. Cassini is currently scheduled to take its last photos of Saturn on September 14th (in the afternoon, US time). These images will be transmitted immediately, and the probe will maintain a continuous communication link for the next 14-15 hours until it disappears forever.
CDSCC expects to receive data from Cassini at 27 kilobits per second as it drops into Saturn. The spacecraft will fire its thrusters at 100 percent in an attempt to keep the antenna pointed at Earth, but eventually it will tumble into the atmosphere, and CDSCC will lose the signal forever.