NASA's Cassini spacecraft is set to start off on its final mission-five ultra-close orbits around Saturn on 13 August 2017.
The mission would be the spacecraft’s last before it plunges into the atmosphere of the ringed planet, bringing an end to its epic 20-year-long journey.
• Cassini will make the first of the five close passes over Saturn at 9:22 p.m on 13 August.
• The spacecraft's point of closest approach to Saturn during these passes will be between about 1,630 and 1,710 kilometres above Saturn's cloud tops.
• The spacecraft is expected to encounter atmosphere dense enough to require the use of its small rocket thrusters to maintain stability.
• The conditions experienced by the spacecraft would be similar to those encountered by it during many of its close orbits of Saturn’s moon Titan, which has its own dense atmosphere.
Speaking on the mission, Earl Maize, Cassini project manager at NASA's Jet Propulsion Laboratory said that the spacecraft’s many passes over Titan helped them prepare for these rapid passes through Saturn’s upper atmosphere.
"Thanks to our past experience, the team is confident that we understand how the spacecraft will behave at the atmospheric densities our models predict.” said Maize.
He further added that the team will consider 14 August pass nominal if the thrusters operate between 10 and 60 percent of their capability. If the thrusters are forced to work harder, meaning the atmosphere is denser than models predict, then the engineers will increase the altitude of the subsequent orbits.
"As it makes these five dips into Saturn, followed by its final plunge, Cassini will become the first Saturn atmospheric probe," said Linda Spilker, Cassini project scientist at JPL. She further added that it has long been a goal in planetary exploration to send a dedicated probe into the atmosphere of Saturn and with this mission they would be laying the groundwork for future exploration.
Unique Data Collection
The close passes would enable Cassini's science instruments, especially the ion and neutral mass spectrometer (INMS), to obtain data on the atmosphere even closer to the planet's cloud tops.
Other Cassini instruments will make detailed, high-resolution observations of Saturn's auroras, temperature and the vortexes at the planet's poles.
The spacecraft’s radar will dig deep into the atmosphere to reveal small-scale features as fine as 25 kilometers wide, nearly 100 times smaller than the spacecraft could observe prior to the Grand Finale.
• On 11 September 2017, a distant encounter with Saturn’s moon Titan will serve as a gravitational version of a large pop-down maneuver, slowing Cassini's orbit around Saturn and bending its path slightly to send the spacecraft towards its final plunge into the planet.
• The final plunge would take place on 15 September. It would happen mid way during its orbit.
• At the moment, all the seven Cassini science instruments, including INMS would be turned on, enabling them to report measurements in near real time.
• The spacecraft is expected to reach an altitude where the atmospheric density would be about twice of what it encountered during its final five passes.
• Once Cassini reaches that point, its thrusters would no longer be able to work against the push of Saturn's atmosphere to keep the spacecraft's antenna pointed towards Earth and all contact will be lost.
• Moments later, the spacecraft will break up like a meteor, ending its 20-year-long journey.
When: 13 August 2017