NASA's Cassini spacecraft will be entering new territory in its final mission phase – Grand Finale. Cassini will be getting extremely close to Saturn's upper atmosphere and explore the final five orbits of the ringed planet.
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Here are the top 7 things to know about Cassini's final journey during the Grand Finale:
1. The spacecraft will make the first flybys of Saturn's five rings on 14 August, Monday at 9:55 am IST (12:22 am EDT). The closest proximity of Cassini will be between 1,630 and 1,710 kilometres (1,010 and 1,060 miles) above the cloud tops.
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2. Cassini is likely to enter Saturn's environment which will be thick enough and would require the small rocket thrusters of the spacecraft to maintain their stability, just like in the close flybys made by the Cassini in Saturn's largest moon Titan's dense atmosphere.
3. "Cassini's Titan flybys prepared us for these rapid passes through Saturn's upper atmosphere," said Earl Maize, Cassini project manager at NASA's Jet Propulsion Laboratory (JPL) in California, according to NASA statement. "Thanks to our past experience, the team is confident that we understand how the spacecraft will behave at the atmospheric densities our models predict."
4. According to Cassini project manager Maize, the pass taking place on 14 August will be considered as nominal if the thrusters of the spacecraft operate between 10 to 60 percent of their ability. The altitude of the preceding orbits will be increased by the engineers if the thrusters are forced to work harder as it would point toward the atmosphere being denser. The altitude of closest approach will be raised to around 200 kilometres (120 miles) using "pop-up maneuver," thrusters in the next passes.
5. Not requiring the pop-up maneuver would mean that the atmosphere is not thicker than expected during the initial three passes. The engineers can use the "pop-down" option to lower the closest approach altitude to a height of around 200 kilometres (120 miles) of the spacecraft during the last two orbits. This would aid Cassini's ions and neutral mass spectrometer (INMS) to accumulate data about the atmosphere from the closer cloud tops of the planet.
"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. "It's long been a goal in planetary exploration to send a dedicated probe into the atmosphere of Saturn, and we're laying the groundwork for future exploration with this first foray."
6. Detailed high-resolution observations of Saturn's temperature, vortexes at planet's poles and its auroras will be made by Cassini's other instruments. The radar of the spacecraft will examine the atmosphere closely to an extent that it can capture features that are up to (25 kilometres) 16 miles wide, which is around 100 times tinier than Cassini could study before the Grand Finale Mission.
7. A distant encounter with Saturn's moon Titan will take place on 11 September, which would 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 toward its 15 September plunge into the planet.
A NASA statement revealed that during the half-orbit plunge, the plan is to have seven Cassini science instruments, including INMS, turned on and reporting measurements in near real time. The spacecraft is expected to reach an altitude where atmospheric density is about twice what it encountered during its final five passes. Once Cassini reaches that point, its thrusters will no longer be able to work against the push of Saturn's atmosphere to keep the spacecraft's antenna pointed toward Earth, and contact will permanently be lost. The spacecraft will break up like a meteor moments later, ending its long and rewarding journey.
