Cassini Will Graze Saturn’s Rings; NASA Scientists Ready For The Mission?
On Nov. 30, 2016, Cassini -- a flagship-class NASA-ESA-ASI robotic spacecraft -- will skim the past outer edge of the Saturn rings as the initial phase of its mission since arriving there in 2004. The Science team calls the first phase of mission's dramatic endgame as "Cassini's Ring-Grazing Orbits."
According to Linda Spiker, Cassini project scientist at NASA's Jet Propulsion Laboratory, Pasadena, California, "The scientific return will be incredible. We'll be studying we just couldn't do any other place."
Phys.Org reported that Cassini will rotate high over and under the poles of Saturn, diving every seven days. This will be in a total of 20 times through the unexplored region at the outer edge of the main rings between Nov. 30, 2016 and April 22, 2017.
"In addition, we have two instruments that can sample particles and gases as we cross the ring plane, so in a sense Cassini is also 'grazing' on the rings," Spiker added.
During the numerous close passes, Cassini's instrument will try to directly sample icy ring particles and molecules of faint gases that are lingering nearly close to the rings. During the first two grazing orbits, Cassini will pass directly through an extremely faint ring produced by tiny meteors striking two small moons Janus and Epimetheus. Rings that will cross in March and April will send the spacecraft through the dusty outer reaches of the "F ring."
However, Earl Maize, Cassini project manager at JPL, said that, "Even though we're flying closer to the F ring than we have, we'll still be more than 4, 850 miles or 7,800 kilometers distant." In addition, "There's very little concern over dust hazard at that range."
Universe Today reported that, "The ultimate 'endgame' is that Cassini will plunge into Saturn with its "Grand Finale," ending the mission on September 15, 2017. Since Cassini is running out of fuel, destroying the spacecraft is necessary to ensure "planetary protection," making sure any potential microbes from Earth that may still be attached to the spacecraft don't contaminate any of Saturn's potentially habitable moons."
Furthermore, during these orbit grazing, the spacecraft will pass as close as about 56,000 miles (990,000 kilometers) above Saturn's cloud tops. Yet with all their exciting science, these orbits are only a run-up to the planet-grazing passes that lie ahead.
Cassini will begin to prepare for its Grand Finale in April 2017 wherein the spacecraft will cross as close as 1,012 miles (1,628 kilometers) above the clouds as it dives repetitively through the narrow spaces between Saturn and its rings, before making its mission-ending plunge into the planet's atmosphere on Sep. 15, 2017. Nonetheless, to prepare Cassini for its Grand Finale before it can leap over the rings, some preparatory works remain.
NASA said that Cassini is scheduled on Dec. 4 2016 to perform a brief burn of its main engine during the first close approach to the rings. This operation is vital for fine-tuning the orbit and setting the accurate course to enable the remainder of the mission.
Next, Cassini will observe Saturn's atmosphere during the orbit-grazing phase to determine how far it extends above the planet. Scientists have observed Saturn's outermost atmosphere to expand and contract slightly with the seasons since Cassini's arrival. Given this variability, the forthcoming data will be important for helping mission engineers determine how close they can safely fly the spacecraft.
"This will be the 183rd and last currently planned firing of our main engine. Although we could still decide to use the engine again, the plan is to complete the remaining maneuvers using thrusters," said Maize.