NASA’s Cassini spacecraft is on final approach to Saturn,
following confirmation by mission navigators that it is on
course to dive into the planet’s atmosphere on Friday, Sept.
Cassini is ending its 13-year tour of the Saturn system with an
intentional plunge into the planet to ensure Saturn’s moons –
in particular Enceladus, with its subsurface ocean and signs of
hydrothermal activity – remain pristine for future exploration.
The spacecraft’s fateful dive is the final beat in the
mission’s Grand Finale, 22 weekly dives, which began in late
April, through the gap between Saturn and its rings. No
spacecraft has ever ventured so close to the planet before.
The mission’s final calculations predict loss of contact with
the Cassini spacecraft will take place on Sept. 15 at 7:55 a.m.
EDT (4:55 a.m. PDT). Cassini will enter Saturn’s atmosphere
approximately one minute earlier, at an altitude of about 1,190
miles (1,915 kilometers) above the planet’s estimated cloud
tops (the altitude where the air pressure is 1-bar, equivalent
to sea level on Earth). During its dive into the atmosphere,
the spacecraft’s speed will be approximately 70,000 miles
(113,000 kilometers) per hour. The final plunge will take place
on the day side of Saturn, near local noon, with the spacecraft
entering the atmosphere around 10 degrees north latitude.
Animation showing Cassini’s orbits around Saturn during the
mission’s final phase, called the Grand Finale. Credit:
When Cassini first begins to encounter Saturn’s atmosphere, the
spacecraft’s attitude control thrusters will begin firing in
short bursts to work against the thin gas and keep Cassini’s
saucer-shaped high-gain antenna pointed at Earth to relay the
mission’s precious final data. As the atmosphere thickens, the
thrusters will be forced to ramp up their activity, going from
10 percent of their capacity to 100 percent in the span of
about a minute. Once they are firing at full capacity, the
thrusters can do no more to keep Cassini stably pointed, and
the spacecraft will begin to tumble.
When the antenna points just a few fractions of a degree away
from Earth, communications will be severed permanently. The
predicted altitude for loss of signal is approximately 930
miles (1,500 kilometers) above Saturn’s cloud tops. From that
point, the spacecraft will begin to burn up like a meteor.
Within about 30 seconds following loss of signal, the
spacecraft will begin to come apart; within a couple of
minutes, all remnants of the spacecraft are expected to be
completely consumed in the atmosphere of Saturn.
Due to the travel time for radio signals from Saturn, which
changes as both Earth and the ringed planet travel around the
Sun, events currently take place there 86 minutes before they
are observed on Earth. This means that, although the spacecraft
will begin to tumble and go out of communication at 6:31 a.m.
EDT (3:31 a.m. PDT) at Saturn, the signal from that event will
not be received at Earth until 86 minutes later.
“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, Cassini
project manager at NASA’s Jet Propulsion Laboratory (JPL) in
Pasadena, California. “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.”
Cassini’s last transmissions will be received by antennas at
NASA’s Deep Space Network complex in Canberra, Australia.
Cassini is set to make groundbreaking scientific observations
of Saturn, using eight of its 12 science instruments. All of
the mission’s magnetosphere and plasma science instruments,
plus the spacecraft’s radio science system, and its infrared
and ultraviolet spectrometers will collect data during the
Chief among the observations being made as Cassini dives into
Saturn are those of the Ion and Neutral Mass Spectrometer
(INMS). The instrument will directly sample the composition and
structure of the atmosphere, which cannot be done from orbit.
The spacecraft will be oriented so that INMS is pointed in the
direction of motion, to allow it the best possible access to
oncoming atmospheric gases.
For the next couple of days, as Saturn looms ever larger,
Cassini expects to take a last look around the Saturn system,
snapping a few final images of the planet, features in its
rings, and the moons Enceladus and Titan. The final set of
views from Cassini’s imaging cameras is scheduled to be taken
and transmitted to Earth on Thursday, Sept. 14. If all goes as
planned, images will be posted to the Cassini mission website
beginning around 11 p.m. EDT (8 p.m. PDT). The unprocessed
images will be available at:
Live mission commentary and video from JPL Mission Control will
air on NASA Television from 7 to 8:30 a.m. EDT (4 a.m. to 5:30
a.m. PDT) on Sept. 15. A post-mission news briefing from JPL is
currently scheduled for 9:30 a.m. EDT (6:30 a.m. PDT), also on
NASA TV is available online at:
A new NASA e-book, The Saturn System Through the Eyes of
Cassini, showcasing compelling images and key science
discoveries from the mission, is available for free download in
multiple formats at:
An online toolkit of information and resources about Cassini’s
Grand Finale and final plunge into Saturn is available at:
Follow the Cassini spacecraft’s plunge on social media using
#GrandFinale, or visit:
The Cassini-Huygens mission is a cooperative project of NASA,
ESA (European Space Agency) and the Italian Space Agency. JPL,
a division of Caltech in Pasadena, manages the mission for
NASA’s Science Mission Directorate, Washington. JPL designed,
developed and assembled the Cassini orbiter.
More information about Cassini:
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