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xx Cassini's Death March
« Thread started on: Apr 12th, 2017, 1:44pm »

Saturn Spacecraft Begins Science Swan-song

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NASA’s Cassini probe will go where no spacecraft has gone before — between a planet and its rings.

Alexandra Witze
12 April 2017

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Scientists still debate the age and origin of Saturn’s rings, but the Cassini craft’s final months promise to tell us more about their provenance. (NASA/JPL)

After 13 years exploring Saturn and its moons, NASA’s Cassini spacecraft has just 5 months left to live. But it will go out with a scientific bang.

On 22 April, Cassini will slingshot past Titan, Saturn’s largest moon, for the last time. Four days later, the probe will hurtle into the unexplored region between the giant planet and its rings. Cassini will thread that 2,400-kilometre-wide gap 22 times before its kamikaze dive into Saturn’s atmosphere on 15 September.

This unprecedented journey promises to yield fresh discoveries for the venerable spacecraft. “It will be like a whole new mission,” says Linda Spilker, Cassini’s project scientist at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California. “There are fundamental new scientific measurements to make.”

Those include the first direct tastes of particles in Saturn’s rings, and of its upper atmosphere; the best measurements yet of the planet’s magnetic and gravitational fields, which could answer long-standing questions such as how fast the planet rotates and how old its rings are; and the sharpest look yet at enigmatic ripples in the rings.

It all begins with the spacecraft’s final fly-by of Titan, the 127th such close encounter. Cassini will scan the moon’s methane lakes one last time, looking for waves, bubbles or other phenomena roiling the surface. Earlier fly-bys have revealed changes in the lakes over time, and the final pass is the last chance to look for seasonal shifts, says Sarah Hörst, a planetary scientist at Johns Hopkins University in Baltimore, Maryland.

Titan’s gravitational pull will fling Cassini into its ‘grand finale’ orbits, plunging between Saturn’s innermost ring and the planet’s cloud tops (see ‘Cassini: the final frontier’). The spacecraft will turn its main antenna forward, to act as a protective shield against any errant ring particles as it whizzes along at 110,000 kilometres per hour.

Since November, the probe has been climbing higher relative to Saturn’s equatorial plane, providing a new vantage point on the planet’s outer rings. The upcoming inner dives will also reveal spectacular new details, says Carolyn Porco, a planetary scientist at the University of California, Berkeley, who leads the mission’s imaging team.

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High-resolution photographs will capture the mysterious propeller-shaped gaps that ripple through some of the rings, probably formed by unseen moonlets. “The rings really are changing before our eyes,” says Jeffrey Cuzzi, a planetary scientist at NASA’s Ames Research Center in Moffett Field, California.

Cassini’s remote-sensing instruments will get their closest look yet at the rings, on sides both lit and unlit by the Sun. Measurements will show how the chemical make-up of the ring particles varies from place to place — information that is crucial for researchers who are trying to tease out which compounds pollute the rings’ otherwise pure ice.

And scientists might finally unravel the rings’ biggest mystery — how old they are and how they formed. Between May and July, Cassini will make its most precise measurements of Saturn’s gravitational field; by tracking the spacecraft’s motion as it flies between the planet and the rings, mission scientists expect to improve their calculations of the mass of the rings by an order of magnitude. A relatively high mass would suggest that the rings were ancient, perhaps formed by a big moon ripped apart billions of years ago. Lighter-weight rings would suggest a more recent formation, perhaps from a visiting comet that disintegrated.

Other fundamental measurements will tackle the giant planet itself. On the grand-finale orbits, Cassini’s magnetometer will measure Saturn’s magnetic field close to the planet. There, it is roughly ten times stronger — and more complex and scientifically interesting — than in areas already probed, says Marcia Burton, a planetary scientist at JPL.

Those data should shed light on long-standing mysteries such as the depth of Saturn’s metallic hydrogen core — which powers its magnetic field — and how quickly the planet rotates. Observations by the Voyager spacecraft in the 1980s suggested that one rotation takes just under 11 hours. But the numbers are different when measured in the northern and southern hemispheres, which hints that something more complicated is going on. “It is hard to imagine how the grand-finale orbits could not lead to a huge improvement in our understanding of Saturn’s magnetic field,” Burton says.

On 15 September, with its tanks almost out of fuel, mission controllers will steer Cassini directly into Saturn. But the craft will still radio back observations of the gases that make up Saturn’s atmosphere. “Even in its final moments, Cassini will be doing groundbreaking science,” says Hörst.

http://www.nature.com/news/saturn-spacecraft-begins-science-swan-song-1.21813?WT.ec_id=NEWSDAILY-20170412

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xx Re: Cassini's Death March
« Reply #1 on: Apr 12th, 2017, 1:59pm »


One of the final command codes was sent yesterday, I do believe.


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xx Re: Cassini's Death March
« Reply #2 on: Apr 15th, 2017, 03:08am »

I think I posted about Saturn's moon 'Pan'. Here is another interesting one. cool

Cassini See's 'Flying Saucer' Moon Atlas Up Close



https://www.nasa.gov/feature/jpl/cassini-sees-flying-saucer-moon-atlas-up-close
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xx Re: Cassini's Death March
« Reply #3 on: Apr 17th, 2017, 01:03am »

I want to see HiRes Miranda photos!
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xx Re: Cassini's Death March
« Reply #4 on: Apr 17th, 2017, 01:09am »

Oh! Wrong planet! laugh
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« Reply #5 on: Apr 17th, 2017, 01:19am »

Say, while I was looking around for HiRes photos of Saturn's moons, I came upon the JPL site where you can download HiRes TIFF files;

https://photojournal.jpl.nasa.gov/new

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xx Re: Cassini's Death March
« Reply #6 on: Apr 26th, 2017, 11:25am »


It's between the rings. We'll find out soon whether or not it survived this pass.....


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« Reply #7 on: Apr 27th, 2017, 09:59am »

Cassini Saturn Probe Survives 1st 'Grand Finale' Dive

By Mike Wall, Space.com Senior Writer
April 27, 2017

NASA's Cassini spacecraft has survived its first plunge through the narrow gap between Saturn's cloud tops and the giant planet's innermost rings, a region that no probe had ever explored before.

The space agency's Deep Space Network Goldstone Complex in California picked up Cassini's signal at 11:56 p.m. PDT yesterday (April 26; 2:56 a.m. EDT and 0656 GMT today, April 27) — nearly a full day after the historic dive took place. Data began coming in from the probe 5 minutes after contact was established, NASA officials said.

"In the grandest tradition of exploration, NASA's Cassini spacecraft has once again blazed a trail, showing us new wonders and demonstrating where our curiosity can take us if we dare," Jim Green, director of NASA's Planetary Science Division, in Washington, D.C., said in a statement.

Read more: http://www.space.com/36630-cassini-saturn-spacecraft-survives-grand-finale-dive.html

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« Reply #8 on: May 2nd, 2017, 11:43am »

Cassini finds ‘big empty’ near Saturn

By Deborah Byrd in Space
May 2, 2017

It’s not totally empty, but the space between Saturn and its rings is much emptier than scientists expected. Cassini will make its 2nd dive through this gap at 3:38 p.m. EDT (19:38 UTC) today.

There’s much less dust between Saturn and its inner rings than expected, said NASA engineers, after last week’s historic dive through this gap by the Cassini spacecraft. Astronomers have been contemplating this maneuver by a spacecraft for decades, since the two Voyager spacecraft passed Saturn in the early 1980s. The fear was that a spacecraft might encounter debris that would suddenly end its mission! But Cassini – which is running out of fuel after orbiting Saturn since 2004 – not only passed through the gap successfully but also found it surprising debris-free. Cassini Project Manager Earl Maize of NASA’s Jet Propulsion Laboratory in Pasadena, California said:

The region between the rings and Saturn is ‘the big empty,’ apparently. Cassini will stay the course, while the scientists work on the mystery of why the dust level is much lower than expected.

Cassini will make its second dive through the gap today (May 2, 2017) at 12:38 p.m. PDT (3:38 p.m. EDT, 19:38 UTC; translate UTC to your time zone)

With information from the first dive in hand, the Cassini team will now move forward with its preferred plan of science observations. NASA said:

A dustier environment in the gap might have meant the spacecraft’s saucer-shaped main antenna would be needed as a shield during most future dives through the ring plane. This would have forced changes to how and when Cassini’s instruments would be able to make observations. Fortunately, it appears that the “plan B” option is no longer needed. (There are 21 dives remaining. Four of them pass through the innermost fringes of Saturn’s rings, necessitating that the antenna be used as a shield on those orbits.)

Based on images from Cassini, models of the ring particle environment in the approximately 1,200-mile-wide (2,000-kilometer-wide) region between Saturn and its rings suggested the area would not have large particles that would pose a danger to the spacecraft.

But because no spacecraft had ever passed through the region before, Cassini engineers oriented the spacecraft so that its 13-foot-wide (4-meter-wide) antenna pointed in the direction of oncoming ring particles, shielding its delicate instruments as a protective measure during its April 26 dive.

The video below represents data collected by Cassini’s Radio and Plasma Wave Science instrument, as it crossed through the gap between Saturn and its rings on April 26. The instrument is able to record ring particles striking the spacecraft in its data. In the data from this dive, there is virtually no detectable peak in pops and cracks that represent ring particles striking the spacecraft. The lack of discernible pops and cracks indicates the region is largely free of small particles. William Kurth, RPWS team lead at the University of Iowa, Iowa City said:

It was a bit disorienting — we weren’t hearing what we expected to hear. I’ve listened to our data from the first dive several times and I can probably count on my hands the number of dust particle impacts I hear.

The team’s analysis suggests Cassini only encountered a few particles as it crossed the gap — none larger than those in smoke (about 1 micron across).

Today’s ring crossing will occur in a region very close to where Cassini passed on last week’s dive. Prior to today’s crossing, Cassini’s cameras have been looking closely at the rings; in addition, the spacecraft was rotated (or “rolled”) faster than engineers have ever allowed it to before, in order to calibrate the magnetometer.

As with the first finale dive, Cassini will be out of contact during closest approach to Saturn, and is scheduled to transmit data from this dive on May 3.

Bottom line: During its April 26, 2017 dive between Saturn and its rings – its first of 22 dives in its Grand Finale this year – the Cassini spacecraft found a relatively dust-free region. Scientists are calling it The Big Empty.

http://earthsky.org/space/cassini-saturn-big-empty-2nd-dive-grand-finale?utm_source=EarthSky+News&utm_campaign=181009ec56-EarthSky_News&utm_medium=email&utm_term=0_c643945d79-181009ec56-394368745&mc_cid=181009ec56&mc_eid=9b2daed519

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xx Re: Cassini's Death March
« Reply #9 on: May 28th, 2017, 08:31am »

It must be fun to sit around and wait...... tongue




Cassini Takes Most Dangerous Saturn Ring Dive Yet

By Sarah Lewin, Staff Writer
May 28, 2017

The Cassini spacecraft completes its sixth dive between Saturn and its rings today (May 28), and this is the most dangerous dive yet. Instead of passing safely between the planet and its rings, the spacecraft is plunging straight through the inner edge of Saturn's D ring.

The spacecraft, which is a collaboration between NASA, the European Space Agency and the Italian Space Agency, will turn its broad, high-gain antenna dish to rest in front of it as a shield during the crossing, for the first time since its very first ring dive, which occurred in April, NASA officials said. (For that dive, researchers didn't know whether the area between the rings and Saturn would be clear of debris.)

This dive is the first of four paths through the planet's faint innermost ring, and it's the deepest Cassini will go into the dusty loop, according to NASA's Grand Finale Orbit Guide. The spacecraft will make the crossing at 10:22 a.m. EDT (1422 GMT), but researchers don't expect to hear back from it until 11:29 p.m. EDT (0329 on May 29 GMT) once it is able to turn and reestablish contact with Earth.

Researchers have identified the 6-minute period when Cassini is most likely to collide with ring particles. During this time, the spacecraft's Radio and Plasma Wave Science instrument will be poised to detect the plasma clouds released when particles hit the antenna dish. The instrument sticks out past the dish, letting it take stock of particles while the rest of the craft is protected, the guide said.

During this orbit around Saturn, Cassini has been taking photos of the edge of the planet's A and F rings, as well as the space between, to investigate the rings' structure and how their particles interact. It also used the Radar instrument to scan all the way from the A ring's outer edge through the C ring, in the first of a three-part radio-wave experiment.

Cassini's next dive will also take it through the edge of the D ring, although not as far, and it will have two more opportunities after that to get firsthand experience of the planet's ephemeral innermost ring.

After Cassini completes all 22 ring dives, it will begin the final phase of its Grand Finale mission: plummeting into Saturn's atmosphere on Sept. 15 in its most dangerous (and fatal) dive of all. The spacecraft will send data back until it loses contact and burns up; the maneuver will protect Saturn's moons from any further contamination by Earth microbes and collect invaluable details about the planet's atmosphere in its last moments.

But in the meantime, Cassini has lots of science to do.

http://www.space.com/37010-cassini-most-dangerous-ring-dive-yet.html

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