Author Topic: Cassini's Grand Finale  (Read 2151 times)

BridgeTroll

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Cassini's Grand Finale
« on: April 05, 2017, 07:55:48 AM »
Where were you on October 15 1997?  Cassini was launched to Saturn on that day...

http://www.popularmechanics.com/space/solar-system/a25949/this-is-how-nasas-saturn-orbiter-will-die/

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This is How NASA's Saturn Orbiter Will Die
NASA announces the final mission for the incredible Cassini spacecraft.
By Avery Thompson
Apr 4, 2017

NASA's Cassini orbiter has done a hero's work since arriving at Saturn in 2004, but the aging spacecraft is reaching the end of its life. Cassini rapidly running out of fuel, so NASA scientists have to decide what kind of funeral to give it. Today, NASA has revealed many details of Cassini's final mission, what NASA is calling Cassini's "Grand Finale." According to NASA, the spacecraft will follow a series of orbits that bring it between Saturn and its rings until finally it will plunge into the planet's atmosphere and die.

It might not seem like a fitting end to such an important spacecraft, but retiring Cassini this way is important to avoid accidentally crashing on one of Saturn's moons. Some of these moons—like Enceladus with its underground water oceans and Titan with its methane lakes and rivers—could potentially be home to primitive extraterrestrial life, and we can't risk contaminating them with the microbes on Cassini.

Instead, the Grand Finale will safely dispose of Cassini by sending it into Saturn's atmosphere. But first, Cassini will make 22 flybys of the planet in the narrow region between Saturn and its rings, which has never been done before. In the process it will collect mountains of unique data that could revolutionize our view of Saturn.

This mission does come with some risk, which is why NASA waited until the very end before undertaking it. Some material from Saturn's rings is always falling toward the surface of the planet, and at the speeds Cassini is traveling, a particle the size of a grain of sand could seriously damage the spacecraft. A really bad impact could destroy individual instruments or disable or destroy the entire craft.

NASA hopes this doesn't happen, and their current understanding of Saturn and its rings predicts that it won't. NASA gives the mission about a 98 percent chance of success, and is prepared for the loss of any equipment. Even if Cassini is completely lost, its trajectory will send it into Saturn anyway so there's no risk to Titan or Enceladus.

And if the mission is successful, there's a great deal we could learn. For starters, these orbits will bring Cassini closer to Saturn's rings than it has ever been, so it will be able to study their age and composition. There's also a chance that Cassini could grab the first ever photograph of one of the individual rocks that make up the rings.

Beyond that, Cassini will spend its remaining time studying Saturn itself, including its atmosphere and magnetic fields. Cassini will learn how deep Saturn's surface winds extend into the planet, the composition and size of Saturn's core, and even how long a day actually lasts on Saturn, which can only be observed from looking at the wobble in Saturn's magnetic field. Because the rings actually block much of Saturn's magnetic field, this mission gives Cassini the first real chance to study them in depth.

After 22 orbits, Cassini will plunge into Saturn's atmosphere on September 15. The thick atmosphere will disintegrate the spacecraft, but before that happens Cassini will record everything it experiences and transmit as much of it as possible back to Earth. In the final few minutes, Cassini will give us its last few bits of data before going out in a literal blaze of glory. And here on Earth we'll have gained an invaluable trove of Saturn's secrets that scientists will study for decades.

<a href="https://www.youtube.com/v/xrGAQCq9BMU?ecver=1" target="_blank" class="new_win">https://www.youtube.com/v/xrGAQCq9BMU?ecver=1</a>

In a boat at sea one of the men began to bore a hole in the bottom of the boat. On being remonstrating with, he answered, "I am only boring under my own seat." "Yes," said his companions, "but when the sea rushes in we shall all be drowned with you."

Tacachale

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Re: Cassini's Grand Finale
« Reply #1 on: April 05, 2017, 10:07:06 AM »
Hmm, October 1997? I was presumably watching the Star Wars Trilogy Special Edition on VHS and probably lamenting the decline of The Simpsons after the release of the shark-jumping episode "The Principal and the Pauper". The next few episodes were better but the show was never the same again.
Do you believe that when the blue jay or another bird sings and the body is trembling, that is a signal that people are coming or something important is about to happen?

spuwho

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Re: Cassini's Grand Finale
« Reply #2 on: April 05, 2017, 10:16:59 AM »
I remember the protests down at the Cape because Cassini had the largest RTG ever sent into space at the time.

I was working in downtown Chicago. Chris Farley died not long after.

BridgeTroll

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Re: Cassini's Grand Finale
« Reply #3 on: April 05, 2017, 10:25:09 AM »
Hmm, October 1997? I was presumably watching the Star Wars Trilogy Special Edition on VHS and probably lamenting the decline of The Simpsons after the release of the shark-jumping episode "The Principal and the Pauper". The next few episodes were better but the show was never the same again.

Rofl... I remember the protests erupting over its launch...

http://www.cnn.com/TECH/9710/04/cassini/
http://articles.latimes.com/1997/sep/22/news/mn-35078


In a boat at sea one of the men began to bore a hole in the bottom of the boat. On being remonstrating with, he answered, "I am only boring under my own seat." "Yes," said his companions, "but when the sea rushes in we shall all be drowned with you."

BridgeTroll

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Re: Cassini's Grand Finale
« Reply #4 on: April 27, 2017, 02:44:02 PM »
http://www.npr.org/sections/thetwo-way/2017/04/26/525696238/cassini-spacecraft-starts-weaving-between-saturn-and-its-rings

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Cassini Spacecraft Starts Weaving Between Saturn And Its Rings
April 26, 20179:13 AM ET
BILL CHAPPELL

If all goes to plan, NASA's Cassini spacecraft will beam new images of Saturn and its rings to Earth early Thursday, sharing data collected Wednesday from its first dive through the gap between the planet and its striped belt of ice and rock particles.

Today's dive also marks the start of the final phase in the craft's 13-year visit to Saturn. Days ago, it used the gravity of Saturn's moon Titan to bend its path toward its eventual destruction on the planet.

Cassini descended below the ring plane around 5 a.m. ET Wednesday, but the antenna it would normally use to send images is instead being used to deflect potentially harmful objects away from its instruments. As it performed the move, the craft's Twitter feed announced, "Shields Up!"

Shields Up! As we pass over #Saturn, we're turning our high-gain antenna into a shield RIGHT NOW to deflect oncoming ring particles. pic.twitter.com/kAxzY53uwT
— CassiniSaturn (@CassiniSaturn) April 26, 2017
"Because that gap is a region no spacecraft has ever explored, Cassini will use its dish-shaped high-gain antenna (13 feet or 4 meters across) as a protective shield while passing through the ring plane," NASA says. "No particles larger than smoke particles are expected, but the precautionary measure is being taken on the first dive."

For today's maneuver, the craft crossed the ring plane as it moved from north to south across Saturn. The gap between Saturn and its rings is about 1,500 miles wide.

Cassini is expected to get back in touch with the Deep Space Network antenna in Goldstone, Calif., by around 3 a.m. ET Thursday; the first images should be available shortly afterward, NASA says.

The move is the first in what NASA is calling Cassini's Grand Finale, as it weaves its way between Saturn and its rings in a series of 22 dives that will culminate in what the agency describes as "a science-rich plunge into Saturn's atmosphere on Sept. 15."

Cassini was launched in 1997; its mission is slated to end one month before the 20-year mark.

Among the photos sent back by Cassini is a unique view of Earth as seen from Saturn, in what was hailed as a new perspective of our "pale blue dot" in space.

When that image was released in 2013, the Two-Way wrote, "Earth and all its trillions of creatures are seen as a speck of light — lower right — in the vastness of space. What's more, Cassini captures Earth while also capturing Saturn's rings."
In a boat at sea one of the men began to bore a hole in the bottom of the boat. On being remonstrating with, he answered, "I am only boring under my own seat." "Yes," said his companions, "but when the sea rushes in we shall all be drowned with you."

BridgeTroll

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Re: Cassini's Grand Finale
« Reply #5 on: September 01, 2017, 02:07:12 PM »
15 days left...

http://www.airspacemag.com/daily-planet/cassinis-last-moments-gory-detail-180964648/

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Cassini’s Last Moments, in Gory Detail
For NASA’s Saturn explorer, the end will come quickly.

By Bruce Lieberman
airspacemag.com
August 29, 2017

Cassini’s remaining life is now measured in days.

On September 11, four days before NASA’s veteran Saturn explorer plunges into the planet’s atmosphere, the spacecraft will whip around the hazy moon Titan in a slingshot maneuver that will seal its fate.

During these final days, Cassini will take one last look around. Onboard cameras will snap pictures of Titan and its hydrocarbon lakes, Saturn’s innermost rings, the bizarre hexagon-shaped jet stream at Saturn’s north pole, and other targets. On the evening of September 14, Cassini will send this last photo album to Earth, about 1.4 billion kilometers away, and the engineers at NASA’s Jet Propulsion Laboratory in Pasadena will post them online.

After that, no more pictures will be taken. But seven other instruments will continue to gather data on the chemical composition of Saturn’s atmosphere, its gravity and magnetic fields, its innermost radiation belts, and its rings—for as long as they can. “We’ll be transmitting the science data back almost as fast as we gather it,” says Tom Burk, Cassini’s attitude control team lead.

The scientists and engineers who operate Cassini have long known the end was coming, because they planned it. After 13 years in orbit around Saturn, the spacecraft’s fuel is running low, and rather than risk an uncontrolled crash into Titan or the icy moon Enceladus, NASA decided to steer it into Saturn’s atmosphere.

The last orbit begins with a final pass over Saturn’s northern hemisphere in the early morning hours of September 15. Descending at 34 kilometers per second, or about 76,000 mph, toward the equator, the spacecraft will dip into the upper atmosphere and remain in daylight, above Saturn’s ring plane, until the very end.

The planet doesn’t have a solid surface, so JPL flight engineers use another marker to track the spacecraft’s descent:  the point at which Saturn’s atmospheric pressure is equal to sea level pressure on Earth, a place they call “1-bar.” That’s about 60,000 km, or just over 37,000 miles, from the giant planet’s center.

Cassini will first “feel” the wispy hydrogen in the planet’s hydrogen-helium atmosphere around 1,700 kilometers above that point, however, where Saturn’s air is 100 billion times thinner than at the 1-bar level. Since Cassini will be moving fast, the transition from the vacuum of space to the atmosphere should be detectable. This initial atmospheric entry is expected to happen at 3:30 a.m. Pacific Time on September 15. As aerodynamic forces begin to tug at the spacecraft, which is 22 feet high and about 13 feet wide, its hydrazine thrusters will begin firing to keep its antenna oriented toward Earth.

By the time Cassini drops to 1,200 km above 1-bar, aerodynamic drag will overwhelm the thrusters’ ability to keep the antenna locked on Earth. As the spacecraft begins to tumble, contact will be lost and the mission will officially end. “The thrusters were never designed to maintain attitude control in the stratosphere of Saturn,” Burk says with a laugh. Between one and two minutes will pass from the time Cassini enters the atmosphere to the time contact is lost.

The Final Minutes

After that, Cassini’s demise will come quickly, probably within four minutes.

NASA may pick up some increases in temperature when Cassini first starts to feel the atmosphere, says Brett Pugh, Cassini’s thermal engineer, who has modeled what is expected to happen during the spacecraft’s last moments. But it’s more likely that gradual heating will be first detected a little lower than that, at 1,600 km—particularly at the spacecraft’s leading edge and its main engine.

At 1,400 km, heating of the spacecraft due to the bombardment of individual molecules in Saturn’s atmosphere is expected to be about 1,400 watts per square meter. That’s akin to the warmth we feel from sunshine on Earth. But once Cassini starts tumbling, its temperature will climb dramatically—about 50- to 100-fold each minute.

The spacecraft will likely lose its multilayer insulation first, as it chars and breaks away. Because Saturn’s upper atmosphere is mostly hydrogen, Cassini won’t technically burn up as it would above Earth. Instead, a front of electrically charged gas, or plasma, will glow at its leading edge.

At 1,100 km above 1-bar, the large dish antenna and 36-foot-long magnetometer boom will weaken, melt and break off. At 800 km, other external components will begin disintegrating, followed by the spacecraft structure itself at 700 km.

At 600 to 700 km above 1-bar, Cassini’s fuel tanks are expected to explode from a buildup of pressure. On this final day, only about 60 kilograms of propellant and oxidizer will be left in the tanks (compared to 3,000 kg when it launched in 1997). Another 30 kilograms of hydrazine fuel that supplies Cassini’s thrusters will remain in a third tank.

“Once a tank explodes, it’ll probably take out the tank next to it, so you might get a burst of flame at that point if the propellant and oxidizer mix,” Pugh says. “Seconds after that, there will be nothing left.”

Cassini won’t likely flame across Saturn’s sky like a shooting star; without oxygen in Saturn’s atmosphere, there will be no combustion. Nevertheless, Cassini will experience temperatures approaching the surface of the sun, about 10,000 degrees Fahrenheit.

By the time it reaches about 350 km above 1-bar, the same altitude that the International Space Station orbits Earth, Cassini will be no more. Back on Earth, Cassini’s flight engineers expect to receive Cassini’s final radio transmission at 4:54 a.m. on September 15—nearly an hour and a half after NASA’s Saturn explorer will have passed into history.


Read more at http://www.airspacemag.com/daily-planet/cassinis-last-moments-gory-detail-180964648/#I1hU3YgBrfBK6J14.99
In a boat at sea one of the men began to bore a hole in the bottom of the boat. On being remonstrating with, he answered, "I am only boring under my own seat." "Yes," said his companions, "but when the sea rushes in we shall all be drowned with you."

BridgeTroll

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Re: Cassini's Grand Finale
« Reply #6 on: September 15, 2017, 01:40:54 PM »
Cassini is gone...  :-\

http://www.popularmechanics.com/space/solar-system/news/a28216/cassini-spacecraft-burns-up-in-saturns-atmosphere/

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The Cassini Spacecraft Burns Up In Saturn's Atmosphere
The ringed planet has been this spacecraft's home for more than 13 years, and today we bid farewell to one of the greatest missions in the history of NASA.

For about 60 seconds, Cassini used the last reserves of its rocket fuel to fire its thrusters, fighting the upper atmosphere of Saturn as it descended to its fate. After receiving a "goodbye kiss" from Titan on September 11—a gravitational sling from the large moon to put the spacecraft on the correct trajectory—Cassini hurled toward Saturn one last time at roughly 75,000 mph, on a collision course to plunge into the planet itself and burn up in the high clouds. The loyal craft fought all the way down to keep its antenna pointed toward Earth, beaming back the final bits of precious science data until the bitter end.

"Who knows how many PhD theses might be in just those final seconds of data," says Linda Spilker, Cassini Project Scientist.

Those final seconds of data represent the first ever direct sampling of Saturn's atmosphere, giving scientists unprecedented information about the makeup of the planet. It's an amazing opportunity to make a new discovery at the ringed world, something Cassini has been doing consistently for 13 years in orbit. From water erupting on the surface of Enceladus, to liquid methane flowing on Titan, to a great atmospheric storm that encircled the planet, and tantalizing clues about the age of Saturn's rings, Cassini has discovered more wonders than anyone could have guessed.

"In 2004, we never dreamt we'd be here in 2017 still talking about Cassini and collecting science data," said Todd Barber, Cassini Propulsion Engineer.

NASA's flagship mission to Saturn has captivated the world, reinvigorating the wonder that only space exploration can bring—the possibility of life beyond Earth, the enormity of the firmament and our place within it.

"The signal of the spacecraft is gone and within the next 45 seconds, so will be the spacecraft," Cassini Program Manager Earl Maize announced in the control room.

Farewell Cassini, a little piece of Earth in the skies of Saturn.
In a boat at sea one of the men began to bore a hole in the bottom of the boat. On being remonstrating with, he answered, "I am only boring under my own seat." "Yes," said his companions, "but when the sea rushes in we shall all be drowned with you."