Reliving Cassini’s final moments: Engineers recreate spacecraft’s fatal plunge into Saturn’s atmosphere

The final full view of Saturn from Cassini, on Sept. 13, 2017. Image Credit: NASA/JPL-Caltech/Space Science Institute/Jason Major

It has been just over a month now since the Cassini spacecraft took its final plunge into Saturn’s atmosphere, ending an incredible mission of 13 years at the ringed giant planet. The probe continued collecting scientific data until the very last moments, and now engineers have been able to reconstruct what happened to it as it met its fate.

The descent into the thick atmosphere was a fiery one with Cassini being increasingly buffeted and battered by atmospheric winds. At first however, the spacecraft was gently rocking back and forth by only fractions of a degree as it made its final approach to Saturn, with only Saturn’s gravity trying to tug at and rotate Cassini.

Illustration of Cassini during its plunge into Saturn’s atmosphere. Image Credit: NASA/JPL-Caltech
Graph showing Cassini’s X- and S-band radio signals as they disappeared from mission control on Sept. 15, 2017. Image Credit: NASA/JPL-Caltech

“To keep the antenna pointed at Earth, we used what’s called ‘bang-bang control,’” said Julie Webster, Cassini’s spacecraft operations chief at NASA’s Jet Propulsion Laboratory in Pasadena, California. “We give the spacecraft a narrow range over which it can rotate, and when it bangs up against that limit in one direction, it fires a thruster to tip back the other way.”

That range was only two milliradians, equal to 0.1 degree. According to the reconstructed data, Cassini was subtly correcting its orientation until about three minutes before final loss of signal.

As Cassini plunged deeper into the atmosphere, the turbulence increased; even though the atmosphere was still tenuous, at about 1,900 kilometres (1,200 miles) above the cloud tops, it began to push against the spacecraft’s 11-metre (36-foot) long magnetometer boom. As a result, Cassini rotated slightly in the backward (aft) direction. Cassini’s thrusters fired in response, to keep the boom from rotating even more, and then began firing longer and more often.

Cassini’s last look at the ocean moon Enceladus as it sets behind the limb of Saturn on Sept. 13, 2017. Photo Credit: NASA/JPL-Caltech/Space Science Institute
Radar image of bright, wispy methane clouds seen in Titan’s northern hemisphere by Cassini on May 7, 2017. Image Credit: NASA/JPL-Caltech/Space Science Institute
One of the most incredible discoveries by Cassini – the water vapour plumes of the moon Enceladus, originating from a subsurface ocean. Photo Credit: NASA/JPL-Caltech

Cassini managed to survive for 91 seconds in this epic battle, before tipping over backward during the last eight seconds and then finally losing radio contact with Earth. The mission was over, as the probe succumbed to the increasing heat and pressure.

At one point, it kind of looked like Cassini was attempting a comeback of sorts, with the radio signal spiking briefly, before disappearing for good. But of course it wasn’t a comeback, which would be impossible.

“No, it wasn’t a comeback. Just a side lobe of the radio antenna beam pattern,” Webster said.

The highest-resolution color image ever taken of Saturn’s rings by Cassini. Photo Credit: NASA/JPL-Caltech/Space Science Institute
A historic view from Saturn, showing the distant Earth as a bright blue speck just below the rings. Photo Credit: NASA/JPL-Caltech/Space Science Institute

There was no way Cassini could have survived this death plunge, and it wasn’t meant to, but the data it collected will be invaluable to scientists and engineers, including for future missions.

“Given that Cassini wasn’t designed to fly into a planetary atmosphere, it’s remarkable that the spacecraft held on as long as it did, allowing its science instruments to send back data to the last second,” said Earl Maize, Cassini project manager at JPL. “It was a solidly built craft, and it did everything we asked of it.”

It has now been 20 years since Cassini was first launched, reaching Saturn in 2004. From that point onward, Cassini revolutionized our knowledge of Saturn and its many moons, right until the very end.

This article was first published on AmericaSpace.

 

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‘All good things’: Cassini finishes its epic mission at Saturn in a blaze of glory

A last look at Saturn: mosaic made from images taken on Sept. 13, 2017 by Cassini. Image Credit: NASA/JPL-Caltech/Space Science Institute/Jason Major

The moment that many people have been waiting for – albeit with great sadness – has finally arrived, with the Cassini spacecraft ending its mission in a literal blaze of glory. At 4:55 AM PT on Sept. 15, the long-lived explorer plummeted into Saturn’s atmosphere for its final act, bringing to a close a 13-year study of Saturn and its moons. As the saying goes, “all good things must come to an end,” and now that time has come for Cassini, which has transformed our knowledge about Saturn and its many bizarre and strange moons.

“The Cassini operations team did an absolutely stellar job guiding the spacecraft to its noble end,” said Earl Maize, Cassini project manager at JPL. “From designing the trajectory seven years ago, to navigating through the 22 nail-biting plunges between Saturn and its rings, this is a crack shot group of scientists and engineers that scripted a fitting end to a great mission. What a way to go. Truly a blaze of glory.”

The very last image of Saturn taken by Cassini before entry into the atmosphere. Image Credit: NASA/JPL-Caltech/Space Science Institute/Jason Major
Montage of infrared images showing the impact site of Cassini on Saturn. Image Credit: NASA/JPL-Caltech/Space Science Institute
A poignant farewell view of the ocean moon Enceladus setting behind the limb of Saturn on Sept. 13, 2017. Photo Credit: NASA/JPL-Caltech/Space Science Institute
One of the last raw images of Saturn’s rings, taken by Cassini on Sept. 15, 2017. Photo Credit: NASA/JPL-Caltech/Space Science Institute
Another one of the last raw images taken of the rings, from Sept. 14, 2017. Photo Credit: NASA/JPL-Caltech/Space Science Institute

Prior to meeting its fate on Saturn, Cassini also gave a “goodbye kiss” to Titan, Saturn’s largest moon. Cassini flew past Titan at a distance of 119,049 kilometres (73,974 miles), and took its final images of this enigmatic world. The spacecraft used Titan’s gravity as a final nudge to propel it on a collision course with Saturn. Cassini passed by Titan hundreds of times during its mission, sometimes very close and sometimes from a distance.

“Cassini has been in a long-term relationship with Titan, with a new rendezvous nearly every month for more than a decade,” said Maize. “This final encounter is something of a bittersweet goodbye, but as it has done throughout the mission, Titan’s gravity is once again sending Cassini where we need it to go.”

“This is the final chapter of an amazing mission, but it’s also a new beginning,” said Thomas Zurbuchen, associate administrator for NASA’s Science Mission Directorate at NASA Headquarters in Washington. “Cassini’s discovery of ocean worlds at Titan and Enceladus changed everything, shaking our views to the core about surprising places to search for potential life beyond Earth.”

A final look at Titan’s northern methane lakes and seas (raw radar image), from Sept. 12, 2017. Image Credit: NASA/JPL-Caltech/Space Science Institute

This final orbit, which brought Cassini to its entry point in Saturn’s atmosphere, is the last of 22 orbits in the Grand Final phase of the mission. Cassini may be gone, but its legacy will live on forever, and the enormous amounts of data that the probe sent back to Earth will be used by scientists for a long time to come as they continue to study Saturn, its moons and the rest of the Solar System in the years ahead.

“Things never will be quite the same for those of us on the Cassini team now that the spacecraft is no longer flying,” said Linda Spilker, Cassini project scientist at JPL. “But, we take comfort knowing that every time we look up at Saturn in the night sky, part of Cassini will be there, too. Cassini may be gone, but its scientific bounty will keep us occupied for many years. We’ve only scratched the surface of what we can learn from the mountain of data it has sent back over its lifetime.”

More information about the Cassini mission is available on the NASA and JPL websites.

This article was first published on AmericaSpace.

 

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‘The last hurrah’: Cassini prepares for fiery end of mission in one week

One of the most surreal views of Saturn from Cassini, backlit by the Sun. Photo Credit: NASA/JPL-Caltech/Space Science Institute

The end is nigh. Those really are not the words that scientists and fans of the Cassini mission at Saturn want to hear, but it’s true. After exploring Saturn and its moons since 2004, the Cassini spacecraft has now entered its final orbit around the ringed gas giant, and today will also make its last pass through the gap between Saturn and its rings. A week from now, Cassini will plunge into Saturn’s thick atmosphere, still recording data as long as it can, until it is crushed by the intense atmospheric pressure. Although the mission will be over, however, the incredible amount of science returned by Cassini will keep scientists busy for many years to come.

“The Cassini mission has been packed full of scientific firsts, and our unique planetary revelations will continue to the very end of the mission as Cassini becomes Saturn’s first planetary probe, sampling Saturn’s atmosphere up until the last second,” said Linda Spilker, Cassini project scientist from NASA’s Jet Propulsion Laboratory in Pasadena, California. “We’ll be sending data in near real-time as we rush headlong into the atmosphere – it’s truly a first-of-its-kind event at Saturn.”

The highest-resolution colour image ever taken of Saturn’s rings by Cassini. Photo Credit: NASA/JPL-Caltech/Space Science Institute
Another close-up raw image view of Saturn’s rings taken by Cassini on June 4, 2017. Photo Credit: NASA/JPL-Caltech/Space Science Institute
Another historic view from Saturn, showing the distant Earth as a bright blue speck just below the rings. Photo Credit: NASA/JPL-Caltech/Space Science Institute
A final, distant view of Enceladus and its water vapour plumes from Cassini. Photo Credit: NASA/JPL-Caltech/Space Science Institute

During the last pass between the planet and its rings, Cassini will fly only 1,680 kilometres (1,044 miles) above the clouds tops. Other milestones upcoming in the next week include one more distant flyby of the largest moon Titan as well as final distant images of Enceladus and the north polar hexagon on Saturn. On Sept. 15, 2017, the spacecraft will enter Saturn’s atmosphere, where communication will cease at about 1,510 kilometres (940 miles) above the cloud tops. After that, Cassini will break up like a brilliant meteor.

Cassini has been one of the most successful space missions in history, revolutionizing our understanding of Saturn and its many moons. It even revealed that two of those moons, Enceladus and Titan, could possible support some form of life.

On Sept. 15, 2017, Cassini will plunge into Saturn’s atmosphere, burning up like a meteor. Image Credit: NASA/JPL-Caltech

“The end of Cassini’s mission will be a poignant moment, but a fitting and very necessary completion of an astonishing journey,” said Earl Maize, Cassini project manager at NASA’s Jet Propulsion Laboratory in Pasadena, California. “The Grand Finale represents the culmination of a seven-year plan to use the spacecraft’s remaining resources in the most scientifically productive way possible. By safely disposing of the spacecraft in Saturn’s atmosphere, we avoid any possibility Cassini could impact one of Saturn’s moons somewhere down the road, keeping them pristine for future exploration.”

All of Cassini’s raw images can be seen here on the mission website.

This article was first published on AmericaSpace.

 

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Image Gallery: Sweeping view across Saturn’s rings

Image Credit: NASA/JPL-Caltech/SSI/Kevin M. Gill

This is actually from 2009, but was just posted again on Facebook and is a stunning view across Saturn’s rings as seen by the Cassini spacecraft. The level of detail is incredible as the rings are illuminated edge-on during that year’s equinox. Cassini is getting very close-up views of the rings again now as it completes its final few orbits before the mission ends on September 15. Image processing by Kevin M. Gill. Larger versions here.

 

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Cassini prepares for one last look at Titan before spectacular end of mission

Two views of Titan from Cassini, using the narrow-angle camera on March 21, 2017, revealing bright methane clouds in the thick, opaque nitrogen atmosphere, and dark dunes, lakes and seas on the surface. Natural color on left, false color on right. Image Credit: NASA/JPL-Caltech/Space Science Institute

There are now less than five orbits left in the Grand Finale until Cassini’s awe-inspiring mission at Saturn comes to an end. With each remaining orbit, Cassini comes closer to plunging into Saturn’s atmosphere, never to be heard from again. Saturn’s largest moon, Titan, assists the spacecraft during this phase of the mission, nudging on it with its gravity to keep Cassini in the right orbits for when it dives between the innermost rings and the planet itself. And now those final moments are almost here.

Cassini made many repeated flybys of Titan during its mission, 127 over 13 years, revealing it to be one of the most bizarre and incredible worlds in our Solar System, with its liquid methane/ethane rain, rivers, lakes and seas. In 2005, Cassini released the Huygens probe, which landed on Titan’s surface, sending back the first-ever images from Titan’s surface. The last close flyby was on April 22, 2017. Cassini used Titan’s gravity to help push it into the right orbits, and even to fly past other moons such as Enceladus.

“Now that we’ve completed Cassini’s investigation of Titan, we have enough detail to really see what Titan is like as a world, globally,” said Steve Wall, deputy lead of Cassini’s radar team at NASA’s Jet Propulsion Laboratory in Pasadena, California.

Previously, Cassini had seen the “magic islands,” unusual patches in some of the seas which seemed to appear and then disappear again. During the most recent flyby, none were seen again however. The features are now thought to most likely be patches of nitrogen bubbles.

NASA has also just released a new video summarizing the amazing findings that Cassini has made at Titan. Titan is a world that in some ways reminds us of Earth, yet is also utterly alien.

Raw image of bright, wispy methane clouds seen in Titan’s northern hemisphere by Cassini on May 7, 2017. Image Credit: NASA/JPL-Caltech/SSI
Radar image from Cassini of Ligeia Mare, the second-largest methane/ethane sea on Titan, near the north pole. Image Credit: NASA/JPL-Caltech/ASI/Cornell
Artist’s conception of Cassini’s final flyby of Titan on April 22, 2017. Image Credit: NASA/JPL-Caltech
The last look at Titan’s surface by Cassini’s radar, on April 22, 2017. Image Credit: NASA/JPL-Caltech/ASI

While there no more close passes of Titan awaiting Cassini, the spacecraft will get a long-distance view again on Sept. 11, just four days before the mission ends. There are still mysteries to be solved on Titan, but those will need to wait for additional future missions, being tentatively planned now, such as an orbiter, a floating probe in one of the lakes or seas or even a submersible probe. It is even conceivable that some form of primitive life could exist on Titan, but it would be unlike anything seen before on Earth.

During Cassini’s last close flyby of Titan, the radar imaged a long swath of the surface that included terrain first seen on the first Titan flyby in 2004. “It’s pretty remarkable that we ended up close to where we started,” said Steve Wall, deputy lead of Cassini’s radar team at NASA’s Jet Propulsion Laboratory in Pasadena, California. “The difference is how richly our understanding has grown, and how the questions we’re asking about Titan have evolved.”

All of Cassini’s raw images can be seen here on the mission website.

This article was first published on AmericaSpace.

 

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