NASA reconstructs Cassini’s last seconds

Nearly a month after NASA’s Saturn-faring spacecraft made its final plunge into the planet’s hostile atmosphere, scientists have reconstructed the final moments before all signals were lost.

The new analysis of Cassini’s data reveals how the craft behaved as it plunged into the ringed planet it had studied for the past 13 years – and, the team says it ‘did everything we asked of it.’

The data show Cassini used gentle pulsations as planned, to keep its antenna pointed at Earth in the hour before atmospheric entry.

Then, once it broke through, it began a ‘battle with Saturn’ to keep its instruments in the right direction, lasting 91 seconds against the harsh environment before its ‘voice’ finally disappeared.

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The new analysis of Cassini’s data reveals how the craft behaved as it plunged into the ringed planet it had studied for the past 13 years. While the data appear to show a quick ‘comeback, the experts say this is not the case. Instead, the apparent spike comes as the Cassini’s unfocused radio signal rotated into view as it tumbled

‘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.

‘We give the spacecraft a narrow range over which it can rotate, and when it bands up against that limit in one direction, it fires a thruster to tip back the other way.’

About an hour before Cassini entered the atmosphere, it began subtly rocking back and forth with a range of just .1 degree as it carried out its thruster pulsations every few minutes.

Then, only a slight tug from Saturn’s gravity was working against it.

Once it reached about 1,200 miles (1,900 kilometers) above the cloud tops, it began its entry. 

As the craft approached Saturn’ its 36-foot-long (11-meter) magnetometer boom was pointed out from its side.

The gas in the harsh atmosphere, however, then began to push against this instrument like a lever, pushing it backward.

To work against this, Cassini had to fire its corrective gas jets, using its thrusters for longer, and more frequent pulses.

In Saturn’s atmosphere, Cassini fired its thrusters at a near constant rate for 91 seconds as it fought to hold its own.

Nearly a month after NASA¿s Saturn-faring spacecraft made its final plunge into the planet¿s hostile atmosphere, scientists have reconstructed the final moments before all signals were lost. An artist's impression is pictured 

Nearly a month after NASA¿s Saturn-faring spacecraft made its final plunge into the planet¿s hostile atmosphere, scientists have reconstructed the final moments before all signals were lost. An artist's impression is pictured 

Nearly a month after NASA’s Saturn-faring spacecraft made its final plunge into the planet’s hostile atmosphere, scientists have reconstructed the final moments before all signals were lost. An artist’s impression is pictured 

CASSINI’S DISCOVERIES IN ITS 20-YEAR MISSION

Cassini launched from Cape Canaveral, Florida in 1997, then spent seven years in transit followed by 13 years orbiting Saturn.

In 2000 it spent six months studying Jupiter before reaching Saturn in 2004.

In that time, it discovered six more moons around Saturn, three-dimensional structures towering above Saturn’s rings, and a giant storm that raged across the planet for nearly a year.

On 13 December 2004 it made its first flyby of Saturn’s moons Titan and Dione.

On 24 December it released the European Space Agency-built Huygens probe on Saturn’s moon Titan to study its atmosphere and surface composition.

There it discovered eerie hydrocarbon lakes made from ethane and methane.

In 2008, Cassini completed its primary mission to explore the Saturn system and began its mission extension (the Cassini Equinox Mission).

In 2010 it began its second mission (Cassini Solstice Mission) which lasted until it exploded in Saturn’s atmosphere.

In December 2011, Cassini obtained the highest resolution images of Saturn’s moon Enceladus.

In December of the following year it tracked the transit of Venus to test the feasibility of observing planets outside our solar system.

In March 2013 Cassini made the last flyby of Saturn’s moon Rhea and measured its internal structure and gravitational pull.

In July of that year Cassini captured a black-lit Saturn to examine the rings in fine detail and also captured an image of Earth.

In April of this year it completed its closest flyby of Titan and started its Grande Finale orbit which finished on September 15.

‘The mission has changed the way we think of where life may have developed beyond our Earth,’ said Andrew Coates, head of the Planetary Science Group at Mullard Space Science Laboratory at University College London.

‘As well as Mars, outer planet moons like Enceladus, Europa and even Titan are now top contenders for life elsewhere,’ he added. ‘We’ve completely rewritten the textbooks about Saturn.’

Then, in the last 20 seconds, it pushed its thrusters to 100 percent capacity.

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According to NASA, the data show the spacecraft began to slowly tumble backward in the final eight seconds.

This pushed its narrowly focused radio signal away from Earth; 83 minutes later, due to the travel time from Saturn, the signal disappeared from the monitors at mission control.

The telemetry data was first to go, according to NASA.

Then, 24 seconds later, there was silence from the spacecraft, as the radio carrier signal disappeared too.

While the data appear to show a quick ‘comeback, the experts say this is not the case.

Instead, the Cassini’s unfocused radio signal rotated into view as it tumbled.

‘No, it wasn’t a comeback,’ Webster said.

‘Just a side lobe of the radio antenna beam pattern.’

From a view of Enceladus setting behind Saturn, to the site where Cassini would make its impact, the new images show just what the spacecraft observed leading up to its demise. Its last image, pictured, is a monochrome look toward Saturn¿s night side, light by sunlight reflected from the planet¿s rings

From a view of Enceladus setting behind Saturn, to the site where Cassini would make its impact, the new images show just what the spacecraft observed leading up to its demise. Its last image, pictured, is a monochrome look toward Saturn¿s night side, light by sunlight reflected from the planet¿s rings

From a view of Enceladus setting behind Saturn, to the site where Cassini would make its impact, the new images show just what the spacecraft observed leading up to its demise. Its last image, pictured, is a monochrome look toward Saturn’s night side, light by sunlight reflected from the planet’s rings

Cassini took its last dive on September 15, but the craft has left a legacy of data for scientists to comb through in the months to come.

‘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.’ 

A week after Cassini’s dramatic ‘death dive’ into Saturn’s atmosphere, NASA released the craft’s final images, revealing stunning last looks at the ringed planet and its mysterious moons.

From a view of Enceladus setting behind Saturn, to the site where Cassini would make its impact, the images show just what the spacecraft observed leading up to its demise.

Cassini circled the planet for 13 years, helping to transform our understanding of the gas giant – and, thanks to its observations, scientists now know two of its moons have potential to host simple life.

Space enthusiast Jason Major used some of Cassini's final images to stitch together a stunning composite of Saturn (pictured) as Cassini began its final dive toward the planet

Space enthusiast Jason Major used some of Cassini's final images to stitch together a stunning composite of Saturn (pictured) as Cassini began its final dive toward the planet

Space enthusiast Jason Major used some of Cassini’s final images to stitch together a stunning composite of Saturn (pictured) as Cassini began its final dive toward the planet

The spacecraft also captured detailed images of Saturn¿s rings, even revealing a look at the small moon Daphnis and the waves it causes in the Keeler Gap, as seen above. The image was captured on September 13

The spacecraft also captured detailed images of Saturn¿s rings, even revealing a look at the small moon Daphnis and the waves it causes in the Keeler Gap, as seen above. The image was captured on September 13

The spacecraft also captured detailed images of Saturn’s rings, even revealing a look at the small moon Daphnis and the waves it causes in the Keeler Gap, as seen above. The image was captured on September 13

In the breathtaking series of photos, NASA shows some of Cassini’s final observations.

Its last image, the space agency reveals, is a monochrome look toward Saturn’s night side, light by sunlight reflected from the planet’s rings.

There, Cassini entered Saturn’s atmosphere just hours later, to embark on its mission-ending plunge.

The spacecraft also captured detailed images of Saturn’s rings, even revealing a look at the small moon Daphnis and the waves it causes in the Keeler Gap.

In photo, a lone ‘propeller’ can be seen.

These are the features created by small moonlets in the rings, as they attempt to open gaps in the ring material, according to NASA.

Space enthusiast Jason Major used some of Cassini’s final images to stitch together a stunning composite of Saturn as Cassini began its final dive toward the planet.

‘Here’s a mosaic of Saturn made from raw images acquired by Cassini on Sept. 13, 2017, as it was on its way toward its dive into the planet’s atmosphere,’ he said in a post on Flickr.

‘These images are uncalibrated for color but were acquired in visible-light RGB filters.’

A week after its dramatic ¿death dive¿ into Saturn¿s atmosphere, NASA has released Cassini¿s final images, revealing stunning last looks at the ringed planet and its mysterious moons. Its last look at the giant moon Titan, on Sept 13, is shown

A week after its dramatic ¿death dive¿ into Saturn¿s atmosphere, NASA has released Cassini¿s final images, revealing stunning last looks at the ringed planet and its mysterious moons. Its last look at the giant moon Titan, on Sept 13, is shown

A week after its dramatic ‘death dive’ into Saturn’s atmosphere, NASA has released Cassini’s final images, revealing stunning last looks at the ringed planet and its mysterious moons. Its last look at the giant moon Titan, on Sept 13, is shown

Cassini circled the planet for 13 years, helping to transform our understanding of the gas giant ¿ and, thanks to its observations, scientists now know two of its moons have potential to host simple life. One of these is the icy moon Enceladus, seen setting behind Saturn in the image above

Cassini circled the planet for 13 years, helping to transform our understanding of the gas giant ¿ and, thanks to its observations, scientists now know two of its moons have potential to host simple life. One of these is the icy moon Enceladus, seen setting behind Saturn in the image above

Cassini circled the planet for 13 years, helping to transform our understanding of the gas giant – and, thanks to its observations, scientists now know two of its moons have potential to host simple life. One of these is the icy moon Enceladus, seen setting behind Saturn in the image above

The Cassini spacecraft may be gone, but the remarkable observations gathered over the craft’s 13-year mission will continue to reveal new insights on Saturn and the mysterious worlds orbiting it for some time to come.

Just days after the dramatic conclusion to the craft’s mission, NASA released a stunning Cassini observation of the planet’s ‘yin-and-yang moon,’ Iapetus.

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The photo is one of Cassini’s last looks at the 914-mile-wide moon, revealing the striking dichotomy of its surface, long known to be bright on one side and dark on the other. 

The strange moon is Saturn’s third-largest satellite.

In photo, a lone ¿propeller¿ can be seen (pictured) These are the features created by small moonlets in the rings, as they attempt to open gaps in the ring material, according to NASA

In photo, a lone ¿propeller¿ can be seen (pictured) These are the features created by small moonlets in the rings, as they attempt to open gaps in the ring material, according to NASA

In photo, a lone ‘propeller’ can be seen (pictured) These are the features created by small moonlets in the rings, as they attempt to open gaps in the ring material, according to NASA

This false-color ‘farewell’ view combines individual frames captured with filters sensitive to ultraviolet, green, and infrared light, according to NASA, and looks toward the Saturn-facing hemisphere of Iapetus.

For centuries, scientists have questioned Iapetus’ unusual ‘yin-yang’ appearance.

But, thanks to Cassini, they may have solved the mystery of its contrasted surface.

‘Cassini observations of Iapetus support the prevailing theory that led to the understanding that the dichotomy of the surface is due to a combination of infalling dust from outside of the moon followed by a migration of water ice from the darker (therefore warmer) areas to the cold, brighter surfaces,’ NASA explains.

In the breathtaking series of photos, NASA shows some of Cassini¿s final observations. This photo, captured on Sept 13, shows a stunning look at Saturn's rings

In the breathtaking series of photos, NASA shows some of Cassini¿s final observations. This photo, captured on Sept 13, shows a stunning look at Saturn's rings

In the breathtaking series of photos, NASA shows some of Cassini’s final observations. This photo, captured on Sept 13, shows a stunning look at Saturn’s rings

As it glanced around the Saturn system one final time, Cassini spacecraft captured view of the giant moon Titan, using its narrow-angle camera on Sep 13

As it glanced around the Saturn system one final time, Cassini spacecraft captured view of the giant moon Titan, using its narrow-angle camera on Sep 13

As it glanced around the Saturn system one final time, Cassini spacecraft captured view of the giant moon Titan, using its narrow-angle camera on Sep 13

The breathtaking image above was captured by Cassini on Sept 13, and shows a look at Saturn's northern hemisphere

The breathtaking image above was captured by Cassini on Sept 13, and shows a look at Saturn's northern hemisphere

The breathtaking image above was captured by Cassini on Sept 13, and shows a look at Saturn’s northern hemisphere

Cassini captured this last look at Iapetus on May 30, from roughly 1.5 million miles away. 

NASA’s Cassini mission came to a ‘bittersweet’ conclusion early Friday morning, as the historic spacecraft plunged into Saturn’s atmosphere to become one with the gas giant planet it had studied for 13 years.

As mission scientists said their farewells to the craft and prepare to examine its final observations, footage emerged of the dramatic moment Cassini first lifted off 20 years ago, to embark on its ‘billion mile trek to Saturn.’

The breathtaking footage takes us back to the Cape Canaveral launchpad on October 15, 1997, as mission control counts down to the start of a journey that brought an ‘incredible wealth of discoveries.’ 

Just days after the dramatic conclusion to the craft¿s mission, NASA has released a stunning new observation of the planet¿s ¿yin-and-yang moon,¿ Iapetus. For centuries, scientists have questioned Iapetus¿ unusual ¿yin-yang¿ appearance. But, thanks to Cassini, they may have solved the mystery of its contrasted surface

Just days after the dramatic conclusion to the craft¿s mission, NASA has released a stunning new observation of the planet¿s ¿yin-and-yang moon,¿ Iapetus. For centuries, scientists have questioned Iapetus¿ unusual ¿yin-yang¿ appearance. But, thanks to Cassini, they may have solved the mystery of its contrasted surface

Just days after the dramatic conclusion to the craft’s mission, NASA has released a stunning new observation of the planet’s ‘yin-and-yang moon,’ Iapetus. For centuries, scientists have questioned Iapetus’ unusual ‘yin-yang’ appearance. But, thanks to Cassini, they may have solved the mystery of its contrasted surface

As mission scientists say their farewells to the craft and prepare to examine its final observations, footage has emerged of the dramatic moment Cassini first lifted off 20 years ago, to embark on its 'billion mile trek to Saturn'

As mission scientists say their farewells to the craft and prepare to examine its final observations, footage has emerged of the dramatic moment Cassini first lifted off 20 years ago, to embark on its 'billion mile trek to Saturn'

The breathtaking footage takes us back to the Cape Canaveral launchpad on October 15, 1997

The breathtaking footage takes us back to the Cape Canaveral launchpad on October 15, 1997

As mission scientists say their farewells to the craft and prepare to examine its final observations, footage has emerged of the dramatic moment Cassini first lifted off 20 years ago, to embark on its ‘billion mile trek to Saturn’

Cassini launched in 1997 from Cape Canaveral Air Force Station in Florida, bringing it past Venus (twice), Earth, and Jupiter on its way to Saturn.

But, it would be many years – and a billion miles – before it reached its target.

‘We have cleared the tower, and the Cassini spacecraft is on its way to Saturn,’ mission control can be heard saying in the 20-year-old footage, as the rocket breaks through the clouds.

The spacecraft arrived to Saturn in 2004, marking the start of its historic 13-year mission studying the planet and its moons.

‘This is the final chapter of an amazing mission, but it’s also a new beginning,’ Thomas Zurbuchen, associate administrator for NASA’s Science Mission Directorate at NASA Headquarters in Washington, said as the space agency marked the end of Cassini’s mission.

‘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.’

After 20 years in space, Cassini spacecraft finally completed its suicide mission at 7:56 a.m. (ET) Friday, plunging into Saturn’s atmosphere.

While we were unable to see Cassini’s dying moments, an animation released by NASA reconstructs the probe’s last few minutes as it tumbled through Saturn’s atmosphere at 77,000mph

'We have cleared the tower, and the Cassini spacecraft is on its way to Saturn,' mission control can be heard saying in the 20-year-old footage, as the rocket breaks through the clouds

'We have cleared the tower, and the Cassini spacecraft is on its way to Saturn,' mission control can be heard saying in the 20-year-old footage, as the rocket breaks through the clouds

‘We have cleared the tower, and the Cassini spacecraft is on its way to Saturn,’ mission control can be heard saying in the 20-year-old footage, as the rocket breaks through the clouds

‘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 confirmation of the mission was received at Nasa’s Jet Propulsion unit at 07:56 EST (12:56 BST).

Upon receiving the news, Earl Maize, program manager for Cassini, announced: ‘The signal from the spacecraft has gone. Congratulations, this has been an incredible mission and incredible spacecraft.’  

The radio signal could be seen to flatline as Cassini was vapourised in the atmosphere

The radio signal could be seen to flatline as Cassini was vapourised in the atmosphere

Pictured is an artist's impression of the moment just before Cassini's death

Pictured is an artist's impression of the moment just before Cassini's death

After 20 years in space, Nasa’s Cassini spacecraft has finally completed its suicide mission, plunging into Saturn’s atmosphere. The confirmation of the mission was received at Nasa’s Jet Propulsion unit at 07:56 EST (12:56 BST)

In its thirteen years at Saturn and two decades in space, the $4 billion (£3 billion) Cassini probe has transformed our understanding of the ringed planet and its moons.

It has watched giant storms on the gas giant, recorded its ring system in stunning detail, and revealed incredible new insights on the potential habitability of Saturn’s moons.

The decision to kill off Cassini was taken because the craft would soon run out of fuel and become impossible to steer. Scientists feared a collision with Titan or Enceladus – two of Saturn’s moons that in the past 10 years have shown a potential to host simple life.  

Nasa’s animation imagine what the ‘death dive’ would have looked like 

First, they expect the probe to have shed layers of insulating material. 

Saturn’s active, ocean-bearing moon Enceladus sinks behind the giant planet in a farewell animation from NASA’s Cassini spacecraft

Then its large external structures, including the 11ft wide dish antenna and 30ft long magnetometer boom will have weakened and broken apart, followed by other body-mounted components, and eventually the leading face of the space craft itself.

It is also possible that propellant left in Cassini’s fuel tanks may have exploded.

Meanwhile, atmospheric friction will have sent temperatures soaring. 

By the time what was left of Cassini reached the cloud tops it would have been transformed into a glowing fragmenting meteor, hotter than the surface of the sun.

Project manager Earl Maize, centre, shakes hands with Bill Heventhal (left) head of Uplink Operations in mission control at Nasa's Jet Propulsion Lab

Project manager Earl Maize, centre, shakes hands with Bill Heventhal (left) head of Uplink Operations in mission control at Nasa's Jet Propulsion Lab

Project manager Earl Maize, centre, shakes hands with Bill Heventhal (left) head of Uplink Operations in mission control at Nasa’s Jet Propulsion Lab

Finally, intense heat and pressure would have caused every part of the space craft to melt and dissociate, scattering its atoms to the winds of Saturn.

Cassini’s death plunge was the climax of a ‘grand finale’ that saw the probe slip between Saturn and its rings in 22 daring orbits.

Fifteen minutes before the end, the voice of Dr Maize could be heard in a live stream from mission control telling his team: ‘This might be a good time to pass out the farewell peanuts.’

Earlier Jet Propulsion Laboratory director Mike Watkins told a Nasa interviewer: ‘It’s kind of a bitter-sweet event for all of us.

‘For me personally, it’s more sweet than bitter, because Cassini has been such a fantastic mission.

During the live feed, experts from Nasa described the event as ‘the last hour of the last chapter of Cassini’s Grand Finale.’  

Cassini science team members Nora Alonge (R), Scott Edgington (C) and Jo Pitesky (L) hug as the final loss of signal from the Cassini spacecraft is confirmed

Cassini science team members Nora Alonge (R), Scott Edgington (C) and Jo Pitesky (L) hug as the final loss of signal from the Cassini spacecraft is confirmed

Cassini science team members Nora Alonge (R), Scott Edgington (C) and Jo Pitesky (L) hug as the final loss of signal from the Cassini spacecraft is confirmed

 

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