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[Chicago Astronomer - Astro Joe]

Approach and Arrival at Saturn

After the long interplanetary cruise from Jupiter the Cassini-Huygens spacecraftwill make a rapid flyby of the moon Phoebe on 11 June 2004. This flyby will bring the spacecraft to within 2000 km of the surface of the moon and is the only chance the spacecraft will have to image in high resolution an outer moon.


During the rapid flyby Cassini will collect spectroscopic and radar data along with images of the surface. This information could help scientisits understand the composition and origin of this distant moon. Initial images, already twice as good as any image returned by Voyager 2, show large craters and variation in surface brightness.

Following the flyby a trajectory correction manouvre will be made on 16 June 2004 to place the Cassini-Huygens spacecraft on a precise intercept course with Saturn

Arrival at Saturn
On 1 July 2004 the Cassini-Huygens spacecraft will arrive at Saturn. This will mark the end of the spacecraft's journey through the Solar System as well as the beginning of its tour of Saturn, its rings, moons, and magnetosphere.

Cassini-Huygens will approach Saturn from below the ring plane. The spacecraft will cross through the large gap between the F-Ring and G-Ring. At this time Cassini-Huygens will be 158 500 kilometres from Saturn's centre. This crossing will occur one hour and 52 minutes prior to the spacecraft's closest approach to Saturn.

The main engine burn begins shortly after Cassini-Huygens has crossed above the rings. The burn will begin on 1 July 2004 at 01:12 UTC and end 97 minutes later at 02:49 UTC.

More at the European Space Agency site: sci.esa.int/science-e/www/object/index.cfm?fobjectid=34955

The site also has a great time table to keep track.

[stargazer]

I got this in an email and wanted to share it with all of you. Now you can watch the Cassini Mission Arrival on the Net.

Watch Cassini's Arrival on the Internet
Jun 29, 2004 - We're now just a couple of days away from Cassini's arrival at Saturn, and I wanted to point you towards some resources on the Internet that you can use to get the most out of this incredible event. Cassini will enter Saturn's orbit on July 1 at 0336 UTC (10:36 pm EDT June 30), and make its closest approach to the planet - for the entire mission - about 90 minutes later.

Both NASA and the ESA will have live coverage of the event available on the Internet, so you can switch back and forth between the two feeds. NASA coverage begins at 0230 UTC and goes until 0540. ESA coverage begins at 0135 UTC and runs until 0500, but it won't be continuous, just broadcasting the major events.

I'll be watching. :-)

Fraser Cain
Publisher
Universe Today

used with permission

B

[Chicago Astronomer - Astro Joe]

I like Fraser and his Universe Today site. Well put together, and lot of time invested. He even took the time to write me back on an occasion.

I would prefer the direct feed from the ESA, as NASA has been known to "edit" feeds.

This should be quite exciting!

[stargazer]

recieved this in an email. Thought I would shaer it with you all.

After a seven-year cruise through the Solar System, the joint NASA/ESA/ASI Cassini-Huygens spacecraft last night successfully entered orbit around Saturn. The Cassini orbiter is now ready to begin its four-year survey of the planet and its moons, while the Huygens probe will be prepared for the next major mission milestone: its release toward the largest moon, Titan, in December.
"This shows international space co-operation at its best," said ESA's Director of Science, Prof. David Southwood, after confirmation of the orbit insertion. "Few deep space planetary missions have carried the hopes of such a large community of scientists and space enthusiasts around the world. Congratulations to the teams in the US and Europe who made this possible and to all participants in the programme, who have a lot to do over the years ahead."

The Saturn Orbit Insertion was the last and most critical manoeuvre performed by the spacecraft to achieve its operational orbit. If it had failed, the spacecraft would have just flown past Saturn and got lost in the outer Solar System.

Cassini-Huygens was launched from Cape Canaveral, Florida, on 15 October 1997, atop a Titan 4B/Centaur, the most powerful expendable launch vehicle in the US fleet at the time. To reach Saturn it had to perform a series of gravity assist manoeuvres around Venus (April 1998 and June 1999), Earth (August 1999) and Jupiter (December 2000).

Last night, Cassini-Huygens approached Saturn from below the plane of its rings. Using its high-gain antenna dish as a shield to protect its fragile body from dust impacts, it first crossed the ring plane at 02:03 UT, some 158 500 kilometres from the centre of Saturn, in the gap that separates the F-ring from the G-ring. About 25 minutes later, at 02:36 UT, the probe fired one of its twin main engines for a 96-minute burn to enter orbit. The signal confirming this ignition took 84 minutes to reach Earth, some 1500 million kilometres from Saturn.

The burn went smoothly and reduced Cassini-Huygens' relative velocity to Saturn while the probe passed only 19 000 kilometres from the planet's upper clouds. After completion of the burn, the probe was tilted first toward Earth to confirm insertion and then toward Saturn's rings in order to take close-up pictures as it flew only a few thousand kilometres above them. This was a unique opportunity to attempt to discriminate individual components within the rings, as Cassini is not planned to come this close to them again. The orbiter's instruments also took advantage of its proximity to the planet to make an in-depth study of its atmosphere and environment.

A second crossing of the ring plane took place at 05:50 UT.

The probe is in perfect shape to begin its tour of the Saturnian system with at least 76 orbits around the ringed planet and 52 close encounters with seven of its 31 known moons. This tour actually began before insertion with a close fly-by of an eighth moon, Phoebe, on 11 June. The primary target for Cassini-Huygens will be the largest of these moons, Titan, with a first fly-by at an altitude of 1200 kilometres on 26 October.

During the coming months, ESA's scientists will prepare for the release of their main contribution to the mission, the Huygens probe, which will be released on 25 December to enter the atmosphere of Titan on 14 January 2005. Built for ESA by an industrial team led by Alcatel Space, this 320 kilogram probe carries six science instruments to analyse and characterise the atmosphere and its dynamics during its descent. If the probe survives the impact on reaching the surface, it will also analyse the physical properties of its environment after landing.

Actually bigger than Mercury, Titan features a hazy nitrogen-rich atmosphere containing carbon-based compounds. The chemical environment on Titan is thought to be similar to that of Earth before life, although colder (-180°C) and lacking liquid water. The in situ results from Huygens, combined with global observations from repeated fly-bys of Titan by the Cassini orbiter, are expected to help us understand the evolution of the early Earth's atmosphere and provide clues about the mechanisms that led to the dawn of life on our planet.

The Cassini orbiter, the largest and most complex deep-space probe ever launched, carries 12 science instruments developed by US and international teams to conduct in-depth studies of Saturn, Titan, the icy moons, the ring system and the magnetospheric environment. Two of the orbiter's instruments were provided by Europe.

"More than twenty years have passed since Pioneer 11 and the Voyagers gave us a first glimpse of Saturn, as they crossed this complex system in only a few days," explained Prof. Southwood, who is also principal investigator for Cassini's magnetometer. "Now, with Cassini, we are here to stay, watch and investigate. And with Huygens we will go even deeper and further, not only plunging into an extraterrestrial atmosphere but also an atmosphere like the early Earth's. This means we are travelling billions of years back into our own past to investigate one of the Universe's best kept secrets: where we came from."

The Cassini-Huygens mission is a co-operation between NASA, ESA, the European Space Agency and ASI, the Italian space agency. The Jet Propulsion Laboratory (JPL), a division of the California Institute of Technology in Pasadena, is managing the mission for NASA's Office of Space Science, Washington.

[starbux]

First pictures from Saturn orbit show rich ring detail

BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: July 1, 2004

The first batch of photographs snapped by the Cassini Saturn orbiter earlier today reached the Jet Propulsion Laboratory around 8:30 a.m., zoomed-in shots of the planet's myriad rings showing a ghostly tapestry of icy, back-lit particles arrayed in sharply defined bands.


One of the images taken by Cassini from orbit of Saturn shows a close-up view of the planet's rings. Credit: NASA/JPL

Much brighter shots showing the rings from the sunlit side were expected to reach Earth later this morning, but scientists were elated at the initial results.

"Look at that structure, it's so regular!" marveled imaging team leader Carolyn Porco as a picture came in showing well-defined bands of brightness and darkness. "I'm wondering if we're looking at a density wave. This looks like it might be a density wave, but I'm not quite sure."

Density waves, caused by gravitational interactions with nearby moons, are thought to be "kissing cousins" of the waves that produce the spiral structure seen in galaxies like Earth's Milky Way.

"These are regions where the rings are communicating gravitationally with the moons exterior to them," Porco explained.

One of the objectives of Cassini's ring research is to study density waves in unprecedented detail and based on the first set of images, scientists will not be disappointed.

"With these kinds of images and with the data we're going to return from Cassini with stellar occulation observations, radio occulation observations, we are going to nail density waves, we are going to understand these critters," Porco said. "This is really a new era in the study of outer planet systems."

A few moments later: "There goes another one, which is mind blowing, absolutely mind blowing," Porco exclaimed. "Look at thatOoh... It's almost everywhere you look here, you can't miss one. They're just all over the place."

A few moments later: "Oh my God, look at that! ... These density waves are like books, just waiting to be read."

But this morning, as raw, unprocessed images flowed in, science wasn't the immediate objective. It was enough just to know Cassini's camera and other systems had worked as planned during close approach to Saturn.

The photo sequence began around 12:30 a.m., 18 minutes or so after Cassini finished a 96-minute rocket firing to brake into orbit around Saturn. Streaking just above the rings at speeds greater than 50,000 mph, Cassini's narrow-angle camera took a series of snapshots, opening its shutter for just five milliseconds per picture to avoid blurring.


One of the images taken by Cassini from orbit of Saturn shows a close-up view of the planet's rings. Credit: NASA/JPL

Each picture was separated from those on either side by about 600 miles because of Cassini's extreme velocity.

"We couldn't take a contiguous ring scan with images overlapping other images because we are speeding across the rings very fast," Porco said. "It takes us about a minute to take a picture and so in the time we shutter the exposure, read out the camera and get ready to take a picture again, we have crossed a thousand kilometers. Our field of view is only about, let's say, 100 to 200 kilometers. So never do we have overlapping images. Never will we be able to put this all together in a nice mosaic."

One of the world's leading ring experts, even Porco was surprised by the level of detail apparent in the first unprocessed pictures.

"I shouldn't be, I suppose, but I am surprised," she reflected. "You can think about this like we have done for 14 years and you know, well, we'll get density waves there and we'll take pictures. But it's remarkable to me at how startling it is to see these images for the first time. ... They're just beautiful, they're very sharp."

One picture that came in about an hour after the first image was received was especially intriguing, showing a density wave on the left with narrower and narrower bands of light and dark and a so-called bending wave on the right.

"Oh my God! This is, oh, this is really exciting!" Porco exclaimed. "If you look, the pattern now is decreasing to the left and that is the mark of a bending wave. ... And a bending wave, it's not the density of the particles that is being moderated or modified as you move across the rings, but it is the height of the ring plane. The darkness is created by shadows. Look at that! It's just a beautiful pair."

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Intriguing. I eagerly await images where some of the camera noise has been removed. Right now it is a bit difficult to tell if grainyness are actual ring particles or noise from the horizontal bands.