The "Cassini" Spacecraft, (named after the Italian Astronomer Giovanni Domenico Cassini), after seven years and 2.2 billion miles, is completing the most complicated and expensive unmanned spaceflight ever attempted is nearing its destination — the exotic and colorful ringed planet Saturn.

Tomorrow evening, the Cassini spacecraft will navigate a treacherous path through the rings of Saturn, fire its retrorocket and, if all goes well, enter a broad looping orbit around the majestic planet, with the ultimate objective of searching for the organic chemicals that are the building blocks of life, and understand the origin of life in our solar system.

Saturn was known to ancient scholars, although its unusual nature did not emerge until Galileo first viewed it through a telescope in 1609.Dutch astronomer Christiaan Huygens, who was the first to see the planet's rings clearly.

Huygens' observations were confirmed by the Italian-French astronomer Giovanni Domenico Cassini. In 1675, he noticed that Saturn's rings were separated into two major sections: The gap is known as the Cassini Division. He also discovered the moons Iapetus, Rhea, Tethys and Dione.

[RAA Comment: Re: Italian-"French" astronomer Cassini. He was given the name Giovanni Domenico Cassini by his parents, Jacopo Cassini and Julia Crovesi, after his birth in Perinaldo (Genoa) Italy. In 1668, at age 43, Louis XIV invited him to Paris to oversee the construction of the Paris Observatory. His 2 year visit was approved by the senate of Bologna and Pope Clement IX. Cassini originally made little attempt to improve his French as he still fully intended to return to his duties in Italy. Almost irresistable offers caused him to stay in France, and he then changed his name to the french version of Jean-Dominique Cassini. To add just one more comment to the question of his name, he was the first of the famous Cassini family of astronomers and as such is often known as Cassini I, who was followed by Cassini II, III, & IV.]

The $3.3-billion program is funded by NASA, the Italian Space Agency, and the European Space Agency.

Over the next four years, the spacecraft will make at least 74 orbits, including 44 close encounters with Saturn's largest moon, Titan. It will also fly past another 16 of the planet's 31 known major moons. With luck, the craft could continue to collect data for 15 years.

Los Angeles Times
By Thomas H. Maugh II,
Times Staff Writer
June 29, 2004

After seven years and 2.2 billion miles, the most complicated and expensive unmanned spaceflight ever attempted is nearing its destination — the exotic and colorful ringed planet Saturn.

On Wednesday evening, the Cassini spacecraft will navigate a treacherous path through the rings of Saturn, fire its retrorocket and, if all goes well, enter a broad looping orbit around the majestic planet.

Over the next four years, the spacecraft will make at least 74 orbits, including 44 close encounters with Saturn's largest moon, Titan. It will also fly past another 16 of the planet's 31 known major moons. With luck, the craft could continue to collect data for 15 years.

On Christmas Eve, the craft will launch a small probe named Huygens to the frigid surface of Titan — the only moon in the solar system with a dense atmosphere — to search for the organic chemicals that are the building blocks of life.

"Our objective is very simple — to allow us to rewrite the story of the 'Lord of the Rings,' " said Charles Elachi, director of the Jet Propulsion Laboratory in Pasadena and principal scientist for the radar probe aboard Cassini.

"Some people have been working 15 years for this," added Robert Mitchell, Cassini program manager at JPL. "Our emotions are starting to build: anticipation, excitement, relief and a bit of anxiety."

The arrival of the craft at Saturn represents, in many ways, the end of an era. Cassini's cost, massive size and payload of 18 scientific instruments sets it "apart from recent interplanetary missions launched under the 'faster, better, cheaper' slogan," said David Doody, a flight operations manager at JPL.

That mantra, developed by former NASA Administrator Daniel S. Goldin, led to a new generation of spacecraft that weigh less, cost less and take less time to develop than any in NASA's history.

With the new emphasis at NASA on a return to the moon and a manned mission to Mars, it seems unlikely that there will be another mission to Saturn in the next few decades, and almost certain that none will be so complex. Scientists are hoping to unravel as many of the planet's secrets as possible with this one.

The craft also holds a special place in the hearts of researchers at JPL because the $3.3-billion program, funded by NASA, the European Space Agency and the Italian Space Agency, was the only major project sustaining the lab during the gap between the loss of Mars Observer in 1993 and the beginning of work on the Mars rovers. In the peak year of 1995, at least 1,500 scientists and engineers at JPL worked on it full or part time.

Cassini faces a difficult obstacle in braking into orbit around Saturn. "This is not a slam-dunk," Mitchell said.

Streaking toward Saturn at 49,000 mph, Cassini will come up from underneath the planet on the sunlit side of the rings and thread its way between the F and G rings — two of the fainter ones near the outer edge of the planet's ring system — an 18,600-mile gap that is undoubtedly littered with undetectable bits of rocks and ice.

The Voyager 2 and Pioneer spacecraft both passed safely through the gap, but experts noted that it would take only one wayward piece of rock or ice hitting the craft to permanently disable it.

Twenty-five minutes after passing through the gap, at 7:36 p.m. PDT, Cassini will fire its engine for 96 minutes to reduce its speed by 1,400 mph, just enough to allow it to be captured by Saturn's gravity.

That is the only maneuver in the entire mission that has to be done precisely, Mitchell said. "Otherwise, it becomes a Saturn flyby."

To that end, the craft carries a redundant rocket motor in case the first one doesn't fire. The computer that operates Cassini will fire the rocket "no matter what happens," Mitchell said. "The spacecraft will not let the burn go by, even in the presence of faults."

While the rocket is firing, the craft will make its closest approach to Saturn, swooping in to a distance of just more than 12,400 miles from the fringes of the atmosphere. The craft will then speed once more through the F-G gap, returning to the underside of the plane of the rings.

This will be the closest the craft will come to the rings. Normally, a spacecraft at this point would be checking its engineering data and returning the information to Earth. But after sending a quick burst of data to confirm the burn, Cassini will focus its attention on the rings.

"We want to look at the rings while we can," Elachi said. "We'll never be that close again."

Only after about an hour of observation will the craft turn its antenna back toward Earth and begin sending back the large amounts of data collected during its entry into orbit.

A miniature "solar system" unto itself, Saturn was known to ancient scholars, although its unusual nature did not emerge until Galileo first viewed it through a telescope in 1609. He discovered that the planet's size varied with time, sometimes appearing much larger than normal.

That mystery was solved nearly half a century later by Dutch astronomer Christiaan Huygens, who was the first to see the planet's rings clearly. He concluded that the planet had appeared large to Galileo when the rings were at a right angle to his rudimentary telescope, and much smaller when he viewed them edge-on. Huygens also discovered Titan in 1655.

Huygens' observations were confirmed by the Italian-French astronomer Giovanni Domenico Cassini. In 1675, he noticed that Saturn's rings were separated into two major sections: The gap is known as the Cassini Division. He also discovered the moons Iapetus, Rhea, Tethys and Dione.

Much of the information about Saturn was gleaned through three previous flybys of the planet: Pioneer 11 in September 1979, Voyager 1 in November 1980 and Voyager 2 in August 1981.

Saturn itself is nearly the size of Jupiter, but it is made mainly of gas and is the only known planet that is less dense than water. If it could be placed in a gigantic bathtub, it would float.

The planet has a massive magnetic field and radiates more energy than it receives from the sun. Its stormy atmosphere has distinct, colored bands that persist for long periods of time and winds that have been clocked at 1,120 mph.

Some unknown process on Saturn also generates low-frequency radio waves, while strong radio outbursts are thought to be caused by "super bolts" of lightning. Cassini's instruments will monitor these processes, mapping the planet's global temperature structure and determining the composition of atmospheric gases, hazes and clouds.

Saturn "offers so much scientific insight because it's so rich in phenomena," said imaging team leader Carolyn C. Porco of the Space Science Institute in Boulder, Colo.

For many scientists and the public, the "center stage" of Cassini's mission will be its study of Saturn's rings, Doody said.

Composed of billions of pieces of ice and rock ranging in size from smoke particles to boulders the size of a house, the rings are broad — about 260,000 miles wide overall — but extraordinarily thin: only tens to hundreds of yards thick.

"We want to find out what they are made of, how old they are, what their dynamic is," Elachi said. "We want to understand their formation because that will shed light on how dust disks [elsewhere in the universe] lead to the formation of planets."

Others want to study the gaps in the rings — how they are formed and how they are maintained over long periods. "For me, that is one of the biggest objectives," Porco said.

Some gaps, such as the Cassini Division, are thought to be caused by the moons in a phenomenon researchers call resonance. The small moon Mimas, for example, orbits outside the rings with a period of 22.6 hours. Objects at the distance of the Cassini Division would have a period of about 11.3 hours.

Any rocks and boulders originally in what is now the Cassini Division would have been tugged repeatedly by Mimas' gravity at the same point in every orbit, nudging them out of the gap.

Other gaps are caused more directly by moons. The particles in a smaller gap called the Encke Division, for example, are swept clear by the tiny moon Pan.

The team also wants to study spoke-like features in Saturn's B ring — one of its largest, near the center of the ring system. Theoretically, such spokes should not exist because the particles at different distances from the planet have different orbital speeds, so the spokes should be quickly torn apart.

The craft will also study Saturn's known moons — 13 of the 31 have been discovered since Cassini was launched — and look for others. "The chances of finding additional moons are very good," Mitchell said.

One of the more intriguing moons is Mimas, only 240 miles in diameter. Mimas bears a massive crater — 80 miles wide — named Herschel, from an impact that nearly shattered the moon. Cassini will fly by looking for cracks from the impact and other features that may reveal its history.

Another alluring target is Enceladus, which Porco and others think may be similar to Jupiter's moon Europa. Tidal stresses on the 310-mile-diameter moon may liquefy water believed to be beneath its surface. Cassini will swoop within 300 miles of the surface to see if this water erupts in geysers to produce fresh snow.

But the most inviting moon of all is Titan. At 3,200 miles across, it is larger than Earth's moon and is enveloped in a dense atmosphere composed mainly of nitrogen.

Titan's atmosphere is rich in organic molecules — much as Earth's may have been before life developed here — and its surface is thought to have large lakes of liquid hydrocarbons. The sun's action on the chemicals produces an orange smog that has prevented previous missions from imaging the moon's surface.

On Dec. 24, Cassini will launch the Huygens probe, built by the European Space Agency, toward Titan. Three weeks later, the 703-pound capsule and its six instruments will parachute to the surface, taking continuous measurements and photographs throughout the 2- to 2 1/2-hour descent.

If scientists are lucky, the probe may even survive for a few minutes on the surface, transmitting data back for as long as the batteries can operate in the moon's minus-289 degree Fahrenheit temperature.

Researchers do not expect the probe to discover life on Titan because it is too cold, but they hope it will give insights into how life might have gotten started elsewhere.

"The most important thing our generation can do is understand the origin of life in our solar system," Elachi said.

Craft Poised to Run Rings Around Saturn
http://www.latimes.com/news/custom/showcase/la-sci-cassini29jun29.story

Cassini Spacecraft Nears Saturn, Photographs Moon
John Roach
for National Geographic News
June 14, 2004

After a seven-year, roundabout planetary voyage, the international Cassini-Huygens spacecraft is poised to begin a four-year tour of Saturn, its rings, and its 31 known moons, including Earthlike Titan. Already the craft has captured unprecedented views of the moon Phoebe.

"In some sense, we'll write the book on Saturn. I know that's sort of a glib phrase, but that's what we'll do," said Dennis Matson, project scientist for the Cassini-Huygens mission at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California.

Located between Jupiter and Uranus, Saturn is 890 million miles (1.43 billion kilometers) from the sun, or ten times the distance from Earth to the sun. Smaller only than Jupiter, Saturn is composed mostly of hydrogen and helium gas, making it the least dense planet in the solar system.

Three NASA spacecraft, Pioneer 11 and Voyager 1 and 2, flew by the ringed planet in 1979, 1980, and 1981. But Cassini-Huygens is the first mission dedicated to the study of the Saturnian system.

What is known about the planet suggests a cold and windy place. The temperature at Saturn's cloud tops is -218 degrees Fahrenheit (-139 degrees Celsius), and winds rip across its equator at 1,100 miles an hour (500 meters a second).

Voyage to Saturn

The U.S. $3.4 billion Cassini spacecraft (named after the 17th-century Italian-French astronomer Jean-Dominique Cassini, who made several key discoveries about Saturn) and the piggybacking Huygens probe named after the Dutch scientist Christian Huygens, who discovered the moon Titan) launched October 15, 1997, from Cape Canaveral, Florida.

The package has been on a 2.2-billion-mile (3.5-billion-kilometer) journey to Saturn, swinging by Venus, Earth, and Jupiter along the way for "gravity-assists," or extra propulsion, and is scheduled to enter orbit around Saturn on June 30.

On arrival, Cassini will thread a 625-mile-wide (1,006-kilometer-wide) gap between two of the planet's ice- and rock-strewn outer rings. It will fire one of its main engines to slow it down as it studies the rings, then re-thread the rings and jockey into position for the first of 76 planned orbits.

Project scientists hope a shield-like antenna will block any dust grains from damaging the spacecraft as it threads and studies the rings. Once the spacecraft is safely in orbit, it will orient the antenna for relaying data to Earth.

JPL's Matson said the international project team is ready for orbit insertion, having tested and retested all systems required for the tricky task. Pioneer 11 successfully threaded the gap between the F and G rings, proving it can be done.

"There's no first-time event, and that's what always gets you—when you have first-time events, something comes up you didn't count on. We've scrubbed all those out, and that's why we're confident," Matson said.

Why Saturn?

Scientists are eager to study the Saturnian system in detail, because they believe it will yield answers to fundamental questions about chemistry and physics, planetary formation, and the conditions that give rise to life.

Four years of detailed investigation of the system will allow scientists for the first time to understand how the various components interact with each other—the difference between knowing the individual parts and the essence of the whole, Matson said.

He uses an analogy of a mechanical clock, where one can measure the wheels and various gears but totally miss out on the essence of what they do. "The essence of it is totally bound up in the interaction between the parts," he said.

Saturn and Jupiter's systems of planet, rings, and moons have long been considered physical models of the process of planetary formation and are referred to as miniature solar systems.

"[Studying] these different experiments in planetary formation will help us understand how the process works," said Ralph Lorenz, a planetary scientist at the University of Arizona in Tucson. Lorenz is an expert on Saturn's moon Titan.

Saturn's largest moon, Titan is a major focus of the Cassini-Huygens mission. Its surface, covered in a thick, smoggy haze, has never been studied in detail, but scientists believe that Titan's atmosphere is rich in organic material. This suggests that Titan may be similar to what Earth was like before life evolved.

"The pre-biotic Earth was probably not as reducing and not as cold, but many of the same chemical steps are there—long overprinted and destroyed on Earth but frozen in place for us to study on Titan," Lorenz said.

On December 24 Cassini will release the European Space Agency's Huygens probe. The probe will enter Titan's thick, nitrogen-rich atmosphere on January 14, 2005, deploy a set of parachutes and begin 2.5 hours of intensive scientific observations.

Images and data will be relayed via Cassini to scientists on Earth, providing details of the unknown landscape. What the probe will land on or in is unknown, but Lorenz has his fingers crossed it will splash into a lake of methane or ethane.

According to Matson, "Titan won't have any secrets left when we get through with it."

Cassini Spacecraft Nears Saturn, Photographs Moon
http://news.nationalgeographic.com/news/
2004/06/0614_040614_cassini.html