Space Cassini-Huygens: In the Saturnian System

That section is now turning the archives to the Cassini mission. That first page is about definitive. The following links allow to find back data about the Saturnian world, and Cassini's observations, as they are in the process of being archived only! cassatu.htm, data and operations at Saturn; cassmoon.htm, data and operation at Saturn's moons; casstita.htm, data and operation at Titan. links back to that page are not available

The Mission

Cassini-Huygens, click to a larger view. picture NASA/JPL

What the Voyagers revealed at the planet was so phenomenal that, just one year later, a joint American and European working group began discussing a mission that would carry on Voyager's legacy at Saturn, a mission named Cassini. Cassini's mission to Saturn, as far as Cassini orbiter was concerned, was a thoroughful study of Saturn's system. Cassini was to be the first craft orbiting Saturn like Galileo had been the first craft orbiting Jupiter (and the first ever to orbit a gas giant as until then previous probes had just flown by there). Performing orbits about a gas giant allows long duration and high-return science about the planet, its moons and its environment. On another hand, ESA Huygens was to dedicatedly study Titan, Saturn's main moon
Cassini-Huygens launched on October, 15th 1997 from Cape Canaveral Air Force Station, Fla. atop a Titan IVB rocket, NASA's largest expendable booster at the time, and headed Saturn via four gravity assisted flybys. Cassini was a very large spacecraft and, unlike Surveyor or Voyager, it required the larger Titan and the improved Centaur like the upper stage with its two-and-a-half ton vehicle. Two gravity assist flybies occurred at Venus (Apr. 26, 1998; June 24, 1999), one at Earth (Aug. 18, 1999), one at Jupiter (Dec. 30, 2000). Cassini was to have scoured 2.2 billion miles (3.5 billion km) when arriving at Saturn. Cassini had been launched by a Titan IV, NASA's heaviest launcher. Radio troubles were seen appearing en route as that could pose problem due to that the proble was to relay Huygens data from Titan. A mock-up of Huygens was parachute-tested in Italy. Cassini was scheduled for a 4-year work in orbit. It was to perform 74 orbits about Saturn, including 44 flybys of Titan, sending back a total of 1 million pictures. Data coming from the probe took from 68 to 90 minutes to reach us according to where Earth is on its orbit. Cassini was to beam data Earth 9 hours a day. Saturn orbit insertion was to occur on July, 1st 2004. Huygens's descent in Titan's atmosphere scheduled on Jan. 14, 2005. Saturn was last visited by Voyager 1 and Voyager 2 in 1980 and 1981. Cassini-Huygens mission was a cooperative mission of NASA, European ESA, and Italian Space Agency. JPL at Caltech, Pasadena, is managing the mission for NASA. Cassini orbiter and its two onboard cameras were designed, developed, and assembled at JPL. Huygens probe was developped by a team at the European Space Technology and Research Center in Noordwijk, the Netherlands. The Italian Space Agency provided the high-gain antenna, much of the radio system and elements of several of Cassini's science instruments. Cassini also featured a radioisotope thermoelectric generator, or RTG. As far as it is concerned Cassini was to perform 45 flybys of Titan permitting high-resolution mapping of the moon with the radar-imaging instrument. The radar can see through the opaque haze of Titan's upper atmosphere. Radar technique was necessary to penetrate Titan's opaque atmosphere. The Huygens probe was to descend into the atmosphere of Titan, collecting data and to land. The probe was to cease beaming few after landing and they didn't know then whether Titan's surface was solid or liquid. Huygens ESA probe had been named from Dutch scientist Christiaan Huygens (1629-1695). Huygens had been born in a wealthy Dutch family traditionally diplomacy-serving the House of Orange. After maths and law studies, he dedicated some time to improve and theorize astronomical telescopes. In 1655 he discovered Titan, Saturn's main moon, and Saturn's rings true nature with a telescope of his own. Huygens was one founder of the French Academy of Sciences in 1666. Huygens was less a great scientist than Newton however, as he was not able to master calculus

The Saturnian System

Saturn is the sixth planet from the Sun and the second largest -after Jupiter- in the solar system. Like Jupiter, Saturn is a gas giant with gas in layers surrounding a solid small core. The most distinctive trait of Saturn is obviously its ring which is a fine show as seen from Earth. Saturn has a vast system of satellites. The ringed planet takes 29 years to complete its orbit. Saturn's rings were believed to be 100 million years old (some thought their history might have spanned several hundred million years) and were thought to originate from collisions occurred at Saturn's moons or from other bodies which were disrupted by the planet's gravitational field. It was believed too that the planet might have had several succeding rings systems since Saturn had formed 4.5 billion years ago. Saturn's ring featured three main zones: an outermost part of the ring called "A ring", a middle (and brightest) part of it called "B ring", and an innermost (and fainter) part called "C ring". Two gaps, the Encke gap and the Cassini division were separations in the ring. Most of what was known at the time of the mission, about Saturn's moons was yielded by Voyager 1 and 2 missions which reached the ringed planet about 1980. Saturn is surrounded by 31 regular, irregular, or inner moons. Titan, by far largest Saturn's moon and like Ganymede at Jupiter one of the largest in the solar system was the sole solar system's moon with an atmosphere. Titan's atmosphere had drawn the scientists' attention as it contained organic compounds, which are at the origin of life

Working at Saturn

After a 6-year cruise, Cassini reached Saturn neighbourhood by 2003's beginnings. On January, 18th 2004 Cassini officially entered the 'Approach Science phase.' Since that moment it performed an uninterrupted series of science observations leading to Saturn orbit insertion. Data about interaction between solar wind and Saturn's magnetosphere, Saturn's rings, Saturn's atmosphere, new satellites, and Titan imaging during last month before orbit insertion were relayed Earth. Cassini then officially entered Saturn system on May, 18th 2004 when gravitational pull of the planet exceeded Sun's. Craft passed then the boundary where ultimate moons are dwelling, about 10 million miles from Saturn. A last trajectory correction maneuver (TCM), slowing Cassini by 8 mph (3.6 m/s) was performed on Wednesday, June, 16th 2004 as a final adjustment before the Saturn Orbit Insertion on July, 1st UT 2004. The insertion was made through a main engine braking so the planet was able to capture the craft. The Saturnian orbit insertion occurred between F and G rings as the probe's antenna served like a protection against micro-meteorids. Cassini had used 4 gravity assist flybys during its 6.5-year and 2.2 billion-mile (3.5 billion km) journey. The craft flew by at Venus (26 April 1998 and 24 June 1999), Earth (18 August 1999), and Jupiter (30 December 2000), each time exchanging energy, gaining speed, and altering its direction. The first next step after orbit insertion was to flyby Titan. After release from the main craft by late 2004, the European ESA probe Huygens successfully descended into Saturn's largest moon's atmosphere and landed there January 14th, 2005

As far as the configuration of the Cassini craft after its launch and arrival at Saturn was concerned, the craft successfully turned to a alternate set of thrusters by early 2009, as the original set of 8 thrusters was weathering. NASA, thus, had the mission to swap to a backup set of propulsion thrusters. The redundant set -or 'branch B'- is an identical set of eight thrusters. The thrusters, on a spacecraft, are used by the craft fo small corrections, for attitude controls of for angular momentum adjustments in the reaction wheel used too for attitude control. Cassini had had to swap to an alternate reaction wheel a few years ago. Since the beginning of 2016, a series of flybys past Titan have progressively raised the tilt of Cassini's orbit with respect to Saturn's equatorial plane, allowing the mission to leap over the rings as beginning on Nov. 30, 2016, Cassini have explored the outer edge of the ring with 20 orbits, approaching within 4,850 miles (7,800 kilometers) of the center of the F ring. A last and unique passage at Titan by April 2017 was to allow the ultimate phase of the mission. That end to Cassini's mission results from that the craft lacks fuel and that it might endanger future exploration of Saturn's moons especially the potentially habitable Enceladus. Following a four-year primary mission (2004-2008) and a two-year extension (called the 'Equinox mission,' 2008-2010), NASA extended Cassini's service by an additional seven years since February 2010. That last extension was called the 'Cassini Solstice Mission,' providing for a total duration of the mission reaching from Saturn's northern winter solstice to a few months past northern summer solstice in May 2017, allowing for a complete seasonal period at Saturn, studying seasonal and other long-term weather changes on the planets and the moons. The Grand Finale, having Cassini safely disposed of in the layers of Saturn, closed the Solstice Mission

With its last approach to Titan in a distant flyby on Sep. 11, 2017 at 5 p.m. EDT, Cassini was directed to its final plunge to Saturn. The probe then reached its last apoapse --the farthest from Saturn on its orbit-- at a distance of 800,000 miles (1.3 million kilometeres) before heading to the ringed planet. Cassini was back in contact with Earth on Sep. 12 as data were streamed down and, on Sep. 13, mission navigators confirmed that the mission was on its course to dive into the planet's atmosphere on Sep. 15 (a calculation predicted that loss of contact with Cassini should occur on Sep. 15 by 7:55 a.m. EDT). Always that same day, by 7:45 p.m. EDT, Cassini began transmitting data and final images, emptying its onboard solid-state recorder of all science data before reconfiguring for a near-real-time data relay during the final plunge. From that moment, communications link with the spacecraft get continuous through the mission's end 12 hours ahead. On Sep. 15, the day of the Cassini final plunge, by 4:55 a.m. EDT, the craft configured itself for the plunge and real-time relay of data, as the transfer of data signaled the beginning of the plunge, which began at 7:55 a.m. EDT and the loss of contact scheduled one minute later. The spacecraft entered the atmosphere on the planet's day side, near local noon, at 9.4 degrees north latitude, 53 degrees west longitude. Telemetry received during the plunge indicated that, as expected, Cassini entered Saturn's atmosphere with its thrusters firing to maintain stability, as it sent back a unique final set of science observations. No images were to be taken during the final plunge into Saturn, as the data transmission rate required to send images was too high and would have prevented other high-value science data from being returned. Cassini's contact with Saturn's atmosphere occurred at a altitude of about 1,190 miles (1,915 kilometers) above the planet's estimated cloud tops --that altitude where the air pressure is 1 bar, equivalent to sea level on Earth-- at a speed of approximately 70,000 miles (113,000 kilometers) per hour. The predicted altitude for loss of signal was about 930 miles (1,500 kilometers) above cloud tops, whence the craft was to begin to burn up like a meteor, being destroyed within a couple of minutes (the craft, generally, in terms of what amateurs can see at Saturn, was destroyed before reaching the 'visible' layers of Saturn, above what is termed the 'well-mixed atmosphere')

for more see mission's official site or Cassini Imaging Team site

Data Overview

to a view of Cassini-Huygens data