Category: Saturn

Time (CET) Event

0551 UTC (12:51 am EST) – Timer triggers power-up of onboard electronics
Triggered by a pre-set timer, Huygens’s onboard electronics power up and the transmitter is set into low-power mode, awaiting the start of transmission.

1013 UTC (5:15 am EST) – Huygens reaches ‘interface altitude’
The ‘interface altitude’ is defined as 1270 kilometres above the surface of the moon where entry into Titan’s atmosphere takes place.

1017 UTC (5:17 am EST) – Pilot parachute deploys
The parachute deploys when Huygens detects that it has slowed to 400 metres per second, at about 180 kilometres above Titan’s surface. The pilot parachute is the probe’s smallest, only 2.6 metres in diameter. Its sole purpose is to pull off the probe’s rear cover, which protected Huygens from the frictional heat of entry.

2.5 seconds after the pilot parachute is deployed, the rear cover is released and the pilot parachute is pulled away. The main parachute, which is 8.3 metres in diameter, unfurls.

1018 UTC (5:18 am EST) – Huygens begins transmitting to Cassini and front shield released
At about 160 kilometres above the surface, the front shield is released.

42 seconds after the pilot parachute is deployed, inlet ports are opened up for the Gas Chromatograph Mass Spectrometer and Aerosol Collector Pyrolyser instruments, and booms are extended to expose the Huygens Atmospheric Structure Instruments.

The Descent Imager/Spectral Radiometer will capture its first panorama, and it will continue capturing images and spectral data throughout the descent. The Surface Science Package will also be switched on, measuring atmospheric properties.

1032 UTC (5:32 am EST) – Main parachute separates and drogue parachute deploys
The drogue parachute is 3 metres in diameter. At this level in the atmosphere, about 125 kilometres in altitude, the large main parachute would slow Huygens down so much that the batteries would not last for the entire descent to the surface. The drogue parachute will allow it to descend at the right pace to gather the maximum amount of data.

1049 UTC (5:49 am EST) – Surface proximity sensor activated
Until this point, all of Huygens’s actions have been based on clock timers. At a height of 60 kilometres, it will be able to detect its own altitude using a pair of radar altimeters, which will be able to measure the exact distance to the surface. The probe will constantly monitor its spin rate and altitude and feed this information to the science instruments. All times after this are approximate.

1157 UTC (6:57 am EST) – Gas Chromatograph Mass Spectrometer begins sampling atmosphere
This is the last of Huygens’s instruments to be activated fully. The descent is expected to take 137 minutes in total, plus or minus 15 minutes. Throughout its descent, the spacecraft will continue to spin at a rate of between 1 and 20 rotations per minute, allowing the camera and other instruments to see the entire panorama around the descending spacecraft.

1230 UTC (7:30 am EST) – Descent Imager/Spectral Radiometer lamp turned on
Close to the surface, Huygens’s camera instrument will turn on a light. The light is particularly important for the ‘Spectral Radiometer’ part of the instrument to determine the composition of Titan’s surface accurately.

1234 UTC (7:34 am EST) – Surface touchdown
This time may vary by plus or minus 15 minutes depending on how Titan’s atmosphere and winds affect Huygens’s parachuting descent. Huygens will hit the surface at a speed of 5-6 metres per second. Huygens could land on a hard surface of rock or ice or possibly land on an ethane sea. In either case, Huygens’s Surface Science Package is designed to capture every piece of information about the surface that can be determined in the three remaining minutes that Huygens is designed to survive after landing.

1444 UTC 9:44 am EST) – Cassini stops collecting data
Huygens’s landing site drops below Titan’s horizon as seen by Cassini and the orbiter stops collecting data. Cassini will listen for Huygens’s signal as long as there is the slightest possibility that it can be detected. Once Huygens’s landing site disappears below the horizon, there’s no more chance of signal, and Huygens’s work is finished.

1514 UTC (10:14 am EST) – First data sent to Earth
Cassini first turns its high-gain antenna to point towards Earth and then sends the first packet of data.

Getting data from Cassini to Earth is now routine, but for the Huygens mission, additional safeguards are put in place to make sure that none of Huygens’s data are lost. Giant radio antennas around the world will listen for Cassini as the orbiter relays repeated copies of Huygens data.

Original Source: ESA News Release

This map illustrates the planned imaging coverage for the Descent Imager/Spectral Radiometer, onboard the European Space Agency’s Huygens probe during the probe’s descent toward Titan’s surface on Jan. 14, 2005. The Descent Imager/Spectral Radiometer is one of two NASA instruments on the probe.

The colored lines delineate regions that will be imaged at different resolutions as the probe descends. On each map, the site where Huygens is predicted to land is marked with a yellow dot. This area is in a boundary between dark and bright regions.

This map was made from the images taken by the Cassini spacecraft cameras on Oct. 26, 2004, at image scales of 4 to 6 kilometers (2.5 to 3.7 miles) per pixel. The images were obtained using a narrow band filter centered at 938 nanometers – a near-infrared wavelength (invisible to the human eye) at which light can penetrate Titan’s atmosphere to reach the surface and return through the atmosphere to be detected by the camera. The images have been processed to enhance surface details. Only brightness variations on Titan’s surface are seen; the illumination is such that there is no shading due to topographic variations.

For about two hours, the probe will fall by parachute from an altitude of 160 kilometers (99 miles) to Titan’s surface. During the descent the camera on the probe and five other science instruments will send data about the moon’s atmosphere and surface back to the Cassini spacecraft for relay to Earth. The Descent Imager/Spectral Radiometer will take pictures as the probe slowly spins, and some these will be made into panoramic views of Titan’s surface.

This map (PIA06172) shows the expected coverage by the Descent Imager/Spectral Radiometer side-looking imager and two downward-looking imagers – one providing medium-resolution and the other high-resolution coverage. The planned coverage by the medium- and high-resolution imagers is the subject of the second map (PIA06173).

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini-Huygens mission for NASA’s Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging team is based at the Space Science Institute, Boulder, Colo. The Descent Imager/Spectral team is based at the University of Arizona, Tucson, Ariz.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov . For images visit the Cassini imaging team home page http://ciclops.org .

Original Source: NASA/JPL News Release

Images returned by NASA’s Cassini spacecraft cameras during a New Year’s Eve flyby of Saturn’s moon Iapetus (eye-APP-eh-tuss) show startling surface features that are fueling heated scientific discussions about their origin.

One of these features is a long narrow ridge that lies almost exactly on the equator of Iapetus, bisects its entire dark hemisphere and reaches 20 kilometers high (12 miles). It extends over 1,300 kilometers (808 miles) from side to side, along its midsection. No other moon in the solar system has such a striking geological feature. In places, the ridge is comprised of mountains. In height, they rival Olympus Mons on Mars, approximately three times the height of Mt. Everest, which is surprising for such a small body as Iapetus. Mars is nearly five times the size of Iapetus.

Images from the flyby are available at http://saturn.jpl.nasa.gov, http://www.nasa.gov/cassini and http://ciclops.org.

Iapetus is a two-toned moon. The leading hemisphere is as dark as a freshly-tarred street, and the white, trailing hemisphere resembles freshly-fallen snow.

The flyby images, which revealed a region of Iapetus never before seen, show feathery-looking black streaks at the boundary between dark and bright hemispheres that indicate dark material has fallen onto Iapetus. Opinions differ as to whether this dark material originated from within or outside Iapetus. The images also show craters near this boundary with bright walls facing towards the pole and dark walls facing towards the equator.

Cassini’s next close encounter with Iapetus will occur in September 2007. The resolution of images from that flyby should be 100 times better than the ones currently being analyzed. The hope is that the increased detail may shed light on Iapetus’ amazing features and the question of whether it has been volcanically active in the past.

With a diameter of about 1,400 kilometers (890 miles), Iapetus is Saturn’s third largest moon. It was discovered by Jean-Dominique Cassini in 1672. It was Cassini, for whom the Cassini-Huygens mission is named, who correctly deduced that one side of Iapetus was dark, while the other was white.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini-Huygens mission for NASA’s Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The European Space Agency built and manages the development of the Huygens probe and is in charge of the probe operations. The Italian Space Agency provided the high-gain antenna, much of the radio system and elements of several of Cassini’s science instruments. The imaging team is based at the Space Science Institute, Boulder, Colo.

Original Source: NASA/JPL News Release

Image credit: NASA/JPL/SSI
Rhea has been heavily bombarded by impacts during its history. In this Cassini image the moon displays what may be a relatively fresh, bright, rayed crater near Rhea’s eastern limb. Rhea is 1,528 kilometers (949 miles) across.

This view is centered on the side of Rhea that faces away from Saturn as the moon orbits. The image was taken in visible light with the Cassini spacecraft narrow angle camera on Nov. 10, 2004, at a distance of 3.6 million kilometers (2.2 million miles) from Rhea and at a Sun-Rhea-spacecraft, or phase, angle of 86 degrees. North is up. The image scale is 21 kilometers (13 miles) per pixel. The image has been magnified by a factor of two and contrast enhanced to aid visibility of surface features.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA’s Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging team is based at the Space Science Institute, Boulder, Colo.

For more information about the Cassini-Huygens mission, visit http://saturn.jpl.nasa.gov and the Cassini imaging team home page, http://ciclops.org .

Original Source: NASA/JPL/SSI News Release

NASA’s Cassini spacecraft successfully flew by Saturn’s moon Iapetus at a distance of 123,400 kilometers (76,700 miles) on Friday, Dec. 31. NASA’s Deep Space Network tracking station in Goldstone, Calif., received the signal and science data that day beginning at 11:47 p.m. Pacific Standard Time.

Iapetus is a world of sharp contrasts. The leading hemisphere is as dark as a freshly-tarred street, and the white, trailing hemisphere resembles freshly-fallen snow.

Friday’s flyby was the first close encounter of Iapetus during the four-year Cassini tour. The second and final close flyby of Iapetus is scheduled for 2007. Next up for Cassini is communications support for the European Space Agency’s Huygens probe during its descent to Titan on Jan. 14.

The Huygens probe successfully detached from the Cassini orbiter on Dec. 24. The data gathered during the descent through Titan’s atmosphere will be transmitted from the probe to the Cassini orbiter. Afterward, Cassini will point its antenna to Earth and relay the data through NASA’s Deep Space Network to NASA’s Jet Propulsion Laboratory, Pasadena, Calif., and on to the European Space Agency’s Space Operations Center in Darmstadt, Germany, which serves as the operations center for the Huygens probe mission. Two of the instruments on the probe — the camera system and the gas chromatograph/mass spectrometer — were provided by NASA.

Raw images from the Iapetus flyby are available at: http://saturn.jpl.nasa.gov/multimedia/images/raw. More information on the Cassini-Huygens mission is available at: http://saturn.jpl.nasa.gov and http://www.nasa.gov/cassini.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. JPL, a division of the California Institute of Technology in Pasadena, manages the Cassini mission for NASA’s Science Mission Directorate, Washington, D.C. JPL designed, developed and assembled the Cassini orbiter. The European Space Agency built and managed the development of the Huygens probe and is in charge of the probe operations. The Italian Space Agency provided the high-gain antenna, much of the radio system and elements of several of Cassini’s science instruments.

Original Source: NASA/JPL News Release

NASA’s Cassini spacecraft is set to cap off 2004 with an encounter of Saturn’s ying-yang moon Iapetus (eye-APP-eh-tuss) on New Year’s Eve.

This is Cassini’s closest pass yet by one of Saturn?s smaller icy satellites since its arrival around the ringed giant on June 30 of this year. The next close flyby of Iapetus is not until 2007.

Iapetus is a world of sharp contrasts. The leading hemisphere is as dark as a freshly-tarred street, and the white, trailing hemisphere resembles freshly-fallen snow.

Cassini will fly by the two-toned moon at a distance of approximately 123,400 kilometers (76,700 miles) on Friday, Dec. 31. This flyby brings to an end a year of major accomplishments and rings in what promises to be a year filled with new discoveries about Saturn and its moons.

“I can think of no better way than this to wrap up what has been a whirlwind year,” said Robert T. Mitchell, program manager for the Cassini mission at NASA’s Jet Propulsion Laboratory, Pasadena, Calif. “The new year offers new opportunities, and 2005 will be the year of the icy satellites.”

In 2005 Cassini will have 13 targeted encounters with five of Saturn’s moons. “We have 43 close flybys of Titan still ahead of us during the four-year tour. Next year, eight of our 13 close flybys will be of Titan. We will also have a number of more distant flybys of the icy satellites, and let’s not forget Saturn and the rings each time we come around,” said Mitchell.

With a diameter of about 1,400 kilometers (890 miles), Iapetus is Saturn’s third largest moon. It was discovered by Jean-Dominique Cassini in 1672. It was Cassini, for whom the Cassini-Huygens mission is named, who correctly deduced that one side of Iapetus was dark, while the other was white.

Scientists still do not agree on whether the dark material originated from an outside source or was created from Iapetus’ own interior. One scenario for the outside deposit of material would involve dark particles being ejected from Saturn?s little moon Phoebe and drifting inward to coat Iapetus. The major problem with this model is that the dark material on Iapetus is redder than Phoebe, although the material could have undergone chemical changes that made it redder after its expulsion from Phoebe. One observation lending credence to the theory of an internal origin is the concentration of material on crater floors, which implies that something is filling in the craters. In one model proposed by scientists, methane could erupt from the interior and then become darkened by ultraviolet radiation.

Iapetus is odd in other respects. It is the only large Saturn moon in a highly inclined orbit, one that takes it far above and below the plane in which the rings and most of the moons orbit. It is less dense than objects of similar brightness, which implies it has a higher fraction of ice or possibly methane or ammonia in its interior.

The last look at Iapetus was by NASA’s Voyager 1 and 2 spacecraft in 1980 and 1981. The Cassini images will be the highest resolution images yet of this mysterious moon. The Iapetus flyby by Cassini follows the successful release of the Huygens probe on December 24.

More information on the Cassini-Huygens mission is available at: http://saturn.jpl.nasa.gov and http://www.nasa.gov/cassini.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. JPL, a division of the California Institute of Technology in Pasadena, manages the Cassini mission for NASA’s Science Mission Directorate, Washington, D.C. JPL designed, developed and assembled the Cassini orbiter. The European Space Agency built and managed the development of the Huygens probe and is in charge of the probe operations. The Italian Space Agency provided the high-gain antenna, much of the radio system and elements of several of Cassini’s science instruments.

Cassini spacecraft targeted satellite encounters for 2005:

Titan: January 14, 2005
Titan: February 15, 2005
Enceladus: March 9, 2005
Titan: March 31, 2005
Titan: April 16, 2005
Enceladus: July 14, 2005
Titan: August 22, 2005
Titan: September 7, 2005
Hyperion: September 26, 2005
Dione: October 11, 2005
Titan: October 28, 2005
Rhea: November 26, 2005
Titan: December 26, 2005

Original Source: NASA/JPL News Release

Just how dense is Titan’s atmosphere expected to be, and how did that influence the design of the probe? – Kepesk

The atmosphere of Titan is denser and thicker than that of the Earth. The surface pressure is 1.5 times that on Earth (1500 mbar). But because Titan gravity is 1/6 of Earth’s, the atmosphere is much more expanded. Huygens will brake at about 300 km altitude, while Earth re-entry vehicles brake at about 60 km altitude.

The probe was designed to brake as high as possible for allowing in-situ sampling of the atmosphere as high as possible (about 165 km). It required a large heat-shield.

The heat-shield design was influenced by the presence of methane in the atmosphere. Methane and nitrogen break apart in the shock layer that forms in front of the probe during the hypersonic entry and form the CN radical which is a strong emitter of violet radiation (during the entry, Huygens radiates as much as 1000 sun for about 30 sec). CN radiates a lot of heat on the heat-shield. The amount of radiation (heat flux) on Huygens heat shield is 3 to 4 times higher than if we would enter in a pure nitrogen atmosphere.

How did Titan “collect” so much organic material and get such a dense atmosphere? Did Titan “collect” the stuff or was the moon lucky and manage not to lose it? – baselle

This is a fundamental question. Answering it is a major scientific objective of the Cassini-Huygens mission. Most (if not all) of the organic matter in Titan’s atmosphere and on the surface comes from the chemical processing of methane. The origin of methane is one of the big mysteries that Huygens should help to solve.

What design considerations were made on the probe to help ensure it would survive a trip to Saturn that took it on flybys to a few other planets along the way? – dave_f

The main design considerations for Huygens long trip to Saturn were to ensure that the temperature of its batteries would be kept cool enough. Huygens is protected by a multi-layer insulation thermal blanket and protected from the sun by the orbiter high-gain antenna until we reached Jupiter. Regular (bi-annual) activations of Huygens during a few hours were designed to monitor its health and calibration and to activate movable instrument mechanisms for their maintenance.

Survived landing will be a bonus, not the goal, with this in mind, was there anything other than timing and synchronicity with the orbiter considered when choosing a “landing” site? – tiderider

Huygens is not a lander. So I prefer to talk about impact or touchdown site. The impact site was not specifically chosen. The main drivers were: i) the entry angle in the atmosphere, ii) the need to descend in the sunlit side of Titan, iii) a low to medium latitude descent, but away from the equator for best wind measurements, and iv) an optimized geometry for the radio link with the orbiter.

Supposing that remarkable observations where recorded by Huygens, how could such observations contribute to our understanding of the solar system evolution? – Keemah

The detailed in-situ measurements by Huygens will be combined with the several-year global observations by the Cassini orbiter during its planned 45+ (more if the mission is extended) Titan flybys in order to better understand the weather on Titan, the chemical composition of the atmosphere, the origin and fate of the methane. In-situ isotopic measurements are a key for understanding the origin and evolution of Titan’s atmosphere. Understanding why Titan has a thick atmosphere (the only moon in the solar system to have a substantial atmosphere) will allow testing theories of planetary formation and evolution.

Are there some atmospheric (or even surface) conditions expected to disturb data transmission from Huygens to Cassini? – Lamahe

The atmosphere is transparent to radio communication between Huygens and Cassini (at 2 GHz). Too large a swing under the parachute may disturb the communication for a few seconds but Huygens will transmit on two radio channels. Key data are transmitted on the two channels but delayed by 6 sec on one of the two channels. This delay will allow all important data to be recovered if the link is interrupted for a short time.

If all goes well, how soon will detailed information about what did the probe observe be made available to the public? Is there a period when certain scientists have exclusive access? – antoniseb

Information will be made available to the public within hours after the data are received on earth on 14th January. Scientists will make every effort to make as much information as possible to the public. But scientists will also publish their research results in scientific literature within months. All Huygens data will be made available to the wide scientific community and to the public at large through ESA and NASA Planetary data archives in 2006.

What advice would you give someone who’s willing to work in space research? – Ola D.

You need to get a good education is mathematics, physics and chemistry, but also in literature and history of sciences in order to be able to communicate your research results to the public. You also need to be motivated to embrace a research career as jobs are difficult to get and not always well paid. If you want to undertake planetary research you need patience and to be unselfish. It took more than twenty years to get to Saturn from mission idea to the arrival. It will take years and decades to analyze all the data that will be returned by Cassini-Huygens. A mission such as Cassini-Huygens goes across generations. Cassini-like missions to Uranus and Neptune will take longer. But it is so exciting to be involved in such voyages that I would encourage all school boys and girls to study sciences and take a chance. It’s worth it. One more piece of advice. Cassini-Huygens is a true example of highly successful international collaboration. Learn a few languages as it will help to enjoy your trips abroad and best appreciate the multi-cultural environment you will work in as I am convinced that planetary exploration must be undertaken through multi-national collaborations.

The European Space Agency?s Huygens probe was successfully released by NASA?s Cassini orbiter early this morning and is now on a controlled collision course toward Saturn?s largest and most mysterious moon, Titan, where on 14 January it will make a descent through one of the most intriguing atmospheres in the solar system to an unknown surface.

The separation occurred at 02:00 UTC (03:00 CET): A few minutes after separation, Cassini turned back to Earth and relayed back information about the separation. This signal then took 1 hour and 8 minutes to cross the 1.2 billion kilometres separating the Cassini spacecraft and Earth.

?Today?s release is another successful milestone in the Cassini/Huygens odyssey?, said Dr David Southwood, ESA?s Director of Science Programmes. ?This was an amicable separation after seven years of living together. Our thanks to our partners at NASA for the lift. Each spacecraft will now continue on its own but we expect they?ll keep in touch to complete this amazing mission. Now all our hopes and expectations are focused on getting the first in-situ data from a new world we?ve been dreaming of exploring for decades?.

Final stage of a seven-year odyssey
The Cassini/Huygens mission, jointly developed by NASA, ESA and the Italian space agency (ASI), began on 15 October 1997, when the composite spacecraft were launched from Cape Canaveral, Florida, atop a Titan 4B/Centaur vehicle. Together, the two probes weighed 5548 kg at launch and became the largest space mission ever sent to the outer planets. To gain sufficient velocity to reach Saturn, they had to conduct four gravity-assist manoeuvres by flying twice by Venus, once by the Earth and once by Jupiter. On 1 July Cassini/Huygens eventually became the first spacecraft to enter an orbit around Saturn.

On 17 December, while on its third orbit around the ringed planet, the Cassini orbiter performed a manoeuvre to enter a controlled collision trajectory towards Titan. As planned, a fine tuning of the trajectory took place on 22 December to place Huygens on its nominal entry trajectrory. While Huygens will remain on this trajectory till it plunges into Titan?s atmosphere on 14 January, the orbiter will perform a deflection manoeuvre on 28 December to avoid crashing onto the moon. Today?s separation was achieved by the firing of pyrotechnic devices. Under the action of push-off springs, ramps and rollers, the probe was released at a relative velocity of about 0.3 m/s with a spin rate of 7 rpm. Telemetry data confirming the separation were collected by NASA?s Deep Space Network stations in Madrid, Spain and Goldstone, California, when the telemetry playback signal from Cassini eventually reached the Earth.

The Huygens probe is now dormant and will remain so for its 20-day coast phase to Titan. Four days before its release, a triply-redundant timer was programmed in order to wake-up the probe?s systems shortly before arrival on Titan.

Exploring Titan?s atmosphere
Huygens is scheduled to enter Titan?s atmosphere at about 09:06 UTC (10:06 CET) on 14 January, entering at a relatively steep angle of 65? and a velocity of about 6 km/s. The target is over the southern hemisphere, on the day side. Protected by an ablative thermal shield, the probe will decelerate to 400 m/s within 3 minutes before it deploys a 2.6 m pilot chute at about 160 km. After 2.5 seconds this chute will pull away the probe?s aft cover and the main parachute, 8.3 m in diameter, will deploy to stabilise the probe. The front shield will then be released and the probe, whose main objective is to study Titan?s atmosphere, will open inlet ports and deploy booms to collect the scientific data. All instruments will have direct access to the atmosphere to conduct detailed in-situ measurements of its structure, dynamics and chemistry. Imagery of the surface along the track will also be acquired. These data will be transmitted directly to the Cassini orbiter, which, at the same time, will be flying over Titan at 60 000 km at closest approach. Earth-based radiotelescopes will also try to detect the signal?s tone directly.

Huygens changing its parachutes
After 15 minutes, at about 120 km, Huygens will release its main parachute and a smaller 3 m drogue chute will take over to allow a deeper plunge through the atmosphere within the lifetime of the probe?s batteries.

The descent will last about 140 minutes before Huygens impacts the surface at about 6 m/s. If the probe survives all this, its extended mission will start, consisting in direct characterisation of Titan?s surface for as long as the batteries can power the instruments and the Cassini orbiter is visible over the horizon at the landing site, i.e. not more than 130 minutes.

At that time, the Cassini orbiter will reorient its main antenna dish toward Earth in order to play back the data collected by Huygens, which will be received by NASA?s 70-m diameter antenna in Canberra, Australia, 67 minutes later. Three playbacks are planned, to ensure that all recorded data are safely transmitted to Earth. Then Cassini will continue its mission exploring Saturn and its moons, which includes multiple additional flybys of Titan in the coming months and years.

A probe deep into space and time
Bigger than Mercury and slightly smaller than Mars, Titan is unique in having a thick hazy nitrogen-rich atmosphere containing carbon-based compounds that could yield important clues about how Earth came to be habitable. The chemical makeup of the atmosphere is thought to be very similar to Earth?s before life began, although colder (-180?C) and so lacking liquid water. The in-situ results from Huygens, combined with global observations from repeated flybys of Titan by the Cassini orbiter, are thus expected to help us understand not only one of the most exotic members of our Solar System but also the evolution of the early Earth’s atmosphere and the mechanisms that led to the dawn of life on our planet.

Europe?s main contribution to the Cassini mission, the Huygens probe, was built for ESA by an industrial team led by Alcatel Space. This 320 kg spacecraft is carrying six science instruments to study the atmosphere during its descent. Laboratories and research centres from all ESA member countries, the United States, Poland and Israel have been involved in developing this science payload. The Huygens atmospheric structure instrument package (HASI) will measure temperature and pressure profiles, and characterise winds and turbulences. It will also be able to detect lightning and even to measure the conductivity and permittivity of the surface if the probe survives the impact. The gas chromatograph mass spectrometer (GCMS) will provide fine chemical analysis of the atmosphere and the aerosols collected by the aerosol collector and pyrolyser (ACP). The descent imager/spectral radiometer (DISR) will collect images, spectra and other data on the atmosphere, the radiation budget, cloud structures, aerosols and the surface. The doppler wind experiment (DWE) will provide a zonal wind profile while the surface science package (SSP) will characterise the landing site if Huygens survives the impact.

The Cassini-Huygens mission is a cooperation between NASA, 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. JPL designed, developed and assembled the Cassini orbiter.

Original Source: ESA News Release

Image credit: ESA
After a seven-year and 3.2 billion km journey from Earth to Saturn, ESA?s Huygens probe, travelling on board NASA?s Cassini mother craft and powered through an umbilical cable, is now ready to separate and continue its journey alone toward Titan, Saturn?s largest moon.

On Christmas night (25 December at 03:00 CET- orbiter time/04:08 CET on the ground) Huygens will be cut loose from Cassini and will coast toward Titan for 20 days, to arrive at its destination on 14 January.

?We have the green light for separation. The joint ESA/NASA team has done all that had to be done to be ready for release. We are looking forward to receiving data on 14 January at ESA?s Spacecraft Operations Centre in Darmstadt, Germany.?, said Claudio Sollazzo, ESA?s Head of Huygens Spacecraft Operations Unit at NASA/JPL in Pasadena, California.

At separation, tension-loaded springs will gently push Huygens away from Cassini onto a ballistic 4-million kilometre path to Titan. The Huygens probe will remain dormant until the on-board timer, which has been loaded on 21 December, wakes it up shortly before it reaches Titan’s upper atmosphere on 14 January.

?We will then have to wait patiently for the most exciting phase of our mission, when Cassini will send back to Earth the Huygens data. The Huygens descent will be accomplished in less then two and half hours and, if the probe survives the impact with the surface, we could expect up to two extra hours of science results before the onboard batteries die out? said Jean-Pierre Lebreton, ESA?s Huygens Mission Manager and Project Scientist, preparing to follow the separation from NASA/JPL in Pasadena.

At about 1200 km above the surface of Titan, the Huygens probe will begin a dramatic plunge through Titan?s thick haze, with the task to analyze the chemical makeup and composition of the moon?s atmosphere as it descends to touchdown on its surface. With Cassini listening to the probe for 4.5 hours, the data gathered during the descent and on the surface will be transmitted continuously by the probe and recorded onboard the Cassini orbiter.

Cassini will then turn away from Titan and point its antenna to Earth and relay the data through NASA’s Deep Space Network to JPL and on to ESA’s Space Operations Centre ESOC in Darmstadt, Germany where the Huygens probe data will be analysed by scientists.

After a successful probe release, on 28 December, the Cassini orbiter will perform a deflection manoeuvre to keep it from following Huygens into Titan’s atmosphere and to establish the required geometry between the probe and the orbiter for radio communications during the probe?s descent. The Cassini-Huygens mission is a cooperation between NASA, 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.

Original Source: ESA News Release

When the European Space Agency’s Huygens spacecraft makes its plunge into the atmosphere of Saturn’s moon Titan on January 14, radio telescopes of the National Science Foundation’s National Radio Astronomy Observatory (NRAO) will help international teams of scientists extract the maximum possible amount of irreplaceable information from an experiment unique in human history. Huygens is the 700-pound probe that has accompanied the larger Cassini spacecraft on a mission to thoroughly explore Saturn, its rings and its numerous moons.

The Robert C. Byrd Green Bank Telescope (GBT) in West Virginia and eight of the ten telescopes of the continent-wide Very Long Baseline Array (VLBA), located at Pie Town and Los Alamos, NM, Fort Davis, TX, North Liberty, IA, Kitt Peak, AZ, Brewster, WA, Owens Valley, CA, and Mauna Kea, HI, will directly receive the faint signal from Huygens during its descent.

Along with other radio telescopes in Australia, Japan, and China, the NRAO facilities will add significantly to the information about Titan and its atmosphere that will be gained from the Huygens mission. A European-led team will use the radio telescopes to make extremely precise measurements of the probe’s position during its descent, while a U.S.-led team will concentrate on gathering measurements of the probe’s descent speed and the direction of its motion. The radio-telescope measurements will provide data vital to gaining a full understanding of the winds that Huygens encounters in Titan’s atmosphere.

Currently, scientists know little about Titan’s winds. Data from the Voyager I spacecraft’s 1980 flyby indicated that east-west winds may reach 225 mph or more. North-south winds and possible vertical winds, while probably much weaker, may still be significant. There are competing theoretical models of Titan’s winds, and the overall picture is best summarized as poorly understood. Predictions of where the Huygens probe will land range from nearly 250 miles east to nearly 125 miles west of the point where its parachute first deploys, depending on which wind model is used. What actually happens to the probe as it makes its parachute descent through Titan’s atmosphere will give scientists their best-ever opportunity to learn about Titan’s winds.

During its descent, Huygens will transmit data from its onboard sensors to Cassini, the “mother ship” that brought it to Titan. Cassini will then relay the data back to Earth. However, the large radio telescopes will be able to receive the faint (10-watt) signal from Huygens directly, even at a distance of nearly 750 million miles. This will not be done to duplicate the data collection, but to generate new data about Huygens’ position and motions through direct measurement.

Measurements of the Doppler shift in the frequency of Huygens’ radio signal made from the Cassini spacecraft, in an experiment led by Mike Bird of the University of Bonn, will largely give information about the speed of Titan’s east-west winds. A team led by scientists at NASA’s Jet Propulsion Laboratory in Pasadena, CA, will measure the Doppler shift in the probe’s signal relative to Earth. These additional Doppler measurements from the Earth-based radio telescopes will provide important data needed to learn about the north-south winds.

“Adding the ground-based telescopes to the experiment will not only help confirm the data we get from the Cassini orbiter but also will allow us to get a much more complete picture of the winds on Titan,” said William Folkner, a JPL scientist.

Another team, led by scientists from the Joint Institute for Very Long Baseline Interferometry in Europe (JIVE), in Dwingeloo, The Netherlands, will use a world-wide network of radio telescopes, including the NRAO telescopes, to track the probe’s trajectory with unprecedented accuracy. They expect to measure the probe’s position within two-thirds of a mile (1 kilometer) at a distance of nearly 750 million miles.

“That’s like being able to sit in your back yard and watch the ball in a ping-pong game being played on the Moon,” said Leonid Gurvits of JIVE.

Both the JPL and JIVE teams will record the data collected by the radio telescopes and process it later. In the case of the Doppler measurements, some real-time information may be available, depending on the strength of the signal, but the scientists on this team also plan to do their detailed analysis on recorded data.

The JPL team is utilizing special instrumentation from the Deep Space Network called Radio Science Receivers. One will be loaned to the GBT and another to the Parkes radio observatory. “This is the same instrument that allowed us to support the challenging communications during the landing of the Spirit and Opportunity Mars rovers as well as the Cassini Saturn Orbit Insertion when the received radio signal was very weak,” said Sami Asmar, the JPL scientist responsible for the data recording.

When the Galileo spacecraft’s probe entered Jupiter’s atmosphere in 1995, a JPL team used the NSF’s Very Large Array (VLA) radio telescope in New Mexico to directly track the probe’s signal. Adding the data from the VLA to that experiment dramatically improved the accuracy of the wind-speed measurements.

“The Galileo probe gave us a surprise. Contrary to some predictions, we learned that Jupiter’s winds got stronger as we went deeper into its atmosphere. That tells us that those deeper winds are not driven entirely by sunlight, but also by heat coming up from the planet’s core. If we get lucky at Titan, we’ll get surprises there, too,” said Robert Preston, another JPL scientist.

The Huygens probe is a spacecraft built by the European Space Agency (ESA). In addition to the NRAO telescopes, the JPL Doppler Wind Experiment will use the Australia Telescope National Facility and other radio telescopes in Parkes, Mopra, and Ceduna, Australia; Hobart, Tasmania; Urumqi and Shanghai, China; and Kashima, Japan. The positional measurements are a project led by JIVE and involving ESA, the Netherlands Foundation for Research in Astronomy, the University of Bonn, Helsinki University of Technology, JPL, the Australia Telescope National Facility, the National Astronomical Observatories of China, the Shanghai Astronomical Observatory, and the National Institute for Communication Technologies in Kashima, Japan.

The Joint Institute for VLBI in Europe is funded by the national research councils, national facilities and institutes of The Netherlands (NWO and ASTRON), the United Kingdom (PPARC), Italy (CNR), Sweden (Onsala Space Observatory, National Facility), Spain (IGN) and Germany (MPIfR). The European VLBI Network is a joint facility of European, Chinese, South African and other radio astronomy institutes funded by their national research councils. The Australia Telescope is funded by the Commonwealth of Australia for operation as a National Facility managed by CSIRO.

The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

Original Source: NRAO News Release