[Space] NASA-ESA - Cassini-Hyugens

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Huygens begins its final journey into the unknown

25 December 2004

ESA PR 67-2004. 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.


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.

For further information, please contact:
ESA Media Relations Division
Tel: +33(0)1.53.69.7155
Fax: +33(0)1.53.69.7690

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Da Spaceflightnow.com:

Cassini takes picture of departing Huygens probe

CASSINI PHOTO RELEASE
Posted: December 26, 2004


Credit: NASA/JPL

The Cassini spacecraft snapped this image of the European Space Agency's Huygens probe about 12 hours after its release from the orbiter. The probe successfully detached from Cassini on Dec. 24, 2004, and is on course for its January 14 encounter with Titan.

The Huygens probe will remain dormant until the onboard timer wakes it up just before the probe reaches Titan's upper atmosphere on Jan. 14, 2005. Then it will begin a dramatic plunge through Titan's murky atmosphere, tasting its chemical makeup and composition as it descends to touch down on its surface. The data gathered during this 2-1/2 hour descent 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 JPL 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. From this control center, ESA engineers will be tracking the probe and scientists will be standing by to process the data from the probe's six instruments.


Credit: NASA/JPL

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.

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Probe travels to surface of Saturn's moon Titan Friday

BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: January 12, 2005

KENNEDY SPACE CENTER, Fla. (CBS) - In one of the boldest space missions ever attempted, a small European-built probe will slam into the atmosphere of Saturn's mysterious moon Titan Friday for a two-and-a-half hour parachute descent to its smog-shrouded surface.


An artist's concept shows Huygens nearing Titan. Credit: ESA

Beaming pictures and a torrent of data to NASA's Cassini Saturn orbiter, the flying saucer-shaped Huygens probe will give scientists their first close-up look at one of the largest expanses of unexplored territory in the solar system.

Researchers are hopeful Huygens will answer their most pressing questions: whether hydrocarbons fall like rain and form pools of liquid ethane and similar compounds on the moon's frigid surface; and what erosional or depositional processes are responsible for covering up impact craters and producing a relatively flat, mountain-free surface.

No matter what Huygens actually sees on the surface, scientists expect to gain insights into the workings of a thick, complex atmosphere that in some respects mirrors Earth's shortly after the planet's birth.

"We ought to be able to see a pretty good panorama of the area that the Huygens probe is going to land in," Jonathan Lunine, a planetary scientist at the University of Arizona, said in a recent interview. "Those pictures will continue all the way down to the surface, they'll be interrupted right at the end when the camera switches over to take what are called spectra, which will tell us about the composition of the surface. So we ought to be able to get a pretty good panorama to start with.

"We ought to be able to see whether the probe came down in an area that's mostly craters or other kinds of land forms. We ought to be able to get a hint of whether there might be pools or lakes of liquid in that area. It won't be immediately apparent whether dark places are liquid or solid, but depending on where the probe lands, we might get some direct information on that. And we might see clouds in the sky toward the horizon.

"There may be some detection of lightning," he said, "although there probably isn't a lot of lightning in Titan's atmosphere. And then after impact, or touchdown, if the antennas aren't pointed in a strange direction, we should be able to get some information about the surface. If we're lucky enough to land in liquid, then the probe should be bobbing up and down and there's a tilt meter that will tell us that. And we might be able to get samples of surface material because the probe will still be warm and anything like these liquid hydrocarbons will vaporize and go up into the sample inlets."

Huygens was released from Cassini on Christmas Eve, placed on a collision course with Titan that was set up to ensure the proper atmospheric entry angle. David Southwood, the European Space Agency's science director, thanked NASA for the lift, saying "now all our hopes and expectations are focused on getting the first in situ data from a new world weÕve been dreaming of exploring for decades."

During flybys of Titan in late October and again in December, Cassini's powerful cameras, an imaging radar system and other instruments mapped the surface in unprecedented detail, revealing a relatively flat terrain and unusual, sharply defined features that defied easy explanation.

Only a handful of large crater-like circular structures were apparent and researchers did not see the sort of specular reflections one might expect from sunlight glinting off a liquid surface.

Whether Huygens will detect standing lakes or pools is a major question mark going into Friday's descent. So far, said Torrence Johnson, a Cassini imaging team member at the Jet Propulsion Laboratory in Pasadena, Calif., "we don't have any evidence (for liquids)."

"Just like we don't have any clear evidence of something we know is a crater, there's nothing there that anybody's willing to hang their hat on yet that yes, we absolutely have a liquid surface," he said in a telephone interview Monday.

"What we saw (in the initial Cassini flybys), of course, was a surface that was much stranger than most of us thought we would see," he said. "The real story so far has been the things we didn't see."

Like large craters, hills or mountain ranges and obvious lakes or river-like structures. But that doesn't mean liquids aren't there. Just that Cassini didn't spot them in its initial looks at the moon.

"It's a distinct possibility that I could be the very first scientist to carry out oceanography on an outer planet of the solar system," said John Zarnecki, principal scientist for the Huygens Science Surface Package. "But equally the probe could land with a thud on hard ground or squelch into a morass of extraterrestrial slime - no one knows for sure.

"In any event, the instruments onboard have been designed to handle a range of possibilities," he said in a statement. "Let's just say that, after a seven-year voyage and twenty years of planning, design and build, I will be extremely pleased to land, whatever the surface."


An artist's concept shows Huygens descending on its parachute. Credit: ESA

Huygens, if it survives long enough, should reveal the surface in sharp detail and send back a wealth of data about its thick atmosphere. But even that will not be enough to answer all the questions posed by the scientific community.

"I think we're going to have to wait several flybys, maybe even several years, before we get a really good indication of what's going on," said Carolyn Porco, the Cassini imaging team leader. "What Huygens will do, of course, is give us a very exquisitely detailed view of one place. So their information will (provide) the 'ground truth' for helping us interpret what we see."

Spinning at 7 rpm for stability, Huygens will slam into the atmosphere Friday at an altitude of 789 miles, traveling at some 12,400 mph. A thick carbon composite heat shield will protect the craft from the fierce heat of atmospheric friction - 21,600 degrees Fahrenheit at maximum - which will quickly slow the probe to more benign speeds. Maximum deceleration is expected to be around 16 Gs.

When the velocity has dropped to about 870 mph, Huygens' aft cover will be pulled away by a pilot chute and the spacecraft's 27-foot-wide main parachute will deploy 2.5 seconds later.

The main chute will be jettisoned 15 minutes later and from that point on, Huygens will ride beneath a smaller 9.8-foot-wide parachute. Impact on the surface at some 11 mph is expected about two-and-a-half hours after entry begins. Regardless of how long Huygens might survive on the surface, Cassini will sink below Titan's horizon about 30 minutes after touchdown.

Assuming the 705-pound Huygens doesn't sink in a hydrocarbon lake, "we have good confidence the probe will survive landing," said European Space Agency mission manager Jean-Pierre Lebreton. "The landing speed is very low. We have capability to do measurements for half an hour on the surface."

Here is a detailed timeline of major entry events on Jan. 14 (in EST; all times represent when an event occurs relative to signals received on Earth). Explanations for key events from the European Space Agency's Huygens website; Cassini timeline events provided by the Jet Propulsion Laboratory:

Jan. 14

02:33 AM (-02h40m) - Cassini solid state recorders prepped for support
02:45 AM (-02h28m) - Cassini transition to thruster control for relay
02:55 AM (-02h18m) - Cassini: final recorder configuration for relay
02:57 AM (-02h16m) - Turn on Probe receivers
03:09 AM (-02h04m) - Cassini turns toward Titan
03:21 AM (-01h52m) - Turn to Titan complete
03:24 AM (-01h49m) - Cassini disables X-band downlink
04:51 AM (-00h22m) - Probe turns transmitters on (low power mode)
05:13 AM (-00h00m) - Probe reaches the discernible atmosphere: 789 miles
05:16 AM (+00h03m) - Probe feels maximum deceleration


05:17 AM (+00h04m) - Pilot chute: 106-118 miles altitude; Mach 1.5; The parachute deploys when Huygens detects that it has slowed to 895 mph, at about 112 miles above Titan's surface. The pilot parachute is the probe's smallest, only 8.5 feet 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 27.2 feet in diameter, unfurls.

05:18 AM (+00h05m) - At about 99 miles above the surface, the front shield is released. Forty-two 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.

05:32 AM (+00h19m) - Main parachute separates and drogue parachute deploys: The drogue parachute is 9.8 feet in diameter. At this level in the atmosphere, about 78 miles 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.

05:49 AM (+00h36m) - Surface proximity sensor activated: Until this point, all of Huygens's actions have been based on clock timers. At a height of 37 miles, 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.

05:56 AM (+00h43m) - Possible icing effects to Probe (31 miles)

06:57 AM (+01h41m) - 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.

07:19 AM (+02h06m) - Cassini closest approach: 37,282 miles flyby at 12,080 mph, 93 deg phase

07:30 AM (+02h17m) - 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.

07:34 AM (+02h21m) - 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 11.2-13.4 mph. 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.

09:44 AM (+04h31m) - 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.

09:46 AM (+04h33m) - Cassini probe data partitions write protected
09:54 AM (+04h41m) - Cassini turns toward Earth
09:57 AM (+04h44m) - Turn to Earth complete
10:06 AM (+04h53m) - Critical sequence ends
10:07 AM (+04h54m) - Post-Probe tracking begins (Canberra)


10:14 AM (+05h01m) - First data sent to Earth: 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.

10:17 AM (+05h04m) - Probe data replay begins (Canberra: 66,360 bps)
12:57 PM (+07h44m) - End playback of first partition
01:04 PM (+07h51m) - Ascending ring-plane crossing: 18.4 Saturn radii
02:00 PM (+08h47m) - Start tracking at Madrid (142,200 bps)
05:07 PM (+11h54m) - End first full playback of all Probe data
08:29 PM (+15h16m) - Full data set on Earth (likely three hours earlier)
10:35 PM (+17h22m) - Start tracking at Goldstone


Jan. 15

07:07 AM (+01d02h) - Power on of orbiter instruments
08:30 AM (+01d03h) - End nominal playback of Probe data


Cassini braked into orbit around Saturn on July 1 after a seven-year voyage from Earth. The original flight plan called for Huygens to enter Titan's atmosphere in late November as Cassini streaked overhead at an altitude of just 746 miles. But engineers were forced to delay Huygens' arrival to this month because of an issue with the radio aboard the Cassini mothership that will be used to relay data from Huygens to Earth.

During a post-launch test, engineers discovered the radio receiver could not cope with the Doppler shift in the frequency of the signal coming from Huygens due to Cassini's high relative velocity. Much like the pitch of a siren changes as a police car races past a stationary observer, the frequency of radio waves can shift a significant amount if relative velocities are high enough.

"Originally, the closing speed of Cassini coming up on Huygens, which is for all practical purposes sitting still once it's in the atmosphere, the closing speed was about 5.8 kilometers per second (13,000 mph)," Cassini program manager Bob Mitchell said in a recent interview. "And because we were coming in almost dead overhead and going off to the right at about 1,200 kilometers (746 miles) altitude."

The solution was to minimize the Doppler shift by reducing the relative velocities of the two spacecraft. That was accomplished by changing Cassini's trajectory slightly and delaying Huygens' release to Christmas Eve. During the Jan. 14 descent, Cassini now will be 37,300 miles from Titan and the difference in velocity between the two spacecraft will never be more than 8,500 mph.

"We have pretty solid evidence that's going to work," Mitchell said. "We did some tests where we used the Deep Space Network stations transmitting an S-band signal with telemetry modulated onto the carrier so that from the receiver's point of view on the Cassini spacecraft, it should have simulated the probe quite accurately. We adjusted the frequency, taking into account the motion of everything, so that the frequency of the received signal at the receiver should very closely if not exactly match the frequency that the receiver will see coming from Huygens."

The tests were successful and a potentially crippling design flaw was resolved with no significant loss of science. And so, the stage is set for a dramatic voyage of discovery.

"Whatever is there is going to look pretty good, I think," Johnson said. "The probe is spinning as it comes down, sort of a spin-scan imager looking out and down at an angle. Of course, the haze will get less as you go down.

"We had hoped that once it got down to within a hundred kilometers of the surface or something like that we'd start seeing things that looked like pictures out of an airplane window. Based on our data, I think that maybe they will still see a very hazy surface even at longer wavelengths at that type of altitude. Because one of the things that we found is that some of the scattering that's producing this fuzzy appearance on the surface is happening down under 10 kilometers. ... But at some point, we ought to start seeing the surface more clearly. It may be in the last 10 kilometers of descent."

Johnson said he was especially looking forward to finding out "what sort of topography there is. Is it all flat down there? Or are there hints of underlying topography?"

"I would hope we would be able to tell the difference between mantle material that's been covered up by soft aerosols and areas where there might be really flat places with lakes, all of which could be hidden in the data we're seeing now at the resolutions we have."

Whatever Huygens sees, "it could be pretty damn spectacular," Johnson said.

[GioFX]

CI SIAMO, IL MOMENTO STA PER ARRIVARE

Tutti i giornali ne parlano , tranne i nostri!

www.cnn.com


Huygens to plumb secrets of Saturn moon

(CNN) -- The Huygens probe will plunge through the orange clouds of Saturn's moon Titan Friday, offering scientists their first glimpse of the mysterious moon.

"It's going to be the most exotic place we've ever seen," said Candice Hansen, a scientist for the Cassini-Huygens mission. "We've never landed on the surface of an icy satellite. We know from our pictures that there are very different kinds of geological processes."

If all goes well, the saucer-shaped Huygens will enter the thick atmosphere of Titan Friday at about 5:13 a.m. (ET). The data should start trickling in about five hours later.

The Cassini-Huygens mission is an unprecedented $3.3-billion effort between NASA, the European Space Agency and Italy's space program to study Saturn and its 33 known moons. The two vehicles were launched together from Florida in 1997.

"The mission is to explore the entire Saturnian system in considerably greater detail than we have ever been able to do before: the atmosphere, the internal structure, the satellites, the rings, the magnetosphere," said Cassini program manager Bob Mitchell at NASA.

The Huygens probe, about the size of a Volkswagen-Beetle, has been spinning silently toward Titan since it detached from the Cassini spacecraft on December 24. Cassini will remain in orbit around Saturn until at least July 2008.

"[The Cassini-Huygens mission] will probably help answer some of the big questions that NASA has in general about origins and where we came from and where life came from," said Mitchell.

Titan's atmosphere, a murky mix of nitrogen, methane and argon, resembles Earth's before life began more than 3.8 billion years ago. Scientists think the moon may shed light on how life evolved on Earth.

Finding living organisms, however, is a remote possibility. "It is not out of the question, but it is certainly not the first place I would look," said Hansen. "It's really very cold." A lack of sunlight has put Titan into a deep-freeze. Temperatures hover around -292 F (-180 C) making liquid water scarce and hindering chemical reactions needed for organic life.

New discoveries
The mysteries of Saturn, the sixth planet from the sun, have always enticed researchers. Scientists are perplexed why Saturn, a gas-giant composed primarily of hydrogen and helium, releases more energy than it absorbs from faint sunlight. Titan is also the only moon in the solar system to retain a substantial atmosphere, one even thicker than Earth's.

The 703-pound, battery-powered probe will parachute through Titan's clouds of methane and nitrogen for two and a half hours sampling gases and capturing panoramic pictures. Soon afterward, Huygens will reach the surface. However, its landing site is still a matter of conjecture. Scientists say it could be solid, slushy or even a liquid sea of ethane and hydrocarbons.

"Those are the kinds of things that we have theories about, but we really don't have data," said Hansen.

Huygens is expected to hit the upper atmosphere 789 miles (1,270 km) above the moon at a speed of about 13,700 mph (22,000 km/h). A series of three parachutes will slow the craft to just 15 mph (24 km/h). The chutes and special insulation will protect Huygens from temperature swings and violent air currents. Strong winds -- in excess of 311 mph (500 km/h) --will buffet the craft, at times dragging Huygens sideways after its parachute is deployed.

Sensors will deduce wind speed, atmospheric pressure and the conductivity of Titan's air. Methane clouds and possibly hydrocarbon rain can be analyzed by an onboard gas chromatograph. A microphone will listen for thunder.

Three rotating cameras will snap panoramic views of the moon capturing up to 1,100 images. A radar altimeter will map Titan's topography and a special lamp will illuminate the probe's landing spot to help determine the surface composition.

Engineers say they are confident that Huygens and its suite of six sensitive instruments will survive the descent.

"From an engineering standpoint, I'm very confident in a positive outcome," said Shaun Standley, an ESA systems engineer for Huygens at the Jet Propulsion Laboratory in California. "We've been over this again and again for the last three years fine-tuning this."

As the largest and most sophisticated interplanetary vehicle ever launched, according to NASA, Cassini-Huygens has performed well on its 2.2-billion mile (3.5 billion km) journey.

Cassini crossed Saturn's rings without mishap in June 2004 and produced the most revealing photos yet of the rings and massive gas-giant. A problem with the design of an antennae on Cassini almost scrapped Huygens' mission, but engineers altered the spacecrafts' flight plans to resolve the transmission problem.

Now, Huygens is on its own.

Controllers can only that hope years of preparation will pay off. "[Huygens] is on its way, we can't contact it," said Standley. "We can't make any changes of anything that is on board. [It's] just waiting for the right moment."

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NASA-ESA CASSINI-HYUGENS MISSION TO SATURN AND TITAN:

- http://saturn.jpl.nasa.gov/home/index.cfm

- http://www.esa.int/esaCP/index.html


TIMELINE:

- http://www.esa.int/esaCP/SEMZGTQ3K3E_index_0.html


NASA TV LIVE COVERAGE:

- http://www.nasa.gov/ram/35037main_portal.ram


HYUGENS POSITION:

[GioFX]

Huygens phones home as it descends!!!!

A radio telescope on Earth has detected a faint signal from the descending Huygens spacecraft, confirming the probe is alive, has survived its super-hot entry into the atmosphere and should be carrying out its scientific exploration on the way to the surface of Saturn's moon Titan.




FRIDAY, JANUARY 14, 2005
1033 GMT (5:33 a.m. EST)

SIGNAL FROM HUYGENS! A radio telescope on Earth has detected a faint signal from the descending Huygens spacecraft, confirming the probe is alive, has survived its super-hot entry into the atmosphere and should be carrying out its scientific exploration on the way to the surface of Saturn's moon Titan.

This is just a signal with no actual data included. The data is being relayed to the Cassini orbit and will be played to Earth later today.

Nonetheless, the fact that a signal has been received to verify that Huygens is functioning prompted screams and cheers in mission control.

[jumpermax]

a leggere ste cose ci si rimane beccare un segnale del genere da questa distanza....

[GioFX]

Originariamente inviato da jumpermax
a leggere ste cose ci si rimane beccare un segnale del genere da questa distanza....

Hyugens sta scendendo sulla faccia nascosta di Titano, ed evidentemente quella esposta alla Terra, per vengono ricevuti i segnali.

[gpc]

Jumper, perchè non esponi anche a Gio la tua teoria sulle foto in bianco e nero?

[jumpermax]

Originariamente inviato da gpc
Jumper, perchè non esponi anche a Gio la tua teoria sulle foto in bianco e nero?

ah fetecchione...
Secondo gpc non possono fare foto a colori perché contrariamente ai rover marziani la sonda è in movimento. Secondo me invece dipende essenzialmente dal fatto che la luce non è sufficiente per fare foto a colori valide... il problema del movimento si risolve facilmente con 3 sensori separati (come ad esempio fanno le sonde che orbitano attorno a marte) La maggior parte delle foto poi non sono prese nello spettro di luce visibile proprio per questo, la luce non è sufficiente per avere immagini dettagliate. Ma se da una foto all'infrarosso si può ricostruire una forma altrettanto non lo si può fare per i colori...

[GioFX]

1115 GMT (6:15 a.m. EST)

Huygens should be continuing its long, parachute-aided fall to the surface of Titan, with the large suite of science instruments operating to study the atmosphere and obtain volumes of pictures. Huygens is doing its work out of view from mission control. Real-time confirmation that the science program is being performed is not available because the craft is sending the information directly to the Cassini orbiter, which itself has turned away from Earth to receive the Huygens data.

Earlier, controllers got a simple tone from Huygens that did announce the craft was at least alive.

A news conference is coming up at 1230 GMT (7:30 a.m. EST). Cassini will resume communications with Earth about three hours later, and the data playback will continue for several hours.


@

PS: ciao gp!

[gpc]

Originariamente inviato da jumpermax
ah fetecchione...
Secondo gpc non possono fare foto a colori perché contrariamente ai rover marziani la sonda è in movimento. Secondo me invece dipende essenzialmente dal fatto che la luce non è sufficiente per fare foto a colori valide... il problema del movimento si risolve facilmente con 3 sensori separati (come ad esempio fanno le sonde che orbitano attorno a marte) La maggior parte delle foto poi non sono prese nello spettro di luce visibile proprio per questo, la luce non è sufficiente per avere immagini dettagliate. Ma se da una foto all'infrarosso si può ricostruire una forma altrettanto non lo si può fare per i colori...

Ma guardalo, ma guardalo!
Gli dico di esporre la sua teoria e lui risponde "Secondo gpc..." Sei proprio diventato un moderatore ormai, non c'è più speranza...

Alllllloraaa...
Jumper dice che non si possono fare foto a colori di Saturno perchè c'è troppa poca luce e quindi vengono solo foto in bianco e nero, io invece gli ho spiegato che le foto a colori sono fatte con tre foto in bianco e nero prese con i filtri relativi ai tre colori fondamentali (al che lui ha detto "sì sì, la so anche io quella storiella..." ) e che, a parte il fatto che di foto a colori ce ne sono eccome, non sempre c'è bisogno di farne tre dello stesso soggetto, sia per una questione di necessità sia per una questione di risparmio di banda.
Inoltre, mentre i rover possono fermarsi e fare i loro mosaici da trecento foto, la sonda si muove e le tre foto, se fatte ad un oggetto troppo vicino, non sarebbero sovrapponibili.
Inoltre, le foto vengono prese a lunghezze d'onda non visibili perchè è a quelle lunghezze d'onda, per esempio, che l'atmosfera di Titano risulta più visibile o che certi fenomeni sono più manifesti, non certamente perchè non c'è abbastanza luce...

Dai Gio, tu che ne pensi? E stai attento, perchè lo sai che discutere con Jumper vuol dire andare avanti finchè uno dei due non è sfinito... (in questo è molto ingegnere, devo riconoscelo... )

PS: Ciao Gio! Hai visto come hanno trattato la missione sulla cometa nell'altro thread? Dicendo che è solo una missione balistica senza nessun senso...

[Lor3nzo76]

Originariamente inviato da jumpermax
Ma se da una foto all'infrarosso si può ricostruire una forma altrettanto non lo si può fare per i colori...

In teoria conoscendo la risposta in frequenza, l'assorbimento e l'emissività dei vari materiali si potrebbe ricostruire il colore a partire da un immagine all'infrarosso, ma prevede che di ogni matriale sostanza o miscela si conosca esattamente il diagramma potere emissivo - frequenza, e nel caso di miscele anche la composizione approssimata.
Così però si va nei matti e si otterrebbe comunque un risultato approssimato, visto che sarebbe impossibile conoscere tutte le variabili con uno scarto decente.

Lore

[GioFX]

Originariamente inviato da jumpermax
ah fetecchione...
Secondo gpc non possono fare foto a colori perché contrariamente ai rover marziani la sonda è in movimento. Secondo me invece dipende essenzialmente dal fatto che la luce non è sufficiente per fare foto a colori valide... il problema del movimento si risolve facilmente con 3 sensori separati (come ad esempio fanno le sonde che orbitano attorno a marte) La maggior parte delle foto poi non sono prese nello spettro di luce visibile proprio per questo, la luce non è sufficiente per avere immagini dettagliate. Ma se da una foto all'infrarosso si può ricostruire una forma altrettanto non lo si può fare per i colori...

Questa volta ha ragione gp, infatti le immagini sono fatte in bianco e nero o con i singoli filtri, per comporre un immagine a colori occorre sovrappore le immagini con i tre filtri relativi ai colori fondamentali.

Per il resto, il tutto viene spiegato in questa discussione di SDC:

http://uplink.space.com/showflat.php...b=5&o=0&fpart=

[gpc]

Originariamente inviato da GioFX
Questa volta ha ragione gp

YYYAAAAAAAAAAAAHHHHHH

Grazie Gio, lo so che queste frasi ti costano almeno cinque anni di vita l'una...

[GioFX]

Originariamente inviato da gpc
YYYAAAAAAAAAAAAHHHHHH

Grazie Gio, lo so che queste frasi ti costano almeno cinque anni di vita l'una...

meno male, non l'ho dovuto dire io...

[jumpermax]

Originariamente inviato da GioFX
Questa volta ha ragione gp, infatti le immagini sono fatte in bianco e nero o con i singoli filtri, per comporre un immagine a colori occorre sovrappore le immagini con i tre filtri relativi ai colori fondamentali.

Per il resto, il tutto viene spiegato in questa discussione di SDC:

http://uplink.space.com/showflat.php...b=5&o=0&fpart=

questo lo so, tant'è che ai tempi delle foto marziane me le ero pure ricostruite per conto mio... gpc come al solito ha riportato la sua versione del mio pensiero che ovviamente non è quello che avevo detto io gli avevo semplicemente fatto notare che la mancanza di luce rende quasi impossibile la realizzazione di foto a colori, del resto basta guardare cosa Cassini ha fotografato quando è passata vicino a Giove

http://saturn.jpl.nasa.gov/multimedi...4866-br500.jpg

e cosa invece abbia preso di saturno

http://saturn.jpl.nasa.gov/multimedi...6060-br500.jpg

per capire come la mancanza di luce renda quasi impossibile una buona foto a colori. Stavolta gpc ha torto...

[GioFX]

ma sono immagini colorate con l'uso dei filtri.

[gpc]

Originariamente inviato da jumpermax
gpc come al solito ha riportato la sua versione del mio pensiero che ovviamente non è quello che avevo detto

Ma sei falso come Ce... ehm, come Giuda!
Guarda che posto i log di icq, eh!

Stavolta gpc ha torto...

Miiii nemmeno davanti all'evidenza cede...

[gpc]

Originariamente inviato da GioFX
ma sono immagini colorate con l'uso dei filtri.

Vediamo se tu riesci a convincerlo che se non ci fosse luce per le foto a colori non ce ne sarebbe nemmeno per quelle in bianco e nero, dato che le foto a colori vengono fatte con quelle in bianco e nero...