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Space => the Universe => Topic started by: Abraxas on June 21, 2007, 01:42:26 am

Title: Cassini–Huygens Probe
Post by: Abraxas on June 21, 2007, 01:42:26 am
Huygens probe

The Huygens probe, supplied by the European Space Agency (ESA) and named after the Dutch 17th century astronomer Christiaan Huygens, is an atmospheric entry probe carried to Saturn's moon Titan as part of the Cassini-Huygens mission. The combined Cassini-Huygens spacecraft was launched from Earth on October 15, 1997. Huygens separated from the Cassini orbiter on December 25, 2004, and landed on Titan on January 14, 2005 near the Xanadu region. It touched down on land (the possibility that it would touch down in an ocean was also taken into account in the design). The probe continued to send data for about 90 minutes after reaching the surface.[/color]

Huygens probe


A scale replica of the probe, 1.3 metres across.
Organization: ESA
Mission type: Lander
Satellite of: Saturn
Launch date: December 25, 2004
Launch vehicle: Cassini orbiter
NSSDC ID: 1997-061C
Webpage: Huygens Homepage
Mass: 319 kg

Title: Re: Huygens probe
Post by: Abraxas on June 21, 2007, 01:44:28 am

Huygens was designed to enter and brake in Titan's atmosphere and parachute a fully instrumented robotic laboratory down to the surface. When the mission was planned, it was not yet certain whether the landing site would be a mountain range, a flat plain, an ocean, or something else, and it was hoped that analysis of data from Cassini would help to answer these questions.

Based on pictures taken by Cassini at 1,200 km away from Titan, the landing site appeared to be, for want of a better word, shoreline. Assuming the landing site could be non-solid, the Huygens probe was designed to survive the impact and splash-down with Titan's liquid surface for several minutes and send back data on the conditions there. If that occurred it was expected to be the first time a human-made probe would land in an extraterrestrial (i.e. non-Earth) ocean. The spacecraft had no more than three hours of battery life, most of which was planned to be taken up by the descent. Engineers only expected to get at best 30 minutes of data from the surface.

The Huygens probe system consists of the 318 kg probe itself, which descended to Titan, and the probe support equipment (PSE), which remained attached to the orbiting spacecraft. Huygens' heat shield was 2.7 m in diameter; after ejecting the shield, the probe was 1.3 m in diameter. The PSE included the electronics necessary to track the probe, to recover the data gathered during its descent, and to process and deliver the data to the orbiter, from which it will be transmitted or "downlinked" to the ground.

The probe remained dormant throughout the 6.7-year interplanetary cruise, except for bi-annual health checks. These checkouts followed preprogrammed descent scenario sequences as closely as possible, and the results were relayed to Earth for examination by system and payload experts.

Prior to the probe's separation from the orbiter on December 25, 2004, a final health check was performed. The "coast" timer was loaded with the precise time necessary to turn on the probe systems (15 minutes before its encounter with Titan's atmosphere), then the probe detached from the orbiter and coasted in free space to Titan in 22 days with no systems active except for its wake-up timer.

The main mission phase was a parachute descent through Titan's atmosphere. The batteries and all other resources were sized for a Huygens mission duration of 153 minutes, corresponding to a maximum descent time of 2.5 hours plus at least 3 additional minutes (and possibly a half hour or more) on Titan's surface. The probe's radio link was activated early in the descent phase, and the orbiter "listened" to the probe for the next 3 hours, including the descent phase, and the first thirty minutes after touchdown. Not long after the end of this three-hour communication window, Cassini's high-gain antenna (HGA) was turned away from Titan and toward Earth.

Very large radio telescopes on Earth were also listening to Huygens's 10-watt transmission using the technique of very long baseline interferometry and aperture synthesis mode. At 11:25 CET on January 14, the Robert C. Byrd Green Bank Telescope (GBT) in West Virginia detected the carrier signal from the Huygens probe. The GBT continued to detect the carrier signal well after Cassini stopped listening to the incoming data stream. In addition to the GBT, eight of the ten telescopes of the continent-wide VLBA in North America, 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, also listened for the Huygens signal.

The signal strength received at Earth from Huygens was comparable to that from the Galileo probe (the Jupiter atmospheric descent probe) as received by the VLA, and was therefore too weak to detect in real time because of the signal modulation by the (then) unknown telemetry. Instead, wide-band recordings of the probe signal were made throughout the three-hour descent. After the probe telemetry was finished being relayed from Cassini to Earth, the recorded signal was processed against a telemetry template, enabling signal integration over several seconds for determining the probe frequency. It was expected that through analysis of the Doppler shifting of Huygens' signal as it descended through the atmosphere of Titan, wind speed and direction could be determined with some degree of accuracy. Through interferometry, it was also expected that the radio telescopes would allow determination of Huygens's landing site on Titan with exquisite precision, measuring its position to within 1 km at a distance from Earth of about 1200 million kilometres). This represents an angular resolution of approximately 170 microarcseconds. A similar technique was used to determine the landing site of the Mars exploration rovers by listening to their telemetry alone.

Title: Re: Huygens probe
Post by: Abraxas on June 21, 2007, 01:45:12 am

The first image released, taken from an altitude of 16 km, showing what are speculated to be drainage channels flowing to a possible shoreline. The darker areas are flat plains, while the lighter areas represent high ground.

Title: Re: Huygens probe
Post by: Abraxas on June 21, 2007, 01:46:39 am

Huygens landing site as determined by descent imagery


Preliminary findings seemed to confirm the presence of large bodies of liquid on the surface of Titan. The photos showed what appear to be large drainage channels crossing the lighter colored mainland into a dark sea. Some of the photos even seem to suggest islands and mist shrouded coastline.

At the landing site there were indications of chunks of water ice scattered over an orange surface, the majority of which is covered by a thin haze of methane. The instruments revealed "a dense cloud or thick haze approximately 18-20 kilometers from the surface". The surface itself was reported to be a clay-like "material which might have a thin crust followed by a region of relative uniform consistency." One ESA scientist compared the texture and color of Titan's surface to a Crème brûlée, but admitted this term probably would not appear in the published papers.

On January 18 it was reported that Huygens landed in "Titanian mud", and the landing site was estimated to lie within the white circle on the picture to the right. Mission scientists also reported a first "descent profile", which describes the trajectory the probe took during its descent.

However, subsequent analysis of the data suggests that surface consistency readings were likely caused by Huygens displacing a large pebble as it landed, and that the surface is better described as a 'sand' made of ice grains.[1] The images taken after the probe's landing show a flat plain covered in pebbles. The pebbles, which may be made of water ice, are somewhat rounded, which may indicate the action of fluids on them.[2]

Further work done on the probe's trajectory indicate that in fact it landed within the dark 'sea' region in the photos. Photos of a dry landscape from the surface contradict the original theory that the dark regions were liquid seas, leading researchers to conclude that while there was evidence of liquid acting on the surface recently, the much anticipated hydrocarbon seas of Titan were in fact absent.

Title: Re: Huygens probe
Post by: Abraxas on June 21, 2007, 01:48:24 am
Detailed Huygens activity timeline


Ellipse shows approximate landing site on this image taken earlier by Cassini. The bright region to the right is Xanadu Regio.
•   Huygens probe separated from Cassini orbiter at 02:00 UTC on December 25, 2004 in Spacecraft Event Time.
•   Huygens probe entered Titan's atmosphere at 10:13 UTC on January 14, 2005 in SCET, according to ESA.
•   The probe landed on the surface of the moon at ~163.1775 degrees east and ~10.2936 degrees south around 12:43 UTC in SCET (2 hours 30 minutes after atmospheric entry).(1.)
There was a transit of the Earth and Moon across the Sun as seen from Saturn/Titan just hours before the landing. The Huygens probe entered the upper layer of Titan's atmosphere 2.7 hours after the end of the transit of the Earth, or only one or two minutes after the end of the transit of the Moon. However, the transit did not interfere with Cassini orbiter or Huygens probe, for two reasons. First, although they could not receive any signal from Earth because it was in front of the Sun, Earth could still listen to them. Second, Huygens did not send any readable data to the Earth; it transmitted data to Cassini orbiter, which relayed the data received to the Earth later. For details about transits of the Earth as seen from Saturn, see also Transit of Earth from Saturn.

Title: Re: Huygens probe
Post by: Abraxas on June 21, 2007, 01:50:04 am

Colour image released from the landing site.

Title: Re: Huygens probe
Post by: Abraxas on June 21, 2007, 01:51:20 am
The Huygens probe had six complex instruments aboard that took in a wide range of scientific data after the probe descended into Titan's atmosphere. The six instruments are:

Huygens Atmospheric Structure Instrument (HASI)

This instrument contains a suite of sensors that measured the physical and electrical properties of Titan's atmosphere. Accelerometers measured forces in all three axes as the probe descended through the atmosphere. With the aerodynamic properties of the probe already known, it was possible to determine the density of Titan's atmosphere and to detect wind gusts. The probe was designed so that in the event of a landing on a liquid surface, its motion due to waves would also have been measurable. Temperature and pressure sensors measured the thermal properties of the atmosphere. The Permittivity and Electromagnetic Wave Analyzer component measured the electron and ion (i.e., positively charged particle) conductivities of the atmosphere and searched for electromagnetic wave activity. On the surface of Titan, the conductivity and permittivity (i.e., the ratio of electric flux density produced to the strength of the electric field producing the flux) of the surface material was measured. The HASI subsystem also contains a microphone, which was used to record any acoustic events during probe's descent and landing; [3] this was only the second time in history that audible sounds from another planetary body had been recorded (a Venera-13 recording being the first).

Doppler Wind Experiment (DWE)

This experiment used an ultra-stable oscillator to improve communication with the probe by giving it a very stable carrier frequency. This instrument was also used to measure the wind speed in Titan's atmosphere by measuring the Doppler shift in the carrier signal. The swinging motion of the probe beneath its parachute due to atmospheric properties may also have been detected. Although the failure of one of Huygens's data channels resulted in this data being lost to Cassini, enough was picked up by Earth-based radio telescopes to reconstruct it. Measurements started 150 kilometres above Titan's surface, where Huygens was blown eastwards at more than 400 kilometres per hour, agreeing with earlier measurements of the winds at 200 kilometres altitude, made over the past few years using telescopes. Between 60 and 80 kilometres, Huygens was buffeted by rapidly fluctuating winds, which are thought to be vertical wind shear. At ground level, the Earth-based doppler shift and VLBI measurements show gentle winds of a few metres per second, roughly in line with expectations.

Title: Re: Huygens probe
Post by: Abraxas on June 21, 2007, 01:52:39 am

Contrast-enhanced version of surface image

Descent Imager/Spectral Radiometer (DISR)

This instrument made a range of imaging and spectral observations using several sensors and fields of view. By measuring the upward and downward flow of radiation, the radiation balance (or imbalance) of the thick Titan atmosphere was measured. Solar sensors measured the light intensity around the Sun due to scattering by aerosols in the atmosphere. This permitted calculation of the size and number density of the suspended particles. Two imagers (one visible, one infrared) observed the surface during the latter stages of the descent and, as the probe slowly spun, they built up a mosaic of pictures around the landing site. In addition, a side-view visible imager obtained a horizontal view of the horizon and of the underside of the cloud deck. For spectral measurements of the surface, a lamp was switched on shortly before landing to augment the weak sunlight.

Title: Re: Huygens probe
Post by: Abraxas on June 21, 2007, 01:54:24 am

Gas Chromatograph Mass Spectrometer (GC/MS)

This instrument is a versatile gas chemical analyzer that was designed to identify and measure chemicals in Titan's atmosphere.[4] It was equipped with samplers that were filled at high altitude for analysis. The mass spectrometer built a model of the molecular masses of each gas, and a more powerful separation of molecular and isotopic species was accomplished by the gas chromatograph.[5] During descent, the GC/MS also analyzed pyrolysis products (i.e., samples altered by heating) passed to it from the Aerosol Collector Pyrolyser. Finally, the GC/MS measured the composition of Titan's surface. This investigation was made possible by heating the GC/MS instrument just prior to impact in order to vaporize the surface material upon contact. The GC/MS was developed by the Goddard Space Flight Center and University of Michigan's Space Physics Research Lab.

Aerosol Collector and Pyrolyser (ACP)

The ACP experiment drew in aerosol particles from the atmosphere through filters, then heated the trapped samples in ovens (using the process of pyrolysis) to vaporize volatiles and decompose the complex organic materials. The products were flushed along a pipe to the GC/MS instrument for analysis. Two filters were provided to collect samples at different altitudes.[6] The ACP was developed by a (French) ESA team at the Laboratoire Inter-Universitaire des Systèmes Atmosphériques (LISA).

Surface-Science Package (SSP)

The SSP contained a number of sensors designed to determine the physical properties of Titan's surface at the point of impact, whether the surface was solid or liquid. An acoustic sounder, activated during the last 100 meters of the descent, continuously determined the distance to the surface, measuring the rate of descent and the surface roughness (e.g., due to waves). The instrument was designed so that if the surface were liquid, the sounder would measure the speed of sound in the "ocean" and possibly also the subsurface structure (depth). During descent, measurements of the speed of sound gave information on atmospheric composition and temperature, and an accelerometer recorded the deceleration profile at impact, indicating the hardness and structure of the surface. A tilt sensor measured pendulum motion during the descent and was also designed to indicate the probe's attitude after landing and show any motion due to waves. If the surface had been liquid, other sensors would also have measured its density, temperature and light reflecting properties, thermal conductivity, heat capacity, and electrical properties (permittivity and conductivity). A penetrometer instrument, that protruded 55mm past the bottom of the Huygens probe descent module, was used to create a penetrometer trace as Huygens landed on the surface by measuring the force exerted on the instrument by the surface as the instrument broke though the surface and was pushed down into the planet by the force of the probe landing itself. The trace shows this force as a function of time over a period of about 400ms. The trace has an initial spike which suggests that the instrument hit one of the icy pebbles on the surface photographed by the DISR camera.

The Huygens SSP was developed by Space Sciences Department of the University of Kent and the Rutherford Appleton Laboratory Space Science Department under the direction of Professor John Zarnecki. The SSP research and responsibility transferred to the Open University when John Zarnecki transferred in 2000.

Title: Re: Huygens probe
Post by: Abraxas on June 21, 2007, 01:55:27 am

Application of multi-layer insulation shimmers under bright lighting during final assembly. The gold color of the MLI is due to light reflecting off of the aluminium coating on the back of sheets of amber colored Kapton.

Title: Re: Huygens probe
Post by: Abraxas on June 21, 2007, 01:56:51 am
Spacecraft design

Huygens was built under the Prime Contractorship of Aérospatiale in Cannes, France now part of Alcatel Alenia Space. The heat shield system was built under the responsibility of Aérospatiale near Bordeaux, now part of EADS SPACE Transportation.


Martin-Baker Space Systems was responsible for Huygens' parachute systems and the structural components, mechanisms and pyrotechnics that control the probe's descent onto Titan. IRVIN-GQ was responsible for the definition of the structure of each of Huygens' parachutes. Irvin worked on the probe's descent control sub-system under contract to Martin-Baker Space Systems.

A critical design flaw resolved

Long after launch, a few persistent engineers discovered that the communication equipment on Cassini had a fatal design flaw, which would have caused the loss of all data transmitted by the Huygens probe.

As Huygens was too small to transmit directly to Earth, it was designed to transmit the telemetry data obtained while descending through Titan's atmosphere to Cassini by radio, which would in turn relay it to Earth using its large 4-meter diameter main antenna. Some engineers, most notably ESA Darmstadt employees Claudio Sollazzo and Boris Smeds, felt uneasy about the fact that, in their opinion, this feature had not been tested before launch under sufficiently realistic conditions. Smeds managed, with some difficulty, to convince superiors to perform additional tests while Cassini was in flight. In early 2000, he sent simulated telemetry data at varying power and Doppler shift levels from Earth to Cassini. It turned out that Cassini was unable to relay the data correctly.

The reason: under the original flight plan, when Huygens was to descend to Titan, it would have accelerated relative to Cassini, causing its signal to be Doppler-shifted. Consequently, the hardware of Cassini's receiver was designed to be able to receive over a range of shifted frequencies. However, the firmware failed to take into account that the Doppler shift would have changed not only the carrier frequency, but also the timing of the payload bits, coded by phase-shift keying at 8192 bits per second.

Reprogramming the firmware was impossible, and as a solution the trajectory had to be changed. Huygens detached a month later than originally planned (December 2004 instead of November) and approached Titan in such a way that its transmissions traveled perpendicular to its direction of motion relative to Cassini, greatly reducing the Doppler shift.[7]

The trajectory change overcame the design flaw for the most part, and data transmission succeeded, although the information from one of the two radio channels was lost due to an unrelated error.

The trajectory change was not the only mitigation to the Doppler shift problem, and software patches were uplinked to several instruments on the probe from the Deutsche Aerospace facility in Darmstadt to further reduce the risk of data loss.

Title: Re: Huygens probe
Post by: Abraxas on June 21, 2007, 01:57:57 am
"Channel A" data lost

Huygens was programmed to transmit telemetry and scientific data to the Cassini orbiter for relay to Earth using two redundant S-band radio systems, referred to as Channel A and B, or Chain A and B. Channel A was the sole path for an experiment to measure wind speeds by studying tiny frequency changes caused by Huygens' motion. In one other deliberate departure from full redundancy, pictures from the descent imager were split up, with each channel carrying 350 pictures.

As it turned out, Cassini never listened to channel A because of an operational commanding error. The receiver on the orbiter was never commanded to turn on, according to officials with the European Space Agency. ESA announced that the program error was a mistake on their part, the missing command was part of a software program developed by ESA for the Huygens mission and that it was executed by Cassini as delivered.

The loss of Channel A means only 350 pictures were received instead of the 700 planned. Also all Doppler radio measurements between Cassini and Huygens were lost. Doppler radio measurements of Huygens from Earth were made, though not as accurate as expected measurement that Cassini would have made; when added to accelerometer sensors on Huygens and VLBI tracking of the position of the Huygens probe from Earth, reasonably accurate wind speed and direction measurements can still be derived.

Amateur contributions

The Huygens mission benefited significantly from amateur contributions. This was enabled by the decision of the imaging science Principal Investigator Marty Tomasko to make the image raw data of the DISR instrument available to the public. The many small and low contrast images had to be assembled into mosaics and panoramas of the landing region in a time consuming process, and space science enthusiasts all around the world began to deal with this challenge. Only some hours later the first mosaics of the Huygens landing region were published,[8] created by Daniel Crotty, Jakub Friedl, Ricardo Nunes and Anthony Liekens. Christian Waldvogel published an improved and colorized Panorama. Another amateur, René Pascal, intensively engaged in the Huygens image processing, developed a method to remove camera artifacts from the images and created a comprehensive mosaic of the region now called Adiri.

Title: Re: Huygens probe
Post by: Abraxas on June 21, 2007, 01:59:09 am

Cassini image of Saturn, February 2004

Title: Re: Huygens probe
Post by: Abraxas on June 21, 2007, 02:03:29 am
Cassini–Huygens timeline

October 15 — Cassini launched at 08:43 UTC.

April 26 — Gravity-assisted flyby of Venus.


June 24 — Gravity-assisted flyby of Venus.
August 18 03:28 UTC — Gravity-assisted flyby of Earth. An hour 20 minutes before closest approach, Cassini made the closest approach to the Moon at 377,000 km, and took a series of calibration images.

January 23 — flyby of Asteroid 2685 Masursky around 10:00 UTC. Cassini took images[1] 5 to 7 hours before at 1.6 million km distance and estimated a diameter of 15 to 20 km.

December 30 — Gravity-assisted flyby of Jupiter. Cassini was at its closest point to Jupiter at this date, and performed many scientific measurements. It also produced the most detailed global color portrait of Jupiter ever produced (seen on the right); the smallest visible features are approximately 60 km (37 miles) across.

May 30 — During the coast phase between Jupiter and Saturn, it was noticed that "haze" became visible in the pictures taken by the narrow-angle camera of Cassini. This was first seen when a picture of the star Maia in the Pleiades was taken after a routine heating period.

July 23 — In late January, a test was performed to remove the "haze" from the narrow-angle camera lens by heating it. Warming the camera to 4 degrees Celsius (39 degrees Fahrenheit) for eight days produced the hoped results. Later, the heating was extended to 60 days, and a picture of the star Spica showed an improvement of more than 90 percent compared to before the heating period. On July 9, a picture showed that the removal procedure was completed successfully, which was announced on July 23.[2]

October 10 — The Cassini science team announced the results of a test of Einstein's theory of gravity, using radio signals from the Cassini probe. The researchers observed a frequency shift in the radio waves to and from the space craft, as those signals traveled close to the Sun. Past tests were in agreement with the theoretical predictions with an accuracy of one part in one thousand. The Cassini experiment improved this to about 20 parts in a million, with the data still supporting Einstein's theory.

February 27 — A new, high-resolution picture of Saturn taken by Cassini on February 9 was released, and it was noted that mission scientists were puzzled by the fact that no "spokes" in Saturn's ring are visible. These dark structures in the "B" section of the ring had been discovered in pictures taken by the Voyager probe in 1981.[3] Another picture, in infrared light, taken on February 16 shows cloud height differences and the same disturbance visible throughout the 1990s in Hubble Space Telescope images.[4]

March 12 — Pictures taken on February 23 do show a feature discovered by Voyager: Clumps in the outer "F"-ring. What could not be ascertained at the time, was the exact lifetime of these clumps, and it is hoped that Cassini will provide conclusive data about this question. The first set of pictures show a set of "clumps" moving along the "F" ring.[5]

March 26 — The Cassini science team published a first sequence of pictures of Saturn showing clouds moving at high speed around the planet. Using a filter to better see water haze on top of the dense cloud cover, motions in the equatorial and southern regions are clearly visible.[6] The pictures were taken during the days from February 15 to February 19.

April 8 — The first "long-term" observation of cloud dynamics in Saturn's atmosphere were published by mission scientists. A set of pictures shows two storms in the southern latitudes merge during a period from March 19 to March 20. Both storms had a diameter of about 1,000 km (620 mi) before they merged

April 15 — NASA announced that two moons discovered by Voyager 1 were sighted again by Cassini in pictures taken on March 10: Prometheus and Pandora. These are no ordinary moons, but their gravitational effects on the "F" ring led scienties to call them "shepherd moons". They fascinate all researchers interested in the dynamic of the ring system, because their orbits are close enough that they interact with each other in a chaotic manner. They have a history of defying predictions of their orbits. One of Cassini's missions will be to monitor the movements of these bodies closely.

May 18 — Cassini entered the Saturn system. The gravitational pull of Saturn began to overtake the influence of the Sun.
May 20 — The first picture of Titan with better resolution than any Earth based observation was released. It was taken May 5 from a distance of 29.3 million kilometers (18.2 million miles).

May 27 — TCM-20, the Phoebe approach TCM (Trajectory Correction Maneuver) was executed at 22:26:00 UTC. This was a 5 minute and 56 second burn of the main engine, which was not used since December 1998. It therefore doubled as a "dress rehearsal" for the 96 minute burn during "Saturn Orbit Insertion" (SOI). However, TCM-20 was mainly designed to change Cassini's velocity by 34.7 m/s (78 mph), setting up a flyby of the moon Phoebe June 11.

June 11 — Cassini flew by the moon Phoebe at 19:33 UT in Spacecraft Event Time at 2068 kilometers distance. All of the eleven onboard instruments operated as expected and all data was acquired. Scientists plan to use the data to create global maps of the cratered moon, and to determine Phoebe's composition, mass and density. It will take scientists several days to pore over the data to make more concrete conclusions.

June 16 — TCM-21 took place with a 38 second main engine burn. It was planned as the last correction of the trajectory of Cassini before SOI. A few days later the final TCM-22 tentatively scheduled for June 21 was cancelled.

July 1 — The Saturn Orbit Insertion burn was successfully executed. It began at 01:12 UT in Spacecraft Event Time and ended at 02:48 UT. Right after that burn, pictures of the rings were taken and sent back to mission scientist.

Scientist were surprised by the clarity and detail of the pictures and will be poring over them for quite some time. "We won't see the whole puzzle, only pieces, but what we are seeing is dramatic," said Dr. Carolyn Porco, Cassini imaging team leader, Space Science Institute, Boulder, Colo. "The images are mind-boggling, just mind-boggling. I've been working on this mission for 14 years and I shouldn't be surprised, but it is remarkable how startling it is to see these images for the first time."

July 2 — Cassini's first flyby of Titan was executed and first close up pictures were sent back to Earth. Due to the planning of the initial orbit, Cassini was passing over the south pole of the moon and from a larger distance than in later flybys. However, during a press conference on June 3, mission scientist presented pictures that are already forcing them to rethink previous theories. It now seems that the darker and brighter albedo features on the surface do represent different materials. But in contrast to expectation, the icy regions seem to be darker than the areas where other (possibly organic) matter is mixed in with the ice.

August 16 — Mission scientists announce the discovery of two new moons of Saturn, and with it the successful start of one of the programs of Cassini: Locating small and yet unknown moons. Later named "Methone" (S/2004 S 1) and "Pallene" (S/2004 S 2), these objects are small compared to other moons and they orbit between Mimas and Enceladus.

August 23 — The last major firing of the main engine took place to adjust the next closest approach to Saturn and avoid the particles in the ring system. After a 51 minute burn, that distance was moved about 300,000 km farther away from Saturn than its smallest distance during SOI. At the same time, the new course will bring Cassini very close to Titan on its next flyby.

September 14 — Final checkout of the Huygens lander was completed successfully. The separation of the probe stays scheduled for December 25, with the landing anticipated on January 14, 2005.

October 26 — The second flyby of Titan (called "Titan-A") was successfully executed. Data started to arrive at the JPL mission center at 01:30 UTC, October 27, and included the highest resolution pictures ever taken of the surface of that moon. Also, first high-resolution infra-red spectra and pictures were taken from the atmosphere and surface. The spacecraft successfully skimmed the hazy, smoggy atmosphere of Titan, coming within 1,176 kilometers of Titan's surface. The flyby was the closest that any spacecraft has ever come to Titan. The pictures, spectra and radar data revealed a complex, puzzling surface. Analysis of all data is on-going. The only glitch during the "Titan-A" event involved the CIRS instrument. During playback the instrument team observed corrupted data. A decision was made to power the instrument off to reboot it. CIRS was powered back on within 24 hours and is currently in its nominal state.

November 23 — The last in-flight checkout of the Huygens probe before separation was completed successfully. All systems are ready for an on-time deployment of the probe.

December 13 — The "Titan-B" flyby was executed successfully and the collected data are analyzed by mission scientists.

December 25 — Huygens probe separated from Cassini orbiter at 02:00 UTC.

December 27 — NASA published a picture of Huygens taken from Cassini two days after release. It reported that the analysis of that picture shows that the probe is on the correct course within the expected error range. These checks were necessary in order to place the orbiter in the correct orientation to receive the data from the probe when it enters Titan's atmosphere.

December 28 — OTM-10 was executed at 03:00 UTC in Spacecraft Event Time. This maneuver, also called the Orbit Deflection Maneuver (ODM), took Cassini off of a Titan-impacting trajectory and on to a flyby trajectory with the required altitude to receive data from the Huygens probe as it plunges into Titan.

December 31 — Cassini's flyby of Iapetus occurred at 18:45:37 UTC at an altitude of 122645 kilometers. First raw pictures were available the next day.

Title: Re: Huygens probe
Post by: Abraxas on June 21, 2007, 02:07:47 am

January 14 — Huygens entered Titan's atmosphere at 09:06 UTC and had landed softly on its surface about two hours later. This was confirmed by the reception of the carrier wave emitted by the probe during its descent and touchdown. At 16:19 UTC the Cassini orbiter started to relay to Earth the scientific data received from the probe. The first picture was released at 19:45 UTC, showing a view from about 16 km above the surface. A second picture taken from the probe at rest on the surface was released a short time later. Analysis of the data is ongoing.

February 15 — Successful Titan flyby, with new regions of its surface scanned by RADAR. Cassini 's mapping RADAR acquired a picture that shows a large crater on Titan, with an estimated diameter of 440 km (273 mi).[7]

February 17 — The first close flyby of Enceladus was executed and first closeup images were sent back to Earth. The flyby distance was about 1180 km (730 mi).

March 9 — The second flyby of Enceladus was performed and Cassini passed the moon with minimum distance of 500 km (310 mi).

March 17 — The Cassini probe reveals that Saturn's moon Enceladus has an atmosphere. It has been described as "substantial" by its discoverers.

March 31 — The fourth planned flyby of Titan with a minimum distance of about 2400 kilometers was executed. Images and other data are currently being evaluated.[8]
April 16 — The fifth planned flyby of Titan with a minimum distance of about 1025 kilometers was executed at 19:12 UTC. This was the closest flyby up to this date, and provided the opportunity to obtain more detailed data on the constituents in the upper atmosphere of Titan. A first analysis of that data showed a large range of complex carbon molecules. On April 25 a mass plot was published that demonstrates the existence of these molecules.

May 3 — Cassini begins Radio occultation experiments on Saturn's Rings, to determine ring particle size distribution, on the scale of centimetres.

May 10 — At the beginning of a period focussed observation of the ring system of Saturn, slated to take until September, mission scientist announced the discovery of a new moon in the "Keeler gap" inside the "A" ring. Provisionally named S/2005 S 1 and later named Daphnis, it was first seen in a time-lapse sequence of images taken on May 1. Imaging scientists had predicted the new moon's presence and its orbital distance from Saturn after last July's sighting of a set of peculiar spiky and wispy features in the Keeler gap's outer edge.

July 14 — The closest flyby of Enceladus with a distance of 175 km (110 mi) was executed successfully. First raw pictures were published.

August 22 — Flyby of Titan with a minimum distance of 3669 km (2280 mi).[9]

September 7 — Flyby of Titan at a distance of 1075 km (668 mi), data gathered partially lost due to software problem.

September 24 — Flyby of Tethys at a distance of 1500 km (900 mi).

September 26 — Flyby of Hyperion at a distance of 1010 km (628 mi), the closest flyby and only visit to the moon during the primary mission.

October 11 — Flyby of Dione at a distance of 500 km (300 mi).

October 28 — Flyby of Titan at a distance of 1400 km (800 mi).

November 26 — Flyby of Rhea at a distance of 500 km (300 mi).

December 26 — Flyby of Titan at a distance of 10410 km (6470 mi).[10]

January 15 — Flyby of Titan at a distance of 2040 km (1270 mi).[11]

February 27 — Flyby of Titan at a distance of 4390 km (2730 mi).[12]

March 18 — Flyby of Titan at a distance of 1950 km (1220 mi).[13]

May 20 — Flyby of Titan at a distance of 1880 km (1175 mi).[14]

July 2 — Flyby of Titan at a distance of 1910 km (1185 mi).[15]

July 27 — NASA confirms the presence of hydrocarbon lakes in Titan's northern polar region.

September 23 — Flyby of Titan at a distance of 960 km (595 mi).[16]

March 1 — NASA releases several remarkable images of Saturn from Cassini, many in angles not possible from Earth

Title: Re: Huygens probe
Post by: Abraxas on June 21, 2007, 02:10:12 am

Picture of Moon during flyby

Cassini orbiter travel milestones
Spacecraft event time Distance from Saturn
2004-Mar-22 07:42:14 50,000,000 kilometers
2004-Apr-12 19:35:12 40,000,000 kilometers
2004-May-04 02:59:09 30,000,000 kilometers
2004-May-25 02:40:06 20,000,000 kilometers
2004-Jun-14 11:15:22 10,000,000 kilometers
Detailed timeline of Huygens mission
All times given after 2005-Jan-14 09:11 UTC are expected event times and may differ from actual event times. This page will be updated after descent has occurred with corrections if they are necessary.

The data used in this section has been slightly out of date, an updated version of ephemeris from ESA was available 2005 January 6.

Huygens probe travel milestones

Spacecraft event time Description

2004-Dec-25 02:00 UTC Huygens separates from Cassini
2004-Dec-25 06:07 UTC 5 kilometers from Cassini
2004-Dec-25 10:13 UTC 10 kilometers from Cassini
2004-Dec-28 01:17 UTC 100 kilometers from Cassini
2004-Dec-28 12:20 UTC 1,000 kilometers from Cassini
2004-Dec-29 00:02 UTC 2,000 kilometers from Cassini
2004-Dec-29 11:39 UTC 3,000 kilometers from Cassini
2004-Dec-29 23:11 UTC 4,000 kilometers from Cassini
2004-Dec-30 10:36 UTC 5,000 kilometers from Cassini
2005-Jan-03 20:01 UTC 4,658,661 kilometers from Titan (farthest distance)
2005-Jan-06 23:40 UTC 4,000,000 kilometers from Titan
2005-Jan-09 01:26 UTC 3,000,000 kilometers from Titan
2005-Jan-10 18:37 UTC 2,000,000 kilometers from Titan
2005-Jan-12 11:20 UTC 1,000,000 kilometers from Titan
2005-Jan-12 15:36 UTC 900,000 kilometers from Titan
2005-Jan-12 19:56 UTC 800,000 kilometers from Titan
2005-Jan-13 00:19 UTC 700,000 kilometers from Titan
2005-Jan-13 04:48 UTC 600,000 kilometers from Titan
2005-Jan-13 09:21 UTC 500,000 kilometers from Titan
2005-Jan-13 13:59 UTC 400,000 kilometers from Titan
2005-Jan-13 18:43 UTC 300,000 kilometers from Titan
2005-Jan-13 23:31 UTC 200,000 kilometers from Titan
2005-Jan-14 04:23 UTC 100,000 kilometers from Titan
2005-Jan-14 04:53 UTC 90,000 kilometers from Titan
2005-Jan-14 05:22 UTC 80,000 kilometers from Titan
2005-Jan-14 05:52 UTC 70,000 kilometers from Titan
2005-Jan-14 06:21 UTC 60,000 kilometers from Titan
2005-Jan-14 06:50 UTC 50,000 kilometers from Titan
2005-Jan-14 07:20 UTC 40,000 kilometers from Titan
2005-Jan-14 07:49 UTC 30,000 kilometers from Titan
2005-Jan-14 08:18 UTC 20,000 kilometers from Titan
2005-Jan-14 08:48 UTC 10,000 kilometers from Titan
2005-Jan-14 08:51 UTC 9,000 kilometers from Titan
2005-Jan-14 08:54 UTC 8,000 kilometers from Titan
2005-Jan-14 08:57 UTC 7,000 kilometers from Titan
2005-Jan-14 08:59 UTC 6,000 kilometers from Titan
2005-Jan-14 09:02 UTC 5,000 kilometers from Titan
2005-Jan-14 09:06 UTC Huygens enters the atmosphere of Titan
2005-Jan-14 11:24 UTC Huygens impacts with the surface of Titan

Celestial phenomena as seen from the landing site in the landing (Titan's) day

The landing day begins at 2005-Jan-08 04:05:08 UTC and ends at 2005-Jan-24 03:26:14 UTC.

According to Huygens predicted descent trajectory provided by ESA/JPL, valid as of January 6, 2005, the probe was projected to land at 10.2936 degrees south and 163.1775 degrees east. Prior to the landing, the location of the landing site could not be known exactly, since the probe will be influenced by the wind in Titan's atmosphere as it descends.

Local apparent solar time Spacecraft event time Description
03:06 2005-Jan-10 05:43 UTC Jupiter rises
03:21 2005-Jan-10 09:43 UTC Phoebe sets
03:55 2005-Jan-10 18:47 UTC Pluto rises
04:56 2005-Jan-11 10:54 UTC Cassini rises
05:03 2005-Jan-11 12:52 UTC Huygens rises
05:06 2005-Jan-11 13:29 UTC Mars rises
05:29 2005-Jan-11 19:36 UTC Venus rises
05:31 2005-Jan-11 20:19 UTC Mercury rises
05:35 2005-Jan-11 21:22 UTC Iapetus rises
05:43 2005-Jan-11 23:20 UTC Sun rises
05:44 2005-Jan-11 23:39 UTC Earth rises
05:44 2005-Jan-11 23:40 UTC Moon rises
06:52 2005-Jan-12 17:54 UTC Neptune rises
07:47 2005-Jan-13 08:32 UTC Uranus rises
08:26 2005-Jan-13 18:46 UTC Earth transit across Sun (1st contact)
08:26 2005-Jan-13 18:53 UTC Earth transit across Sun (2nd contact)
08:35 2005-Jan-13 21:20 UTC Moon transit across Sun (1st contact)
08:36 2005-Jan-13 21:22 UTC Moon transit across Sun (2nd contact)
08:48 2005-Jan-14 00:34 UTC Earth transit across Sun (Greatest)
08:58 2005-Jan-14 03:13 UTC Moon transit across Sun (Greatest)
09:09 2005-Jan-14 06:15 UTC Earth transit across Sun (3rd contact)
09:09 2005-Jan-14 06:23 UTC Earth transit across Sun (4th contact)
09:12 2005-Jan-14 07:10 UTC Cassini transit the meridian
09:20 2005-Jan-14 09:03 UTC Moon transit across Sun (3rd contact)
09:20 2005-Jan-14 09:05 UTC Moon transit across Sun (4th contact)
09:20 2005-Jan-14 09:06 UTC Huygens enters the atomsphere
09:28 2005-Jan-14 11:11 UTC Jupiter transit the meridian
09:28 2005-Jan-14 11:24 UTC Huygens impacts with the surface
09:35 2005-Jan-14 13:08 UTC Cassini sets
10:11 2005-Jan-14 22:41 UTC Pluto transit the meridian
10:23 2005-Jan-15 01:48 UTC Hyperion sets
11:14 2005-Jan-15 15:27 UTC Iapetus transit the meridian
11:26 2005-Jan-15 18:36 UTC Mars transit the meridian
11:48 2005-Jan-16 00:36 UTC Venus transit the meridian
11:50 2005-Jan-16 01:09 UTC Mercury transit the meridian
11:59 2005-Jan-16 03:26 UTC Earth transit the meridian
11:59 2005-Jan-16 03:27 UTC Moon transit the meridian
12:00 2005-Jan-16 03:44 UTC Sun transit the meridian
13:05 2005-Jan-16 21:02 UTC Neptune transit the meridian
13:56 2005-Jan-17 10:39 UTC Uranus transit the meridian
15:49 2005-Jan-18 16:41 UTC Jupiter sets
16:26 2005-Jan-19 02:24 UTC Phoebe rises
16:26 2005-Jan-19 02:36 UTC Pluto sets
17:46 2005-Jan-19 23:42 UTC Mars sets
17:55 2005-Jan-20 02:08 UTC Iapetus sets
18:08 2005-Jan-20 05:35 UTC Venus sets
18:10 2005-Jan-20 06:06 UTC Mercury sets
18:14 2005-Jan-20 07:20 UTC Earth sets
18:14 2005-Jan-20 07:21 UTC Moon sets
18:17 2005-Jan-20 08:09 UTC Sun sets
19:18 2005-Jan-21 00:10 UTC Neptune sets
20:05 2005-Jan-21 12:46 UTC Uranus sets
21:31 2005-Jan-22 11:44 UTC Phoebe transit the meridian

Timeline of Huygens landing process

Spacecraft event time Description

2005-Jan-11 12:00 UTC Orbiter rise in the east (azimuth = 93 degrees) as seen from the landing site
2005-Jan-14 06:50 UTC Orbiter turns on probe radio link receivers
2005-Jan-14 07:02 UTC Orbiter begins to turn radio dish toward Titan
2005-Jan-14 07:14 UTC Orbiter turn to Titan complete; 3 minutes later orbiter X-band downlink disabled
2005-Jan-14 08:29 UTC Saturn occulted by Titan as seen from Huygens
2005-Jan-14 08:38 UTC Saturn's rings occulted by Titan as seen from Huygens
2005-Jan-14 08:44 UTC Probe turns transmitters on; low power mode
2005-Jan-14 09:06 UTC Huygens enters the atomsphere of Titan
2005-Jan-14 09:09 UTC Huygens feels maximum deceleration
2005-Jan-14 09:10 UTC Deploy pilot chute
2005-Jan-14 09:10 UTC Release aft cover
2005-Jan-14 09:10 UTC Deploy main parachute
2005-Jan-14 09:11 UTC Begin transmission to Cassini orbiter
2005-Jan-14 09:11 UTC Release front shield; transmitters switch to high power mode; instruments configured for descent and measurements commence
2005-Jan-14 09:25 UTC Main parachute separates; deploy stabilizing drogue chute
2005-Jan-14 09:42 UTC Surface proximity sensor activated
2005-Jan-14 09:49 UTC Possible icing effects on probe
2005-Jan-14 09:50 UTC Gas Chromatograph Mass Spectrometer begins sampling atmosphere
2005-Jan-14 11:12 UTC Orbiter makes its closest flyby of Titan at an altitude of 59996 kilometers at a speed of 5401 meters per second and 93 degree phase angle (azimuth = 278 degrees, elevation = 33 degrees as seen from the landing site)
2005-Jan-14 11:23 UTC Turn on descent imager lamp
2005-Jan-14 11:24 UTC Huygens impact with surface of Titan
2005-Jan-14 13:11 UTC Orbiter sets in the west (azimuth = 272 degrees) as seen from the landing site
2005-Jan-14 13:37 UTC Orbiter stops probe data collection

Saturn tour

Body Date (UTC) Altitude (kilometer)
Phoebe 2004-Jun-11 19:33 1,997
Titan 2004-Oct-26 15:30 1,200
Titan 2004-Dec-13 11:38 1,200
Probe Release 2004-Dec-25 02:00 
Iapetus 2005-Jan-01 02:28 65,000
Titan 2005-Jan-14 11:12 60,000
Titan 2005-Feb-15 06:58 1,577
Enceladus 2005-Feb-17 03:30 1,176
Enceladus 2005-Mar-09 09:08 500
Titan 2005-Mar-31 20:05 2,402
Titan 2005-Apr-16 19:12 1,025
Enceladus 2005-Jul-14 19:58 175
Mimas 2005-Aug-02 04:01 48,842
Titan 2005-Aug-22 08:53 3,758
Titan 2005-Sep-07 08:01 1,025
Tethys 2005-Sep-24 01:36 1,500
Hyperion 2005-Sep-26 01:46 500
Dione 2005-Oct-11 17:59 500
Titan 2005-Oct-28 04:04 1,451
Rhea 2005-Nov-26 22:37 500
Titan 2005-Dec-26 18:59 10,409
Titan 2006-Jan-15 11:41 2,043
Titan 2006-Feb-27 08:25 1,813
Titan 2006-Mar-19 00:06 1,951
Titan 2006-Apr-30 20:58 1,855
Titan 2006-May-20 12:18 1,879
Titan 2006-Jul-02 09:21 1,906
Titan 2006-Jul-22 00:25 950
Titan 2006-Sep-07 20:13 950
Titan 2006-Sep-23 18:54 950
Titan 2006-Oct-09 17:25 950
Titan 2006-Oct-25 15:53 950
Titan 2006-Dec-12 11:37 950
Titan 2006-Dec-28 10:02 1,500
Titan 2007-Jan-13 08:36 950
Titan 2007-Jan-29 07:13 2,726
Titan 2007-Feb-22 03:10 950
Titan 2007-Mar-10 01:47 950
Titan 2007-Mar-26 00:21 950
Titan 2007-Apr-10 22:57 950
Titan 2007-Apr-26 21:31 950
Titan 2007-May-12 20:08 950
Titan 2007-May-28 18:51 2,426
Titan 2007-Jun-13 17:46 950
Tethys 2007-Jun-27 19:51 15,859
Titan 2007-Jun-29 17:02 1,944
Titan 2007-Jul-19 00:37 1,300
Rhea 2007-Aug-30 01:28 5,116
Titan 2007-Aug-31 06:35 3,212
Iapetus 2007-Sep-10 12:34 1,227
Titan 2007-Oct-02 04:54 950
Titan 2007-Nov-19 00:58 950
Titan 2007-Dec-05 00:06 1,300
Titan 2007-Dec-20 22:53 950
Titan 2008-Jan-05 21:25 950
Titan 2008-Feb-22 17:39 950
Enceladus 2008-Mar-12 19:07 1,000
Titan 2008-Mar-25 14:35 950
Titan 2008-May-12 10:10 950
Titan 2008-May-28 08:33 1,348

Title: Re: Cassini–Huygens Probe
Post by: Abraxas on June 21, 2007, 02:14:33 am

Jupiter flyby picture

Title: Re: Cassini–Huygens Probe
Post by: Abraxas on June 21, 2007, 02:15:23 am

'F' Ring and shepherd moons

Title: Re: Cassini–Huygens Probe
Post by: Abraxas on June 21, 2007, 02:16:17 am

Titan seen from Cassini

Title: Re: Cassini–Huygens Probe
Post by: Abraxas on June 21, 2007, 02:17:16 am

This image of Saturn's moon Phoebe was taken by Cassini spacecraft at 16:10 UT on 2004-Jun-11

Title: Re: Cassini–Huygens Probe
Post by: Abraxas on June 21, 2007, 02:18:11 am

Ring edge as seen by Cassini

Title: Re: Cassini–Huygens Probe
Post by: Abraxas on June 21, 2007, 02:19:01 am
False color image of Titan

Title: Re: Cassini–Huygens Probe
Post by: Abraxas on June 21, 2007, 02:19:52 am

Huygens is released on its way to Titan.

Title: Re: Cassini–Huygens Probe
Post by: Abraxas on June 21, 2007, 02:21:07 am

First picture from the surface of Titan


First closeup view of Enceladus

Title: Re: Cassini–Huygens Probe
Post by: Abraxas on June 21, 2007, 02:22:00 am

Mass plot for Titan's atmosphere

Title: Re: Cassini–Huygens Probe
Post by: Abraxas on June 21, 2007, 02:23:01 am

One of the incredible images of Saturn released by NASA on March 1, 2007. The image was taken on January 19 of that year.

Title: Re: Cassini–Huygens Probe
Post by: Abraxas on June 21, 2007, 02:23:56 am

Huygens's distance from Tit

Title: Re: Cassini–Huygens Probe
Post by: Abraxas on June 21, 2007, 02:24:57 am

Downlink timeline of acquired Huygens Probe data from Cassini Orbiter to Earth.