European Space Agency's Huygens Probe Set to Detach From Cassini Orbiter

The highlights of the first year of the Cassini-Huygens mission to Saturn can be broken into two chapters: first, the arrival of the Cassini orbiter at Saturn in June, and second, the release of the Huygens probe on Dec. 24, 2004, on a path toward Titan.

The Huygens probe, built and managed by the European Space Agency (ESA), is bolted to Cassini and fed electrical power through an umbilical cable. It has been riding along during the nearly seven-year journey to Saturn largely in a "sleep" mode, awakened every six months for three-hour instrument and engineering checkups. In three days, it will be cut loose from its mother ship and will coast toward Saturn's moon Titan, arriving on Jan. 14, 2005.

"As partners with ESA, one of our obligations was to carry the Huygens probe to Saturn and drop it off at Titan," said Robert T. Mitchell, Cassini program manager at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "We've done the first part, and on Christmas Eve we will release Huygens and tension-loaded springs will gently push it away from Cassini onto a ballistic free-fall path to Titan."

Once freed from Cassini, the Huygens probe will remain dormant until the onboard timer wakes it up shortly before the probe reaches Titan's upper atmosphere on Jan. 14. Then it will begin a dramatic plunge through Titan's murky atmosphere, tasting the 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 ESA'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.

Currently, both the orbiter and the probe are on an impact trajectory with Titan. This is the only way to ensure that Cassini delivers the probe in the right location. A confirmation of successful release is expected to be received from NASA's Deep Space Network tracking stations at Madrid, Spain and Goldstone, Calif., shortly before 8:00 p.m. PST on Dec. 24. A team of JPL engineers and ESA mission managers will be monitoring spacecraft activities at JPL during the release phase of the mission.

On Dec. 27, the Cassini orbiter will perform a deflection maneuver to keep it from following Huygens into Titan's atmosphere. This maneuver will also establish the required geometry between the probe and the orbiter for radio communications during the probe descent.

Two of the instruments on ESA's Huygens probe, the descent imager and spectral radiometer camera and the gas chromatograph-mass spectrometer, are contributions from NASA and American academia.

The imaging camera will take advantage of the Huygens probe's rotation, using two imagers to observe the surface of Titan during the late stages of descent for a view of the regions around the impact site. A side-looking imager will view the horizon and the underside of any cloud deck. More than just a camera, the instrument is designed to measure concentrations of argon and methane in the atmosphere and determine the size and density of particles. The instrument will also determine if the local surface is a solid or liquid, and if solid, its topography. The principal investigator is Dr. Martin G. Tomasko of the University of Arizona, Tucson, Ariz.

Although Titan's atmosphere is primarily nitrogen and methane, scientists believe it contains many other gases that are present only in small amounts. These trace gases can reveal critical details about the origin and evolution of Titan's atmosphere. Because trace gases are rare, they are difficult or impossible to observe remotely, so direct measurements must be made.

The gas chromatograph-mass spectrometer instrument will sample gas directly from Titan's atmosphere as the Huygens probe descends by parachute. Data from the instrument will allow researchers to investigate the chemical composition, origin and evolution of the atmosphere of Titan. The instrument was designed and built by NASA's Goddard Space Flight Center, Greenbelt, Md., and is led by the principal investigator, Dr. Hasso Niemann.

Updates on the Huygens probe release will be 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.

What I did not realize is that there are two US instruments on the probe. Also another team has quite a few Americans on it. If you actually look at the teams this is less and ESA proper mission but lower level national and regional space groups under the cover of the ESA.

Somehow I did not get this before.

By the way, if they have a higher success rate it is only because there are lees of them and until recently they have been less adventurous in scope and intent.

Up until SOHO a great many ESA missions were managed operationally in conjunction with the USA.

But they are starting to have more cutting edge projects. I really like Herchel (only about 12% American) and Gia (or what ever they are clling it now) which is all European. While it is fine to be a ESA booster, you should put it in perspective.

Cassini ready to launch European probe to Saturn moon Titan

http://www.bakersfield.com/state_wire/story/5168202p-5206817c.html

The Associated Press

Posted: Thursday December 23rd, 2004, 6:35 PM
Last Updated: Thursday December 23rd, 2004, 6:35 PM

PASADENA, Calif. (AP) - With a gentle shove on Christmas Eve, the Cassini spacecraft will launch the European Space Agency's Huygens probe on a course that should send it plunging into the atmosphere of Saturn's big moon Titan.

The probe must be released precisely on course because it has no means of maneuvering and will remain dormant until a timer wakes it up for entry into Titan's hazy hydrocarbon-laced atmosphere and a parachute descent to the surface on Jan. 14.

Confirmation of a successful release should be received by NASA's Deep Space Network antennas in Spain and Goldstone, Calif., just before 8 p.m. PST Friday, Jet Propulsion Laboratory said.

The $3.3 billion Cassini-Huygens mission, a project of NASA, ESA and the Italian space agency, was launched on Oct. 15, 1997, from Cape Canaveral, Fla., to study Saturn, its spectacular rings and many moons.

During the nearly seven years Cassini took to reach the ringed planet, the attached probe was powered through an umbilical cable and awakened from sleep mode every six months for tests.

Cassini entered orbit around Saturn in June and has made several passes by Titan in preparation for the probe's release.

Friday evening, tension-loaded springs will push Huygens away from Cassini on a free-fall toward Titan.

On Dec. 27 Cassini will perform a course change to avoid following the probe into Titan.

Huygens is designed to make a 2 1/2-hour descent by parachute to the surface of the moon, which, according to some theories, could have lakes of methane.

Instruments aboard the probe will investigate the atmosphere's chemistry and cameras will try to record images of the surface. It's not known whether Cassini will drop into liquid or onto a hard surface, where it may operate for a few minutes.

As long as it is operating, Huygens will be transmitting data back to Cassini, which will later turn around to point its antenna at Earth and send the data to the Deep Space Network and on to ESA's Space Operations Center in Darmstadt, Germany.

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On the Net:

http://saturn.jpl.nasa.gov

http://www.nasa.gov/cassini

January 14, 2005: Huygens at Titan

05.28.04

The Huygens probe will usher in 2005 with its landmark mission at Titan. After a seven-year journey strapped to the side of the Cassini Orbiter, Huygens will be set free on Dec. 25, 2004. The Probe will coast for 20 days en route to Titan.

Image right:Artists's rendition of the Huygens probe at Titan. Image credit: NASA/JPL

Prior to the probe's separation from the orbiter, the "coast" timer will be loaded with the precise time necessary to turn on the probe systems (15 minutes before the initial encounter with Titan's atmosphere). Then the probe will separate from the orbiter and coast to Titan for 20 days with no systems active except for its wake-up timer.

Huygens will separate from Cassini at 30 centimeters (about 12 inches) per second and a spin rate of seven revolutions per minute to ensure stability during the coast and entry phase. Five days following the release of the probe, Cassini will perform a deflection maneuver. This will place the orbiter in the proper geometry to collect the data during the probe mission. The probe will continue in this mode until it reaches the top of Titan's atmosphere.

Titan's nitrogen-rich atmosphere extends 10 times further into space than Earth's atmosphere. This means the outer fringes of Titan's atmosphere reach almost 600 kilometers (373 miles) into space. When the probe detects this region of Titan's atmosphere, the sleep timer will go off, awakening the probe's science instruments.

Huygens is equipped with six science instruments designed to study the content and dynamics of Titan's atmosphere and collect data and images on the surface.

Descent Through Titan's Atmosphere Artist's rendition of the Huygens probe separating from Cassini.

Artist's rendition of the Huygens probe separating from Cassini.

Huygens will make a parachute-assisted descent through Titan's atmosphere, collecting data as the parachutes slow the probe from super sonic speeds. Five batteries onboard the probe are 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. These batteries are capable of generating 1800 Watt-hours of electricity.

Image right: Artist's Concept: Huygens probe separating to enter Titan's atmosphere. Image credit: NASA/JPL

The probe's radio link will be activated early in the descent phase, and the orbiter will "listen" to the probe for the next three hours, which includes the descent plus 30 minutes after impact. Not long after the end of this three-hour communication window, Cassini's high-gain antenna (HGA) will be turned away from Titan and toward Earth.

The peak heat-flux is expected in the altitude range below 350 kilometers (217 miles) down to 220 kilometers (137 miles), where Huygens rapidly decelerates from about 21,600 kilometers (21,600 miles) per hour to 1,440 kilometers (895 miles) per hour in less than two minutes.

At this speed, the parachute deployment sequence initiates, starting with a mortar pulling out a Pilot Parachute which, in turn, pulls away the aft cover and deploys the Main Parachute. After inflation of the 8.3 meter (27.2 feet) diameter main parachute, the front shield is released to fall from the Descent Module.

Then, after a 30 second delay built into the sequence to ensure that the shield is sufficiently far away to avoid instrument contamination, the Gas Chromatograph Mass Spectrometer (GCMS) and Aerosol Collector and Pyrolyser (ACP) inlet ports open and the Huygens Atmospheric Structure Instrument (HASI) boom deploy. The Descent Imager/Spectral Radiometer (DISR) cover is ejected two minutes later.

Image left: Huygens Probe Descent Profile. Click for larger image
Image credit: NASA/JPL/ESA

The main parachute is sized to pull the Descent Module safely out of the front shield. It is jettisoned after 15 minutes to avoid a protracted descent and a smaller 3-meter (10-foot) diameter parachute is deployed. The descent will last between two and two and half hours.

During its descent, Huygens' camera will capture more than 1,100 images, while the Probe's other five instruments will sample Titan's atmosphere and determine its composition.

Data from Huygens will be relayed to the Cassini Orbiter passing overhead. The data will be stored onboard Cassini's Solid State recorders (SSR) for playback to Earth.

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