Huygens probe
A scale replica of the probe, 1. 3 metres across.
Organization	ESA/ASI/NASA
Major contractors	Aérospatiale, now Thales Alenia Space
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

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 European Space Agency ( ESA) established in 1975 is an intergovernmental organisation dedicated to the exploration of space, currently with 17 member The Italian Space Agency (Agenzia Spaziale Italiana ASI) was founded in 1988 to promote coordinate and conduct space activities in Italy The National Aeronautics and Space Administration ( NASA, ˈnæsə is an agency of the United States government, responsible for the nation's public space program Aérospatiale was a French Aerospace manufacturer that primarily built both civilian and military Aircraft and Rockets The company was created in 1970 Thales Alenia Space is the company born after Thales had bought the participation of Alcatel in the two Joint-ventures between Alcatel and Finmeccanica Events 274 - Roman Emperor Aurelian "MMIV" redirects here For the Modest Mouse album see " Baron von Bullshit Rides Again " The International Designator (or NSSDC ID) is an international naming convention for Satellites It consists of the launch year a 3-digit incrementing launch number The European Space Agency ( ESA) established in 1975 is an intergovernmental organisation dedicated to the exploration of space, currently with 17 member Christiaan Huygens (ˈhaɪgənz in English ˈhœyɣəns in Dutch) ( April 14, 1629 &ndash July 8, 1695) was a Dutch TemplateInfobox Planet.--> Titan (ˈtaɪtən, or as Cassini–Huygens is a joint NASA / ESA / ASI Robotic spacecraft mission currently studying the planet Saturn and its The combined Cassini-Huygens spacecraft was launched from Earth on October 15, 1997. EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001 Events 533 - Byzantine General Belisarius makes his formal entry into Carthage, having conquered it from the Year 1997 ( MCMXCVII) was a Common year starting on Wednesday (link will display full 1997 Gregorian calendar Huygens separated from the Cassini orbiter on December 25, 2004, and landed on Titan on January 14, 2005 near the Xanadu region. Events 274 - Roman Emperor Aurelian "MMIV" redirects here For the Modest Mouse album see " Baron von Bullshit Rides Again " Events 1129 - Formal approval of the Order of the Templar at the Council of Troyes. Year 2005 ( MMV) was a Common year starting on Saturday (link displays full calendar of the Gregorian calendar. Xanadu (often called "Xanadu Regio" though this is not its official name is a highly reflective area on It touched down on land, although the possibility that it would touch down in an ocean was also taken into account in its design. Even though it was never officially designated a lander, the probe continued to send data for about 90 minutes after reaching the surface.

Overview

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. A mountain is a Landform that extends above the surrounding Terrain in a limited area with a peak In Geography, a plain is an area of land with relatively low relief — meaning that it is flat An ocean (from Greek, ''Okeanos'' (Oceanus) is a major body of saline water, and a principal component of the Hydrosphere.

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.

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. Events 274 - Roman Emperor Aurelian "MMIV" redirects here For the Modest Mouse album see " Baron von Bullshit Rides Again " 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' 10-watt transmission using the technique of very long baseline interferometry and aperture synthesis mode. Very Long Baseline Interferometry (VLBI is a type of astronomical interferometry used in Radio astronomy. 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 Robert C Byrd Green Bank Telescope ( GBT) is the world's largest fully steerable Radio telescope and the world's largest land-based movable structure 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. Los Alamos (Los Álamos meaning "The Cottonwoods quot is a Townsite and Census-designated place (CDP in Los Alamos County, Fort Davis is a Census-designated place (CDP in Jeff Davis County, Texas, United States. North Liberty is a city in Johnson County, Iowa, United States. The Kitt Peak National Observatory ( KPNO) is a United States astronomical Observatory located on a 2096 m (6880 ft peak of the Brewster is a city in Okanogan County, Washington, United States. Owens Valley is the arid valley of the Owens River in southeastern California in the United States. Mauna Kea is a Dormant volcano in the Hawaiian Islands, one of five volcanoes which together form the Island of Hawaii.

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. Galileo was an Unmanned spacecraft sent by NASA to study the Planet Jupiter and its moons Named after the Astronomer The Very Large Array ( VLA) is a Radio astronomy Observatory located on the Plains of San Augustin, between the towns of Magdalena Telemetry (synonymous with Telematics) is a Technology that allows the remote measurement and reporting of Information of interest to the system designer 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' landing site on Titan with exquisite precision, measuring its position to within 1 km at a distance from Earth of about 1200 million kilometres. The metre or meter is a unit of Length. It is the basic unit of Length in the Metric system and in the International This represents an angular resolution of approximately 170 microarcseconds. Angular resolution describes the resolving power of any image forming device such as an optical or Radio telescope, a Microscope, a Camera A minute of arc, arcminute, or MOA is a unit of angular measurement, equal to one sixtieth (1/60 of one degree. A similar technique was used to determine the landing site of the Mars exploration rovers by listening to their telemetry alone. NASA 's Mars Exploration Rover ( MER) Mission is an ongoing robotic mission of exploring Mars, that began in 2003 with the sending of

Findings

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. 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. Events 350 - Generallus Magnentius deposes Roman Emperor Constans and proclaims himself Emperor Mission scientists also reported a first "descent profile", which describes the trajectory the probe took during its descent.

However, 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.

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. Methane is a Chemical compound with the molecular formula. It is the simplest Alkane, and the principal component of Natural gas. 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. Clay is a naturally occurring material composed primarily of fine-grained Minerals which show plasticity through a variable range of Water content, and " 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. Crème brûlée (or Crème brulée in L'Orthographie 1990) ( French for "burnt cream" ˌkrɛm bruːˈleɪ in English, kʁɛm bʁyˈle

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]

Detailed Huygens activity timeline

Ellipse shows approximate landing site on this image taken earlier by Cassini. The bright region to the right is Xanadu Region. Xanadu (often called "Xanadu Regio" though this is not its official name is a highly reflective area on

Coloured image released from the landing site.

Contrast-enhanced version of surface image

• Huygens probe separated from Cassini orbiter at 02:00 UTC on December 25, 2004 in Spacecraft Event Time. Events 274 - Roman Emperor Aurelian "MMIV" redirects here For the Modest Mouse album see " Baron von Bullshit Rides Again " Spacecraft Event Time (SCET is the time an event occurs at a spacecraft
• Huygens probe entered Titan's atmosphere at 10:13 UTC on January 14, 2005 in SCET, according to ESA. Events 1129 - Formal approval of the Order of the Templar at the Council of Troyes. Year 2005 ( MMV) was a Common year starting on Saturday (link displays full calendar of the Gregorian calendar.
• 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. A transit of Earth across the Sun as seen from Saturn takes place when the planet Earth passes directly between the Sun and Saturn obscuring

See also Detailed timeline of Huygens mission. This page lists a chronology of events which have occurred or are expected to occur during the Cassini-Huygens mission to Saturn and Titan.

Instrumentation

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. An accelerometer is a device for measuring Acceleration and gravity induced reaction forces 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. The electron is a fundamental Subatomic particle that was identified and assigned the negative charge in 1897 by J An ion is an Atom or Molecule which has lost or gained one or more Valence electrons giving it a positive or negative electrical charge e. , positively charged particle) conductivities of the atmosphere and searched for electromagnetic wave activity. On the surface of Titan, the conductivity and permittivity (i. Permittivity is a Physical quantity that describes how an Electric field affects and is affected by a Dielectric medium and is determined by the ability e. , the ratio of electric displacement field to its electric field) of the surface material was measured. In Physics, the electric displacement field (also called electrical field/flux density is a Vector field \mathbf{D} that appears in Maxwell's equations In Physics, the space surrounding an Electric charge or in the presence of a time-varying Magnetic field has a property called an electric field (that can The HASI subsystem also contains a microphone, which was used to record any acoustic events during probe's descent and landing; ^[3] this was the first time in history that audible sounds from another planetary body had been recorded.

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. Oscillation is the repetitive variation typically in Time, of some measure about a central value (often a point of Equilibrium) or between two or more different states This instrument was also used to measure the wind speed in Titan's atmosphere by measuring the Doppler shift in the carrier signal. The Doppler effect (or Doppler shift) named after Christian Doppler, is the change in Frequency and Wavelength of a Wave for 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' data channels resulted in this data being lost to Cassini, enough was picked up by Earth-based radio telescopes to reconstruct it. A radio telescope is a form of directional Radio antenna used in Radio astronomy and in tracking and collecting data from Satellites 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. A telescope is an instrument designed for the observation of remote objects and the collection of Electromagnetic radiation. 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. Very Long Baseline Interferometry (VLBI is a type of astronomical interferometry used in Radio astronomy.

Descent Imager/Spectral Radiometer (DISR)

As Huygens was primarily an atmospheric mission, the DISR instrument was optimized to study the radiation balance inside Titan's atmosphere. Its visible and infrared spectrometers and violet photometers measured the up- and downward radiant flux from an altitude of 145 kilometers down to the surface. A spectrometer is an Optical instrument used to measure properties of Light over a specific portion of the Electromagnetic spectrum, typically used In the broadest sense a photometer is any instrument used to measure Illuminance or Irradiance. Solar aureole cameras measured how scattering by aerosols varies the intensity directly around the Sun. Technically an aerosol is a suspension of fine solid particles or liquid droplets in a gas Three imagers, sharing the same CCD, periodically imaged a swath of around 30 degrees wide, ranging from almost nadir to just above the horizon. A charge-coupled device ( CCD) is an analog Shift register, that enables the transportation of analog signals (electric charges through successive stages (capacitors The nadir (from Arabic ندير nadeer نظير nathir, "opposite" is the astronomical term for the point directly Aided by the slowly spinning probe they would built up a full mosaic of the landing site, which, surprisingly, became clearly visible only below 25 kilometer altitude. All measurements were timed by aid of a shadow bar, which would tell DISR when the Sun had passed through the field of view. Unfortunately, this scheme was upset by the fact that Huygens rotated in a direction opposite to that expected. Just before landing a lamp was switched on to illuminate the surface, which enabled measurements of the surface reflectance at wavelengths which are completely blocked out by atmospheric methane absorption.

DISR was developed at the Lunar and Planetary Laboratory at the University of Arizona under the direction of Martin Tomasko, with several European institutes contributing to the hardware. The Lunar and Planetary Laboratory (LPL is a Research center for Planetary science located in Tucson, Arizona. The University of Arizona (also referred to as UA, U of A, or Arizona) is a Land-grant and space-grant public institution

Gas Chromatograph Mass Spectrometer (GC/MS)

A worker in the Payload Hazardous Servicing Facility (PHSF) stands behind the bottom side of the experiment platform for the Huygens probe. Gas chromatography-mass spectrometry ( GC-MS) is a method that combines the features of Gas-liquid chromatography and Mass spectrometry to identify different

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, a high-voltage quadrupole, collected data to build 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. Mass spectrometry is an analytical technique that identifies the chemical composition of a compound or sample based on the Mass-to-charge ratio of charged particles ^[5] During descent, the GC/MS also analyzed pyrolysis products (i. Gas chromatography-mass spectrometry ( GC-MS) is a method that combines the features of Gas-liquid chromatography and Mass spectrometry to identify different e. , samples altered by heating) passed to it from the Aerosol Collector Pyrolyser. Finally, the GC/MS measured the composition of Titan's surface. Gas chromatography-mass spectrometry ( GC-MS) is a method that combines the features of Gas-liquid chromatography and Mass spectrometry to identify different This investigation was made possible by heating the GC/MS instrument just prior to impact in order to vaporize the surface material upon contact. Gas chromatography-mass spectrometry ( GC-MS) is a method that combines the features of Gas-liquid chromatography and Mass spectrometry to identify different The GC/MS was developed by the Goddard Space Flight Center and University of Michigan's Space Physics Research Lab. The Goddard Space Flight Center ( GSFC) is a major NASA space research laboratory established on May 1, 1959 as NASA's first space flight The University of Michigan Ann Arbor ( U of M, U-M, UM or simply Michigan) is a top-ranked Coeducational public research

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. Particulates, alternatively referred to as particulate matter (PM or fine particles, are tiny particles of solid or liquid suspended in a gas Pyrolysis is the Chemical decomposition of organic materials by heating in the absence of Oxygen or any other reagents except possibly Steam In Planetary science, volatiles, are that group of elements and compounds with low boiling points (see volatile) that are associated with a planet's or moon's The products were flushed along a pipe to the GC/MS instrument for analysis. Gas chromatography-mass spectrometry ( GC-MS) is a method that combines the features of Gas-liquid chromatography and Mass spectrometry to identify different 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). The European Space Agency ( ESA) established in 1975 is an intergovernmental organisation dedicated to the exploration of space, currently with 17 member

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. Sonar (which started as an Acronym for sound navigation and ranging) is a technique that uses Sound propagation (usually underwater to navigate 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. Sound is a vibration that travels through an elastic medium as a Wave. 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. A pendulum is a mass that is attached to a pivot from which it can swing freely 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). The density of a material is defined as its Mass per unit Volume: \rho = \frac{m}{V} Different materials usually have different Permittivity is a Physical quantity that describes how an Electric field affects and is affected by a Dielectric medium and is determined by the ability A penetrometer instrument, that protruded 55 mm 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 400 ms. 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 University of Kent is a plate glass campus University in Kent, England. John C Zarnecki is an English Sir Arthur Clarke Award winning professor and researcher in Space science The SSP research and responsibility transferred to the Open University when John Zarnecki transferred in 2000. Open University is also the name of other institutions See Distance education or the Open Universities category for a list

Spacecraft design

Application of multi-layer insulation shimmers under bright lighting during final assembly. Multi-layer insulation, or MLI, is thermal insulation composed of multiple layers of thin sheets The gold color of the MLI is due to light reflecting from the aluminium coating on the back of sheets of amber colored Kapton. WikipediaNaming Kapton ® is a Polyimide film developed by DuPont which can remain stable in a wide range of temperatures from -269 °C to +400 °C (4 K - 673 K

Huygens landing on Titan: a large picture on the seashore building of the Cannes Mandelieu Space center

Huygens was built under the Prime Contractorship of Aérospatiale in its Cannes Mandelieu Space Center, France, now part of Thales Alenia Space. Aérospatiale was a French Aerospace manufacturer that primarily built both civilian and military Aircraft and Rockets The company was created in 1970 The Cannes Mandelieu Space Center is an industrial plant dedicated to Spacecraft manufacturing located on both towns of Cannes and Mandelieu in France Thales Alenia Space is the company born after Thales had bought the participation of Alcatel in the two Joint-ventures between Alcatel and Finmeccanica The heat shield system was built under the responsibility of Aérospatiale near Bordeaux, now part of EADS SPACE Transportation. EADS Astrium Space Transportation was formed in June 2003 from the Space Infrastructure division of Astrium (whose core was originally ERNO) and the

Parachute

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. Martin-Baker Aircraft Co Ltd is a British manufacturer of Aircraft Ejection seats and was a pioneer in their design and manufacture A parachute is a device used to slow the motion of an object through an atmosphere by creating drag. IRVIN-GQ was responsible for the definition of the structure of each of Huygens' parachutes. IRVIN-GQ is a company that designs manufactures and supplies a range of parachutes and emergency rescue and survival equipment to the military coastguard and civilian aerospace markets 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 potentially 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. In Telecommunications transmission is the process of sending propagating and receiving an analogue or digital information signal over a physical point-to-point or Telemetry (synonymous with Telematics) is a Technology that allows the remote measurement and reporting of Information of interest to the system designer Radio is the transmission of signals by Modulation of electromagnetic waves with frequencies below those of visible Light. 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. Darmstadt is a city in the Bundesland Boris Smeds (born 16 October 1944) is a Swedish radio engineer and European Space Agency employee noted for detecting a critical flaw in 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. 2000 ( MM) was a Leap year that started on Saturday of the Common Era, in accordance with the Gregorian calendar. The Doppler effect (or Doppler shift) named after Christian Doppler, is the change in Frequency and Wavelength of a Wave for 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. The Doppler effect (or Doppler shift) named after Christian Doppler, is the change in Frequency and Wavelength of a Wave for 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. In Computing, firmware is a computer program that is Embedded in a hardware device for example a Microcontroller. In Telecommunications, a carrier wave, or carrier is a Waveform (usually Sinusoidal) that is modulated (modified with an input signal Material Transmitted over a network (either computer or telecommunications network) includes both Data and information that identifies the source and destination A bit is a binary digit, taking a value of either 0 or 1 Binary digits are a basic unit of Information storage and communication Phase-shift keying (PSK is a Digital Modulation scheme that conveys data by changing or modulating the phase of a reference signal In Telecommunications and Computing, bitrate (sometimes written bit rate, data rate or as a Variable R or f b

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. Uplink An uplink (UL or U/L is the portion of a communications link used for the transmission of signals from an Earth terminal DaimlerChrysler Aerospace AG or DASA, was the former aerospace subsidiary of Daimler-Benz AG (later DaimlerChrysler) from 1989 Darmstadt is a city in the Bundesland

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. Telemetry (synonymous with Telematics) is a Technology that allows the remote measurement and reporting of Information of interest to the system designer The S band ranges from 2 to 4  GHz, crossing the (artificial boundary between UHF and SHF at 3 Channel A was the sole path for an experiment to measure wind speeds by studying tiny frequency changes caused by Huygens's 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. Very Long Baseline Interferometry (VLBI is a type of astronomical interferometry used in Radio astronomy.

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 Nuñes and Anthony Liekens. Christian Waldvogel published an improved and colorized Panorama. Globus Cassus is an art project and book by Swiss architect and artist Christian Waldvogel presenting a conceptual transformation of Planet Earth into a much bigger hollow 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. Adiri is a large bright Albedo feature on Saturn 's moon Titan. ^[9]

References

See also

• Cassini-Huygens
• Cassini-Huygens timeline
• Europlanet

Bibliography

• (French)(English) Guy Lebègue, (trad. Cassini–Huygens is a joint NASA / ESA / ASI Robotic spacecraft mission currently studying the planet Saturn and its This page lists a chronology of events which have occurred or are expected to occur during the Cassini-Huygens mission to Saturn and Titan. Europlanet is a network linking planetary scientists from across Europe. Guy Lebègue, is a French engineer in the space domain graduated from École centrale Paris, alumni 1962 Robert J. Amral), « Huygens Space probe: A Seven-Year journey! », in Revue aerospatiale, n°76, March 1991. The Aerospatiale company had always strong Public relations. Among the means was a Magazine, monthly published.

External links

• Huygens probe lands on Titan: a scientific leap for mankind
• Amateur compositions of images, preceding NASA and ESA releases
• European Space Agency Cassini-Huygens website, including videos of the descent
• ESA Huygens scientific information
• Interactive Flash-Animation of Cassini orbits through 2008
• Latest News on the Huygens Probe
• NASA's Cassini-Huygens page
• New Scientist — Cassini-Huygens: Mission to Saturn
• Planetary Society's Saturn coverage
• Raw images from descent
• Surface Mosaics and extensive Image Processing by an Amateur
• The Huygens Probe: Science, Payload and Mission Overview
• Exploratorium webcasts about Saturn and Titan
• ESA Bulletine on Huygens