Huygens (spacecraft)
Mission type | Lander |
---|---|
Operator | ESA / ASI / NASA |
COSPAR ID | 1997-061C |
Website | Huygens home page |
Spacecraft properties | |
Manufacturer | Thales Alenia Space (then Aérospatiale)[1] |
BOL mass | 320 kg (710 lb) |
Power | 1800 Wh total |
Start of mission | |
Launch date | 08:42, October 15, 1997 (UTC) |
Rocket | Cassini orbiter |
Deployment date | December 25, 2004 |
End of mission | |
Last contact | 13:37, January 14, 2005 (UTC) |
Landing date | 12:43, January 14, 2005 (UTC) |
SCET UTC) | |
Landing site | 10°34′23″S 192°20′06″W / 10.573°S 192.335°W[2] |
ESA quadrilateral mission insignia for Huygens Cluster → |
Huygens (
The combined Cassini–Huygens spacecraft was launched from
Huygens touched down on land, although the possibility that it would touch down in an ocean was also taken into account in its design. The probe was designed to gather data for a few hours in the atmosphere, and possibly a short time at the surface. It continued to send data for about 90 minutes after touchdown.
Overview
Huygens was designed to enter and brake in Titan's atmosphere and parachute a fully instrumented robotic laboratory 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 thought that analysis of data from Cassini would help to answer these questions.
Based on pictures taken by Cassini 1,200 km (750 mi) above Titan, the landing site appeared to be a shoreline. Assuming the landing site could be non-solid, Huygens was designed to survive the impact, splash down on a liquid surface on Titan, and send back data for several minutes under these conditions. If that occurred it was expected to be the first time a human-made probe would land in an extraterrestrial ocean. The spacecraft had no more than three hours of battery life, most of which was planned to be used during the descent. Engineers expected to get at most only 30 minutes of data from the surface.
The Huygens probe system consists of the 318 kg (701 lb) probe itself, which descended to Titan, and the 30 kg (66 lb) kg probe support equipment (PSE), which remained attached to the orbiting spacecraft. Huygens' heat shield was 2.7 m (8.9 ft) in diameter. After ejecting the shield, the probe was 1.3 m (4.3 ft) 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 where it was transmitted or "downlinked" to the Earth.
The probe remained dormant throughout the 6.7-year interplanetary cruise, except for semiannual health checks.[7] 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 25 December 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 three 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 towards Earth.
Very large
The signal strength received on Earth from Huygens was comparable to that from the
Findings
Huygens landed at around 12:43 UTC on January 14, 2005 with an impact speed similar to dropping a ball on Earth from a height of about 1 m (3 ft). It made a dent 12 cm (4.7 in) deep, before bouncing onto a flat surface, and sliding 30 to 40 cm (12 to 16 in) across the surface. It slowed due to friction with the surface and, upon coming to its final resting place, wobbled back and forth five times. Huygens' sensors continued to detect small vibrations for another two seconds, until motion subsided about ten seconds after touchdown. The probe kicked up a cloud of dust (most likely organic
At the landing site there were indications of pebbles of water ice scattered over an orange surface, the majority of which is covered by a thin haze of
The surface was initially 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 colour of Titan's surface to a crème brûlée (that is, a hard surface covering a sticky mud-like subsurface). Subsequent analysis of the data suggests that surface consistency readings were likely caused by Huygens pushing a large pebble into the ground as it landed, and that the surface is better described as a "sand" made of ice grains[11] or snow that has been frozen on top.[9] The images taken after the probe's landing show a flat plain covered in pebbles. The pebbles, which may be made of hydrocarbon-coated water ice, are somewhat rounded, which may indicate the action of fluids on them.[12] The rocks appear to be rounded, size-selected and size-layered as though located in the bed of a stream within a dark lakebed, which consists of finer-grained material. No pebbles larger than 15 cm (5.9 in) across were spotted, while rocks smaller than 5 cm (2.0 in) are rare on the Huygens landing site. This implies large pebbles cannot be transported to the lakebed, while small rocks are quickly removed from the surface.[13]
The temperature at the landing site was 93.8
Huygens found the brightness of the surface of Titan (at time of landing) to be about one thousand times dimmer than full solar illumination on Earth (or 500 times brighter than illumination by full moonlight)—that is, the illumination level experienced about ten minutes after sunset on Earth, approximately late
Detailed Huygens activity timeline
- Huygens separated from Cassini orbiter at 02:00 UTC on 25 December 2004 in Spacecraft Event Time.
- Huygens entered Titan's atmosphere at 10:13 UTC on 14 January 2005 in SCET, according to ESA.
- The probe landed on the surface of Titan at about 10.6°S, 192.3°W 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. Huygens 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 the 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 directly to Earth. Rather, it transmitted data to the Cassini orbiter, which later relayed to Earth the data received.
Instrumentation
Huygens had six instruments aboard that took in a wide range of scientific data as the probe descended through 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.
Doppler Wind Experiment (DWE)
This experiment used an ultra-stable
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 km (90 mi) down to the surface. Solar aureole cameras measured how scattering by aerosols varies the intensity directly around the Sun. Three imagers, sharing the same CCD, periodically imaged a swath of around 30 degrees wide, ranging from almost nadir to just above the horizon. Aided by the slowly spinning probe they would build up a full mosaic of the landing site, which, surprisingly, became clearly visible only below 25 km (16 mi) 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 scientific objectives of the experiment fall into four areas including (1) measurement of the solar heating profile for studies of the thermal balance of Titan; (2) imaging and spectral reflection measurements of the surface for studies of the composition, topography, and physical processes which form the surface as well as for direct measurements of the wind profile during the descent; (3) measurements of the brightness and degree of linear polarization of scattered sunlight including the solar aureole together with measurements of the extinction optical depth of the aerosols as a function of wavelength and altitude to study the size, shape, vertical distribution, optical properties, sources and sinks of aerosols in Titan’s atmosphere; and (4) measurements of the spectrum of downward solar flux to study the composition of the atmosphere, especially the mixing ratio profile of methane throughout the descent."[16]
Gas Chromatograph Mass Spectrometer (GC/MS)
This instrument is a gas chemical analyzer that was designed to identify and measure chemicals in Titan's atmosphere.
Aerosol Collector and Pyrolyser (ACP)
The ACP experiment drew in
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.
The Huygens SSP was developed by the Space Sciences Department of the University of Kent and the Rutherford Appleton Laboratory Space Science Department (now RAL Space) under the direction of Professor John Zarnecki. The SSP research and responsibility transferred to the Open University when John Zarnecki transferred in 2000.
Spacecraft design
Huygens was built under the Prime Contractorship of Aérospatiale in its Cannes Mandelieu Space Center, France, now part of Thales Alenia Space. The heat shield system was built under the responsibility of Aérospatiale near Bordeaux, now part of Airbus Defence and Space.
Parachute
Critical design flaw partially 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 Huygens.[21][22]
Since Huygens was too small to transmit directly to Earth, it was designed to
This was because under the original flight plan, when Huygens was to descend to Titan, it would have accelerated relative to Cassini, causing the
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 travelled perpendicular to its direction of motion relative to Cassini, greatly reducing the Doppler shift.[21]
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.
Channel A data loss
Huygens was programmed to transmit
Cassini never listened to channel A because of an error in the sequence of commands sent to the spacecraft. The receiver on the orbiter was never commanded to turn on, according to officials with the European Space Agency. ESA announced that the error was a mistake on their part, the missing command was part of a command sequence developed by ESA for the Huygens mission, and that it was executed by Cassini as delivered.
Because Channel A was not used, only 350 pictures were received instead of the 700 planned. All
Contributions from citizen science projects
The fact that Huygens rotated in the opposite direction than planned delayed the creation of surface mosaics from the raw data by the project team for many months. On the other hand, this provided an opportunity for some citizen science projects to attempt the task of assembling the surface mosaics. This was possible, because the European Space Agency approved the publication of the DISR raw images and gave the permission for citizen scientists to present their results on the internet.[23] Some of these citizen science projects have received a lot of attention in the scientific community,[24] in popular scientific journals[25][26][27][28] and in the public media.[29][30] While the media liked to present the story of amateurs outperforming the professionals,[25][28][29] most of the participants understood themselves as citizen scientists, and the driving force behind their work was a desire to find out and show as much as possible of the hitherto unknown surface of Titan. Some enthusiasts projects were the first at all to publish surface mosaics and panoramas of Titan already the day after Huygens landed,[31] another project worked with the Huygens DISR data for several months until virtually all images with recognizable structures could be assigned to their correct position, resulting in comprehensive mosaics and panoramas.[32] A surface panorama from this citizen science project was finally published in the context of a Nature review by Joseph Burns.[33]
Landing site
The probe landed on the surface of Titan at 10°34′23″S 192°20′06″W / 10.573°S 192.335°W.
See also
- Cassini–Huygens timeline
- Cassini retirement
- Europlanet
- List of missions to the outer planets
- Titan Mare Explorer
- Titan Saturn System Mission
- Galileo probe
References
Citations
- ^ "HUYGENS".
- . Retrieved January 4, 2018.
- ^ Rincon, Paul (January 15, 2005). "Huygens sends first Titan images". BBC News. Retrieved August 30, 2016.
- ^ a b "Solstice Mission Overview". NASA. Archived from the original on December 17, 2008. Retrieved January 21, 2013.
- ^ "Cassini-Huygens". European Space Agency. Retrieved March 22, 2019.
- ^ "Cassini-Huygens Mission Facts". European Space Agency. Retrieved March 22, 2019.
- ^ "Cassini–Huygens Mission". NASA. Archived from the original on February 19, 2013. Retrieved January 30, 2013.
- ^ "Radio astronomers confirm Huygens entry in the atmosphere of Titan". European Space Agency. January 14, 2005. Retrieved March 22, 2019.
- ^ a b "Bounce, Skid, Wobble: How Huygens Landed on Titan". www.jpl.nasa.gov. 2012. Retrieved January 19, 2015.
- ^ "Tropical Methane Lakes on Saturn's Moon Titan". saturntoday.com. 2012. Archived from the original on November 3, 2012. Retrieved June 16, 2012.
- ^ Titan probe's pebble 'bash-down', BBC News, April 10, 2005.
- ^ New Images from the Huygens Probe: Shorelines and Channels, But an Apparently Dry Surface Archived August 29, 2007, at the Wayback Machine, Emily Lakdawalla, January 15, 2005, verified March 28, 2005
- ^ S2CID 4414457.
- PMID 20184181.
- S2CID 189778612.
- ^ M G Tomasko; D Buchhauser; M Bushroe; L E Dafoe; L R Doose; A Eibl; C Fellows; E M Farlane; G M Prout; M J Pringle. The Descent Imager/Spectral Radiometer (DISR) Experiment on the Huygens Entry Probe of Titan. Space Science Reviews, 104, no. 1/2, (2002): 467-549.
- S2CID 1794678.
- S2CID 4344046.
- S2CID 54502443.
- ^ "SSP: Surface Science Package". ESA Science & Technology. European Space Agency. December 7, 2005. Retrieved August 20, 2012.
- ^ a b c d Oberg, James (October 4, 2004). "Titan Calling". IEEE Spectrum. (offline as of 2006-10-14, see Internet Archive version)
- ^ How Huygens avoided disaster, James Oberg, The Space Review, January 17, 2005.
- ^ "Enthusiast compositions of the Huygens images". Anthony Liekens. Archived from the original on January 6, 2022. Retrieved February 14, 2022.
In an article of Der Spiegel Online, a spokesperson of ESA confirms that this publication of raw images, to allow open source editing and compositing, is part of a study by ESA to see if the publication of the raws is indeed a good strategy.
- .
- ^ JSTOR 27858574.
- ^ Mac Robert, Alan (May 2005). "Amateurs-just amateurs". Astronomy Now. UK: Pole Star Publications Ltd. pp. 67–69.
- ^ Mac Robert, Alan (January 2005). "Wild, Weird Titan Reveals More Secrets". Sky & Telescope. United States: American Astronomical Society.
- ^ a b Goldman, Stuart J. (May 2005). "Landscapes on Titan: amateurs scoop the pros: spacecraft-imagery openness may lead to amateurs beating planetary scientists to the punch". Sky & Telescope. United States: American Astronomical Society.
- ^ a b "Amateurs who beat Nasa over the moon". The London Times. UK. January 21, 2005. p. 32.
- ^ de Goursac, Olivier (July 23, 2005). "Titan enfin dévoilé" [Titan finally unveiled]. Le Figaro Magazine (in French). France: Socpresse/Dassault.
- ^ "Enthusiast compositions of the Huygens images". Anthony Liekens. Archived from the original on January 6, 2022. Retrieved February 14, 2022.
- ^ "Panoramic Views and Landscape Mosaics of Titan stitched from Huygens Raw Images". René Pascal. Retrieved February 14, 2022.
- S2CID 4412744.
Bibliography
- Nature 438, Dec. 2005 - The results analyzed in nine articles, letters to the editor and related media are available with free access online.
Further reading
- Ralph Lorenz (2018). NASA/ESA/ASI Cassini-Huygens: 1997 onwards (Cassini orbiter, Huygens probe and future exploration concepts) (Owners' Workshop Manual). Haynes Manuals, UK. ISBN 978-1785211119.
External links
- Amateur compositions of images, preceding NASA and ESA releases Archived January 17, 2005, at the Wayback Machine
- 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
- Surface Mosaics and extensive Image Processing by an Amateur
- "The Huygens Probe: Science, Payload and Mission Overview"
- Exploratorium webcasts about Saturn and Titan
- ESA Bulletin on Huygens
- Engineering the parachute and computer systems on the Huygens probe