Data Set Overview: This data set contains the engineering data of theHuygens probe, measured during its mission on 14 January 2005. The total number of engineering parameters is ~ 1600.It was decided to archive in the PDS only aselection of the most useful parameters (217). However, allthe data are stored in their original format in the EXTRAS directory.  Data Set Identifier:  The 'DATA_SET_ID' is a unique alphanumeric identifier for the data sets. It looks something like:  XX-Y-ZZ-U-WWW  Acronym | Description | Example -------------------------------------------------------------- XX | Instrument Host ID | HP -------------------------------------------------------------- Y | Target ID | SSA (for Saturn satellite) -------------------------------------------------------------- ZZ | Instrument ID | HK (for HouseKeeping) -------------------------------------------------------------- U | Data level (here | 2-3 | CODMAC levels are used) | --------------------------------------------------------- WWW | Version number | V1.0   Documents: The DOCUMENT directory contains the files that provide documentation andsupplementary information to assist in understanding and using the dataproducts. Structure of DATA Directory: Below /DATA/ the directories are named after the Huygens probe subsystems.They are:CDMS: Command and Data Management SubsystemsSASW: Support Avionics SoftwarePOSW: Probe Onboard SoftwarePDRS: Probe Data Relay SubsystemEPSS: Electrical Power SubsystemEXP: Experiments A specific folder for the spin is accessible: SPIN Then, subdirectories are named after specific subsubsystems or payload: CDMUB: Command and Data Management Unit Chain BCASU: Central Acceleration Sensor UnitRASU: Radial Acceleration Sensor UnitPSAB: Probe Support Avionics Chain BDISR: Descent Imager Spectral RadiometerHASI: Huygens Atmospheric Structure InstrumentACP: Aerosol Collector PyroliserSSP: Surface Science PackageGCMS: Gas Chromatograph and Mass SpectrometerTUSO: Transmitter Ultra Stable OscillatorRUSO: Receiver Ultra Stable OscillatorPROXSENSORA: Proximity Sensor (radar) Chain APROXSENSORB: Proximity Sensor (radar) Chain BTIMER: Huygens timersTEMP: Temperature sensorsPCDU: Power Conditioning & Distribution UnitLNAA: Low Noise Amplifiers Chain ATXB: Transmitter Chain B.  File naming convention: The data product file naming convention is as follows: HK___.TAB  Warnings: Overall the data quality is very good. The user of the data must beinformed about the following warnings: (1) Datation: The value of To, official start of the descent, maybe updated later. However, the difference will not exceed one second. (2) Completeness of the data: it must be understood that the engineeringparameters on channel A were lost [read INSTRUMENT_HOST.CAT].Therefore, (and unfortunately) less data are archived. (3) Radar calibration:The altitude needed to be calibrated. An explanation is givenin the file HUYGENS_RADAR_ALTITUDE_CALIBRATION in the CALIBdirectory. Two data products (tables) can be found in theDATA directory. (4) Computation of the Huygens spin rate:It was necessary to reconstruct the spin rate, see text in INSTRUMENT.CAT .  CALIB Directory:This directory contains four files summarizing the calibrationinformation of the Huygens engineering data. In addition, a document provides information on thecorrection of the radar altitude data. Software: The data are stored as ASCII files and do not needany specific software.No software is included with this data set. EXTRAS directory: All the engineering parameters are stored in their original formatin this directory. Open questions: During the proprietary period (18 months), the data analysis of theengineering data led to the publications of one article in Nature, one inJournal of Geophysical Research, and a number of proceedings (SeeREFERENCE.CAT). At the time of archiving, there are still some open issues:(1) Why Huygens spun in the opposite direction ten minutes after the startof the descent?(2) Why the descent duration lasted so long (12 minutes more than thepredictions)?(3) What is the final attitude of the probe on the surface?(4) Why the altitudes given by the proximitor sensor (chain B) do not agreewell with the altitudes calculated from pressure and temperaturemeasurements? Review:  The Huygens data sets were reviewed in two steps: (1) a review of the Experimenter-to-archive-ICD, in 2004. (2) a review of the data sets, in 2006. Procedures and details of this process can be obtained from the ESA archive team:  Olivier Witasse or Joe Zender ESA ESTEC Keplerlaan 1 2200 AG Noordwijk The Netherlands Olivier.Witasse@esa.int or Joe.Zender@esa.int  This data set was reviewed by an external reviewer.

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