PDS_VERSION_ID = PDS3 LABEL_REVISION_NOTE = "Version 2, Project Scientist Team, 4 July 2006" RECORD_TYPE = STREAM OBJECT = TEXT INTERCHANGE_FORMAT = ASCII PUBLICATION_DATE = 2006-08-01 NOTE = "N/A" END_OBJECT = TEXT END This dataset contains housekeeping (engineering) data obtained by the Huygens probe during its mission on 14 January 2005. The data set has been organized in various directories one level below the root: CALIB: contains five documents which provide calibration information. CATALOG: contains required PDS files needed to support the data analysis. DATA: contains the data. DOCUMENT: contains the necessary documentation to understand the data. EXTRAS: contains additional files, especially all the engineering data in the original format provided by the flight control team. INDEX: contains indes files. Before accessing the data, it is recommended to read first the document entitled "EAICD" ( = Experiment to Archive Interface Control Document), in the DOCUMENT directory, EAICD folder. It describes the content of the archive. Then, it is suggested to read the CATALOG files, especially MISSION.CAT, INSTRUMENT_HOST.CAT, INSTRUMENT.CAT and DATASET.CAT. OVERVIEW.TXT under /DOCUMENT is a useful overview of the engineering parameters. CAVIAT ====== (A) The Huygens trajectory The knowledge of the Huygens trajectory is of primary importance for the payload data analysis. The official trajectory reconstruction is the result of a common effort; it is produced from a subset of the Huygens experiments and housekeeping data by the Huygens Descent Trajectory Working Group (DTWG). The DTWG input files and the derived trajectory is archived within the Huygens DTWG data set. The Huygens Probe auxiliary data ((e.g. aerodynamic coefficients, Probe physical properties, parachute characteristics) are archived within the Huygens housekeeping (HK) data set. Warnings: It should be pointed out that the reconstruction of descent trajectory of the Huygens probe is not coherent with the altitude profile retrieved from the Huygens radar altimeter. Different approaches/methods for descent trajectory reconstruction resulted in altitude and velocity profiles that show discrepancy, not consistent with uncertainty range relevant to models and measurements. The reason for this discrepancy is at present still under investigation. Results of future analysis could imply the need to reconsolidate the trajectory. (B) Time information Any user of the Huygens data must be aware of the following: 1. The T0 time, official start of the descent, is known with an accuracy of 0.125 seconds. Its official UTC value is 2005-014T09:10:20.828 . 2. Time can be displayed differently from one Huygens data set to another, as shown in the two tables a) and b). Time units SEC, MSEC and HH:MM:SEC indicate that the time is given w.r.t. T0, whereas UTC indicates that it is independent from the precise value of T0. a) =================================================================================== Huygens data set | ACP | GCMS |SSP | HASI | Time unit in the data products | UTC | UTC |SEC | MSEC | Time unit for the keyword START_TIME | UTC | UTC |UTC | UTC | Time unit for the keyword SPACECRAFT_CLOCK_START_COUNT| MSEC| MSEC |SEC |HH:MM:SEC| Time unit for the keyword NATIVE_START_TIME | SEC | SEC |SEC | MSEC | =================================================================================== b) =================================================================================== Huygens data set | DISR| DWE |HK | DTWG | Time unit in the data products | N/A | UTC |UTC | UTC | Time unit for the keyword START_TIME | UTC | UTC |UTC | UTC | Time unit for the keyword SPACECRAFT_CLOCK_START_COUNT| SEC | N/A |SEC | N/A | Time unit for the keyword NATIVE_START_TIME | N/A | N/A |SEC | N/A | =================================================================================== For more information about the data please contact: Jean-Pierre Lebreton ESA ESTEC 2200 AG Noordwijk The Netherlands Jean-Pierre.Lebreton@esa.int For more information about the dataset and about the ESA Planetary Data Archive please contact the European Space Agency at the European Research and Technology Center (ESTEC), Noordwijk, The Netherlands: Olivier Witasse ESA ESTEC 2200 AG Noordwijk The Netherlands Olivier.Witasse@esa.int For further information about the dataset and about the PDS please contact the Atmospheres Node of the Planetary Data System at ..... Lyle Huber Department of Astronomy New Mexico State University P.O. Box 30001, MSC 4500 Las Cruces, NM 88003-0001 Phone: 505-646-1862 Email: lhuber@nmsu.edu Here are two useful websites: www.rssd.esa.int/psa pds.jpl.nasa.gov