PDS_VERSION_ID = PDS3 LABEL_REVISION_NOTE = "VERSION 2, JFB, 2005-11-17" RECORD_TYPE = STREAM OBJECT = TEXT INTERCHANGE_FORMAT = ASCII PUBLICATION_DATE = 2005-11-17 NOTE = "N/A" END_OBJECT = TEXT END This volume follows the structure outlined below: ROOT | |- AAREADME.TXT The file you are reading. | | |- VOLDESC.CAT A description of the contents of this | CD_ROM volume in a format readable by | both humans and computers. | |- [CATALOG] A directory containing information | | about the ACP data sets | | | |- CATINFO.TXT Description of files in this directory. | | | |- MISSION.CAT Description of the Cassini-Huygens | | mission. | | | |- INSTRUMENT_HOST.CAT Description of the Huygens Probe | | | |- INSTRUMENT.CAT Description of the ACP instrument. | | | |- DATASET.CAT Descriptions of the ACP data set. | | | |- PERSONNEL.CAT A listing of the people involved in the | | production of these data sets. | | | |- REFERENCE.CAT A list of relevant references. | |- [DOCUMENT] A directory containing supporting | documentation. | |- [INDEX] A directory containing an index of data | files. | | |- [DATA] A directory containing the data files and PDS labels describing the contents of those files. ================================================================= FILE FORMAT ================================================================= Most data files on this disc are accompanied by detached PDS labels, which describe their contents. Some data files and PDS TEXT objects include attached labels. Labels have the same file name as the primary data file but have a suffix ".LBL" appended. 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 the PI team: G Israel, C Szopa, M Cabane, J-F Brun, C Pennanech CNRS/SA brun@aerov.jussieu.fr 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 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 ESTEC/ESA Phone: +31 71 565 8015 owitasse@rssd.esa.int