HUYGENS DESCENT TRAJECTORY WORKING GROUP Huygens-DTWG Experimenter to Archive Interface Control Document HUY-DTWG-IF-0002 Issue 4, Rev. 4 January 2007 Prepared by B. Kazeminejad / D. Atkinson Table of Contents DISTRIBUTION LIST........................................... 3 ACRONYMS AND ABBREVIATIONS.................................. 4 1. INTRODUCTION............................................. 5 2. OVERVIEW OF PROCESS AND PRODUCT GENERATION............... 7 3. ARCHIVE FORMAT AND CONTENT............................... 10 Catalog Directory........................................... 11 Index Directory............................................. 12 Browse Directory and Browse Files........................... 12 Geometry Directory.......................................... 12 Gazetteer Directory......................................... 13 Document Directory.......................................... 13 Data Directory.............................................. 13 Distribution List Recipient Organisation Function ------------------------------------------------------------------------------------------ Olivier Witasse ESA/ESTEC/RSSD, The Netherlands PSA Joe Zender ESA/ESTEC/RSSD, The Netherlands PSA Lyle Huber New Mexico State University, USA PDS Jean-Pierre Lebreton ESA/ESTEC/RSSD, The Netherlands Huygens Mission Operations Manager John Zarnecki Open University, UK SSP Principal Investigator Marty Tomasko LPL, University of Arizona, USA DISR Principal Investigator Michael Bird Universität Bonn, Germany DWE Principal Investigator Guy Israel CNRS, France ACP Principal Investigator Marcello Fulchignoni Université Paris 7, France HASI Principal Investigator Hasso Nieman NASA GSFC, USA GCMS Principal Investigator Claudio Sollazzo ESA/ESOC, Germany Huygens Operations Manager Dennis Matson NASA JPL, USA Cassini Project Scientist Acronyms and Abbreviations ACP Aerosol Collector & Pyrolyser AOA Angle-of-Attack AD Applicable Document CNRS Centre National de la Rechereche Scientifique ASCII American Standard Code for Information Interchange DISR Descent Imager & Spectral Radiometer DTWG Descent Trajectory Working Group DWE Doppler Wind Experiment EAICD Experimenter to (Science) Archive Interface Control Document ESA European Space Agency ESOC European Space Operations Centre ESTEC European Space Research & Technology Centre ET Ephemeris Time GCMS Gas Chromatograph & Mass Spectrometer HASI Huygens Atmospheric Structure Instrument HPOC Huygens Probe Operations Centre HSWT Huygens Science Working Team IDS Interdisciplinary Scientist LPL Lunar and Planetary Laboratory NAIF Navigation and Ancillary Information Facility NASA National Aeronautics and Space Administration NAV Navigation PDS Planetary Data System PSA Planetary Science Archive PI Principal Investigator PST Project Science Team RAU Radar Altimeter Unit SCLK Spacecraft Clock SSP Surface Science Package SZA Solar Zenith Angle UTC Universal Time Coordinated 1. Introduction 1.1 Purpose and Scope The Huygens Descent Trajectory Working Group (DTWG) was chartered in 1996 as a subgroup of the Huygens Science Working Team (HSWT) with the responsibility to reconstruct the Huygens probe entry and descent trajectory and its attitude from the official NASA/ESA hand-off point at 1270 km down to the surface [AD.5]. The primary objective of this EAICD document is to provide the readers of this document a detailed explanation of the derived DTWG data available at the archive. The intention is to define all DTWG data products accurately. The secondary objective of this document is to provide a formal interface for communication between the Huygens DTWG and the archiving authority. 1.2 Contents This document describes the DTWG data as presented to the PSA and PDS data archive. It includes information on how the data is processed, formatted, labeled, and uniquely identified. The document discusses general naming schemes for data volumes, data sets, data, and label files. Standards used to generate the product are explained. The designs of the data set structure and the data product are given. 1.3 Intended Readership The staff of the archiving team (Planetary Science Archive for ESA , Planetary Data System for NASA) and any potential user of the DTWG final archive. 1.4 Applicable Documents [AD.1] Planetary Data System Preparation Workbook, February 1, 1995, Version 3.1, JPL, D-7669, Part 1 [AD.2] Planetary Data System Standards Reference, October 30, 2002, Version 3.5, JPL, D-7669, Part 2 [AD.3] Huygens DTWG Experimenter to DTWG Interface Control Document, HUY-DTWG-IF-0001, Issue 9, Rev. 1 [AD.4] B. Kazeminejad, University of Graz, Austria, PhD Thesis "Methodology Development for the Reconstruction of the Huygens Entry and Descent Trajectory", 2005. [AD.5] D.H. Atkinson, B. Kazeminejad et al. “ Huygens probe entry and descent trajectory analysis and reconstruction techniques” Planetary and Space Science, Volume 53, Issue 5, p. 586-593 [AD.6] D.H. Atkinson, DTWG Rules of the Road, Rev. June 2003 [AD.7] M. Pérez-Ayúcar et al. “ A Simulated Dataset of the Huygens Mission “, Proc. Int. Workshop “Planetary Probe Atmospheric Entry and Descent Trajectory Analysis and Science”, Lisbon Portugal, 6-9 October 2003 (ESA SP-544, February 2004). [AD.8] B. Kazeminejad et. al. “Huygens' Entry and Descent through Titan's Atmosphere – Methodology and Results of the Trajectory Reconstruction”, Planetary and Space Sciences, Special Edition on Huygens, 2007. Note that [AD. 3] provides complementary information which is relevant for the proper specification and understanding of the DTWG archiving effort. [AD. 3] is therefore provided as part of the DTWG Archive Volume. 1.5 Contact Names and Addresses Dr. David H. Atkinson DTWG Chair Department of Electrical and Computer Engineering University of Idaho Moscow, ID 83844-1023, USA Email: atkinson@ece.uidaho.edu Tel: +1-(208) 885-6870 Fax: +1-(208) 885-7579 Dr. Bobby Kazeminejad DTWG Co-chair German Aerospace Center (DLR) German Space Operations Center (GSOC) Space Flight Technology 82234 Wessling, Germany Email: Bobby.Kazeminejad@dlr.de Tel: +49-(0)-8153-28-2603 Fax: +49-(0)-8153 28-1450 2. Overview of Process and Product Generation Using probe science and engineering measurements, the DTWG reconstructed the Huygens probe entry and descent trajectory from the official NASA/ESA interface point (defined to be at an altitude of 1270 km above Titan’s surface) down to probe impact on the surface. The DTWG utilized probe housekeeping and science instrument data as outlined in [AD.3]. The sampling rate of the reconstructed trajectory is 1 second. An overview of the reconstruction methodology is provided in Sec. 2.2 and a more detailed description (including the mathematical formulation, computational flow, and application of the algorithm to specific test cases) is provided in [AD.4] and [AD.8]. 2.1 DTWG Product Summary The DTWG product comprises two sets of products, the entry phase and the descent phase products. The Huygens probe entry phase is defined to start at the interface epoch (i.e., the time at which the spacecraft was predicted to reach an altitude of 1270 km above Titan’s surface) and continue to T0, the intiation of the parachute sequence. The descent phase starts at T0 and ends at the impact of the probe on Titan’s surface. The DTWG Product sampling rate is 1 Hz. Longitude and latitude are provided as Titan-centered coordinates. For the entry phase files probe altitudes are relative to Titan's reference surface at 2575.0 km w.r.t. Titan's center (referred to as "reference altitude"). For the descent phase the probe altitude is provided w.r.t. the probe's landing site on Titan's (actual) surface (referred to "surface altitude"). Table 1: Summary of the DTWG entry phase data product set: -------------------------------------------------------------------------------------- Data Product Data Product Parameters Units -------------------------------------------------------------------------------------- HUY_DTWG_ENTRY Probe reference altitude [km] Probe trajectory west longitude [deg] Probe trajectory latitude [deg] Probe angle-of-attack (AOA) (1-sigma uncertainties) HUY_DTWG_ENTRY_AERO Reconstructed entry phase aerodynamic parameters: [AMU] Mach Nr, Knudsen Nr, Drag coefficient, Reynold Nr, Molecular Mass HUY_DTWG_ENTRY_MASS Modelled probe mass during entry phase (based on a modelled heat shield mass ablation) [kg] HUY_DTWG_ENTRY_EME2000_POS Probe cartesian position vector In Titan-centered EME2000 reference system (1-sigma uncertainties) [km] HUY_DTWG_ENTRY_EME2000_VEL Probe cartesian inertial velocity vector [km/s] In Titan-centered EME2000 reference system (1-sigma uncertainties) Table 2: Summary of the DTWG descent phase data product set: -------------------------------------------------------------------------------------- Data Product Data Product Parameters Units -------------------------------------------------------------------------------------- HUY_DTWG_DESCENT_POS Atmospheric pressure at probe [hpa] Probe surface altitude [km] Probe trajectory west longitude [deg] Probe trajectory latitude [deg] (1-sigma uncertainties) HUY_DTWG_DESCENT_VEL Atmospheric pressure at probe [hpa] Probe surface altitude [km] Probe vertical (descent) velocity [m/s] (1-sigma uncertainties) 2.2 Reconstruction Overview The DTWG product is derived according to [AD.3] from two sets of input: 1. The DTWG Input Data, including all the relevant instrument and housekeeping data made available to the Huygens DTWG to perform the reconstruction of the probe entry and descent trajectory. 2. The Huygens Probe Initial Conditions and Event File provided by the PST to the DTWG, comprising the probe initial conditions, physical constants and epochs of important events during the probe mission. Both the DTWG Input Data and the Huygens Probe Initial Conditions and Event File are described in [AD. 3] which is provided as part of the DTWG Archive Volume. The reconstruction procedure is described in detail in [AD.4] and [AD.8]. A short overview is given here: Entry Phase Reconstruction The probe entry phase is defined as the portion of the trajectory starting from the official NASA/ESA interface point at 1270 km altitude down to T0, the time at which the Parachute Deployment Device (PDD) was fired (at an altitude of about 160 km). The probe entry phase is reconstructed by numerically integrating the equations of motion in a Titan-centered EME2000 coordinate system. The integration of the equations of motion requires the knowledge of the full probe state vector (i.e., the cartesian position and velocity vector specified in the integration reference system) at an initial epoch. The entry state vector is provided by the Cassini Navigation team to ESA together with the estimated interface epoch (in Ephemeris Time) and the corresponding state vector uncertainties in the form of a text kernel. This information is made available to the DTWG by the PSA via the Huygens Probe Initial Conditions and Event File (also in the form of a NAIF text kernel) which is also archived. Descent Phase Reconstruction The descent trajectory reconstruction is based on more than just one instrument dataset. The altitude and descent speed are derived from: - HASI pressure and temperature measurements - HASI impact measurement (time of impact) - GCMS molecular mass measurements The probe horizontal (meridional and zonal) drift is reconstructed from - DWE zonal wind measurements - DISR-derived meridional drift The mathematical formulation of the reconstruction algorithm as well as the reconstruction strategy is described in detail in [AD.4] and [AD.4] as well as in the file INSTRUMENT.CAT in the CATALOG directory. 3. Archive Format and Content The DTWG provides 1 Archive Volume consisting of 1 Data Set containing the results of the DTWG reconstruction effort. 3.1 Data Set ID and Data Product File Naming Convention The DTWG Data Set ID is HP-SSA-DTWG-6-TRAJECTORY-V1.0 and contains eight data products as listed in Table 3 with the corresponding names as specified in Table 4. Table 3: The seven DTWG Data Products. ------------------------------------------------------------------------------------------ Product Nr. Short description of data product ------------------------------------------------------------------------------------------ #1 Reconstructed entry phase position vector in spherical coordinates, angle-of-attack profile #2 Reconstructed aerodynamic entry phase numbers #3 Probe entry phase mass (taking into account heat shield mass ablation) #4 Reconstructed entry phase trajectory position vector in inertial Cartesian coordinates (Titan-centered EME2000 system) #5 Reconstructed entry phase velocity vector in inertial Cartesian coordinates (Titan-centered EME2000 system) #6 Descent phase: reconstructed trajectory (pressure, altitude, longitude and latitude) #7 Descent phase: reconstructed descent velocity (with respect to impact point on Titan's surface) The following names are used for the the various data products in the DATA File directory: Table 4: DTWG data product file names. ------------------------------------------------------------------------------------------ Product Nr. DTWG data product file names ------------------------------------------------------------------------------------------ #1 HUY_DTWG_ENTRY.TAB #2 HUY_DTWG_ENTRY_AERO.TAB #3 HUY_DTWG_ENTRY_MASS.TAB #4 HUY_DTWG_ENTRY_EME2000_POS.TAB #5 HUY_DTWG_ENTRY_EME2000_VEL.TAB #6 HUY_DTWG_DESCENT_POS.TAB #7 HUY_DTWG_DESCENT_VEL.TAB 3.2 Standards Used in Data Product Generation PDS Standard version 3.5 is used for the design of the DTWG archive. The time standard for the DTWG products is UTC in the exact format YYYY-MM-DDTHH:MM:SS.### In addition to UTC the DTWG products also provide a column with ET and elapsed seconds since T0 (the initiation epoch of the parachute sequence). 3.3 Data Validation The DTWG reconstruction software has been validated in an extensive testing phase using input data from past planetary entry missions (e.g., the Mars Pathfinder Mission) and a simulated Huygens data set [AD.7]. For the reconstruction of the actual Huygens entry and descent trajectory, sanity checks and comparisons with results from independent reconstruction efforts by the HASI team have been performed. Checks for completeness of the archived data set and the compatibility with PSA and PDS standards have been performed by the archiving responsible of the DTWG and the PSA and PDS teams. 3.4 Directory Structure and Contents The directory structure of the DTWG Data Volume follows the PDS conventions (see Fig. 2) and is described here. Catalog Directory The catalog directory contains the following data set catalog files: * CATINFO.TXT (general information about the files in the data set) * SOFT.CAT (description of the software provided in the SOFTWARE directory) * MISSION.CAT (description of the Cassini/Huygens mission) * PERSONNEL.CAT (responsible for trajectory reconstruction and data set providers) * REFERENCE.CAT (list of references) * INSTRUMENT.CAT ( description of trajectory reconstruction and DTWG membership) * INSTHOST.CAT (Huygens probe mission description) * DATASET.CAT (provides dataset overview) Index Directory The Index Directory only contains the standard index files Browse Directory and Browse Files The Browse Directory contains the following plots in the form of *.jpg files together with the corresponding label files: * ENTRY_ALT.JPG (entry phase: altitude vs. time plot) * ENTRY_ALT.LBL (entry phase: altitude vs. time plot label) * DESC_ALT.JPG (descent phase: altitude vs. time plot) * DESC_ALT.LBL (descent phase: altitude vs. time plot label) * DESC_VEL.JPG (first portion of descent phase: descent velocity vs. time) * DESC_VEL.LBL (first portion of descent phase: descent velocity vs. time label) Furthermore a BROWS_INFO.TXT provides a detailed description of the plot contents, which is should be considered as a required reading for a proper understanding of the plots in that directory. Geometry Directory The Geometry Directory contains all the files from the official NASA/ESA interface delivery that were relevant to the DTWG reconstruction effort. All files are either NAIF text or NAIF binary SPICE kernels. The beginning of all file names specify the date the files were delivered by the Cassini Navigation team to ESA: * 050214_LS_NAIF0007.TXT (Leap second file necessary for time conversion) * 050214_PCK.TXT (Planetary constant text kernel) * EVENT_FILE_04042005.TXT (Event file containing timing of important probe invents as well entry phase initial conditions and uncertainties) * HUY_AERDB1_ALCATEL.TXT (Huygens aerodynamic database, first part) * HUY_AERDB2_ALCATEL.TXT (Huygens aerodynamic database, second part) * SPACECR_148.TXT (Huygens spacecraft constants file) * GEOMINFO.TXT (file containing a detailed overview of the files in the GEOMETRY directory) The Probe Initial Conditions and Event File is defined in [AD.3]. The Leap Second File is a NAIF text kernel file used to convert time from UTC to ET. Software Directory N/A . The sofware routines are archived in the EXTRAS directory. Gazetteer Directory No Gazetteer Directory is needed. Document Directory The Document Directory contains all the relevant documents needed to understand the major technical and mathematical aspects of the DTWG reconstruction effort. The following documents are provided: * [AD.3]: B. Kazeminejad, Experimenter to DTWG Interface Document, HUY-DTWG-IF-0001 v9.0, 2005 * [AD.4]: B. Kazeminejad, PhD Thesis “Methodology Development for the Reconstruction of the Huygens Entry and Descent Trajectory”, University of Graz, Austria, 2005. with the corresponding filenames: - EXPERIMENT_TO_DTWG_ICD.ASC, *.PDF, *.LBL - KAZEMINEJAD_PHD_THESIS, *.PDF, *.LBL Also included in the Document Directory are the following documents: * DTWG Experimenter to Archive Interface Document (this document) * [AD7] A simulated dataset of the Huygens mission. * [AD6] D.H. Atkinson, DTWG Rules of the Road, Rev. June 2003 With the corresponding file names - EAICD.ASC, *.DOC, *.LBL - SIMULATED_DATA_SET2004, *.LBL, *.PDF. - RULES_OF_THE_ROAD.TXT, *.LBL Data Directory The Data Directory contains the data products as listed in Table 4. EXTRAS Directory. The EXTRAS directory contains three folders: INPUT_FILES: This folder contains a description of the input files used by the DTWG tool for the computation of the Huygens trajectory. The file naming and the format are explained in the document "EXPERIMENTER_TO_DTWG_ICD". The list of files is: DISR_WIND_27032006.DAT HASI_XSERVO_CONING.DAT_PP DWE_ZWIND_27032006.DAT_PP HASI_YPIEZO_04022005.DAT_PP GCMS_MOLFRACT_CH4_04052005.DAT_PP HASI_ZPIEZO_04022005.DAT_PP GCMS_MOLFRACT_N2_04052005.DAT_PP HK_RAU1_20052005.DAT_PP HASI_PIEZO_IMPACT_05052005.DAT_PP HK_RAU2_20052005.DAT_PP HASI_PPI_CORR_08012007.DAT_PP SSP_ACCI_IMPACT_15012005.DAT_PP HASI_TEM_CORR_08012007.DAT_PP SSP_APIS_25082005.DAT_PP HASI_XPIEZO_04022005.DAT_PP DTWG_SOFTWARE: This folder contains a ZIP file with all the routines of the DTWG software. BSP_FILE: This folder contains the files 050214_PE_DE405 and SAT199.BSP, which are a NAIF binary file containing the ephemerides of Saturn and its satellites.