Data Set Overview
=================
 
This data set contains the engineering data of the
Huygens 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 a
selection of the most useful parameters (217). However, all
the 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 and
supplementary information to assist in understanding and using the data
products.
 
Structure of DATA Directory
===========================
 
Below /DATA/ the directories are named after the Huygens probe subsystems.
They are:
CDMS: Command and Data Management Subsystems
SASW: Support Avionics Software
POSW: Probe Onboard Software
PDRS: Probe Data Relay Subsystem
EPSS: Electrical Power Subsystem
EXP: 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 B
CASU: Central Acceleration Sensor Unit
RASU: Radial Acceleration Sensor Unit
PSAB: Probe Support Avionics Chain B
DISR: Descent Imager Spectral Radiometer
HASI: Huygens Atmospheric Structure Instrument
ACP: Aerosol Collector Pyroliser
SSP: Surface Science Package
GCMS: Gas Chromatograph and Mass Spectrometer
TUSO: Transmitter Ultra Stable Oscillator
RUSO: Receiver Ultra Stable Oscillator
PROXSENSORA: Proximity Sensor (radar) Chain A
PROXSENSORB: Proximity Sensor (radar) Chain B
TIMER: Huygens timers
TEMP: Temperature sensors
PCDU: Power Conditioning & Distribution Unit
LNAA: Low Noise Amplifiers Chain A
TXB: 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 be
informed about the following warnings:
 
(1) Datation: The value of To, official start of the descent, may
be updated later. However, the difference will not exceed one second.
 
(2) Completeness of the data: it must be understood that the engineering
parameters 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 given
in the file HUYGENS_RADAR_ALTITUDE_CALIBRATION in the CALIB
directory. Two data products (tables) can be found in the
DATA 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 calibration
information of the Huygens engineering data.
 
In addition, a document provides information on the
correction of the radar altitude data.
 
Software
========
 
The data are stored as ASCII files and do not need
any specific software.
No software is included with this data set.
 
EXTRAS directory
================
 
All the engineering parameters are stored in their original format
in this directory.
 
Open questions
==============
 
During the proprietary period (18 months), the data analysis of the
engineering data led to the publications of one article in Nature, one in
Journal of Geophysical Research, and a number of proceedings (See
REFERENCE.CAT). At the time of archiving, there are still some open issues:
(1) Why Huygens spun in the opposite direction ten minutes after the start
of the descent?
(2) Why the descent duration lasted so long (12 minutes more than the
predictions)?
(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 agree
well with the altitudes calculated from pressure and temperature
measurements?
 
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.

N/A