Data Set Information
DATA_SET_NAME VEGA1 HALLEY FLYBY MAGNETOMETER DATA
DATA_SET_ID VEGA1-C-MISCHA-3-RDR-HALLEY-V1.0
NSSDC_DATA_SET_ID NULL
DATA_SET_TERSE_DESCRIPTION These are magnetometer data (MISCHA) from the Vega 1 spacecraft flyby of comet Halley, 28 Feb 1986 through 10 Mar 1986.
DATA_SET_DESCRIPTION
Data set Overview
  =================
   On MARCH 6, 1986, AT 7:20:06 UT, the Vega spacecraft passed the nucleus
   of comet Halley at a distance of 8,890 km with a relative velocity of 78
   km/s. The magnetic field experiments MISCHA carried four fluxgate
   sensors, with three sensors mounted on a boom at the end of the solar
   panels and the fourth sensor mounted one meter closer.  During the
   cruise phase, the TRASSA-1 mode of the instrument (1 vector/2.5 min) was
   used.  The sensors were switched to the TRASSA-2 mode (1 vector/min)
   during the flyby which started roughly two days before the encounter.
   From 3 h before closest approach (CA) until 1 hour after CA, the HS-mode
   (1 vector/6s) and the DT-mode (1 vector/100ms) was used [DELVAETAL1991].
 
 
  Parameters
  ==========
   The MISCHA experiment delivered a time series of measurements of the
   magnetic field.   Four quantities were collected: three rectangular
   components (Bx, By, Bz) at one position and a fourth component, Bu, in
   the direction of Bx, but at a position closer to the spacecraft.  The
   field components measured by the sensor are composed of both the
   interplanetary contribution and the field from the spacecraft called the
   offset.
 
 
  Processing
  ==========
   Data are first converted from the Rohdata files to Flat Files with an
   ASCII .hed file (/DOCUMENT/PROCESS/DATACONV/flatspec); this is
   ''original'' data. A further processing is done to provide offsets and
   corrections for the spacecraft spin; two methods are used for this step
   which are outlined in the calibration paper (DELVAETAL1990) which is
   provided as a series of GIF images located in the 'DOCUMENT/CALIB'
   directory.   The main correction is to account for the magnetic field of
   the spacecraft and the offsets introduced by the spin of the spacecraft
   around one primary axis.
 
   Offsets were also  determined through a correlation technique or through
   a set of linear equations. The actual method used is given through a
   number after the actual offset value:
 
   example:
   22 dec 84 13 34 22             -> begin of time interval
   23 dec 84 08 17 00             -> end   ''  ''     ''
      5.5  0.0  0.5  9.5          -> offset values Ox,Oy,Oz,Ou
      0                           -> method (0-spin,1-Russell,2-Hedgecocke)
      0.                          -> flag to be set (0.= NO problems)
 
 
  Data
  ====
  The data are provided in five forms: original, master, survey, FBT1SE,
  and FBT2SE.
 
  Original file
 
  The flat file of original data has components of the magnetic field, as
  measured by the MISCHA experiment, in the coordinate system of the
  spacecraft, termed PSeudo SOlar (PSSO).   In addition, a Bt and BUX (Bu-
  Bx) is provided as well as a clock time with epoch started on Jan 1,
  1965; a quality flag indicates missing data.
 
  MASTER file
 
  The MASTER file of the magnetic field data, measured by the MISCHA -
  experiment on board of the Vega spacecraft, contains the following types
  of data: the magnetic field data, the position of the space- craft in
  heliocentric (solar) ecliptic coordinates and in heliographic coordinates
  from the prime meridian, information about the orientation of the
  spacecraft, magnetic field data after calibration and rotation to a
  coordinate system centered at the spacecraft with x - axis to the sun and
  (x,y) - plane in its orbital plane ( i.e. equal to the ecliptic). In
  addition, quality flags give information about missing or bad data.
 
  SURVEY file
 
  The SURVEY file of the magnetic field data, measured by the MISCHA -
  experiment on board of the Vega spacecraft, contains the following types
  of data: the position of the spacecraft in heliocentric (solar) ecliptic
  coordinates (H.SE), magnetic field data in a coordinate system centered
  at the spacecraft with x - axis to the sun and (x,y) - plane in its
  orbital plane (i.e. almost equal to the ecliptic). In addition, quality
  flags give information about missing or bad data.
 
  FBT1SE file
 
  The S*FBT1SE file of the magnetic field data, measured by the MISCHA -
  experiment on board of the Vega spacecraft, contains the following types
  of data: the position of the spacecraft in heliocentric (solar) ecliptic
  coordinates (H.SE), magnetic field data in a coordinate system centered
  at the spacecraft with x - axis to the sun and (x,y) - plane in its
  orbital plane (i.e. almost equal to the ecliptic plane), z approx. to
  ecliptic north pole. In addition, quality flags give information about
  missing or bad data.
 
 
  The magn. field data in these files are collected from FOUR different
  modes:
  - for some time intervals (around closest approach), data are available
    with high time resolution (DT or 1 vector/(0.1 sec));
  - for other intervals, data are available in HS mode = 1 vector/(6 sec);
  - for other intervals, data are available in T2 mode = 1 vector/(60 sec);
  - for other intervals, data are available in T1 mode = 1 vector/(150
    sec).
 
  Data have been AVERAGED down to a common resolution of 150 sec. So the
  whole file has an EQUAL time resolution of 1 vector/(150 sec). The times
  have been averaged and are in the header, in the list of intervals marked
  with DT, HS, T2.
 
  FBT2SE file
 
  The S*FBT2SE file of the magnetic field data, measured by the MISCHA -
  experiment on board of the Vega spacecraft, contains the following types
  of data: the position of the spacecraft in heliocentric (solar) ecliptic
  coordinates (H.SE), magnetic field data in a coordinate system centered
  at the spacecraft with x - axis to the sun and (x,y) - plane in its
  orbital plane (i.e. almost equal to the ecliptic). In addition, quality
  flags give information about missing or bad data.
 
  The magn. field data in these files are collected from THREE different
  modes:
  - for some time intervals (around closest approach), data are available
    with high time resolution (DT or 1 vector/(0.1 sec));
  - for other intervals, data are available in HS mode = 1 vector/(6 sec);
  - for other intervals, data are available in T2 mode = 1 vector/(60 sec).
 
  Data have been AVERAGED down to a common resolution of 60 sec. So the
  whole file has an EQUAL time resolution of 1 vector/(60 sec). The times
  have been averaged and are in the header, in the list of intervals marked
  with DT, HS.
 
  Ancillary Data
  ===============
   During some short time periods , the spacecraft is spinning about one
   fixed axis (x-axis).  As described in the processing reference, the
   state  of the spacecraft spin are called spinning sessions as outlined
   in the table below (which is also provided in
   /DOCUMENT/OFFSET/B0OFFSET.ASC):
 
  1.  spinning sessions of vega1
  ______________________________
     from                     to                       flatfile
     date, hour           day  date, hour       day
  1  22-12-84 15:16:28  357  23-12-84 09:58:58  358    b01ct1
  2  26-12-84 14:34:44  361  14-01-85 09:54:39   14      ''
  3  18-01-85 09:02:08   18  21-01-85 08:14:39   21      ''
  4  02-02-85 10:12:09   33  18-02-85 13:28:45   49      ''
  5  09-03-85 09:32:42   68  14-03-85 07:26:27   73      ''
 
 
  Coordinate Systems
  ==================
   The MISCHA data were initially submitted in multiple coordinate systems,
   but after discussions with the submitter, the following three are being
   reviewed.
 
   PSSO - coordinate system: PSuedo SOlar coordinate system: spacecraft
   centered, x-axis only approximately directed to the sun (slight
   deviation possible), z-axis only approximately to ecliptic pole and
   (xy)- plane approximately the ecliptic in case of three-axis-
   stabilisation; in case of one-axis stabilisation of spacecraft no
   information about z-axis.
 
   SE - coordinate system: Solar Ecliptic system: spacecraft-centered, x-
   axis to sun, (xy)-plane is orbital plane of spacecraft, i.e. nearly
   equal to the ecliptic plane, z-axis nearly to ecliptic pole.
 
   H.SE - coordinate system: Heliocentric Solar Ecliptic system: (xy)-plane
   is the ecliptic, x-axis to vernal equinox 1950, z-axis to ecliptic pole
 
 
  Software
  ========
   An initial program, MISCHA, is used to convert the Rohrdata to flat
   files; the MASTERFILE program applies the offset corrections using a
   B0*offse.* file.
 
   The files flattesthed.asc/.dat and example.asc can be used to control
   data conversion from the flat file data format to an other data format.
   The files contain the same data so it is easy to compare a conversion.
 
   For more information about the flat file data format read the Flat File
   Specification document (flatspec.doc)
 
 
  Media/Format
  ============
   The standard distribution format for the data is CDROM.
DATA_SET_RELEASE_DATE 1997-08-13T00:00:00.000Z
START_TIME 1986-02-28T10:16:08.000Z
STOP_TIME 1986-03-10T11:59:34.000Z
MISSION_NAME VEGA 1
MISSION_START_DATE 1984-12-15T12:00:00.000Z
MISSION_STOP_DATE 1986-04-01T12:00:00.000Z
TARGET_NAME 1P/HALLEY 1 (1682 Q1)
HALLEY
TARGET_TYPE COMET
COMET
INSTRUMENT_HOST_ID VEGA1
INSTRUMENT_NAME FLUXGATE MAGNETOMETER
INSTRUMENT_ID MISCHA
INSTRUMENT_TYPE FLUXGATE SENSOR
NODE_NAME Small Bodies
ARCHIVE_STATUS ARCHIVED
CONFIDENCE_LEVEL_NOTE
Confidence Level Overview
  =========================
 
   For SE - FLYBY data-files:
   1. Additional offset correction was done very carefully with variable
   offsets, in addition to the constant ones already applied
   Constant offsets are for V1: (-10, -5, 40)
   Example for additional offset correction:
   for 1986-03-05  07:21:15:00:  (Ox, Oy, Oz= -3, 4, 1  in PSSO -data)
   This leads to a substantial difference in B-total after offset-
   correction!
 
   Transformation to SE from PSSO was done with variable matrices,
   according to the S/C position. However, the difference should not be too
   large for times close to the closest approach .
 
   The Z(PSSO) sensor clearly saturates near C/A; there is no mention of
   the digitization/quantization that was performed.
 
 
  Review
  ======
 
   The MISHCA data is part of the Small Bodies Node review in Dec 2002.
 
 
  Data Coverage and Quality
  =========================
   During the cruise and flyby phases there are data gaps which are not
   explained.  In addition, for Vega 2, one of the sensors was lost after
   encounter on Mar 9, 1986, so from that time forward, only Bx data was
   available.
 
 
  Limitations
  ===========
   Since the SE-data have been better offset-corrected and better
   transformed, it is recommenced to use the SE data as much as possible;
   they should be more reliable.
CITATION_DESCRIPTION Delva, M., and A. V. Dyachkov, VEGA1 HALLEY FLYBY MAGNETOMETER DATA, VEGA1-C-MISCHA-3-RDR-HALLEY-V1.0, NASA Planetary Data System, 1997.
ABSTRACT_TEXT On MARCH 6, 1986, AT 7:20:06 UT, the Vega spacecraft passed the nucleus of comet Halley at a distance of 8,890 km with a relative velocity of 78 km/s. The magnetic field experiments MISCHA carried four fluxgate sensors, with three sensors mounted on a boom at the end of the solar panels and the fourth sensor mounted one meter closer. During the cruise phase, the TRASSA-1 mode of the instrument (1 vector/2.5 min) was used. The sensors were switched to the TRASSA-2 mode (1 vector/min) during the flyby which started roughly two days before the encounter. From 3 h before closest approach (CA) until 1 hour after CA, the HS-mode (1 vector/6s) and the DT-mode (1 vector/100ms) was used [DELVAETAL1991].
PRODUCER_FULL_NAME SMALL BODIES NODE
SEARCH/ACCESS DATA
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