| DATA_SET_DESCRIPTION |
Data Set Overview ================= This data set consists of magnetic field vector data recorded by the Fluxgate Magnetometer on board the Pioneer 11 spacecraft, during the Jupiter encounter period. Data include 36 second averages of the magnetic field in RJ spherical coordinates and spacecraft trajectory data in System III (1957.0), west longitude. Data ==== Data Sampling ------------- These data are provided in 36 second averages. The resolution from which the averages were generated is unknown. The fluxgate magnetometer data is multiplexed into one of the Science Subcom formats available on the spacecraft. Two separate 6-bit words per subcom cycle are assigned to the instrument and thus 3 complete cycles are required to read out the contents of the output buff. At a bit rate of 2048 bps, a complete subcom cycle requires 6 second and a vector measurement is obtained approximately every 18 to 24 second depending on the actual roll rate of the spacecraft, which is nominally 5 revolutions per minute [ACUNA&NESS1974]. Data Format ----------- The Pioneer 11 magnetometer data for Jupiter encounter were originally written on an ASCII magnetic tape. The original file was re-formatted into ASCII. The data file contains the following data columns: -------------------------------------------------------------------- Column Column Column Name Format Description -------------------------------------------------------------------- TIME A24 Time in yyyy-mm-ddThh:mm:ss.sssZ R F6.3 Spacraft distance from Jupiter in Rj LAT F7.2 Spacecraft System III (1957) Latitude LON F8.3 Spacecraft System III (1957) West Longitude BR F9.5 Radial component of the magnetic field in RJ coordinates BTHETA F9.5 Polar component of the magnetic field in RJ coordinates BPHI F9.5 Azimuthal component of the magnetic field in RJ coordinates -------------------------------------------------------------------- Coordinate System ================= System III (1957.0) is a planetographic spherical coordinates. In this system, the Jovian rotation period is defined to be 9h55m29.37s and the Central Meridian Longitude is defined at 00:00 UT on January 1, 1957. RJ coordinates is based on two principle directions, Jupiter to Pioneer 11, R, and Jupiter spin axis, J. X=R points away from Jupiter. Y is a vector in the direction of J cross R. Z is X cross Y. Radial direction, R points away from Jupiter, polar direction, THETA is positive northward, and azimuthal direction, PSI, parallel to the X-Y plane, positive eastward. Instrument Calibration ====================== The fluxgate magnetometer was calibrated at the GSFC Magnetic Test Facility by means of a 2 meter diameter, single axis Helmholtz coil system. Typically hysteresis observed after exposure to 2.5 mT fields was less than 1 part in 10**3 (one count). Temperature stability is better than +/-0.5% over the temperature range of -20 to +40 degree Celsius in spite of the open loop design of the instrument. This is due to the fact that the characteristics of the magnetic material used in the sensor cores are fairly independent of temperature over the indicated range. The stability figure includes the A/D converter drift and a large portion of it is due to the single ramp design of the latter. Nevertheless, minimum power consumption requirements and flight qualified component availability precluded the used of more stable A/D converter designs [ACUNA&NESS1974].
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