Data Set Information
DATA_SET_NAME GIOTTO EXTENDED MISSION ELECTRON PARTICLE ANALYSER V1.0
DATA_SET_ID GIO-C-EPA-3-RDR-GRIGG-SKJELL-V1.0
NSSDC_DATA_SET_ID
DATA_SET_TERSE_DESCRIPTION
DATA_SET_DESCRIPTION Data Set Overview : This dataset contains count rates from the Energetic Particle Analyser (EPA) experiment aboard the Giotto spacecraft during its flyby of comet P/Grigg-Skjellerup during July of 1992. The solid-state detectors of the EPA detected energetic ionizing particles (electrons, protons, heavier ions), but no magnetic fields or time of flight indicators were included. Thus it is difficult to determine what type of particles are being detected, and the calculation of the energy spectrum becomes rather complicated. It is because of this that only count rates are included in the archive. Parameters : The dataset is broken into 4 separate tables, one for each energy channel of the instrument. The tables list count rates per second, averaged over a one-minute interval, for each of eight geometric sectors. The thresholds in each energy channel depend on species. Values for the two species most likely to be encountered near the comet during the flyby are given in this table: Channel Protons H(2)O+ ------- ------- ------ 1 29- 46 keV 78- 115 keV 2 40- 77 97- 145 3 78- 215 144- 270 4 217-3500 280-3500 The two EPA detectors which produced the data for this archive are oriented at a 45 degree angle to the spin axis of the space craft, which was antiparallel to the motion of the spacecraft relative to the comet. During the flyby data were taken so that odd-numbered sectors came from one detector and even-numbered sectors from another. The following table lists the look directions of each sector, relative to the spacecraft Z-axis. Theta is the angle to the spin axis; phi is the rotation in the spin direction from the plane containing the sun and Z axis. NOTE that the spin axis is equal to the spacecraft -Z (minus Z) axis. All angles are in degrees. Sector Detector Theta Phi ------ -------- ----- --- 1 1 135 -102.5 2 2 45 -57.5 3 1 135 -12.5 4 2 45 32.5 5 1 135 77.5 6 2 45 122.5 7 1 135 167.5 8 2 45 -147.5 Modification History : This dataset was originally received as five separate ASCII files covering successive time segments of the flyby, with averages for all four channels appearing under headers with the start and stop time for the averages. These files were concatenated in chronological order, split into four files by energy channel, and reformatted. The stop time for each average which was included in the original file has been dropped from these files because it was invariably one minute later than the listed start time. Additionally, the invalid data flag in the original file (-100.000) has been changed to -999.999 to conform with the standard null data values in other PDS data sets. Data : Each energy channel table covers the entire observation period in one minute intervals. Sector averages are listed in the order given above. Where data measurements were not recorded, a null value flags the drop-out. There is also an extended data gap in all sectors of all channels during the period 1992 July 9 UT 1810 to July 10 UT 0420. Records with all null count rates make this period. There are no time gaps in the records in the data files. NOTE: the count rates in energy channel 1 are contaminated by sunlight in sectors 2, 5, 6, 7 and 8. Ancillary Data : None known Coordinate System : During the encounter, the spacecraft spin axis (the -Z axis) was oriented almost in the ecliptic plane, nearly perpendicular to the spacecraft-sun line. In the Comet Solar Ecliptic (CSE) coordinate system, the comet is at the origin, the X axis points toward the sun and Y is parallel to the ecliptic so that the positive Z axis is toward the North. Then theta is the angle from the Z axis and phi is azimuth in the XY plane, with phi:0 for the Sun. During closest approach, the orientation of the spin axis is: theta : 90.0 degrees phi : 90.4 degrees (CSE) In CSE, the look directions listed above become (alpha is the angle to the comet-sun line): Sector Theta Phi Alpha ------ ----- --- ----- 1 46.3 -101.8 98.5 2 53.4 62.2 68.0 3 81.2 -45.3 46.0 4 112.3 50.3 53.7 5 133.7 -77.4 80.9 6 126.6 118.6 112.6 7 98.8 -133.9 133.3 8 67.7 130.5 127.0 Software : None Media/Format : This dataset is to be included in the Giotto Extended Mission CDROM produced by the Small Bodies Node (SBN) of the Planetary Data System. Copies of the CD will be available to researchers from the SBN, or to others through the National Space Science Data Center.
DATA_SET_RELEASE_DATE 1995-02-01T00:00:00.000Z
START_TIME 1992-07-09T04:20:00.000Z
STOP_TIME 1992-07-11T03:14:00.000Z
MISSION_NAME GIOTTO EXTENDED MISSION
MISSION_START_DATE 1990-01-01T12:00:00.000Z
MISSION_STOP_DATE 1992-01-01T12:00:00.000Z
TARGET_NAME 26P/GRIGG-SKJELLERUP 1 (1922 K1)
TARGET_TYPE COMET
INSTRUMENT_HOST_ID GIO
INSTRUMENT_NAME ENERGETIC PARTICLE EXPERIMENT
INSTRUMENT_ID EPA
INSTRUMENT_TYPE PARTICLE DETECTOR
NODE_NAME Small Bodies
ARCHIVE_STATUS SAFED
CONFIDENCE_LEVEL_NOTE Confidence Level Overview : Confidence level unspecified. Review : Pending Data Coverage and Quality : Unknown Limitations : Because of the lack of species discrimination, the reduction and interpretation of these data are complex. However, there was a third detector mounted at the same angle to the spin axis as the second detector, which was covered with an aluminized plastic foil. This covering absorbed low-energy protons (up to about 350 keV) but allowed electron with energy greater than 20 keV to penetrate. Count rates in the covered detector never exceeded those in the neighboring detector by more than 10 percent (the typical difference was less than 1 percent), indicating that EPA observed primarily positive ions during the flyby. The count rates from the covered detector are not included in this dataset.
CITATION_DESCRIPTION Unknown
ABSTRACT_TEXT This dataset contains count rates from the Energetic Particle Analyser (EPA) experiment aboard the Giotto spacecraft during its flyby of comet P/Grigg-Skjellerup during July of 1992. These data were not formally reviewed by the PDS.
PRODUCER_FULL_NAME PDS SMALL BODIES NODE
SEARCH/ACCESS DATA
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