NSSDCA ID: PSFP-00375
Availability: Archived at NSSDC, accessible from elsewhere
This description was generated automatically using input from the Planetary Data System.
This data set contains magnetic-field data acquired during the cruise and tour phases of the Cassini mission to Saturn. The data set begins with data collected on 16 August (day 228), 1999 and ends on 17 November (day 321), 2005 when the instrument failed. On 16 August, 1999 two days before the spacecraft commenced Earth swingby, the magnetometer boom was unfurled into its extended position; a configuration it maintained for the remainder of the mission. Magnetic-field data acquired prior to boom deployment are limited and are significantly affected by spacecraft noise. These data are of no scientific value and, consequently, do not form part of this data set.
Cassini carried two magnetometers: a fluxgate magnetometer (FGM) and a vector-helium magnetometer capable of operating in both vector and scalar mode (V/SHM). This data set contains the magnetic- field and calibration data recorded by these two instruments, together with supplementary instrument and spacecraft data. The data are divided into time periods of one day and saved in files using the UCLA flatfile system. In this system, data are recorded in binary files that have associated text header files describing the format and content of the data.
The magnetic-field data are contained in the FGM, VHM and SHM data products which can be identified from the 'mrdcd' in their file names. The FGM and VHM data are raw data which may be calibrated using the Cal02 software package provided in the /SOFTWARE directory and the calibration files in the /CALIB directory. The SHM submitted is already calibrated. The calibrated data may optionally be transformed into a range of coordinate systems (see below) using the TransCal software package in conjunction with SPICE kernels available from the Navigation and Ancillary Information Facility (NAIF). Spacecraft attitude data contained in the CHATT data files which can be identified from the 'ecdcd' in their file names may be used in lieu of the SPICE C kernel.
Additional data, such as analog, command validation, configuration image, error counter and user-defined engineering data, are included in this archive for completeness and are not required for processing the magnetic-field data.
Data are received from Cassini in science or housekeeping telemetry packets. Data from both these streams form part of this data set. The naming convention used for data files allows the telemetry source and date of acquisition to be readily determined from the file name. On any given date, the science and housekeeping data for a particular magnetometer cover the same time interval to within a few seconds. Science and housekeeping data files have identical formats and are processed in exactly the same way.
The magnetic-field data have been extracted from telemetry packets, assigned time tags, and formatted into simple binary tables of values in engineering units (data numbers). The data are provided in sensor coordinates. Software included with this archive may be used to convert these data to nanoTesla and tranform them into alternative time and coordinate systems.
The full set of MAG data products is Data Description FGM Vector data from fluxgate magnetometer VHM Vector data from helium magnetometer SHM Scalar data from helium magnetometer ANA Analog data from magnetometer control unit CMD Command validation information CON Configuration image data from MAG DPU ERR Error counter information CHATT Channelised attitude data for spacecraft CHUSR Channelised user-defined engineering data
The format of files containing these data products is described in full in the archive volume SIS, found on this volume called the 'THE CASSINI MAGNETIC FIELD INVESTIGATION' by Dougherty et al.
Each row in the VHM/FGM binary tables is composed of the following columns: 1. time (in SCLK counts since 00:00:00.000Z 1 Jan 1958) 2. X_{VHM,FGM} (in engineering units) 3. Y_{VHM,FGM} (in engineering units) 4. Z_{VHM,FGM} (in engineering units) 5. MAGStatus 6. VHMStatus/FGMStatus
SHM data is given in the following columns: 1. time TAI (SCET in seconds since 12:00:00.000Z 1 Jan 2000) 2. B_SHM (in nT) 3. X_IAU_S (in Km) 4. Y_IAU_S (in Km) 5. Z_IAU_S (in Km)
The units of the preprocessed magnetic-field data are given as nanoTesla (nT). They represent the X, Y, and Z sensor values at the given time. These values were converted into nT using the following: FGM and VHM: nT = (value - 8192) / 8192 * factor. The value of the factor is determined from the range given with each vector using the following table:
Range FGM Factor VHM Factor 0 40 32 1 400 256 2 10000 - 3 44000 -
The MAGStatus data are an array of bits that describe the status of the MAG equipment, as set out in the following table. FIELD SIZE NAME BYTE BIT PacketType 1 Housekeeping/Science-data flag 0 7 MSB SCAS 1 SCAS status 0 6 AverageType 1 Average Type (fixed/running) 0 5 SHMFlag 1 SHM Flag 0 4 VHMFlag 1 VHM Flag 0 3 FGMFlag 1 FGM Flag 0 2 ADCFlag 1 ADC Flag 0 1 MCI 9 Measurement Cycle Interrupt 0-1 0,7-0 LSB,MSB Average 5 TimeCode Missing 2 2 sparebits 2 spare two bits 2 1-0 BIU Discretes 34 16 PROM 1 PROM program 3 7 MSB ConfigEnable 1 Config-Enable 3 6 PSU_2 1 PSU 2 3 5 PSU_1 1 PSU 1 3 4 Processor_B 1 Processor B 3 3 Processor_A 1 Processor A 3 2 SleepMode 1 Sleep Mode 3 1 Reset 1 Reset 3 0 LSB
The FGMStatus data are an array of bits that describe the status of the FGM, as set out in the following table.
FIELD SIZE NAME BYTE BIT rg 2 Range 0 7-6 MSB IFCFlag 1 IFC Flag on/off 0 5 autorange 1 AutoRange on/off 0 4 TimeStatus 4 time quality status 0 3-0 LSB sparebyte 8 spare bits 1 7-0 CalibId 8 Calibration Id 2 7-0 CoordId 8 Field Angle data 2 7-0
The VHMStatus data are an array of bits that describe the status of the VHM, as set out in the following table.
FIELD SIZE NAME BYTE BIT rg 1 Range (debugging only) 0 7 MSB TimeStatus 4 time quality status 0 6-3 sparebits 2 spare bits 0 2-0 LSB Digital 8 Digital Status word 1 7-0 CalibId 8 Calibration Id 2 7-0 CoordId 8 Field Angle data 3 7-0
The Cassini spacecraft clock (SCLK) is a counter that advances by one tick nominally every 1/256 seconds. SCLK times have the format cccc:ttt, in which cccc specifies the number of full counts that have elapsed (one full count = 256 ticks), and ttt indicates by how many ticks the clock has advanced towards the next count, since the epoch 00:00:00Z 1 January 1958. SCLK counts may also include a partition number, p/cccc:ttt. This number is initially 1 but is incremented during the mission if the SCLK counter is reset or somehow interrupted or altered. The following discussion assumes a partition number of 1. For other partition numbers, the determination of SCLK times requires knowledge of the time at which the current partition was initiated. SCLK times are commonly recorded in MAG files as decimal counts. Time may also be represented in MAG files as Spacecraft Event Time (SCET) which, for Cassini, is Universal Time Coordinated (UTC). The relationship between SCLK and SCET/UTC is dependent on the count rate of the Cassini SCLK. Like most counter-based clocks, this rate is not constant but drifts with time. Consequently, conversion of SCLK times to SCET/UTC times requires knowledge of the drift rates. These rates are recorded in the SCLK/SCET coefficients file maintained by the Cassini Spacecraft Operations (SCO) team at JPL. As the Cassini mission progresses, the difference between SCLK and SCET will typically be of order tens of minutes. Times in MAG data files The times associated with magnetic-field vectors in MAG data files are SCLK counts since epoch 1958. The times associated with magnetic-field scalar values in MAG data files are SCET in seconds since epoch 2000 in TAI (International Atomic Time) Times in MAG header files
FIRST TIME SCLK time of first record in data file; derived from primary header of CHDO file
LAST TIME SCLK time of last record in data file; derived from primary header of CHDO file
SCLK (in ABSTRACT) SCLK count obtained from tertiary header of CHDO file; also converted into year, day of year, month, date, time format; may differ from FIRST TIME by some minutes
SCET (in ABSTRACT) year, day of year, month, date, time format; determined from corrected SCLK count; also converted into an equivalent SCET count of seconds since 1958
Times in MAG label files START_TIME SCLK time of first record in data file; obtained from FIRST TIME in flatfile header
STOP_TIME SCLK time of last record in data file; obtained from LAST TIME in flatfile header
SPACECRAFT_CLOCK_START_COUNT SCLK time of first record in data file; determined from SPICE utility CHRONOS using START_TIME; format p/ssss.ttt SPACECRAFT_CLOCK_STOP_COUNT SCLK time of last record in data file; determined from SPICE utility CHRONOS using STOP_TIME; format p/ssss.ttt
SCLK (in NOTE) SCLK count obtained from tertiary header of CHDO file; also converted into year, day of year, month, date, time format; obtained from flatfile-header ABSTRACT; may differ from START_TIME by some minutes SCET (in NOTE) year, day of year, month, date, time format; determined from corrected SCLK time; also converted into an equivalent SCET count of seconds since 1958; obtained from flatfile-header ABSTRACT
MAG data are raw data that have been preprocessed to extract them from the telemetry packets received from the spacecraft. This preprocessing converted raw voltages into magnetic-field measurements with engineering units (nT-like) and assigned individual times to each field measurement, the time of the first vector in a packet corresponds to the start time of the packet and the other vectors are calculated from that, for more information see the 'Confidence Level Overview' in this file. Software that converts these data to calibrated nT and transforms them to different time and coordinate systems is included with this archive. One exception to this is SHM data for which fully calibrated data are archived.
The software required to calibrate and transform MAG data into alternative time and coordinate systems is provided as executable files for PC and as source code for compilation on other platforms. The packages are
Cal02 - calibrates vector data and transforms them from sensor coordinates to spacecraft coordinates, and, TransCal - converts SCLK counts into International Atomic Time, transforms vector data from spacecraft coordinates into alternative coordinate systems, and appends spacecraft trajectory data to transformed data records. Following are examples of typical user input to these packages. User guides giving full descriptions of the implementation and operation of these software packages are contained in this archive they are called the 'Cassini MAG Data Processing Software: CAL02 User Guide' and 'Cassini MAG Data Processing Software: TransCal User Guide' both by Joyce Wolf of JPL.
Cal02 -------- Input FlatFile: Enter full flatfile name: g:\cal58\9923b_mrdcd_hkvhmn Enter 0 if input is FGM, 1 if VHM: 1 Enter 1 to SWAP BYTES on INPUT flatfile, 0 not to swap: 1 Output FlatFile,Default is g:\cal58\9923b_mrdcd_hkvhmn_C Enter full flatfile name: Enter 1 to SWAP BYTES on OUTPUT flatfile, 0 not to swap: 1
Default Report File: g:\cal58\9923b_mrdcd_hkvhmn_C_Rpt.txt Enter Report filename: Report File g:\cal58\9923b_mrdcd_hkvhmn_C_Rpt.txt Opened NCOLS 6 RECL 28
Enter Calibration Flatfile name: g:\cal58\VHM_ESB58_CAL Data Recs Written = 7064 Invalid Data Recs Not Calibrated = 0 Flatfiles Closed Press Enter to Exit
TransCal -------- Enter Report File Name: transcal_rpt.txt Opened Report File transcal_rpt.txt
Enter Reference Body ID (399 for Earth, 699 for Saturn, 599 for Jupiter, 10 for Sun): 399 Available Coordinate Systems: 0 J2000 1 ECLIPJ2000 2 IAU_VENUS 3 IAU_EARTH 4 GSE 5 GSM 6 RTN 7 CASSINI (no transformation) 8 J3 (IAU_JUPITER) 9 JMAG XYZ 10 JMAG RTP 11 S3 (IAU_SATURN) 12 SATURN RTP 13 SUN-SATURN Enter Number of Coordinate System: 4 Enter Q to use Quaternions from flatfile, C to use C-Kernel file: c Enter Name of SPICE Metafile with KERNELS_TO_LOAD: esblist.txt Spice Kernels Loaded = 6 Enter Input Flatfile Name (s/c coords): g:\cal58\9923b_mrdcd_hkvhmn_C Enter 1 to SWAP BYTES on INPUT Flatfile; 0 not to swap: 1 Enter Output Flatfile Name: 9923b_mrdcd_hkvhmn_gse Enter 1 to SWAP BYTES on OUTPUT Flatfile; 0 not to swap: 1 Epoch1958 = 1
Working. Number of Vectors Read: 7064 Number of Vectors Written: 2364 End TRANSCAL. Press Enter to Exit
\begindata KERNELS_TO_LOAD = ('..\spicekernels\naif0007.tls', '..\spicekernels\pck00006.tpc', '..\spicekernels\cas00080.tsc', '..\spicekernels\JUP100-95-05.bsp', '..\spicekernels\010612_010613ra.bc' )
Additional data that form part of this archive volume include magnetometer-calibration data in /CALIB and SPICE kernels in /GEOMETRY. These data are used in calibrating the magnetic- field measurements and, if desired, transforming them into other coordinate systems.
Data such as analog, command validation, configuration image, error counter and user-defined engineering data, are included in this archive for completeness and are not required for processing the magnetic-field data.
The range of available coordinate systems includes: No., Name, Definition: 0 J2000 SPICE inertial reference frame Earth equinox and equator at J2000 epoch 1 ECLIPJ2000 SPICE inertial reference frame Earth equinox and ecliptic at J2000 epoch 2 IAU_VENUS SPICE body-fixed frame 3 IAU_EARTH SPICE body-fixed frame 4 GSE Geocentric Solar Ecliptic X is Earth to Sun, Z is north ecliptic pole 5 GSM Geocentric Solar Magnetic X is Earth to Sun, Z in plane containing X and north magnetic pole 6 RTN X is Sun to spacecraft, Z in plane containing X and Sun's rotation axis 7 CASSINI Spacecraft coordinates 8 J3 (IAU_JUPITER) SPICE body-fixed frame 9 JMAG XYZ Z is Jupiter dipole, X in plane containing Z and prime meridian from IAU_JUPITER 10 JMAG RTP X is Jupiter to spacecraft, Y in plane containing X and Jupiter dipole 11 IAU_SATURN SPICE body-fixed frame 12 SATURN RTP X is Saturn to spacecraft, Y is south in plane containing X and Saturn axis 13 SUN-SATURN X is Saturn to Sun, Z is north in plane containing X and Saturn axis.
These data are available on-line from the Planetary Data System (PDS) at:
https://pds-ppi.igpp.ucla.edu/data/CO-E_SW_J_S-MAG-2-REDR-RAW-DATA-V1.0/
Questions and comments about this data collection can be directed to: Dr. Edwin V. Bell, II
Name | Role | Original Affiliation | |
---|---|---|---|
Dr. David J. Southwood | Data Provider | Imperial College | d.southwood@ic.ac.uk |
Dr. Peter Slootweg | General Contact | Imperial College | p.slootweg@imperial.ac.uk |