Cassini Magnetometer Raw Bundle Cassini MAG Command Validation Information Data Collection Description PDS3_DATA_SET_ID = CO-E/SW/J/S-MAG-2-REDR-RAW-DATA-V2.0 PDS3_DATA_SET_RELEASE_DATE = 2019-05-16 START_TIME = 1997-10-28T04:44:37.910 STOP_TIME = 2017-09-15T10:31:49.073 PRODUCER_FULL_NAME = PETER SLOOTWEG Collection Overview ================= This collection contains contains Cassini MAG command-validation housekeeping data. The collection begins with data collected on 28 October (day 301), 1997. 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 collection. 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 collection contains 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 data in this collection is 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 the bundle this collection belongs to. 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 full set of MAG data products is Data Description CMD Command validation information The format of files containing these data products is described in full in the volume SIS, found in the document-mag collection, in the Cassini bundle, called the 'THE CASSINI MAGNETIC FIELD INVESTIGATION' by Dougherty et al. Data ==== Each row in the CMD binary tables is composed of the following fields: 1. SCLK (in SCLK counts since 00:00:00.000Z 1 Jan 1958) 2. CMD Ctr (Valid command counter) 3. CMD Code (Last valid command code) 4. CMD Code_2 (Second last valid command code) 5. CMD Code_3 (Third last valid command code) 6. CMD Invd (Invalid command code) 7. L CMD INVD (Last invalid command code) 8. Error (Error code) 9. STATUS (Status information for spacecraft attitude data) Data Parameters =============== MAGStatus --------- 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 3-4 8 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 MAG times --------- 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 Ancillary data ============== This command validation data, are not required for processing the magnetic-field data. Confidence Level Overview ========================= There is irregular timing in the data samples. This is caused by the limited resolution of the msec counter in the time field. For example, there are 128 FGM vectors in each science packet, the time of the packet corresponds to the time of the first vector in the packet. Times are calculated for the other vectors using the known onboard vector sample rate and average exponent. These calculated times don't have the reduced resolution of the msec counter. Thus at the first vector of each packet there can be a small time jump due to the msec counter resolution. This time difference is maximum 8 msecs (not 4msecs which is the resolution of the counter) because the DPU software only generates even msec values due to internal truncation. Data Coverage and Quality ------------------------- There are routine events that cause data quality problems so chronological listings of them have been included in the document-mag collection, of the Cassini bundle: -calibration activities superimpose calibration data on top of science data and are documented in SCAS_TIMES.ASC (for more information on calibration activies refer to 'THE CASSINI MAGNETIC FIELD INVESTIGATION' by Dougherty et al in the document-mag collection, located in the Cassini bundle.) -data spikes may be seen at instrument range changes. Range changes are documented in RANGE_CHANGES.ASC -mode changes affect which sensors produce instrument data and spikes or rapid changes in data averaging may be seen at mode changes. The first few packets after the instrument is unmuted or after Science Packets recommence can be highly or incorrectly averaged. MODE_CHANGES.ASC lists the times of these events. -date corruption of the on-board memory (SSR) shown through spurious range changes lasting only one vector. The times of these corrupted vectors are listed in SPURIOUS_RANGE_CHANGES.ASC Data gaps may be instrument related (e.g. a sensor turning on/off) or mission related (e.g. telemetry downlink problems). The former are documented in MODE_CHANGES.ASC. All mission related gaps are listed in GAP_FILEs - GAP_FILE_SCI_HK.ASC for science data in the housekeeping packets and in GAP_FILE_SCI_SD.ASC for science data in the science packets. Instrument related gaps of less than one day also show up in the GAP_FILES as well as in MODE_CHANGES.ASC Most of the information in the GAP_FILEs are extracted from packets received reports and so follow a fixed-width tabular format. Multi-day gaps are not documented in the source listings and have been added manually with a different format including an explanation of the gap - if a reason is known. A summary of scientifically significant gaps is included in the data-coverage-gaps.txt file. Gaps ---- Please note that the different phases of the mission are described in the Cassini Mission Description, which is available in the Cassini bundle, or from PDS. References ========== Asmar, S.W., and N.A. Renzetti, The Deep Space Network as an Instrument for Radio Science Research, Jet Propulsion Laboratory Publication 80-93, Rev.1, 15 April 1993. Cassini Mission Plan, Revision N (PD 699-100), JPL Document D-5564, Jet Propulsion Laboratory, Pasadena, CA, 2002. Dougherty, M.K., S. Kellock, D.J. Southwood, A. Balogh, E.J. Smith, B.T. Tsurutani, B. Gerlach, K.H. Glassmeier, F. Gleim, C.T. Russell, G. Erdos, F.M. Neubauer, and S.W.H. Cowley, The Cassini Magnetic Field Investigation, Space Science Reviews, Vol. 114, Nos. 1-4, pp. 331-383, September 2004 Dougherty, M.K., S. Kellock, A.P. Slootweg, and N. Achilleos, CO-E/SW/J/S-MAG-2-REDR-RAW-DATA-V2.0, CASSINI MAGNETOMETER RAW DATA V2.0, NASA Planetary Data System, 2019. Kellock, S., P. Austin, A. Balogh, B. Gerlach, R. Marquedant, G. Musmann, E. Smith, D. Southwood and S. Szalai, Cassini dual technique magnetometer instrument (MAG), Proc. SPIE, Denver, Colorado, 2803, 141, 1996. Smith, E.J., M.K. Dougherty, C.T. Russell, and D.J. Southwood, Scalar helium magnetometer observations at Cassini Earth swing-by, J. Geophys. Res., 106, 30129, 2001.