Cassini Magnetometer Raw Bundle
Cassini Analog Data from the MAG Control Unit 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 = 1997-10-28T04:45:37.827
STOP_TIME = 2017-09-15T10:31:49.073
PRODUCER_FULL_NAME = PETER SLOOTWEG
Collection Overview
=================
This collection contains contains Cassini MAG analog housekeeping data
from the magnetometer control unit. 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 data 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.
This analog housekeeping data are not required for processing the
magnetic-field data.
Data are received from Cassini in science or housekeeping telemetry
packets. Data from the housekeeping stream form a part of this
collection. 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
ANA Analog data from magnetometer control unit
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 ANA binary tables is composed of the following
fields:
1. SCLK (in SCLK counts since 00:00:00.000Z 1 Jan 1958)
2. PreampOut Subcommutated VHM data - pre-amplifier output.
3. IRDectBias Subcommutated VHM data - infrared detector bias.
4. HeLmpRFAmp Subcommutated VHM data - He lamp RF amplifier.
5. HeCllRFAmp Subcommutated VHM data - He cell RF amplifier.
6. BIU VCCSPV Subcommutated VHM data - BIU VCC, BIU supply voltage.
7. +/-3.75V Subcommutated VHM data - +/-3.75 V supply.
8. +/-12V Subcommutated VHM data - +/-12 V supply.
9. +/-6.2V Subcommutated VHM data - +/-6.2 V supply.
10. VCOMonitor Subcommutated SHM data - VCO (Voltage Controlled
Oscillator) monitor.
11. +/-7V Subcommutated SHM data - +/-7V supply.
12. Detect2fg Subcommutated SHM data - Detected 2fo.
13. VCOModltn Subcommutated SHM data - VCO modulation.
14. +7.5V Subcommutated FGM data - +7.5V supply.
15. -7.5V Subcommutated FGM data - -7.5V supply.
16. Field(3) Subcommutated FGM data - X, Y, and Z component of
magnetic field respectively.
19. PSU (2) Subcommutated FGM data - Power Supply Unit 1 and 2
respectively.
21. Ground F Subcommutated FGM data - FGM Ground.
22. Reference Subcommutated DPU data - Reference voltage.
23. A_VCC Subcommutated DPU data ? Supply voltage processor
system A
24. P12V Subcommutated DPU data ? ADC (Analog Digital Converter)
supply voltage of active processor system
25. M12V Subcommutated DPU data ? ADC supply voltage of active
processor system
26. B_VCC Subcommutated DPU data ? Supply voltage processor
system B
27. Ground D Subcommutated DPU data ? DPU Ground
28. SOURCE Subcommutation maintenance data derived from source
sequence count of packets
Data Parameters
===============
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 analog 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.
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