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NASA Space Science Data Coordinated Archive Header



Availability: Archived at NSSDC, accessible from elsewhere

Time span: 1995-11-06 to 2003-09-21


This description was generated automatically using input from the Planetary Data System.

Data Set Overview ================= This data set contains raw magnetic field data acquired by the Galileo Orbiter magnetometer at Jupiter. The data set covers the time period from 1995-11-06T00:21:30 UT (Jupiter approach) until the end of mission (March 2003). The raw magnetometer data set includes various forms of data: recorded high time resolution, real-time survey (RTS), optimal averager (opt/avg), snapshot, and the calibration parameters required to generate processed data products. In addition corrected rotor angles and spacecraft relative clock and cone angles are provided to simplify future calibration and reprocessing of the data. These data have been extracted from the packetized telemetry stream, time-tagged and time-ordered, and had duplicate records removed. Obviously corrupted data (e.g. spikes) have also been removed. MAG data are uncalibrated and provided in data numbers. Parameters ========== Data Sampling: Data acquisition strategies varied throughout the mission. High time resolution data were acquired only for short intervals near targeted satellite encounters and occasionally elsewhere in the magnetosphere. These data were recorded to tape and played back during the 'cruise' portion of each orbit. During the Jupiter Approach period, most fields and particles (MWG) instruments were off. The magnetometer, on the other hand, acquired low resolution (opt/avg) data. During the bulk of the prime mission, the MWG instruments were allowed to acquire continuous RTS data whenever the spacecraft was inside 50 Jovian radii (Rj). When the MWG was not returning RTS data, MAG used its opt/avg capability to acquire low time resolution averages of the field. In general, these are ~32 minute averages, although some higher rate data (1-8 minute) were used to fill small gaps in RTS data coverage. RTS, opt/avg, and snapshot data were all stored in the MAG internal memory buffer. RTS data were continuously averaged at MAG memory address 4800 and transmitted to Earth in real-time. When an Opt/Avg ON command was given data were stored in the MAG memory buffer beginning at address 4800 and continuing to higher addresses until Opt/Avg OFF was commanded, another Opt/Avg ON was commanded and the MAG buffer began filling at 4800 again, or the MAG memory buffer filled. Opt/avg data was returned to Earth via Memory Read-Out (MRO) as telemetry permitted. Since RTS and opt/avg data used the MAG memory buffer in different ways, they could not be collected simultaneously. Snapshot data, which completely filled the MAG memory buffer, could likewise not be collected simultaneously with opt/avg, and caused periodic spikes in RTS data. Snapshot corruption of RTS data is discussed in more detail in the 'Data Quality and Coverage' section of this document. For a more detailed discussion how MAG RTS, opt/avg, and snapshot data are collected, please refer to [KIVELSONETAL1992]. When high-resolution data were available, but the RTS data were either lost or corrupted, simulated RTS (sRTS) data have been generated from the high-resolution data. sRTS data were averaged down to the RTS rate, then interpolated to be continuous with the existing RTS data. During the prime mission, the RTS data rate varied, depending the downlink capability. MAG has several different possible RTS data rates depending on the telemetry format: ---------------------------------------------------------------Table 1. MAG RTS Rates ---------------------------------------------------------------Format MAG bit rate Time between samples Corner Freq. (bps) (seconds) (mf) (Hz) ---------------------------------------------------------------A-D 2 24 36 1/34 E 4 12 18 1/34 F 6 8 12 1/17 G 8 6 9 1/17 H 12 4 6 1/17 I 18 8/3 4 1/17 Similarly, the opt/avg data can be acquired at different rates. The relatively high data rates fill the MAG internal memory buffer more quickly and are only used to cover short data disruptions. ---------------------------------------------------------------Table 2. Optimal Averager Data Rates ---------------------------------------------------------------Time between samples Buffer fill time Corner Freq. (RIM) ( (day/hh:mm) (Hz) ---------------------------------------------------------------1 00:01:00.67 03:22 1/67 2 00:02:01.33 06:44 1/134 4 00:04:02.67 13:29 1/268 8 00:08:05.33 1/02:58 1/536 16 00:16:10.67 2/05:56 1/1072 32 00:32:21.33 4/11:51 1/2144 The instrument has the ability to acquire longer time averages, but these modes were not used at Jupiter. After the prime mission ended (December 1997), RTS data acquisition was limited to a few days near perijove with the exception of a few orbits. When RTS data were acquired, they were acquired exclusively in the 2 bps (24 sec/sample) telemetry formats. There were no modifications to the opt/avg data acquisition strategy associated with the end of the prime mission. Both the opt/avg and the RTS data processor compute field averages by applying a recursive filter and decimate algorithm to the data. The instrument applies a calibration, decimates vectors down to minor frame (mf) samples (2/3 second) and despins the data using the spin angle value broadcast on the spacecraft bus. The corner frequencies of the recursive filter are provided in tables 1 and 2 for the various sample durations. BOTH RTS AND THE OPT/AVG DATA ARE TIME TAGGED AT THE TIME OF DECIMATION (END OF AVERAGE) IN SPACECRAFT EVENT TIME (UTC). Averaged data overlay high time resolution data acquired at the same time best when these data are shifted in time by about 1/3 of the average length. MAG uses fixed gains to acquire data [KIVELSONETAL1992]. Gain states must be changed manually by sending a gain change command to the instrument. There are 3 ranges of field strengths that the instrument can measure: ---------------------------------------------------------------Table 3. Magnetometer Ranges ---------------------------------------------------------------Field Range (nT) Magnetometer, range min max ---------------------------------------------------------------1/64 - 32 Outboard low field 1/4 - 512 Outboard high field, Inboard low field 8 - 16384 Inboard high field The outboard magnetometer, low field mode was used to acquire data beyond 60 Rj and the inboard magnetometer, high field mode was used to acquire data inside of 9 Rj. During the prime mission, the both the inboard low field and the outboard high field modes were used to acquire data between 9-60 Rj. As the outboard magnetometer is further out from the main body of the spacecraft on the boom than the inboard magnetometer it is impacted less by spacecraft fields. For this reason it was initially preferred over the inboard magnetometer. However, the outboard magnetometer began to experience abrupt changes in the sensor zero levels towards the end of the prime mission. As a result, the inboard magnetometer, low field mode was used to acquire data between 9-60 Rj throughout the remainder of the mission. The AACS data are provided at the same rate as any MAG data available for the same interval. MAG can be transformed from the various possible rotor coordinate systems by using the values of the rotor right ascension (RA), declination (DEC), twist, and spin phase (Spin) angles. Spin also allows transforming MAG data between spinning and despun (IRC) spacecraft coordinates. Calibrations to the spin plane sensors must be applied in the spinning reference frame. The spacecraft relative clock (clock) and cone (cone) give information regarding the relative positions of the Galileo rotor and scan platforms. Both clock and cone may be useful in removing spacecraft interference due to sources on the scan platform. Neither clock nor cone angles are returned in the spacecraft telemetry stream. Rather they are calculated from the rotor and scan platform angles that are returned. Clock and cone have been calculated in the following way: 1) Convert Scan Platform RA, DEC, and twist into a C-Matrix 2) Get unit vectors along platform M and L axis 3) Convert Rotor RA, DEC, and twist to Cartesian coordinates 4) Calculate cone angle (the angle between the Scan Platform the Rotor spin axis) and correct C-Matrix for cone position 5) Convert Scan Platform C-Matrix into Stator C-Matrix 6) Get 'N' axis of stator 7) Calculate clock angle (the angle between the spinangle and the stator N axis) Processing ========== The MAG data are raw. The data have merely been unpacked from the packetized telemetry and formatted into time-ordered tabular formats. Spikes and other obviously corrupted data have been removed. However, the data are 'processed' in the instrument and a preliminary calibration is applied as part of that processing. The RTS and opt/avg data are irrecoverably altered by instrument processing. The only further processing that can be performed on these data is to change the sensor offset corrections. In the case of the high time resolution (LPW) data, the first step in any form of processing is to remove the onboard calibration and then apply an updated calibration. Both the onboard calibration and the calibration updates are provided a part of this data set. The AACS data have been interpolated to correct bad and missing data. These corrected AACS values have then been used in transforming the MAG data from spacecraft to geophysical coordinates. Data ==== The raw telemetry data are logically separated into several data types. These include: MAG RAW LPW - high time resolution data, includes both recorded (LPW) and record rate change coverage (RRCC) data merged and properly time ordered MAG RAW RTS - real-time survey data, including both data returned in real-time and those where the CDS buffer needed to be dumped to tape in order to order to prevent buffer overflow MAG RAW OPT AVG - data from the MAG opt/avg; data returned in memory readouts (MROs) has been merged with the data returned in the LPW stream MAG RAW ENG - MAG temperature and offset estimate data returned in the engineering data stream MAG RAW SNAPSHOT - brief (7 sec) 'snapshots' of the field at the full instrument sample rate (30 samples/sec) AACS CORRECTED LPW - LPW rate corrected rotor angles and uncorrected relative clock and cone angles AACS CORRECTED RTS - RTS rate corrected rotor angles. Each of these data types are stored in separate files. In general, data from a single orbit is included in a data file. For some of the more data rich orbits, further subdivision is necessary. -----------------------------------------------------------LPW data (SRC = spinning rotor coordinates) -----------------------------------------------------------Column Type Description <units> -----------------------------------------------------------time char Spacecraft event time, seconds since 1966 sclk char Spacecraft clock (rim:mf:mod10:mod8) Bx int X field component in spinning coords <DN> By int Y (along boom) field component <DN> Bz int Z (spin aligned) field component <DN> -----------------------------------------------------------RTS data (IRC = inertial rotor coordinates) -----------------------------------------------------------Column Type Description <units> -----------------------------------------------------------time char Spacecraft event time, seconds since 1966 sclk char Spacecraft clock (rim:mf:mod10:mod8) Bx int Southward field component <DN> By int Eastward field component <DN> Bz int Anti-Earthward field component <DN> -----------------------------------------------------------Opt/Avg data (IRC coordinates) -----------------------------------------------------------Column Type Description <units> -----------------------------------------------------------time char Spacecraft event time, seconds since 1966 sclk char Spacecraft clock (rim:mf:mod10:mod8) Bx int Southward field component <DN> By int Eastward field component <DN> Bz int Anti-Earthward field component <DN> -----------------------------------------------------------Snapshot data (sensor coordinates) -----------------------------------------------------------Column Type Description <units> -----------------------------------------------------------time char Spacecraft event time, seconds since 1966 sclk char Spacecraft clock (rim:mf:mod10:mod8) sen1 int Sensor 1 field component in spinning coords <DN> sen2 int Sensor 2 field component in spinning coords <DN> sen3 int Sensor 3 field component in spinning coords <DN> -----------------------------------------------------------Eng data (IRC coordinates) -----------------------------------------------------------Column Type Description <units> -----------------------------------------------------------time char Spacecraft event time, seconds since 1966 sclk char Spacecraft clock (rim:mf:mod10:mod8) inb_Temp float Temperature of the inboard sensor <K> out_Temp float Temperature of the outboard sensor <K> ele_Temp float Temperature of the MAG electronics <K> adc_Temp float A/D converter temperature <K> Bx_avg int Average of spinning Bx (offset error) <DN> By_avg int Average of spinning By (offset error) <DN> -----------------------------------------------------------AACS data (LPW rate) -----------------------------------------------------------Column Type Description <units> -----------------------------------------------------------time char Spacecraft event time, seconds since 1966 rotattr float Rotor right ascension (EME-50) <radians> rotattd float Rotor declination (EME-50) <radians> rotattt float Rotor spin phase angle (EME-50) <radians> spinangl float Rotor spin phase angle (ECL-50) <radians> screlclk float Spacecraft relative clock angle <radians> screlcon float Spacecraft relative cone angle <radians> -----------------------------------------------------------AACS data (RTS rate) -----------------------------------------------------------Column Type Description <units> -----------------------------------------------------------time char Spacecraft event time, seconds since 1966 rotattr float Rotor right ascension (EME-50) <radians> rotattd float Rotor declination (EME-50) <radians> rotattt float Rotor spin phase angle (EME-50) <radians> spinangl float Rotor spin phase angle (ECL-50) <radians> Ancillary Data ============== There are several files that are provided in addition to the data files themselves that may be of value to the user. These include the following: MAG GAP LISTING - a detailed list of the timing and cause of data gaps MAG EVENT TABLE - a table of important spacecraft and instrument commands and events MAG_CALIB_SURVEY.TXT - a description of RTS and OPT AVG data onboard calibration procedures along with a time history of z-sensor offsets MAG_CALIB_HIGHRES.TXT - a description of high-resolution (LPW) data calibration procedures, including a description of the calibration used to process each recording Coordinate Systems ================== The data are provided in three coordinate systems, spinning spacecraft (LPW), despun spacecraft (RTS, opt/avg, Eng), and sensor coordinates (snapshot). The rotor portion of the spacecraft spins to allow the fields and particles instruments to see a larger fraction of the sky and to provide spacecraft stability. The coordinate system that is fixed with respect to the rotor (SRC), spins in an inertial frame. In this frame, the SRC Y-axis points away from the spin axis along the magnetometer boom. The SRC Z-axis is the rotor spin axis, and is positive in the opposite direction from the high gain antenna. X completes the right-handed set. Effects of the rotor spin can be removed by 'despinning' the data by using either the 'rotor twist angle' or the 'rotor spin angle'. When the data are despun by using the spin angle, as broadcast on the spacecraft bus, the resulting data are in inertial rotor coordinates (IRC). In this frame, the X-axis is nearly aligned with the ecliptic normal (positive southward), the Z-axis points anti-earthward, and Y completes the right-handed set. Earthward pointing of the antenna is maintained for communication purposes to within ten degrees. The rotor right ascension, declination, and twist angle in the AACS data stream allow the data to be rotated into the inertial EME-50 reference frame. The MAG sensors are not perfectly aligned with respect to the rotor (spinning) coordinate system. In addition, two of the MAG sensors can be 'flipped' to change which sensor is nearly aligned with the spin axis. Sensor 1 is fixed along the boom direction (SRC Y-axis). Sensors 2 and 3 flip. When the instrument is in the 'flip left' state, sensor 3 is along the SRC Z-axis (spin axis) and sensor 1 oriented opposite the SRC X axis. In the flip right state, sensor 3 is along the SRC References ========== [KIVELSONETAL1992] The Galileo Magnetic Field Investigation, Space Science Rev. 60, 357, 1992

These data are available on-line from the Planetary Data System (PDS) at:

Alternate Names



  • Planetary Science: Fields and Particles

Additional Information



Questions and comments about this data collection can be directed to: Dr. Edwin V. Bell, II



NameRoleOriginal AffiliationE-mail
Dr. Margaret Galland KivelsonData ProviderUniversity of California, Los
Dr. Margaret Galland KivelsonGeneral ContactUniversity of California, Los
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