Data Set Information
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| DATA_SET_NAME |
MGS MARS MAG MAPPING DETAIL WORD RESOLUTION V1.0
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| DATA_SET_ID |
MGS-M-MAG-1-MAP/HIGHRES-FLUX-V1.0
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| NSSDC_DATA_SET_ID |
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| DATA_SET_TERSE_DESCRIPTION |
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| DATA_SET_DESCRIPTION |
: Overview: : This data set contains vector magnetic field data acquired by the Fluxgate section of the Magnetometer / Electron Reflectometer instrument aboard the Mars Global Surveyor (MGS) spacecraft. The data are provided at a variable time resolution depending on the telemetry rate available to the investigation for the time period beginning with the prime mission mapping (1999-03-08). The data in the dataset cover the entire mapping time period (prime mission mapping and extended mission). The data are calibrated and provided in physical units (nT). Since high time resolution spacecraft engineering (in particular, measurements of power subsystem currents) data are not available, the calibration does not fully compensate for spacecraft fields. Estimates based on the linearly interpolating available spacecraft engineering data have been used. The variable fields associated with articulation of the high gain antenna have been removed. The data are provided in payload coordinates and Sun-State (SS) coordinate system. For some applications, data processed in this manner are still useful. However, for most applications, use of the fully calibrated, fullword data products that are also available through the PDS is recommended. The magnetometers on Mars Global Surveyor (MGS) are not boom mounted. They are mounted at the outer edge of the two solar panels, and both are about the same distance from the center of the spacecraft. In the traditional dual magnetometer technique, one of the two magnetometers is mounted at the end of a boom (outboard mag) and the other mounted closer to the spacecraft body (inboard mag). The data acquisition scheme usually allows for more rapid sampling of one or the other magnetometer to optimize the telemetry allocation usage. The outboard mag is usually describes as the the primary mag, the inboard as the secondary. On the Mars Observer mission, the magnetometer sensors were boom-mounted; Mars Global Surveyor uses flight spares mounted at the edge of the solar panels, approximately 5.2 meters away from the spacecraft center. MGS data processing software is based upon software developed for Mars Observer. For MGS, we will preserve the terminology outboard and inboard mag for simplicity but we must define which is which. By definition, the MGS OUTBOARD MAG is on the S/C +Y solar panel the MGS INBOARD MAG is on the S/C -Y solar panel The bulk of the telemetry allocation is utilized by the outboard magnetometer. : Sampling: : The instrument samples the magnetic field at a rate of 32 samples per second by using a clock system derived from the spacecraft system real-time interrupt (RTI) clock. Raw samples are averaged in the instrument according to the telemetry mode for the spacecraft and the data allocation for the MAG/ER investigation. The MAG investigation utilizes a data compression scheme to make efficient use of spacecraft telemetry while at the same time preserving the ability to recover gracefully from spacecraft telemetry errors and the like. A primary MAG full word sample consists of a 12 bit value for the x component, a 12 bit sample for the y component, a 12 bit sample for the z component (all in sensor coordinates) and a 4 bit range word (bit one is an autorange/manual range switch; bits 2,3,4 are the 0-7 range designation). Each primary MAG full word sample is followed by 23 difference samples in which the 6 bit difference from the previous value is telemetered, effectively doubling the data rate obtained within the telemetry allocation. Reconstructed full words are generated in ground data processing for high rate (detail) data. Full word samples, occur every 0.75s, 1.5s, or 3.0s depending on the telemetry allocation. There are 23 detail words between full words occurring every 0.03125s, 0.0625s, or 0.125s depending on the telemetry allocation. Onboard averages are non-overlapping boxcar averages. Time tags are placed at the center of the averaging interval. The data rate allocation is summarized in the following table: Data Rate Primary Samples Secondary Samples (bits/sec) (samples/second) (samples/second) ----------------------------------------------------------- 324 8 1/6 648 16 1/3 1296 32 2/3 The magnetic field is sampled over a large dynamic range (+/- 4 nT to +/- 65536 nT) by automatically adjusting the instrument response (gain) in the magnetometer electronics. The nominal resolution of the 12-bit analog-to-digital (A/D) converter is provided in the following table: Range Max Field Resolution (12-bit) (+/- nT) (+/- nT) ----------------------------------------------------------- 0 4 0.002 1 16 0.008 2 64 0.032 3 256 0.128 4 1024 0.512 5 4096 2.048 6 16384 8.192 7 65536 32.768 Actual ranges may be expected to deviate from the nominal (design) range by varying amounts, ranging from as much as 5%. The instrument noise level is 0.006 nT rms over a 10 Hz bandwidth. Note that in-flight performance is limited by the level of magnetic noise generated by the MGS spacecraft and the instruments it carries. Magnetic field fluctuations are best studied in either the sensor coordinate system (fixed to and aligned with the spacecraft solar panels) or the spacecraft payload coordinate system, since large differences in rms fluctuations can be seen in these components. The sensor y component evidences shows the smallest rms fluctuations of approximately 0.05 nT, whereas the x and z components are more variable with time and often exceed 0.5 nT. : Processing: : Raw data are processed by applying a series of corrections which include sensor zero levels offsets, gain factors, scaling to physical units, and subsequent rotation into payload and geophysical coordinates. The instrument zero levels and gains are quite stable over large temperature ranges and time periods. Of more concern is the magnetic field generated by the spacecraft itself. In flight tests suggest that variation of the spacecraft field observed at the position of the magnetometer sensors when they are articulated in the frame of reference of the spacecraft is about 5 nT (static field). It is believed that this field is largely due to the TWTA amplifiers mounted on the communications dish (which was not deployed until after mapping orbit began). For Science Phasing orbits (SPO), the solar panels did not articulate and compensation for spacecraft fields can be done by simple adjustment to the instrument zero table; this method was used in the production of SPO datasets. Note that this method only works for SPO mission phase, and requires a stationary high gain antenna as well. NOTE that special spacecraft maneuvers were needed before an adequate spacecraft magnetic field model could be developed. These maneuvers were executed in late 1999 and February, 2000 (HGA articulation sequences). The February 2000 maneuvers resulted in a model for the field of the HGA. : Spacecraft Field Estimation and Compensation: : The spacecraft field estimation and compensation is a bit involved. The magnetometer measures the field due to all sources, the ambient field plus that of the spacecraft. The spacecraft may generate magnetic fields in many ways; the estimation problem is largely one of identifying correctly what on the spacecraft is responsible for the interference. It is usually very helpful to have specialized tests pre-launch to identify the prominent sources. Often one finds that it is impractical to operate the spacecraft in precisely the manner it will in space (e.g., powered by solar panels, power subsystem state, component articulations, thermal environment, and so on). Pre-launch tests of the MGS spacecraft identified permanent magnets on the High Gain Antenna (HGA) as the most significant source and sources associated with the power subsystem primary harness which were partially corrected. We categorize spacecraft sources as static or dynamic. Static fields are due to permanent magnetization, for example, magnets or magnetized objects. Magnetic fields are also produced by current loops, for example in power subsystems, solar arrays, batteries, and so on; these often scale with a known current and are called dynamic fields. For MGS, during mapping operations, the HGA is articulated in the frame of reference of the spacecraft (spacecraft payload coordinates, PL for short) as are the two solar panels upon which the magnetometer sensors are located. Each sensor also has an associated zero offset (for each range) vector which must also be estimated. Note that a spacecraft generated static magnetic field that is in the same reference coordinates as the sensor (sensor coordinates) will behave as a sensor offset. Spacecraft maneuvers conducted in February, 2000 were very helpful in characterizing the static field associated with the HGA. Of course, since the HGA is constantly articulating, the ''static'' field of the HGA is time variable as seen by the sensors. These maneuvers were designed to map the magnetic field of the HGA: the sensors (and solar panels) were set at fixed locations and the HGA was rotated in elevation several times. The field of the HGA could then be determined from the difference between the vector field at the two sensor locations. The difference must be used to eliminate the time variable, and mostly much larger, ambient field. A more complete model of the field at each sensor takes into account the possibility of a static field associated with the spacecraft and fixed in spacecraft pl coordinates (Bc), as well as dynamic fields both fixed in sensor coordinates (Bod) and fixed in spacecraft payload coordinates (Bcd). The former might arise from imperfect cancellation of current loops on the solar panels and the latter might arise from loops associated with power circuits fixed to the spacecraft body. These sources are to be characterized in flight and on orbit about Mars. The ambient field is large (to 250 nT) and variable, all of which looks like very large amplitude ''common mode'' noise to our sensors (in this effort; the ambient field is of course most welcome otherwise). So we can only use the difference between the measurements to characterize the spacecraft field. The magnetic field is modeled in sc payload coordinates (applies to both ib and ob sensors) Bpl : [ HGA ] Bs + [ T ] Bo + Ba + Bc + [ T ] Bod + Bcd where Bpl is the field in cartesian payload coordinates, Bs is the field of the HGA assembly, in cartesian coordinates, in the HGA coordinate system; [HGA] is the transformation from HGA coordinates to spacecraft payload coordinates. [T] is the transformation from sensor to s/c payload coordinates. Bo is the sensor zero offsets, constant (static) Ba is the ambient field in sc payload coordinates Bc is the spacecraft (body) field (static) in payload coordinates Bod is field in sensor coordinates that scales with the power system current (cartesian coordinates) Bcd is the spacecraft (body) field (dynamic) in payload coordinates that scales with power system current Bod and Bcd are DYNAMIC spacecraft fields we ASSUME they both scale with a spacecraft current as follows: inboard mag dynamic field scales with solar array -y panel current; outboard mag dynamic field scales with solar array +y panel current; Bcd, the spacecraft body field, scales with total current (sao_i) output from the (shunted) arrays. This is the current that goes into the power subsystem on the s/c we use the observation Bpl (inboard) - Bpl (outboard) to remove the ambient field. Pure sensor rotations will constrain Bo, and coupled displacements/rotations (from solar panel movements) or HGA articulations will be used to constrain the spacecraft field Bs, modeled as an offset dipole about the HGA origin. A generalized inverse procedure is used to estimate the parameters of the various sources, e.g., the dipole coefficients of the HGA and the offset of the HGA source from the defined center of the HGA coordinate system; or scale factors (nT/A) for the x,y,z components of the dynamic field associated with solar panel current. The current spacecraft magnetic field model (that used in the processing of this data) is described in sc_mod.ker, provided with the MGS magnetometer fullword resolution data release. It uses an offset dipole for the HGA (tests demonstrated that no improvement in the fit resulted from using a higher degree and order spherical harmonic), referenced to the HGA coordinate system (which is at the end of the HGA boom, see SPICE documentation). We found that no additional static spacecraft field was needed and so this is zero in the current release. The dynamic fields are at present imperfectly estimated but amount to about 0.2 nT/A or less in each sensor. This dataset should be used in combination with the MGS magnetometer fullword resolution data set which includes additional variables, largely to let the user know exactly what spacecraft fields have been removed from the observations, and the calibration status of the data. In the command line variable in the attached header for these files: CMD_LINE : -mars -magonly -odl -detail -sc -ss time dday ob_bpl ob_b you find an option ''-sc'', this means that the spacecraft field estimated using the model described in the ''sc_mod.ker'' file has been removed from the vector field. In addition to the variables ob_b (vector ambient magnetic field, ob mag) and posn (spacecraft position) we have added ob_bpl (ob mag in payload coordinates). A few plots of the HGA articulation sequences and the model fit to the (differenced) data are included in the fullword data set documentation directory. : Media/Format: : The data are provided as ASCII tables of time series data. These files are referred to as standard time series files (STS files), and all such files have a .STS suffix. Each file has an attached header (called an ODL header, which represents the data producer's object definition language, distinct from the PDS Object Description Language). The header contains text describing the file processing and structure. The attached (machine readable) header provides sufficient information to understand what is in the file. A sample header is given below; it consists of nested OBJECT : KEYWORD and END_OBJECT pairs. This attached header is documentation, applied to the output file by the analysis program. Any detached header you see with these data has not been generated by the investigator team, but has been added by the PDS for compatibility purposes. The header, as well as any other non-numeric ASCII, can easily be stripped with the following AWK script: # # script for files with odl # # this script will reject records until object # and end object statements are resolved (x:0) # /OBJECT/ && !/END_OBJECT/ { ++x } /END_OBJECT/ { --x } x : 0 && $0 !~ /[A-z]/ { # print $0 } The attached header provides a level of traceability for the data product. All of the SPK and CK kernels loaded by the processing program, and used by the processing program to compute spacecraft position and attitude, can be readily identified in the CK_DOCUMENTATION and SPK_DOCUMENTATION objects. There are several of each that need be consulted to perform the necessary transformations. Please refer to JPL NAIF documentation for information regarding the SPK and CK kernels. The user may use either the attached or detached headers for automated plotting, depending on the software you have. PDS-provided software (if any) uses the detached headers (PDS label files). The OBJECT : RECORD / END_OBJECT nest describes the data in each record, but you must also be cognizant of the CMD_LINE keyword to interpret the vector variables. For example, the lines below indicate that OBJECT : VECTOR NAME : OB_B ALIAS : OUTBOARD_B_J2000 TYPE : REAL OBJECT : SCALAR NAME : X FORMAT : 1X,F9.3 UNITS : NT ... the variable ob_b (also known as outboard_b_J2000) is a real vector variable, consists of scalar components x, and so on, in units nanoteslas. Note that the instrument range is carried as a fourth component of the magnetic field vector, as this practice preserves reversibility. Range values R>7 indicate automatic range selection on board, with the range : R-8. The range is coded as a four bit binary, with the most significant bit (8) turned on in auto range mode. The CMD_LINE options -odl -magonly -ss specify that odl header is requested; mag data only is processed, and magnetic field and position vectors are TRANSFORMED INTO SUN-STATE COORDINATES. This is why you need be cognizant of the CMD_LINE when you interpret the record. In the CMD_LINE, the option -Mars is implied, unless another body is specified, denoting that the center of Mars is the center of the coordinate system. If instead the option -phobos or -deimos appeared on the command line, the coordinate system is relative to these bodies instead. (In the following sample attached header, double quotation marks have been replaced by pairs of single quotation marks for the sake of PDS compatibility. A real attached header can contain double quotation marks. Also, a few lines have been slightly condensed to reduce line length for ease of display in the present file.) SAMPLE ATTACHED HEADER FOLLOWS OBJECT : FILEOBJECT : HEADER PROGRAM : mgan CMD_LINE : -mars -magonly -odl -detail -sc -ss time dday ob_bpl ob_b DATE : Tue Jun 26 18:41:27 2007 HOST : lepmom COMMENT : This version MGAN compiled with F77 revision. 5.0 and spicelib MSOP_SCI V.6 (GENERIC_TOOLKIT V.N0049 on MAY 21, 2007 by P.J. Lawton (ADNET at NASA/GSFC). TITLE : MARS GLOBAL SURVEYOR MAG/EROBJECT : CK_DOCUMENTATION MGS Solar Array Orientation CK File for Aerobraking-2 : Created by Boris Semenov, NAIF/JPL April 3, 1999 Orientation Data in the File -------------------------------------------------------- This file contains orientation and angular velocity data for the Mars Global Surveyor (MGS) +Y and -Y nominal solar array frames -- 'MGS_LEFT_SOLAR_ARRAY' and 'MGS_RIGHT_SOLAR_ARRAY' -- relative to the 'MGS_SPACECRAFT' frame. The NAIF ID codes for the 'MGS_LEFT_SOLAR_ARRAY' and 'MGS_RIGHT_SOLAR_ARRAY' frames are -94001 and -94002. This C-kernel provides the nominal orientation of the MGS solar arrays. However, this does NOT reflect the fact that the -Y solar panel did not fully deploy after launch, stopping short byEND_OBJECTOBJECT : CK_DOCUMENTATION MGS Spacecraft Orientation CK File for Aerobraking-2 : Created by Boris Semenov, NAIF/JPL, April 3, 1999 Orientation Data in the File -------------------------------------------------------- This file contains orientation and angular velocity data for the Mars Global Surveyor (MGS) spacecraft frame, 'MGS_SPACECRAFT', relative to the 'J2000' inertial frame. The NAIF ID code for the 'MGS_SPACECRAFT' frame is -94000. Status -------------------------------------------------------- This file was created by merging daily CK files produced by the MGSEND_OBJECTOBJECT : CK_DOCUMENTATION MGS Solar Array Orientation CK File for Mapping, Cycles 1-3 : Created by Boris Semenov, NAIF/JPL, June 18, 1999 Orientation Data in the File -------------------------------------------------------- This file contains orientation and angular velocity data for the Mars Global Surveyor (MGS) +Y and -Y nominal solar array frames -- 'MGS_LEFT_SOLAR_ARRAY' and 'MGS_RIGHT_SOLAR_ARRAY' -- relative to the 'MGS_SPACECRAFT' frame. The NAIF ID codes for the 'MGS_LEFT_SOLAR_ARRAY' and 'MGS_RIGHT_SOLAR_ARRAY' frames are -94001 and -94002. This C-kernel provides the nominal orientation of the MGS solar arrays. However, this does NOT reflect the fact that the -Y solar panel did not fully deploy after launch, stopping short byEND_OBJECTOBJECT : CK_DOCUMENTATION Mars Global Surveyor High Gain Antenna Stowed Gimbal Orientation CK File : Orientation Data in the File -------------------------------------------------------- This file contains orientation and angular rate data for the Mars Global Surveyor (MGS) High Gain Antenna (HGA) Elevation and Azimuth gimbal frames. The orientation of the 'MGS_HGA_EL_GIMBAL' is given with respect to the 'MGS_HGA_HINGE' frame; orientation of the 'MGS_HGA_AZ_GIMBAL' is given with respect to the 'MGS_HGA_EL_GIMBAL' frame. Status -------------------------------------------------------- This file contains gimbal orientation for the stowed HGA position (EL : -95 degrees, AZ : 180 degrees) for the period of time from theEND_OBJECTOBJECT : CK_DOCUMENTATION ****************************************************************************** MGS -Y Solar Array Steady Attitude CK File : Version -------------------------------------------------------- Version 1.1 -- by Boris Semenov, NAIF/JPL, January 17, 2000 File coverage was extended to January 1, 2005. Deflection angle values were not changed. Version 1.0 -- by Boris Semenov, NAIF/JPL, September 16, 1998 Initial Release. END_OBJECTOBJECT : CK_DOCUMENTATION ****************************************************************************** Mars Global Surveyor High Gain Antenna Hinge Orientation CK File : Created by Boris Semenov, NAIF/JPL, March 30, 1999 Orientation Data in Orientation Data in the File -------------------------------------------------------- This file contains orientation and angular rate data for the Mars Global Surveyor (MGS) High Gain Antenna (HGA) deployment hinge frame 'MGS_HGA_HINGE' with respect to the 'MGS_SPACECRAFT' frame. Status -------------------------------------------------------- END_OBJECTOBJECT : SPK_DOCUMENTATION Mars Global Solar Array / MAG Structures SPK File: This SPK file (FK) contains location of various MGS solar array structures and MAG sensors with respect to each other. If You're in a Hurry ---------------------------------------------------------------------- In case you are not interested in details and just looking for the right NAIF code of a particular MAG sensor IT to use it in a call to SPKEZ, here is the list: -94051 +Y MAG Sensor ID; -94052 -Y MAG Sensor ID; Version and DateEND_OBJECTOBJECT : SPK_DOCUMENTATION ; mar022-9000.bsp LOG FILE ; ; Created 1993-02-04/12:39:30.00. ; ; BEGIN NIOSPK COMMANDS LEAPSECONDS_FILE : naf0000c.tls SPK_FILE : mar022-9000.bsp SPK_LOG_FILE : mar022-9000.log NOTE : Made by CHA on Feb 4 1993 SOURCE_NIO_FILE : /scratch/naif/ephem/nio/gen/de202.nio BODIES : 3, 399, 4, 10 BEGIN_TIME : 1990/1/01 END_TIME : 2000/1/01 SOURCE_NIO_FILE : /scratch/naif/ephem/nio/gen/mar022-9000.nio BODIES : 401, 402, 499 BEGIN_TIME : 1990/1/01 END_TIME : 2000/1/01 ; END NIOSPK COMMANDSEND_OBJECTOBJECT : SPK_DOCUMENTATION Ephemeris DE403s 14-NOV-1995 Objects In This Ephemeris Name Id-code ------------------------------------ Sun...............................10 Mercury Barycenter.................1 Mercury..........................199 Venus Barycenter...................2 Venus............................299 Earth Moon Barycenter..............3 Moon.............................301 Earth............................399 Mars Barycenter....................4 Mars.............................499 Jupiter Barycenter.................5 Saturn Barycenter..................6 Uranus Barycenter..................7 Neptune Barycenter.................8END_OBJECTOBJECT : SPK_DOCUMENTATION Mars Global Surveyor Antenna Structures SPK File: This SPK file (FK) contains location of various MGS antenna structures with respect to each other. If You're in a Hurry If You're in a Hurry------------------------------------------------------------------------------ In case you are not interested in details and just looking for the right NAIF code of a particular MGS antenna center to use it in a call to SPKEZ, here is the list: -94 s/c ID; -94000 s/c frame center ID; -94073 HGA center ID (reflector axis @ reflector rim plane); -94074 LGT1 center ID (center of the patch); -94075 LGT2 center ID (center of the patch);END_OBJECTOBJECT : SPK_DOCUMENTATION Mars Global Surveyor Aerobraking-2 SPK file, MGSNAV Solution : Created by Boris Semenov, NAIF/JPL, March 28, 1999 Objects in the Ephemeris -------------------------------------------------------- This file contains ephemeris data for the Mars Global Surveyor (MGS) spacecraft. NAIF ID code for MGS is -94. Approximate Time Coverage -------------------------------------------------------- This file covers Aerobraking-2 (AB2) phase of the MGS mission (orbits 573 through 1683): END_OBJECTEND_OBJECTOBJECT : RECORDOBJECT : VECTOR NAME : TIME ALIAS : TIME TYPE : INTEGER OBJECT : SCALAR NAME : YEAR FORMAT : 1X,I4 END_OBJECT OBJECT : SCALAR NAME : DOY FORMAT : 1X,I3 END_OBJECT OBJECT : SCALAR NAME : HOUR FORMAT : 1X,I2 END_OBJECT OBJECT : SCALAR NAME : MIN FORMAT : 1X,I2 END_OBJECT OBJECT : SCALAR NAME : SEC FORMAT : 1X,I2 END_OBJECT OBJECT : SCALAR NAME : MSEC FORMAT : 1X,I3 END_OBJECTEND_OBJECTOBJECT : SCALAR NAME : DDAY ALIAS : DECIMAL_DAY TYPE : REAL FORMAT : F13.9END_OBJECTOBJECT : VECTOR NAME : OB_BPL ALIAS : OUTBOARD_B_PAYLOAD TYPE : REAL OBJECT : SCALAR NAME : X FORMAT : 1X,F9.3 UNITS : NT END_OBJECT OBJECT : SCALAR NAME : Y FORMAT : 1X,F9.3 UNITS : NT END_OBJECT OBJECT : SCALAR NAME : Z FORMAT : 1X,F9.3 UNITS : NT END_OBJECT OBJECT : SCALAR NAME : RANGE FORMAT : 1X,F4.0 END_OBJECTEND_OBJECTOBJECT : VECTOR NAME : OB_B ALIAS : OUTBOARD_B_J2000 TYPE : REAL OBJECT : SCALAR NAME : X FORMAT : 1X,F9.3 UNITS : NT END_OBJECT OBJECT : SCALAR NAME : Y FORMAT : 1X,F9.3 UNITS : NT END_OBJECT OBJECT : SCALAR NAME : Z FORMAT : 1X,F9.3 UNITS : NT END_OBJECT OBJECT : SCALAR NAME : RANGE FORMAT : 1X,F4.0 END_OBJECTEND_OBJECTEND_OBJECTEND_OBJECT END SAMPLE ATTACHED HEADER The Science Team's naming convention for these files is mYYdDDD[pX]_TTTTTT.sts, where YY is the 2 digit year, DDD indicates the day of year (where Jan 1 : day 001), and TTTTTT is 'detail'. The optional pX indicates which periapsis of the day is included in the file. The PDS file naming convention for these data is the same as the science team's, but with all letters uppercase. The internal structure of each file is: Sample UT: Time of the sample (UT) provided as a set of integers that contain the year, day of year, hour, minute, second, and millisecond when the sample was acquired at the spacecraft. Decimal Day: Another representation of the sample time as a decimal day of year (Jan 1 at 00:00 UT : 1.000). mag_vector: Array[3] giving B-field components in the (OB_BPL) order Bx, By, Bz in the payload coordinate system. Range: Gain range of the instrument at the time of (OB_BPL) the sample. Sample quantization is gain range dependent. A negative value indicates a detail word (verus fullword) entry. mag_vector: Array[3] giving B-field components in the (OB_B) order Bx, By, Bz in the sun-state coordinate system. Range: Gain range of the instrument at the time of (OB_B) the sample. Sample quantization is gain range dependent. A negative value indicates a detail word (verus fullword) entry. : Coordinate Systems: : There are two principal coordinate systems used to represent the data in this archive: payload and sun-state (ss). Cartesian representations are used for both coordinate systems. The payload coordinate system is the frame of reference of the spacecraft. The ss coordinate system is defined using the instantaneous Mars-Sun vector as the primary reference vector (x direction). The X-axis lies along this vector and is taken to be positive toward the Sun. The Mars velocity vector is the second vector used to define the coordinate system. The negative of the velocity vector is used as a secondary reference vector so that the vector cross product of x and y yields a vector z parallel to the northward (upward) normal of the orbit plane of Mars. This system is sometimes called a Sun-State (SS) coordinate system since its principal vectors are the Sun vector and the Mars state vector. : Ancillary Data: : Ancillary data can be found in the MGS magnetometer fullword resolution data set. : Software: : There is no software provided with this data archive.
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| DATA_SET_RELEASE_DATE |
2008-06-18T00:00:00.000Z
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| START_TIME |
1999-03-08T12:00:00.000Z
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| STOP_TIME |
N/A (ongoing)
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| MISSION_NAME |
MARS GLOBAL SURVEYOR
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| MISSION_START_DATE |
1994-10-12T12:00:00.000Z
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| MISSION_STOP_DATE |
2007-09-30T12:00:00.000Z
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| TARGET_NAME |
MARS
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| TARGET_TYPE |
PLANET
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| INSTRUMENT_HOST_ID |
MGS
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| INSTRUMENT_NAME |
MAGNETOMETER
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| INSTRUMENT_ID |
MAG
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| INSTRUMENT_TYPE |
MAGNETOMETER
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| NODE_NAME |
Planetary Plasma Interactions
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| ARCHIVE_STATUS |
LOCALLY_ARCHIVED
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| CONFIDENCE_LEVEL_NOTE |
: Review: : The major uncertainty in these data is in the imperfect removal of spacecraft magnetic contamination. Since high time resolution spacecraft engineering (in particular, measurements of power subsystem currents) data are not available, the calibration does not fully compensate for spacecraft fields. Estimates based on the linearly interpolating available spacecraft engineering data have been used. The variable fields associated with articulation of the high gain antenna have been removed. : Limitations: : Cruise observations indicate that the static spacecraft field is bounded by approximately +/- 5 nT at the sensor locations, as the sensors are articulated about the spacecraft body. For operations prior to mapping phase of the mission, the solar panels are largely fixed in the frame of reference of the spacecraft, moving only to assume the appropriate configuration for aerobraking near periapsis (and return). During these mission phases, it is possible to approximate the spacecraft field as a fixed offset, and remove it by adjustment of the sensor zero table. This is how the SPO dataset was reduced. The cruise observations, and SPO and aerobraking phase (AB) observations, were all acquired with the antenna in the stowed configuration. Prelaunch magnetic mapping indicated that the traveling wave tube amplifiers (TWTA's) on the antenna dish are the leading source of static magnetic field contamination. Mapping orbit data have been processed with a spacecraft magnetic field model used to compensate for spacecraft interference. This is described above. The model is deemed to be accurate at this time for the HGA source, but less so for the dynamic sources related to the power subsystem. We estimate the ambient field to be accurate to within 1 nT for all times when the solar panels are not illuminated. With illuminated solar panels the error is expected to be a few nT, depending on the configuration of the panels. The solar array currents in the MGS magnetometer fullword resolution data set should always be checked to confirm that the data are calibrated. When solar array currents were not available, '-999' was entered in the SAM_I, SAP_I, and/or SAO_I fields of the magnetometer fullword resolution data, and the data are not calibrated. The sample UT of the fullword data in these detail word data files may differ from the sample UT in the fullword data set by up to several milliseconds. During the mission, the most recent (at that time) SPICE spacecraft clock (SCLK) kernel file was used for processing the fullword data set. Since the end of February 2006, the MGS_SCLKSCET.00061.tsc (2006-02-26) version of the SCLK kernel file has been used for all processing. : Data Coverage: : Gaps in data coverage exist for many reasons including telemetry outages and inadequate pointing and/or other engineering information. Gaps are not filled with flagged data. The reason that data are missing may include on or more of the following: 1.) No magnetometer data available because it was not recorded on the MGS spacecraft, for operational reasons. 2.) Magnetometer data was available but the solar panel CK kernel file was not available and observations could not be transformed into spacecraft payload coordinates. 3.) Magnetometer data was available but the spacecraft CK kernel was not available and observations could not be transformed into the desired coordinate system. 4.) Magnetometer data was available but the spacecraft SPK kernel was not available and the position vector could not be computed. 5.) Magnetometer data was available but the spacecraft HGA kernel was not available and the position of the HGA could not be determined. 6.) When solar array currents were not available, '-999' was entered in the SAM_I, SAP_I, and/or SAO_I fields (see the MGS magnetometer fullword resolution data) and the dynamic field was not calculated.
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| CITATION_DESCRIPTION |
Unknown
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| ABSTRACT_TEXT |
Unknown
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| PRODUCER_FULL_NAME |
DR. JOHN E. P. CONNERNEY
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| SEARCH/ACCESS DATA |
Planetary Plasma Interactions Website
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Planetary Data System.png)
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