Mars Global Surveyor (MGS) MAG Full Word Low Resolution Data Description MAG - Magnetometer PDS3 DATA_SET_ID = MGS-M-MAG-3-MAP1/FULLWORD-RES-MAG-V1.0 = MGS-M-MAG-3-PREMAP/FULLWORD-RES-MAG-V1.0 ORIGINAL DATA_SET_NAME = MGS MARS/MOONS MAG/ER MAPPING MAG FULL WORD RESOLUTION V1.0 = MGS MARS/MOONS MAG/ER PRE-MAP MAG FULL WORD RESOLUTION V1.0 START_TIME = 1997-09-14T00:42:11.743 STOP_TIME = 2006-11-02T23:23:46.707 PDS3 DATA_SET_RELEASE_DATE = 2009-05-04 PRODUCER_FULL_NAME = DR. JOHN E. P. CONNERNEY ==================================================================== PDS4 Collections: ================= browse-full-calib (urn:nasa:pds:mgs-mager:browse-full-calib) browse-full-map-pc (urn:nasa:pds:mgs-mager:browse-full-map-pc) browse-full-premap-mars-pc (urn:nasa:pds:mgs-mager:browse-full-premap-mars-pc) data-full-map-pc (urn:nasa:pds:mgs-mager:data-full-map-pc) data-full-map-ss (urn:nasa:pds:mgs-mager:data-full-map-ss) data-full-premap-mars-pc (urn:nasa:pds:mgs-mager:data-full-premap-mars-pc) data-full-premap-mars-ss (urn:nasa:pds:mgs-mager:data-full-premap-mars-ss) data-full-premap-phobos-pc (urn:nasa:pds:mgs-mager:data-full-premap-phobos-pc) data-full-premap-phobos-ss (urn:nasa:pds:mgs-mager:data-full-premap-phobos-ss) Overview: ========= This collection 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 Aerobraking Phase 1A (1997-09-12). The data in the collection cover the entire premapping period (ends 1999-03-08) until the end of mission. The data are calibrated and provided in physical units (nT). In addition, instrumental and spacecraft effects have been removed from the data during processing. The data are provided in several geophysical coordinate systems in order to make them directly usable for many analysis problems. 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. This archive consists of outboard full word samples, which occur every 0.75s, 1.5s, or 3.0s, 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. Instrument calibration is routinely monitored inflight. 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. The dynamic fields are still under study but a preliminary model is provided and used in the reduction of this dataset (July, 2000). ==================================================================== 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 this 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 includes additional variables, largely to let the user know exactly what spacecraft fields have been removed from the observations. In the command line variable in the attached header for these files: CMD_LINE = -mars -odl -magonly -pc -sc time dday ....etc 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_rms (root mean square of the difference words) and ob_bscpl (vector static spacecraft field in pl coordinates) and ob_bdpl (vector dynamic spacecraft field in pl coordinates) and three current measurements from the spacecraft engineering data base sam_i, sap_i, sao_i, for the -y solar array, +y solar array, and total (shunted) solar output all in milliamperes. A few plots of the HGA articulation sequences and the model fit to the (differenced) data are included in the 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 -pc specify that odl header is requested; mag data only is processed, and magnetic field and position vectors are TRANSFORMED INTO PC COORDINATES. This is why you need be cognizant of the CMD_LINE when you interpret the record. The very same data, transformed into sun-state coordinates, will have an identical header but for the CMD_LINE, with -ss substituted for -pc to indicate that magnetic field and position vectors have been transformed into the sun-state coordinate system. 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 = FILE OBJECT = HEADER PROGRAM = mgan CMD_LINE = -mars -odl -magonly -pc -sc time dday ob_b posn ob_rms ob_bscpl ob_bdpl sam_i sap_i sao_i DATE = Sat Jun 24 15:28:31 2000 HOST = lepmgs COMMENT = This version MGAN compiled with F77 revision. 4.2 and spicelib MSOP_SCI V.6 (GENERIC_TOOLKIT V.N0049 on JUN 04, 2000 by J.E.P. CONNERNEY (NASA/GSFC). TITLE = MARS GLOBAL SURVEYOR MAG/ER OBJECT = 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 by END_OBJECT OBJECT = 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 MGS END_OBJECT OBJECT = 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 by END_OBJECT OBJECT = CK_DOCUMENTATION MGS Spacecraft 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) 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 MGS END_OBJECT OBJECT = 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 the END_OBJECT OBJECT = CK_DOCUMENTATION MGS HGA Gimbals Orientation CK File for Mapping, Cycles 1-3 =========================================================================== Created by Boris Semenov, NAIF/JPL, June 20, 1999 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 -------------------------------------------------------- END_OBJECT OBJECT = 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_OBJECT OBJECT = CK_DOCUMENTATION ****************************************************************************** Mars Global Surveyor High Gain Antenna Hinge Orientation CK File ========================================================================== Created by Boris Semenov, NAIF/JPL, March 30, 1999 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_OBJECT OBJECT = 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 Date END_OBJECT OBJECT = 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 COMMANDS END_OBJECT OBJECT = 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.................8 END_OBJECT OBJECT = 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 ------------------------------------------------------------------------------ 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_OBJECT OBJECT = 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_OBJECT OBJECT = SPK_DOCUMENTATION Mars Global Surveyor Mapping SPK file, MGSNAV Solution =========================================================================== Created by Boris Semenov, NAIF/JPL, June 14, 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 first three 28-day mapping cycles of the Mapping phase of the mission (mapping orbits 1 through 1040): END_OBJECT END_OBJECT OBJECT = RECORD OBJECT = 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_OBJECT END_OBJECT OBJECT = SCALAR NAME = DDAY ALIAS = DECIMAL_DAY TYPE = REAL FORMAT = F13.9 END_OBJECT OBJECT = 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_OBJECT END_OBJECT OBJECT = VECTOR NAME = POSN ALIAS = SC_POSITION TYPE = REAL OBJECT = SCALAR NAME = X FORMAT = 1X,F11.3 UNITS = KILOMETERS END_OBJECT OBJECT = SCALAR NAME = Y FORMAT = 1X,F11.3 UNITS = KILOMETERS END_OBJECT OBJECT = SCALAR NAME = Z FORMAT = 1X,F11.3 UNITS = KILOMETERS END_OBJECT END_OBJECT OBJECT = VECTOR NAME = OB_RMS ALIAS = OUTBOARD_RMS TYPE = REAL OBJECT = SCALAR NAME = X FORMAT = 1X,F8.3 UNITS = NT END_OBJECT OBJECT = SCALAR NAME = Y FORMAT = 1X,F8.3 UNITS = NT END_OBJECT OBJECT = SCALAR NAME = Z FORMAT = 1X,F8.3 UNITS = NT END_OBJECT OBJECT = SCALAR NAME = RANGE FORMAT = 1X,F4.0 END_OBJECT END_OBJECT OBJECT = VECTOR NAME = OB_BSCPL ALIAS = OUTBOARD_BSC_PAYLOAD TYPE = REAL OBJECT = SCALAR NAME = X FORMAT = 1X,F7.3 UNITS = NT END_OBJECT OBJECT = SCALAR NAME = Y FORMAT = 1X,F7.3 UNITS = NT END_OBJECT OBJECT = SCALAR NAME = Z FORMAT = 1X,F7.3 UNITS = NT END_OBJECT OBJECT = SCALAR NAME = RANGE FORMAT = 1X,F4.0 END_OBJECT END_OBJECT OBJECT = VECTOR NAME = OB_BDPL ALIAS = OUTBOARD_BD_PAYLOAD TYPE = REAL OBJECT = SCALAR NAME = X FORMAT = 1X,F7.3 UNITS = NT END_OBJECT OBJECT = SCALAR NAME = Y FORMAT = 1X,F7.3 UNITS = NT END_OBJECT OBJECT = SCALAR NAME = Z FORMAT = 1X,F7.3 UNITS = NT END_OBJECT OBJECT = SCALAR NAME = RANGE FORMAT = 1X,F4.0 END_OBJECT END_OBJECT OBJECT = SCALAR NAME = SAM_I ALIAS = SA_-Y_CURRENT TYPE = INTEGER UNITS = MILLIAMPERES FORMAT = I8 END_OBJECT OBJECT = SCALAR NAME = SAP_I ALIAS = SA_+Y_CURRENT TYPE = INTEGER UNITS = MILLIAMPERES FORMAT = I8 END_OBJECT OBJECT = SCALAR NAME = SAO_I ALIAS = SA_OUTPUT_CURRENT TYPE = INTEGER UNITS = MILLIAMPERES FORMAT = I8 END_OBJECT END_OBJECT END_OBJECT END SAMPLE ATTACHED HEADER The PDS file naming convention is YYDDD[PX].STS, where YY is the 2 digit year and DDD indicates the day of year (where Jan 1 = day 001). The optional PX indicates which periapsis of the day is included in the file. The Science Team's naming convention is mYYdDDD[pX]_TT.sts, where YY is the 2 digit year, DDD indicates the day of year (where Jan 1 = day 001), and TT is 'pc' for planetocentric coordinates or 'ss' for sun-state coordinates. The optional pX indicates which periapsis of the day is included in the file. The body to which the data pertain (Mars or Phobos) can be ascertained from the ORIGINAL_PRODUCT_ID line of the file's PDS label; if the file name in quotation marks begins with 'm' or 'p', then the data are from Mars or Phobos respectively. The reference body also can be determined from the attached header, as described above. Although the data are provided in several different coordinate systems, the internal structure of each file (after the header) is identical. The structure 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_B) order Bx, By, Bz. The coordinate system is file dependent. Range: Gain range of the instrument at the time of (OB_B) the sample. Sample quantization is gain range dependent. SC_pos_vector: The location of the spacecraft at the time (POSN) of the mag vector in the same coordinate system as the field data. OB_RMS: A four vector giving the root mean square of the outboard delta words (there are 23 delta words between fullwords, sampled at either 32, 16, or 8 per second depending on data rate allocation). OB_BSCPL: A four vector giving the (static) spacecraft field in payload coordinates (this has been removed from the measured field to compensate for spacecraft field); see sc_mod.ker OB_BDPL: A four vector giving the (dynamic) spacecraft field in payload coordinates (this has been removed from the measured field to compensate for spacecraft field); see sc_mod.ker SAM_I: Solar array (-Y panel) current from sc engineering data base in units mA SAP_I: Solar array (+Y panel) current from sc engineering data base in units mA SAO_I: Solar array output current (total) from sc engineering data base uin units mA For SAM_I, SAP_I, and SAO_I, '-99' is used as a fill value when the solar array currents are negative. This denotes data when the spacecraft was in darkness. '-999' is used as a fill value when the solar array currents data is not available for the time. Data from each coordinate system provided are stored in separate files. For PDS supplied data, the coordinate system can be determined from the name of the subdirectory of the DATA/MAG directory in which the file occurs (PCENTRIC or SUNSTATE). It also can be determined from the quoted string in the ORIGINAL_PRODUCT_ID line in the PDS label for the file: if this string contains '_pc' or '_ss', then the file is in planetocentric coordinates or in sun-state coordinates, respectively. The coordinate system also can be determined from the CMD_LINE in the attached file header, as described above. ====================================================================== Coordinate Systems: =================== There are two principal coordinate systems used to represent the data in this archive: sun-state (ss) and planetocentric (pc). Cartesian representations are used for both coordinate systems. 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. The planetocentric coordinate system is body-fixed and rotates with the body as it spins on its axis. The body rotation axis is the primary vector used to define this coordinate system. Z is taken to lie along the rotation axis and be positive in the direction of angular momentum. The X-axis is defined to lie in the equatorial plane of the body, perpendicular to Z, and in the direction of the prime meridian as defined by the IAU. The Y axis completes the right-handed set. Data in the vicinity of the moons of Mars (Phobos and Deimos) are provided in separate files in moon centered coordinate systems. The planetocentric and SS data follows the definitions above with the reference body being the moon. ====================================================================== Ancillary Data: =============== A table of spacecraft orbit parameters (time and location of periapsis) is provided as ancillary or supplementary data along with this collection. ====================================================================== Review: ======= The major uncertainty in these data is in the imperfect removal of spacecraft magnetic contamination. The on-orbit magnetic contamination is now under study, as the spacecraft assumed mapping configuration with the steerable antenna deployed; all data prior to mapping orbit were acquired with the antenna stowed. ====================================================================== 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. This is currently under study. 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. ====================================================================== 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 and the dynamic field was not calculated.