| 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 = FILE
OBJECT = 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/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
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 -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
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
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
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_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_OBJECT
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
END_OBJECT
END_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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