| 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 Aerobraking Phase 1A
(1997-09-12). The data in the dataset cover the entire premapping
period (ends 1999-03-08).
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 names of
the directories in the directory tree. (For data on CD or DVD media,
this can be ascertained from the name of the disk volume, since
the PDS has placed Mars and Phobos data on separate disks.) It
also 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. In the
PDS disk series (level 1 archive) containing these data, the moon
data and Mars data are provided on separate disks. In the
online archive, these data are placed in separate directories.
====================================================================
Ancillary Data:
===============
A table of spacecraft orbit parameters (time and location of
periapsis) is provided as ancillary or supplementary data along
with this data set.
====================================================================
Software:
=========
There are no software provided with this data archive.
|
.png)
.png)
