PDS_VERSION_ID = PDS3
LABEL_REVISION_NOTE = "1998-06-14, S. Joy, initial draft;
2002-09-02, S. Joy, generalized to all mission phases;
2003-08-18, S. Joy, minor revisions after peer review;"
OBJECT = DATA_SET
DATA_SET_ID = "GO-J-POS-6-REDR-ROTOR-ATTITUDE-V1.0"
OBJECT = DATA_SET_INFORMATION
DATA_SET_NAME = "
GO JUPTER POS ANCILLARY ROTOR ATTITUDE V1.0"
DATA_SET_COLLECTION_MEMBER_FLG = N
START_TIME = 1995-11-28T01:34
STOP_TIME = 2003-09-21T18:45
DATA_SET_RELEASE_DATE = 2002-09-14
PRODUCER_FULL_NAME = "MR. STEVEN P. JOY"
DETAILED_CATALOG_FLAG = Y
ARCHIVE_STATUS = "LOCALLY ARCHIVED"
DATA_OBJECT_TYPE = "TABLE"
CITATION_DESC = "
Joy, S.P., Mafi, J.N., GO JUPTER POS ANCILLARY ROTOR ATTITUDE V1.0,
GO-J-POS-6-REDR-ROTOR-ATTITUDE-V1.0, NASA Planetary Data System, 2002"
ABSTRACT_DESC = "
This data set contains the attitude data for the rotor of the
Galileo spacecraft. The data provided are derived from the
Attitude and Articulation Control System (AACS) data downlink as
provided by the Galileo project to the magnetometer team. This
data set covers portions of the Jupiter Approach (JA) and all
orbit operation mission phases (J0-J35). The data are
discontinuous. The sampling frequency varies with mission phase.
The coverage period is from 1995-11-28T01:34 to 2001-09-21
(exact time of last sample is currently unknown)."
DATA_SET_TERSE_DESC = "
This data set contains the attitude data for the rotor of the Galileo
spacecraft. The data provided cover portions of the Jupiter Approach
(JA) and all orbit operation mission phases (J0-J35)."
DATA_SET_DESC = "
Overview
========
This data set contains the attitude data for the rotor of the Galileo
spacecraft. The data provided are derived from the Attitude and
Articulation Control System (AACS) data downlink as provided by the
Galileo project to the magnetometer team. This data set covers
portions of the Jupiter Approach (JA) and all orbit operation mission
phases (J0-J35). The data are discontinuous. The sampling frequency
varies with mission phase. The coverage period is from
1995-11-28T01:34 to 2001-09-21 (exact time of last sample
is currently unknown).
Data Sampling
=============
The data set is derived from 3 downlink sources, depending on the mission
phase. During the recorded intervals, attitude data are played back with
the other recorded fields and particles data. During these periods data are
available every minor frame (~2/3 second). Attitude data in these periods
are all sampled at the same time, no interpolation is required.
When real-time Science (RTS) data are being acquired, attitude data are
acquired simultaneously once every 5 major frames (~5 minutes).
When neither RTS or recorded data are being acquired, AACS data are
only returned in the engineering stream, not as a true data stream. The
data during these intervals are subcommutated. Right Ascension (RA),
Declination (DEC), and Rotor Twist values are not synchronously sampled.
In order to make the data from these intervals useful, the RA and DEC data
have been linearly interpolated to the time of the twist samples. Samples
from these intervals are available about once every two hours. Only the
MAG and DDS instruments acquire data during these mission phases. This
sampling frequency is adequate given the long averages acquired by these
instruments during these mission phases.
Data Processing
===============
When data are simultaneously available from all three AACS channels, no
processing is applied other than to convert data numbers into radians.
When data are not simultaneously sampled, the RA and DEC values are
linearly interpolated between samples to the time of the TWIST samples.
Beginning in Phase 2A, the rotor spin angle was no longer included in the
downlink. This value is calculated on the ground by using the values of
RA, DEC, and TWIST and the difference between Earth's equatorial and
ecliptic poles.
The EME-50 to System III (1965) rotation matrix is computed by using the
SPICE SPK kernel S980326B.XSP (final prime mission reconstruction). These
values can be reproduced by using the following pseudo-code fragment:
INTEGER I, LU
CHARACTER*24 SCLK
DOUBLE PRECISION ET, E502J2K (3,3), J2K2S3(3,3), E502S3(3,3)
C
C Load Kernels
C
CALL CLPOOL()
CALL LDPOOL ('P_CONST.KER')
CALL LDPOOL ('LEAP_SEC.KER')
CALL LDPOOL ('P_CONST.KER')
CALL SPKLEF ('GLL_JUP.SPK', LU)
C
C Begin loop through data, reading a sclk and computing a matrix
C
READ (10, 999) SCLK
CALL SCS2E (-77, SCLK, ET)
CALL IRFTRN ('FK4', 'J2000', E502J2K)
CALL BODMAT (599, ET, J2K2S3)
C
C Reverse sign of row three to make system left handed
C
DO 10, I = 1, 3
10 J2K2S3(3,I) = -J2K2S3(3,I)
CALL MXM(E502J2K, J2K2S3, E502S3)
C End loop, E502S3 contains the EME50 -> System III rotation matrix
Data
====
All data are archived in a single ASCII table.
Column Type Description <units>
-______________________________________________________________
time char Spacecraft event time (UTC), PDS time format.
sclk char Spacecraft clock counter.
RA real Rotor right ascension, EME-50. <radians>
DEC real Rotor declination, EME-50. <radians>
TWIST real Rotor EME-50 spin phase angle. <radians>
SPIN real Rotor ECL-50 spin phase angle. <radians>
A11 real EME50->SYS3 matrix row 1, column 1 value.
A12 real EME50->SYS3 matrix row 1, column 2 value.
A13 real EME50->SYS3 matrix row 1, column 3 value.
A21 real EME50->SYS3 matrix row 2, column 1 value.
A22 real EME50->SYS3 matrix row 2, column 2 value.
A23 real EME50->SYS3 matrix row 2, column 3 value.
A31 real EME50->SYS3 matrix row 3, column 1 value.
A32 real EME50->SYS3 matrix row 3, column 2 value.
A33 real EME50->SYS3 matrix row 3, column 3 value.
Ancillary Data
==============
There are several SPICE kernels used in the production of this data set.
All of the SPICE kernels used to produce this data set are contained on
the MWG archive volume DVD in the EXTRAS/SPICE/KERNELS directory.
The kernels (PDS PRODUCT_ID) used to create this were:
S980326B.TSP - Prime Mission Reconstruction (JA - E12)
S000131A.TSP - GEM reconstruction (E12-E26)
S020128A.TSP - GMM (I27-I33) reconstruction, A34/J35 predict.
MK00062B.TSC - Galileo spacecraft clock kernel.
NAIF0007.TLS - Leapseconds kernel.
PCK00006.TPC - Planetary constants kernel.
Coordinates
===========
The basic rotor coordinate system has its Z-axis aligned with the spin
axis (positive in the opposite direction as the HGA) and its +Y-axis
pointing outward from the spacecraft body along the magnetometer boom.
X completes the right handed set. This coordinate system spins with the
rotor at a period of approximately 19 seconds.
Earth Mean Equator and dynamical equinox of Besselian year 1950 (EME-50)
is an inertial coordinate system used by the Galileo project for
navigation purposes. This system also commonly known as Fundamental
Catalog (4) or 'FK4' by the SPICE software. At the reference epoch, this
system has its +Z axis parallel to the Earth's north pole and its +X axis
points to the first point of Aries.
System III (1965) is the standard planetographic (left handed) coordinate
system as defined by the IAU for Jupiter [DESSLER1983]. The Central
Meridian Longitude is taken at 00 UTC on January 1, 1965. The rotation
period for Jupiter is defined to be 9h 55m 29.71s (870.536 deg/day). "
CONFIDENCE_LEVEL_NOTE = "
The AACS data are basically raw data that have been converted to physical
units. There are some data spikes and dropouts (zero filled) in the data
set. In areas where RA and DEC values needed to be linearly interpolated,
obviously bad points were edited out before interpolating. No attempt has
been made to interpolate data in the vicinity of spacecraft maneuvers.
The spacecraft has a wobble that is less than a milliradian in amplitude.
Linear interpolation, where applied does not reproduce this wobble. The
basic attitude data is expected to be reliable at nearly the quantization
level of about 0.0001 radians.
During the Phase 2A mission the rotor spin angle is no longer included
in the downlink. The difference between the spin angle and the twist
angle is strictly a function of the rotor RA and DEC. This difference is
computed on the ground and subtracted from the twist angle to generate
spin angle where it is missing (after May, 1996).
The rotation matrix data have been generated by software from the Galileo
project approved SPICE kernels. The software has been tested extensively
and verified. Data can be considered to be reliable to the precision
implied by the number of significant digits provided."
END_OBJECT = DATA_SET_INFORMATION
OBJECT = DATA_SET_TARGET
TARGET_NAME = JUPITER
END_OBJECT = DATA_SET_TARGET
OBJECT = DATA_SET_TARGET
TARGET_NAME = IO
END_OBJECT = DATA_SET_TARGET
OBJECT = DATA_SET_TARGET
TARGET_NAME = EUROPA
END_OBJECT = DATA_SET_TARGET
OBJECT = DATA_SET_TARGET
TARGET_NAME = GANYMEDE
END_OBJECT = DATA_SET_TARGET
OBJECT = DATA_SET_TARGET
TARGET_NAME = CALLISTO
END_OBJECT = DATA_SET_TARGET
OBJECT = DATA_SET_TARGET
TARGET_NAME = AMALTHEA
END_OBJECT = DATA_SET_TARGET
OBJECT = DATA_SET_TARGET
TARGET_NAME = "IO PLASMA TORUS"
END_OBJECT = DATA_SET_TARGET
OBJECT = DATA_SET_HOST
INSTRUMENT_HOST_ID = GO
INSTRUMENT_ID = POS
END_OBJECT = DATA_SET_HOST
OBJECT = DATA_SET_REFERENCE_INFORMATION
REFERENCE_KEY_ID = "DESSLER1983"
END_OBJECT = DATA_SET_REFERENCE_INFORMATION
END_OBJECT = DATA_SET
END