PDS_VERSION_ID = PDS3
LABEL_REVISION_NOTE = "
2000-01-24, Paul Fieseler, initial draft;
2002-03-08, B. Harris, minor reformatting;
2003-08-18, S.P. Joy, minor revisions after peer review;
2005-01-04, B. Harris, added coordinate descriptions;"
OBJECT = DATA_SET
DATA_SET_ID = "GO-J-SSD-5-DDR-STAR-SENSOR-V1.0"
OBJECT = DATA_SET_INFORMATION
DATA_SET_NAME = "GO JUP SSD DERIVED ELECTRON FLUX V1.0"
DATA_SET_COLLECTION_MEMBER_FLG = N
START_TIME = 1995-12-07T00:01
STOP_TIME = 2000-12-31T23:53
DATA_SET_RELEASE_DATE = 2000-10-01
PRODUCER_FULL_NAME = "MR. PAUL FIESELER"
DETAILED_CATALOG_FLAG = Y
ARCHIVE_STATUS = "LOCALLY ARCHIVED"
DATA_OBJECT_TYPE = TABLE
CITATION_DESC = "
Fieseler,P.D., GO JUP SSD DERIVED ELECTRON FLUX V1.0,
GO-J-SSD-5-DDR-STAR-SENSOR-V1.0, NASA Planetary Data System, 2000"
ABSTRACT_DESC = "
The Galileo star scanner is providing data on the instantaneous
flux of 1.5 to 30 MeV electrons in the Jovian environment. It is
able to measure fluxes of ~1 x 105 electrons cm-2 sec-1 or greater
which generally means the data are usable inside of about 12 and
rarely as far out as 16.5 Jovian Radii (RJ). Typically, the data
points are spaced about 400 or 80 seconds apart with infrequent
periods of more rapid data depending upon the operational mode.
It should be noted that data are generally accurate in time to
only within 20 seconds without special processing. Pitch angle
information generally cannot be extracted from this data set.
Separate files exist for the Jovian insertion event (J0) and
all subsequent perijove passes except J5 which occurred during
a period of solar conjunction."
DATA_SET_TERSE_DESC = "
This data set contains Galileo Star Scanner data (electron flux,
1.5 to 30 Mev) from Jupiter 0 Orbit through end of mission."
DATA_SET_DESC = "
Data Set Overview
=================
The Galileo star scanner is providing data on the instantaneous
flux of 1.5 to 30 MeV electrons in the Jovian environment. It is
able to measure fluxes of ~1 x 105 electrons cm-2 sec-1 or greater
which generally means the data are usable inside of about 12 and
rarely as far out as 16.5 Jovian Radii (RJ). Typically, the data
points are spaced about 400 or 80 seconds apart with infrequent
periods of more rapid data depending upon the operational mode.
It should be noted that data are generally accurate in time to
only within 20 seconds without special processing. Pitch angle
information generally cannot be extracted from this data set.
Separate files exist for the Jovian insertion event (J0) and
all subsequent perijove passes except J5 which occurred during
a period of solar conjunction.
Data
====
Time: GMT-UTC time of the measurement in PDS
format: yyyy-mm-ddThh:mm:ss.sss.
(Note: This accurately reflects when the data was telemetered,
not the actual time the data was taken which could be up to
20 seconds earlier. All data is referenced to the time it
occurred on the spacecraft time and not ground receipt time.
Occasional periods of much higher rate telemetry do occur
(e.g. parts of orbit C21) where data is telemetered every
2/3 second.)
Sclk: A spacecraft counter from which time information is derived. The
left hand integers are termed RIMs and increment 1 unit per
60.66666 seconds. The center two integers are termed
'minor frames' and increment from 0 to 90 at a rate of 1 unit
per 2/3 second. When this cycle is complete one digit is added
to the RIM count. The final integer is termed an 'RTI' and
increment from 0 to 9 at a rate of 1 unit per 0.0666666 seconds.
When this cycle is complete, one unit is added to the minor
frame count.
Star Code: This is a hexadecimal representation of the star
scanner health and status. It is collected at the same
instant as Raw Star Intensity and the reading of Raw
Background count.
Position 1 - always should be '0'. Any other number indicates
data is suspect.
Position 2 - always should be 'x'. Any other letter is a flag
for suspect data.
Position 3 - 'f' indicates normal operation
'1', '2', '5', '6' or '7' indicates anomalous star
scanner operation. Suspect data.
'3' or '4' star scanner is having difficulty
recognizing stars. All data is fine unless
otherwise noted in notes column.
Position 4 and 5 - Two letters that convert to an 8 bit binary
word (hexadecimal). For example C7 = 11000111.
First two bits should always be 11. Other
numbers mean that the star scanner is
re-starting and data is suspect.
The final six numbers are a binary
representation of recognized stars. In the C7
example, three stars are recognized, most
likely because only three stars have been
loaded into the star scanner memory.
Day of Year (DOY): A fractional representation of the time at which
the data was telemetered in GMT-UTC. All data is
in spacecraft time and not ground receipt time.
January 1 is DOY 001.
For example, 6 pm on March 1, 1996 (a leap year)
is DOY 61.7500000.
Twist: Spacecraft rotor twist angle in degrees. It is an inertially
based angle using the EME-50 coordinate system. Twist is the
angle between the projection of the 1950 North Celestial Pole
onto the spacecraft X-Y plane and the -X axis of the rotor
(spinning portion of the spacecraft). This represents the angle
at which the raw background and star intensity data was
telemetered, but not necessarily the angle at which the data
was taken. It is used to subtract out the effects of
'star corruption' (see Fieseler [2000]) in the creation of the
filtered and compensated data sets. It is a real number which
varies from 0 to 360 degrees.
Raw Star Intensity: The intensity of the most recently recognized
star in counts. An integer which can scale from
0 to 16,383. Sirius is about 4200 counts and the
star scanner is linear for spectrally similar
stars. The instrument, however, has a sharp
spectral response in the blue and so reddish
stars are much dimmer than might otherwise be
expected. Star intensity is put into a buffer
for downlink only when a star is recognized. After
this, the stale data remains in the buffer until
the next star is seen. This buffer is generally
only checked and relayed to the ground once per
several minutes in most telemetry modes. Star
intensity information is primarily used to
subtract out the effects of 'star corruption'
[Fieseler, 2000] in the creation of the
compensated data set.
Raw Background: Far from Jupiter, this is just average brightness of
the sky, including stars, nebulae, zodiacal light
taken over the previous 25.6 milliseconds. This is
termed 'star corruption' Near Jupiter, electron
bombardment adds signal and eventually overwhelms
the light from background sources. An integer which
can scale from 1 to 16,383. It is placed into at the
same time as star intensity. This buffer is generally
only checked and read-out once per several minutes in
most telemetry modes.
Filtered: This is the filtered data which is derived from the Raw
background, Star Intensity and Twist data. It represents the
measured background light with the star corruption
(deterministic effects of background light) subtracted out.
A value of -50 means that this data had to be thrown out of
the processing because the star light could not be
subtracted out in this instance. Although this data
frequently appears to be an integer, it is actually real as
fractional values are do occur in some orbits.
Compensated: This is the compensated data set which is derived from
the filtered data. It linearizes the star scanner data
(detector saturation becomes a factor in some cases) and
corrects for gain changes in the photomultiplier tube.
A real number. A value of -50 means that this data had
to be thrown out of the processing because the star light
could not be subtracted out of the filtered data in this
instance.
Error low: This is the estimated error in the compensated data applied
on the low side. It is comprised of an RSS'ed series of
independent or nearly independent worst case instrument
errors, biases and computational errors. It accounts for
aging and radiation damage to the star scanner equipment,
noise in the background radiation data after being averaged,
noise in the star light subtracted out of the filtered data,
attitude errors, calculational errors and biases caused by
magnetic and temperature effects.
Error high: This is the estimated error in the compensated data
applied on the high side. It is comprised of an RSS'ed
series of independent or nearly independent worst case
instrument errors, biases and computational errors. It
accounts for aging and radiation damage to the star
scanner equipment, noise in the background radiation data
after being averaged, noise in the star light subtracted
out of the filtered data, attitude errors, calculational
errors and biases caused by magnetic and temperature
effects.
Flux: This is the omnidirectional flux of electrons in particles/cm-2
sec-1 between ~1.5 and 30 MeV external to the spacecraft. Due to
the steep decrease of electron flux with energy, it can also be
thought of as simply integral flux above 1.5 MeV. It is thought
to be no more accurate than within a factor of five. It is an
integer which would built from knowledge of the jovicentric
distance and the Compensated data. The equation used was
Flux = 1755 * Compensated Counts * RJ^1.1208
Where RJ is the most recently Estimated RJ rather than the
actual RJ at the instant the data was taken. This does not
cause an error of more than a few percent. The user is
cautioned that this is equation is preliminary - the star scanner
data are self-consistent but the attempt to calculate a flux is
less certain and was based primarily upon comparison with EPD
data. This flux parameter was forced to a value of zero for all
cases where the jovicentric distance was outside 20 RJ or when
it, due to slightly negative values in the compensated counts,
would have given a negative flux.
Range: Distance from Jupiter center of mass in Jupiter Radii.
Latitude: Planetographic latitude of the spacecraft in degrees.
West Longtitude: Planetographic (West) longitude of the spacecraft in
degrees.
L: Distance at which a dipole field line crosses the dipole equator.
L is given by L = R sin*2(Magnetic Latitude) where R is the distance
from the center of Jupiter.
Magnetic Latitude: Angle with respect to the dipole equator where the
dipole axis tilts 9.6 degrees towards
system III (1965.0) West Longitude.
Magnetic Longtitude: Angle around the dipole axis with respect to the
prime meridian. The prime meridian can be
considered to intersect with 202 degrees west
longitude of System III (1965.0).
Notes: Text notes describing the transition to different star scanner
operation modes, suspected problems with the data not captured
under Star Code and other points of interest.
The files of this data set are in the following structure:
NAME TYPE Description
----------------------------------------------------------------------
PDS Time char UTC time
Spacecraft Clock char Spacecraft clock time
Star Code char Star Scanner status code
Day of Year float Decimal day of year
Twist float Spacecraft rotor angle (degrees)
Raw Star Intensity Int Star intensity (counts)
Raw Background Int Background intensity (counts)
Filtered Data float Raw intensity minus background
Compensated Data float calibrated star intensity
Error, Low float Bottom limit from error estimate
Error, High float Top limit from error estimate
Flux Int Electron flux
R float Distance from Jupiter to spacecraft (Rj)
Latitude float Planetographic latitude (degrees)
West Longitude float Planetographic west longitude (degrees)
L float Distance at which a dipole field line
crosses the dipole equator
Magnetic Latitude float angle to dipole equator (degrees)
Magnetic Longitude float angle to dipole equator (degrees)
Notes char note on changes in data
Coordinate System
=================
Satellite-Centered Planetographic (Right Handed) Coordinates (SPRH)
-------------------------------------------------------------------
SPRH is a spherical 'planetocentric' coordinate system, centered
at the satellite. The magnetic field components are the standard
right-handed spherical triad: R, Theta, and Phi. R is radial
(along the line from the center of the satellite to the center of
the spacecraft), and positive away from the satellite. Phi, the
azimuthal component, is parallel to the satellite's
planetographic equator (Omega x R) and positive in a right-handed
sense. Theta, the 'southward' component, completes the
right-handed set. Trajectory components are also right-handed.
Since all of the satellites studied are nearly phase locked to
Jupiter, the SPRH prime meridian is effectively the sub-Jupiter
meridian. More precise definitions are provided by the IAU [1994]
(see Table 4). Longitude is measured from the prime meridian and
is positive in a right-handed sense (see figure below). R is the
radial distance (satellite's center to spacecraft center).
Latitude is planetocentric.
System III [1965] Coordinates (SYS3)
------------------------------------
System III [1965] (SYS3) magnetic field vector components form
the standard right-handed spherical triad (R, Theta, Phi) for a
Jupiter centered system. Namely, R is radial (along the line from
the center of Jupiter to the center of the spacecraft), and
positive away from Jupiter. Phi, the azimuthal component, is
parallel to the Jovigraphic equator (Omega x R) and positive in
the direction of corotation. Theta, the 'southward' component,
completes the right-handed set.
For SYS3 trajectory both east and west longitudes are provided.
West longitudes are related to east longitudes by to the
algorithm:
west longitude = 360. - east longitude <degrees>
West longitude is defined such that it appears to increase with
time for a stationary observer [DESSLER1983]. Note, however, that
R, latitude, and west longitude constitute a left handed set. The
SYS3 1965 prime meridian is the sub-Earth longitude of
1965-01-01 00:00 UT. The spin rate (which was determined from the
rotation rate of the magnetic field) is 9 hrs 55 min 29.719 sec.
(See [DESSLER1983] for a discussion on Jovian longitude). R is the
radial (Jupiter's center to spacecraft center) distance. Latitude
is planetocentric.
"
CONFIDENCE_LEVEL_NOTE = "There are currently
(as of November, 2000) 28 separate data files reflecting
the 28 orbits Galileo has made of Jupiter and the J0 orbit insertion
event. One orbit, J5, is not included as the spacecraft was behind the
sun in that instance. In general, the star scanner is insensitive to
electrons outside of about 12 RJ although the files often go out
beyond 35 RJ."
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 = "IO PLASMA TORUS"
END_OBJECT = DATA_SET_TARGET
OBJECT = DATA_SET_HOST
INSTRUMENT_HOST_ID = GO
INSTRUMENT_ID = SSD
END_OBJECT = DATA_SET_HOST
OBJECT = DATA_SET_REFERENCE_INFORMATION
REFERENCE_KEY_ID = FIESELER2000
END_OBJECT = DATA_SET_REFERENCE_INFORMATION
END_OBJECT = DATA_SET
END