Flight. Center. (GSFC). Flight Dynamics. Division. (FDD) by the Earth. Radiation. Budget ... 5 is a summary with ... An overview of the ERBS attitude system and.
N(Jb-
13414
THE EFFECTS OF SEASONAL AND LATITUDINAL EARTH INFRARED RADIANCE VARIATIONS ON ERBS ATTITUDE CONTROL* M. Phenneger,
J. Dehen,
Computer
D. Foch,
Sciences
E. Harvie,
M. Virdy
Corporation
ABSTRACT Analysis Budget
performed Satellite
in the Flight (ERBS)
Dynamics
Attitude
Facility
Determination
by the Support
Earth
Radiation
team
illustrates
the pitch attitude control motion and roll attitude errors induced by Earth infrared (IR) horizon radiance variations. IR scanner and inertial reference unit (IRU) pitch mission are analyzed
and roll flight data spanning 4 years of the ERBS to illustrate the changes in the magnitude of the
errors
of the
The mates
on time analysis
scales
represents
attitude
period,
months,
opportunity errors
and
seasons.
to compare
with
flight
prelaunch
esti-
measurements.
As a
of this work the following additional information is obtained: of an average model of these errors and its standard devia-
tion,
a measurement
tions
to the
mean ERBS
a unique
of radiance-induced
consequence an assessment
orbital
current
to determine Earth
and
IR radiance
motion model derived from fine attitude determination.
verify data
flight
previously base,
data
in
" This work was supported by the National Aeronautics and Space Space Flight Center (GSFC), under Contract NAS 5-31500.
and place
proposed
correc-
the possibility of
IRU
Administration
data
of a for
(NASA)/Goddard
1.0
INTRODUCTION
This paper presents analysis performed in the Goddard Space Flight Center Flight Dynamics Division (FDD) by the Earth Radiation Budget Satellite (ERBS) Determination Support team. The analysis was performed to measure the ERBS (IR)
horizon
scanner
sensing
errors
induced
by seasonal
Earth's 1R horizons. pare prelaunch and
The ERBS mission attitude early postlaunch estimates
flight
of these
measurements
conclusions
about
analysis of data experiment. The data
base
derived
the
FDD
In addition,
Earth
Horizon
from the Nimbus-7 effects on estimates
derived
from
the
by a difference
telemetry and roll reference
errors.
LIMS
are
used
pitch
and
roll
to illustrate
pitch
errors
the
on time
and
and
attitude
changes scales
system,
geometry and Earth pulse seasonal radiance variations, the errors using the ERBS flight
data
errors.
ware
system
and
the
12 spacecraft,
roll
of the
actual Utility errors and Data
Base
to corroborate
(HRDB)
from
are
angles
evaluated.
obtained
Radiance
from
the earlier
(LIMS) radiance errors
processed
are
IR scanner
magnitude
orbital
of the
period,
horizon
a month,
radiance-induced
and
1 ),ear.
description
of the
ERBS
IR
relating this orbit charac-
scanner
sensing
a brief
of attempts
the original results and
between model
to model
ERBS future
1977 and to correct
early
explanation the
of the
flight
data
IR sensor with this
modeling system
soft-
using
two
radiance profiles. Section 5 is a summary applications of this analysis.
with
OVERVIEW
1984 evaluated the methods IR scanner flight data (Ref.
postlatmch
data
from
the
ERBS,
of applying 1). Flight
were
used
an data
Earth from
to compare
the
IR scanner response to the modeled response using the Horizon Radiance Modeling (HRMU) (Ref. 2). Differences in the actual Earth horizon radiance pitch and roll relative to the model were found to occur due to limitations in the Earth IR model IR scanner from
ments
the
in two
compared here
attempts
as follows. Section 2 is an overview errors, a description of the ERBS
a brief
4 provides
result
including
Data
in the
2.0
Analysis performed IR horizon radiance
Radiance
in the
processing. Section 3 describes how the errors are caused by explains the concept and procedures applied here to extract flight system telemetry data, and presents and describes the
Section
schemes for rescaling conclusions about the
and
analysis
variations
opportunity to comattitude errors with
from batch least squares estimates of pitch and reference unit (IRU). Averages of these differ-
The remaining sections of this paper are analysis to earlier analysis of IR radiance teristics
this
analysis,
pitch and roll propagations attitudes using the inertial
ences
latitudinal
Limb Infrared Monitor of the Stratosphere of these errors, due to adjustments to the
earlier
between
and
data offers a unique of radiance-induced
(GSFC) Attitude infrared
as
program profiles
sensitivity Nimbus-7 IR spectral
with a model the
HRDB
(Ref.
to short LIMS
duration
experiment,
passbands
similar
of the LIMS 3).
The
cold
data
HRDB
(Ref. 4) and a data base of (Ref. 5). The LIMS comparison
cloud
effects.
which
included
to those
used
using
a data
was
developed
worldwide indicated
base
balloon that the
horizon for
of Earth using
radiance
IR horizon the
measure-
scanners,
IR spectra LOWTRAN
were
referred computer
and rocketsonde temperature modeled IR horizon intensities
to
for the polar latitudes were underestimated for the summer seasonand overestimated for the winter season. An overview of the ERBS attitude Table
system
and
orbital
characteristics
is
provided
in
1. Table
1.
ERBS Orbit
and Attitude
Characteristics
Orbit: Semimajor
axis:
6891
Inclination:
57 deg
Eccentricity:
0.0014
Attitude
(near-frozen
orbit)
Parameters:
Angular
momentum
Nominal
geodetic
Nominal
yaw = 0.0
Attitude
Sensors:
Two
Adcole
Two
ITHACO
One
Schoenstedt
Two
IRUs
One
gyrocompass
Attitude
biased, pitch
fine
Earth
and
deg
Sun sensors
Scanwheel
for solar
64x64
fluxgate
Northrop
onboard
analog
momentum
ITHACO
Four
orbit pairs
pitch
ERBS
and
scan 16.1
pitch-yaw
cone
adjust
and pitch/roll
(l.s.b.)
gyros
0.001
4.68
mg (l.s.b.)
deg/sec
0.03125
hydrazine
of yaw turn hydrazine
(l.s.b.)
deg
(l.s.b.)
plane
The
scanner between
The of the uses 15
torque
turn
meter
squared
(ATm 2) magnetic
dipole
rods for roll control
employ a rotating prism lens and a single-flake thermistor with a lx2.deg field of view (FOV), which sweeps along a
revolutions
scanner
are
50-ampere control
DESCRIPTION
at 2000 and
thrusters
thrusters
axis 50 ATm 2 dipole
microns. geometry
IR
0.025
deg
(1.s.b.)
scanwheels
IR SCANNER
inflight
averaged
deg
wheel
The ITHACO IR scanwheels bolometer to sense the Earth 45-deg
orbit
illumination
deg 0.004
processor
One roll axis and one yaw axis, torque rods for pitch momentum
2.1
array
magnetometer
rate
per
deg
IR sensors
three-axis
1 revolution
Actuators:
Two
Two
oriented,
roll = 0.0
or 180.0
with three
One pitch
Two
km
per
cone
axes
canted
10 deg
scanner
optics
normalized and
20
minute
and
on
locator 20
and
The
opposite
from
for nominal
threshold deg
are
down
(rpm). the
sides
pitch
axis.
attitude logic.
25
deg,
IR passband
(Ref. For
this,
of the Figure
is between spacecraft
14 in the
1 illustrates
the
6). the
respectively,
Earth from
IR the
pulse inward
is
DIRECTION "OF SCAN DIRECTION OF SCAN
INSTANTANEOUS FIELDS OF VIEW
LOCAL VERTICAL
X SUN INTERFERENCE (SIR)
Figure
and
1.
In-Flight
outward
horizons
Earth
pulse
is shown
vides
a reference
(LOS)
to index
computed
Geometry Pitch
in Figure
pulse angles
from are
Kp
the
horizon
2. A magnetic which
the
computed
DIRECTION TRAVEL OFOF SUB,SATELLITE POINT
triggering pickoff
acquisition (f_in
and
Sensing
threshold
mounted of signal
Qout
System
voltage.
on the (AOS)
in Figure
2).
sensor and
loss
The
pitch
for
A typical body
pro-
of signal angle
is
as
R and
L designate
is a geometry-dependent
Roll
,_ HORIZON
of the ERBS IR Horizon = 0, Roll = 0, Yaw = 0
to determine
P=+ where
REGION
is computed
Kp [(ff_,-
the
right
and
constant.
Q_os) left For
+ (f_
-
side
scanner
ERBS
Kp
Dh_)] angles,
(1) respectively,
and
where
-- 0.2462.
as R = K, (f_R _ QL)
and
(2) (_R, L,_
where
Kr
Figure
3 shows
a polar regions
= 0.247. the scanner
ground
traces at 5-minute
intervals
for both
an equatorial
and
view of the Earth. It can be seen that the AOS and LOS threshold computation (indicated by hashmarks in the figure) are separated by a wide range of latitudes
LOS THRESHOLD COMPUTATION
AOS THRESHOLD COMP
UTATION
,1 Jl-
A2
.....
I A1 I I I
I o
i !
i-a. i-O ne iii Iiii '5
0.4A2 0.4A1
9 _'1in
_out
J
!
w
Am --
ACQUISITION
OF SIGNAL
Figure
2.
The
L_
(AOS)
Horizon
MAGNETIC
REFERENCE
Locator
Logic
and the
in the equatorial regions, and that the left and northern and southern extremes of the orbit.
3.0
The
horizon
magnetic scan
control
relatively.
system
traces.
between the normalization
pitch (MCS)
The
and
roll
right
errors
IR Scanner
scanners
loop
are
are
most
severe
brightening
at the
horizon
caused
month
Earth
widely
and
pitch
errors
east-west gradients that AOS and LOS horizons
are
near
(LOS)
Pulse
separated
at the
by
input
radiance
gradients
winter
and
ERBS
along
summer
an
increased
Roll
errors
Earth
width
the
seasons
for
horizon will decrease north-south gradient at this
location
are
on the average will be zero. At the midlatitudes, for either scanner are at maximum latitudinal
include the latitude regions where ance variation. These are latitudes
to the
latitudes. The gradient causes the threshold edge of the Earth pulse intensity to vary
causes
zero.
IR scanner
in the
threshold voltage. Likewise, a diminished radiance at the Earth width. When the ERBS is on the Equator, a minimal any
are
in the
control
gradients
polar latitudes and the temperate region intensity and the rising A
OF SIGNAL
HORIZON RADIANCE ERRORS FROM FLIGHT DATA
radiance-induced
ground
LOSS PULSE
the stratosphere experiences the between 40 deg and the poles.
a
given
the sensed occurs for
dependent
on
near 40 deg, the separation and
greatest seasonal Thus, the pitch
radierrors
will be maximum. At the highest and lowest latitudes, the left and right scanner traces are at north and south extremes, where differences between the 80 deg and 40 deg radiance intensities LOS near
horizon zero.
will determine points
are
the the
peak same
roll errors. for each
At these scanner
points and
the
pitch
latitudes errors
are
of the
AOS
expected
and to be
I
f
/
/
l" J POLAR VIEW
Figure 3.
ERBS IR Horizon Scanner Ground Tracks Intervals
on the Earth st 5-Minute
3.1
ERROR
The
flight
pitch
system
and
Fine
Attitude
induced
signal pitch
equal
error
errors that
IRU.
to the
cause
radiance-induced
from
The
error the
roll error
(FADS)
therefore
the
cause
pitch
for
minus
and
along
does
signal
not
should
caused
unambiguously
vary
with
by magnetic
tude
data
from
3.2
the for
dipole
the
procedure
archived
data
Data
Adjuster
subsystem
to the
roll
solutions
FORTRAN angles
activity.
The
isolates
that occurs Data Relay
are
Engineering
IR
radiance-induced
by processing 4 years
in the
program,
the
these
errors
try. The +5 deg averaged average
bias
are
error
is used
data
set.
latitude. for each
pitch errors
to be zero determined
one-orbit to five
month.
These
torques
at a daily
IR
average
wheels,
scanner steps
of IRU
IR horizon
orbits
and
roll
error
to a null
pitch
and
radiance
roll
roll
atti-
errors.
antenna will not
operations, to write
between
processed
Since
transponder appear in the
to the
Attitude
for this analysis,
then
subtracts
and
to produce
roll
are
angles
averaged
are due
to orbital
for each
1-deg
geometry
of the month
the the
latitude
pitch
zero and and
latitude
in each
of the
at
IRU
pitch (AHF).
pitch
bins
radiance roll
errors
averaged 4 years
A
north-
and reduce biases, the
latitude, profile
where symme-
between errors
and
horizon
on the
to form
roll
and roll
scanner
0-deg
The
and
File
IRU IR
1988.
pitch
History the
telemetry
and
improve the accuracy and AGSS processing to be
by the averaged
1984
processing,
over
shifted
attitude
IR scanner
further
representations
orbits
of ERBS
After
and
representations
were
The
with three
by
for intermittent
reaction
periodic
written
FADS
These
expected
values
by the
subtraction
selected
of mission
written
scanner
errors.
averaged
but line
The
with
ward and southward sides of each orbit to statistically the data volume. To remove the effect of IR scanner monthly
latitude
in response to the high-gain Satellite (TDRS) contacts,
of the AGSS
derived
utility
from
IR scanner is sensed
PROCEDURE
spanning
Processed
thus
The
is approximately
control.
motion.
error,
roll
begins
from
roll control,
nulled
pitch
and
the
motion
pitch,
precession
33-deg
attitude
induced
to null this
roll.
radiance-
rate. IR scanner roll minus FADS-IRU roll error in IR scanner output.
precession
COMPUTATION
analysis
data
indicate
and
Horizon
6)
output.
is continuously
radiance
pitch
(Ref.
caused by control system and environmental torques is registered and the IRUs, this motion will not contribute to the difference.
pitch rotation Tracking and
ERROR
The
the
IR scanner
true spacecraft motion by both the IR scanners Similarly, activation data.
error
motion
IRU-based
(AGSS)
loop.
FADS-IRU
for continuous
nutation
to precess
pitch
IR scanner
However,
in IR scanner
is not used
System
control
pitch
IR scanner
axis
IR scanner
the pitch
pitch
error
by subtracting
Support
telemetry.
rate of 4-deg per day, which is the ascending node roll is approximately equal to the radiance-induced In summary,
computed
from ERBS
thus
downlink
dipoles
pitch
are Ground
to the
IR scanner
signal
magnetic
spacecraft
Attitude
input
in the
difference,
the
errors
ERBS
Subsystem
is the
radiance-induced
of
the
by the
is received
The IR scanner activation
CONCEPTS
Determination pitch
pitch
error
horizon
roll determined
IR scanner
the
COMPUTATION
-5 and
were
again
an overall
3.3
FLIGHT
DATA
ANALY_;I_;
RESULTS
The pitch and roll errors obtained plotted versus subsatellite latitude mean
and
the
northward
(N)
from flight data analysis for each month of the year are in Figures 4a and 4b. The standard deviations from the
and
southward
size and type of the plot symbols. each plot. The tick marks on the The
following
characteristics
IR radiance-induced errors roll
are
unusual
when
errors
in the
winter
launch
analysis
nificantly
change
July, the the error data
a high
The
errors
the
The
Southern Northern with
For
adjacent
radiance
IR scanner
scanner
between
HRDB
errors
is clearly
51 viewing Earth
the
profiles,
a model pulse
with
deg
Earth
and
winter The
in this
stratosphere.
of the pitch
of the
counterparts. evident
pattern February
higher
pitch
and
the
pre-
than errors effects
4 year
are
sig-
of
the
averaged
Finally
for
data
June
and
exceed these
not
•
Two
•
Nonlinear
derived
parameters
orbital
and
radius
pulsed
optics.
pulse
input
orbit
horizon
angle
actual for
The
signal
significantly
components
of the
components components
alter
computa-
time
constants,
HRMU
input
is
The
is derived
computes FOV
scanner
to compute
the
from
The year
from
sensor
sweeps step
pitch
to
function
of
across
the Earth, function output
pulse and
of
response
response
electronics
are
the
for each
interpolated
this. output
electronics. of the
set
IR passband
is
Earth
as is done
roll error
computed
using
sigthe
(1) and (2). The HRMU model of the has shown that the following approxima-
results:
electronics in the
data
a latitude
scanner
month
and
inclination.
optical
HRMU
is determined
IR scanner
the
the
from
As the
a specific
a detailed
height and angle of incidence to for each month in 20-deg latitude profile
over
is computed.
radiance
crossing in the
one
This
IR spectra
in the profile.
scanner
from
normalization
angles according to Equations is not precise, and experience
do
are
model composed of the orbital geometry, electronics. The input characteristics of
the IR radiance,
energy
horizon
over
and
latitude.
represented
spacecraft
limiting
l0
magnitude
summer
in the
by the HRMU
FOV,
HRDB
on the
the
The
horizon crossing ERBS IR scanner made
the
the largest, the standard deviations do not describes the results of analysis to simulate
threshold
and
by integrating
incident
expected
tions
+90 the
of the bolometer
the
The
by the
to the right of of 0.1 deg.
and
times
of brightness versus FOV tangent data are in a set of nine profiles
angles
signal.
onboard
include
and
radiance
convolved
nals
profile These -90
the
months
December
to five
Hemisphere
similarity
modeled
tilt angles
by integrating
the
indicated
THE FLIGHT DATA WITH THE HORIZON RADIANCE MODELING UTILITY
electronics
mounting
the IR horizon the Earth data. bins
of the
months.
Hemisphere
season
of annual
most
is two
tion using an Earth IR model and an IR scanner the IR scanner optics, and the signal processing the
are
HRMU.
MODELING
horizon
of flight
is as expected.
seasons
their
radiance level
with
summer
months when the errors are amplitude. The next section
using
4.0
and
from
in the
indicates
be noted.
roll
compared
predicted.
different
gradual that
and
direction
The number of orbits averaged is noted ordinate at 0 deg latitude are at intervals
should
pitch
(S)
transfer
electronics
functions are
not
are modeled;
not
included these
are
voltage
0"2908
f
-0.1517
10 1
0.3244
-0
.__.
2228
Z
]2 01478
-0
LD 0
1671 _
I10
I
I -0
"_44
0
I
ta.J ,jq
2629
i 21[i[iiIiii [ .... 7,i iii17
-01695
U9 ,