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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

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