Author(s)
Wong, Yan Chun.
Title
Satellite anomalies and electrostatic surface discharges.
Publisher
Monterey, California. Naval Postgraduate School
Issue Date
1991
URL
http://hdl.handle.net/10945/28512
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NAVAL POSTGRADUATE SCHOOL
Monterey, California
SATELLITE ANOMALIES AND
ELECTROSTATIC SURFACE DISCHARGES
by
Yan Chun Wong
September, 1991
Thesis Advisor:
Approved
Dr. Richard C. Olsen
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SUPPLEMENTARY NOTATION The views expressed in this thesis are those of the author and do not
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i.
COSATI CODES
FIELD
GROUP
ABSTRACT (Continue on
I.
18
SUB-GROUP
reverse
if
SUBJECT TERMS (Continue on reverse
if
necessary and identify by block number)
Spacecraft Charging, Surface Charging
Spacecraft Anomalies, Active Charge Control
necessary and identify by block number)
Various aspects of the space environment can cause on-orbit satellite anomalies.
Studies have shown that adverse interactions between the natural space environment and
space systems can have deleterious consequences comparable to those caused by human or
lesign errors.
Electrostatic surface discharge (ESD) electron caused electromagnetic
mlse (ECEMP) and single event upset (SEU) are the three most common anomaly producing
lechanisms in space systems.
The plasma environment, such as in geosynchronous orbit, can
:ause differential charging of satellite components and lead to ESD's on satellite surfaces
By using the Spacecraft Anomaly Manager (SAM) software package, spacecraft anomaly
lata of operational satellites contained in the database of National Geophysical Data
Center (NGDC) were analyzed.
The analysis concluded that ESD is directly related to
geomagnetic storm activity and ESD related anomalies are local time and seasonal dependent,
'roper engineering solutions should be integrated into satellite designs to prevent ESD
:rom causing anomalies.
This can be done effectively on multi-satellite programs such as
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Item 19 CONT'D
Active charge control is recommended for DoD satellites which cannot
tolerate functional anomalies due to ESD's, and on the first flight of new
Passive engineering solutions should be integrated into
satellite designs.
satellite designs.
GPS.
11
SECURITY CLASSIFICATION OF THIS PAGE
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Satellite
is
unlimited.
Anomalies and
Electrostatic Surface Discharges
by
Yan Chun Wong
Major, United States Marine Corps
B.S., University of
Submitted
Arizona, 1978
in partial fulfillment
of the requirements for the degree of
MASTER OF SCIENCE
IN
SYSTEMS TECHNOLOGY
(SPACE SYSTEMS OPERATIONS)
from the
NAVAL POSTGRADUATE SCHOOL
September 1991
ABSTRACT
Various aspects of the space environment can cause on-orbit
satellite
anomalies. Studies have shown that adverse interactions between the natural space
environment and space systems can have deleterious consequences comparable to
those caused by
human
or design errors.
electron caused electromagnetic pulse
the three most
common anomaly
plasma environment, such
as in
Electrostatic surface discharge (ESD),
(ECEMP), and
single event upset
producing mechanisms
geosynchronous
orbit,
in
(SEU)
space systems.
are
The
can cause differential charging
of satellite components and lead to ESD's on satellite surfaces.
By using the Spacecraft Anomaly Manager (SAM) software package,
spacecraft anomaly data of operational satellites contained in the database of
National Geophysical Data Center
that
(NGDC) were
analyzed.
The
analysis concluded
ESD is directly related to geomagnetic storm activity and ESD related
anomalies
are local time and seasonal dependent.
Proper engineering solutions should be
integrated into satellite designs to prevent
ESD
be done
is
effectively
recommended
to ESD's,
on
for
multi-satellite
DoD
and on the
satellites
first
flight
from causing anomalies. This can
programs such as GPS. Active charge control
which cannot tolerate functional anomalies due
of
new
satellite
solutions should be integrated into satellite designs.
IV
designs.
Passive engineering
TABLE OF CONTENTS
I.
II.
SPACE ENVIRONMENT AND SPACECRAFT CHARGING
1
A.
INTRODUCTION
1
B.
ENVIRONMENTAL INTERACTIONS
2
1.
Surface Charging
4
2.
Bulk Charging
7
3.
Single Event Upset
(SEU)
SURFACE CHARGING AND ANOMALIES
9
14
A.
OVERVIEW
14
B.
SURFACE CHARGING
15
C.
CHARGING MECHANISM
15
D.
DEBYE LENGTH
19
E.
WAKE EFFECT
20
F.
CURRENTS
21
G.
ANOMALIES
22
1.
DSCS
23
2.
CTS-Hermes
25
3.
P78-2,
SCATHA
26
H.
III.
a.
Two Minute Data
b.
State
c.
Timing Errors
Change
in
in
Loss
29
Magnetic Field Monitor
VLF
Plasma Wave Analyzer
29
29
4.
METEOSAT
30
5.
SMS-GOES
32
6.
MARECS-A
34
7.
Anik
D
36
ANOMALIES AND SOLAR ACTIVITIES
ANOMALY ANALYSIS
38
40
A.
ANOMALY DATA SOURCES
40
B.
SPACECRAFT ANOMALY MANAGER (SAM)
40
C.
ANALYSIS
41
1.
General
41
2.
Solar Cycle Correlation
43
3.
Phantom Commands Due To Surface Charging
47
a.
GOES
48
b.
GGO
49
c.
GW0101
52
d.
METEOSAT
55
e.
DSCS
59
f.
GPS
61
VI
1
4.
IV.
LIST
Surface Charging and
GPS
SUMMARY AND CONCLUSIONS
July 89 to
March 90 Data
63
65
A.
SUMMARY
65
B.
CONCLUSIONS
67
C.
RECOMMENDATIONS
68
OF REFERENCES
69
INITIAL DISTRIBUTION LIST
72
VI
ACKNOWLEDGMENTS
The author wishes
to express his appreciation to Professor R.C.
scholarly advice, time, and patience.
The author
and H.C. Koons of Aerospace Corporation
Olsen for
also wishes to thank D.J.
for the
DSCS-1 anomaly
his
Gorney
information,
Captain Mike Scardera of 2nd Space Control Squadron, 2nd Space Wing Operations,
USAF,
for the recent
GPS anomaly
data,
and D.C. Wilkinson and J.H. Allen of
National Geophysical Data Center for the Spacecraft Anomaly Manager
software and the associated anomaly data.
vin
(SAM)
I.
A.
SPACE ENVIRONMENT AND SPACECRAFT CHARGING
INTRODUCTION
Recent technological advances have allowed man
earth environment into a
new
frontier.
This expansion
to
is
expand beyond the near
accomplished through the
launching of satellites into various earth orbits. The more satellites
more we
learn about our space environment surrounding Earth.
space environment has proven to be hostile to
amounts of research being directed
One
these hostilities.
to
satellites
we
launch, the
Unfortunately, the
and has resulted
in large
determine both the causes and remedies for
of the areas receiving attention
is
in
unexpected
satellite
anomalies.
Satellites operating in this hostile
cosmic
rays, energetic protons,
environment interact with elements such as
and plasma.
Studies have confirmed that adverse
interaction can cause on-orbit anomalies and can lead to serious consequences to the
operation of the
process, has
satellite.
For instance, spacecraft charging, an anomaly producing
been an ongoing concern
since
the early days of satellite flights
(Whipple, 1965). The majority of observed charging events have come from
in
geosynchronous
orbit, as first
reported by DeForest (1977).
Applications Technology Satellite 5 (ATS-5) showed that
as high as -10,000 Volts in eclipse
and -200 Volts
satellites
The observations from
ATS-5 charged
in sunlight.
to potentials
Potentials of these
magnitudes can produce damagin. electrostatic discharges and possibly lead to
environment related anomalies.
By studying space environment
of these
related anomalies,
one can determine the cause
anomalies and then solve the charging problem through improved
engineering designs. Solutions can utilize either active or passive charge control on
A
board the spacecraft.
simple passive charge control measure such as properly
grounding loose wires or increasing the shielding thickness
is
sometimes
solve the environmental charging problem. Active charge control
passive measures
fail to
resolve the problem.
economic impact must be
should be implemented.
satellites,
future
upon.
it
carefully
weighed
can be determined
focus of this thesis
charging, and to determine
The remainder
to
may be needed
of the anomaly and
if
its
determine which control measure
Therefore, by carefully analyzing anomaly data of various
if
there
Department of Defense (DoD)
The
The magnitude
sufficient to
if
is
is
a need for active charge control aboard
satellites,
or
if
passive techniques can be relied
to evaluate satellite anomalies caused by surface
active charge control
is
necessary.
of this chapter shall briefly examine the physical processes of
spacecraft charging, discharging, and their related satellite anomalies.
ENVIRONMENTAL INTERACTIONS
B.
Various factors of our near earth space environment interact with spacecraft.
The
•
following
is
a
list
Acoustic Noise
of environmental factors which can interact with spacecraft:
Air Pressure
Asteroids
Atmospheric Noise
Cosmic Rays
Deep Space
Ions
Eclipses
Electromagnetic Interference
Magnetic Storms
Micrometeors
Plasma
Radiation Belt
Solar Flares
From
the above
list,
cosmic
rays, eclipses,
plasma, radiation
belt,
and solar
flares
represent the environmental factors most closely related to spacecraft charging.
Spacecraft charging
potential relative to
results
its
is
the process through which a spacecraft gains an electrical
surroundings.
This accumulation of charge on a spacecraft
from interactions between spacecraft and the ambient plasma or radiation
environment.
Spacecraft charging can be divided into three types:
external) charging,
2.
bulk (or internal) charging of dielectrics, and
single high energy particles through the spacecraft.
processes are:
1.
3.
surface (or
passage of
The consequences
of these
surface charging results in electrostatic surface discharge (ESD);
internal charging results in Electron
Caused ElectroMagnetic Pulse (ECEMP); and
the passage of single high energy particles usually results in Single Event Upset
(SEU).
1.
Surface Charging
Surface charging
phenomenon
is
by far the best known and most easily identifiable
associated with spacecraft environment interactions.
It is
the result of
emission and collection of charged particles both to and from the exposed external
surfaces of the spacecraft. Surface charging
satellite surfaces
is
produced by interactions between the
and the space plasma, magnetic
1965). (see Figure 1)
The majority
field,
and solar radiation (Whipple,
of the particles affecting the charge state are
electrons and ions, with energies ranging from
1
electron volt (eV) up to 50 thousand
electron volts (50 keV) in the plasma environment.
Because of the different
geometry and material properties of the spacecraft surface, different areas on the
surface can be charged to different levels.
In general, surface charging can be
broken down into two types based on the spacecraft's acquired
compared with the
potential of
its
surroundings.
are frame and differential charging. (Olsen, et
Frame
occurs
when
plasma.
The two
al.,
relative potential
types of surface charging
1981)
charging, sometimes referred to as absolute or
mainframe charging,
the satellite, as a whole, acquires a net potential relative to the ambient
Frame charging
is
nearly instantaneous, with characteristic periods on the
order of micro seconds. Differential charging, on the other hand, takes place
different parts of the spacecraft are charged to different potentials,
and
it
when
occurs
Plasma environment
Surface interaction
Surface currents
Secondary particles
Backscattered
Figure
1.
In surface charging, currents from the
and photoelectrons
Robinson, 1989)
electrons,
(after
more gradually
charging
may produce
is
more
electrostatic
potentials.
Differential
strong local electric fields, and also can affect the frame
satellite.
From an anomaly
significant than
surface
discharge
effect point of view, differential
frame charging for
(ESD) between
it
can lead to surface arcing or
satellite
surfaces
of
different
This "arcing and sparking" can result in direct damage to spacecraft
components and
electronics.
of ambient electrons, ions, secondary
on the external surface of the satellite body,
(with periods on the order of seconds to minutes).
charging level of the
charging
movement
result in a net current
is
(Koons
also
known
et al.,
1988)
to
produce spurious interfering pulses to onboard
In
geosynchronous
differential charging.
orbit,
spacecraft
Differential charging
sunlight tends to keep
all
anomalies are often caused by
particularly
is
common
in sunlight, since
illuminated surfaces near the plasma potential, whereas
shaded dielectric surfaces can charge to large negative potentials.
on the order of one thousand
Typically, potential differences
needed
produce an ESD.
to
Each
ESD
an
results in
volts are
electric arc discharge
from
regions of high electrostatic potential to regions of lower electrostatic potential and
each arc discharge produces an equilibrium redistribution of charge. Arcs generate
a transient electromagnetic pulse (EMP), and the
signals in electronic circuits,
wiring.
environment
is
known
attributable to ESD's,
in
can produce undesired
and induce anomalous currents
Both the discharge and the resulting
unintended logic changes
EMP
electronics.
EMP
in internal satellite
cause satellite anomalies from
In geosynchronous orbit, the plasma
to cause differential charging
on
spacecraft.
Anomalies
due to surface charging alone, have been known to cause
command errors, spurious signals, phantom commands, degraded sensor performance,
component
failures,
and even complete mission
loss.
A specific example of a severe
spacecraft charging event occurred on September 22, 1982 and was recorded by the
P78-2
satellite's
on board pulse analyzer and surface
different spacecraft anomalies occurring
The most
serious
mode changes
in
was a two minute
on
that day
potential monitor.
which were attributed to ESD's.
loss of data; the other
two experiments. (Koons
et
al.,
Three
1988)
two were uncommanded
Bulk Charging
2.
Bulk or internal charging, also referred
to as
deep
dielectric charging,
is
the build up of charge on and within dielectric materials or well insulated floating
conductors inside the spacecraft.
to 5
MeV, can
inside the
Energetic electrons, with energies from 300
keV
penetrate through the surface of the spacecraft and deposit charges
Faraday cage of the spacecraft (see Figure
2).
(Robinson, 1989, pp. 3-22)
penetrating radiation
electronics
Figure
2.
box
Internal discharge results from charges deposited directly
on or
in well insulated
regions
inside the Faraday cage of the spacecraft, (after Robinson, 1989)
Internal charging
is
dependent on four
factors:
environment, shielding
thickness of the spacecraft, and the characteristics and shape of the charged material.
When
the rate at which the energetic electrons deposit
on the surface or embed
inside a bulk dielectric
is
greater than the rate at which the charge leaks out,
potential will begin to increase in magnitude.
potential reaches the
breakdown value of the
These internal discharges are known
ECEMP,
to
Once
the generated electric field
dielectric, internal discharge will occur.
produce electromagnetic interference or
a sharp pulse of electromagnetic energy, which can penetrate into the
nearby sensitive electronic components and cause noise, malfunction, or even burn
out of circuit boards.
Following the discovery of the surface charging phenomenon, there
remained
satellite
anomalies which could not be explained by simply invoking the
mechanism
surface charging
still
--
other charge mechanisms were present.
satellites operation, discharges associated with satellite
of discharges (surface and internal) were recognized.
During
anomalies, two distinct types
Shaw
et al. (1976) categorized
these two types of discharge by whether they correlated with the
known
charging mechanism or could not be explained by surface charging.
The Voyager
spacecraft experienced 42 power-on-reset
(FDS) during
was
first
to
its
the Flight
I
Data Subsystem
passage through the radiation belts of Jupiter. Meulenberg (1976)
propose that there was a bi-layer discharge mechanism through the
dielectrics within spacecraft.
observed
(PORs) within
surface
satellite
This type of mechanism could possibly explain the
anomalies that did not correlate with discharges caused only by
surface charging.
Leung,
et
al.,
(1986) correlated these
POR
events with the high energy
spectrum of particles causing internal charging. Later, after studying the
8
viability of
Vampola
the internal charging mechanism,
examples of internal charging
most
common
at
(1987) presented several definitive
geosynchronous
altitude.
Of the examples
cause associated with deep dielectric charging
insulating covers
on cables exposed
given, the
the deposition in the
is
directly to the space environment.
Single Event Upset (SEU)
3.
Because of
(SEU's)
in
their high energy,
cosmic rays cause Single Event Upsets
micro electronics when spacecraft operate
sensitive
in
a radiation
environment. "Single Event Upsets occur in micro electronics when a single particle,
usually a heavy ion or proton, deposits
circuit to
at a sensitive
cause that circuit to change state" (Robinson, 1989, pp.
soft errors (in the sense of
usually takes place in
as part of
enough charge
its
wrong
memory, or
function. Binder et
circuits in the
The
bit values)
digital logic
al.
but no
damage
1-9).
node
in the
SEU's cause
to hardware.
SEU
which requires information retention
(1982) identified specific upsets in "flip-flop" type
space environment which he attributed to the effect of SEU's.
basic
SEU mechanism
involves a single particle passing through the
electronic circuit, leaving a track of electron hole pairs.
When
this track crosses
a
depletion region, the electric field in the depletion region separates the charges in
the track so that the charges do not recombine.
and
lasts
bit.
This change of state
The
circuit.
upset
long enough,
is
critical
it
If this
can be interpreted by the
is
characterized by a
charge pulse
circuit as a
"bit-flip" in
determined by the chip feature
size.
change
memory
charge concentration the particle must
is
hit in
strong enough
in state
of the
represented by the
order to cause an
Figure 3 illustrates the
SEU
normal
non-normal
incidence
incidence
n-region
sensitive region can be the
reversed biased junction
Figure
3.
Single Event Upset
Diagram (Robinson,
mechanism. The volume the
chip feature size.
probability of
transfer
particle
must
1989, Figure 4-2).
hit to
cause an upset
is
determined by the
This sensitive volume determines the cross section or the
SEU.
(LET) of the
Figure 4 illustrates
ionizing particle
of ability to ionize the material along
As our micro
chip
is
its
this cross section as the linear
varied.
of the particle
is
a measure
path. (Robinson, 1989, pp. 4-4)
technology
performance of Integrated Circuits
LET
energy
(IC's) has
has
advanced
in
recent
years,
the
been improved by increasing both the
processing speed and reducing the power requirement for individual circuits.
Consequently, these technological advances have required increasingly smaller charge
10
simplest approximation
/
cross-section
q
d
o
S3
3
Threshold
LET
Figure
4.
times path length
Classical Experiment Cross-Section.
The two key parameters
rate are the threshold and the cross-section at large
LET
for
determining the
SEU
times path length. (Robinson, 1989, Figure
4-3).
magnitudes to store comparable quantities of coded information. As a
result,
each
succeeding generation of integrated circuits has become increasingly susceptible to
SEU's when spacecraft are operated
in the radiation
the lesser charge dependence for information storage
become more
is
that smaller disruptions have
likely to significantly disturb the integrity of integrated circuits.
The higher degree
designing
environment. The net effect of
modern
satellites.
of susceptibility to
The SEU
rate can
SEU's
is
a major concern in
be minimized by applying proper
passive controls such as better spacecraft engineering designs in conjunction with
11
Global Positioning
hardening programs.
example of the degree of
SEU
anomaly data reported
to
Satellites
susceptibility
the
modern
(GPS) provide an illuminating
satellites
may
experience.
anomaly database maintained by the National
Geophysical Data Center showed that of the 564 reported anomalies
attributable to SEU's.
and telemetry,
Bit-flips
tracking,
GPS
all
were
directly
occurred in the navigation processor, clock register,
and command (TT&C) subsystem. According to Captain
Scardera (1991) of the 2nd Space Control Squadron, 2nd Space Wing Operations,
U.S. Air Force Space
anomalies
in
block
1
Command who
GPS
is
an engineer working on the
due to SEU's have not reoccurred
in the block
particles. Figures 5
respectively.
The
and 6 are the drawings of the
These drawings
GPS
method
block
project,
2 satellites
For instance, simply
after incorporating proper engineering design modifications.
increasing the shielding thickness has been an effective
GPS
1
against high energy
and block 2
satellites
illustrate the differences in their surface designs.
following chapter shall discuss in greater detail the physics behind surface
charging and the anomalies caused by ESD's. Chapter three shall analyze anomaly
data for several
results
of our
geosynchronous
satellites that
analysis,
DoD
the
were caused by surface charging.
Finally,
from the
requirement of active charge control for future
satellites will
be discussed.
12
Figure
5.
A GPS
block
Figure
6.
A GPS
block 2
1 satellite.
satellite.
13
II.
A.
SURFACE CHARGING AND ANOMALIES
OVERVIEW
Spacecraft charging often leads to serious operational anomalies (Rosen, 1976).
The tendency
larger,
of
modern
spacecraft design has been to allow satellites to
and more autonomous. Any functional anomalies are undesirable;
satellites missions,
any anomaly cannot be tolerated.
commercial sectors have great
done
for certain
Since both the military and
interest in spacecraft operations,
to understand the causes
become
much work
has been
and determine the cures for spacecraft charging.
Subsequently, operational solutions have been found for the anomalies once the
charging mechanisms and design deficiencies were understood.
Surface charging/discharging
mechanisms.
It
is
one of many forms of anomaly producing
was discovered on the early space
space plasma environment,
satellites will
flights.
When
develop charges on their exposed external
surfaces because of interactions between satellites and plasma.
orbits,
such as the geosynchronous
plasma, and surface charging
is
operating in the
In high-altitude
orbit, satellites are greatly affected
a major concern.
by space
Previously, low altitude surface
charging was thought to be insignificant because of low plasma temperatures and
high electron densities. However, a recent study conducted by Frooninckx and Sojka
(1991) revealed that satellites operating in the upper ionosphere are also affected by
the surface
charging phenomenon.
Defense Meteorological
14
Satellite
Program
(DMSP)
polar orbiting satellites at an altitude of 840 kilometers (km), can develop
and have recorded
electric potentials as severe as -1430 volts.
suggested to be related to solar cycles.
surface charging
mechanism
in
More
research
is
These
activities are
required on the low altitude
order to design charge control systems that will
prevent future surface charging related anomalies.
B.
SURFACE CHARGING
Surface charging
is
the
phenomenon associated
with charge build up on exposed
external surfaces of spacecraft as discussed in chapter one.
interaction
between the
When
solar radiation.
geomagnetic
tail
will
is
a plasma
in
field,
and
heated and accelerated towards Earth from the
it
rushes into the synchronous orbit
Unless the complete outer surface of the
hot plasma.
conductive and electrically connected, different parts of the spacecraft
be charged to different voltages. At times, adjacent surfaces can be more than
a thousand volts apart.
that exceeds a
The
harness.
differential charge build
breakdown threshold
between the surfaces and
C.
is
a consequence of the
and the space plasma, magnetic
region of the magnetosphere,
and bathes spacecraft
spacecraft
satellite surfaces
It is
at
some
point.
up generates an
electric field
This in turn leads to arcing
results in large electrical transients in the spacecraft
These transients lead
to anomalies in satellite behavior.
CHARGING MECHANISM
By
definition, space
an imaginary surface
plasma
in the
is
in a neutral
charge
state.
The
net current across
plasma environment must be zero so that the overall
15
charge neutrality of the plasma can be maintained.
zero, then there will be charge built
An
the other side.
up on one
will
is
be zero.
surface (Figure
is
not
and decrease on
equilibrium will eventually be established and the net current
large
enough
to hold a significant
The only requirement
number of charges
the net current flow
side of the surface
flow will return to zero after some period of time.
surface which
If
Across an imaginary closed
amount of plasma, the net current
for this condition to exist
is
that
an equal
(both positive and negative) flow in opposite directions across the
7).
(Net current across
any surface
is
zero)
Figure 7. Across any imaginary surface within the plasma, there are an equal number of positive
and negative charges flowing in opposite directions across the surface and the net current is zero.
16
When
any solid body
(i.e.,
a satellite)
Charge
currents are changed drastically.
body
until
is
immersed
will build
in the
plasma, compensating
up on the surface of the
an equilibrium between the body and the ambient plasma
the net current flow across the surface
accumulates charge, and a sheath
is
becomes
formed.
If
zero.
is
solid
reached and
During that time, the body
no discharges occur, the body
will
eventually reach an equilibrium with the surrounding plasma and the radiation
environment so that a surface can be drawn around the body and there
any net current flowing through
it.
The shape and material properties of
have much influence over the locations and levels of charges.
distribution
on and around
Consider plasma
in a
will not
The
be
satellites
potential
the satellite can be very complex. (Robinson, 1989)
thermal equilibrium state;
charge neutrality condition of plasma.
electron) traveling in one direction,
Within
this
this state
would
satisfy the
plasma, for every proton (or
on an average, there
is
a proton (or electron)
traveling in the opposite direction (see Figure 6). Although the speeds of an electron
and proton are
vastly different,
and negative charge
can absorb charges,
on the average there are equal numbers of positive
carriers contained in the
is
imagined volume.
When
a body, which
inserted into the plasma, electrons and protons are stopped
from reaching the opposite
side
and charges
will
be absorbed by the surface of the
body.
From
the equipartition theorem, the average velocities of the electrons and
protons in the thermal equilibrium plasma can be calculated by the following
equation:
17
—kT=—mv 2
where k
is
velocity,
and
Boltzmann's constant,
m
is
the mass.
T
is
the plasma temperature, v
Because the proton mass
electron mass, the average electron velocity
Since the current
velocity.
particle density,
assuming
it is
(1)
is
is
much
is
much
is
the average
heavier than the
greater than the average proton
proportional to the average velocity and charged
the
same
for both charged particles in the plasma, the
electron current will flow to the surface of the body at a higher rate than the
proton's.
A
negative charge potential will build up on the body surface (Figure
8).
This process will continue until the electric field produced by the accumulation of
Figure
is
8.
Since the average velocity of the electron
flowing to the surface of the body
at a
is
faster than the proton's, the electron current
higher rate than the proton.
charged to a negative potential.
18
Therefore, the surface
is
charge
is
strong enough to repel electrons and attract positive ions.
when
equilibrium condition will be reached
Eventually, an
the net current to the surface reaches
zero.
Spacecraft surfaces are
made
of different shapes and materials of various
Typical conducting materials are aluminum, or conducting paint;
characteristics.
typical insulating surfaces are the glass covers of silicon solar cells,
used for thermal blankets.
properties,
it
is
a
on a
surface,
surface. This effect
these
complex system
determines photoelectric
ions impact
Since
is
yields,
materials
analyze.
to
possess different electrical
Surface
and secondary emission
one or more electrons
and the kapton
(material)
When
yields.
will typically
properties
electrons or
be emitted from the
called secondary emission. Secondary emission, which depends
on the material plays an important
role in determining the net current to the surface.
DEBYE LENGTH
D.
In plasma physics the parameter which describes the distance over which an
electric field exists in the
plasma
is
the
Debye
eJcT
— =7430
-69
where
e
is
the permittivity constant, k
of the electrons in degrees Kelvin,
kT
is
r?
c
the plasma temperature in eV.
earth radii
(R e ), the Debye length
length (A) in meters.
is
the
*I
Boltzmann constant,
electron density, e
When
is
large
19
(2)
is
a spacecraft
compared
T
is
temperature
the electronic charge,
is
and
at high altitude, 5 to 7
to the
dimension of the
spacecraft. Individual particle trajectories are controlled by the electric
near the
fields
As an example, consider a
spacecraft.
magnetosphere where the plasma temperature, kT,
electron density,
6
?7
e
is
10 [e/m
3
From Equation
].
is
typical
approximately 8
(2),
the
and magnetic
case
in
keV and
Debye length X
is
the
the
equal
to 665 meters,
which
Because of
the electrons envelop the vehicle with a distribution similar to the
this,
considerably larger than typical spacecraft dimensions.
is
"vacuum" solution of Laplace's equation
In contrast, at low altitudes,
velocity of the spacecraft
length
is
short
compared
is
i.e.,
(V^ =
Low
at
0).
Earth Orbit (LEO), or when the
high compared to the thermal velocities, the
to the spacecraft
Debye
and the particles trajectories are strongly
influenced by the presence of the plasma sheath around the vehicle.
E.
WAKE EFFECT
Spacecraft in low altitude earth orbits have orbital velocities on the order of 7
At
km/sec.
km/sec
for
altitude of 1,000
H
+
and
0.8
km/sec
ionosphere produces a wake.
km, the thermal velocities of the ambient ions
for
It
180 km/sec.
The
The movement
.
The
electrons tend to
electrostatic field that results
in the void
in the void but are retarded
from charge separation
20
fill
electron thermal velocity at that altitude
fill
pp. 2-40)
3
of a spacecraft through the
takes a finite time for the ions to
created behind the passing spacecraft.
is
+
is
at the
by the
wake. (Robinson, 1989,
F.
CURRENTS
Since charged particles are moving, they can be treated as currents; the
equilibrium potential of the spacecraft can be determined by the balance of currents.
The
currents to a surface in space must be balanced at an equilibrium, otherwise
charge will build until current balance
attained.
is
The
principal charging currents
are due to the ambient electrons and the emitted photoelectrons.
The space environment
is
the surface of the spacecraft.
the
In a
main
factor in determining currents to
plasma environment, the density of the plasma
determines the type of current flowing to the surface.
affects the radiation
surfaces
sum
the surface
density,
if
the surface
to zero.
is
The current
density also
induced conductivity which in turn affects the leakage current
throughout the material. This
in equilibrium,
and from
zero.
Or
if
latter effect
is
is
conducting,
the surface
is
all
is
each point on
directly proportional to the
j
plasma, q
particle.
(3)
the primary current of charged particles, n
is
is
the charge on a particle, and v average
With the same
the spacecraft and
its
velocity distribution,
surface
plasma
as:
j-nqv
'
~ average
where
When
currents to the connected conducting
insulating, the net current to
The primary current
and can be expressed
important for dielectric charging.
more
is
is
the density of surrounding
the average velocity of the
plasma of greater density
will
quickly than a plasma of lesser density.
21
charge
Referring back to Figure
due to ambient electrons and
the net current to a surface
1,
ions,
is
sum
the
of currents
secondary electrons, and photoelectrons.
To
calculate the spacecraft potential, the current balance equation can be written as:
where the
I
e
and
The
surface.
I
Ij
e/e
are the primary electron and ion currents from the plasma to the
and
I
e/i
are the secondary emission currents due to incoming
electrons and ions respectively.
bs
The
to backscattering electrons.
exposed to photons.
I
is
I
the current of electrons leaving the surface due
if
the surface
in a
way
is
from photoemission.
Photoemission has
similar to secondary emission;
characteristics of the surface material.
Finally, the last term,
other current which has not been mentioned. This
may
it
I
depends on the
OIher
repre-ents any
include current due to
law current from spacecraft, thruster operation, ion engine current, wake
anything else. At equilibrium,
G.
is
In most space charging environments, the largest current
interacting with the spacecraft surface
been characterized
photocurrent resulting
photo is
I tota]
=
0, if
Ohm's
effect, or
the "environment" not changing.
ANOMALIES
If
one had
to define the
simplest term, an anomaly
spacecraft.
failure.
An anomaly
spacecraft, in the
any unscheduled, undesirable event occurring to the
can range from a simple data
The most common
command
is
word "anomaly" associated with
type of anomaly
is
the
causes satellites to perform a task which
22
bit error to
a total mission
phantom command. Phantom
it
was not given intentionally
as
part of the operations.
page 6
an example of phantom
is
The remainder
satellite
The two minute
anomalies.
loss of data
command
onboard P78-2
satellite given
on
caused anomaly.
of this section provides examples of surface charging related
In these examples, satellites experienced various degrees of
subsystem on orbit malfunctions, and their mission performances were directly
impaired.
Although these
environmental
effects, they
works rather than as
1.
were not properly designed
satellites
to
exclude
should be looked upon with gratitude for their pioneering
failures
due
to
poor engineering designs.
DSCS
The
first
major
satellite
system to have environmental problems was DSCS,
a military communications satellite.
drew a great deal of speculation
on November
11,
The complete mission
DSCS-1 was launched
as to the cause of the failure.
1971 into geostationary orbit. Figure 9
DSCS
failure of the first
is
DSCS
a drawing of the
satellite.
The
original failure report
characteristics have
is
no longer
been obtained from Aerospace Corporation, courtesy of Dr.
Harry Koons. The Orbit Data Acquisition Program
orbit incidents maintained by the
The
available, however, the failure
failure of
(ODAP)
Aerospace Corporation
DSCS-1 was
in
is
a depository of on-
Los Angeles, CA.
attributed to a geomagnetic storm.
The
failure
report stated that within the electrical power and distribution subsystem, there was
a power interface switching mechanism to work the load control assembly.
power
interface
switch
failed
and
there
23
was
no
power
available
to
This
the
Figure
9.
A DSCS
satellite.
communications subsystem. This caused the mission to be terminated because the
switch logic assembly
failure
commands were
was attributed
enhanced electron
recommended
grounded
that
to
flux
all
ineffective in correcting the problem.
ESD. The ESD was
associated
with
a
The
a result of charging induced by the
geomagnetic
storm.
The
report
(where possible) external conductive surfaces be properly
in all future satellites to eliminate differential charging during
storms. (Koons, 1991)
24
geomagnetic
CTS-Hermes
2.
An early experiment
designed to study
satellite
anomalies was to place the
Transient Event Counter (TEC), on the joint Canadian-American Communications
Technology
Satellite
(CTS). CTS, called Hermes, was launched on January
from Cape Canaveral by
orbit at 116°
GHz,
three axis stabilization.
10.
(2)
on
orbit
Figure 10
is
Communications Technology
The purpose
of the
1976
and placed into geostationary equatorial
West Longitude. Hermes was designed
transmission at 12-14
Figure
a Delta rocket
17,
to test three technologies:
deployment of
light solar cell panels,
and
(1)
(3)
a drawing of Hermes.
Satellite
TEC was to
(CTS), Hermes.
identify transients in the spacecraft wiring
harnesses which could be attributed to the spacecraft charging phenomenon.
It
was
designed to sense and count electrical transients which exceed 5 volts in amplitude
at rise times of less
than 0.3 /^sec which could cause switching of spacecraft logic
25
circuits.
first
Stevens and Klinect (1977) studied the data collected by the
year of
its
TEC during the
operation. In the data there were 215 transient events detected in the
system wire harnesses which were presumably due to spacecraft charging events. All
satellite
data had been verified to the fact that no
commands were being executed
and there were no power fluctuations concurrent with the TEC-sensed
Among
the data, 65 percent were multiple transients.
The
transients.
cause, as explained by
Stevens and Klinect (1977), was that the large insulator areas on the satellite did not
discharge
all at
Rather, a discharge occurred in one region which in turn
once.
triggered discharges in another area. Also, the data
showed
that the distribution of
the events appeared to be random; satellites could be charged by the geomagnetic
substorm environment
at
about local midnight, but the discharge might not occur for
several hours.
There was a part
that
failure
on Hermes
as well.
was induced by spacecraft charging occurred.
On June
out.
The most probable
location of the short
1976, an
anomaly
A short circuit took place on the
experiment power bus. The short lasted 24 seconds, and
burn
8,
was
it
caused the power bus to
at the
power
insulating diodes
which were exposed to the environment; a moderate substorm was recorded a few
hours preceding the short.
3.
P78-2,
SCATHA
Following the
DSCS
to understand the source of the
One
accident, a complete mission failure, a massive effort
anomaly was
initiated (Robinson, Jr, 1989, pp. 1-2).
part of this effect was the launch of the P78-2 spacecraft, the Spacecraft
26
Charging At High Altitude
satellite
(SCATHA),
inclination angle, 185
had two
initial
spacecraft.
Table
I.
program. The United States Air Force P78-2
see Figure 11, was launched on January 30, 1979 with 27°
km
perigee, and 43,905
objectives:
effects (Shane, 1977).
experiments,
(SCATHA)
to
km
apogee. The
SCATHA spacecraft
measure the charging characteristics and material
Other elements of the
SCATHA
and development of computer models
The experimental equipment onboard P78-2
The experimental equipment onboard P78-2
IDENTIFICATION
program included ground
for
surface
charging
are listed in Table
satellite.
TITLE
VLF
HF
SCI
Engineering Experiment Plus
Receivers
SC2
Spacecraft Sheath Fields Plus Energetic Ions
SC3
High Energy
SC4
Satellite Electron
and
Particle Spectrometer
And
Positive Ion
Beam
System
SC5
Rapid Scan
SC6
Thermal Plasma Analyzer
SC7
Light Ion
SC8
Energetic Ion Composition Experiment
SC9
UCSD
Particle Detector
Mass Spectrometer
Charged
Particle
Experiment
SC10
Electric Field
sen
Magnetic Field Monitor
ML12
Spacecraft Contamination Plus Thermal
Monitor
Control Materials Monitoring
TPM
Transient Pulse Monitor
27
I.
on
GSPC
ELECTRIC FIELD EXP.
OSPC
MAGNETOMETER
Figure 11. The P78-2
SCATHA
satellite.
With the successful
flight of the
P78-2
satellite,
a great deal has
been
learned about surface charging from data collected by instruments on board the P782.
These data validated that there
is
a close
tie
between surface charging and the
space environment.
On September 22,
1982, a large
number
of intense electrostatic discharges
were detected by the engineering instruments aboard the P78-2
satellite.
In only one
day, the Pulse Analyzer detected 29 pulses; 17 of the pulses exceeded the
voltage discrimination level which was set to 7.4 V.
also detected 29 pulses
The Transient Pulse Monitor
and most of them were coincidental
detected by the Pulse Analyzer.
maximum
in
During the same time period the
time with those
satellite
Surface
Potential Monitor experiment measured the largest differential surface charging
observed in the data analyzed since launch. The gold sample voltages exceeded -300
28
V
on four separate occasions.
Each time the voltage exceeded
were recorded by the Pulse Analyzer. Three
on P78-2 on
that day.
The most
serious
two were uncommanded mode changes
a.
loss of data.
two experiments. (Koons
et
The other
al.,
1988)
Two Minute Data Loss
A two minute period was missing from the
satellite.
ESD's
different spacecraft anomalies occurred
was a two minute
in
this value,
tape-recorded data of the
Although no pulse was recorded near the two minutes when data were
missing by the pulse detectors, the signature of a pulse appeared in the data from the
Very-Low-Frequency (VLF) Wave Analyzer experiment. Each pulse detected by the
Pulse Analyzer also produced an anomalous output from the
was believed
VLF
experiment.
It
that the discharge caused the pulse code modulation subsystem to lose
synchronization.
b.
State
A
Change
filter
in
select
occasionally changed state.
occurring on the vehicle.
Magnetic Field Monitor
relay in the
Magnetic Field Monitor experiment
This occurred during the time
One
such
filter state
when
discharges were
change occurred on September 22,
1982.
c
Timing Errors
in
VLF Plasma Wave Analyzer
Anomalous timing errors occurred
The
VLF
in the
VLF Plasma Wave Analyzer.
experiment collected data from two sensors, an electric antenna and a
magnetic antenna.
The experiment contained
29
a counter that counted the
Main
Frame
sync pulses from the telemetry system.
per second.
At every
The
16 sync pulses the antenna
pulses occurred at the rate of one
was switched. The anomaly
that
occurred on September 22, 1982 was a failure of the antenna to switch properly after
The
virtually every discharge.
switching failures coincided with four of the discharge
pulses in the two minute data loss period. (Koons et
4.
al.,
1988)
METEOSAT
METEOSAT-F1
(Figure 12) suffered from a
number
of non-damaging
operational anomalies that were attributed to ESD's caused by differential charging.
Phantom commands, mentioned on page
problem
METEOSAT-F1
24, are
of
two
geostationary orbit.
built
pre-operational
METEOSAT-F1
and operated by the
(ESA)
initiated the
meteorological
program
to
satellites
be
for the
put
meteorological data to weather forecasting
METEOSAT-F1
was launched
in
November
and was furnished with a high-resolution radiometer which takes pictures
three spectral bands:
in
and F2 were the meteorological spacecraft,
ESA to provide
agencies in the European sector.
1977,
by the switching
illustrated
encountered.
In 1972 the European Space Agency
development
now
the visible, thermal infrared, and water vapor bands.
23,
in
The
radiometer was an electro-optical instrument with a 40cm diameter telescope and was
capable of providing two images of the Earth in the visible and infrared wavebands
every 25 minutes.
On November
24,
1977
METEOSAT-F1
experienced inadvertent stop of
radiometer scanning soon after operations had begun. The cause of the anomalous
30
Figure 12.
status
A METEOSAT
satellite.
change was traced
to a
few sensitive
circuits.
Robbins (1979) studied the
Meteosat Fl anomalies and found that anomalies were more
common
at times of
high geomagnetic activity. In three years of operation Meteosat Fl experienced over
150
anomalies.
Hoping
to
correct
improvements were incorporated
the
problem,
into the building of
the
circuits
two
design
METEOSAT-F2:
grounding of the outer layer of the thermal shields
potential build up on those surfaces.
Replacing electronic
following
in
order to avoid high
by relays in the radiometer stops circuit in order
to increase the level of energy
needed
1982)
31
to trigger the
radiometer stops. (Hoge,
METEOSAT-F2
was launched on June
The decrease was
anomalies was dramatically reduced.
improvements. (Johnstone,
et
The number
1981.
19,
of
attributed to the design
1985)
al.,
SMS-GOES
5.
After the testing of several meteorological instruments aboard the ATS-1
and ATS-3
the
first
satellites in geostationary orbit (the first satellites in geostationary orbit),
American geostationary meteorological
was named Synchronous Meteorological
named
was launched
satellite
Satellite
(SMS).
Subsequent
as Geostationary Operational Environmental Satellite
GOES-4 was
launched on September
The GOES-4 (Figure
13)
and
-5 also suffered
Visible and Infrared Spin Scan Radiometer
The
in the east-west direction.
direction.
phantom command
May
The
It
were
first
22, 1981.
effects with their
(VISSR) subsystems.
principal onboard instrument,
VISSR. This instrument observed
flights
(GOES).
and GOES-5 was on
1980,
9,
in 1974.
an atmospheric sounder, was the
the earth using the spin of the spacecraft to scan
A mirror was stepped to produce scans in the north-south
There were eight channels of data taken
in
both visible and infrared
regions of the spectrum.
The VISSR subsystems aboard GOES-4 and
anomalous changes
in its state
for
October 1989
to
GOES-4, and
March 1990
had shown instances of
corresponding to false commands.
anomalous commands recorded during a
March 1990
-5
15
14 anomalous
for
month period from November 1988
commands
GOES-5. The
32
There were 13
first
in a six
to
month period from
anomaly observed on GOES-4
Figure
13.
on March
same
step.
A GOES-4
29, 1981
satellite.
was an uncommanded stepping of the VISSR mirror.
time, the gain in one of the visible channels (Ch 6) had an
On
April
1,
1981, the mirror again began
magnetograms examined
activity,
uncommanded
uncommanded
shortly after these anomalies
At the
stepping.
gain
Ground
showed evidence of substorm
suggesting that these anomalies were environmentally induced. (Robinson,
1989, pp. 5-7)
A
search for the cause revealed that part of the
radiation cooler was ungrounded.
through a wire which went into the
VISSR second
stage
The inner member of this assembly was grounded
VISSR
electronics package.
charge built up on the ungrounded radiator
33
until a
It
was proposed that
breakdown occurred across the
The
insulating epoxy bonding the two parts together.
then conducted through the ground wire into the
performed on the GOES-5 spacecraft which
at
VISSR
Tests
electronics.
the time was awaiting launch
confirmed that the radiator was indeed ungrounded.
ground the radiator, and did not experience
was
resulting current surge
GOES-5 was
this particular
modified to
command anomaly
again.
(Robinson, 1989, pp. 5-7)
6.
MARECS-A
In
shown
in
December
Figure
14,
after launching.
1981,
MARECS-A,
satellite,
experienced some unexpected spurious switching problems soon
Most
(65 percent) of these spurious switching problems
harmless triggering of telemetry latches.
operation of the
an ESA's telecommunication
satellite
However, a more serious impact on the
was caused by uncommanded
functions for the attitude control since
it
were
triggering of back-up
could disturb the communication
traffic.
(Lechte, 1986, pp. 24-2)
MARECS-A
anomalies showed a seasonal variation; most of them
occurred around the equinoxes.
MARECS-A spurious
as
There was a good correlation between observed
switchings anomalies and the distribution of sunspot
measured by the Ap-index over a year (Lechte,
a good correlation between
1987). Figure 15
MARECS-A anomalies
(in the
shows there was
period between 1982 and
1985) and the diurnal variation of the electron flux as measured on
ATS-5.
There seems
to
be a delay between the maxima of the
switchings. In early 1982, the
onboard
safety
34
numbers
SCATHA
flux
mode "Emergency Sun
and
and spurious
Reconfiguration
/C T~T\
Figure
14.
MARECS-A
satellite.
-
60
-
40
20
B"
16
W
SPACECRAFT LOCAL TIME
ElECTRONFllX DATA SOORCD
SCATHA
ATS 5
SCATHA
-
Figure
15.
ATS
SOrV.. SOO KeV
(t«V
50eV...S0
KtV
leV .60
5
Diurnal distribution
MARECS-A
spurious switchings and electronflux. (Lechte, 1986,
pp. 24-3)
35
(ESR)" actually temporarily interrupted the communication
ESA decided to investigate the
The
link.
After
reasons for the spurious disturbances on
investigation concluded that most of the spurious switchings
ESD's. The findings would be implemented into the future
to eliminate the switching
problem on subsequent
satellite
MARECS-A
this
anomaly,
MARECS-A.
were caused by
design in order
satellites.
(Lechte,
1986, pp. 24-3)
7.
Anik
D
Canadian geosynchronous domestic
built
by
SPAR
satellites,
D
(Figure 16), were
with Hughes as their bus and reaction control system supplier. Anik
Dl and D2 were launched
in
August 1982 and November 1984 respectively.
Numerous observed anomalies occurred on Anik
One
by phantom commands.
D
Anik
series satellites
rather serious event which took place onboard
led to a temporary loss of control of the satellite
Anomalies were believed
to
which were caused
and a consequent
Anik
loss of fuel.
have been caused by electrostatic discharges, and the
thermal blanket was considered to be the primary source of ESD. (Wadham, 1986)
Anik
that
on March
satellite
8,
anomalies were studied by
1985 the Anik
D2
Wadham
were transmitted
mounted on the despun platform.
He pointed
out
despin control system malfunctioned and the
despun platform suddenly spun up. There was a temporary
since these data
(1986).
via the
Wadham
loss of all telemetry data
communications antenna which was
thought
this
anomaly was a unique
occurrence because of the following events had taken place simultaneously:
36
Figure
•
16.
Anik
A change
not the
•
•
D
satellite.
receivers
The
disabling of logic circuitry intended to indicate to the despin control loop
any
loss of the pilot signal.
The
disabling of logic circuitry intended to indicate
no longer pointing
•
which told the despin control system whether or
were locked to the pilot uplink.
in status of the logic
command
The
if
the earth sensors were
at the earth.
switching of logic circuitry controlling the earth sensor selection, from the
North sensor
to the
South sensor.
•
The
resetting of the timing of
•
The
catastrophic failure of one of the redundant telemetry encoders.
one of the telemetry subcommutators.
37
Wadham
satellite
indicated
only two of the
if
occurred;
it
Wadham
Wadham
there
postulated that a large arc discharge
originated at the thermal wrap
antenna reflector or
at the
(1986) also pointed out that prior to and up to the time of the
was unusually high geomagnetic
activity
level for several days thereafter.
unbalanced due
to the
antenna
activity
in
the
magnetosphere.
became very low and remained
at a
low
Because the despun section was dynamically
offset, the
spin-up caused the satellite to wobble, and
caused a nutation control thruster to
fire.
equivalent to about a year of stationkeeping.
H.
on the back of the communications
thermal shield on the front.
Immediately after the event, the
in turn
three events had occurred, the
would not have spun up. The control system could not cope with the three
events occurring simultaneously.
event,
first
The
net result was a loss of fuel
(Wadham,
1986)
ANOMALIES AND SOLAR ACTIVITIES
When
the space environment lacks lower energy particles, and
is
rich in
electrons with energies above one keV, surface charging and discharging will occur.
This usually happens during magnetic substorms or solar particle events. Electrical
discharges on surfaces of geosynchronous spacecraft due to differential charging were
reported to occur at higher rates during periods of increased geomagnetic
The
SCATHA
satellite
which was launched
sample negatively charged to 3
change in electron
kV
flux during a
in
in 1979,
activity.
on one occasion had a kapton
concurrence with several orders of magnitude
substorm expansive phase (Reagan,
38
et
al.,
1981).
Allen (1991) studied the solar and geomagnetic
during March, 1989.
A
list
activities
which took place
of the consequences for space systems was given.
They
included:
GOES-7 communications
•
circuit
anomaly,
lost
imagery, and communications
outage
Three low altitude NOAA polar orbiting weather satellites and the USAF
DMSP had trouble unloading torque due to the uncommonly large ambient
magnetic field changes.
•
Japanese geostationary communications satellite CS-3B had failure and
permanent loss of half of the dual redundant command circuitry on board.
•
A
•
series of seven
commercial geostationary communications
satellites
had
considerable problems maintaining operational attitude orientation within
specified ranges.
The Japanese
•
scintillations;
geostationary meteorological satellite
Data transmissions were
Geostationary communications
•
lost for
satellites
GMS-3
reported operational anomalies.
Historically major flares increased magnetic storms
on Earth, causing power
outages and disrupting electromagnetic communications. Between
1990,
16 major solar flares were reported
heightened solar
activity raised
suffered severe
about one hour.
(Lancaster,
concerns about the
1991).
reliability of
December
20-30,
This period of
space based military
support for operations (Desert Shield) in the Mideast during the following months.
It
was
and
felt that
these solar activities might severely disrupt military communications
satellite surveillance.
39
III.
ANOMALY ANALYSIS
ANOMALY DATA SOURCES
A.
The
(NGDC)
thesis,
it
Solar-Terrestrial Physics Division of the National Geophysical
in Boulder,
will
Colorado maintains a Spacecraft Anomaly Database. In
be referred
time, location,
Data Center
to as the
NGDC database.
Each entry includes the
this
date,
and other pertinent information concerning incidents of spacecraft
operational disorders attributable to the space environment.
The
NGDC
database
covers the period from July 1973 to April 1989 (6652 days) and contains 3387 entries
from 24 different
and
to
analysis.
The
satellite types.
The
NGDC
supports retrospective data requests
NGDC also accepts anomaly data directly from satellite operators
keep the database current.
A
second set of data was helpfully provided by Captain Scardera of the 2nd
Space Control Squadron, 2nd Space Wing Operations, U.S. Air Force Space
Command,
in the
from July 1989
B.
to
form of operational anomaly reports on the GPS's
March
for the period
1990.
SPACECRAFT ANOMALY MANAGER (SAM)
The NGDC's anomaly database
is
maintained in
dBASE
compatible computers. The Spacecraft Anomaly Manager
software package developed to facilitate database access.
40
III
type
(SAM)
The
is
SAM
files for
IBM
a custom built
performs a
full
range of functions to manage, display, and analyze anomaly data.
and unify data collection format
to establish
in a
intends to aid users in the creation of their
submission to
satellites for
C.
NGDC
their respective
and re-dissemination.
General
From
for analysis
local time
the
NGDC database, anomaly data from six satellites were
by the Spacecraft Anomaly Manager
local time
and by month
Histograms of reported anomalies by
family of satellites.
The number
same because not
all
Histograms of
local time
plotted against local time, and
in
it
(McPherson
et al., 1976).
month
to
static
SAM
will plot all
reported data for that
may
not be
in
charge buildup and subsequent
for all records in the
illustrates the
anomalies peaks
for
to facilitate surface charging analysis.
and seasonal anomaly occurrences can be used
agreement with the
distribution
plots histograms of
anomalies were reported with a local time.
discharge. Figure 17 shows histogram of
is
for correlation of
of data points for these two histograms
determine spacecraft susceptibility
This
SAM
selected
local time will plot only data reported with a
local time while histograms of anomalies by
events.
(SAM) program
and seasonal dependencies on surface charging.
anomaly count by
to
ready to use format, but also
own databases on
for data archive
not only tries
ANALYSIS
1.
the
It
NGDC database
preponderance of midnight
to
dawn
historical recognition that the local time
the
dawn
sector,
as
shown
in
Figure
This local time dependence mirrors the local time
41
18
count
190!
Spacecraft
Anomaly
By Local Time For
All Records
180
170
160
150
140
130
120
11CH
100
90
-|
80
70
60
00 01 02 03 04 05 06 07 08 09 10
11
12 13 14 15 16 17 18 19 20 21 22 23
Local Time
Figure 17.
Local time distribution of
Figure 18.
Local time dependence of
(McPherson
et al, 1976,
all
anomalies
in the
SAM
circuit upset for several
Figure 1)
42
database.
DoD
and commercial
satellites.
dependence
al.
Reasoner
(1976).
shown
in
for satellite charging at geosynchronous orbit, as
Figure
19.
et al.
found by Reasoner
et
analyzed 40 days of data from ATS-6 with the results that
Significant charging
was found approximately 50 percent of the
time at geosynchronous orbit in the midnight to dawn sector on ATS-6.
12
06
18
00
Figure 19.
HOURS
I.
T
Local time distribution of ATS-6 spacecraft charging events. (Reasoner
et
al.,
1976,
Figure 7)
Figure 20
is
plotted against month;
pattern
is
not well
a histogram of
it
known
SAM
for all
anomaly records
in the
database
shows a curious increase during the equinox seasons. This
or fully understood.
It will
be found to be repeated
in the
consideration of individual satellites which follows.
2.
Solar Cycle Correlation
The
possible link between spacecraft anomalies and the 11 year solar cycle
can also be considered using the
NGDC
database.
43
The
NGDC
database provides
Spacecraft
count
Anomaly
By Month For
JAN
All Records
FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC
Month
Figure 20.
Monthly
a rough idea of
some
•
anomalies
how anomalies have
in the
SAM
database.
varied over the last two solar cycles. There are
In the early seventies, the anomaly data collection was
As time went
Data
still
in its infancy,
and
few data points were gathered.
by, there
were greater number of satellites on
ytheir anomalies to the
•
all
limitations:
relatively
•
distribution of
NGDC
database.
collection for this edition of the database
anomaly counts
1989, therefore, the
orbits that reported
in
was terminated
that year are
after April 19,
not useful for the
comparison.
Figure 21 plotted
and
it
There
all
shows two maxima. The
is
a
minimum from
reported anomalies of
1975,
first is at
NGDC database versus year,
and the second
In Figure 21, there
1977 to 1980.
of anomaly counts in two distinct periods.
The
44
first
period
is
is
is
from 1983
to 1986.
a definite decrease
from 1977
to 1980,
and
Spacecraft Anomalies
Count
700
n
All Records (Feb
1,
1971
Apr
-
19, 1989)
650
600
550
500
450
400
350
J
300
250
200
150
a
100
ilLLJ
50
72 73 74 75 76 77 78 79 80 81
71
82 83 84 85 86 87 88 89
Year
Figure 21.
Anomaly counts
the second period
is
in the
to 1990.
It
The anomaly occurrences
activities plotted in
SAM
Figure 22
at 1988.
numbers between 1971
1986.
per year
Figure 22.
database.
is
a plot of the annual average sunspot
shows two minima of solar minimum
in Figures 21
seem
to be lagging
1976 and
behind the solar
Careful comparison indicates a high degree of anti-
correlation between anomalies and sunspot numbers.
we might
in
expect, and needs to be reconsidered
when
This
is
contrary to the trend
the 1989-1990 anomaly records
are updated.
This relationship
Anomaly data
of the
is
GOES
further pursued by considering one family of satellites.
satellite series
anomaly occurrences plotted by year
mentioned
earlier,
data collected
in
were chosen.
Figure 23 represents
for the respective variants of
1989 only covered the
45
first
GOES.
quarter of 1989.
As
Annual Average Sunspot Numbers
180
1971-1989
160
140
lull
71
72
73
74
75
76
77
79
78
80
81
82
83
84
85
86
87
89
88
Year
Figure 22. The annual average sunspot number from 1971 to 1989.
Spacecraft Anomalies
GOI
4,5,6
and 7
Legend
GOES 4
GOES
5
GOES
6,7
w
82
Figure 23. Anomaly counts of
83
all
84
85
variants of
86
GOES
46
87
88
89
satellites in the
SAM
database.
Furthermore,
of them.
GOES-6 and
In Figure 23,
anomaly occurrences
the
GOES
results
anomaly
from the
at
-7 data
GOES
were plotted together because there were so few
series satellite
anomaly data show a minimum of
1985 and 1986. Comparison of Figures 22, and 23 shows that
distribution correlates to solar activity. This
total database.
is
in contrast to the
when data
This behavior should be reexamined
available from the high magnetic activity years
--
1990 and 1991.
Phantom Commands Due To Surface Charging
3.
Anomalies associated with surface charging events are
considered to occur from midnight to dawn. Reasoner et
et
al.
same
(1976) showed that phantom
local time pattern as
NGDC
shown
commands and
(1976), and
al.
satellite
earlier in Figures 18,
traditionally
and
McPherson
charging followed the
19.
The
initial plot
of
data (Figure 17) revealed that majority of anomalies occurred during that
time period.
satellites will
This relationship was utilized in
be focused on
time and month
dawn period and
will
this
same
this study.
Studies of the individual
period. Histograms of
be used to analyze
ESD
local time should
For
satellites at
show a
geosynchronous
local
related anomalies for the midnight to
relatively higher
concentrated in the period between midnight and 0600 hour
to ESD's.
anomaly counts by
also for seasonal dependencies in surface charging.
anomaly count versus
eclipse,
are
if
Histograms of
anomaly count
the anomalies are due
altitude, there are
two periods of solar
each lasting 45 days centered around the vernal and autumnal equinoxes.
The maximum period
of eclipse in one day can last up to 1.2 hours. (Agrawal, 1986)
47
Histograms of anomaly count by month might show an increase of anomaly count
in
these two solar eclipse periods for surface charging related anomalies.
a.
GOES
All reported anomalies of the
a total of 144 anomalies for the period from
by local time and month
in Figures
GOES
family in the
March 1981
to April 1989,
24 and 25 respectively.
observing the plotted data available for the local time analysis,
were plotted
In Figure 24, by
it is
clear that
from
GOES
Count
24
NGDC database,
By
-I
Local Time
22
20
18161412
108
|
6-
I
4
1
2
I
iLiiilJ
W W
00 01 02 03 04 05 06 07 08 09 10
11
ULa-J
1213 14 15 16 17 18 19 20
21 22 23
Local Time
Figure 24. Local time distribution of
all
GOES
anomalies.
midnight to 0700 there was a significantly higher occurrence of anomalies than for
any other time of the day.
(spring),
Figure 25 shows that in the months of March/April
and September/October
(fall)
anomaly counts were much higher than other
48
GOES
Count
By Month
JAN
FEB MAR APR MAY JUN
JUL AUG SEP OCT NOV DEC
Month
Figure 25.
Monthly
distribution of
all
GOES
anomalies.
months. Further considerations of these areas of peak
activity
was done by plotting
anomalies which occurred from between 0000 to 0700 local time of Figure 24 versus
month
in Figure 26.
It is
clear that the spring
and
fall
seasons, March/April and
September/October, have unusually high anomaly occurrences
midnight to dawn period.
patterns; reported
GOES
in the traditional
GOES family satellite anomalies exhibited the classic ESD
anomaly data
seasonal dependencies. There
is
clearly
showed the midnight
no obvious eclipse dependence
(i.e.,
to
dawn and
no increase
at
the 2300 or 0000 relative to 0200-0300 local time).
b.
GG0
The
next satellite considered here will be called
identity of this satellite
is
confidential.
Figure 27
49
is
GG0.
The
true
the histogram of anomalies by
GOES
Count
By Month
JAN
(00 to 07 Local Time)
FEB MAR APR MAY JUN
JUL AUG SEP OCT NOV DEC
Month
Figure 26. Monthly distribution of
GOES
GG0
Count
50
anomalies between 0000 to 0700 hour local time.
All Data
By Local Time
45
40
35
30
25
20
15
10
5
lUlUliLhll
00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23
Local Time
Figure 27. Local time distribution of
all
GG0
anomalies.
50
local time of
1989.
There
GGO which
has 429 data points for the period from July 1973 to
March
a relatively high anomaly count occurring between 0000 and 0400
is
local time.
Figure 28
is
a plot of the total
covers the period from February 1971 to
GGO
March
satellite
1989.
data by
month which
In this plot, the
anomaly
counts clearly shows a strong seasonal dependency, with peaks at April and October,
corresponding to the vernal and autumnal equinox periods.
GGO
Count
100
All Data, by
IS
fi
JAN
Month
FEB MAR APR MAY JUN
JUL AUG SEP OCT NOV DEC
Month
Figure 28.
Monthly
distribution of
Figure 29
restricted to anomalies
clearer seasonal
is
all
GGO
anomalies.
a histogram of the anomaly count plotted by
from 0000
dependence than
to
in
0700
local time.
Figure 29 shows a
Figure 28. This indicates that
51
month but
GGO
much
anomalies
from 0000
to
0700
local time (traditional surface charging)
dependence than the
set of
anomalies which include effects such as SEU.
GG0
Count
By Month, 00 To 07
JAN
have a stronger seasonal
FEB MAR APR MAY JUN
Local Time
JUL AUG SEP OCT NOV DEC
Month
Figure 29.
Monthly
distribution of
The nature
GG0
anomalies from 00 to 07 local time.
of the seasonal dependence (Figures 28, 29), can be
considered further. Figure 30 shows histograms of anomaly occurrences by local time
for April
specific
and October data so
that the midnight to
dawn
correlation of these two
months can be examined. Figure 30 shows a midnight
There are two other groups which are from 1000
They appear
c
to
be unrelated
to 1300,
to
dawn
distribution.
and from 2000
to 2300.
to the traditional association with surface charging.
GW0101
A
second confidential
satellite is identified as
reported 294 anomalies between January
14,
52
1975 and
GW0101. GW0101
November 26, 1976 (682
days).
GGO
Count
April and October Data, by Local
Time
Legend
April
October
04 05 0607 08 09 10
1 1
12 13 14 15 16 17 18 192021 2223
Local Time
Figure 30.
Figure 31
There
is
is
Local time distribution of
GGO
anomalies for April and October.
the histogram of the anomaly count by local time of the
data.
a distribution of anomaly occurrences which indicates that there were
anomaly causes other than surface charging,
anomaly count
is
A
high,
which
is
abnormal
for
i.e.,
ECEMP. At
ESD
2000
From
substantially higher than
all
GW0101 anomaly
this plot,
anomaly counts
other months; a
local time, the
induced anomalies.
histogram of anomaly count versus month of
plotted in Figure 32.
equinox.
GW0101
in
GW0101
data
is
March and April were
much lower peak
is
centered on the
fall
data show a very strong seasonal dependency, especially
around spring equinox.
Figure 33
plotted versus local time.
is
a closer look of the
A significant 61
March and April anomaly
counts,
percent of the total anomalies of 180 data
53
GW0101
Local Time
00 01 02 03 04 05 06 07 08 09 10
11
12 13 14 15 16 17 18 19 20 21 22 23
Local Time
Figure 31.
Local time distribution of
all
GW0101
anomalies.
GW0101
ALL
JAN
Figure 32.
FEB
Data, by
Month
MAR APR MAY JUN JUL AUG
Month
Monthly distribution of
all
GwOlOl anomalies.
54
SEP
OCT NOV DEC
GW0101
Count
15
March and
by Local Time
April,
14
13
12
11
10
9
8
7
6
5
4
3
2
1
00 01 02 03 04 05 06 07 08 09 10
12 13 14 15 16 17 18 19 20 21 22
11
Local
Time
GW0101
Local time distribution of March and April
Figure 33.
points, occurred in these
two months alone.
Even by
spring equinox, they do not produce the midnight to
expected
for
ESD
induced
anomalies.
These
environmentally induced anomalies other than
Note
dependence.
(Figure 22).
It
satellite (see
<L
that these anomalies
ESD
restricting the plots to the
dawn
distribution typically
distributions
suggest
that
can have a strong seasonal
were recorded during solar minimum
appears that a large percentage of 1975-76 anomalies were from
this
Figure 21).
METEOSAT
METEOSAT
total of 193
anomalies.
anomalies were described earlier
METEOSAT anomalies,
a 3458 day period between
May
4,
for
METEOSAT
-1
and
-2,
1977 and October 22, 1986.
55
chapter two.
A
were reported
for
in
Figure 34
is
the
histogram of the anomaly count by local time of
all
METEOSAT
data.
There
is
a
higher anomaly count period from 0300 to 0700 local time, and there appears to be
an approximately three hour delay from the
This delay was noted by
traditional midnight to
Wrenn and Johnstone
dawn
period.
(1986).
METEOSAT
Count
18 i
All Data, by Local
Time
16
14
12
10
8
6
4
2
-\
00 01 02 03 04 05 06 07 08 09 10
11 12 13 14 15 16 17 18 19
20 21 22 23
Local Time
Figure 34. Local time distribution of
A
third,
METEOSAT
There are two maxima located
an unusually high peak,
noted by Frezet
anomalies.
histogram of anomaly count by month of
plotted in Figure 35.
and a
all
et al. (1988); they
in
may be due
to
METEOSAT
at the spring
May. The spring and
fall
and
fall
data
is
seasons
dependency was
found that the anomaly pattern followed the
shadowing of the mirror assembly, indicating that
the seasonal effect
all
this
might be the cause.
shadowing patterns over the year for
56
Hence,
this satellite.
METEOSAT
Count
30
ALL
Month
Data, by
28
26
24
22
20
18
16
14
12
10
8
6
4
JAN
FEB
MAR APR MAY
JUN
JUL
AUG
SEP
OCT NOV DEC
Month
Figure 35.
Monthly
distribution of
Anomaly data
34 were plotted by month
also
two maxima
third peak.
in
in
METEOSAT
for the period
anomalies.
from 0300
to
0700
Figure 36 at March and September with
Anomaly data
local time of Figure
Figure 36 for seasonal correlation analysis. There are
for the period
34 were also plotted by month
at
all
in
May
between 1200 and 2300
Figure 37 for further analysis.
as the unexplained
local time of Figure
Two maxima
exist
March and October.
Anomalies
for
March, April, September, and October
in
Figure 36 are
plotted in histograms (anomaly count versus local time) as Figure 38 for the midnight
to
dawn
analysis.
Data
in
Figure 38 show a peak a 0600 local time. There four high
anomaly periods which are
Most anomalies occurred
at
in the
0300/0700, 1000/1100, 1600/1800, and 2300 hours.
period from 0600 and 0800 hour. Data in Figure 38
57
METEOSAT
Coun
15
By Month, 03
-
14
-
13
-
12
-
11
-
10
-
to
07 Local Time
1
9
H
B
8
7
6
-
5
-
H
I 1 1 1 1 1 I
1
4
H
3
2
1
-
KBBKKBBBB
m I
JAN
FEB
MAR APR MAY
JUN
JUL
wr
I
r
K
AUG SEP OCT NOV DEC
Month
Figure 36. Monthly distribution of
METEOSAT
anomalies from 03 to 07 local time.
METEOSAT
By Month,
JAN
FEB
12 to 23 Local
MAR APR MAY
JUN
JUL
Time
AUG SEP OCT NOV DEC
Month
Figure 37. Monthly distribution of
METEOSAT
58
between 1200 to 2300 Local Time.
METEOSAT
Count
15
March/April, and September/October
14
Legend
13
-
12
-
///<
March/April
igp September/
a&s October
11
Id
9
8
7
-
6
5
•4
3
2
1
••
•
000102030405060708091011121314151617181920212223
Local Time
Figure 38.
Local time distribution of March and April
shows a midnight
to
METEOSAT
dawn dependency; however,
anomalies.
the anomalies were occurring with
a three hour delay from the normally encountered local time distribution.
and Johnstone (1986) attributed
shadowing patterns.
In
this
summary,
to the
geometry of the
METEOSAT
satellite,
data showed that
its
Wrenn
and the
anomalies
exhibited a seasonal dependence, and there were other causes of satellite anomalies
beside ESD's illustrated by variations from the expected distributions in time and
season.
The seasonal dependence may have been due
to
shadowing of the mirror
cavity.
DSCS
As introduced
in
page 23, the
environmental problems. Figure 39
time.
DSCS
satellites
had a
is
total of
DSCS
satellite
the histogram of the
DSCS
system had many
anomalies by
local
128 reported anomalies, 125 of which were
59
DSCS
Count
13
All Data, by Local
Time
12
11
10
-1
9
8
7
6
5
4
-
3
2
luli
1
ill!
00 01 02 03 04 05 06 07 08 09 10
11
12 13 14 15 16 17 18 19 20 21 22 23
Local Time
Figure 39. Local time distribution of
all
DSCS
anomalies.
reported with the local time of the anomaly, for the period between
1973 and July
18, 1987.
In Figure 39, there
is
peak
at
2300
local time
Figure 40
DSCS
is
There are two
from October
to January.
distinct
peaks
The peak
at April
in April
may be
DSCS
is
a
satellites in
month
may be
October through
correlated to spring equinox as
associated with
DSCS
fall
equinox.
The
third
anomalies have a seasonal
from the solstice/equinox pattern found
for other satellites.
This could be due to illumination patterns which also vary with seasons.
60
for all
and August, and a third large peak
peak, from October through January, indicates that
differs
Also, there
the histogram of the anomaly counts by
previously found, and the August
dependence which
METEOSAT.
which may be eclipse related.
anomalies. Anomalies mostly occurred on
January.
22,
evidence of a three hour delay of the
midnight to dawn anomaly occurrences as with
significant
December
Monthly
Figure 40.
distribution of
all
DSCS
anomalies.
GPS
/
GPS are semi-synchronous altitude (approximately 20,200 km) orbiting
satellites.
The
and three
satellites in
operational constellation consists of 18 satellites in
each plane. The
in 1978; the design of block
out of 564
total,
two
first
block one satellite was launched
satellites started in 1982.
Among
the
GPS
data, 120
only 23 percent had been reported with a local time between
January 30, 1985 and July
17, 1987.
Figure 41
by local time. There are three maxima of
through 1900.
GPS
six orbital planes,
The 0500/0600 peak
analysis of these three
maxima were
is
is
the histogram of the
interest:
GPS
anomalies
0000/0100, 0500/0600, and 1600
the highest of the three peaks.
Seasonal
plotted but not found to be useful due to
insufficient data for the analysis.
61
GPS
Count
18
All Data, by Local
Time
16
14
-I
12
10
UlluijlldJj
00 01 02 03 04 05 06 07 08 09 10
11
12 13 14 15 16 17 18 19 20 21 22 23
Local Time
Figure 41. Local time distribution of
Figure 42 shows
October
6,
1984 and August
significantly larger than the
since local time
all
all
18,
GPS
564 reported
GPS
anomalies occurring between
1987 in a 1046 day period.
one used
was not available
anomalies.
for the midnight to
for all anomalies.
dawn
This data set
analysis in Figure 41
There are two peak periods
(January through February, and April through June) in Figure 42.
anomalies occurred during the
There are no obvious
GPS
anomalies
(at
to satellites at the
first
half of the year, but
signs of seasonal
dependency
is
Most of the
March was unusually
in this Figure.
quiet.
In general, the
semi-synchronous altitude) shows a different pattern compared
geosynchronous
altitude.
62
GPS
All Data, by
JAN
Figure 42.
4.
Monthly
MAR APR MAY JUN JUL AUG
Month
distribution of
GPS
all
Surface Charging and
A
nine
FEB
Month
GPS
anomalies.
July 1990 to
March 90 Data
July 89 to
survey of the anomaly logs for the
month period from
OCT NOV DEC
SEP
March
GPS
91.
system was conducted for the
These logs were obtained from
Captain Scardera of the 2nd Space Control Squadron, 2nd Space Wing Operations,
U.S. Air Force Space
induced
Command. The
"soft errors", requiring that
of the anomaly count versus
month
136 anomalies
memory be
for these
all
had the appearance of
reloaded.
GPS
Figure 43
is
SEU
a histogram
Block 2 anomalies. Unfortunately,
the April, May, June of 1991 data were not available for the analysis, and Figure 43
was unable
to present a full year data cycle.
in the fall/winter.
The anomaly counts
for
If
there
is
a trend,
GPS, semi-synchronous
it
is
a broad peak
orbiting satellites,
demonstrated that most anomalies were caused by other anomaly producing
mechanisms such
as SEU's.
63
The anomaly count
versus local time plot was not available since the
anomaly data provided did not include
recommended
satellite
that the local time of the
anomaly reports so
later analysis.
It
that these
would also be useful
local time information.
However,
anomaly should be included
anomaly reports would be more useful
if
eclipse/sun conditions were noted.
JUL
AUG
July 1990 to
SEP
Figure 43. Monthly distribution of
OCT
GPS
March 1991
NOV
Month
DEC
JAN
FEB
MAR
anomalies from July 1990 to March 1991.
64
is
in all future
GPS
By Month,
it
for
SUMMARY AND CONCLUSIONS
IV.
A.
SUMMARY
Various
of
aspects
shown
Studies have
anomalies.
space
the
environment can cause
on-orbit
satellite
between natural space
that adverse interactions
environment and space systems can have deleterious consequences comparable to
those caused by
human
or design errors.
Electrostatic discharge (ESD), electron
caused electromagnetic pulse (ECEMP), and single event upset (SEU) are the three
most
common anomaly
producing mechanisms in space systems.
environment, such as experienced
in
geosynchronous
charging of satellite components and lead to
Anomalies attributable
spurious signals,
in section
From
shown
ESD
G
loss.
on the surface of
known
to cause
Numerous examples
of
ESD
spacecraft.
command
errors,
part failure, and
related anomalies have
of chapter two.
the analysis, geosynchronous altitude satellites suffered anomalies have
local time (midnight to
data into histograms
anomalies
alone have been
can cause differential
phantom commands, degraded sensor performance,
even complete mission
been given
to
ESD
orbit,
The plasma
in
may be
dawn) and seasonal dependencies. Plotting anomaly
a viable
order to determine
if
method
to analyze
the anomalies
were
ESD
geosynchronous
related.
Once
satellite
the cause
of anomalies can be identified, then proper charge control measures can be included
65
in the future satellites designs.
same cause would be
Hopefully, anomalies of the
eliminated.
By using
Anomaly Manager (SAM) software package,
the Spacecraft
anomaly data of operational
Center
(NGDC)
satellites
spacecraft
contained in the National Geophysical Data
database were analyzed. Histograms of various anomaly data were
plotted by year, local time, and
month
for solar cycle, local time (midnight to dawn),
and seasonal dependencies.
Effects due to season
magnetic
tail
may be
and the neutral
related to the change in location of the earth's
During the equinox seasons, the
sheet.
satellite is in
the center of the plasma sheet, while in the solstice seasons, the satellite
may
rise
above or drop below the plasma sheet. (Nagai, 1987)
All
NGDC
reported anomalies were plotted by year in attempt to correlate
spacecraft anomalies to the solar cycle; data in the
NGDC
database had shown a
high degree of anti-correlation between spacecraft charging related anomalies and
sun spot numbers. Anomaly data of
the solar cycle correlation analysis.
GOES
It
satellites
were also plotted by year
was concluded that the
GOES
for
data exhibited
a high degree of correlation between anomalies and the solar cycle.
Next, data in the
NGDC database for six operational
satellites
were plotted
histograms, which displayed the anomaly count by local time or month.
that
It
in
was found
GOES family satellite anomalies showed a strong midnight to dawn and seasonal
dependencies.
The
GOES
patterns which imply
ESD
histograms exhibited the classic anomaly distribution
causes.
GGO
66
had 429 reported anomalies.
Analysis
revealed that most of
anomalies were attributed to surface charging which were
its
both local time (midnight to dawn) and seasonally dependent.
exhibits
some midnight
to
around March and April.
dawn dependency and
METEOSAT
For
hour delay for the midnight
to
anomalies, histograms showed a four
dawn dependence,
only one of the possible causes of anomalies.
dawn
to
seasonal dependence than the other
satellites.
at
the anomalies again
dawn, dusk, and midnight.
showed a
that surface charging
The DSCS anomalies showed a
hour delay from the normal midnight
showed peaks
GW0101
a strong seasonal dependency
METEOSAT histograms suggested
seasonal dependence.
Satellite
pattern,
was
three
and also showed a different
The NGDC's GPS anomaly data
No
obvious seasonal dependence was
found.
recent
Finally,
Command
GPS
for the period
anomalies obtained from the U.S. Air Force Space
between July 89
The anomaly data
dependency.
to
(primarily
March 90 were analyzed
SEU) showed
for seasonal
a modest fall/winter
enhancement.
B.
CONCLUSIONS
From
the anomaly analysis performed on the data of operational satellites
contained in the
Force Space
NGDC
Command,
database and recent
GPS anomaly
data from the U.S. Air
the following conclusions can be drawn:
Anomaly occurrence
patterns
imply they are caused by
ESD
show peaks
in the
midnight-dawn region which
induced by surface charging.
67
•
•
Anomaly occurrences caused by ESD's
ESD
are related to the solar cycle.
related anomalies are local time dependent with peaks in the equinox
seasons.
•
•
•
ESD
related anomalies are seasonal dependent.
Histograms are an effective manner to display anomaly occurrences for both
local time and seasonal dependency analysis.
SAM
is
an useful analytical tool which can quickly determine an anomaly data
anomalies are related to the surface charging mechanism.
set if the
RECOMMENDATIONS
C.
From
for future
•
the result of the
DoD
anomaly
geosynchronous
analysis,
satellites is
an active charge control requirement
recommended
as follows:
Proper engineering solutions should be integrated into satellite designs to
ESD from causing anomalies. This can be done effectively on multisatellite programs such as GPS.
prevent
•
Active charge control
is
recommended
tolerate functional anomalies
due
for all
to ESD's,
DoD
satellites
and on the
which cannot
first flight
of
all
new
Active charge control devices, such as a plasma emitter, can
satellite designs.
consistently maintain the desired spacecraft surface potential (Olsen, 1981).
•
Passive charge control measures, such as thicker shielding and electrostatic
recommended to be integrated into all satellite designs. Passive
charge control measures showed general success in all applications (Olsen et
cleanliness, are
al.,
1988).
Additionally,
it
is
recommended
that the Air
Force Space
Command
include local time, location, and sun/eclipse information of satellites
anomaly reports on
GPS
to the National
Boulder, Colorado.
68
should
when submitting
Geophysical Data Center
(NGDC)
in
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Electrostatics, Vol.20, pp. 21-30, 1987.
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Domestic Communications Satellites," Advisory Group for Aerospace Research &
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71
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%X\ 54 V
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Thesis
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Satellite anomalies and
electrostatic surface
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Thesis
W756 Wong
Satellite anomalies and
c.l
electrostatic surface
discharges.