(CME; ref. 1) exposed two substantially different collector materials to the hypervelocity particle environment on the Long. Duration. Exposure. Facility. (LDEF).
N95- 23833 "i
NATURAL ON LDEF'S
Friedrich
AND
ORBITAL
TRAILING
AND
DEBRIS
FORWARD-FACING
-41"?
)
.
-,
1'
/i="
SURFACES
Ronald
HiJrz
P. Bernhard
Lockheed Engineering & Science Co. Houston, Texas 77058 (713) 483-5018 / FAX (713) 483-5347
SN4, NASA / Johnson Space Center Houston, Texas 77058 (713) 483-5042 / FAX (713) 483-5347
Thomas
PARTICLES
_,
Donald
H. See
E. Brownlee
Dept. of Astronomy; U. of Washington Seattle, Washington 98195 (206) 543-8575 / FAX (203) 685-0403
Lockheed Engineering & Science Co. Houston, Texas 77058 (713) 483-5027 / FAX (713) 483-5347
ABSTRACT
Approximately 1000 impact craters on the Chemistry of Meteoroid Experiment (CME) have been analyzed by means of Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Analysis (EDXA) to determine the compositional make-up of projectile residues. This report completes our systematic survey of gold and aluminum surfaces exposed at the trailing-edge (A03) and forward-facing (AI 1) LDEF sites, respectively. The major categories for the projectile residues were (a) natural, with diverse subgroups such as chondritic, monomineralic silicates, and sulfides, and (b) man made, that were classified into aluminum (metallic or oxide) and miscellaneous materials (such as stainless steel, paint flakes, etc). On CME gold collectors on LDEF's trailing edge -11% of all craters >!00 lam in diameter were due to man-made debris, the majority (8.6%) caused by pure aluminum, -31.4% were due to cosmic dust, while the remaining 58% were indeterminate via the analytical techniques utilized in this study. The aluminum surfaces located at the AI 1 forward-facing site did not permit analysis of aluminum impactors, but -9.4% of all craters were demonstrably caused by miscellaneous debris materials and -39.2% were the result of natural particles, leaving -50% which were indeterminate. Model considerations and calculations are presented that focus on the crater-production rates for features >100 lam in diameter, and on assigning the indeterminate crater population to man-made or natural particles. An enhancement factor of 6 in the crater-production rate of natural impactors for the"forward-facing" versus the "trailing-edge" CME collectors was found to best explain all observations (i.e., total crater number[s], as well as their compositional characteristics). Enhancement factors of 10 and 4 are either too high or too low. It is also suggested that -45% of all craters >!00 I_m in diameter are caused by manmade impactors on the AI 1 surfaces. This makes the production debris, a factor of 40 higher on the forward-facing sides as opposed
rate for craters >100 lam in diameter, to the trailing-edge direction.
resulting
from orbital
INTRODUCTION
The
"Chemistry
collector
materials
(LDEF).
The active
that
collectors
the
deployment.
This
of Micrometeoroids to the
Experiment"
hypervelocity
experiment were instrument
particle
consisted
protected
of clamshell-type
against
exposed
(CME;
environment
-0.82
ref. 1) exposed on the
devices
contamination m 2 of high-purity
Long
two
that could
during gold
all
substantially
Duration be opened
ground
(>99.99%
Facility
and closed
handling Au)
different
Exposure and
on LDEF's
such LDEF
trailing
415
PRECEDING
Pp,:_- _, _.i..P,_ ,,o_
',',_ -.':
:L._:EF,
edge(i.e., Bay A03). The actualcollectorsconsistedof sevenindividual panels(-20 x 57 cm each;-0.5 mm thick). The Au collectorsexhibitedrelatively low craterdensities(refs. 1 and2) becausethe trailing edge inherently yields the smallestparticle flux (ref. 3) on a non-spinningplatform, and becausethe collectors were only exposedfor a total of 3.4 years (ref. 1). In contrast,the passiveexperiment continuously exposed,for 5.7 years,commercialgradealuminum surfaces(AI 1100 series,annealed, >99% pure A1) in the forward-facing,A11 location. Six individual panels(-41 x 46 cm, each;3.2 mm thick) provided-1.1 m2 of cumulativesurfacearea. The purposeof CME was to hypervelocity analyzing
craters. additional
craters
on the gold
above
some
craters
investigations
current
work
primarily
subclasses.
However,
the presence
determination
isotopic
detailed
analyses
populations
199 craters
surfaces
satellite larger
LDEF
was
stabilized
(ref.
(e.g.,.
The present
gravity-gradient
analytical
Compositional arranged type
effort
Initially
416
we spent
it was
found
craters
of some
organic-molecule
and
man-made
be
permits
the
aspects.
The
materials,
and
for the above
content
will
and forward-
detailed
particles
adapted
828 craters
procedures
objectives.
-- in principle (refs.
-- the
2 and 4), as well
(ref. 6).
However,
to the characterization
and
able
while
spin-stabilized
such
of entire
all
of the six A 11 aluminum
compositional
replacement
adds to these
to place
them
previously
satellites,
on four
particle
from the stratosphere
Mission
specifically
and by being
of projectile
and a LINK
at 90 ° to the beam
nature,
to all craters
findings
parts earlier
analyzed
LDEF
(refs.
offers
12),
or the
environment,
originated
potential
10), or of
by characterizing
dust
surfaces the
9 and
11 and
analyses
into a dynamic
classifications
(refs.
from
to yield
a since spin-
substantial
(e.g., refs. 3, 14, 15).
analysis
(SEM),
of these
make-up
dust recovered
Maximum
stabilized,
Unlike
and
-200
Unquestionably,
in many
natural
via
refs. 4, 5, 6, 7 and 8).
ANALYTICAL
Microscope
some
on the Au-collectors the
Station.
with and sufficient
that they are not readily
as Solar
of events
information
within
and mineralogical
of interplanetary
such
13).
number spacecraft.
directional
followed
the analysis
into
consistent
refer
the
on the trailing-edge
incomplete
with
analyzed
The results
Mir or Space
particles
(ref. 5) and potential
analyzed
space-retrieved
fragments
chemical
are so time consuming
we
the
are qualitative,
of unmelted
and projectiles
during
much
to classify
characteristics
In general,
Palapa
attempts
associated
1 and 2) primarily
Therefore,
size that impinge
and remain
residues (refs.
systematically
surfaces.
materials.
such as LDEF, nature
the
reports
We now have
host
threshold
on
progress
on the aluminum
respective
spacecraft,
of craters
We have
the
than some
Our analyses
of the detailed
as their
developed
larger
information earlier
collectors.
craters
on
are of a survey-type
associated
panels.
size
of a non-spinning
current
compositional
complements
and -800
crater
for particles
surfaces
obtain
report
on the A 11 aluminum
substrates
arbitrary
representative facing
The present
path.
considerable that
eXL
METHODS
residues Energy
Although efforts
an uncomfortably
was
Dispersive
AND
conducted
using
X-Ray
(EDX)
we characterize in optimizing large
FINDINGS
fraction
an ISI-SR50 analyzer
our analyses the signal
Scanning a Si(Li)
as qualitative
to noise
of craters
using
yielded
ratio
and of a survey-
of the
spectra
Electron detector,
X-Ray
that
spectra.
contained
no
detectablesignalabovethat of the background. Therefore,we useda numberof cratersto investigatea rangeof electron-beamgeometries(diameterandtake-offangle),low- andhigh-beamvoltage,andwidely variablecounttimes (minutesto hours). Fromtheseeffortsit wasdeterminedthat a relatively high-beam voltage(25-20KeV) andlong counttimes(500-1000seconds)with the specimentilted at 30° yieldedthe best results. It is our belief that high-beamvoltagesare best becausethe surfacerelief of the crater interiorstendsto be unevenpermittingexcitationof morenear-surfacespecimenvolumecomparedto less penetrative,low-energyelectrons. Count times in excessof 1000 secondsdo not appreciablyimprove signalto noiseratiosanddo not warrantthe additionalexpenditureof resources. Contaminationof our surfaceswas not a significant problembecausethe compositionof common contaminantsdiffer dramaticallyfrom many projectile residues. Nevertheless,we have observedSi-Ca rich deposits in some crater interiors that, presumably,were derived from outgassedRTV (ref. 16). Interestingly,suchdepositscanhavedistinctlyasymmetricdistributionsin somecraters,substantiatingthe macroscopicLDEF observationsof highly directionalflow of gaseouscontaminantsandtheir condensates. We also observesome intrinsic, heterogeneouslydistributedcontaminants,the result of manufacturing proceduresin our collector materials,mostnotably as in the gold andSi in the aluminum. The anodized layer
on the aluminum
consideration. Si, Mg,
Fe, as well
population
The sources The
natural
coatings
for colliding
and
fragments
only as melts; large Fe-Ni them.
of olivine particles
sulfides
grains,
The "orbital-debris" Ti-C1 rich residues originating
from
aluminum
above
category
"aluminum"
cells
only,
particles
protective
only
be detected
is not amenable
particles of category
had
of thermal
will
be
solid
referred
amounts
was
used
of
in the
waste
found
made
were
to as "miscellaneous"
form,
but
analysis. debris,
on
matrix
and
or oxidized.
and their
wellby
occurrence
high
occasion
suggesting
stainless
hardware,
14).
are found,
melts/glasses,
yet that
attached
steel,
(3) Ag, Cu, or Pb-Sn
metallic
compositional
up of relatively
chondritic
and
of thermal
characterized
representing
of spacecraft
dust,
in LEO (ref.
rich particles
chondritic
paints,
ablation
dumped
in molten
fine-grained
spacecraft
or "man-made".
from explosions
bums,
silicates,
rich particles
they
into
or interplanetary
result
rocket
that are largely
on the gold collectors to direct
dust,
particles
and human
some
significant craters
"natural"
(3) Fe-Ni-sulfide
components whether
cosmic
with minor
(1) Fe-Ni-Cr
electrical
are either
Monomineralic
are preserved.
was taken
from this report).
are mostly
associated
in meteorites,
specifying
could
erosion,
contained
or other
of these
The man-made
(2)
particles
and pyroxene
contained
(LEO)
into (1) chondritic,
these
analyzed
of satellites,
oxygen
from this source
that none
as micrometeoritic,
matrices.
without
substrates 1-3
atomic
common
orbit
products
are frequently
impacts
solar
impactors
facing
Fe;
characteristic
aluminum
aluminum
and
crater
were excluded
(ref. 10).
fragmentation
fine-grained
these
every
but background
to the degree
are described or asteroids
can be subdivided
of Si, Mg,
E00H
in low-Earth
collisions,
homogenized,
to plate,
(i.e., these craters
comets
particle
particles
plate
contaminants
encountered
small
concentrations unmelted
from plate
projectiles
and the associated from
contain
below
from either
"Natural" mixed
as other
studies
particles
and originate collisions,
varied
On the A11 aluminum
and
particle
surfaces
to
(2) Zn-
rich residues
(4) particles
that
Obviously
such
on the forward-
Throughout as opposed
this report, to the
the pure
4.
417
For many natural
individual
dust grains
crater
melts
craters
(e.g.,
was
observed
residues,
Generally,
this melt variability
the same
classification
x-ray
or pyroxenes)
as well,
unmelted from
one may obtain
olivines
suggesting
the
with
the largest
presence
relates
spectra variations
Nevertheless,
into natural
and man-made
this particle
mixed
elemental
specimen
specific
However,
occurring
of incompletely
to subtly different
specimen.
that reflect
and their mixtures.
in those
mineral
and
that
(refs.
different
is slight
minerals
within
craters
melts
ratios among
heterogeneity
component
variability
contained
17 and
spectra
does
of
the pure
not
18).
obtained affect
our
sources.
RESULTS 45
A03
Trailing
Edge
40 23
35
Most this
summarizing
report
earlier with
are
updates
in
of
yet
statistical
with
Figure
all analyses
plots
the
Stainless
25
[_
Paint
60
•
Natural
112
•
Indeterminate
to date
the
_¢_
0 10
20
from
Figure
All _
by natural,
for
-68% on the gold and 77% on the aluminum collectors. It is
80
particles
160
320
640
1280
accounting
160
320
640
1280
Facing
_[]] Electrical
13
[]
Stainless
41
[-]
Paint
286
_
Natural
287
•
Indeterminate
cosmic100
Forward
16
160 140 120
dust
80
180
particle
1 that the majority of craters that contain identifiable residues caused
40
relative
of the major
We conclude
were
Steel
15
1
=_
types.
[]
1
number-frequency
illustrate
frequencies
]]_] Electrical
1
2O
of recognized projectile types versus crater size. The intent is to
2
increased
significance.
summarizes
2), in
Aluminum
30
our
progress report (ref. minor modifications
substance,
and
figures
I
Steel
60
equally -50%
important to of all craters
contain to
sufficient
be
and
residue
analyzed
methods
by
(also
8).
see
Most
structures are set of craters
note did
mass
our
refs. likely
that not
2, 5, 7 these
a velocity-biased with encounter
sufficiently
eject
or all of the projectile
melts
from
cavity
(ref.
418
the
growing
20
SEM
velocities most
40
high
to
crater
19), if not as vapors
0 10
20
40
80
Crater Diameter
0tm)
Figure I. The analysis frequency of man-made and natural impactor residues detected on the trailing-edge (A03) and forward-facing (All) CME surfaces. Note that aluminum impactors cannot be detected on the All aluminum collectors. The indeterminate population of craters either contained insufficient projectile mass to be detected by SI'M EDX methods (predominantly) and/or material that was categorized as contamination (only a few cases). The smallest craters on both surfaces are a representative sample only, and not a complete sampling (see ref. 2).
(e.g.,
refs. 2 and 5), or they are the result
particles
?) that are easily
The man-made 23 aluminum
A11
aluminum
detectors
are totally
dominated
versus
4 miscellaneous
particles collectors
do not permit
are of the "miscellaneous"
stainless-steel
particles
note the dominance
of paint
paint
was
the
flake
identified
on
flakes
investigators
from
their results
(refs.
various
on
the
Specifically,
2 and
CME
essentially
by definition.
components
on the forward-facing
include
surface
on these
41 paint
E00E,
flakes,
E00F
13
and E00G.
(41 craters),
whereas
Trailing
Edge
only
1
Natural +
10 2
Man Made Indeterminate TOTAL
01
confirmed
(ref.
1,
Z
10 o
by others
o I
>30 _tm and >75 pm
in
on
aluminum
the
appear
population.
Smaller
in the data of
the
3.5 years
years
for the aluminum
and
than
and
surfaces the
the
trailing-edge
rates
I
I
Ill
I
l
I
I
I
l
II
3
IO
AI 1 Forward
10
Facing
10 2
10 I
[ref. to
"----0---- TOTAL lif t
I
tl
10
I
I
I
I
IIII
l
i
i
i
t
'
I
Ill
l
I
Diameter
I
l
I
I
I
I
4
1¢ Crater
forward-facing
illustrated
Indeterminate
5.7
analysis
surfaces
as
i
10 o
10
0tm)
as
illustrated in Figure 1. It is much more instructive to consider craterproduction
l
some
it is not possible of
I
crater
the absolute
for the gold
compare
frequencies
10 3
I
2
are merely
larger
(i.e.,
directly
I
opu
given size depends on total exposure time of the two collector surfaces
Therefore,
IIIII
craters
small
In addition, of craters
I
respectively,
investigated.
number
gold
surfaces,
representative
I
10
on in
that all craters diameter
I
of the crater
populations that were analyzed the two collector surfaces differed
and
particles
man-made edge
The size distribution
1]).
These
on components
A03
_
(ref. 8).
which
all man-made
forward-facing
collectors.
of
on the trailing
15) was
were
and
gold surfaces,
that the
and
somewhat
presence
impactors
of aluminum
however,
with those
the
surprising
low-density
on the trailing-edge
Note,
4, 5, 6,
surfaces
are consistent
observed
porous,
10 3
7 and 8) have analyzed projectile residues associated with LDEF craters
(e.g., highly
particles
impactors).
of electrical
edge.
Other
properties
by aluminum
recognition
category,
and 16 fragments
In particular, trailing
projectile
vaporized.
sources
(i.e.,
of unusual
in
Figure 2. The crater-production rates on LDEF's trailing edge and the AI 1 location by both natural and man-made impactors. Again, note the substantial population of indeterminate craters. Also note that total production rates on these CME surfaces are akin to those of refs. 20 and 21, as summarized in Table 1.
419
Figure crater
2, which sizes
corrects
(e.g.,
ref. 3).
and the inability slope
Table
significant;
facing and
considering
surfaces
were
1100 series
sizes,
as is the CME
the vastly
production
is substantial,
size
are
aluminum
clearly
collector
rate for craters higher
than
consequence
crater
of
among
Humes
the CME
Our
sampling
lower
for craters
DIAMETER
>50
with our
this
is somewhat The
See et al.
See et al. is good data
from
at all
100 _tm to 500
as -20%.
CME 100
TRAILING Total
420
them
of Humes
and
are not
orientation
aluminum).
or See et al. by as much
uncertainty.
CRATER
1100
yet
in the case
in
plates.
>I 0
the oxide
changes
plots.
For the A03
others,
Table I. Crater-production rates (N/m2/y) for select crater sizes on CME's trailing-edge forward-facinl]/A! I i 52°offof LDEF's leading edge / aluminum collectors.
and
subtle
yet such differences
(i.e., gold versus
lam in diameter;
of Humes
statistical
those
6061-T6
Agreement
of incomplete
craters/projectiles
Also,
classes,
of identical
from Figure 2 and compares
with
substrates
>1000
those
of indeterminate collectors.
See et al. (ref. 22).
aluminum,
surfaces.
comparison
error bars on these cumulative
agreement
of anodized
for direct
fraction
that were extracted
in excellent
it is still within the
large
statistical
rates
different
permits
on the aluminum
(ref. 20 and 21 )and
for the CME
are modestly
difference range
are
and
for the different
we avoided
all composed
aluminum
lam in diameter
particles
are observed
of Humes
rates
histories
the unfortunately
crater-production
rates
crater-production
fortuitous
again
for clarity,
1 lists specific
exposure
for aluminum
size frequency)
the crater-production total
Note
to analyze
(i. e., relative
statistically
for different
on cratering
theory
differs
in strength
between
aluminum
(refs.
19, 23) and
Also note the differences between surfaces of Table 1 were anodized;
affected
gold is so ductile
which
many
of the small
that the crater
craters
size resulting
in our from
a
given our
projectile total
(ref. 1) is (fortuitously)
crater-production
others.
Furthermore,
(depending direction.
is new
craters
size;
of these
particles
6-10 higher
to that of aluminum and
A03
crater-production
see Table
work
Those
diameters
analyzed.
for the A11 direction
CME
19, 23).
surfaces
surfaces
is that we can assign by natural
Typically,
1).
compared
on the
(ref.
are consistent
forward-facing
produced
by 2:1 (see Table
locations
rate
1) on the
to the present craters.
at all crater
orbital-debris
similar
for the A11
total
and unique
to -50%
debris
the
on specific
What origins
rates
cosmic-dust
The production
the observations
compared
impactor
craters
consistent
of
higher
trailing-edge
compositions
frequent
outweigh
than
those
cratering
speaking,
of-5-7
to the
are more
rate of natural
to the A03 location,
generally
with
is a factor
specific
impactors
Very
events
and orbital-
produced
by
is a factor
of
with (ref. 3).
INTERPRETATIONS
Particle
As previously
discussed
the hypervelocity diameter
environment
to particle origin
given
velocity,
damage
and
projectile
risks
that
the
model
generalized
conditions.
basis.
This
conversion
of a measured
cratering
to particle
studies,
mass
when
kinetic
crater
reader,
at present
at a
collisional
diameter
to some
one for collisional
as well as some
is not possible
crater directly
energy,
estimating
and the most critical
the general
from
not only relate
some
of particles
we remind
way to characterize
conversion
size and mass
population
The
part of LDEF
diameter
Particle
and useful
but it is the only way of assigning or to some
However,
of a crater
general
or mass
of this section.
particle
and management.
major
insights.
collector
debris,
assumptions
for aluminum
empirical
were
respectively.
The
We used
Projectile
except
resulting
projectile
rates
in the cratering
from
for such
17.9 which
2.
and
by definition,
(ref.
and
1.75 km/s
km/s
(natural)
of our peers,
without
range their
substantial
Projectile
(ref.
particles
(man-made)
for the
to be 2.7 g/cm 3. Most
substantial
effects
(refs.
the
of these
cratering
1) as the
velocities,
15) for natural
and man-made
7.8 km/s
(ref.
basic
normal
and
to
man-made
respectively All
on
aluminum
assumptions
19 and 23; i.e., factors
are
of 3-5 in
of densities).
fluxes only those
their
we used
in gold
results.
Kessler
for natural and
Principally,
experiments
identical
3) and
was assumed
will have
Obviously,
a plot, because
dedicated
essentially
Zook
for a reasonable sizes
ref. 2 for details).
own,
yield
for all impactors
Figure
equations;
(see our
from
12 km/s
density,
masses
be considered
23, and
and
density
projectile
production
as follows
adopted
collectors
constrained
resulting
are of ref.
Use of Ref. 19 would
surface,
trailing-edge
surfaces. well
under
(ret_ 2), the most
is on a particle-size
processes,
to a single
conversion
Our
the
and formative
And Fluxes
assumptions.
equations the
in space
size and mass is a crucial
risk assessment
report
size will be the subject
to a particle's model
in our earlier
Frequency
man-made
indeterminate
are
presented
craters
which
versus
natural
craters
possess
in Figure have
3,
along
identified
origin
provides
unknown
with
projectile
the residue
the impact
encounter
crater can
velocity
velocities
and
421
require
additional
below)
to
assumptions
(see
converted
into
be
associated
impactors.
calibration
simply
!0 z
A03 Trailing
Projectile solves
for
some 101
velocity dependent constant with which the crater diameter relates to the impactor unit crater impactors than
the
made
(Dcrater=K*Dimpactor).
size
are
from
fast
substantially
crater
slow
The to
size can lead to seemingly results. Note that the are
natural
ones
less
-----E]-- Natural
man-
--O-10 l
projectile
on the trailing basis,
•
E]
Man Made --O--l
t
l
flail
l
l
l
t
lllll
I
I
I
llllll
Id
I
I
I
I
IIII
10 3
I0
lozl 0
Z
than edge,
l
----I--
101
confusing man-made
abundant
on a projectile-size
!0 °
conversion
diameter
craters
At natural
smaller
comparatively
particles.
Edge
_II
Forward
Facing
yet =
the reverse
lO t
applies, and man-made particles (of very slow velocity) become more abundant than cosmic dust.
Thus,
(high
we re-emphasize
2) that great discussing
care of
natural relative from
on
versus LDEF.
absolute
an
(Figure
analysis 1), from
projectile relative
sizes
frequency
basis
a crater-productions
frequencies
are the result Table
Debris
dominates
trailing
edge,
whereas
particle
size;
man-made
diameter much
dominate between
422
and cosmic can
(by some
debris
and projectile
fluxes factor
for the
debris
l
IIIIII
l
category
sizes
a particle-flux constant.
l
*
llllll
l
*
l
lllll
10 _
velocities.
for some
typical
to become at particle
forward-facing at all sizes,
basis
10 _
projectile
in similar
typically
and the A03 trailing-edge
of 500
1.65 ? 0.68 ?
These
in highly
were
vastly
now a complete
used
indeterminate
low speeds
impactors
more favorable,
rates
(that
agree
with others
population;
the
CME
rates
scenarios high
and man-made
were
neither
indeterminate
to their
this argues
Population
to the man-made
roles of natural
analytical
et al.,
particles
by
crater
Kessler
that
population
to
impactors.
total crater-production
and
on
database,
the possible
the relative where
use our
constraints
around
Crater
on the trailing
by Kessler debris
as contributors
or man-made
In evaluating
for
comprehensive
revolve
gold surfaces, also
modeled
account
A11
(AI I)
7 ? 2.8 ?
?
The Indeterminate
elliptical
value
(A03) and forward-facing
(A03) 0.29 0.98 9 0.98
FACING
66
particles
with
DIAMETER (Ittm) >50 >!00
FORWARD
of orbital-debris
side for small
At face
category,
on the
to the miscellaneous
directions.
20.5 14 1.6 12.4
Total Population Natural Man Made Miscellaneous Aluminum
particles
on the forward-facing
miscellaneous
in the forward-facing
>5
findings
our forward-facing
surfaces
Table 2. Flux (N/m2/Year) of known particles of select sizes on CME's trailing-edge collector surfaces.
The presence
between
aluminum
and trailing-edge of-20
for particles
distributions
abundant
not detect
of forward-facing
The latter has an enhancement
size-frequency
relatively
among
that we could
our comparisons
l.tm in diameter)
variable
effects
directions.
reemphasize
this restricts
debris
size-dependent
of our
scenarios
are presented, craters
encounter
on
the
(Table
labeled
S1 and
velocities
on the gold and should
and
1) are modestly
be quantitatively
will
$2 in Figure surfaces loss
Au substrate.
22])
4. are
to form
higher
tolerate
than
the
The
All
We
rigorous those
of
formation
first
caused
of impactor.
accounted
on the trailing-edge
pure
20, 21 and
below)
gold
associated
rely
a >99.99%
[refs.
(presented
trailing-edge
we heavily
having
by
of
scenario
(SI)
natural
dust
debris
impacts
for, as well as categorized
423
as either aluminumor miscellaneousdebris. In addition,we postulatethat the crater-productionrate by cosmic-dustparticles(ref. 3) on the forward-facingsurface (-52 ° off the actual leading edge) is a factor of 6 higher
than
on the trailing
aluminum
and miscellaneous
aluminum
surfaces.
edge.
Scenario
debris
1
2OO
2 ($2) follows
materials
Ref. 15 and transfers
of the trailing-edge
Aluminum
Observed
Scenario
I
frequency
of
to the forward-pointing
Indeterminate
Natural
Scenario
(S 1 )
_,
the relative
gold collector
2
(82)
180
.... 168
160 ,,m
A
140 86
¢_ ;_
120
_ o_--,
100 80
93
1,1
_"
60
t_
_
40 ---17.5
20
10.1
15.6
0 A03
Figure 4. categories instructive
of these
>100
model
calculations
lam in diameter.
are visualized
This diameter
was
surfaces.
We note that Scenario
1 yields
identified
craters.
the remaining
known
to have
aluminum The facing
This relegates resulted
category
overall
-35%
ratio
from
miscellaneous
of man-made
orientation.
Thus,
feature
site with a debris for aluminum
and
origin.
We have
miscellaneous
-74 debris
dust
location
particles
of Scenario
chosen
A03
-55%
done
facing location. Using the above ratio, total of 59 aluminum craters for A11.
in Scenario of all craters
A11
well
(best)
(15.6 leaves
represented
58 craters
on both
(74-16)
-0.79
for
CME
to the 66
16 of which
are
in the pure
to miscellaneous
1 is (74:94)
debris.
for the
to be due to natural
forwardimpactors,
debris.
of indeterminate
2) from
rates
compares
man-made,
of aluminum seem
production
x 6), which
as being
the observed
see Table
the observed
by miscellaneous
a complement
this by transferring (1.5:0.4;
This
ratio (58:16)
are caused
2 is to first associate particles
craters (168-94)
materials.
impacts
and -10%
4, using
as being
craters
and an -3.6:1
to natural
for the A11
in Figure
a total of 94 natural
for the A11 surface,
are due to pure aluminum
The main
424
A11
Visualization of the model calculations (S 1 and $2) presented in the text. The numbers associated with the various projectile refer to the number of craters produced by such impactors. We found illustration of the absolute production rates more and more easily related to Table 1 than normalized fractions and percentages.
Results craters
A03
A11
craters
crater-production the trailing
edge
on the A11
ratio to the
of-3.75 forward-
one associates with the 15.8 miscellaneous craters (15.8 x 3.75) a This result is virtually identical with Scenario 1, albeit by totally
fortuitous
coincidence.
that seem numbers:
compatible
1) Note
It nevertheless with
that our production
the values
(-140)
modest
changes
impactors
changes
in the relative
observed
by CME.
Scenario
1 totally
2)
between
trailing-edge
for craters
results
of 150 natural
for aluminum
natural
craters
that Scenario Based
caused
of man-made (1.9:17.5)
natural
crater-production
edge
compositional
observations.
will precipitate
Any
very specific
It must be emphasized in Table
aluminum
2 the
seems
difficult
While compare
we have
rates.
and constraint. will be needed indeterminate
crater
to approximate crater
category.
rate
that our own (Table This
1, and leaves
of 4 between particles,
factor
trailing
because were
factor
virtually
that an enhancement
factor
and
edge
of and
not enough
observed).
Note
natural
(1.5:0.4)
diameter
particles
man-made
2. from
the total observed
diameter
depends
on both
fractions
of man-made exceed
particle
the scope
be done the size
craters.
way
5.6 (3.9:0.7)
impactors
scales.
with
craters
indeterminate
considerations
and velocity,
it
to ultimately
only
of the
The
Therefore,
at millimeter
proper
population
and natural
value
here.
particles,
at present
above
the
specific
particles.
Deconvolution crater
the A03
> 100 p,m in diameter. of small
impactors
are the only
Table
differs
population
_tm in diameter
this can
3 and
yet any
only for craters
edge
accommodate
and preferred
I.tm in diameter
or mass
populations,
to
8 is viable, advocated
is 0.109
The trailing
too
low
could
a mixture
craters
of 6 on the A11 versus
in the
for >100 versus
represents
natural
factor
5 and
for the >10
of natural
surface versus
edge
seem
are valid
the actual
Such calculations
on the trailing
A11 location.
from those
impactors
as in Figure
4
between
conclusions
from having
population
of man-made
while
that differ
particle
crater
by some
high, factor
is 3.75
impactor
such
benefits
Note
we suggest
enhanced
of aluminum
that
into man-made The latter
substantial population(s)
is 9.6 (168:17.5).
for the forward-facing
too
populations
frequencies
different
residues,
Because
seems seem
ratio
above
1, and
here is that
of 6 in the crater-production
x 9.6) for Scenario
fraction
and 8.6 (10.3:1.2)
the relative
the
identifiable
population
production
debris particles
impactor
that of the forward-facing
average
enhancement
increase
argued
and quantify
containing crater
to infer
whereas
again that the above
to miscellaneous
natural
too low for natural
(74:168)
10
particle
steady
for >50 p,m in diameter
of
in Scenario
The point
15.6 x 9.6 = 62, yet 66 craters
Total
particles
factors
only be accommodated 2.
orientations.
that the indeterminate
and 0.44
rate by natural
enhancement
seems
impacts,
impactors.
for the trailing
(15.6
than
by this consideration.
we conclude
by cosmic-dust
and
LDEF
an enhancement
(i.e.,
2 is unaffected
on the foregoing
be entirely
result
factor
results
to the detailed
higher
rate can precipitate
versus
As a result,
hand,
surface
would
58 to -30)
93 to 65 in Scenario
_tm in diameter
impacts
impactors.
On the other
the A I 1 forward-facing
projectiles
yield
apply
is somewhat
could
(from
scenarios
caveats
The latter values
crater-production
>100
two
on the A11 surface
of man-made
and forward-facing
different
However,
on the enhancement
factor
10 is too high.
Note
in the total
depends
in a total
from
frequency
1) enhancement no room
surface;
the aluminum
the natural
dramatically
populations.
20, 21 and 22.
decreasing
by decreasing
that the two
crater
rate of 168 craters
of Refs.
by substantially relatively
shows
the observed
of crater-
as a firm upper repetitive responsible
limit
iterations for the
of this report.
425
For the time being made
objects
should
be increased
All,
following
natural particle
relative
on
miscellaneous
flux of-1000
3.
3.
and suggest
trailing-edge
by factors
Scenarios with
of
the
3.75
1 and
missing
fluxes
roles of natural
on the Chemistry
that the particle
surfaces,
and
that
flux for manthe natural
By the same token,
observed)-
flux
the flux on
of 1.4 (94natur_a, modeled:66natur_, observed) for
2 leave
the
aluminum
(59aluminum,
Our modeled
the relative
craters
be increased
deal
factor
in Figure
rates
for the
of 2.8 (15.6natural modeled:5.5natural should
largely
is a
about
correct
to Figure
and
All
the best estimates the analysis
factor
S1 scenario,
untouched flux
crater-production
3 is essentially
by some
the
impactors,
essentially
we use the above
in Figure
miscellaneous
category
on
modeled:15.8miscellaneous,
are summarized and man-made
of Micrometeoroids
A11.
observed)
in Figure impactors
debris
5.
category
The
aluminum
higher
than
These
fluxes
that could
the
represent
be extracted
from
Experiment.
10 a
A03 Trailing
Edge CONCLUSIONS
10 2
'_
10 _
We
have
chemically 10 o
and
projectile Modeled
of 10 "1
i
i
•
•
•
.,.i
|
|
i
|
¢ |..|
101
,o°
.
.
•
•
.
...
All
Forward
LDEF 10_
of
101 Modeled Modeled
Natural
,
,
,
, , ,,,|
|
.
.
. ....,
10 ,
Projectile
.
,
1o_
Diameter
10
(lam)
Figure 5. Particle-flux curves that would result from our models (see text), which represent the best estimates about the relative roles of natural and man-made impactors based on the analyses of -lO00 craters on the Chemistry of Micrometeoroids Experiment.
426
of electronic
man-made
impactors
devices
are significant
is approximately
as well. half
that
of natural
-50
motion)
the
in
The
by mafic
Man-made
impactors
by
aluminum
pure
population preferentially
surfaces,
while
rate of craters
particles
in the
steel
trailing in
particles
compositions,
Fe-Ni-rich
impinges
ref.
consists, of
silicates
and
(see
the
population
pyroxene)
in
forward-facing to
bulk
rate
is a factor
abundance,
chondritic
of the lam
lam deep
a
-52 °
production >100
compared
substantial
The production
craters
6 higher
followed
. . . ...
The
and
(A11;
of
with 10
edge
particles
decreasing
]0 !
of orbital
and
edge.
10 °
Experiment,
24) due to natural direction
Man Made ----o----
Chemistry
direction
impact
the
in -1000
the
trailing
satellite.
diameter
by
the
off the plane
Facing
on
Micrometeoroid
forward-facing
103
fragments
remaining
craters
representing
I0 _
10 z
qualitatively
residue
individual
Man Made
characterized
(olivine; sulfides.
are
dominated
particles; of paint
a flakes
on the
front
particles
and
> 100 _tm in diameter forward-facing
(All)
direction, made
and -10%
impactors
Although present
is a factor the
unexpected
for the trailing of-40
activity
provides
will hopefully hazard.
between
trailing
lead to some
in the
further
on the
revision
most
difference
in the crater-production
and forward-facing
impactors
the statistically
assist
The absolute
of man-made
and has already
report
edge.
trailing
edge
of the particulate
significant
refinement
pointing
is modest,
of LDEF. it was
environment
in LEO
of particle
compositions
compilation
of environmental
directions
rate by man-
models
and
the
nevertheless
(ref.
15).
The
to date.
associated
It
collisional
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