Natural and orbital debris particles on LDEF's trailing and forward ...

2 downloads 18 Views 973KB Size Report
(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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