airborne dust investigation

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15 Νοε 2013 (πριν από 3 χρόνια και 11 μήνες)

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MICROMED:

A compact dust detector for Martian
airborne dust investigation

3M
-
S3
-

Space Research Institute Moscow, Russia

October 8
-
12, 2012


F
.

Esposito
1
,

C
.

Molfese
1
,

F
.

Cortecchia
1
,

F
.

Cozzolino
1
,

S
.

Ventura
2
,

F
.

D’Amato
3
,

L
.

Gambicorti
3


1



INAF

Osservatorio

Astronomico

di

Capodimonte,

Naples,

Italy
;

2



ESA

ESTEC,

Noordwijk
;

3



Istituto

Nazionale

di

Ottica
,

Florence,

Italy


The

scientific

goal

is

the

characterisation

of

airborne

dust

properties

close

to

the

Mars

surface
.


Measurements

concerns

the

following

physical

quantities
:



Atmospheric dust particle size
distribution (single grain detection)




Number density of particles vs.
size




Time evolution of the former
quantities, vs. short term variations
/ local events (e.g. wind, dust devils,
dust storms)

MicroMED:

Physical quantities to be measured

Martian

atmosphere

contains

always

a

significant

load

of

suspended

dust


Airborne

dust

has

important

effects

on

morphological

evolution

of

the

surface
.


Aeolian

erosion,

redistribution

of

dust

on

the

surface

and

weathering

are

mechanisms

which

couple

surface

and

atmospheric

evolution
.

Dust in the atmosphere of Mars (1/10)

The

exchanges

occur

in

the

planetary

boundary

layer,

i
.
e
.

the

turbulent

region

from

surface

to

a

few

hundred

meters

height
.

Moreover,

airborne

dust

severely

impacts

on

the

climate

of

Mars,

influencing

the

thermal

behaviour

of

the

troposphere
.




Indeed,

dust

absorbs

solar

irradiation

mainly

in

the

VIS

(re
-
emiting

it

in

the

IR),

locally

warming

the

troposphere
.



Even

in

case

of

moderate

dust

scenario,

the

influence

of

dust

on

Martian

thermal

structure

is

critical,

while

during

global

dust

storms

>

80
%

of

sunlight

is

absorbed

by

dust
.


The

amount

and

size

distribution

of

dust

in

the

atmosphere

is

controlled

by

lifting

processes

and

wind

transport
.

Dust in the atmosphere of Mars (2/10)

Up

to

now,

mechanisms

for

dust

lifting

and

feedbacks

on

the

atmospheric

circulation

are

not

well

understood
.


As

an

example,

the

irregular

occurrence

and

mechanisms

for

the

growth

of

global

dust

storm

are

not

explained

by

models
.


In

order

to

understand

and

proper

model

Martian

atmospheric

circulation

and

meteorology

it

is

necessary

to

understand

how

dust

is

lifted

and

maintained

in

the

atmosphere

and

which

is

the

amount

and

size

distribution

of

the

lifted

dust
.

Dust in the atmosphere of Mars (3/10)

The

amount

and

size

distribution

of

airborne

dust

depends

on

the

lifting

mechanisms
.

Dust

on

Earth

is

generally

emitted

due

to

the

drag

force

of

wind
.


As

wind

speed

increase,

sand

particles

of



100

m
m

size

are

first

moved

by

fluid

drag
.


After

lifting

they

hop

along

the

surface



saltation


Saltation

can

mobilize

particles

of

a

wide

range

of

sizes

(splashing,

creep,

suspension)
.

Mechanisms for dust entrainment

Dust in the atmosphere of Mars (4/10)

Few

wind

measurements

have

been

performed

from

landers

on

Mars
.


These

have

shown

that

the

light

Martian

atmosphere

rarely

exceed

the

saltation

fluid

threshold

(also

confirmed

by

the

results

of

mesoscale

and

global

circulation

models)
.


The

ubiquitous

sand

dunes

on

Mars

appeared

almost

motionless

by

lander

and

orbiter

observations,

and

were

supposed

to

be

formed

in

a

previous

climate,

in

a

thicker

atmosphere
.

Dust in the atmosphere of Mars (5/10)

Recent

observations

by

high

resolution

images

(e
.
g
.

HiRISE)

have

revealed

widespread

movements

of

dunes

and

ripples

at

many

locations

on

Mars
.



Results

show

that

the

Martian

thin

atmosphere

blows

sand

in

this

dune

field

at

rates

not

much

lower

than

Earth’s

much

thicker

atmosphere

does

on

terrestrial

dunes
.


Dust in the atmosphere of Mars (6/10)

This

could

be

explained

by

the

recent

results

that,

once

initiated,

saltation

can

be

sustained

down

to

speed

of

only

10
%

of

the

initiation

threshold,

thus

allowing

saltation

to

occur

at

<<

wind

speed
.


On

Mars

lower

g

and

air

density

imply

that

grain

trajectories

are

higher

and

longer

than

on

Earth



grains

are

accelerated

by

wind

for

longer

time



impact

threshold

u
*t_impact

comparable

with

that

on

Earth
.


But

lower

air

density



higher

fluid

threshold

on

Mars

(


1

order

of

magnitude)




The

ratio

of

impact

to

fluid

threshold

on

Mars

is

lower

(
10
%
)

than

on

Earth

(
80
%
)
.


Dust in the atmosphere of Mars (7/10)

Other

suggested

mechanisms

for

dust

lifting

on

Mars



MER

MI

and

Curiosity

MAHLI

discovered

that

dust

often

occurs

as

low
-
strength

sand
-
sized

spheroid

agglomerates

possibly

due

to

electrostatic

processes
.

These

structures

need

lower

wind

speeds

to

be

disrupted

and

lifted

into

the

atmosphere
.




Thermophoresis
.


Occurs

when

solar

irradiation

warms

the

upper

mm

of

the

surface

more

than

the

surrounding

atmosphere
.

Gases

embedded

in

the

pore

spaces

of

the

surface

can

transfer

enough

momentum

to

dust

particles

to

cause

them

to

lift
.

Dust in the atmosphere of Mars (8/10)



Sublimation

of

CO
2

ice

below

or

around

dust

particles

may

provide

them

with

the

momentum

required

for

the

injection

into

the

atmosphere
.



Electric

field
.


Electric

fields

can

be

generated

during

normal

saltation

and

inside

dust

devils

vortices

or

dust

storms
.


Laboratory

experiments

demonstrated

that

electric

fields

can

enhance

dust

lifting
.

Other

suggested

mechanisms

for

dust

lifting

on

Mars

Dust in the atmosphere of Mars (9/10)

The

amount

of

dust

in

the

atmosphere

and

its

size

distribution

depends

on

the

processes

responsible

for

the

dust

lifting
.

They

are

the

key

parameters

influencing

Martian

climate

and

surface

weathering
.

Dust in the atmosphere of Mars (10/10)

The

information

about

size

distribution

of

atmospheric

dust

has

been

mainly

retrieved

from

remote

optical

measurements
.

Complex

vertical

distribution

of

dust

mixing

ratio
.



Peak

@

15
-
25

km

observed

by

the

Mars

Climate

Sounder

on

MRO

during

nothern

spring

and

summer

(McCleese

et

al
.
,

2010
)
.


Another

peak

likely

present

in

the

PBL

(
0
-
15

km)
.



Sharp

decrease

above

~

25

km
.


The

information

that

can

be

obtained

by

in

situ

measurements

over

different

time

spans

represents

a

key

input

in

different

areas

of

interest
:

in science


to

determine

present

climatic

conditions

at

Mars

surface


to

derive

information

about

past

history

of

Mars

climate


to

derive

information

about

dust

loading

mechanism

(if

coupled

with

wind

and

other

environmental

measurements)


to

study

dust

storms

properties

and

evolution



to

provide

ground
-
truth

for

validation

of

data

coming

from

orbiter

observations

in Mars operations


to

evaluate

hazardous

conditions

due

to

Martian

dusty

environment


to

place

constraints

on

operative

conditions

at

Mars


to

support

definition

of

future

Mars

exploration

missions

MicroMED:

Scientific objectives

Instrument concept:

From MEDUSA to MicroMED


Optical

Stage

with

laser

diode

source

in

separated

box

coupled

to

the

main

body

with

optical

fiber


Dust

Accumulation

Stage

below

the

Optical

Stage



Water

Vapour

Measure

Stage

in

external

unit
.



Dust

Deposition

and

Electrification

Sensor

(DDES)

as

external

unit
.

Water
Vapour
Stage

Laser
Diode
Assemby

Optical
Fiber

Inlet

OS

Vacuum
pump

Dust Accumulation
Stage

Optical
fiber
connector

MEDUSA configuration in Humboldt

MEDUSA successfully passed the PDR
with TRL > 5.3

DDES

MicroMED configuration

Inlet


Vacuum
Pump

Optical
detection
Stage

MicroMED Envelope 100 x 60 x 165 mm
3

mirror

Laser diode

Collimator optics

MEDUSA

MicroMED

Total Mass

2243 g

500 g (without ME) (TBC)

Total Maximum Power
Consumption

21.44 W

1.6 W (only PE)

Sampling Head

Nozzle

Minimized tube

Collecting mirrors aperture

±
33
°

in FW direction

±
47
°

in BW direction

±
65
°

at 90
°

direction

Sampling Volume

1.2 mm x 0.32 mm x 3 mm

1 mm x 1 mm x 0.08 mm

Detector(s)

Sensing Area: 50 mm
2

Responsivity: 0.5 A/W

Sensitivity Area: 50 mm
2

Responsivity: 0.5 A/W

Laser Diode

Wavelength: 808 nm

Optical Power: 1000 mW

Wavelenght: 850 nm

Optical Power: 100 mW

Pump

Maximum Flow Rate: 5.5 l/min

Maximum Flow Rate: 1.0 l/min

Microbalance for dust

Mass Sensitivity: 5.09
∙10
8

Hz/g/cm
2

NO

Microbalance for water vapour

Mass Sensitivity: 2.47
∙10
9

Hz/g/cm
2

NO

Proximity Electronics

4 Channels

(2 for Forward Scattering + 2 for
Backward Scattering)

1 Channel with 2 outputs:

low gain 10
5
, high gain 10
7

MEDUSA vs MicroMED


Dust particles sampled by a pump cross a
collimated light beam emitted from an
infrared laser diode.



Dust particles sizes can be measured by
the scattered light collected with the
mirror on a photodiode.



MicroMED measures abundance and size
distribution of dust in Martian atmosphere

MicroMED working principles

Inlet

and

outlet

shape

design,

sampling

rate,

sampling

volume

and

air

and

dust

flow

section

have

been

designed

in

order

to

be

compliant

with

the

following

technical

requirements
:




to

have

a

small

fraction

of

coincidence

f

(e
.
g
.

<

0
.
05
),

in

order

to

have

a

single

particle

counter,

and

a

large

number

of

particles

detected

in

a

short

time

(
120

s)




to

concentrate

the

dust

and

air

flux

in

a

small

area

(e
.
g
.

1

x

1

mm
2
)

coincident

with

the

sampling

volume

generated

by

the

laser

beam




to

avoid

turbulence

inside

the

instrument




not

to

alter

the

size

distribution

and

volume

density

of

sampled

dust

particles





to

be

able

to

sample

particles

with

size



20

m
m




inlet

and

outlet

tubes

protruding

inside

the

MicroMED

body

shall

not

be

invasive
:

they

shall

not

intercept

the

laser

beam,

nor

produce

shadow

on

the

mirror

or

detector
.


MicroMED fluid
-
dynamic design

Fluid
-
dynamic

design

has

been

tested

in

a

Martian

simulation

chamber
.


Preliminary

tests

results

show

that

particles

captured

by

MicroMED

are

conveyed

concentrated

in

a

section

1

x

1

mm
2

perpendicular

to

the

flow,

as

predicted

by

Fluent

simulations
.

MicroMED fluid
-
dynamic design

MicroMED fluid
-
dynamic design



Inside sampling vol.

0.4 mm from the centre

At the edge of sampl. vol.

0.5 mm from the centre

Outside sampling vol.

0.6 mm from the centre

Experimental set
-
up

Optical design is driven by the following requirements:



To concentrate the laser beam in a small area in order to obtain high power density
with a low power laser



To be able to detect particles in the size range 0.4


20
m
m in diameter



To be able to detect single particles (
having a small fraction of coincidence
f

(e.g. <
0.05)
)



To maximise the power density in the sampling volume



To produce a beam with uniform intensity inside the sampling volume (in order to avoid
that the same particle could produce different signal if intercepting the beam in
different points)

MicroMED optical design

MicroMED optical design

Scattered light

Evaluation considering:


Spherical dust particles
(Mie theory)



optical power: 100mW



Radiation loss: 30%
(ZEEMAX simulations)



angle of collected
scattered light: 130
°


Minimum detectable dust
particle size:

<
0.2
m

楮 牡r極i

MicroMED: performances evaluation

Signal vs. size

Coincidence fraction
f
= 1.2

10
-
4
in constant haze
and 4


10
-
3

during dust devils

MicroMED: performances evaluation

Signal vs. size

Optical system is almost ready.


Optics have been produced and aligned.


Integration and performance tests foreseen in November 2012

OS

laboratory

breadboard

has

been

able

to

detect

0
.
5

m
m

grains
.

This

is

very

close

to

the

OS

nominal

performances

(det
.

Limit
:

0
.
2

m
m)
.

Similar tests on the MEDUSA instrument

MicroMED operations:


Minimum 4 runs of 160 s
per SOL are foreseen.

For each Run


130 s laser diode ON


130 s Pump On


160 s PE on

Element Assembly


Power
Consumption

Energy
/Run

Proximity

Electronics

0.170 W

Pump

0.5 W

Laser Diode

0.5 W

Total

(including DC/DC converter

dissipation)

1.560 W

0.058
Wh

MicroMED Operations


MicroMED

is

the

lighter

and

reduced

resources

version

of

the

MEDUSA

instrument

on
-
board

the

Humboldt

payload

with

TRL

>

5
.
3
.



It

is

able

to

measure

the

size

distribution

and

number

density

of

dust

particles

in

the

atmosphere

of

Mars
.



The

information

that

will

be

provided

by

MicroMED

are

crucial

for

climate

modelling

and

for

future

missions

planning
.



The

performances

are
:












MicroMED

BB

is

under

development
.




BB

is

foreseen

to

be

completed

and

tested

within

Feb
.

2013
.

MicroMED performances and Technical

specification

Detected Dust Size

0.4..20

m
m diameter

Power

1.6 W

Mass

500 g

Conclusions