Liquid
‐
water
and
solid
‐
Ice
fields
surrounding
a
descending
melt
probe
Paul
E.
Dimotakis
and
Daniel
B.
Lang
California
Institute
of
Technology
2023
NASA
Cryobot
Workshop
presentation
21
‐
23
February
2023
California
Institute
of
Technology
Pasadena,
California
91125
Dimotakis
&
Lang
(2023)
doi:10.7907/az3w
‐
xv24
Acknowledgments
Discussions:
physics
and
modeling
•
Georgios
Matheou,
Connecticut
University
Support
•
Program
•
NASA/Caltech/JPL:
Fred
Y.
Hadaegh,
Kevin
P.
Hand,
Charles
D.
Norton,
Jeff
L.
Hall
•
Caltech/E&AS:
Ling
Y.
Lin,
Susan
D.
Powell
•
Funding
–Initially
•
Caltech
Northrop
Chair
in
Aeronautics:
Paul
D.
•
Caltech
gift
funds:
Foster
and
Coco
Stanback Space
Innovation
Fund
•
Caltech
Alumnus
gift:
Michael
J.
Kaiserman
•
Small/pilot
NASA/JPL:
Material
CTE
issues.
Project
manager:
Thomas
A.
Cwik
•
Funding
–Currently
•
NASA/Caltech/JPL:
Test
‐
cell/experiment
development,
probe
optimization,
experiments,
modeling
and
simulation.
Project
managers:
Kevin
P.
Hand
(initially),
Jeff
L.
Hall
(recently)
•
Caltech
Northrop
Chair
in
Aeronautics:
Paul
D.
2
Dimotakis
&
Lang
(2023)
Goals,
scope,
and
approach
3
Goals:
•
Investigate
descent
melt
‐
probe
behavior
to
document
and
understand
heat
‐
flow
and
dynamics
of
•
surrounding
liquid
‐
melt
layer
and
•
surrounding
ice
field
•
Optimize
melt
‐
probe
design,
performance,
and
efficiency
•
Development
and
validation
of
integrated
physics
‐
based
predictive
models
Scope:
•
Experiments
guided/aided
by
simulations
and
physical
modeling
•
Presently,
fresh
‐
water
ice
investigations
with
controlled
variable
ice
temperature
•
Later,
salt
‐
water
ice
Approach:
•
Concurrent,
time
‐
dependent
measurements
and
modeling
•
Ice
‐
field
and
melt
‐
layer
optical
and
temperature
•
Surrounding
melt
layer
•
Internal
descent
‐
probe
temperature
•
Descent
velocities
•
Refreezing
•
Thermal
heat
‐
flow
modeling
to
guide
probe
design/optimization
and
physical
models
•
Descent
velocities
vs.
heating
rate
profiles
and
ice
‐
field
temperature
•
Physics
‐
based
model
development,
predictions,
and
validation
•
Liquid
‐
layer
extent
and
optimization
•
Ice
melting
•
Ice
‐
field
thermal
response
Dimotakis
&
Lang
(2023)
Challenges
Descent
rate,
compression
,
+,
...
Melt
descent
probe:
Radioisotope
‐
powered
(e.g.,
Pu
‐
238)
If
descent
time
is
not
to
exceed
ൎ
one
(Earth)
year
•
One
Earth
year:
푡
୷ୣୟ୰
ൎ
3.2
ൈ
10
s
and
•
Assumed
ice
thickness:
푧
୧ୡୣ
ൎ
10 km
ൌ
10
mm
ሺ
ൎ
Mt. Everest height
ሻ
•
Transit/descent:
푡
୷ୣୟ୰
푧
୧ୡୣ
⁄
ൎ
3.2 s mm
⁄
ൎ
0.5 min cm
⁄
ൎ
1 hr/m
Melt
‐
probe
must
operate/survive
over
Europa’s
ice
‐
field
푇
,
푝
‐
range:
•
100 K
൏푇
୧ୡୣ
൏
273 K
(fresh
water),
and
10
ିଵଶ
bar
൏푝
୧ୡୣ
,
ୱ୲ୟ୲
൏
4
ൈ
10
ଶ
bar
First
Law
of
Thermodynamics
(conservation
of
energy):
•
Internal
‐
energy
per
unit
time,
퐸
ሶ
[Watts]
,
to
heat
and
melt
ice,
푄
ሶ
[Watts]
,
and
work
rate
to
compress
surrounding
ice
raising
its
temperature,
푊
ሶ
[Watts]
,
all
derive
from
the
heating
rate
provided,
per
unit
descent
rate,
푤
ሾ
mm/s
ሿ
:
푄
ሶ
ต
୦ୣୟ୲୧୬
୰ୟ୲ୣ
ൌ
퐸
ሶ
ถ
୧ୡୣ
୧୬୲ୣ୰୬ୟ୪ିୣ୬ୣ୰୷
୰ୟ୲ୣ
െ
푊
ሶ
ถ
୧ୡୣ
ୡ୭୫୮୰ୣୱୱ୧୴ୣି୵୭୰୩
୰ୟ୲ୣ
•
Europa’s
compressive
natural
tidal
and
thermal
‐
excursion
stresses,
plus
ice
differential
thermal
‐
expansion/
‐
compressive
stresses,
for
a
given
melt
‐
probe
descent
rate,
푤
,
•
Low
‐
temperature
ice
hardness
is
comparable
to
that
of
granite
4
푤
Ice
Ice
Ice
Ice
Melt
water
Refreeze
푞
ሶ
Melt
water
푝
푝
Melt
probe
푞
ሶ
푞
ሶ
푞
ሶ
푞
ሶ
푞
ሶ
Dimotakis
&
Lang
(2023)
Ice
test
cell
Integrated
fused
‐
section
clear
material
•
CTE
‐
matched
to
ice
•
High
‐
quality
optical
access
•
Irregular
octagon
(viewing
sides
are
larger)
•
Optical
test
cell
height:
∼
310 mm
ሺ
12.2
ᇱᇱ
ሻ
•
Viewing
sides
width:
∼
134 mm
ሺ
5.3
′′ሻ
Separate
bottom,
side,
and
top
cooling
plates
•
Aluminum
with
embedded
copper
coolant
tubes
•
CTE
isolation:
bottom,
sides,
and
top
•
Chiller
with
controlled
‐
temperature
recirculating
coolant
•
Controlled
cooling
rate/heat
‐
flux:
bottom,
sides,
top
Embedded
temperature
sensors
•
Heat
‐
flow
control
and
ice
‐
field
temperature
measurements
Top
at
‐
pressure
access/housing
for
melt
‐
probe
Cooling
‐
freezing
under
controlled
atmosphere
and
pressure,
or
(near
‐
)vacuum
5
Dimotakis
&
Lang
(2023)
Experiment
set
‐
up
–
Optics,
+
...
Assembled
on
vibration
‐
isolation
4
ᇱ
ൈ
8
′
optical
table
Test
‐
cell
assembly
•
Insulating
‐
foam
enclosure
with
purged
(triple
‐
gap)
windows
for
condensation
mitigation
and
control
•
Continuous
enclosure
purging
using
(oil
‐
free)
LN
ଶ
‐
Dewar
boil
‐
off
•
Top:
probe
housing/release
assembly
Shadowgraph
Z
‐
configuration
•
Astronomical
‐
quality
250mm
휙
,
푓
/4
,
휆
/16
opposed
parabolic
mirror
pair
•
Solid
‐
state
laser
light
source
•
Computer
‐
controlled
acquisition:
monitoring,
data,
and
image
Measurements
during
cooling
and
runs:
multi
‐
channel
temperatures,
optical
descent,
heating
‐
power,
probe
internal
temperature
6
Dimotakis
&
Lang
(2023)