Deep Impact
First Look Inside a Comet
Michael F. A’Hearn
Outline
•
•
•
•
Scientific Objectives, Mission Overview, Context
Cratering Physics
The Target and Environment
Measurements and Observations
Meudon - 2002 Jun 13
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Fundamental Goal
• Explore the interior of a cometary
nucleus
• Recreate a natural phenomenon
under controlled circumstances
• Excavate a football field 7 stories
deep in a true, controlled
experiment
• Conceptually simple!
• Technically challenging!
Meudon - 2002 Jun 13
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Simple But Challenging
Even 33 Years Ago
"It [an asteroid] was racing past them at almost thirty miles a second;
they had only a few frantic minutes in which to observe it closely. The automatic cameras
took dozens of photographs, the navigation radar's returning echoes were carefully recorded
for future analysis - and there was just time for a single impact probe.
The probe carried no instruments; none could survive a collision at such cosmic speeds.
It was merely a small slug of metal, shot out from Discovery on a course which should
intersect that of the asteroid.
.....They were aiming at a hundred-foot-diameter target, from a distance of thousands of
miles...
Against the darkened portion of the asteroid there was a sudden,
dazzling explosion of light. ...”
____________________
Arthur C. Clarke, 1968. In 2001: A Space Odyssey. Chapter 18
Meudon - 2002 Jun 13
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Science Team
M. F. A’Hearn, PI
Management, Emission
Spectra, Coma relation to
nucleus, PDS Archiving
M. J. S. Belton, Deputy PI
Imaging, Rotation
A. Delamere
B. Instrumentation
J. Kissel
Dust, Ejecta from crater
K. Klaasen
Mission operations,
Geomorphology
L. A. McFadden, EPO Dir.
Outreach, Reflection
Spectroscopy, geology
K. J. Meech
Earth-based observing
program
H. J. Melosh
Cratering - numerical
simulations
P. Schultz
Cratering - experiments
J. Sunshine
Reflection spectroscopy,
analysis
J. Veverka
Relation among comets &
asteroids, Data processing
pipeline
D. K. Yeomans
Dynamics, Radio science
Meudon - 2002 Jun 13
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Scientific Objectives
•
Primary Scientific Theme
– Understand the differences between interior and surface
– Determine basic cometary properties
– Search for pristine material below surface
•
Secondary Scientific Theme
– Distinguish extinction from dormancy
•
Additional Science Addressed
– Address terrestrial hazard from cometary impacts
– Search for heterogeneity at scale of cometesimals
– Calibration of cratering record
Meudon - 2002 Jun 13
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Mission Overview
•
•
2 spacecraft – Smart Impactor + Flyby
Fly together until 1 day before impact
– 1-year heliocentric orbit with Earth return to provide lunar calibration
of instruments and test of targeting
– 6-month Earth-to-comet trajectory
•
Smart Impactor
– Impactor Targeting Sensor (ITS)
• Scale 10 microrad/pixel
• Used for active navigation to target site
• Images relayed via flyby to Earth for analysis
– Cratering mass (~370 kg at 10.2 km/s)
• Excavates ~100-meter crater in few*100 seconds
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Mission Overview (continued)
•
Flyby Spacecraft
– Diverts to miss by 500 km
– Slows down to observe for 800 seconds
– Instruments body-mounted – spacecraft rotates to follow comet
during flyby
•
Instruments on Flyby Spacecraft
– High Resolution Imager (HRI)
• CCD imaging at 2 microrad/pixel
• 1-5 micron long-slit spectroscopy (R>200, 10 microrad/pix)
– Medium Resolution Imager (MRI)
• CCD imaging at 10 microrad/pixel
• Identical to ITS but with filter wheel added
•
Major Earth-based Observing Campaign
Meudon - 2002 Jun 13
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Spacecraft Overview
Instruments
MRI, ITS, HRI
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Inter-Planetary Trajectory
Mars at
Encounter
Meudon - 2002 Jun 13
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Interplanetary Trajectory
Earth-Relative Interplanetary Trajectory
Opening Launch Day - January 2, 2004
Rotating Coordinates
Distance from Sun in AU
Encounter
1.6 AU
Earth
One-year
Earth-to-Earth
Loop
t
30 days
1.4 AU
1.2 AU
1.0 AU
Sun
Meudon - 2002 Jun 13
Deep Impact - First Look Inside a Comet
0.8 AU
View from North Ecliptic
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Flyby Geometry Varies With Launch
Date
A.
The spacecraft’s position with respect
to the Moon for A) Opening, B) Middle,
and C) Closing Launch Dates.
Sun
Earth/Moon Flyby on
December 31, 2004 for
Opening Launch Date
(January 2, 2004)
CALIBRATION SEQUENCES WILL BE VERY
LAUNCH DATE DEPENDENT!
S/C
Inbound
t
6 hrs
Moon
Orbit
t
1 day
S/C
Outbound
Earth
Launch
Date
(2004)
2-Jan
6-Jan
11-Jan
14-Jan
21-Jan
Perigee
Moon at S/C
Closest Approach
Moon at
S/C Perigee
North Ecliptic View
B.
Sun
Earth/Moon Flyby on
January 9, 2005 for
Middle Launch Date
(January 11, 2004)
Moon
Orbit
t
1 day
Moon at S/C Perigee
Moon at S/C Closest Approach
Meudon - 2002 Jun 13
Sun
Earth/Moon Flyby on
January 20, 2005 for
Closing Launch Date
(January 22, 2004)
Earth
S/C
Outbound
Moon
Orbit
t
1 day
Moon at S/C
Closest Approach
(near Perigee)
North Ecliptic View
Earth
Flyby
Earth Flyby Altitude
Date/Time
(km)
31-Dec-04 1,350
04-Jan-05 3,447
09-Jan-05 6,357
12-Jan-05 8,235
19-Jan-05 13,146
S/C
Inbound
t
6 hrs
S/C
Inbound
t
6 hrs
Perigee
C.
Lunar
Flyby
Lunar Flyby Distance
Date/Time
(km)
1-Jan-05
245,319
5-Jan-05
108,605
8-Jan-05
207,715
11-Jan-05 118,829
19-Jan-05 379,207
Earth
Perigee
S/C
Outbound
North Ecliptic View
Deep Impact - First Look Inside a Comet
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Encounter Schematic
Impactor Release
E-24 hours
AutoNav Enabled
E-2 hr
ITM-1 Start
E-88 min
ITM-2
E-48 min
ITM-3
E-15 min
Tempel-1
Nucleus
64
kbps
2-way
S-band
Crosslink
500 km
Flyby S/C
Deflection Maneuver
E-23.5 hr
Science and
Autonav Imaging to
Impact + 800 sec
Flyby S/C Science
And Impactor Data
at 175 kbps*
Flyby Science
Realtime Data
at 175 kbps*
Shield Mode
Attitude through
Inner Coma
TCA +
TBD sec
Flyby S/C Science
Data Playback at 175 kbps*
to 70-meter DSS
* data rates without Reed-Solomon encoding
Meudon - 2002 Jun 13
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Look-back
Imaging
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Context – Comets Unknown
•
Mass – no data
– Density and Surface Gravity uncertainty >10x
•
Strength
– Tensile strength < 103dyn/cm2 at km scale
– Nothing else known
•
Stratification
– Know only irradiated mantle on new comets
– Ice to rock ratio unknown
•
Shape
– Data only for 1P/Halley and 19P/Borrelly
•
Photometric Properties very uncertain
•
Coma dust and rocks very uncertain
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Cometary Dichotomies
•
•
•
•
•
•
Comets have the most primitive,
accessible material in the SS
Comets must become dormant
There must be many dormant
comets masquerading as NEAs
We know more chemical and
physical details than for other
small bodies in the SS
Abundances in the coma are
used to infer ices in the protoplanetary disk
Comets break apart under small
stresses
Meudon - 2002 Jun 13
•
•
•
•
•
•
We do not know what is hidden
below the evolved surface layers
Is the ice exhausted or sealed in?
We can not recognize dormant
comets among NEAs
We do not know how to use these
details to constrain models of
nuclei
Abundances in the coma differ
significantly but in unknown
ways from nuclear abundances
Variation of strength with scale is
totally unknown
Deep Impact - First Look Inside a Comet
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Everything We Know Directly
QuickTime™ and a
decompressor
are needed to see this picture.
H. U. Keller
Meudon - 2002 Jun 13
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L. Soderblom
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What We Won’t Know
•
•
•
•
•
•
•
Shape Details and Topography
Phase Function
Density
Mass
Dust environment
Rotational axis
Cratering Physics
Meudon - 2002 Jun 13
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Nuclear Models
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Interior Model?
Meudon - 2002 Jun 13
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Evolutionary Models
Benkhoff-Huebner model has density increasing
monotonically from surface to 10s of meters. PrialnikMekler model has a dense layer of water ice at surface
with lower density material below.
Meudon - 2002 Jun 13
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Context – Other Small-Body
Missions
Mission
Launch
Encounter
Encounter
Encounter End Mission
NEAR
96/02/17
97/06/27
98/12/23
00/02/14
( 253)Mathilde (433) Eros
(rend)
DS-1
98/10/25 99/07/28
01/09/23
(9969) Braille 19P/Borrelly
Stardust
99/02/12
04/01/02
81P/Wild 2
Muses C
02/12/xx 05/09/xx
1998 SF36
CONTOUR 02/07/04 03/11/12
06/06/18
(08/08/18)
2P/Encke 73P/S-W 3 (6P/d'Arrest)
Rosetta
03/01/20 06/07/10
08/07/23
11/07/27
( 4979)Otawara (140)Siwa 46P/Wirtanen
Deep Impact 04/01/06 05/07/04
9P/Tempel 1
Goal
01/02/12 surface
surface
06/01/15 sample
return
07/06/xx sample
return
diversity
14/xx/xx ~1m deep
+ tomog.
~25m deep
Dates are yy/mm/dd
Meudon - 2002 Jun 13
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Cratering Physics
Which physics will matter?
Possible Scenarios
•
Crater formation on an intact nucleus
– Gravity controlled crater
– Compression controlled crater
•
•
•
Aerogel-like capture of the impactor
Split nucleus
Crater formation on an intact nucleus
– Strength controlled crater
•
•
Shattered nucleus
Transit through the nucleus
•
Above are roughly in order of decreasing probability (as
guessed by the PI)
N.B.: K.E. of Impactor << Gravitational Binding Energy of
Cometary Nucleus
•
Meudon - 2002 Jun 13
Deep Impact - First Look Inside a Comet
D. K. Yeomans
CSR page 1-12
mfa - 23
Cratering Physics
• Gravity control expected
–
–
–
–
Size and time sensitive to cometary properties
Size ~ (impactor mass)1/3
Size insensitive to other properties
Details of early ejecta (speed, jets) sensitive to shape and density
Strength control possible
Size depends on impactor density (as does speed of early ejecta) –
much smaller than under gravity control;
greater depth/diameter than under gravity control;
details sensitive to shape of impactor
Compression control possible
Scaling relationships not known
Mechanism newly proposed to explain Mathilde’s craters
Schultz’s experiments with perlite suggest it occurs when “particles” are
comparable in size to impactor
Distinguish mode by ejecta morphology and crater size
Meudon - 2002 Jun 13
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Ejecta Cone
Figures are for gravity
controlled situations.
If strength controlled,
cone detaches from
surface.
If volatiles exist under
inert material,
vaporization drives
ejecta that tend to fill
in cone.
If compression
controlled, much less
total ejecta in cone
and no final rim.
Meudon - 2002 Jun 13
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Cratering Flow Pattern
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Crater Section
Meudon - 2002 Jun 13
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Crater Scaling
Different Cometary Bulk Densities
Different Target Materials
(Affects Gravitational Acceleration)
Crater Depths
300
50
200
40
200
100
50
150
Depth (m)
Crater Diameter (m)
Crater Diameter (m)
30
20
100
Surface Density = 0.3 g/cc
Cometary Bulk Density = 0.8 g/cc
Surface Density = 0.3 g/cc
Cometary Bulk Density = 0.8 g/cc
Surface Density = 0.3 g/cc
10
100
200
400
600
1000
Impactor Mass (kg)
70
30
100
100
200
400
600
Im pactor Mass (kg)
1000
200
400
600
1000
Impactor Mass (kg)
Crater depth combines excavation with compression
and displacement. Varies with target material
D ~ m1/3
D ~ rc-1/6
D ~ Rc-1/6
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Formation Time Scaling
Different Cometary Bulk Densities
m1/6
T~
T ~ rc-2/3
T ~ Rc-2/3
550
50
450
Crater Formation Time (s)
800-sec observing
window provides large
margin for extreme
cometary properties,
even down to bulk
density 0.1 g/cc
(Affects Gravitational Acceleration)
400
350
300
250
200
Surface Density = 0.3 g/cc
150
100
200
400
600
1000
Im pactor Mass (kg)
Most important thing is to know impactor properties
Meudon - 2002 Jun 13
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Impactor Designed to Optimize
Cratering
Debris
Shields
note:
radiator not
shown is
debris shield
too
Launch vehicle adaptor not shown
Design simplifies adding mass at start of I&T
Stacked plates can easily be made porous
Science traded less copper for more front mass
Meudon - 2002 Jun 13
Deep Impact - First Look Inside a Comet
Radiator shown in
translucent blue
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Crater Mass Design
Impactor Spacecraft Specification Compliance Verification
Cratering Mass Requirements
Method
3.2.4.6.1-1a Concentrate as much
Meet
Analysis
mass as possible in the forebody.
Analysis
3.2.4.6.1-1b Provide for flexibility in
Meet
Inspection
Impactor dry mass.
3.2.4.6.1-1c Forebody to approximate
Meet
Analysis
a hemispherical profile.
3.2.4.6.1-1d Average (nonhomogeneouse) forebody density in the
Meet
Analysis
range of 2.5-5.5 gm/cc, with higher
3.2.4.6.1-1e Forebody diameter > .5
meter and a diameter to depth ratio
Meet
Analysis
between 2:1 and 4:1.
Comments
Minimize structure mass using
material choices and analysis
Mass can be adjusted within 80144 kg.
Hemispherical shape with
cutout for ITS
Density range 3.0-5.5 gm/cc
Diameter .64 meter
Diameter to depth ratio 4:1
Largest disk
15.8 Kg (38 lbs) min weight
Meudon - 2002 Jun 13
37.2
Kg (82 lbs) max weight
Deep Impact - First Look Inside a Comet
Mass 7 disks bolted together
Match drilled pins for shear
Located in the forebody
Mounted to the main deck
Disks C11000 copper
Each disk chamfered to
approximate a sphere
Cutout for ITS
Specific values documented in SER
DI-IMP-STR-006
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Speed of Early Ejecta
Solid Copper
Porous Copper
Ejecta Velocities
Comparison
PLATE porous
~ 0.5-1.5 km/s
CAP solid
~ up to 5 km/s ,
high initial
temperatures
Porosity of
plate reduces
ejecta velocity!
Easier to track
ejecta!
J. D. O’Keefe
Meudon - 2002 Jun 13
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Baseline Prediction
•
•
Assumes Gravitationally Controlled Crater
Crater
– Diameter ~110m
– Depth ~ 27m
– Formation Time ~ 200 s
•
Ejecta
– Max velocity ~ 2 km/s
– Negligible quantity of “boulders”
– Clumping of ejecta to allow tracking
•
Long-term changes
– New “active area”
– Outgassing jet that may last days to months
– Increased ratio of CO & CO2 to H2O
Meudon - 2002 Jun 13
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Target Properties - 9P/Tempel 1
What Can We Know Before Impact?
Wilhelm Tempel
Target Requirements Easily Met
Property
CSR Requirement
Current Value
Radius
> 2 km
3.1 km
Approach Phase
< 70°
63°
Solar Elongation
> 70°
104°
Earth Range
< 1.3 AU
0.89 AU
Rotation Period
“long”
42 h
Dust
Prediction in CSR
Fig 1.2-8
Prediction validated
Meudon - 2002 Jun 13
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Target Update – Nucleus
•
Size and albedo
– Keck #1 + UH 88”, 2000 August 21; poor weather
– <R> = 3.1±0.5 km, pR ~ 0.03- 0.04
•
Rotation
– UH 88” – many runs, HST – 1 run, several runs at Lowell and ESO and La
Palma, since Jan 1999
– Partially analyzed – P ~ 42 hours
– Axis orientation and sense of rotation MAY be determinable well before
impact, but not yet confident
•
Shape
– Axial ratio > 1.3, probably < 2
Meudon - 2002 Jun 13
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Nuclear Radius Determined
Keck, thermal IR (10.7 mm), 21 Aug 2000 composite
Radial profiles of thermal IR image
separate dust from nucleus
UH 88”, optical (0.7 mm), 21 Aug 2000
Meudon - 2002 Jun 13
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Slow Rotation of 9P/Tempel 1
P/Tempel 1 Mar 1999 data (Meech et al)
Model: P=1.7478; a=5.8,b=c=3.28km; A=0.04; C-type Hapke; Phi=180@JD2451206.94898
16.0
15.9
15.8
15.7
M(1,1,a)
15.6
15.5
15.4
15.3
15.2
15.1
15.0
2451253
2451254
2451255
2451256
2451257
2451258
2451259
2451260
2451261
2451262
2451263
Julian Days
P/Tempel 1 All 1999 data (Meech et al)
Model: P=1.7478 d; a=5.8,b=c=3.28km; A=0.04; C-type Hapke; Phi=180@JD2451206.94898
16.0
15.9
15.8
15.7
15.6
15.5
M(1,1,a)
15.4
15.3
15.2
15.1
15.0
14.9
14.8
14.7
14.6
14.5
2451197
2451207
2451217
2451227
2451237
2451247
2451257
Julian Days
Meudon - 2002 Jun 13
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Target Update – Dust
•
IRAS survey remapped and re-calibrated (January 2000), data from
5 days post-perihelion to several months post-perihelion in 1983;
preliminary models fitted
•
IRAS pointed observations to be recalibrated (one pre-perihelion
observation included)
•
Keck run – August 2000 (7 1/2 months post-perihelion)
Meudon - 2002 Jun 13
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IRAS Survey Image
Tempel 1
Dust Trail in Orbit Plane
Best image of dust
trail from comet
Tempel 1. 1983
Zodiacal
Dust
Density of old dust in
orbit plane is low
compared to dust
currently released near
nucleus!
Meudon - 2002 Jun 13
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Revised IRAS Results Limit Dust
R. Walker
HCON 421
R=1.56
=1.26
Trail visible
but very faint
Meudon - 2002 Jun 13
Improved spatial resolution and better flux
calibration (10-50% fainter; 25K hotter).
These are the only data sensitive to large
(> 10 mm) particles in inner coma.
HCON 339 1983 Jul 13, T+5 days
HCON 421 1983 Aug 24, T+46 days
Deep Impact - First Look Inside a Comet
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IRAS and Keck Results
Recalibration of IRAS data
constrains size distribution
of large dust 5 days after
perihelion.
Meudon - 2002 Jun 13
Light curve implies dust production is dropping at
perihelion. Allows interpolation or extrapolation of
other data to time of our impact. (Scaling of IR data
to optical data is done empirically.)
Deep Impact - First Look Inside a Comet
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Design Models
•
•
Due to uncertainties, must assume specific models to which
system is designed
Models needed include
–
–
–
–
•
Photometric behavior of dust and nucleus,
Shape and topography of nucleus,
Dust environment,
Cratering process
Must consider worst-case models while designing to a nominal
model
Design models are conservative to encompass cases that are
worse, in whatever sense, than best prediction!
Design models allow flight system design to be mature now!
Meudon - 2002 Jun 13
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Design Model – Photometry
•
Phase function for nucleus derived from recent observations of 2P/Encke
at large phase
• Bi-directional reflectance assumed
• Dust phase function from observations at 1P/Halley
• Dust brightness near opposition scaled from optical observations of
Tempel 1 in 1983
• Nuclear brightness near opposition from HST and UH-88” observations of
Tempel 1 in 1997-1999
_________________
> Average nuclear pixel is brighter than maximum plausible jet brightness at
limb
> Phase function for nucleus is assumed at dark end of range
> Targeting is straightforward (unlike at Halley)
> Predictions confirmed (within 2x) at Borrelly (DS 1)
> To be confirmed again at Encke (CONTOUR)
Meudon - 2002 Jun 13
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Phase Functions
Design Case Selected from Many
Adopted Phase Laws for Nucleus and Dust
<<<<<
Nuclei
Ga
-0.252
Phase
[deg]
0
5
10
15
20
25
30
40
50
60
70
80
90
100
110
120
130
140
150
160
170
180
Normalized Phase Fcn
Dust
Nucleus
3
6
<=index 0.030m/deg 0.035m/deg 0.040m/deg
1.000
1.000
1.000
1.000
1.000
0.933
0.755
0.871
0.851
0.832
0.900
0.570
0.759
0.724
0.692
0.847
0.431
0.661
0.617
0.575
0.813
0.325
0.575
0.525
0.479
0.793
0.245
0.501
0.447
0.398
0.793
0.185
0.437
0.380
0.331
0.747
0.106
0.331
0.275
0.229
0.720
0.060
0.251
0.200
0.158
0.710
0.034
0.191
0.145
0.110
0.690
0.020
0.145
0.105
0.076
0.667
0.011
0.110
0.076
0.052
0.747
0.006
0.083
0.055
0.036
0.000
0.004
0.063
0.040
0.025
0.000
0.002
0.048
0.029
0.017
0.000
0.001
0.036
0.021
0.012
0.000
0.001
0.028
0.015
0.008
0.000
0.000
0.021
0.011
0.006
0.000
0.000
0.016
0.008
0.004
0.000
0.000
0.012
0.006
0.003
0.000
0.000
0.009
0.004
0.002
0.000
0.000
0.007
0.003
0.001
index=>
0
1
2
Meudon - 2002 Jun 13
Encke
IAU
#NUM!
0.54602
0.38189
0.27957
0.20897
0.15784
0.11976
0.06892
0.03913
0.02190
0.01245
0.00781
0.00597
0.00551
0.00535
0.00479
0.00355
0.00190
0.00058
0.00006
0.00000
0.00000
3
>>>>>
Q
-0.092
Encke
Orig L-B
#NUM!
0.59631
0.44261
0.34287
0.27133
0.21752
0.17597
0.11771
0.08148
0.05951
0.04707
0.04091
0.03858
0.03818
0.03823
0.03765
0.03571
0.03202
0.02646
0.01907
0.01004
0.00000
4
<<<<<
Dust
>>>>>
Gb
0.15
typ ast
IAU
0.061m/deg
#NUM!
1.000
0.67889
0.755
0.55105
0.570
0.46407
0.431
0.39824
0.325
0.34559
0.245
0.30198
0.185
0.23298
0.106
0.18018
0.060
0.13821
0.034
0.10414
0.020
0.07625
0.011
0.05354
0.006
0.03541
0.004
0.02151
0.002
0.01156
0.001
0.00520
0.001
0.00181
0.000
0.00042
0.000
0.00004
0.000
0.00000
0.000
0.00000
0.000
5
6
Deep Impact - First Look Inside a Comet
Ney &
Kiselev &
Merrill
Chernova
C/West P/Ash-Jack C/Meier
1.00
1.0000
1.0000
0.92
0.7447
0.7798
0.85
0.5649
0.6607
0.77
0.5248
0.6138
0.70
0.5346
0.65
0.6026
0.60
0.50
0.45
0.45
0.45
0.45
0.45
0.55
0.80
1.50
2.50
4.00
7.00
10.00
15.00
20.00
0
1
2
Krasno.
P/Halley
1.0000
0.9333
0.9000
0.8467
0.8133
0.7933
0.7933
0.7467
0.7200
0.7100
0.6900
0.6667
0.7467
Schleich.
P/Halley
1.0000
0.9376
0.8872
0.8318
0.7834
0.7447
0.7244
0.6730
0.6486
0.6607
0.6918
3
4
mfa - 45
Design Model – Shape
Stooke’s Halley Model
(fit to data)
Gaskell’s Accretion Model
(Theoretical)
Meudon - 2002 Jun 13
Deep Impact - First Look Inside a Comet
mfa - 46
Shape Model Partly Confirmed
•
•
•
•
Rotational light curve suggests axial ratio < original specification
and < in Gaskell’s theoretical model
No comets have light curves suggesting dumbbell structure
(whereas some asteroids do)
Large-scale concavity on surface of Borrelly (DS 1) makes
targeting somewhat more difficult but not impossible
Will evaluate again at Encke (CONTOUR – Nov 2003) to determine
if large-scale concavity is likely to exist
Meudon - 2002 Jun 13
Deep Impact - First Look Inside a Comet
mfa - 47
Design Model – Dust
Best power-law fit
to IRAS spectral
energy distribution
Design Model
CSR Model
CSR model confirmed as good prediction. Design model, defined before
IRAS data were available, is conservative to allow for asymmetries and
other factors.
Conservative design model has good
margin for uncertainties
Meudon - 2002 Jun 13
Deep Impact - First Look Inside a Comet
mfa - 48
Dust Model Validated
Steeper power laws inconsistent with IRAS data - lack of 10-mm silicate emission
Shallow power laws, such as m-0.2, inconsistent with optical data
No data very sensitive to particles with m > 0.1 g
Meudon - 2002 Jun 13
Deep Impact - First Look Inside a Comet
mfa - 49
Dust Model Validated
•
IRAS data confirm that design model was conservative for mid-range
of dust particles
•
Improved optical scaling also confirms conservatism for smaller particles
•
Distribution by mass not well constrained but definitely different than
for P/Halley
•
Extensive search shows no evidence for significant asymmetries
within coma
Meudon - 2002 Jun 13
Deep Impact - First Look Inside a Comet
mfa - 50
Instruments and Measurements
Instrument Platform Assembly for Flyby
Spacecraft Maintains Instrument and ACS
Sensors in Alignment
Star
Trackers
Debris
Shielding
HRI
Instrument
IRU
Low Gain
Antenna
Instrument
Platform
Meudon - 2002 Jun 13
MRI
Instrument
Deep Impact - First Look Inside a Comet
mfa - 52
ITS Optics and Electronics Fit Into
Allocated Impactor Volumes
ITS
Instrument
Thermal
Radiator
ITS
Electronics
Meudon - 2002 Jun 13
Deep Impact - First Look Inside a Comet
ITS
Thermal
Strap
mfa - 53
Visible Imagers
Parameter
HRI
MRI
ITS
FOV [mrad]
2.05
10.2
10.2
IFOV [mrad]
2
10
10
l [mm]
0.3-1.0
0.3-1.0
0.3-1.0
PSF FWHM
[pix@0.7mm]
<1.3
<0.6
<0.6
Full Frame
Rate [s-1]
1/1.7
1/1.7
1/1.7
Radiometric
Sensitivity
Stars to
m~11.3 in 0.1
s
Stars to
m~11.3 in 0.1
s
Stars to
m~11.3 in 0.1
s
Boresight
Alignment
<1 mrad
<1 mrad
N/A
Meudon - 2002 Jun 13
Deep Impact - First Look Inside a Comet
CCDs
1024x1024 active
area
Bilateral frame
transfer
(2 1024x512
shielded areas)
mfa - 54
IR Spectrometer
Parameter
Capability
Units
Slit FOV
2.6
Mrad
IFOV
10
mrad
l
1.05-4.8
mm
PSF FWHM
<1
Pix@2.5mm
Resolving
Power, l/dl
744@1.04mm
209@2.6mm
385@4.8mm
Radiometric
Sensitivity
CO 300 kR/dl
Full Frame
Rate
1/1.75
Meudon - 2002 Jun 13
Detector
Rockwell HgCdTe with
“Hawaii” MUX
1024x512 with 2x2
readout binning
s-1 for 1.75s
exposure
Deep Impact - First Look Inside a Comet
mfa - 55
CO Lines Drive HRI IR Sensitivity
1400
H2O
Surface Brightness (kR)
1300
150 K
145 K
140 K
135 K
CO Requirement
Pre-Impact
3.5 um Requirement
1200
1100
1000
900
800
700
600
500
H2CO
CO 2
400
300
200
100
CO
0
2.5
3.0
3.5
4.0
4.5
5.0
Wavelength (microns)
Removing background suppression (band-limit) filters and reducing bench
temperature to 135K improves limits to 200 kR/dl
Should reach T ~140K but goal is 135K
Meudon - 2002 Jun 13
Deep Impact - First Look Inside a Comet
mfa - 56
Instrument Functional Block
Diagrams
HRI
Dichroic Beamsplitter
Filter Wheel
Shutter
CCD
Telescope
IR Spectrometer
IR FPA
Radiative
Cooler
SIM Bench
CCD
Electronics
LVDS to S/C (Vis)
IR
Electronics
LVDS to S/C (IR)
Electronics
Controller
HRI Electronics
1553 Bus
MRI & ITS
Filter Wheel (MRI only)
Shutter
CCD
1553 Bus
CCD
Electronics
LVDS
Telescope
Controller
Meudon - 2002 Jun 13
Deep Impact - First Look Inside a Comet
mfa - 57
High Resolution Instrument (HRI)
Overview
HRI Telescope
HRI Spectral
Imaging
Module (SIM)
View Looking down HRI Boresight
Meudon - 2002 Jun 13
Deep Impact - First Look Inside a Comet
mfa - 58
13:16:13
JBAER
HRI Spectral Imager Module (SIM)
Layout
•Basic design unchanged since PDR
•Focal Plane IR Filter dropped
•Improved modeling of the focal plane
TM2 S26
11:02:56
DGALLAGH
PR2 S21-24
PR1 S17-20 CLM1 S15
FM3 S27
TM3 S29
BS S8-9
75.00
TM17S13
HRI rebuild
SLIT S12 Positions:
1-3 JWB
MM
4-Feb-01
75.00
HRI-SIM
Meudon - 2002 Jun 13
Deep Impact - First Look Inside a Comet
HRI-SIM
DJG
MM
30-Oct-01
mfa - 59
SIM Assembly
The spectral imaging module of
the High Resolution Instrument
consists of an aluminum box
containing mirrors and prisms
carefully placed to guide
photons from the comet,
through prisms, to disperse the
light into its spectral
components and to a focus on
the detector. This unit is sitting
on an optical bench, a strong,
stable and flat platform
designed for high precision
alignments.
Meudon - 2002 Jun 13
Deep Impact - First Look Inside a Comet
mfa - 60
SIM Assembly
Dennis Gallagher and Bryan
Martin of Ball Aerospace and
Technologies Corp, in Boulder,
CO, prepare to align mirrors
and prisms, the optical
components of the infrared
spectral imaging module part of
the High Resolution Instrument
which will fly on the flyby
spacecraft of the Deep Impact
mission.
This instrument will monitor
the composition of the comet
before, during and after impact
by the impactor spacecraft.
Meudon - 2002 Jun 13
Deep Impact - First Look Inside a Comet
mfa - 61
SIM Assembly
With the spectral imaging
module on the optical bench,
theodolites, tools that measure
vertical and horizontal angles
with high precision,are used
to align the mirrors and
prisms so that photons will
travel through the unit and
onto the detectors without
straying from their path. After
alignment, the mirrors and
prisms are bolted into place.
Eighteen days are scheduled
for this task.
Meudon - 2002 Jun 13
Deep Impact - First Look Inside a Comet
mfa - 62
Geometric Constraints on Data
•
•
Phase angle on approach 63°
Impactor Release
– 1 day before impact
– Range ~ 870,000 km
•
Flyby at impact
– Range ~ 8600 km
•
Flyby at last image
– 800s after impact
– Range ~ 700 km
– Rotation 45°
Meudon - 2002 Jun 13
Deep Impact - First Look Inside a Comet
mfa - 63
Impactor Measurements
•
•
Images for navigation as needed
Images for science at intervals of √d, where d is distance from
impact
– Early images are full frame
– Later images are sub-frames, down to 128x128, due to limitations of Sband link from impactor to flyby
– Best resolution if no dust hits - 20 cm
– Best resolution if dust hits are major problem - 1.5 m
•
Largest challenge
– Knowing time of impact in order to know when to switch image sizes
– A priori time ±30s 3-s
– Determine to ±5s 3-s from flyby rotation and uplink to impactor in
order to shift image sequence in time
Meudon - 2002 Jun 13
Deep Impact - First Look Inside a Comet
mfa - 64
Flyby Measurements
•
Before impact
–
–
–
•
At time of impact
–
–
•
Images of ejecta cone
Spectra of down-range ejecta
Track ejecta with images
After crater complete
–
–
–
•
High speed imaging subframes (1282)for light curve, initially dt < 0.17s
Shift to full frame at slower rate as time increases
Shortly after impact until crater completely formed
–
–
–
•
Monitor rotation of nucleus (brightness) & coma activity for weeks
Map coma with narrow-band filters
Map nucleus & innermost coma in filters and with spectrometer
Map nucleus & crater in filters and spectrometer
Spectra off limb for changes in outgassing
Final crater image with resolution ~ 3-4m
Look-back imaging
–
–
Minutes to hours after flyby
Images and spectra to study changes in activity and map other side of nucleus
Meudon - 2002 Jun 13
Deep Impact - First Look Inside a Comet
mfa - 65
Sample Data
•
Meudon - 2002 Jun 13
Barringer Meteor Crater seen with
comparable number of pixels as
Deep Impact crater assuming
nominal model for cratering
Deep Impact - First Look Inside a Comet
mfa - 66
Analysis Approach
•
•
•
•
•
•
•
•
Determine cratering regime debris cone detachment, lack of
ejecta
Confirm regime from scaling
relations
IF GRAVITY DOMINATED (i.e., one
possible analysis scenario)
Estimate porosity from half-angle
of debris cone
Estimate subsurface structure
from blockiness of crater walls
Estimate density ratio of impactor
to target from shape of
expanding plume
Determine buried ices from gasdriven jet pushing through ejecta
Determine layering of regolith
from crater walls
Meudon - 2002 Jun 13
•
•
•
•
•
Determine coefficients for scaling
laws applicable to small bodies in
the solar system
Determine composition of ejected
debris from downrange near-IR
spectra
Estimate differentiation of ices by
comparing pre- and post- spectra
of outgassing
Test for amorphous ice by
searching for exothermic reaction
driving outgassing above
sublimation rate
Determine composition of cool
debris and cometary surface from
spectra
Deep Impact - First Look Inside a Comet
mfa - 67
Earth-Based Observing Program
How all astronomers can participate
Earth-Based Geometry
•
•
•
Geocentric Distance ~ 0.89 AU
Solar Elongation ~ 104°
Declination ~ -10°
Meudon - 2002 Jun 13
Deep Impact - First Look Inside a Comet
mfa - 69
Earth-Based Elevations
Meudon - 2002 Jun 13
Deep Impact - First Look Inside a Comet
mfa - 70
Impact Time
80
70
CTIO
Paranal
Elevation Angle (deg)
60
50
Goldstone
40
30
La Palma
20
Goldstone
Madrid
Paranal
Paranal (Nautical)
Paranal (Day)
CTIO
CTIO (Nautical)
CTIO (Day)
La Palma
La Palma (Nautical)
Teide
Teide (Nautical)
DSN Redundancy
10
Madrid
0
Current baseline
70
2100
2300
0100
Canberra
60
IMPACT!
Baseline at CSR orals
Elevation Angle (deg)
3/4 July 2005 (UT)
Mauna Kea
Mauna Kea (Nautical)
Mauna Kea (Day )
Palomar
Goldstone
Canberra
50
Mauna Kea
40
30
Palomar
20
Goldstone
10
IMPACT!
0
0500
Meudon - 2002 Jun 13
0600
Deep Impact - First Look Inside a Comet
0700
0800
4 July 2005 (UT)
mfa - 71
Earth-Based Observing
Feature
CSR Orals Baseline
PDR Baseline
Chile: CTIO, La
Hawai’i:- Mauna
Prime Region
Silla, Campanas,
Kea, Haleakala
Paranal
CTIO - .44, .75
Weather MKO - .58, .83
La Silla - .42, est .8
photometric, usable
Haleakala - ?, ?
Paranal - .72, est >.9
Canaries
S. California
Backup Region
La Palma - ?, .96 Palomar - ?, est >.9
HST window
Meudon - 2002 Jun 13
±45 min
Deep Impact - First Look Inside a Comet
±25 min
mfa - 72
Earth-Based Goals
•
•
Thermal and scattered light curves at high speed
Emission-line spectroscopy at all wavelengths - euv to radio
– Temporal resolution - 1s allowed by photon statistics for strongest
optical lines
– Spatial resolution - limited e.g. to 1 arcsec ~ 700 km, i.e. a point source
•
•
•
X-ray emission
Long-term monitoring
Imaging & morphology at all wavelengths
– Spatial & temporal resolution - significant ejecta to > 1 arcsec takes
tens of minutes although fastest ejecta get there in 5 minutes
– Long-term existence of jets - weeks? months?
– Long-term astrometry for non-gravitational accelerations
Meudon - 2002 Jun 13
Deep Impact - First Look Inside a Comet
mfa - 73
What’s Missing?
•
•
•
•
•
•
Seismometry of impact
Accelerometers on impactor
In situ chemical analysis of gas and dust
Reliable method for measuring mass of nucleus
High spatial resolution at time of impact
Evolution of crater beyond 800 sec
Meudon - 2002 Jun 13
Deep Impact - First Look Inside a Comet
mfa - 74