Transcript Huygens at Titan Michael Bird Radioastronomisches Institut Universität Bonn

Huygens at Titan
Michael Bird
Radioastronomisches Institut
Universität Bonn
Bonn, 25 Jan 2005
Outline
•
•
•
•
getting there
14 January 2005
lifting Titan’s veil
Huygens DWE: an update
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getting there
the journey
is the destination.
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Cassini/Huygens
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Cassini/Huygens
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KSC, Cape Canaveral: 15 Oct 1997
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Cassini SOI: 1 July at 02:36 UT
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Christmas Day 2004
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14 January 2005
7 years, 3 months and
4 billion km from launch
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Huygens Descent on Titan
From
Atmospheric Entry
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To
Touchdown on Surface
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Huygens Targetting Error
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Huygens Landing Error
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Huygens: Descent Scenario
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Huygens events (UTC)
One Way Light Time = 1 h 07 m 06 s
Event
Spacecraft Event
Time (UTC)
Earth receive time
(UTC)
Entry into Titan atmosphere
09:06:59
10:14:05
Deploy pilot parachute (t0)
09:10:21
10:17:27
Start Radio transmission
09:11:09
10:18:15
Huygens Signal Detection at
Green Bank Telescope
na
10:25:00
Change parachutes
09:25:21
10:32:27
Impact on surface
11:38:11
12:45:17
End of link with Cassini
12:50:24
13:57:30
Last Huygens signal detection
na
at Parkes Telescope
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15:56:55
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Huygens Mission Intervals
Predicted vs. Actual
Interval
Predicted Duration
(hh:mm:ss)
Actual Duration
(hh:mm:ss)
Descent Time
02:15:00
02:27:50
Cassini Link Time
02:18:00
03:40:03
Cassini Link from Surface
00:03:00
01:12:13
Total Observed Survival Time
< 05:00:00
05:38:55
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lifting Titan’s veil
Yet do thy cheeks
look red as Titan’s face
W. Shakespeare
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Titan: Pre-Cassini/Huygens (1)
• PTitan orbit = 15.9 d, PSaturn orbit = 29.4 yr, obliquity = 27°
• Bulk density = 1.88 g cm-3, ~ Callisto & Ganymede (~50% ice, ~50% rock)
• Atmospheric Composition:
N2
0.77 – 0.92 (0.97)
Ar
0.05 – 0.17 (<0.001)
CH4 0.03 – 0.07 (0.023)
other hydrocarbons and nitriles
• Haze from photodissociation of CH4:  = 2-5 in visible,  < 1 in near-IR.
• Tsurface = 94 K, Psurface = 1.5 bar.
• Tropopause (42 km): T = 71 K; Scale height in troposphere = 20 km
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Titan: Pre-Cassini/Huygens (2)
Mild
Greenhouse
Effect
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Optically
Thick
Aerosol
Haze
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Huygens Investigations
Investigation
Acronym
PI
Huygens Atmosphere
Structure Instrument
HASI
M. Fulchignoni, Obs. Paris-Meudon (F)
Descent Inager/Spectral
Radiometer
DISR
M. Tomasko, U. Arizona, Tucson, AZ (USA)
Gas Chromatograph / Mass
Spectrometer
GCMS
H. Niemann, NASA/GSFC, Greenbelt, MD
(USA)
Aerosol Collector and
Pyrolyzer
ACP
G. Israel, SA-CNES, Verrieres-de-Buisson
(F)
Surface Science Package
SSP
J. Zarnecki, Open U., Milton Keynes (UK)
Doppler Wind Experiment
DWE
M. Bird, U. Bonn (D)
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HASI atmospheric profiles
pressure
temperature
Psurf= 1.463 bar
Tsurf= 93.8 K
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GCMS Atmospheric Constituents
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ACP Schematic
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SSP: Impact on Surface
‘wet sand
or clay’
(crème brûlée)
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DISR: first images
drainage
canals;
fluvial
activity
fluid:
CH4
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‘dry’
lakebed
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DISR: Selected Details
methane springs?
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water ice shoals?
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DISR: side-looking imager
h: 8 km
res: 20 m
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DISR: 360 Panorama
ground fog
h: 8 km; s: 20 m
horizontal velocity: 1-2 m s-1
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landing site
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DISR:
on the surface
‘orange tint from
reflectance spectra’
‘mouse’
5 cm
85 cm
‘dirty water ice,
not hydrocarbon ice’
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Huygens
Doppler Wind Experiment:
An Update
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DWE Concept
•
•
Goal: In situ determination of zonal wind
speed along Huygens descent path
Approach: Record Doppler effect on
Huygens carrier signal => radial velocity
–
Input parameters:
1. Huygens descent speed, meridional speed
2. Huygens starting position
3. Cassini position & velocity
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DWE Hardware
Ultra-stable Oscillators (USOs)
• TUSO on
Huygens
Probe
• RUSO in
Huygens
Receiver on
Cassini
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Huygens Doppler: PCO#1
TUSO/RUSO
TCXO/TCXO
3 hours
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No power!
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DWE from Earth: Geometry
• Huygens antenna
pointed only ~30° from
Earth
• Better SNR than for
Galileo Probe detection
at Jupiter
• Probe velocity
projection in direction
to Earth nearly
antiparallel to
projection in direction
to Orbiter
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75°
60°
45°
30°
15°
240°
210°
Track of Orbiter
180°
150°
120°
Probe
0°
-15°
-30°
Track of
Sub-Earth
Point
-45°
-60°
-75°
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GBT
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Parkes
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Earth-based DWE: Huygens Frequency
Change of parachutes
GBT
Impact on surface
Parkes
Time (SPM)
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prograde
zonal wind
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VLBI network as seen from Titan: 14 Jan 2005
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VLBI station visibility
entry
landing
orbiter battery
Parkes
GBT
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Huygens Art Contest
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Lebe Wohl, Huygens
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