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The Cassini-Huygens Mission to Saturn and Titan

Professor John C. Zarnecki

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Saturn and Titan

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Saturn

Most distant planet visible with the naked eye 2nd largest planet in the solar system Gas giant – primarily Hydrogen and Helium 34 known moons at present 1.5 billion km mean distance from the sun, 10 x more distant than the

Earth Unique complex ring system

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Titan

Saturn’s largest moon

Discovered by Christiaan Huygens in 1655

Diameter of 5150 km

Atmospheric pressure of 1.5 bar

Surface temperature ~ 96 K (-177°C)

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Why Titan?

Only planetary satellite with atmosphere (column mass ~ 10

x value for Earth)

Surface – obscured by photochemical haze

Atmosphere – mainly N2 with CH4 and an array of

hydrocarbons and nitriles

Indirect evidence for surface seas/lakes (i.e. a methane

‘source’)

A ‘primordial atmosphere’ (but frozen!) → an ancient earth?

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The Cassini/Huygens Mission

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The Cassini Spacecraft

Joint ESA/NASA mission

Launched 15th October 1997

6.7 m high 2125 kg at launch After a 7 year (4 billion

km) journey, Cassini arrived at Saturn in July 2004.

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The Gravity Assist Trajectory

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Saturn Orbit Insertion

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The Huygens Probe

Determine atmospheric composition

Study aerosol properties and cloud physics

Characterise the upper atmosphere

Imaging the surface for the first time

Determine the physical properties of the surface material

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IndustryLogicaCMG – Mission critical on-board software, including Probe

control software, Cassini/Huygens communications relay software and in flight software maintenance.

Martin Baker Space Systems – Parachute systems and related structural components, mechanisms and pyrotechnics.

Irvin Aerospace – Sub-contractor to Martin Baker responsible for definition of each of the three disk gap band parachutes.

IGG Component Technology - Centralised procurement and testing of electrical, electronic and electromechanical components.

SciSys – Mission control system development and operational support.

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List of Instruments1. Huygens Atmospheric Structure

Instrument (HASI) Fulchignoni, Paris, France.

2. Gas Chromatograph Mass Spectrometer (GCMS) Niemann, NASA, USA

3. Aerosol Collector and Pyrolyser (ACP) Israel, CNRS, France.

4. Descent Imager/Spectral Radiometer (DISR) Tomasko, Arizona, USA

5. Doppler Wind Experiment (DWE) Bird, Bonn, USA

6. Surface Science Package (SSP) Zarnecki, OU, UK.

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The Surface Science Package(SSP)

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SSP Flight Integration

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SSP Sensor Description

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Selected Properties Measured by SSP

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ATMOSPHERESOLIDMUDLIQUID

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ACC-I (Internal Accelerometer)

Piezoelectric accelerometer Max ~100 g detection Impact dynamics measurement

(deceleration)

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ACC-E (Penetrometer)

Piezoelectric force transducer

Protrudes from probe base

First instrument to touch Titan’s surface

Impact measurement of penetration through the surface layer (mechanical properties of the surface)

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TIL (Probe Attitude)

Measures tilt relative to 1 axis

Electrolytic liquid in a glass vial

Fluid movement relative to electrodes → tilt angle

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API-V (Speed of Sound)

2 piezoelectric transducers generate ultrasonic pulse

Alternate Tx/Rx mode Arranged facing each

other Time taken for pulse

to be detected → speed of sound in the Titan atmosphere (molecular mass)

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API-S (Sounder)

10 resonant piezoelectric plates

Simultaneously form a 20° acoustic beam

Orientated towards the surface

Surface profile echoes Ocean/lake sounder

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THP (Thermal Properties)

Thin wire technique 50 µm Pt wire pulsed with

high current

RΩ(t) measured Thermal conductivity

derived (gas mixture components)

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DEN (Density)

Archimedes’ principle Float suspended in

chamber

Buoyancy in immersed liquid measured by strain gauges → density

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REF (Refractometer)

Critical angle refractometer Linear photodiode array and

specially designed prism

Refractive index of immersed liquid measured (light-dark transition)

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PER (Permittivity and Conductivity)

Stacked parallel plates

Capacitance measured Permittivity and conductivity

of the liquid measured

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Landing On Titan

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Arrival and Descent

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Possible Landing Scenarios

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High Altitude Images

Altitude 16.2 km, 40m per pixel resolution

Credits: ESA/NASA/University of Arizona

Altitude 8 km, 20m per pixel resolution

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High Altitude Images

Credits: ESA/NASA/University of Arizona

Altitude 16.2 km, 40 m per pixel resolution

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A View from 10 km

Credits: ESA/NASA/University of Arizona

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Views at the surface

Credits: ESA/NASA/University of Arizona

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The Impact on the Surface

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The Impact on the Surface

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Impact Simulations Over 100 vertical and

oblique drops into 16 different substrate materials.

Coarse Gravel Sand

SiliBeads Crème Brulee Drop Test Rig

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Impact Simulations

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Impact Simulations

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Impact Dynamics – First Look

• ACC-I (deceleration):35ms deceleration pulse, peak 15g – Huygens probe decelerated over circa 16cm; Model comparison suggests material with uniform strength vs. depth, ~10

N cm-2

• ACC-E (penetration force):50N resistance with some variation – possibly a pebble strike, possible sub-surface granular structure on cm scale or finer

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API-S Surface Detection

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API-V

Speed of sound increases with temperature at lower altitude

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SSP Data Summary

• SSP has received ALL of its Science Data via Channel B.

• All SSP sensors have given the expected output for the atmospheric and surface conditions encountered.

• We have data up to T0 + 13,046secs (3hrs, 37mins, 26secs).

• Data from surface for 1hr, 9 mins, 36secs

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17 January 2005L.Gurvits and the Huygens VLBI Tracking Team

Doppler (wind and more….) measurements

Huygens carrier at Green Bank, Mk5 VLBI

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Acknowledgements

• SSP Science Team• Huygens Science Team• ESA• NASA• Polish Academy of Sciences• University of Manchester• Rutherford Appleton Laboratory• Particle Physics and Astronomy Research

Council