The Doppler Wind Experiment

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Measuring the Zonal Winds on Titan The Huygens
Probe Doppler Wind Experiment
Dr. David H. Atkinson Dept. Electrical Computer
Engineering University of Idaho 8 April 2005
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Cassini/Huygens
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HST
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Voyager 1
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GCMS
Atmospheric Structure Instrument
Accelerometers
Surface Science Package
Command Data Management Unit (CDMU)
Transmitter Ultrastable Oscillator (TUSO)
Descent Imager
Radar Altimeter Antennas
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Batteries
PCDU
ACP
SSP
GCMS
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KSC, Cape Canaveral 15 Oct 1997
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Cassini SOI 1 July at 0236 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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Titan Pre-Cassini/Huygens
N2, CH4, and H2 atmosphere cause a mild
greenhouse effect that raises the surface
temperature by 21K.
High altitude optically thick organic haze
absorbs solar visible but is transparent to IR,
cooling surface temp by about 9K. (anti-greenhouse
effect).
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Huygens Scientific Payload

• ACP - Aerosol Collector and Pyrolyser (G. Israel,
  France)
• Collection of aerosols for chemical-composition
  analysis.
• GCMS - Gas Chromatograph and Mass Spectrometer
• (H. Niemann, NASA GSFC)
• gas chemical analyser designed to identify and
  quantify various atmospheric constituents.
• DISR - Descent Imager Spectral Radiometer
• (M. Tomasko, U. Arizona)
• images and spectral measurements. Also spectra of
  the surface material will be acquired.
• DWE - Doppler Wind Experiment (M. Bird, U. Bonn)
• Wind measurements using Probe/Orbiter radio
  signal
• HASI - Huygens Atmosphere Instrument
• (M. Fulchignoni, Italy)
• physical and electrical properties of the
  Atmosphere
• SSP - Surface Science Package (J. Zarnecki, UK)
• physical properties of the surface at the impact
  site

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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 gt radial velocity
• Input parameters
• Huygens descent speed, meridional speed
• Huygens starting position
• Cassini position velocity

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DWE Hardware
Ultra-stable Oscillators (USOs)

• TUSO on
• Huygens Probe
• RUSO in
• Huygens
• Receiver on
• Cassini Orbiter

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No power!
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Channel B Temperature Compensated Crystal
Oscillator
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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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Huygens VLBI Network
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Parkes Telescope Australia
Green Bank Telescope West Virginia
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Huygens Radio Tracking Net
1018 UTC-ERT
1230 UTC-ERT
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101815 UTC-GRT
101810 UTC-GRT
Green Bank Telescope
Huygens! ( -171 dBm)
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Huygens Frequency GBT Parkes
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DWE Preliminary Results

• Zonal winds above boundary layer are PROGRADE
• Low-velocity layer between 60-80 km
• Stong positive/negative wind shear
• Unexpected, but evident in some GCMs
• Considerable turbulence above 100 km
• Near surface winds are weak ( 1-2 m/s)

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Adieu, Huygens