The Huygens Doppler Wind Experiment:Results from Titan

Michael Bird(Radiostronomisches Institut, Universität Bonn)

And the DWE Team

EGU Vienna - April 25, 2005

Vienna EGU, 25 April 20052

Huygens DWE

The DWE Team• M.K. Bird, R. Dutta-Roy, Y. Dzierma Radioastronomisches Inst., Univ. Bonn, Auf dem Hügel 71, 53125 Bonn, Germany• M. Allison NASA Goddard Inst. for Space Studies, 2880 Broadway, New York, NY 10025, USA• D.H. Atkinson Dept. of Elec. & Computer Engineering, Univ. of Idaho, Moscow, ID 83844, USA• S.W. Asmar, W.M. Folkner, D.V. Johnston, R.A. Preston Jet Propulsion Laboratory, Caltech, 4800 Oak Grove Dr, Pasadena, CA 91109, USA• P. Edenhofer Institut für HF-Technik, Universität Bochum, 44780 Bochum, Germany• D. Plettemeier Elektrotechnisches Institut, Technische Univ. Dresden, 01062 Dresden, Germany• G.L. Tyler Center for Radar Astronomy, Stanford University, Stanford, CA 94305, USA• L.I. Gurvits, S.V. Pogrebenko, I.M. Avruch Joint Inst. for VLBI in Europe, P.O. Box 2, 7990 AA Dwingeloo, The Netherlands

Vienna EGU, 25 April 20053

Huygens DWE

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

Vienna EGU, 25 April 20054

Huygens DWE

DWE Hardware

• TUSO on Huygens Probe

• RUSO in Huygens Receiver on Cassini

Ultra-stable Oscillators (USOs)

Vienna EGU, 25 April 20055

Huygens DWE

Cassini

TCXOTCXO

TCXORUSO

TCXOTUSO

Channel B

Channel A

Earth

“Channel C”

Huygens Signal paths

Huygens Data

HuygensReceivers

HuygensProbe

Vienna EGU, 25 April 20056

Huygens DWE

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

0°

15°

30°

45°

60°

75°

-15°

-30°

-45°

-60°

-75°

Track ofSub-Earth

Point

Track of OrbiterProbe

180°210°240° 150° 120°

20º

Vienna EGU, 25 April 20057

Huygens DWE

Huygens Radio Tracking Net

10:18 UTC-GRT 12:30 UTC-GRT

GBT

VLBA

MK

KP

PTOV

MK

Parkes

VLBA

Vienna EGU, 25 April 20058

Huygens DWE

Huygens VLBI NetworkFacility Start UTC Stop UTC Comment

GBT 09:31:10 12:15:00 DWE: Real time RSR detection

VLBA Fort Davis 09:31:10 13:45:00

VLBA North Liberty 09:31:10 13:15:00

VLBA Owens Valley 09:30:09 14:49:14 DWE: No nodding – on Titan continuously

VLBA Pie Town 09:30:11 14:15:04 DWE: No nodding – on Titan continuously

VLBA Los Alamos 09:31:10 14:00:00

VLBA Brewster 09:31:10 14:48:00

VLBA Kitt Peak 09:31:10 14:15:00 DWE

VLBA Mauna Kea 09:31:10 16:00:00 DWE

Parkes 12:26:23 16:00:00 DWE: Real time RSR detection

Hobart 11:13:10 16:00:00

Ceduna 10:13:10 16:00:00

Mopra 10:10:10 16:00:00

Kashima 09:31:10 16:00:00

Shanghai 10:01:10 16:00:00

Urumqi 11:31:10 16:00:00 Calibration only, no Huygens signal at 2040 MHz

ATCA 10:01:10 16:00:00 Calibration only, no Huygens signal at 2040 MHz

Onsala 19:01:10 22:15:00

Wettzell 21:46:10 22:15:00

Vienna EGU, 25 April 20059

Huygens DWE

GBT Parkes

Vienna EGU, 25 April 200510

Huygens DWE

GBT Huygens!(~ -171 dBm)

Flux density 125 Jy

10:18:15 UTC-GRT10

just noise

Vienna EGU, 25 April 200511

Huygens DWE

Huygens Frequency: GBT + Parkes

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Huygens DWE

Huygens Frequency: GBT + predicts

Vienna EGU, 25 April 200513

Huygens DWE

Huygens Frequency: Parkes + Predicts

predictedimpact

Vienna EGU, 25 April 200514

Huygens DWE

Parkes: Huygens Impact on Titan

Vienna EGU, 25 April 200515

Huygens DWE

Zonal Wind Retrieval

LSCEWNSdesLS nvvvvv

)(

)coscoscos(cos

1NSNSdesdesCCLS

DWC

EW vvvvv

0fc

vf

LS

R Doppler shift:

where

= radial velocity between transmitter and receiver

Vienna EGU, 25 April 200516

Huygens DWE

GBT

(1) Raw Doppler

(2) Only Huygens Motion

(3) Huygens Descent Velocity

(4) Huygens Horizontal Velocity

Doppler Components

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Huygens DWE

Zonal Wind Velocity

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Huygens DWE

Zonal Wind Height Profile

Vienna EGU, 25 April 200519

Huygens DWE

DWE: Preliminary Results• Zonal winds above boundary layer are

PROGRADE

• Huygens drifted 3.95º (~175 km) eastward

• Low-velocity layer between 60-100 km – Stong positive/negative wind shear– ‘Unexpected’, but evident in some models

• Considerable turbulence above 100 km

• Near surface winds are weak (~ 1-2 m/s)