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Akatsuki : Venus Climate Orbiter

Akatsuki : Venus Climate Orbiter. Takeshi Imamura Japan Aerospace Exploration Agency. Venus Climate Orbiter/Akatsuki (PLANET-C project). First Japanese Venus mission Science target : Mechanism of super-rotation Structure of meridional circulation Meso-scale processes

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Akatsuki : Venus Climate Orbiter

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  1. Akatsuki : Venus Climate Orbiter Takeshi Imamura Japan Aerospace Exploration Agency

  2. Venus Climate Orbiter/Akatsuki(PLANET-C project) • First Japanese Venus mission • Science target : • Mechanism of super-rotation • Structure of meridional circulation • Meso-scale processes • Formation of H2SO4 clouds • Lightning • Active volcanism, inhomogeneity of surface material • Zodiacal light (during cruise) • Launch : May 2010  Arrival: December 2010 • Mission life :More than 2 Earth years

  3. Comparative planetary meteorology

  4. Hypotheses of super-rotation Stratosphere Acceleration Thermal tides Waves or Turbulence • Which is working? Any other mechanisms? • Key parameters: Planetary-scale waves, Meridional circulation, Large-scale turbulence Cloud Troposphere Gravity waves Hadley circulation Thermal tides NP Eq SP NP Eq SP NP Eq SP

  5. Cloud processes • Dynamics of cloud formation, role of meridional circulation in transporting cloud-related species • Origin of UV markings • Whether lightening occurs or not Schubert (1983)

  6. Concept of meteorological satellite • Capturing global structures with emphasis on the low latitude  Wide FOV imaging from equatorial orbit • Covering spatial scales from meso to global  Large-format 2D detectors • Covering time scales from hours to months  Continuous sampling, repeating for all orbits • Studying vertical structures  Multi-wavelength imaging + radio science

  7. Near-IR windows IRTF2.3um Galileo/NIMS 金星フライバイ時の夜面観測

  8. Observation from an orbiter Lightning and airglow camera Longwave IR camera (cloud temperature) • 4 cameras sounding different altitudes, a high-speed lightning detector, and an ultra-stable oscillator for radio science • Constructing 3-D model of atmospheric dynamics Ultraviolet imager (stratosphere) 1-mm camera (surface) 2-mm camera (lower atmosphere) Radio science (vertical structure)

  9. Ultra Stable Oscillator （USO） Digital Electronics （DE） 1mm Camera （IR1) 2mm Camera （IR2) Side panel of spacecraft Ultraviolet Imager （UVI） 283,365nm 550～770nm ~10mm Lightning and Airglow Camera （LAC） Longwave InfraRed camera (LIR)

  10. Onboard instruments

  11. Resolution: 10-20 km Observations to be conducted during one orbital revolution Successive Global images of atmosphere and ground surface (~24 hours) Limb images (~0.5 hour) Orbital period: 30 hours Close-up images/ Lightning/Airglow (~3 hours x 2) Temperature / H2SO4 vapor / Ionosphere by radio occultation

  12. Orbital motion synchronized with the super-rotation Spacecraft 60 m/s westward flow near the cloud base A concept similar to geostationary meteorological satellite (movie provided by M. Odaka)

  13. Wavelengths for cloud-tracking 365nm, cloud top (65km), dayside 10mm, cloud top (65km), dayside & nightside 2.02mm, cloud top(65m), dayside 365 nm image taken by PVO/OCPP 8.6 um image taken by Subaru telescope, high-pass filtered Cloud altimetry by VenusExpress/VIRTIS 0.9mm, lower cloud (50km), dayside 2.3mm, lower cloud (50km), nightside * Cloud top and bottom will be covered on both dayside and nightside. 0.98 um image taken by Galileo/SSI 2.3 um image taken by Galileo/NIMS

  14. Accuracy of wind velocity measurement • Cloud position accuracy is assumed to be 1 pixel. • Mean meridional circulation is obtained by averaging large number of vectors and will be determined with much higher accuracy than above estimates.

  15. Latitude and local solar time of radio occultation • 360-deg local time coverage in the tropics Thermal tides including sub-cloud region • Intensive observation in the sub-solar region  Origin of ‘cells’ • Locations probed by radio occultation will be imaged by cameras a short time before or after the occultation.

  16. 3-D sounding

  17. Complementary missions Coordinated observations are being planned.

  18. Telemetry rate Bitrate (kbps) • Bit rate is relatively high during the 1-2 months following VOI (Venus Orbit Insertion). • Well-laid observation plan is needed to reduce the data volume. Days after VOI

  19. Orbit just after VOI Night global view Limitation of solar angle (26.5o) Earth Lightning / airglow Radio occultation Day/night global view Limb view Radio occultation Close-up/ Stereo viewing

  20. Data processing pipeline Level 0 : Uncompressed images • Level 2 and Level 3 data will be released to the public with PDS-like label files. Level 1 : Calibrated images with FITS header Level 2 : Calibrated images with FITS header, including geometry information Level 3 : Wind vectors and other higher-level products on longitude-latitude grids in NetCDF format

  21. Automatic Level 3 processing • Limb fitting to precisely determine the direction of camera FOV • Projection onto longitude-latitude grids assuming typical cloud height (2 levels) • Cloud tracking by cross correlation method • Correction of erroneous vectors (Method developed by Toru Kouyama at U. Tokyo/ISAS)

  22. LIR LAC UVI IR1 IR2 組み立て

  23. ロケット結合アダプターとの適合試験

  24. 振動試験 熱真空試験

  25. 2010年5月21日　打ち上げ フェアリングに収納

  26. First light UVI 365nm LIR 10μm IR1 0.9μm

  27. 金星到着までの道のり • 金星の公転軌道面は３°傾斜している • 地球から打ち上げられた「あかつき」は地球の公転軌道面に沿って金星に向かう。 • 金星接近時に金星が地球の公転軌道面と同じ位置にあるため、少ないエネルギーで探査機は金星に到着できる。 • [イメージ図] 金星 太陽 金星の公転軌道 地球の公転軌道 • 2010年5月打ち上げ • →2010年12月金星到着予定 地球

  28. Summary • VCO/Akatsuki will address the unique dynamical state of the Venus atmosphere with systematic sampling of meteorological variables from equatorial orbit. • Three-dimensional structure of the atmosphere and its temporal variation will be observed by using 4 cameras, a high-speed lightning detector and radio occultation. • Data processing pipeline is under development. Wind vectors as well as image data and radio occultation data will be released to the public. The dataset will enable quantitative studies of eddy momentum transport and meridional circulation.

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