Current status of Japanese Venus Orbiter, Akatsuki

1. Current status of Japanese Venus Orbiter, Akatsuki Takeshi Imamura, Akatsuki Team Japan Aerospace Exploration Agency

2. Venus Climate Orbiter/Akatsuki • Scientific objectives • 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 : from October) • Launch : May 21, 2010  Arrival: December 7, 2010 • VOI-1 on Dec 7 : Insertion to 96-h orbit • VOI-2 on Dec 11 : Insertion to 48-h orbit • VOI-3 on Dec 13 : Insertion to 30-h orbit • The condition of the spacecraft is normal. Three cameras (UVI, IR1, LIR) and USO have already been turned on and tested. IR2 will be turned on soon. • Nominal operation will start in late December or January.

3. LIR LAC UVI IR1 IR2 USO

4. Akatsuki launch: May 21, 2010

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

6. Zodiacal light observation (next week ~ November)

7. Onboard instruments

8. Orbital motion Disk diameter < 12° North pole visible Venus 12° FOV N.P. (km) Orbital motion

9. Wavelengths for cloud-tracking 10mm, cloud top (65km), dayside & nightside 365nm, cloud top (65km), dayside 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 are covered both on the dayside and nightside 0.98 um image taken by Galileo/SSI 2.3 um image taken by Galileo/NIMS

10. Orbital motion partially synchronized with the super-rotation Spacecraft 60 m/s westward flow near the cloud base - Time evolution of meso-scale processes - Precise determination of wind vectors A concept similar to geostationary meteorological satellite (movie provided by M. Odaka)

11. Perfect synchronization with super-rotation Akatsuki’s partial synchronization Coverage of global viewing Time Time ~1 day 5-7 days 0°360° 0°360° Longitude in a reference frame rotating with the super-rotation Longitude in a reference frame rotating with the super-rotation

12. Detectable modes • Wavenmber-1 waves have been detected at the cloud top by spectral analysis of UV brightness (DelGenio & Rossow, 1990) • Equatorial mode : c-U = 16 m/s  intrinsic period = 27 days • Midlatitude mode : c-U = -32 m/s  intrinsic period = 10 days • Given the repetition period of full longitudinal coverage of 5-7 days, the Nyquist frequency is formally 10-14 days. • However, with the continuous data over up to 1 day in each orbital revolution, much faster waves will also be covered. Especially eastward fast modes are easy to be detected.

13. Latitude and local solar time of radio occultation • 360-deg local time coverage in the tropics Thermal tides, Diurnal variation of cloud region • Sometimes the locations probed by radio occultation will be imaged by cameras a short time before or after the occultation.

14. Stability of USO after the launch • X-band downlink generated from the USO frequency was recorded on June 2, 2010. • Allan dev. is on the order of 10-13 for 1-1000 sec.

15. Receiving VEX radio occultation signals using Usuda antenna in Japan • April 40, May 6, and June 16 in 2010 • The performances of the ground system and data processing software were verified. Static stability H2SO4 vapor mixing ratio

16. 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

17. An example of FITS data (Earth UV image) (FITS creating software developed by Manabu Yamada)

18. An example of netCDF data (Venus Express VMC) (netCDF creating software developed by Kazunori Ogohara)

19. Telemetry rate 130 images will be acquired in each orbital revolution

20. Dec 15, 2010 32kbps Orbital motion Disk diameter < 12° Lightening and airglow North pole visible IR1 0.9um, 0.97um, 1.01um, IR2 1.73, 2.26, 2.32um, LIR 10um Venus Earth 12° FOV N.P. IR1 0.9um, UVI 365nm, LIR limb IR1 0.9um, IR2 2.02um, UVI 283, 365nm, LIR 10um UVI 365nm x 7 times, LIR 10um (km) night_delux, night_delux_ir1 night_delux, night_slim_ir1 LAC day_delux vicinity_slim_7 limb lir RS

21. Jan 15, 2011 32kbps Orbital motion Disk diameter < 12° North pole visible Venus 12° FOV N.P. (km) night_delux, night_delux_ir1 night_delux, night_slim_ir1 LAC day_delux vicinity_slim_7 limb lir RS

22. Feb 15, 2011 16kbps Orbital motion Disk diameter < 12° North pole visible Venus 12° FOV N.P. (km) LAC day_slim day_delux vicinity_slim_7 RS

23. Mar 15, 2011 16kbps Orbital motion Disk diameter < 12° North pole visible Venus 12° FOV N.P. (km) LAC day_slim day_delux vicinity_slim_7 RS

24. Apr 15, 2011 8kbps Orbital motion Disk diameter < 12° North pole visible Venus 12° FOV N.P. (km) LAC day_slim day_delux night_slim vicinity_slim_7 RS

25. May 15, 2011 8kbps Orbital motion Disk diameter < 12° North pole visible Venus 12° FOV N.P. (km) night_delux, night_delux_ir1 LAC day_slim night_slim

26. Summary • VCO/Akatsuki will address the unique dynamical state of the Venus atmosphere with systematic sampling of meteorological variables from equatorial orbit. • The condition of the spacecraft is normal. Three cameras (UVI, IR1, LIR) and USO have already been turned on and tested. IR2 will be turned on soon. • Star calibration observations and tests of major ‘Observation programs’ will be done before VOI. • The start of zodiacal light observation was postponed to October. • Data processing pipeline is under development. Wind vectors as well as image data and radio occultation data will be released to the public 1 year after acquisition.