AKATSUKI RETURNS TO VENUS

Transcription

1 AKATSUKI RETURNS TO VENUS MASATO NAKAMURA, NOBUAKI ISHII, TAKESHI IMAMURA, TAKEHIKO SATOH, TAKUMI ABE, CHIKAKO HIROSE, ATSUSHI YAMAZAKI, JUNICHI NAKATSUKA, TSUTOMU ICHIKAWA, TOMOAKI TODA, HIROYUKI TOYODA, SUMITAKA TACHIKAWA, YUKIO KAMATA, MAKOTO SUZUKI, TAKAO M. SATO, SHIN-YA, MURAKAMI, YUKIO YAMAMOTO, NAOMOTO IWAGAMI, MAKOTO TAGUCHI, TESUYA FUKUHARA, SHIGETO WATANABE, YUKIHIRO TAKAHASHI, MUNETAKA UENO, MANABU YAMADA, GEORGE L. HASHIMOTO, NARU HIRATA, TORU KOUYAMA, KAZUNORI OGOHARA, HIROKI ANDO, KO-ICHIRO SUGIYAMA, HIROKI KASHIMURA, AND SHOKO OHTSUKI

2 VENUS SEEN ON JANUARY 1, 2016 Akatsuki is now orbiting this planet

3 PLANET-C the Venus Climate Orbiter Science goal : Atmospheric dynamics Lightning, Cloud physics, Active Volcano, Geological Survey Launch : Summer 2010 Arrival : December, > 2015 Near-IR UV Near IR camera 1 l=0.9, 0.97, 1.01mm Near IR camera 2 l=1.65, 1.73, 2.02, 2.26, 2.32mm Longwave IR camera l=8-12mm UV camera 3-D meteorological observation by multi-wavelength cameras l=283, 365nm Lightning and Airglow camera l=777, 551, 558nm

4 AKATSUKI FOCUSES VENUSIAN METEOROLOGY Westerly wind Earth Venus Trade wind Superrotation wind velocities are generally much smaller than the planetary rotation and the wind direction depends on the latitude Winter Westerly wind Summer Mars? The factors which determine the atmospheric circulation regime are not well understood Titan Superrotation Studying Venus turns out to be a new meteorology which can be applied both to Venus and Earth

5 SPACECRAFT Body Weight Mission instruments 1.04 [m] x 1.45 [m] x 1.40 [m] (dry) 321 kg (wet) 518 kg (@launch) (wet) 377 kg (2015/5/1) 1μm camera (IR1) 2μm camera (IR2) Longwave infrared camera (LIR) UV imager(uvi) Lightning and Airglow camera (LAC) Ultra Stable Oscillator (USO) Propulsion system Antenna Orbital maneuver engine (OME): Reaction control system(rcs): HGA-T/R (X band) MGA-A/B (X band) LGA-A/B (X band) 500N class 23N class x 8 3N class x 4 5

6 An Ultraviolet Imager (UVI) detects SO 2 and unknown material absorption patterns at 283 nm and 365 nm, respectively, at an altitude of approximately 65 km, and the image sequence reflects cloud motions at this altitude. At almost the same altitude, the cloud top temperature is detected by a long Infrared camera (LIR) at a wavelength of 8-12 mm. Movement of the cloud temperature pattern also provides information on cloud motions. At lower altitudes of approximately 50 km, 1 mm, and 2 mm, infrared cameras (IR1 & IR2) are used to capture images. Observation wavelengths are 0.9, 0.97, and 1.01 µm, and 1.74, 2.02, 2.26, and 2.32 µm, respectively. Furthermore, hotspots might be detected by IR1, which may represent active volcanoes. Lightning and Airglow Camera (LAC) is a high speed photometer with a 30 kh sampling rate used to detect possible lightning in the Venusian atmosphere, which can be an indicator of vertical air flow. OBSERVATION BY 5 CAMERAS

7 L AURORE. CHANTS DU RHIN Georges Bizet (piano: Peter Vanhove)

8 Failure of VOI on December 7 th, :26JST Spacecraft was discovered Orbit Plan 2010/12/7 Nominal case: 9:01:00JST OME stop Actually 8:51:38JST End of Occultation 09:12:03JST No telemetry Venus Start of Occultation 08:50:43JST OME start 2010/12/7. 08:49JST 8

9 Reaction Control System should be used for orbital maneuver instead of broken OME thrust RCS (23N x8) Broken OME(500N)

10 THERMAL CONDITION Differences of heat input in Venus orbit and in AKATSUKI s orbit after 2010 VOI

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12 2 J2000 Ecliptic coordinate meet Venus on 7 December, ORBITAL MANEUVER( ) 2011 Orbital maneuver (DV1-3)was done to meet VENUS on 22 November, 2015 Orbit analysis revealed that the spacecraft would crash with Venus very shortly July 2015 additional maneuvers (DV4-1,2,3) was done to correct the orbit to 2015/1/1 2015/12 月 /2 月 2015/5 月 金星 2015/5 月 遠日点 (2015/5 月, 12 月 ) VOI-R (2015/12 月 ) 太陽 あかつき 近日点 (2015/2 月, 8 月 ) 2015/1/1 DV4(2015/7 月 ) 2015/7 月 2015/1/1 2015/7 月 地球 2015/2 月 2015/8 月 2015/8 月 Venus Earth Akatsuki Akatsuki Events Earth Events Venus Events Akatsuki dv Earth dv Venus dv DV4 2015/07 ΔV 89m/s x 10 8 km Last perihelion 2015/8/30 12

13 VOI-R1 Geometry (Sun center) Dec 7, 2015 Dec 7, 2015 VOI-R1 Nov 9, 2015 Planet-C Earth Nov 9, 2015 Venus cliptic coordinate Sun Red: Venus, Green: Planet-C Ticks: every one day Dec 1, 2015 [Sun centered] Attitude change for VOI-R1 Dec 6, 2015 Dec 7, 2015 VOI-R1 3

14 VOI-R1 ON 7 DECEMBER, 2015 Doppler monitor

15 1 ST LIGHTS The distance between the spacecraft and Venus is about 70,000 km and the apparent diameter of Venus is about 10. The solar phase angle at the sub-observer point was ~45 with the evening terminator in view. No data reduction procedures were performed on the images except for several onboard processing steps (i.e., median filtering and subtraction of the dark current for IR1 and UVI, desmearing for UVI, and accumulation of 32 images and subtraction of a shutter image for LIR). The spatial resolution of the IR1 and UVI images shown is ~15 km/pixel. IR2 s first image was captured 4 days later, at 12:33UT on December 11, 2015, because 4 days were required to cool the imaging device to approximately 70 K. This observation was done at 2.02mm. The distance from Venus to the spacecraft was 410,000 km.

16 Observation plan based on the new orbit Successive Global imaging of atmosphere and ground surface Limb images Orbital period : 10.5 days Ground station Temperature / H 2 SO 4 vapor / Ionosphere by radio occultation - Close-up images - Stereo viewing - Lightning - Airglow

17 IR images by Galileo and VCO IR2 Galileo 2.3µm image VCO IR and 2.26mm image

18 UVI This 283-nm image was acquired with UVI at 13:13 UT on 25 April As this wavelength is in the SO2 absorption band, we can investigate the distribution of materials (SO2) for the Venus clouds (sulfuric acid). The spacecraft altitude was 108,000 km. This 365-nm image was acquired with UVI at 16:17 UT on 6 May Although the absorbent of this wavelength is still unknown, higher contrast allows to study the cloud morphology and dynamics in detail. The spacecraft altitude was 80,000 km. 18

19 IR1 simulation This 1.01-um night-side image was acquired with IR1 at 00:38 UT on 21 January This visualizes spatial variations of thermal emission from the Venus surface with dark features corresponding to low-temperature or highelevation areas. The large low-temperature area is Aphrodite. The image compares to the elevation map in which higher elevation is brighter (courtesy of the National Institute of Advanced Industrial Science and Technology). The spacecraft altitude was 38,000 km. This 0.90-um day-side image was acquired with IR1 at 18:01 UT on 06 May Although the Venus disk appears featureless at a glance, one can find numerous cloud patterns once processed. Such cloud patterns are believed to originate from several km below the cloud top. The image processing includes interpolation of a few lines in the center and enhancement of the features. The spacecraft altitude was 65,000 km. 19

20 IR2 25 March 2016, ~0.1 million km distance, 2.26and 1.75 um wavelength). This 2.26-um night-side image was acquired with IR2 at 07:03 UT on 26 April Spatiallyinhomogeneous clouds are visualized as silhouette with the back light of thermal emission from the lower and hotter atmosphere. The clouds seem to be very complex and turbulent. The image has been processed to enhance the features. The spacecraft altitude was 76,000 km. This 2.02-um day-side image was acquired with IR2 at 16:07 UT on 06 May At this wavelength, variations in cloud top altitude are visualized due to the light absorption by CO2, the primary component of the Venus atmosphere. The image displays relatively low cloud-top altitudes near both poles and complex clouds near the equator. The image has been processed to enhance the features. The spacecraft altitude was 81,000 km. 20

21 LIR LIR acquired whole planet image at 8-12µm just after the orbit insertion on 7 Dec It shows various scale temperature structures at the upper cloud top. A bow shape structure seen near the terminator was unexpected and the most surprising one, existing over 4 days without rotating the planet with the super rotation. This 10-um image was acquired with LIR at 08:15 UT on 15 April 016. LIR visualizes spatial variations of cloud-top temperature with remarkable high temperature in the south polar region. The impressive bow-shape feature, seen in December 2015, is not obvious. However, similar structures exist and are noticed once the contrast of the image is enhanced. The spacecraft altitude was 63,000 km. 21

22 LIR Brightness temperature distribution at the cloud-top obtained by LIR at 10:15, 14:15, and 18:15 UT on April 15, The center-bottom point in each plot corresponds to the south pole. It is clear that the direction in which a high-temperature region extends equatorward from the polar vortex is rotated counter clockwise from 270 at 10:15 to 240 at 18:15. Periodic structures seen around the terminator are artifacts. 22

23 CONCLUSIONS AKATSUKI became the first Japanese probe orbiting a solar planet 15 years after the proposal to ISAS in All the sub systems are working perfectly. The spacecraft will send data over a period of at least two years, highlighting a new era for Japanese exploration whereby data on the continuously changing planet will be delivered to the world. 23