PDS_VERSION_ID = PDS3 RECORD_TYPE = STREAM LABEL_REVISION_NOTE = " 2016-10-18 Initial version by K. McGouldrick; 2017-02-16 revised by S. Murakami; 2017-04-15 revised by S. Murakami; 2017-05-11 revised by S. Murakami; 2017-10-11 revised by S. Murakami; 2017-11-09 revised by R. D. Lorenz and S. Murakami; 2018-04-05 revised by S. Murakami; 2018-09-11 revised by S. Murakami; 2019-01-17 revised by S. Murakami; 2020-11-11 revised by S. Murakami; 2021-04-21 revised by S. Murakami; " OBJECT = MISSION MISSION_NAME = "VENUS CLIMATE ORBITER" OBJECT = MISSION_INFORMATION MISSION_START_DATE = 2010-05-20 MISSION_STOP_DATE = "NULL" MISSION_ALIAS_NAME = {"PLANET-C", "AKATSUKI"} MISSION_DESC = " Most of the contents in this description are extracted from [NAKAMURAETAL2011]. Mission Overview ================ AKATSUKI, also known as Venus Climate Orbiter (VCO) and PLANET-C was successfully launched at 21:58:22 (UTC) on May 20, 2010 using the H-IIA F17 Launch Vehicle. The main goal of the mission is to understand the Venusian atmospheric dynamics, super-rotation, and cloud physics, with the explorations of the ground surface and the interplanetary dust also being the themes. The Venusian atmosphere was studied during the Venus Express mission of the European Space Agency. AKATSUKI was also designed to study the Venusian atmosphere, but in contrast to the Venus Express strategy, five cameras with narrowband filters will image Venus at different wavelengths to track the distributions of clouds and minor gaseous constituents at different heights. In other words, we aim to study the Venusian atmospheric dynamics in three dimensions, while Venus Express collected mainly spectroscopic observations of the atmosphere. The mission started with the mission name and the spacecraft name ``PLANET-C'', which means Japan's third planetary explorer succeeding SUISEI (PLANET-A), which observed Halley's comet, and NOZOMI (PLANET-B), which could not complete its mission to explore Mars. About half year before launch, the Japan Aerospace Exploration Agency (JAXA) officially decided the nickname of the PLANET-C as ``Venus Climate Orbiter'' and also as ``AKATSUKI'' that is a Japanese word meaning ``dawn''. After the successful cruise from Earth to Venus, which took about half a year, the propulsion system malfunctioned during the Venus orbit insertion (VOI) maneuver on December 7, 2010 [NAKAMURAETAL2011; HIROSEETAL2012]. The orbital maneuvering engine (OME) was shut down at 158 s during VOI, while 12 min of operation had been planned. Consequently, the spacecraft did not attain Venus orbit; instead, it entered an orbit around the sun with a period of 203 days. The OME was ultimately found to be broken and unusable, but most of the fuel still remained. Thus, a decision was made to use the reaction control system (RCS) thrusters for orbital maneuvers in November 2011, which were successfully executed so that AKATSUKI would re-encounter Venus in 2015. After the orbital maneuvers in November 2011, the orbital period became 199 days and the encounter with Venus was set for November 22, 2015. This specific date was originally chosen to achieve the shortest encounter time given the spacecraft's now limited expected lifetime. However, a detailed trajectory analysis revealed that the orbit around Venus after insertion on November 22, 2015, would be unstable. Therefore, to achieve a more stable orbit, another orbital maneuver was performed in July 2015 to set the spacecraft on a trajectory to meet Venus on December 7, 2015, just 5 years after from the failure of the VOI. After December 1, 2015, the spacecraft's orbit was just outside of Venus's orbit and the velocity of the spacecraft relative to the sun was less than that of Venus, which allowed Venus to catch up to the spacecraft from the trailing side. On December 7, 2015, the spacecraft approached the planet from outside of Venus's orbit and VOI-Revenge 1 (VOI-R1) procedure was implemented by using four 23 Newton class thrusters of the RCS. VOI-R1 burn (1228 s) was successfully achieved from 23:51:29 on December 6 through 00:11:57 on December 7 (UTC, onboard time). AKATSUKI is the first Japanese satellite to orbit a planet. After the VOI-R1, the apoapsis altitude was ~440,000 km with an inclination of 3 degrees and orbital period of 13 days and 14 h. For the dual purposes of decreasing the apoapsis altitude and avoiding a long eclipse during the orbit, a trim maneuver was performed at the first periapsis. The apoapsis altitude was ~360,000 km with a periapsis altitude of 1,000 -- 8,000 km, and the period is 10.5 days. On April 4, 2016, orbital maneuver PC1 was successfully achieved during about 15 seconds to avoid long eclipses during the orbit. After the PC1, the apoapsis altitude was ~370,000 km with a periapsis altitude of 1,000 -- 10,000 km, and the period is 10.8 days. On October 7, 2020, orbital maneuver PC2 was successfully achieved during about 4 seconds to avoid very long umbra and penumbra. The mission has been described in many papers [OYAMAETAL2002; ISHIIETAL2004; NAKAMURAETAL2007; NAKAMURAETAL2011; NAKAMURAETAL2014; NAKAMURAETAL2016]. Science Goals ============= Venus is one of the most attractive targets in the solar system when we seek to understand how terrestrial planets differentiate into various types. Venus is our nearest neighbor, and has a size very similar to the Earth's. However, previous spacecraft missions discovered an extremely dense (~92 bar) and dry CO2 atmosphere with H2SO4-H2O clouds floating at 45 -- 70 km altitudes, and exotic volcanic features covering the whole planet. The abundant gaseous CO2 brings about a high atmospheric temperature (~740 K) near the surface via greenhouse effect. The atmospheric circulation is also much different from the Earth's. AKATSUKI aims to solve the mystery of the atmospheric circulation and cloud formation of Venus, with secondary targets being the exploration of the ground surface and the zodiacal light observation during the cruise to Venus. The exploration of the Venusian meteorology is important not only for understanding the climate of Venus but also for a general understanding of planetary fluid dynamics. AKATSUKI will explore the Venusian atmosphere using a set of sophisticated optical instruments dedicated to meteorological study and radio occultation technique. Such an approach complements the Venus Express mission, which aimed to understand the Venusian environment with a different approach. Instruments =========== The onboard science instruments altogether sense multiple height levels of the atmosphere to model the three-dimensional structure and dynamics. The lower atmosphere and the surface on the nightside are investigated by the 1-um Camera (IR1). The altitude region from the middle and lower clouds to 10 km below the cloud base on the nightside is covered by the 2-um Camera (IR2). The dayside middle and lower clouds are mapped by IR1. The dayside cloud top is observed principally by the Ultraviolet Imager (UVI) and also by IR2. The Longwave Infrared Camera (LIR) has an ability to observe the cloud top of both dayside and nightside. The Lightning and Airglow Camera (LAC) searches for lightning and maps airglows on the nightside. Radio Science (RS) complements the imaging observations principally by determining the vertical temperature profile and its spatial and temporal variabilities using Ultra-Stable Oscillator (USO). The typical altitude levels probed by the infrared wavelengths are discussed by [TAKAGI&IWAGAMI2011]. IR1, IR2, UVI and LIR are cameras with large-format detector arrays, and have much common features in the image data format. They are operated sequentially as a unit in many cases. For these reasons, a dedicated camera control unit called the Digital Electronics unit (DE) was developed to conduct sequential exposures using these cameras and to process the image data from these cameras before storing them in the data recorder. The basic specifications of the cameras are summarized in Table 1. The cameras have Field of Views (FOVs) of 12 degrees or larger; given a FOV of 12 degrees, the full disk of Venus can be captured in one image at distances of >8.5 Rv. Brief descriptions of the science instruments are given below. Table 1. Basic specifications of the instruments. +---+--------+------------+------------------+---------+----------------+ |Cam|FOV(deg)|Detector |Filters |Bandwidth|Targets | +===+========+============+==================+=========+================+ |IR1|12 x 12 |Si-CSD/CCD |1.009 um (night) |0.0391 um|Surface, Clouds | | | |1024 x 1024 +------------------+---------+----------------+ | | | pixels|0.969 um (night) |0.0386 um|H2O vapor | | | | +------------------+---------+----------------+ | | | |0.898 um (night) |0.0289 um|Surface, Clouds | | | | +------------------+---------+----------------+ | | | |0.900 um (day) |0.0091 um|Clouds | | | | +------------------+---------+----------------+ | | | |0.750 um, Diffuser|0.4000 um|(Flat field) | +---+--------+------------+------------------+---------+----------------+ |IR2|12 x 12 |PtSi-CSD/CCD|1.735 um (night) |0.043 um |Clouds, | | | |1024 x 1024 +------------------+---------+ Particle size | | | | pixels|2.26 um (night) |0.058 um | | | | | +------------------+---------+----------------+ | | | |2.32 um (night) |0.038 um |CO below clouds | | | | +------------------+---------+----------------+ | | | |2.02 um (night) |0.040 um |Cloud-top height| | | | +------------------+---------+----------------+ | | | |1.65 um (night) |0.300 um |Zodiacal light | +---+--------+------------+------------------+---------+----------------+ |UVI|12 x 12 |Si-CCD |283 nm (day) | 13 nm |SO2 at cloud top| | | |1024 x 1024 +------------------+---------+----------------+ | | | pixels|365 nm (day) | 15 nm |Unknown absorber| | | | +------------------+---------+----------------+ | | | |320 nm, Diffuser | 100 nm |(Flat field) | +---+--------+------------+------------------+---------+----------------+ |LIR|16.4 |uncooled |10 um (day/night) | 4 um |Cloud top | | | x 12.4|bolometer | | |temperature | | | |328 x 248 | | | | | | | pixels | | | | +---+--------+------------+------------------+---------+----------------+ |LAC|16 x 16 |8 x 8 |777.4 nm (night) | 9 nm |OI lightning | | | |multi-anode +------------------+---------+----------------+ | | |avalanche |543 nm (night) | 136 nm |O2 Herzberg II | | | |photodiode | | |airglow | | | | +------------------+---------+----------------+ | | | |557.7 nm (night) | 5 nm |OI airglow | | | | +------------------+---------+----------------+ | | | |545.0 nm (night) | 5 nm |(Background) | +---+--------+------------+------------------+---------+----------------+ 1-um Camera (IR1) ----------------- IR1 [IWAGAMIETAL2011] was designed to image the dayside of Venus at 0.90 um wavelength and the nightside at 0.90, 0.97 and 1.01 um wavelengths, which are located in the atmospheric windows [TAYLORETAL1997]. These windows allow radiation to penetrate the whole atmosphere. The dayside 0.90 um images visualize the distribution of clouds illuminated by sunlight. Although the dayside disk at this wavelength appears almost flat, small-scale features with contrasts of ~3% are observed and considered to originate in the middle and lower cloud region [BELTONETAL1991]. Tracking of such cloud features provides the wind field in this region. On the nightside, IR1 measures the thermal radiation mostly from the surface and a little from the atmosphere. The 0.97 um radiation is partially absorbed by H2O vapor, and thus the comparison of this radiance with radiances at other wavelengths allows the estimation of H2O content below the cloud. Measurements at 0.90 and 1.01 um will yield information about the surface material [BAINES2000; HASHIMOTO&SUGITA2003], and are expected to find out hot lava ejected from active volcanoes by utilizing the high sensitivity of the radiance to temperature in this wavelength region [HASHIMOTO&IMAMUR2001]. As imaging instruments, IR1 and IR2 have many common features. These cameras share electronics for A/D conversion since the detector arrays in these cameras are electronically nearly identical. Each of the cameras consists of a large baffle which eliminates stray light from the sun, refractive optics, a filter wheel, and a 1040 x 1040 pixels detector array (1024 x 1024 area is used). The optics and the detector array altogether yield an effective FOV of 12 degrees, giving the pixel resolution of ~6 km from the distance of 5 Rv. The detector array of IR1 is a Si-CSD (charge sweeping device)/CCD which is cooled down to 260 K to achieve a signal-to-noise ratio of ~300 on the dayside and ~100 on the nightside. 2-um Camera (IR2) ----------------- IR2 [SATOHETAL2016] utilizes the atmospheric windows at wavelengths of 1.73, 2.26, and 2.32 um; the first two suffer only CO2 absorption, while the last one contains a CO absorption band. At these wavelengths the outgoing infrared radiation originates from the altitudes 35 -- 50 km. To track cloud motions a series of 2.26 um images will be mostly used. As the small-scale inhomogeneity of the Venusian cloud layer is thought to occur predominantly at altitudes 50 -- 55 km [BELTONETAL1991], the IR2 observations should yield wind maps in this region. As CO is photochemically produced above the cloud and subsequently transported to the deeper atmosphere (such sinks are not yet precisely located), the distribution of CO should give us information about the vertical circulation of the atmosphere. We will extract the CO distribution at 35 -- 50 km altitudes by differentiating images taken at 2.26 and 2.32 um [COLLARDETAL1993; TSANGETAL2008]. To study the spatial and temporal variations in the cloud particle size, the cloud opacities at 2.26 and 1.73 um, together with the IR1 1.01-um and 0.90-um images, will be analyzed with the aid of radiative transfer calculations [CARLSONETAL1993]. IR2 employs two additional wavelengths. At 2.02 um, which is located in a prominent CO2 absorption band, we expect to observe the variation of the cloud-top altitude as intensity variations of the reflected sunlight similarly to the cloud altimetry by Venus Express VIRTIS using the 1.6-um CO2 band [TITOVETAL2009]. The astronomical H-band centered at 1.65 um aims at observing the zodiacal light. IR2 utilizes a 1040 x 1040 pixels PtSi sensor (1024 x 1024 area is used), which has advantages such as the high stability, uniformity and durability against energetic radiation. The architecture of the device is based on a technology of the 512 x 512 PtSi detector which was applied to astronomical observations [UENO1996]. To suppress the thermal electrons in the detector, it is cooled down to 65 K by a Stirling cooler. Heat is also removed from the lens and lens housing, making these components be cooled down to ~170 K. The resultant signal-to-noise ratio is expected to be over 100 when imaging the Venusian nightside. For observing the zodiacal light, the camera optics is designed to suppress the instrumental background as well as the stray light. The large baffle of the camera is very useful for interplanetary dust (IPD) observations, because it provides us with very wide coverage in the solar elongation angle from 180 degrees (anti-solar direction) to 30 degrees. The PtSi sensor is specially designed to realize precise measurements of the instrumental zero level. The stability of the zero level is essentially important for the IPD observations, because the target is extending beyond the instantaneous FOV of the camera. Ultraviolet Imager (UVI) ------------------------ The solar ultraviolet radiation scattered from the Venusian cloud top shows broad absorption between 200 nm and 500 nm wavelengths. SO2 explains the absorption between 200 nm and 320 nm, while the absorber for >320 nm has not yet been identified [ESPOSITOETAL1997]. UVI is designed to map the ultraviolet contrast at 283 nm for observing SO2 and at 365 nm for the unknown absorber. UVI [YAMAZAKIETAL2018] will make clear the spatial distributions of these ultraviolet absorbers and their relationships with the cloud structure and the wind field. The tracking of ultraviolet markings yields wind vectors at the cloud top [ROSSOWETAL1990]. The mixing ratios of both SO2 and the unknown absorber are considered to increase precipitously with decreasing the altitude below the cloud top [POLLACKETAL1980; BERTAUXETAL1996], and thus the spatial distributions of these species should be sensitive to vertical air motions [TITOVETAL2008]. In addition to nadir-viewing observations, limb observations will visualize the vertical structure of the haze layer above the main cloud [BELTONETAL1991]. UVI utilizes an ultraviolet-coated backthinned frame transfer Si-CCD with 1024 x 1024 pixels. Given the FOV of 12 degrees, the pixel resolution is ~16 km at the apoapsis (distance of 13 Rv) and ~6 km from the distance of 5 Rv. The signal-to-noise ratio is expected to be ~120 when viewing the dayside Venus. Longwave Infrared Camera (LIR) ------------------------------ LIR [TAGUCHIETAL2007; FUKUHARAETAL2011] detects thermal emission from the cloud top in a wavelength region 8 -- 12 um to map the cloud-top temperature, which is typically ~230 K. Unlike other imagers onboard AKATSUKI, LIR is able to take images of both dayside and nightside with equal quality. The cloud-top temperature map will reflect mostly the cloud height distribution, whose detailed structure is unknown except in the northern high latitudes observed by Pioneer Venus OI [TAYLORETAL1980] and the southern high latitudes observed by Venus Express VIRTIS [PICCIONIETAL2007]. LIR has a capability to resolve a temperature difference of 0.3 K, corresponding to a few hundred-meters difference in the cloud height. The images taken by LIR will visualize convective cells and various types of waves within the cloud layer. Tracking of the movements of blocky features will also yield wind vectors covering both dayside and nightside. Such a full local time coverage has never been achieved in the previous wind measurements, and will enable, for example, the derivation of zonal-mean meridional winds for the first time. The sensor unit of LIR includes optics, a mechanical shutter, an image sensor and its drive circuit, and a baffle that keeps direct sunlight away from the optical aperture. The image sensor is an uncooled micro- bolometer array with 328 x 248 pixels for a FOV of 16.4 degrees x 12.4 degrees. Since the sensor can work under room temperature, huge and heavy cryogenic apparatus which is usually necessary for infrared devices is unnecessary. The frame rate of the image sensor is 60 Hz, and several tens of images obtained within a few seconds will be accumulated to increase the signal-to-noise ratio. Given the FOV of 12.4 degrees for 248 pixels, the pixel resolution is ~70 km on the Venus surface when viewed from the apoapsis (13 Rv), and is ~26 km from the distance of 5 Rv. Lightning and Airglow Camera (LAC) ---------------------------------- LAC [TAKAHASHIETAL2008] searches for lightning flashes and maps airglow emissions on the nightside disk of Venus when AKATSUKI is located in the eclipse (umbra) of Venus. A major goal of the lightning observation is to settle the controversy on the occurrence of lightning in the Venusian atmosphere. The distribution of lightning, if it exists, should reflect the microphysics of clouds and the dynamics of mesoscale convection. The 777.4 nm [OI] line of atomic oxygen is utilized for lightning observation, since this line is considered as the most strong emission from lightning discharges according to a laboratory experiment simulating the Venusian atmosphere [BORUCKIETAL1996]. Possible lightning flashes were detected on the nightside disk of Venus at this wavelength by using a ground-based telescope [HANSELLETAL1995]. LAC also measures emissions in two airglow bands to study the global-scale circulation and small-scale waves in the lower thermosphere. One is the O2 Herzberg II emission centered at 552.5 nm wavelength, which is considered a consequence of the recombination of atomic oxygen in downwelling and is the strongest emission among the visible Venusian airglows [SLANGERETAL2001]. The other is the 557.7 nm [OI] emission; though Venera 9 and 10 failed to detect this emission [KRASNOPOLSKY1983]. [SLANGERETAL2001; SLANGERETAL2006] observed it using a ground-based telescope. LAC has a FOV of 16 degrees. The detector is a multi-anode avalanche photo-diode (APD) with 8 x 8 pixels of 2 mm square each. Among the 64 pixels of the APD, 4 x 8 pixels are allocated to 777.4 nm for lightning detection, 2 x 8 pixels are allocated to 480 -- 605 nm for O2 Herzberg II emission, 1 x 8 pixels are allocated to 557.7 nm emission, and 1 x 8 pixels are used for an airglow-free background at 545.0 nm. These wavelengths are covered by using rectangular interference filters fixed on the detector. In the lightning observation mode, individual lightning flashes are sampled at 32 kHz by pre-triggering. Lightning flashes with an intensity of 1/100 of typical terrestrial lightning would be detected when viewed from 1,000 km altitude. For mapping airglows, the Venusian nightside is scanned by changing the direction of the FOV. The detector's one pixel corresponds to 35 km resolution on the Venusian surface viewed from 1,000 km altitude, and 850 km resolution from 3 Rv altitude. Ultra-Stable Oscillator (USO), used for Radio Science (RS) ---------------------------------------------------------- RS [IMAMURAETAL2011] aims to determine the vertical structure of the Venusian atmosphere using radio occultation technique. In this experiment, the spacecraft transmits radio waves toward the tracking station (Usuda Deep Space Center of Japan) and sequentially goes behind the planet's ionosphere, neutral atmosphere, and solid planet as seen from the tracking station, and reemerges in the reverse sequence. During such occultation events the neutral and ionized atmospheres of the planet cause bending, attenuation and scintillation of radio waves. The received signal is recorded with an open-loop system and analyzed offline. The frequency variation observed at the tracking station yields the time series of the bending angle, from which the vertical profile of the refractive index is derived. The refractive index profile yields the temperature profile of the neutral atmosphere by assuming hydrostatic balance [FJELDBOETAL1971]. The height range of the Venusian neutral atmosphere accessible by radio occultation is approximately 32 -- 90 km; below 32 km the radius of curvature of the ray path becomes smaller than the distance to the planet center. The ionospheric electron density profile is also derived from the refractive index profile. From the observed signal power variation, the sub-cloud H2SO4 vapor densities [JENKINSETAL1994] and the intensity of small-scale density fluctuation [WOOETAL1980] are obtained. The uniqueness of AKATSUKI RS as compared to the previous radio occultation experiments at Venus is that low latitudes can be probed many times thanks to the near-equatorial orbit, so that broad local time regions are covered. Another merit of AKATSUKI is that the locations probed by RS can be observed by the cameras a short time before or after the occultations. An ultra-stable oscillator (USO) provides a stable reference frequency which is needed to generate the X-band downlink signal used for RS. The USO is a heritage from the USOs flown onboard the ESA's Rosetta and Venus Express spacecraft [HAEUSLERETAL2006]. The instruments, with acronym and Principal Investigator (PI), are summarized below: Instrument Acronym PI ---------------------------- -------- ------------------ 1-um Camera IR1 Naomoto Iwagami 2-um Camera IR2 Takehiko Satoh Longwave Infrared Camera LIR Makoto Taguchi Ultraviolet Imager UVI Shigeto Watanabe Lightning and Airglow Camera LAC Yukihiro Takahashi Ultra-Stable Oscillator USO (RS) Takeshi Imamura Shared module for instruments ============================= Digital Electronics unit (DE) ----------------------------- DE is a controller for IR1, IR2, UVI and LIR. To conduct a set of camera operations which is repeated many times (every 2 hours in nominal global imaging), the main satellite system controller (Data Handling Unit, DHU) triggers the DE unit. DE, then, sequentially triggers detailed observation sequences of the cameras including filter wheel and gain settings, exposure, and data transfer. DE is also responsible for arithmetic data processing, data compression, and telemetry data formatting and packeting. To repeat a variety of observation sequences, each of which includes complicated manipulations of multiple cameras as a unit, we prepared a set of ``observation programs'' and installed them in DE. For example, the ``dayside deluxe'' observation program setups the cameras, takes images using all dayside filters of the four cameras sequentially, conducts arithmetic data processing, compresses the acquired image data, and shutdowns the cameras, within 26 minutes. The observation programs will be updated several times during the mission depending on the results of the observations. The arithmetic data processing includes dark signal subtraction, dead pixel correction, computation of median from multiple images, averaging of images, and flat field correction. The data compression method is either the lossless compression algorithm by the ``HIREW'' developed by NEC Ltd. [TAKADAETAL2007] which is also known as ``StarPixel Lossless'' or the JPEG2000 lossless/lossy compression [BOLIEKETAL2000]. Since the derivation of wind vectors from high- resolution cloud images might require high fidelity data acquisition, we will use lossless data compression as far as possible. However, in the epochs of low telemetry rate, lossy compression will also be adopted. Mission Phases ============== CRUISE ------ Mission Phase Start Time : 2010-05-20 Mission Phase Stop Time : 2010-12-06 ----------------------- ---------- ----------------------------------- Event Date Description ----------------------- ---------- ----------------------------------- Launch 2010-05-20 21:58:22 UTC, H-IIA F17 Launch Vehicle, from Tanegashima Space Center in Kagoshima, Japan. Test maneuver (APH-1) 2010-06-28 10:00:00 UTC, the orbital maneuvering engine (OME) was used near aphelion during 13 seconds. delta-V was 12.2 m/s. This maneuver also served as a test of the OME. Trim maneuver 1 (TRM-1) 2010-11-08 01:00:00 UTC, four RCS thrusters were used during 21 seconds. delta-V was 2.9 m/s. Trim maneuver 2 (TRM-2) 2010-11-22 00:00:00 UTC, four RCS thrusters were used during 2.125 seconds. delta-V was 0.27 m/s. Trim maneuver 3 (TRM-3) 2010-12-01 00:00:00 UTC, four RCS thrusters were used during 0.375 seconds. delta-V was 0.04 m/s. SUN ORBITING ------------ Mission Phase Start Time : 2010-12-07 Mission Phase Stop Time : 2015-12-06 ----------------------- ---------- ----------------------------------- Event Date Description ----------------------- ---------- ----------------------------------- Venus orbit insertion 1 2010-12-07 00:00:00 UTC, that is the closest (VOI-1) time between Venus and the spacecraft. The OME was started at 23:49:00 UTC on 2010-12-06 to enter the orbit, but was shut down at 158 seconds, while 718 seconds of operation had been planned. Planned delta-V was 748 m/s, but achieved delta-V was only 135 m/s. The VOI-1 was failed. The expected communications blackout due to occultation by Venus was from 23:54:00 to 00:12:02. After the occultation, communications blackout continued. The spacecraft was found at 01:26:17, and entered in heliocentric orbit with the period of 203 days, perihelion 0.61AU and aphelion 0.74AU. Superior-conjunction 2011-06-25 from 2011-06-17 to 2011-07-05, command operation could not be carried out. Test maneuver 1 (TM1) 2011-09-07 02:50:00 UTC, OME was used during 2 seconds. Test maneuver 2 (TM2) 2011-09-14 02:50:00 UTC, OME was used during 5 seconds. Disposal of Oxidizer 2011-09-30 03:02:00 UTC, oxidizer was disposed Test (DOX Test) during 60 seconds. delta-V was 1.9 m/s. Disposal of Oxidizer 1 2011-10-06 02:53:00 UTC, oxidizer was disposed (DOX1) during 360 seconds. delta-V was 7.6 m/s. Disposal of Oxidizer 2 2011-10-12 03:23:00 UTC, oxidizer was disposed (DOX2) during 540 seconds. Disposal of Oxidizer 3 2011-10-13 04:53:00 UTC, oxidizer was disposed (DOX3) during 540 seconds. Total delta-V of DOX2 and DOX3 was 16 m/s. Delta-V 1 (DV1) 2011-11-01 04:22:00 UTC, four RCS thrusters were used during 587 seconds. delta-V was 88.6 m/s. Delta-V 2 (DV2) 2011-11-10 04:37:00 UTC, four RCS thrusters were used during 544 seconds. delta-V was 90.6 m/s. Delta-V 3 (DV3) 2011-11-21 04:57:00 UTC, four RCS thrusters were used during 342 seconds. delta-V was 63.5 m/s. Superior-conjunction 2015-02-11 from 2015-02-05 to 2015-02-14, command operation could not be carried out. Delta-V 4-1 (DV4-1) 2015-07-17 04:00:00 UTC, four RCS thrusters were used during 93 seconds. delta-V was 17.5 m/s. Delta-V 4-2 (DV4-2) 2015-07-24 04:00:00 UTC, four RCS thrusters were used during 303 seconds. delta-V was 56.3 m/s. Delta-V 4-3 (DV4-3) 2015-07-31 04:00:00 UTC, four RCS thrusters were used during 74 seconds. delta-V was 13.6 m/s. Trim maneuver 2015-09-11 02:30:00 UTC, four RCS thrusters for VOI-R1 (TRM-R1) were used during 6.4 seconds. delta-V was 1.1 m/s. PRIMARY SCIENCE PHASE --------------------- Mission Phase Start Time : 2015-12-07 Mission Phase Stop Time : 2018-03-31 ----------------------- ---------- ----------------------------------- Event Date Description ----------------------- ---------- ----------------------------------- Venus orbit insertion, 2015-12-07 00:00:00 UTC, four RCS thrusters Revenge (VOI-R1) were used during 20 min and 28 seconds. delta-V was 134.8 m/s. The spacecraft successfully entered the orbit. The apoapsis altitude was ~440,000 km with an inclination of 3 degrees and orbital period of 13 days and 14 h. +Y-axis inversion 2015-12-09 23:36:00 UTC, from south to north. Maneuver for phase 2015-12-20 14:11:00 UTC, four RCS thrusters control (VOI-R2) were used during 94 seconds. +Y-axis inversion 2016-02-08 23:16:00 UTC, from north to south. Maneuver for phase 2016-04-04 07:28:00 UTC, four RCS thrusters control (PC1) were used during 15 seconds. delta-V was 2.2 m/s. Superior-conjunction 2016-06-07 from 2016-05-29 to 2016-06-15, command operation could not be carried out. +Y-axis inversion 2016-11-24 05:00:00 UTC, from south to north. +Y-axis inversion 2017-02-01 04:30:00 UTC, from north to south. +Y-axis inversion 2017-11-16 01:00:00 UTC, from south to north. Superior-conjunction 2018-01-09 from 2017-12-29 to 2018-01-21, command operation could not be carried out. +Y-axis inversion 2018-02-23 03:00:00 UTC, from north to south. EXTENDED SCIENCE PHASE 1 ------------------------ Mission Phase Start Time : 2018-04-01 Mission Phase Stop Time : 2021-03-31 ----------------------- ---------- ----------------------------------- Event Date Description ----------------------- ---------- ----------------------------------- +Y-axis inversion 2018-04-04 05:41:00 UTC, from south to north. Long umbra and penumbra 2018-07-29 Umbra and Penumbra 12:00 -- 15:48 UTC (~228 min) Umbra 12:37 -- 15:05 UTC (~148 min) Long umbra and penumbra 2018-08-09 Umbra and Penumbra 04:31 -- 06:45 UTC (~133 min) Umbra 04:36 -- 06:37 UTC (~120 min) +Y-axis inversion 2018-10-04 04:00:00 UTC, from north to south. Long umbra and penumbra 2019-01-19 Umbra and Penumbra 23:32 -- 02:09 UTC (~156 min) Umbra 23:43 -- 02:01 UTC (~138 min) Long umbra and penumbra 2019-01-30 Umbra and Penumbra 11:06 -- 16:08 UTC (~302 min) Umbra 12:01 -- 15:20 UTC (~199 min) +Y-axis inversion 2019-02-06 00:00:00 UTC, from south to north. +Y-axis inversion 2019-06-19 03:30:00 UTC, from north to south. Attitude anomaly event 2019-08-11 until 2019-09-04T03:00:00, the spacecraft was off-nominal attitude. Superior-conjunction 2019-08-14 from 2019-08-07 to 2019-08-21, command operation could not be carried out. +Y-axis inversion 2020-03-05 06:15:00 UTC, from south to north. +Y-axis inversion 2020-07-28 02:00:00 UTC, from north to south. Maneuver for phase 2020-10-07 12:22:00 UTC, four RCS thrusters control (PC2) were used during 4 seconds. delta-V was 0.52 m/s. Long penumbra 2020-12-15 Penumbra 15:38 -- 22:30 UTC (~412 min) Long penumbra 2020-12-24 Penumbra 21:35 -- 01:45 UTC (~250 min) +Y-axis inversion 2021-01-21 01:50:00 UTC, from south to north. Superior-conjunction 2021-03-26 from 2021-03-19 to 2021-04-03, command operation could not be carried out. EXTENDED SCIENCE PHASE 2 ------------------------ Mission Phase Start Time : 2021-04-01 Mission Phase Stop Time : 2024-03-31 (planned) ----------------------- ---------- ----------------------------------- Event Date Description ----------------------- ---------- ----------------------------------- " MISSION_OBJECTIVES_SUMMARY = " Mission Objectives Overview =========================== Venus Climate Orbiter Science Objectives [NAKAMURAETAL2007; NAKAMURAETAL2011] 1-um Camera (IR1) [IWAGAMIETAL2011] ----------------------------------- - Visualize the distribution of clouds illuminated by sunlight at dayside. - Derive wind vectors using dayside images. - Estimate of H2O content below the cloud. - Get information about the surface material and find out hot lava ejected from active volcanoes. 2-um Camera (IR2) [SATOHETAL2016] --------------------------------- - Extract the CO distribution at 35 -- 50 km altitudes by differentiating images taken at 2.26 and 2.32 um and get information about the vertical circulation of the atmosphere. - Analyze the spatial and temporal variations in the cloud particle size using 2.26 and 1.735 um filters, together with the IR1 1.01-um and 0.90-um (nightside) images, with the aide of radiative transfer calculations. - Derive wind vectors using dayside and nightside images. - Observe the variation of the cloud-top altitude with images at 2.02 um. - Observe the zodiacal light by 1.65 um filter that is the astronomical H-band. Ultraviolet Imager (UVI) [YAMAZAKIETAL2018] ------------------------------------------- - Observe solar ultraviolet radiation scattered from the Venusian cloud top, by the unknown absorber using 365 nm filter and by SO2 using 283 nm filter. - Derive wind vectors using 283 nm and 365 nm filters. - Determine vertical motions using mixing ratios of both SO2 and the unknown absorber. - Visualize the vertical structure of the haze layer by limb observations. Longwave Infrared Camera (LIR) [TAGUCHIETAL2007; FUKUHARAETAL2011] ------------------------------------------------------------------ - Map the cloud-top temperature by observing thermal emission from the cloud top in a wavelength region 8 -- 12 um. - Visualize convective cells and various types of waves within the cloud layer, and derive wind vectors covering both dayside and nightside. Lightning and Airglow Camera (LAC) [TAKAHASHIETAL2008] ------------------------------------------------------ - Search for lightning flashes using 777.4 nm [OI] line of atomic oxygen with high speed sampling rate, 32 kHz. - Map airglow emissions on the nightside disk of Venus. Ultra-Stable Oscillator (USO) [IMAMURAETAL2011] ----------------------------------------------- - Determine the vertical structure of the Venusian atmosphere using radio occultation technique. 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