Akatsuki (spacecraft)
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, also known as the Venus Climate Orbiter (VCO) and Planet-C, is a
Japan Aerospace Exploration Agency The is the Japanese national air and space agency. Through the merger of three previously independent organizations, JAXA was formed on 1 October 2003. JAXA is responsible for research, technology development and launch of satellites into o ...
(JAXA)
space probe A space probe is an artificial satellite that travels through space to collect scientific data. A space probe may orbit Earth; approach the Moon; travel through interplanetary space; flyby, orbit, or land or fly on other planetary bodies; o ...
tasked with studying the
atmosphere of Venus The atmosphere of Venus is the layer of gases surrounding Venus. It is composed primarily of supercritical carbon dioxide and is much denser and hotter than that of Earth. The temperature at the surface is 740  K (467 °C, 872  ...
. It was launched aboard an H-IIA 202 rocket on 20 May 2010, but failed to enter orbit around Venus on 6 December 2010. After the craft orbited the Sun for five years, engineers successfully placed it into an alternative Venusian
elliptic orbit In astrodynamics or celestial mechanics, an elliptic orbit or elliptical orbit is a Kepler orbit with an eccentricity of less than 1; this includes the special case of a circular orbit, with eccentricity equal to 0. In a stricter sense, i ...
on 7 December 2015 by firing its
attitude control Attitude control is the process of controlling the orientation of an aerospace vehicle with respect to an inertial frame of reference or another entity such as the celestial sphere, certain fields, and nearby objects, etc. Controlling vehicle ...
thrusters for 20 minutes and made it the first Japanese satellite orbiting Venus. By using five different cameras working at several wavelengths,'' Akatsuki'' is studying the stratification of the atmosphere, atmospheric dynamics, and cloud physics. Astronomers working on the mission reported detecting a possible
gravity wave In fluid dynamics, gravity waves are waves generated in a fluid medium or at the interface between two media when the force of gravity or buoyancy tries to restore equilibrium. An example of such an interface is that between the atmosphere a ...
(not to be confused with
gravitational waves Gravitational waves are waves of the intensity of gravity generated by the accelerated masses of an orbital binary system that propagate as waves outward from their source at the speed of light. They were first proposed by Oliver Heaviside i ...
) in Venus' atmosphere in December 2015. Including link to Tetsuya Fukuhara ''et al.''
"Large stationary gravity wave in the atmosphere of Venus" (preview/subscription)
''
Nature Geoscience ''Nature Geoscience'' is a monthly peer-reviewed scientific journal published by the Nature Publishing Group. The Chief Editor is Tamara Goldin, who took over from Heike Langenberg in February 2020. It was established in January 2008. Scope The ...
'' via NYTimes link, 16 January 2017.


Mission

''Akatsuki'' is Japan's first planetary exploration mission since the failed Mars orbiter ''Nozomi'' probe which was launched in 1998. ''Akatsuki'' was originally intended to conduct scientific research for two or more years from an elliptical orbit around Venus ranging from in altitude, but its alternate orbit had to be highly elliptical ranging between 1,000 km and 10,000 km at its nearest point and about 360,000 km at its farthest. This larger orbit takes 10 days to complete instead of the originally planned 30 hours. The budget for this mission is ¥14.6 billion () for the satellite and ¥9.8 billion (US$116 million) for the launch. Observations include cloud and surface imaging from an orbit around the planet with cameras operating in the infrared, visible and UV wavelengths to investigate the complex Venusian
meteorology Meteorology is a branch of the atmospheric sciences (which include atmospheric chemistry and physics) with a major focus on weather forecasting. The study of meteorology dates back millennia, though significant progress in meteorology did no ...
and elucidate the processes behind the mysterious
atmospheric super-rotation Atmospheric super-rotation is the state where a planet's atmosphere rotates faster than the planet itself. The atmosphere of Venus is one example of extreme super-rotation; the Venusian atmosphere circles the planet in just four Earth days, much fa ...
. On Venus, while the planet rotates at 6 km/h at the equator, the atmosphere spins around the planet at 300 km/h. Other experiments are designed to confirm the presence of
lightning Lightning is a naturally occurring electrostatic discharge during which two electrically charged regions, both in the atmosphere or with one on the ground, temporarily neutralize themselves, causing the instantaneous release of an average ...
and to determine whether
volcanism Volcanism, vulcanism or volcanicity is the phenomenon of eruption of molten rock (magma) onto the surface of the Earth or a solid-surface planet or moon, where lava, pyroclastics, and volcanic gases erupt through a break in the surface called a ...
occurs currently on Venus.


Spacecraft design

The main
bus A bus (contracted from omnibus, with variants multibus, motorbus, autobus, etc.) is a road vehicle that carries significantly more passengers than an average car or van. It is most commonly used in public transport, but is also in use for cha ...
is a box with two solar arrays, each with an area of about . The solar arrays provide over 700 W of power while in Venus orbit. The total mass of the spacecraft at launch was . The mass of the science payload is . Propulsion is provided by a bi-propellant,
hydrazine Hydrazine is an inorganic compound with the chemical formula . It is a simple pnictogen hydride, and is a colourless flammable liquid with an ammonia-like odour. Hydrazine is highly toxic unless handled in solution as, for example, hydrazine ...
-
dinitrogen tetroxide Dinitrogen tetroxide, commonly referred to as nitrogen tetroxide (NTO), and occasionally (usually among ex-USSR/Russia rocket engineers) as amyl, is the chemical compound N2O4. It is a useful reagent in chemical synthesis. It forms an equilibrium ...
orbital maneuvering engine and twelve mono-propellant hydrazine reaction control thrusters, eight with of thrust and four with . It is the first spacecraft to use a ceramic (
silicon nitride Silicon nitride is a chemical compound of the elements silicon and nitrogen. is the most thermodynamically stable and commercially important of the silicon nitrides, and the term "silicon nitride" commonly refers to this specific composition. It ...
) retrofire thruster. The total propellant mass at launch was . Communication is via an 8 GHz, 20-watt
X-band The X band is the designation for a band of frequencies in the microwave radio region of the electromagnetic spectrum. In some cases, such as in communication engineering, the frequency range of the X band is rather indefinitely set at approxi ...
transponder using the high-gain antenna. The high-gain antenna is flat to prevent heat from building up in it. ''Akatsuki'' also has a pair of medium-gain horn antennas mounted on turntables and two low-gain antennas for command uplink. The medium-gain horn antennas are used for housekeeping data downlink when the high-gain antenna is not facing Earth.


Instruments

The scientific payload consists of six instruments. The five imaging cameras are exploring Venus in wavelengths from ultraviolet to the mid-infrared: #the Lightning and Airglow Camera (LAC) is looking for lightning in the
visible spectrum The visible spectrum is the portion of the electromagnetic spectrum that is visible to the human eye. Electromagnetic radiation in this range of wavelengths is called '' visible light'' or simply light. A typical human eye will respond to ...
(552-777 nm) #the ultraviolet imager (UVI) is studying the distribution of specific atmospheric gases such as
sulfur dioxide Sulfur dioxide (IUPAC-recommended spelling) or sulphur dioxide (traditional Commonwealth English) is the chemical compound with the formula . It is a toxic gas responsible for the odor of burnt matches. It is released naturally by volcanic a ...
and the famous unknown absorber at
ultraviolet Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30  PHz) to 400 nm (750  THz), shorter than that of visible light, but longer than X-rays. UV radiation ...
wavelengths (283–365 nm) #the longwave infrared camera (LIR) is studying the structure of high-altitude clouds at a wavelength where they emit heat (10 μm) #the infrared 1 
μm The micrometre ( international spelling as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer ( American spelling), also commonly known as a micron, is a unit of length in the International System of Uni ...
camera (IR1) is imaging on the night side heat radiation (0.90–1.01 μm) emitted from Venus's surface and help researchers to spot
active volcanoes An active volcano is a volcano which is either erupting or is likely to erupt in the future. An active volcano which is not currently erupting is known as a dormant volcano. Overview Tlocene Epoch. Most volcanoes are situated on the Pacific ...
, if they exist. While on the day side, it sensed the solar near-infrared radiation (0.90 μm) reflected by the middle clouds. Unavailable for observation after December 2016 due to an electronic failure.Initial products of Akatsuki 1-μm camera
. ''Earth, Planets and Space''. 2018, vol. 70, nbr. 6.
#the infrared 2 μm camera (IR2) studied the night side lower clouds' opacity to the thermal emission from the surface and deeper atmosphere (1.74–2.32 μm). It also sensed on the day side the band at 2.02 μm, which can be used to infer the altitude of the top of the clouds. Finally, the 1.65-μm filter was used during the cruise phase to study the zodiacal light. Unavailable for observation after December 2016 due to an electronic failure. #the Ultra-Stable Oscillator (USO) for performing
radio occultation Radio occultation (RO) is a remote sensing technique used for measuring the physical properties of a planetary atmosphere or ring system. Atmospheric radio occultation Atmospheric radio occultation relies on the detection of a change in a radio ...
experiments.


Public relations

A public relations campaign was held between October 2009 and January 2010 by
the Planetary Society The Planetary Society is an American internationally-active non-governmental nonprofit organization. It is involved in research, public outreach, and political space advocacy for engineering projects related to astronomy, planetary science, a ...
and
JAXA The is the Japanese national air and space agency. Through the merger of three previously independent organizations, JAXA was formed on 1 October 2003. JAXA is responsible for research, technology development and launch of satellites into o ...
, to allow individuals to send their name and a message aboard ''Akatsuki''. Names and messages were printed in fine letters on an aluminium plate and placed aboard ''Akatsuki''. 260,214 people submitted names and messages for the mission. Around 90 aluminium plates were created for the spacecraft, including three aluminium plates in which the images of the
Vocaloid is a singing voice synthesizer software product. Its signal processing part was developed through a joint research project led by Kenmochi Hideki at the Pompeu Fabra University in Barcelona, Spain, in 2000 and was not originally intended to b ...
Hatsune Miku , also called Miku Hatsune, and officially code-named CV01, is a Vocaloid software voicebank developed by Crypton Future Media and its official anthropomorphic mascot character, a 16-year-old girl with long, turquoise twintails. Miku's pers ...
and her super deformed-styled figure Hachune Miku were printed.


Operations


Launch

''Akatsuki'' left the Sagamihara Campus on 17 March 2010, and arrived at the
Tanegashima Space Center The (TNSC) is the largest rocket-launch complex in Japan with a total area of about 9.7 square kilometers. It is located on the southeast coast of Tanegashima, an island approximately south of Kyushu. It was established in 1969 when the ...
's Spacecraft Test and Assembly Building 2 on 19 March. On 4 May, ''Akatsuki'' was encapsulated inside the large
payload fairing A payload fairing is a nose cone used to protect a spacecraft payload against the impact of dynamic pressure and aerodynamic heating during launch through an atmosphere. An additional function on some flights is to maintain the cleanroom envi ...
of the
H-IIA H-IIA (H-2A) is an active expendable launch system operated by Mitsubishi Heavy Industries (MHI) for the Japan Aerospace Exploration Agency. These liquid fuel rockets have been used to launch satellites into geostationary orbit; lunar o ...
rocket that launched the spacecraft, along with the
IKAROS IKAROS (Interplanetary Kite-craft Accelerated by Radiation Of the Sun) is a Japan Aerospace Exploration Agency ( JAXA) experimental spacecraft. The spacecraft was launched on 20 May 2010, aboard an H-IIA rocket, together with the ''Akatsuki'' ...
solar sail Solar sails (also known as light sails and photon sails) are a method of spacecraft propulsion using radiation pressure exerted by sunlight on large mirrors. A number of spaceflight missions to test solar propulsion and navigation have been ...
, on a 6-month journey to Venus. On 9 May, the payload fairing was transported to the Tanegashima Space Center's Vehicle Assembly Building, where the fairing was mated to the H-IIA launch vehicle itself. The spacecraft was launched on 20 May 2010 at 21:58:22 ( UTC) from the Tanegashima Space Center, after being delayed because of weather from its initial 18 May scheduled target.


Orbit insertion failure

''Akatsuki'' was planned to initiate orbit insertion operations by igniting the orbital maneuvering engine at 23:49:00 on 6 December 2010 UTC. The burn was supposed to continue for twelve minutes, to an initial Venus orbit with an apoapsis altitude of , a periapsis altitude of , and a 30 h
orbital period The orbital period (also revolution period) is the amount of time a given astronomical object takes to complete one orbit around another object. In astronomy, it usually applies to planets or asteroids orbiting the Sun, moons orbiting pla ...
. The orbit insertion maneuver was confirmed to have started on time, but after the expected blackout due to
occultation An occultation is an event that occurs when one object is hidden from the observer by another object that passes between them. The term is often used in astronomy, but can also refer to any situation in which an object in the foreground blocks ...
by Venus, the communication with the probe did not recover as planned. The probe was found to be in safe-hold mode, spin-stabilized state with ten minutes per rotation. Due to the low communication speed through the low-gain antenna, it took a while to determine the state of the probe. JAXA stated on 8 December that the probe's orbital insertion maneuver had failed. At a press conference on 10 December, officials reported that ''Akatsuki''s engines fired for less than three minutes, far less than what was required to enter into Venus orbit. Further research found that the likely reason for the engine malfunction was salt deposits jamming the valve between the helium pressurization tank and the fuel tank. As a result, engine combustion became oxidizer-rich, with resulting high combustion temperatures damaging the combustion chamber throat and nozzle. A similar vapor leakage problem destroyed the
NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeedin ...
Mars Observer The ''Mars Observer'' spacecraft, also known as the ''Mars Geoscience/Climatology Orbiter'', was a robotic space probe launched by NASA on September 25, 1992, to study the Martian surface, atmosphere, climate and magnetic field. During the int ...
probe in 1993. As a result, the probe was in a heliocentric orbit, rather than Venus orbit. Since the resulting orbit had an orbital period of 203 days, shorter than Venus' orbital period of 225 days, the probe drifted around the Sun compared to Venus.


Recovery efforts

JAXA developed plans to attempt another orbital insertion burn when the probe returned to Venus in December 2015. This required placing the probe into "hibernation" or safe mode to prolong its life beyond the original 4.5-year design. JAXA expressed some confidence in keeping the probe operational, pointing to reduced battery wear, since the probe was then orbiting the Sun instead of its intended Venusian orbit. Telemetry data from the original failure suggested that the throat of its main engine, the orbit maneuver engine (OME) was still largely intact, and trial jet thrusts of the probe's onboard OME were performed twice, on 7 and 14 September 2011. However, the thrust was only about , which was 10% of expectations. Following these tests, it was determined that insufficient
specific impulse Specific impulse (usually abbreviated ) is a measure of how efficiently a reaction mass engine (a rocket using propellant or a jet engine using fuel) creates thrust. For engines whose reaction mass is only the fuel they carry, specific impulse is ...
would be available for orbital maneuvering by the OME. It was concluded that the remaining combustion chamber throat was completely destroyed by transient ignition of the engine. As a result, the selected strategy was to use four hydrazine
attitude control Attitude control is the process of controlling the orientation of an aerospace vehicle with respect to an inertial frame of reference or another entity such as the celestial sphere, certain fields, and nearby objects, etc. Controlling vehicle ...
thrusters, also called
reaction control system A reaction control system (RCS) is a spacecraft system that uses thrusters to provide attitude control and translation. Alternatively, reaction wheels are used for attitude control. Use of diverted engine thrust to provide stable attitude con ...
(RCS), to drive the probe into orbit around Venus. Because the RCS thrusters do not need oxidiser, the remaining 65 kg of oxidiser (
MON Mon, MON or Mon. may refer to: Places * Mon State, a subdivision of Myanmar * Mon, India, a town in Nagaland * Mon district, Nagaland * Mon, Raebareli, a village in Uttar Pradesh, India * Mon, Switzerland, a village in the Canton of Grisons * A ...
) was vented overboard in October 2011 to reduce the mass of the spacecraft. Three peri-Venus orbital maneuvers were executed on 1 November, 10 and 21 November 2011 using the RCS thrusters. A total delta-''v'' of 243.8 m/s was imparted to the spacecraft. Because the RCS thrusters' specific impulse is low compared to the specific impulse of the OME, the previously planned insertion into low Venusian orbit became impossible. Instead, the new plan was to place the probe in a highly elliptical orbit with an apoapsis of a hundred thousand kilometers and a periapsis of a few thousand kilometers from Venus. Engineers planned for the alternate orbit to be prograde (in the direction of the atmospheric super-rotation) and lie in the orbital plane of Venus. The method and orbit were announced by JAXA in February 2015, with an orbit insertion date of 7 December 2015. The probe reached its most distant point from Venus on 3 October 2013 and had been approaching the planet since then.


Orbit insertion

After performing the last of a series of four trajectory correction maneuvers between 17 July and 11 September 2015, the probe was established on a trajectory to fly past Venus on 7 December 2015, when ''Akatsuki'' would make a maneuver to enter Venus orbit after a 20-minute burn with four thrusters that were not rated for such a hefty propulsive maneuver. Instead of taking about 30 hours to complete an orbit around Venus—as was originally planned—the new orbit targeted would place ''Akatsuki'' in a nine-day orbit after an adjustment in March 2016. After JAXA engineers measured and calculated its orbit following the 7 December orbital insertion, JAXA announced on 9 December that ''Akatsuki'' had successfully entered the intended elliptical orbit, as far as from Venus, and as close as from Venus's surface with an orbital period of 13 days and 14 hours. A follow-up thruster burn on 26 March 2016 lowered ''Akatsukis apoapsis to about , periapsis altitude periodically changing from 1,000 to 10,000 km, and shortened its orbital period from 13 to about 10 days.


Status

The orbiter started its two-year period of "regular" science operations in mid-May 2016. Since 9 December 2016, the near-infrared 1-μm and 2-μm cameras have been unavailable for observations due to an electronic failure. Its long-wave infrared camera, ultraviolet imager, and lightning and airglow camera continue normal operation. By April 2018, ''Akatsuki'' finished its regular observation phase, and entered an extended operation phase. Extended operations are approved until the end of 2020, with further mission extensions to be considered based on the spacecraft's condition at that time. ''Akatsuki'' has enough fuel to continue operating for at least 2 more years as of November 2019. As of December 2021, ''Akatsuki'' continues in operation and collecting data, without a planned end-of-mission date.


Science

Three hours after insertion in December 2015 and in "a few glimmers in April and May" 2016 the craft's instruments recorded a "bow-shape feature in the atmosphere stretching 6,000 miles, almost pole to pole — a sideways smile". Scientists on the project termed the feature a "
gravity wave In fluid dynamics, gravity waves are waves generated in a fluid medium or at the interface between two media when the force of gravity or buoyancy tries to restore equilibrium. An example of such an interface is that between the atmosphere a ...
" in the planet's winds above the
Aphrodite Terra Aphrodite Terra is one of the three continental regions on the planet Venus, the others being Ishtar Terra and Lada Terra. It is named for Aphrodite, the Greek equivalent of the goddess Venus, and is found near the equator of the planet. Aphrod ...
region of rift valleys and mountains reaching heights of over 4,000 metres. The mission is collecting data in all relevant spectral bands from ultraviolet (280 nm) to mid-infrared wavelengths (10 μm). Images from the ''Akatsuki'' orbiter revealed something similar to
jet stream Jet streams are fast flowing, narrow, meandering air currents in the atmospheres of some planets, including Earth. On Earth, the main jet streams are located near the altitude of the tropopause and are westerly winds (flowing west to east) ...
winds in the low and middle cloud region, which extends from 45 to 60 kilometers in altitude. The wind speed maximized near the equator. In September 2017, JAXA scientists named this phenomenon 'Venusian equatorial jet'. They also published results on equatorial winds at the cloud-top level by tracking clouds on the UV spectrum. A significant result in 2018 is the appearance of thick clouds of small particles near the transition between upper and middle clouds, what was described as a "new and puzzling morphology of the complex cloud cover." By 2017, the science team published 3D maps on the Venus atmosphere structure. The physical quantities retrieved include the pressure, the temperature, the vapor density, and the ionospheric electron density and their variations. By the year 2019, the first results about the morphology, temporal changes and the winds at the middle clouds of Venus were published and merited the cover in Geophysical Research Letters, reporting unexpectedly high contrasts that might indicate the presence of absorbers like water. To image lightning, the orbiter has sight of the dark side of Venus for about 30 minutes every 10 days.Hunt for optical lightning flash in Venus using LAC onboard Akatsuki spacecraft
Takahashi, Yukihiro; Sato, Mitsuteru; Imai, Masataka. 19th EGU General Assembly, EGU2017, proceedings from the conference held 23–28 April 2017 in Vienna, Austria., p.11381.
As of July 2019, it has accumulated 16.8 hours of observations of the night side, and no lightning has been detected.Constraints on Venus Lightning From Akatsuki's First 3 Years in Orbit.
Ralph D. Lorenz, Masataka Imai, Yukihiro Takahashi, Mitsuteru Sato, Atsushi Yamazaki, Takao M. Sato, Takeshi Imamura, Takehiko Satoh, Masato Nakamura. ''Geophysical Research Letters''. 3 July 2019.


Gallery

File:Venus - October 24 2018.png, An image of Venus with AKATSUKI Ultraviolet Imager (UVI) 283 365 UVI 2018 06 03 08 03.jpg, An image of Venus with a crescent shaped area that is illuminated by sunlight. The image was taken with UVI. 174 226 232 date 2016 07 11 14 10.jpg, An image of the night side of Venus with the AKATSUKI 2-μm Camera (IR2). In the dark areas the light is absorbed by clouds. 097 101 surface date 2016 07 12 04 05.jpg, An image of the surface of Venus with the AKATSUKI 1-μm Camera (IR1).


See also

* * * List of Venus probes * * *


References


External links


Venus Climate Orbiter ''Akatsuki'' official website

JAXA ''Akatsuki'' Planet-C page







Detailed ''Space Review'' article about ''Akatsuki'' and its recovery

Venus Climate Orbiter ''Akatsuki''
(PDF, 1.72 Mb)



by the
Planetary Society The Planetary Society is an American internationally-active non-governmental nonprofit organization. It is involved in research, public outreach, and political space advocacy for engineering projects related to astronomy, planetary science, a ...
{{Use American English, date=January 2014 Missions to Venus Japanese space probes Space probes launched in 2010 JAXA Orbiters (space probe) Spacecraft launched by H-II rockets