View source for Engineering:Akatsuki (spacecraft)

{{short description|JAXA mission to study Venus via orbiting probe (2010–present)}}
{{DISPLAYTITLE:''Akatsuki'' (spacecraft)}}
{{Infobox spaceflight
| name                  = ''Akatsuki''
| image                 = Akatsuki-1.jpg
| image_caption         = A model of the spacecraft ''Akatsuki''

| operator              = JAXA
| mission_type          = [[Astronomy:Venus|Venus]] orbiter
| website               = {{URL|https://global.jaxa.jp/projects/sas/planet_c/|JAXA}}<br />{{URL|http://www.jaxa.jp/countdown/f17/index_e.html|JAXA Special Site}}
| COSPAR_ID             = 2010-020D
| SATCAT                = 36576
| mission_duration      = ~2 years (science phase)<br> elapsed: {{time interval|20 May 2010}}

| spacecraft_type       =
| manufacturer          = [[Company:NEC|NEC Space Technologies]]
| dry_mass              = {{convert|320|kg|lb|abbr=on}}
| launch_mass           = {{convert|517.6|kg|abbr=on}}<ref name=Takeshi2011/>
| dimensions            = {{convert|1.04|x|1.45|x|1.44|m|ft|abbr=on}}
| power                 = >700&nbsp;watts at 0.7 [[Astronomy:Astronomical unit|AU]]<ref name=Takeshi2011/>

| launch_date           = {{start-date|20 May 2010, 21:58:22|timezone=yes}}&nbsp;UTC<ref name=spaceflightnow>{{cite news | author=Stephen Clark | title=H-2A Launch Report – Mission Status Center | url=http://www.spaceflightnow.com/h2a/akatsuki/status.html | work=Spaceflight Now | date=20 May 2010| access-date=20 May 2010| archive-url= https://web.archive.org/web/20100520013452/http://spaceflightnow.com/h2a/akatsuki/status.html| archive-date= 20 May 2010 | url-status= live}}</ref>
| launch_rocket         = [[Engineering:H-IIA|H-IIA 202]] 
| launch_site           = Tanegashima YLP-1
| launch_contractor     =

| last_contact          =
| decay_date            =

| orbit_epoch           =
| orbit_reference       = [[Astronomy:Cytherocentric orbit|Cytherocentric]]
| orbit_periapsis       = {{convert|1,000-10,000|km|mi|sp=us}} changing periodically<ref name=jaxapdf/>
| orbit_apoapsis        = {{convert|370,000|km|mi|sp=us}}<ref name=jaxapdf/>
| orbit_inclination     = 3.0°
| orbit_period          = 10.8 days<ref name="insertion TJT"/>
| orbit_eccentricity    = 0.971
| apsis                 = cytherion

|interplanetary         =
 {{Infobox spaceflight/IP
   |type                = flyby
   |note                = failed insertion
   |object              = [[Astronomy:Venus|Venus]]
   |arrival_date        = 6 December 2010, 23:49:00&nbsp;UTC
   |distance            = {{convert|550|km|mi|sp=us}}
 }}
 {{Infobox spaceflight/IP
   |type                = orbiter
   |object              = [[Astronomy:Venus|Venus]]
   |arrival_date        = 7 December 2015<ref name="Akatsuki-Successful-Orbit-Gizmag">{{cite news|last1=Szondy|first1=David|title=Akatsuki probe enters orbit around Venus|url=http://www.gizmag.com/jaxa-venus-akatsuki-orbit/40770/|access-date=7 December 2015}}</ref><ref name="Akatsuki-Sucessful-Orbit-SpaceFlightNow">{{cite news|last1=Clark|first1=Stephan|title=Japanese probe fires rockets to steer into orbit at Venus|url=https://spaceflightnow.com/2015/12/06/japanese-space-probe-to-steer-into-orbit-around-venus/|access-date=7 December 2015}}</ref>
   |orbits              =
 }}
}}

[[File:Animation of Akatsuki trajectory.gif|300px|thumb|right|Animation of ''Akatsuki'' trajectory from 21 May 2010 to 31 December 2016
{{legend-line|solid purple 2px|''Akatsuki''}}
{{legend-line|solid lime 2px|Venus}}
{{legend-line|solid blue 2px|Earth}}
{{legend|yellow|Sun}}
]]

{{nihongo|'''''Akatsuki'''''|あかつき, 暁|| "Dawn"}}, also known as the '''Venus Climate Orbiter''' ('''VCO''') and '''Planet-C''', is a Japan Aerospace Exploration Agency (JAXA) [[Engineering:Space probe|space probe]] tasked with studying the [[Astronomy:Atmosphere of Venus|atmosphere of Venus]]. It was launched aboard an [[Engineering:H-IIA|H-IIA 202 rocket]] on 20 May 2010,<ref>{{cite web |author=Chris Bergin |title=AXA H-IIA carrying Akatsuki and IKAROS launches at second attempt |url=http://www.nasaspaceflight.com/2010/05/axa-launch-h-iia-carrying-akatsuki-ikaros/ |work=NASASpaceFlight |date=20 May 2010 |access-date=19 November 2010}}</ref> but failed to enter orbit around Venus on 6 December 2010. After the craft [[Astronomy:Heliocentric orbit|orbited the Sun]] for five years, engineers successfully placed it into an alternative Venusian [[Astronomy:Elliptic orbit|elliptic orbit]] on 7 December 2015 by firing its [[Astronomy:Spacecraft attitude control|attitude control]] thrusters for 20 minutes and made it the first Japanese satellite orbiting Venus.<ref name="Akatsuki-Successful-Orbit-Gizmag"/><ref name="Akatsuki-Sucessful-Orbit-SpaceFlightNow"/><ref>{{cite news |last1=Limaye |first1=Sanjay |title=Live from Sagamihara: Akatsuki Orbit Insertion – Second Try |url=http://www.planetary.org/blogs/guest-blogs/2015/12060740-live-from-sagamihara.html |access-date=7 December 2015}}</ref><ref>{{cite web |url=http://www.popularmechanics.com/space/a17432/japan-venus-probe/ |title=Japan's Long Lost Venus Probe May Boom Back to Life |first=John |last=Wenz |work=Popular Mechanics |date=21 September 2015 |access-date=14 October 2015}}</ref>

By using five different cameras working at several wavelengths,'' Akatsuki'' is studying the stratification of the atmosphere, atmospheric dynamics, and cloud physics.<ref name="Overview 2011">{{cite journal |title=Overview of Venus orbiter, Akatsuki |journal=Earth, Planets and Space |date=May 2011 |last1=Nakamura |first1=N. |display-authors=0 |volume=63 |issue=5 |pages=443–457 |issn=1880-5981 |doi=10.5047/eps.2011.02.009 |bibcode=2011EP&S...63..443N |doi-access=free }}<!--|access-date=7 December 2015 --></ref><ref name="Akatsuki Exploring the Venusian Atmosphere">{{cite web |title=Exploring the Venusian Atmosphere – AKATSUKI/PLANET-C |url=http://global.jaxa.jp/countdown/f17/special/movie_e.html |website=Akatsuki Special Site |access-date=5 December 2015}}</ref> Astronomers working on the mission reported detecting a possible [[Gravity wave|gravity wave]] (not to be confused with gravitational waves) in Venus' atmosphere in December 2015.<ref name="NYT-20170116">{{cite news |last=Chang |first=Kenneth |title=Venus Smiled, With a Mysterious Wave Across Its Atmosphere |url=https://www.nytimes.com/2017/01/16/science/venus-wave-akatsuki.html |date=16 January 2017 |work={{wipe|The New York Times}} |access-date=17 January 2017 }} Including link to Tetsuya Fukuhara ''et al.'', [http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2873.html "Large stationary gravity wave in the atmosphere of Venus" (preview/subscription)], ''[[Earth:Nature Geoscience|Nature Geoscience]]'' via NYTimes link, 16 January 2017.</ref>

==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 {{convert|300|to|80000|km|mi|abbr=on}} in altitude,<ref name=Takeshi2011/> but its alternate orbit had to be highly elliptical ranging between {{convert|1,000|and|10,000|km}} at its nearest point and about {{convert|360000|km}} at its farthest. This larger orbit takes 10 days to complete instead of the originally planned 30 hours.<ref>{{Cite web | url=http://global.jaxa.jp/article/2016/interview/vol95/index.html | title=JAXA &#124; Takeshi Imamura Project Scientist, AKATSUKI "Venus Unveiled: A Planet Beyond Our Imagination"}}</ref> The budget for this mission is [[Finance:Japanese yen|¥]]14.6 billion ({{US$|174 million}}) for the satellite and ¥9.8 billion (US$116 million) for the launch.<ref name=Spacedaily>{{cite web|url=http://www.spacedaily.com/reports/Japan_probe_shoots_past_Venus_may_meet_again_in_six_years_999.html|title=Japan probe shoots past Venus, may meet again in six years|access-date=3 December 2011|publisher=Spacedaily.com|author=Staff writers|date=8 December 2010}}</ref>

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 [[Physics:Meteorology|meteorology]] and elucidate the processes behind the mysterious [[Earth:Atmospheric super-rotation|atmospheric super-rotation]]. On Venus, while the planet rotates at {{convert|6|km/h}} at the equator, the atmosphere spins around the planet at {{convert|300|km/h}}. Other experiments are designed to confirm the presence of [[Astronomy:Lightning|lightning]] and to determine whether volcanism occurs currently on Venus.<ref name=planet_c/>

===Spacecraft design===
The main [[Engineering:Satellite bus|bus]] is a {{convert|1.45|xx|1.04|xx|1.44|m|ft|abbr=on}} box with two [[Physics:Solar panels on spacecraft|solar arrays]], each with an area of about {{convert|1.4|m2|abbr=on}}. The solar arrays provide over 700&nbsp;W of power while in Venus orbit. The total mass of the spacecraft at launch was {{convert|517.6|kg|abbr=on}}.<ref name=Takeshi2011>{{cite journal| last1=Takeshi| first1=Oshima| last2=Tokuhito| first2=Sasaki |title=Development of the Venus Climate Orbiter PLANET-C (AKATSUKI) |journal=NEC Technical Journal| volume=6| issue=1| pages=47–51| url=https://www.nec.com/en/global/techrep/journal/g11/n01/pdf/110110.pdf}}</ref> The mass of the science payload is {{convert|34|kg|abbr=on}}.<ref name=VKO>{{cite web| url=http://www.stp.isas.jaxa.jp/venus/E_plan.html| title=Mission overview| access-date=3 December 2011| publisher=PLANET-C Team/JAXA}}</ref>

Propulsion is provided by a {{convert|500|N|adj=on|lk=on}} bi-propellant, [[Chemistry:Hydrazine|hydrazine]]-[[Chemistry:Dinitrogen tetroxide|dinitrogen tetroxide]] orbital maneuvering engine and twelve mono-propellant hydrazine reaction control thrusters, eight with {{convert|23|N|abbr=on}} of thrust and four with {{convert|3|N|abbr=on}}.<ref name=Takeshi2011/> It is the first spacecraft to use a ceramic ([[Chemistry:Silicon nitride|silicon nitride]]) retrofire thruster.<ref>{{cite web|title=Venus Climate Orbiter "AKATSUKI" (PLANET-C)|date=5 September 2017 |url=https://global.jaxa.jp/projects/sat/planet_c/topics.html|publisher=JAXA|access-date=11 April 2023}}</ref> The total propellant mass at launch was {{convert|196.3|kg|abbr=on}}.<ref name=Takeshi2011/>

Communication is via an 8&nbsp;GHz, 20-watt [[Astronomy:X-band|X-band]] transponder using the {{convert|1.6|m|adj=on|abbr=on}} high-gain antenna. The high-gain antenna is flat to prevent heat from building up in it.<ref name="Akatsuki Exploring the Venusian Atmosphere" /> ''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.<ref name=Takeshi2011/>

==Instruments==
The scientific payload consists of six instruments. The five imaging cameras are exploring Venus in wavelengths from ultraviolet to the mid-infrared:<ref name=PlanSoc>{{cite web|url=http://www.planetary.org/explore/topics/akatsuki/|title=Akatsuki (Venus Climate Orbiter / Planet-C)|publisher=The Planetary Society|access-date=19 November 2010|archive-date=18 March 2012|archive-url=https://web.archive.org/web/20120318214905/http://www.planetary.org/explore/topics/akatsuki/|url-status=dead}}</ref><ref name=Nakamura2007>{{cite journal|last=Nakamura|first=Masato|author2=Imamura, Takeshi|author3= Ueno, Munetaka |title=Planet-C: Venus Climate Orbiter mission of Japan|journal=Planetary and Space Science|volume=55|issue=12|pages=1831–1842|url=http://www.stp.isas.jaxa.jp/venus/docs/vco.pdf|doi=10.1016/j.pss.2007.01.009|bibcode = 2007P&SS...55.1831N |display-authors=0|year=2007}}</ref>
#the Lightning and Airglow Camera ('''LAC''') is looking for lightning in the [[Physics:Visible spectrum|visible spectrum]] (552–777&nbsp;nm)
#the ultraviolet imager ('''UVI''') is studying the distribution of specific atmospheric gases such as [[Chemistry:Sulfur dioxide|sulfur dioxide]] and the famous unknown absorber at [[Physics:Ultraviolet|ultraviolet]] wavelengths (283–365&nbsp;nm)
#the longwave infrared camera ('''LIR''') is studying the structure of high-altitude clouds at a wavelength where they emit heat (10&nbsp;μm) 
#the infrared 1&nbsp;[[Micrometre|μm]] camera ('''IR1''') is imaging on the night side [[Physics:Infrared|heat radiation]] (0.90–1.01&nbsp;μm) emitted from Venus's surface and help researchers to spot active volcanoes, if they exist. While on the day side, it sensed the solar near-infrared radiation (0.90&nbsp;μm) reflected by the middle clouds. Unavailable for observation after December 2016 due to an electronic failure.<ref name="1μm">[https://earth-planets-space.springeropen.com/articles/10.1186/s40623-017-0773-5\ Initial products of Akatsuki 1-μm camera] {{Webarchive|url=https://web.archive.org/web/20180603085349/https://earth-planets-space.springeropen.com/articles/10.1186/s40623-017-0773-5|date=3 June 2018}}. ''Earth, Planets and Space''. 2018, vol. 70, nbr. 6. {{doi|10.1186/s40623-017-0773-5}}</ref><ref name="March 3" />
#the infrared 2&nbsp;μm camera ('''IR2''') studied the night side lower clouds' opacity to the thermal emission from the surface and deeper atmosphere (1.74–2.32&nbsp;μm). It also sensed on the day side the {{CO2}} band at 2.02&nbsp;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.<ref name='March 3'/>
#the Ultra-Stable Oscillator ('''USO''') for performing [[Astronomy:Radio occultation|radio occultation]] experiments.

== Public relations ==
A public relations campaign was held between October 2009 and January 2010 by [[Organization:The Planetary Society|the Planetary Society]] and [[Organization:JAXA|JAXA]], to allow individuals to send their name and a message aboard ''Akatsuki''.<ref name=messages>{{cite web | title=Messages From Earth: Send your Message to Venus on Akatsuki | url=http://www.planetary.org/special/fromearth/akatsuki | publisher=The Planetary Society | date=2010 | access-date=2 April 2010 | archive-url=https://web.archive.org/web/20100407062824/http://www.planetary.org/special/fromearth/akatsuki | archive-date=7 April 2010 | url-status=dead | df=dmy-all }}</ref><ref>{{cite web|url=http://www.jaxa.jp/event/akatsuki/index_e.html|title=We will deliver your message to the bright star Venus – Akatsuki Message Campaign|publisher=JAXA|access-date=19 November 2010|archive-date=25 November 2010|archive-url=https://web.archive.org/web/20101125183251/http://www.jaxa.jp/event/akatsuki/index_e.html|url-status=dead}}</ref> Names and messages were printed in fine letters on an aluminium plate and placed aboard ''Akatsuki''.<ref name=messages/> 260,214 people submitted names and messages for the mission.<ref>{{cite web | title=AKATSUKI Message Campaign | url=http://www.jaxa.jp/projects/sat/planet_c/topics_e.html | publisher=JAXA | date=2010 | access-date=2 April 2010 | archive-date=5 October 2013 | archive-url=https://web.archive.org/web/20131005015626/http://www.jaxa.jp/projects/sat/planet_c/topics_e.html | url-status=dead }}</ref> Around 90 aluminium plates were created for the spacecraft,<ref>{{cite web|url=http://www.oita-press.co.jp/localNews/2010_127405922506.html|script-title=ja:金星へ届け！ 県民が寄せ書き|trans-title=Hoping that It Will Reach Venus! Residents of The Prefecture Write Something Together|language=ja|work=Oita Godo Shimbun|date=17 May 2010|access-date=20 July 2010|url-status=dead|archive-url=https://web.archive.org/web/20100520030452/http://www.oita-press.co.jp/localNews/2010_127405922506.html|archive-date=20 May 2010|df=dmy-all}}</ref> including three aluminium plates in which the images of the [[Software:Vocaloid|Vocaloid]] [[Software:Hatsune Miku|Hatsune Miku]] and her super deformed-styled figure Hachune Miku were printed.<ref>{{cite web|url=http://journal.mycom.co.jp/articles/2010/03/12/planet-c_ikaros/index.html|title=打ち上げを目前に控えた「あかつき」と「IKAROS」の機体が公開|trans-title=The Airframes of "Akatsuki" And "IKAROS" just before Those Launch Are Opened|language=ja|work=Mycom Journal|publisher=Mainichi Communications|date=12 March 2010|access-date=20 July 2010|url-status=dead|archive-url=https://web.archive.org/web/20100314074209/http://journal.mycom.co.jp/articles/2010/03/12/planet-c_ikaros/index.html|archive-date=14 March 2010|df=dmy-all}}</ref>

==Operations==

===Launch===
[[File:H-IIA F17 launching AKATSUKI.jpg|thumb|upright|The launch of ''Akatsuki'']]
''Akatsuki'' left the [[Organization:Sagamihara Campus|Sagamihara Campus]] on 17 March 2010, and arrived at the Tanegashima Space Center's Spacecraft Test and Assembly Building 2 on 19 March. On 4 May, ''Akatsuki'' was encapsulated inside the large [[Engineering:Payload fairing|payload fairing]] of the [[Engineering:H-IIA|H-IIA]] rocket that launched the spacecraft, along with the [[Engineering:IKAROS|IKAROS]] [[Physics:Solar sail|solar sail]], 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.<ref name=planet_c_index>{{cite web|url=http://www.jaxa.jp/projects/sat/planet_c/topics_e.html|title=Venus Climate Orbiter "AKATSUKI" (PLANET_C): Topics|publisher=JAXA|date=1 November 2011|access-date=3 December 2011|archive-date=5 October 2013|archive-url=https://web.archive.org/web/20131005015626/http://www.jaxa.jp/projects/sat/planet_c/topics_e.html|url-status=dead}}</ref>

The spacecraft was launched on 20 May 2010 at 21:58:22 ([[Physics:Coordinated Universal Time|UTC]]) from the Tanegashima Space Center,<ref name=planet_c/> after being delayed because of weather from its initial 18 May scheduled target.<ref>{{cite news | title=Bad weather postpones Japan rocket launch | url=https://phys.org/news/2010-05-bad-weather-postpones-japan-rocket.html |website=phys.org| date=18 May 2010 | access-date=11 April 2023}}</ref>

===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]].<ref name=planet_c_index/> The burn was supposed to continue for twelve minutes, to an initial Venus orbit with an apoapsis altitude of {{convert|80000|km|mi|abbr=on}}, a periapsis altitude of {{convert|300|km|abbr=on}}, and a 30 h [[Astronomy:Orbital period|orbital period]].<ref>{{cite web|url=https://global.jaxa.jp/countdown/f17/overview/akatsuki_e.html|title=Akatsuki Mission overview|language=en|access-date=23 January 2022}}</ref>

The orbit insertion maneuver was confirmed to have started on time, but after the expected blackout due to [[Astronomy:Occultation|occultation]] 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.<ref>{{cite web |url=http://www.jaxa.jp/countdown/f17/img/topics_20101207-3_j.pdf |script-title=ja:金星探査機「あかつき」の状況について |trans-title=About the State of Venus Probe Akatsuki |language=ja |date=7 December 2010 |access-date=7 December 2010}}</ref>  Due to the low communication speed through the low-gain antenna, it took a while to determine the state of the probe.<ref>JAXA's press briefing, 22:00, 7 December 2010 JST</ref> JAXA stated on 8 December that the probe's orbital insertion maneuver had failed.<ref name="ABC">{{cite web | title=Japan's Venus Probe Fails to Enter Orbit | url=https://abcnews.go.com/Technology/wireStory?id=12339589 | work=ABC News | access-date=8 December 2010}}</ref><ref name="planetary">{{cite web | title=Akatsuki Mission statement | url=http://planetary.org/about/press/releases/2010/1207_Akatsuki_Mission_Statement.html | publisher=[[Organization:The Planetary Society|The Planetary Society]] | access-date=8 December 2010 | url-status=dead | archive-url=https://web.archive.org/web/20120314034926/http://planetary.org/about/press/releases/2010/1207_Akatsuki_Mission_Statement.html | archive-date=14 March 2012 | df=dmy-all }}</ref> 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.<ref>{{cite journal|title=Venus miss is a setback for Japanese programme|author=David Cyranoski|journal=Nature|volume=468|issue=7326|pages=882|date=14 December 2010|doi=10.1038/468882a|pmid=21164456|bibcode=2010Natur.468..882C|doi-access=free}}</ref> 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 [[Organization:NASA|NASA]] [[Astronomy:Mars Observer#Encounter with Mars|Mars Observer]] probe in 1993.<ref name=Nakamura2014/>

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,<ref>http://ccar.colorado.edu/ASEN5050/projects/projects_2016/Branham_Breana/voi.html {{Webarchive|url=https://web.archive.org/web/20171001214043/http://ccar.colorado.edu/ASEN5050/projects/projects_2016/Branham_Breana/voi.html |date=1 October 2017 }} (retrieved 13 June 2017)</ref> 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 [[Engineering:Safe mode (spacecraft)|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.<ref>{{cite news| title=Japanese Venus Probe Misses Orbit| url=http://www.aviationweek.com/aw/generic/story_channel.jsp?channel=space&id=news/awx/2010/12/08/awx_12_08_2010_p0-275060.xml| newspaper=Aviation Week & Space Technology}}{{Dead link|date=August 2023 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>

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.<ref name=planet_c_index/> However, the thrust was only about {{convert|40|N}}, which was 10% of expectations. Following these tests, it was determined that insufficient [[Physics:Specific impulse|specific impulse]] 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 [[Astronomy:Spacecraft attitude control|attitude control]] thrusters, also called [[Engineering:Reaction control system|reaction control system]] (RCS), to drive the probe into orbit around Venus. Because the RCS thrusters do not need oxidiser, the remaining {{convert|65|kg}} of oxidiser ([[Chemistry:Mixed oxides of nitrogen|MON]]) was vented overboard in October 2011 to reduce the mass of the spacecraft.<ref name=Nakamura2014>{{Cite journal | doi = 10.1016/j.actaastro.2013.07.027| title = Return to Venus of the Japanese Venus Climate Orbiter AKATSUKI| journal = Acta Astronautica| volume = 93| pages = 384–389| date = 2014| last1 = Nakamura | first1 = M. | last2 = Kawakatsu | first2 = Y. | last3 = Hirose | first3 = C. | last4 = Imamura | first4 = T. | last5 = Ishii | first5 = N. | last6 = Abe | first6 = T. | last7 = Yamazaki | first7 = A. | last8 = Yamada | first8 = M. | last9 = Ogohara | first9 = K. | last10 = Uemizu | first10 = K. | last11 = Fukuhara | first11 = T. | last12 = Ohtsuki | first12 = S. | last13 = Satoh | first13 = T. | last14 = Suzuki | first14 = M. | last15 = Ueno | first15 = M. | last16 = Nakatsuka | first16 = J. | last17 = Iwagami | first17 = N. | last18 = Taguchi | first18 = M. | last19 = Watanabe | first19 = S. | last20 = Takahashi | first20 = Y. | last21 = Hashimoto | first21 = G. L. | last22 = Yamamoto | first22 = H. |bibcode = 2014AcAau..93..384N | arxiv = 1709.09353 | s2cid = 110719337}}</ref>

Three peri-Venus orbital maneuvers were executed on 1 November,<ref name=planet_c>{{cite web| url=http://www.jaxa.jp/projects/sat/planet_c/index_e.html| title=AKATSUKI orbit control at perihelion| publisher=JAXA| date=1 November 2011| access-date=3 December 2011| archive-date=13 May 2012| archive-url=https://web.archive.org/web/20120513140027/http://www.jaxa.jp/projects/sat/planet_c/index_e.html| url-status=dead}}</ref> 10 and 21 November 2011 using the RCS thrusters. A total [[Astronomy:Delta-v|delta-''v'']] of {{convert|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.<ref name="Feb SFN">{{cite news| title=Japanese craft to get second chance after missing Venus in 2010| url=http://spaceflightnow.com/2015/02/07/japanese-craft-to-get-second-chance-after-missing-venus-in-2010/}}</ref> The probe reached its most distant point from Venus on 3 October 2013 and had been approaching the planet since then.<ref>{{cite web| url=http://www.stp.isas.jaxa.jp/venus/images/gallery/open_campus_2013/akatsuki_journey_3_A4_2013.pdf | script-title=ja:「あかつき」の旅 (2013年特別公開向け資料)| date=26 August 2013| access-date=8 June 2014| language=ja| publisher=PLANET-C Team/JAXA}}</ref>

===Orbit insertion===
[[File:Animation of Akatsuki trajectory around Venus.gif |thumb |right |Animation of ''Akatsuki''{{'s}} trajectory around Venus from 1 December 2015<br>{{legend2|magenta| ''Akatsuki''}}{{·}}{{legend2| Lime |Venus}}]]
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.<ref name=Akatsuki-Successful-Orbit-Gizmag /><ref name=Akatsuki-Sucessful-Orbit-SpaceFlightNow /><ref>{{cite web| url=http://global.jaxa.jp/projects/sat/planet_c/topics.html#topics5594| title=AKATSUKI: Orbit successfully controlled| date=5 August 2015| access-date=10 September 2015| publisher=PLANET-C Team/JAXA}}</ref>  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.<ref name="insertion TJT">{{cite news |url=http://www.japantimes.co.jp/news/2015/12/07/national/science-health/jaxa-plans-fire-probes-thrusters-second-attempt-venus-orbit/ |title=Japanese probe fires thrusters in second bid to enter Venus orbit |work=The Japan Times |date=7 December 2015 |access-date=7 December 2015 }}</ref>

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 {{convert|440000|km|abbr=on}} from Venus, and as close as {{convert|400|km|abbr=on}} from Venus's surface with an orbital period of 13 days and 14 hours.<ref>{{cite web |title=Venus Climate Orbiter "AKATSUKI" Inserted Into Venus' Orbit |publisher=JAXA |date=9 December 2015 |url=http://global.jaxa.jp/press/2015/12/20151209_akatsuki.html}}</ref>

A follow-up thruster burn on 26 March 2016 lowered ''Akatsuki'''s apoapsis to about {{convert|370000|km|abbr=on}}, periapsis altitude periodically changing from {{convert|1,000|to|10,000|km}}, and shortened its orbital period from 13 to about 10 days.<ref name=jaxapdf>{{cite web| url=https://global.jaxa.jp/activity/pr/brochure/files/sat17.pdf|access-date=22 January 2022|title=AKATSUKI:PLANET-C project}}</ref><ref name="insertion TJT"/>

===Status===

The orbiter started its two-year period of "regular" science operations in mid-May 2016.<ref>{{cite news |title=Japanese orbiter officially begins science mission at Venus |url=https://spaceflightnow.com/2016/05/17/japanese-orbiter-officially-begins-science-mission-at-venus/ |work=Spaceflight Now |first=Steven |last=Clark |date=17 May 2016 |access-date=26 November 2019}}</ref> Since 9 December 2016, the near-infrared 1-μm and 2-μm cameras have  been unavailable for observations due to an electronic failure.<ref name="1μm" /><ref name='March 3'>{{cite web |url=http://www.isas.jaxa.jp/en/topics/000902.html |title=Two cameras on Akatsuki pause observations |publisher=JAXA |date=3 March 2017 |access-date=6 May 2017}}</ref> Its long-wave infrared camera, ultraviolet imager, and lightning and airglow camera continue normal operation.<ref name='March 3'/>

By April 2018, ''Akatsuki'' finished its regular observation phase, and entered an extended operation phase.<ref>{{cite web |url=http://www.isas.jaxa.jp/outreach/isas_news/files/ISASnews446.pdf |script-title=ja:「あかつき」定常観測フェーズ終了 |page=4 |language=ja |periodical=ISAS News |issue=446 |date=May 2018 |issn=0285-2861}}</ref> 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.<ref>{{cite web |last=Nakamura |first=Masato |url=https://fanfun.jaxa.jp/jaxatv/files/20191119_akatsuki-01.pdf |title=あかつきの現状 |trans-title=Current Status of Akatsuki |publisher=[[Organization:Institute of Space and Astronautical Science|ISAS]]/[[Organization:JAXA|JAXA]] |date=19 November 2019 |access-date=26 November 2019 |language=ja}}</ref>

As of December 2021, ''Akatsuki'' continues in operation and collecting data, without a planned end-of-mission date.<ref>{{cite web |last=Nakamura |first=Masato |url= https://akatsuki.isas.jaxa.jp/en/topics/news/001262.html |title= Venus explorations will continue |publisher=[[Organization:Institute of Space and Astronautical Science|ISAS]]/[[Organization:JAXA|JAXA]] |date=7 December 2021|access-date=22 March 2022}}</ref>

==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".<ref name='Nakamura 2018'>[https://link.springer.com/article/10.1186/s40623-018-0916-3 Special issue "Akatsuki at Venus: The First Year of Scientific Operation]. Masato Nakamura, Dmitri Titov, Kevin McGouldrick, Pierre Drossart, Jean-Loup Bertaux, Huixin Liu. ''Earth, Planets and Space''. December 2018.</ref> Scientists on the project termed the feature a "[[Gravity wave|gravity wave]]" in the planet's winds above the [[Astronomy:Aphrodite Terra|Aphrodite Terra]] region of rift valleys and mountains reaching heights of over {{convert|4,000|m}}.<ref name="NYT-20170116"/> The mission is collecting data in all relevant spectral bands from ultraviolet (280&nbsp;nm) to mid-infrared wavelengths (10 μm).<ref>{{cite journal|doi=10.1016/j.icarus.2017.01.027|title=Overview of useful spectral regions for Venus: An update to encourage observations complementary to the Akatsuki mission|journal=Icarus|volume=288|pages=235–239|year=2017|last1=Peralta|first1=J.|last2=Lee|first2=Yeon Joo|last3=McGouldrick|first3=K.|last4=Sagawa|first4=H.|last5=Sánchez-Lavega|first5=A.|last6=Imamura|first6=T.|last7=Widemann|first7=T.|last8=Nakamura|first8=M.|bibcode=2017Icar..288..235P|doi-access=free}}</ref>

Images from the ''Akatsuki'' orbiter revealed something similar to [[Earth:Jet stream|jet stream]] winds in the low and middle cloud region, which extends from {{convert|45|to|60|km}} in altitude.<ref>{{cite news | last = Bouic | first = Damia | title = A new look at Venus with Akatsuki | newspaper = [[Organization:The Planetary Society|The Planetary Society]] Blog | publisher = [[Organization:The Planetary Society|The Planetary Society]] | date = 16 January 2018  | url = http://www.planetary.org/blogs/guest-blogs/2018/0116-a-new-look-at-venus-with-akatsuki.html | access-date = 2018-01-28 }}</ref> The wind speed maximized near the equator. In September 2017, JAXA scientists named this phenomenon 'Venusian equatorial jet'.<ref name="Update Sep 2017">{{cite web |url=http://global.jaxa.jp/projects/sat/planet_c/topics.html#topics10633 |title=Venus: Jet-setting atmosphere |work=Japan Aerospace Exploration Agency (JAXA) |date=5 September 2017 |access-date=2017-09-26 }}</ref> They also published results on equatorial winds at the cloud-top level by tracking clouds on the UV spectrum.<ref>[https://earth-planets-space.springeropen.com/articles/10.1186/s40623-017-0775-3 Mean winds at the cloud top of Venus obtained from two-wavelength UV imaging by Akatsuki]. Takeshi Horinouchi, Toru Kouyama, Yeon Joo Lee, Shin-ya Murakami, Kazunori Ogohara, Masahiro Takagi, Takeshi Imamura, Kensuke Nakajima, Javier Peralta, Atsushi Yamazaki, Manabu Yamada and Shigeto Watanabe. ''Earth, Planets and Space'' {{doi|10.1186/s40623-017-0775-3}} Published: 15 January 2018.</ref> 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."<ref name='Nakamura 2018'/> By 2017, the science team published 3D maps on the Venus atmosphere structure.<ref name='Nakamura 2018'/> The physical quantities retrieved include the pressure, the temperature, the {{chem|H|2|SO|4}} vapor density, and the ionospheric electron density and their variations.<ref name='Nakamura 2018'/> By the year 2019, the first results about the morphology, temporal changes<ref>[https://blogs.agu.org/geospace/2019/04/29/new-research-takes-deeper-look-at-venuss-clouds/ New research takes deeper look at Venus’s clouds], 29 April 2019</ref> and the winds at the middle clouds of Venus were published and merited the cover in ''[[Earth:Geophysical Research Letters|Geophysical Research Letters]]'', reporting unexpectedly high contrasts that might indicate the presence of absorbers like water.<ref>{{Cite journal|title=Morphology and Dynamics of Venus's Middle Clouds With Akatsuki/IR1|journal= [[Earth:Geophysical Research Letters|Geophysical Research Letters]] |volume=46|issue=5|pages=2399–2407|author1=J. Peralta|author2=N. Iwagami|author3=A. Sánchez‐Lavega|author4=Yeon Joo Lee|author5=R. Hueso|author6=M. Narita|author7=T. Imamura|author8=P. Miles|author9=A. Wesley|author10=E. Kardasis|author11=S. Takagi |doi=10.1029/2018GL081670|year=2019|bibcode=2019GeoRL..46.2399P|arxiv=1903.02883|s2cid=119195952}}</ref>

To image lightning, the orbiter has sight of the dark side of Venus for about 30 minutes every 10 days.<ref name=Takahashi>[http://adsabs.harvard.edu/abs/2017EGUGA..1911381T 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.</ref> As of July 2019, it has accumulated 16.8 hours of observations of the night side, and no lightning has been detected.<ref>[https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2019GL083311 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. ''[[Earth:Geophysical Research Letters|Geophysical Research Letters]]''. 3 July 2019. {{doi|10.1029/2019GL083311}}</ref>

==Gallery==
<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 [[Chemistry:Carbon dioxide|{{CO2}}]] 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)
</gallery>

==See also==
* {{annotated link|Engineering:IKAROS}}
* {{annotated link|Astronomy:List of missions to Venus}}
* [[Astronomy:List of Solar System probes#Venus probes|List of Venus probes]]
* {{annotated link|Engineering:Nozomi (spacecraft)|Nozomi}}
* {{annotated link|Astronomy:Sakigake}}
* {{annotated link|Engineering:Suisei (spacecraft)|Suisei}}

==References==
{{Reflist}}

== External links ==
<!-- Per WP:ELMINOFFICIAL, choose one official website only -->
* [http://akatsuki.isas.jaxa.jp/en/ Venus Climate Orbiter ''Akatsuki'' official website]
* [https://global.jaxa.jp/projects/sas/planet_c/ JAXA ''Akatsuki'' Planet-C page]
* [http://www.jaxa.jp/countdown/f17/index_e.html JAXA ''Akatsuki'' Special Site]
* [http://www.darts.isas.jaxa.jp/planet/project/akatsuki/index.html.en DARTS (ISAS JAXA) Akatsuki Science Archive]
* [http://www.stp.isas.jaxa.jp/venus/top_english.html Planet-C page (Solar Terrestrial Physics Group)]
* [http://www.thespacereview.com/article/2822/1  Detailed ''Space Review'' article about ''Akatsuki'' and its recovery]
* [http://www.jaxa.jp/countdown/f17/pdf/presskit_akatsuki_e.pdf Venus Climate Orbiter ''Akatsuki''] (PDF, 1.72 Mb)
* [http://www.stp.isas.jaxa.jp/venus/paper/index.htm ''Akatsuki'' – List of scientific publications]
* [https://www.planetary.org/blogs/guest-blogs/2018/0116-a-new-look-at-venus-with-akatsuki.html A new look at Venus with Akatsuki] by the Planetary Society

{{2015 in space}}
{{Venus spacecraft}}
{{Solar System probes}}


[[Category:Missions to Venus]]
[[Category:Japanese space probes]]
[[Category:Orbiters (space probe)]]

{{Sourceattribution|Akatsuki (spacecraft)}}