:IKAROS

The IKAROS probe is the world's first spacecraft to use solar sailing as the main propulsion.{{cite book|url=https://www.nasa.gov/sites/default/files/atoms/files/beyond-earth-tagged.pdf|title=Beyond Earth: A Chronicle of Deep Space Exploration, 1958–2016|page=2|last1=Siddiqi|first1=Asif A.|lccn=2017059404|isbn=9781626830424|publisher=NASA History Program Office|edition=second|year=2018|id=SP2018-4041|series=The NASA history series|location=Washington, DC}} It was designed to demonstrate four key technologies (comments in parentheses refer to figure):

1. Deployment and control of a large, thin solar sail membrane (grey-blue areas numbered 3)
2. Thin-film solar cells integrated into the sail to power the payload (black rectangles numbered 4)
3. Measurement of acceleration due to radiation pressure on the solar sail
4. Attitude control by varying the reflectance of 80 liquid crystal panels embedded in the sail (orange rectangles numbered 2)

The mission also includes investigations of aspects of interplanetary space, such as gamma-ray bursts, solar wind and cosmic dust.{{cite web |url=http://www.jaxa.jp/press/2010/07/20100714_ikaros_j.html |title=小型ソーラー電力セイル実証機「IKAROS（イカロス）」のガンマ線バーストの観測成功について|language=ja |publisher=JAXA |date=14 July 2010 |access-date=15 July 2010}}

The probe's ALADDIN instrument (ALDN-S and ALDN-E) measured the variation in dust density{{cite web|url=http://www.lpi.usra.edu/meetings/lpsc2011/pdf/2647.pdf|title=COSMIC DUST DETECTION BY THE IKAROS-ARRAYED LARGE-AREA DUST DETECTORS IN INTERPLANETARY SPACE (ALADDIN) FROM THE EARTH TO VENUS|last=Yano|first=H.|work=42nd Lunar and Planetary Science Conference (2011)|access-date=14 February 2011|display-authors=etal}} while its Gamma-Ray Burst Polarimeter (GAP) measured the polarization of gamma-ray bursts during its six-month cruise.{{cite journal|arxiv=1010.5305|title=Gamma-Ray Burst Polarimeter – GAP – aboard the Small Solar Power Sail Demonstrator IKAROS|last=Yonetoku|first=D.|date=26 October 2010|display-authors=etal|doi=10.1093/pasj/63.3.625|volume=63|issue=3|journal=Publications of the Astronomical Society of Japan|pages=625–638|bibcode = 2011PASJ...63..625Y }}

IKAROS was to be followed by a {{convert|40|×|40|m}} sail, the Jupiter Trojan Asteroid Explorer, which was intended to journey to Jupiter and the Trojan asteroids, with a proposed goal of returning an asteroid sample to Earth in the 2050s.{{cite web|url=http://www.jspec.jaxa.jp/e/activity/ikaros.html |archive-url=https://web.archive.org/web/20080922170700/http://www.jspec.jaxa.jp/e/activity/ikaros.html |url-status=dead |archive-date=22 September 2008 |title=IKAROS Project |access-date=12 July 2010 |year=2008 |publisher=JAXA |quote=The second mission will take place in the late 2010s. It will involve a medium-sized solar power sail with a diameter of {{convert|50|m}}, and will have integrated ion-propulsion engines. The destinations of the spacecraft will be Jupiter and the Trojan asteroids. }}[https://www.hou.usra.edu/meetings/lpsc2018/pdf/1406.pdf SCIENCE AND EXPLORATION IN THE SOLAR POWER SAIL OKEANOS MISSION TO A JUPITER TROJAN ASTEROID.] (PDF). T. Okada, T. Iwata, J. Matsumoto, T. Chujo, Y. Kebukawa, J. Aoki, Y. Kawai, S. Yokota, Y. Saito, K. Terada, M. Toyoda, M. Ito, H. Yabuta, H. Yurimoto, C. Okamoto, S. Matsuura, K. Tsumura, D. Yonetoku, T. Mihara, A. Matsuoka, R. Nomura, H. Yano, T. Hirai, R. Nakamura, S. Ulamec, R. Jaumann, J.-P. Bibring, N. Grand, C. Szopa, E. Palomba, J. Helbert, A. Herique, M. Grott, H. U. Auster, G. Klingelhoefer, T. Saiki, H. Kato, O. Mori, J. Kawaguchi. 49th Lunar and Planetary Science Conference 2018 (LPI Contrib. No. 2083).

{{cite web

|url=http://www.space.com/8800-japan-solar-sail-toast-space-science.html

|title=Japan's Solar Sail Is the Toast of Space Science

|author=Jeremy Hsu

|publisher=space.com

|date=21 July 2010

|access-date=8 December 2016

}}

{{Cite news

|url=http://www.japantimes.co.jp/news/2016/07/21/national/science-health/huge-sail-will-power-jaxa-mission-trojan-asteroids-back/

|title=JAXA reveals asteroid probe solar panel

|author=Shusuke Murai

|publisher=The Japan Times

|date=21 July 2016

|access-date=8 December 2016

|newspaper=The Japan Times Online

}}

The Jupiter Trojan Asteroid Explorer was a finalist for Japan's Institute of Space and Astronautical Science (ISAS)' 2nd Large Mission Class. The winning mission was LiteBIRD.

File:Ikaros solar sail key numbered bottom line.svg:{{ordered list

|(blue square on a line) Tip mass {{convert|0.5|kg|abbr=on}}, 1 of 4.

| (orange rectangle) Liquid crystal device, 1 of 80.

| (blue square) Membrane {{convert|7.5|μm|abbr=on}} thick, {{convert|20|m}} on the diagonal.

| (black rectangle) Solar cells {{convert|25|μm|abbr=on}} thick.

| (yellow and blue lines) Tethers.

| (blue disc) Main body.

| (yellow dots) Instruments.}}]]

The square sail, deployed via a spinning motion using {{convert|0.5|kg|lb|adj=on}} tip masses (key item 1 in figure at right), is {{convert|20|m|abbr=on}} on the diagonal and is made of a {{convert|adj=on|7.5|μm}} thick sheet of polyimide (key item 3 in figure at right). The polyimide sheet had a mass of about {{convert|10|g/m2|oz/sqft}}, resulting in a total sail mass of {{convert|2|kg}}, excluding tip masses, attached panels and tethers. A thin-film solar array is embedded in the sail (key item 4 in figure at right). PowerFilm, Inc. provided the thin-film solar array.{{cite web|author=Claire M. Umali |title=Japan tests power of solar sails in deep space |url=http://www.ecoseed.org/en/technology/emerging-renewables/article/28-emerging-renewables/7067-japan-tests-power-of-solar-sails-in-deep-space |archive-url=https://web.archive.org/web/20101202070314/http://ecoseed.org/en/technology/emerging-renewables/article/28-emerging-renewables/7067-japan-tests-power-of-solar-sails-in-deep-space |url-status=dead |archive-date=2 December 2010 |work=EcoSeed |date=4 May 2010 |access-date=25 January 2011 }} Eighty blocks of LCD panels are embedded in the sail,{{cite web|url=http://www.jaxa.jp/press/2010/07/20100723_ikaros_e.html|title=Small Solar Power Sail Demonstrator 'IKAROS': Successful Attitude Control by Liquid Crystal Device |date=23 July 2010 |publisher=Japan Aerospace Exploration Agency (JAXA)}} whose reflectance can be adjusted for attitude control (key item 2 in figure at right). The sail also contains eight dust counters on the opposite face as part of the science payload.{{cite web | title=Small Solar Power Sail Demonstrator | url=http://www.jaxa.jp/projects/sat/ikaros/index_e.html | publisher=JAXA | date=11 March 2010 | access-date=7 May 2010 | archive-date=30 October 2013 | archive-url=https://web.archive.org/web/20131030175323/http://www.jaxa.jp/projects/sat/ikaros/index_e.html | url-status=dead }}{{cite web|url=http://www.jspec.jaxa.jp/e/activity/ikaros.html |archive-url=https://web.archive.org/web/20080922170700/http://www.jspec.jaxa.jp/e/activity/ikaros.html |url-status=dead |archive-date=22 September 2008 |title=IKAROS Project |year=2008 |publisher=JAXA |access-date=30 March 2010 }}

File:IKAROS solar sail.jpg|IKAROS spaceprobe in flight (artist's depiction)

File:IKAROS-SAIL.jpg|IKAROS model

IKAROS was successfully launched together with Akatsuki (the Venus Climate Orbiter) aboard an H-IIA rocket from the Tanegashima Space Center on 21 May 2010.{{citation needed|date=December 2020}}

IKAROS spun at 20–25 revolutions per minute and finished unfurling its sail on 10 June 2010.{{cite news | last=Edwards | first=Lin | title=IKAROS unfurls first ever solar sail in space | publisher=PhysOrg | date=11 June 2010 | url=http://www.physorg.com/news195460006.html | access-date=11 June 2010 }}{{cite news | author=Staff writers| title=Japanese Spacecraft Deploys Solar Sail | work=Space.com | date=11 June 2010 | url=http://www.space.com/missionlaunches/japan-spacecraft-deploys-solar-sail-100611.html | access-date=11 June 2010 }}{{cite news | last=Amos| first=Jonathan | url=http://news.bbc.co.uk/2/hi/science_and_environment/10293284.stm| title=Japan unfurls Ikaros solar sail in space| work=BBC News | date=11 June 2010 | access-date=25 January 2011}} The craft contains two tiny ejectable cameras, DCAM1 and DCAM2. DCAM2 was used to photograph the sail after deployment on 14 July 2010.{{cite news | author=Staff writers | title=Mini-camera pictures Japan's Ikaros solar sail | url=http://news.bbc.co.uk/1/hi/science_and_environment/10328584.stm | work=BBC News | access-date=17 June 2010 | date=16 June 2010}}

Acceleration and attitude control (orientation) were successfully tested during the remaining six-month voyage to Venus. On 9 July 2010, JAXA confirmed that IKAROS was being accelerated by its solar sail,{{cite press release | title=About the confirmation of photon acceleration of "IKAROS" the small solar-sail demonstrating craft | work=JAXA website press release | publisher=Japan Aerospace Exploration Agency | date=9 July 2010 | url=http://www.jaxa.jp/press/2010/07/20100709_ikaros_j.html | access-date=25 January 2011 |language=ja |quote=Graph suggests approx 1.1mN force}} and on 23 July announced successful attitude control. Over a 23-hour period of time, the solar angle of the sail was changed by a half a degree, not by using thrusters, but by dynamically controlling the reflectivity of the 80 liquid crystal panels at the outer edge of the sail so that the sunlight pressure would produce torque.{{cite press release |url=http://www.jaxa.jp/press/2010/07/20100723_ikaros_e.html |title=Small Solar Power Sail Demonstrator 'IKAROS'Successful Attitude Control by Liquid Crystal Device| publisher=Japan Aerospace Exploration Agency (JAXA) |date=23 July 2010 | access-date=25 January 2011}}

IKAROS continues to spin at approximately 2 rpm, requiring the LCD panels to be cycled at that rate for attitude control.{{citation needed|date=December 2020}}

According to JAXA, IKAROS finished all planned experiments in Dec 2010, but the mission continued beyond that date "in order to enhance the skill of controlling solar sail".{{cite news|url=http://www.jspec.jaxa.jp/e/activity/ikaros.html |archive-url=https://web.archive.org/web/20080922170700/http://www.jspec.jaxa.jp/e/activity/ikaros.html |url-status=dead |archive-date=22 September 2008 |title=Solar Power Sail Demonstrator "IKAROS" |publisher=Japan Aerospace Exploration Agency (JAXA) |access-date=30 December 2012 }} On 30 November 2012, JAXA announced that IKAROS had been recognized by Guinness World Records as the world's first solar sail spacecraft between planets, and that its two separated cameras, DCAM1 and DCAM2, had been recognized as the smallest size of a spacecraft flying between planets.{{cite news |url=http://www.jaxa.jp/projects/sat/ikaros/index_e.html |title=IKAROS world record certified! |publisher=Japan Aerospace Exploration Agency (JAXA) |date=30 November 2012 |access-date=30 December 2012 |archive-date=30 October 2013 |archive-url=https://web.archive.org/web/20131030175323/http://www.jaxa.jp/projects/sat/ikaros/index_e.html |url-status=dead }}{{cite news |url=http://ajw.asahi.com/article/behind_news/social_affairs/AJ201212300014 |title=JAXA's solar spacecraft gets Guinness World Records entry |publisher=The Asahi Shimbun |date=30 December 2012 |access-date=30 December 2012 |archive-url=https://web.archive.org/web/20130213125558/https://ajw.asahi.com/article/behind_news/social_affairs/AJ201212300014 |archive-date=13 February 2013 |url-status=dead }}

As of 2012, the IKAROS continued to spin, but its attitude control had degraded. This resulted in unexpected sail motions and as a result, downlink through the medium-gain antenna was only intermittently available. The project team was dissolved on 28 March 2013, although a trial receipt of data was planned for a later date.{{citation needed|date=December 2020}}

The project was reactivated on 20 June 2013 in the expectation that the satellite would wake up from a hibernation state as more power from the solar panels became available. The team was able to receive telemetry from the IKAROS between 20 June and 12 September 2013, after which contact was again lost. The loss of contact was around the predicted time of the spacecraft again entering a low-power hibernation mode as power from the solar panels decreased. Available communication time through the Usuda Deep Space Center antenna was limited, so data was gathered only intermittently to estimate the speed, trajectory and rotation of the satellite.{{cite web |url=http://www.isas.jaxa.jp/home/IKAROS-blog/?itemid=1011 |title=今日の IKAROS(2013/06/20) – Daily Report – June 20, 2013| publisher=Japan Aerospace Exploration Agency (JAXA) |date=20 June 2013 | access-date=8 June 2014 |language=ja}}{{cite web |url=http://www.isas.jaxa.jp/home/IKAROS-blog/?itemid=1018 |title= 今日の IKAROS(12/7) – Daily Report – Dec 7, 2013 | publisher=Japan Aerospace Exploration Agency (JAXA) |date=20 June 2013 | access-date=8 June 2014 |language=ja}} As of August 2013, acceleration from the IKAROS sail had changed the craft's speed by approximately {{convert|400|m/s|mph}} in total.{{cite web |url=http://www.isas.jaxa.jp/home/IKAROS-blog/?itemid=1017|title=今日の IKAROS(8/29) – Daily Report – Aug 29, 2013 | publisher=Japan Aerospace Exploration Agency (JAXA) |date=29 August 2013 | access-date=8 June 2014 |language=ja}}

Transmissions were again received on 22 May 2014, the spacecraft flying at a distance of about 230 million kilometers from the Earth. By May 2014, IKAROS was on a ten-month orbit around the Sun, spending seven months of each orbit in hibernation mode due to insufficient power.{{cite news |url=http://www.isas.jaxa.jp/j/topics/topics/2014/0526.shtml |title= IKAROS：3回目の冬眠モード明けについて | publisher=Japan Aerospace Exploration Agency (JAXA) |date=26 May 2014 | access-date=8 June 2014 |language=ja}} By 23 April 2015, the spacecraft woke up from hibernation mode for the 4th time and was flying at a distance of about 120 million kilometers from the Earth.{{cite news |url=http://global.jaxa.jp/projects/sat/ikaros/topics.html#topics4577 |title=IKAROS wakes up from hibernation mode for the 4th time |work=JAXA |date=30 April 2015 |access-date=24 May 2015 }} On 21 May 2015, JAXA could not receive a signal from IKAROS and concluded that the spacecraft had shifted to the hibernation mode for the fifth time, as expected. Based on the last data received during May 2015, the position of IKAROS at the time was about 110 million kilometers away from the Earth, and about 130 million kilometers from the Sun.{{cite news |url=http://global.jaxa.jp/projects/sat/ikaros/topics.html |title=IKAROS enters hibernation mode for 5th time |work=JAXA |date=29 May 2015}}

From the gamma-ray polarization data of GAP, Toma et al.{{cite journal |title=Strict Limit on CPT Violation from Polarization of γ-Ray Bursts |author=Kenji Toma |journal=Physical Review Letters |date=December 2012 |volume=109 |issue=24 |page=241104 |doi=10.1103/PhysRevLett.109.241104 |arxiv = 1208.5288 |bibcode = 2012PhRvL.109x1104T |display-authors=etal |pmid=23368301|s2cid=42198517 }} put a stricter limit on CPT violation. It is an improvement of eight orders of magnitude over previous limits.{{Cite journal |title=Synopsis: Distant Bursts Show no Signs of Predicted Light Rotation |journal = Physical Review Letters|volume = 109|issue = 24|pages = 241104|author=Michael Schirber |doi=10.1103/PhysRevLett.109.241104 |pmid = 23368301|bibcode = 2012PhRvL.109x1104T|year = 2012|arxiv = 1208.5288| s2cid=42198517 }}{{cite web |url=http://www.ipmu.jp/node/1458 |title=Strict Limit on CPT Violation from Gamma-Ray Bursts |publisher=Kavli Institute for the Physics and Mathematics of the Universe |date=7 December 2012 |access-date=16 December 2012 |archive-date=23 March 2013 |archive-url=https://web.archive.org/web/20130323004146/http://www.ipmu.jp/node/1458 |url-status=dead }}

JAXA scientists stated on 9 July 2010 that the measured thrust force by the solar radiation pressure on IKAROS' {{Convert|196|m2|adj=on|sp=us}} sail is {{Convert|1.12|mN}}.{{cite web|url=http://www.jspec.jaxa.jp/ikaros_channel/e/index.html |archive-url=https://web.archive.org/web/20100819085236/http://www.jspec.jaxa.jp/ikaros_channel/e/index.html |url-status=dead |archive-date=19 August 2010 |title=IKAROS – All News Channel |work=JAXA |date=9 July 2010 |access-date=24 May 2015 }}

{{Portal|Spaceflight}}

• {{annotated link|CubeSail}}
• {{annotated link|CubeSail (UltraSail)}}
• {{annotated link|LightSail 2}}
• {{annotated link|List of missions to Venus}}
• {{annotated link|Near-Earth Asteroid Scout}}
• {{annotated link|NanoSail-D2}}
• {{annotated link|OKEANOS}}

{{Reflist}}

• {{Cite journal |url=https://archive.ists.or.jp/upload_pdf/2008-d-57.pdf |title=Development of Deployment System for Small Size Solar Sail Mission |volume=7 |pages=Pd_87–Pd_94 |author=Osamu Mori|journal=Transactions of the Japan Society for Aeronautical and Space Sciences, Space Technology Japan |date=6 July 2008 |access-date=9 May 2011|display-authors=etal|bibcode=2009TrSpT...7.Pd87M |doi=10.2322/tstj.7.Pd_87 |doi-access=free }}
• {{Cite journal |url=https://archive.ists.or.jp/upload_pdf/2009-o-4-07v.pdf |title=First Solar Power Sail Demonstration by IKAROS |volume=8 |pages=To_4 |author=Osamu Mori|journal=27th International Symposium on Space Technology and Science |date=9 July 2009 |access-date=6 March 2010|display-authors=etal|bibcode=2011TJSAI...8To425M }}

{{Commons category|IKAROS}}

• [http://www.jaxa.jp/press/2010/06/20100628_ikaros_e.html Successful Image Shooting by the Second Separation Camera] – 28 June 2010 JAXA press release
• [http://www.isas.jaxa.jp/e/forefront/2011/tsuda/index.shtml Solar Sail Navigation Technology of IKAROS]
• {{YouTube|id=7_6HOqBkP2o|title=小型ソーラー電力セイル実証機「IKAROS」(Small Solar Power Sail Demonstrator) by JAXA}}

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