A 1:64 scale model of the IKAROS spacecraft
|Mission duration||~0.5 years
elapsed: 6 years, 6 months and 18 days
|Launch mass||315 kg (694 lb)|
|Dimensions||Solar sail: 14 m × 14 m (46 ft × 46 ft) (area: 196 m2 (2,110 sq ft))|
|Start of mission|
|Launch date||21:58:22, 20 May 2010|
|Launch site||Tanegashima Space Center, LA-Y|
|Reference system||Heliocentric orbit|
|Flyby of Venus|
|Closest approach||8 December 2010|
IKAROS (Interplanetary Kite-craft Accelerated by Radiation Of the Sun) is a Japan Aerospace Exploration Agency (JAXA) experimental spacecraft. The spacecraft was launched on 21 May 2010, aboard an H-IIA rocket, together with the Akatsuki (Venus Climate Orbiter) probe and four other small spacecraft. IKAROS is the first spacecraft to successfully demonstrate solar sail technology in interplanetary space.
The IKAROS probe is the world's first spacecraft to use solar sailing as the main propulsion. It was designed to demonstrate four key technologies (comments in parentheses refer to figure):
- Deployment and control of a large, thin solar sail membrane (grey-blue areas numbered 3)
- Thin-film solar cells integrated into the sail to power the payload (black rectangles numbered 4)
- Measurement of acceleration due to radiation pressure on the solar sail
- Attitude control by varying the reflectance of 80 liquid crystal panels embedded in the sail (orange rectangles numbered 2)
The probe's ALADDIN instrument (ALDN-S and ALDN-E) measured the variation in dust density while its Gamma-Ray Burst Polarimeter (GAP) measured the polarization of gamma-ray bursts during its six-month cruise.
IKAROS is to be followed by a 50 m (160 ft) sail, intended to journey to Jupiter and the Trojan asteroids, later in the decade, with a stated goal of returning an asteroid sample to Earth in the 2050s.  
The square sail, deployed via a spinning motion using 0.5-kilogram (1.1 lb) tip masses (key item 1 in figure at right), is 20 m (66 ft) on the diagonal and is made of a 7.5-micrometre (0.00030 in) thick sheet of polyimide (key item 3 in figure at right). The polyimide sheet had a mass of about 10 grams per square metre, resulting in a total sail mass of 2 kilograms, 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. Eighty blocks of LCD panels are embedded in the sail, 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.
IKAROS spun at 20–25 revolutions per minute and finished unfurling its sail on 10 June 2010. The craft contains two tiny ejectable cameras, DCAM1 and DCAM2. DCAM2 was used to photograph the sail after deployment on 14 July 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 is being accelerated by its solar sail, 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.
IKAROS continues to spin at approximately 2 rpm, requiring the LCD panels to be cycled at that rate for attitude control.
According to JAXA, IKAROS finished all planned experiments in Dec 2010, but the mission has continued beyond that date "in order to enhance the skill of controlling solar sail." 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. 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.
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. As of August 2013, IKAROS was continuing to gain speed. At that time, it had gained approximately 400 m/s of velocity from its solar sail.
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. 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. 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 May 2015 data the position of the IKAROS at the time was about 110 million kilometers away from the Earth, and about 130 million kilometers from the sun. Data showed no anomaly in the IKAROS spacecraft. JAXA expects the 5th wake up of IKAROS in the northern hemisphere winter of 2016.[needs update]
JAXA scientists stated that the measured thrust force by the solar radiation pressure on IKAROS' 196 m2 sail is 1.12 millinewtons.
- LightSail 2, a private solar sail project of the Planetary Society
- List of missions to Venus
- Lunar Flashlight, a solar sail orbiter to the Moon
- NanoSail-D2, an American solar sail deployed in LEO in January 2011
- Solar sail
- Mori et al. (2009)
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- Yano, H.; et al. "COSMIC DUST DETECTION BY THE IKAROS-ARRAYED LARGE-AREA DUST DETECTORS IN INTERPLANETARY SPACE (ALADDIN) FROM THE EARTH TO VENUS" (PDF). 42nd Lunar and Planetary Science Conference (2011). Retrieved 14 February 2011.
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The second mission will take place in the late 2010s. It will involve a medium-sized solar power sail with a diameter of 50m, and will have integrated ion-propulsion engines. The destinations of the spacecraft will be Jupiter and the Trojan asteroids.
- Jeremy Hsu (21 July 2010). "Japan's Solar Sail Is the Toast of Space Science". space.com. Retrieved 8 December 2016.
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- Staff writers (16 June 2010). "Mini-camera pictures Japan's Ikaros solar sail". BBC News. Retrieved 17 June 2010.
- "About the confirmation of photon acceleration of "IKAROS" the small solar-sail demonstrating craft". JAXA website press release (Press release) (in Japanese). Japan Aerospace Exploration Agency. 9 July 2010. Retrieved 25 January 2011.
Graph suggests approx 1.1mN force
- "Small Solar Power Sail Demonstrator 'IKAROS'Successful Attitude Control by Liquid Crystal Device" (Press release). Japan Aerospace Exploration Agency (JAXA). 23 July 2010. Retrieved 25 January 2011.
- "Solar Power Sail Demonstrator "IKAROS"". Japan Aerospace Exploration Agency (JAXA). Retrieved 30 December 2012.
- "IKAROS world record certified!". Japan Aerospace Exploration Agency (JAXA). 30 November 2012. Retrieved 30 December 2012.
- "JAXA's solar spacecraft gets Guinness World Records entry". The Asahi Shimbun. 30 December 2012. Retrieved 30 December 2012.
- "今日の IKAROS(2013/06/20) – Daily Report – June 20, 2013" (in Japanese). Japan Aerospace Exploration Agency (JAXA). 20 June 2013. Retrieved 8 June 2014.
- "今日の IKAROS(12/7) – Daily Report – Dec 7, 2013" (in Japanese). Japan Aerospace Exploration Agency (JAXA). 20 June 2013. Retrieved 8 June 2014.
- "今日の IKAROS(8/29) – Daily Report – Aug 29, 2013" (in Japanese). Japan Aerospace Exploration Agency (JAXA). 29 August 2013. Retrieved 8 June 2014.
- "IKAROS：3回目の冬眠モード明けについて" (in Japanese). Japan Aerospace Exploration Agency (JAXA). 26 May 2014. Retrieved 8 June 2014.
- "IKAROS wakes up from hibernation mode for the 4th time". JAXA. 30 April 2015. Retrieved 24 May 2015.
- "IKAROS enters hibernation mode for 5th time". JAXA. 29 May 2015.
- Kenji Toma; et al. (December 2012). "Strict Limit on CPT Violation from Polarization of γ-Ray Bursts". Physical Review Letters. 109 (24): 241104. arXiv: . Bibcode:2012PhRvL.109x1104T. doi:10.1103/PhysRevLett.109.241104.
- Michael Schirber. "Synopsis: Distant Bursts Show no Signs of Predicted Light Rotation". American Physical Society. Retrieved 16 December 2012.
- "Strict Limit on CPT Violation from Gamma-Ray Bursts". Kavli Institute for the Physics and Mathematics of the Universe. 7 December 2012. Retrieved 16 December 2012.
- "IKAROS – All News Channel". JAXA. 9 July 2010. Retrieved 24 May 2015.
- Osamu Mori; et al. (6 July 2008). "Development of Deployment System for Small Size Solar Sail Mission" (PDF). 26th International Symposium on Space Technology and Science. Retrieved 9 May 2011.
- Osamu Mori; et al. (9 July 2009). "First Solar Power Sail Demonstration by IKAROS" (PDF). 27th International Symposium on Space Technology and Science. Retrieved 6 March 2010.
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