NamesOversize Kite-craft for Exploration and Astronautics in the Outer Solar system
Jupiter Trojan Asteroid Explorer
Mission typeTechnology demonstration,
Possible sample return
COSPAR ID Edit this at Wikidata
Mission duration≈12 years
>30 years for optional sample return
Spacecraft properties
Spacecraft typeSolar sail
ManufacturerISAS and DLR
Launch mass1400 kg
Landing mass≈100 kg
Payload massSpacecraft: 30 kg
Lander: 20 kg [1]
DimensionsSail/solar panel:
40×40 m (1600 m2) [2]
Lander: 65 × 40 cm [1]
PowerMax: 5 kW at Jupiter [2]
Start of mission
Launch date2026
RocketH-IIA or H3[1]
Launch siteTanegashima Space Center
ContractorMitsubishi Heavy Industries
Jupiter Trojan lander
Landing date2039 [2]
Main telescope
Capacity16 Kbps [3]
Large Mission Class

OKEANOS (Oversize Kite-craft for Exploration and Astronautics in the Outer Solar system) was a proposed mission concept to Trojan asteroids, which share Jupiter's orbit, using a hybrid solar sail for propulsion; the sail was planned to be covered with thin solar panels to power an ion engine. In situ analysis of the collected samples would have been performed by either direct contact or using a lander carrying a high-resolution mass spectrometer. A sample-return to Earth was an option under study.[4]

OKEANOS was a finalist for Japan's Institute of Space and Astronautical Science (ISAS)' 2nd Large Mission Class to be launched in 2026,[2][5][6] and possibly return Trojan asteroid samples to Earth in the 2050s.[6][7] The winning mission was LiteBIRD.


The OKEANOS mission was a concept first proposed in 2010 to fly together with the Jupiter Magnetospheric Orbiter (JMO) as part of the cancelled Europa Jupiter System Mission – Laplace.[8]

In its latest formulation, the OKEANOS mission and LiteBIRD were the two finalists of Japan's Large Mission Class by the Ministry of Education, Culture, Sports, Science and Technology. LiteBIRD, a cosmic microwave background astronomy telescope, was selected.[9]

Analyzing the composition of the Jupiter Trojans may help scientists understand how the Solar System was formed. It would also help determine which of the competing hypotheses is right:[10] remnant planetesimals during the formation of Jupiter, or fossils of building blocks of Jupiter, or captured trans-Neptunian objects by planetary migration. The latest proposal included a lander to perform in situ analyses.[11][12] There were several options for this mission, and the most ambitious one proposed to retrieve and send samples to Earth for extensive investigations.[13] Had it been selected in April 2019 for development, the spacecraft would have launched in 2026,[2] and may had offered some synergy with Lucy spacecraft that will flyby multiple Jupiter Trojans in 2027.[14]


The spacecraft was projected to have a mass of about 1,285 kg (2,833 lb) including a possible lander [3] and would have been equipped with solar electric ion engines.[5] The 1600 m2 sail would have had a dual purpose of solar sail propulsion and solar panel for power generation. If a lander had been included, its mass would have been no greater than 100 kg. The lander would have collected and analyzed samples from the asteroid. A more complex suggested concept would have had the lander take off again, rendezvous with the mothership and transfer the samples for their transport to Earth.

Solar sail and solar panels

The unique proposed sail was a hybrid that would have provided both photon propulsion and electric power. JAXA referred to the system as a Solar Power Sail.[3][15] The sail would have been made of a 10 μm-thick polyimide film measuring 40 × 40 meters (1600 m2),[2] covered with 30,000 solar panels 25 μm thick, capable of generating up to 5 kW at the distance of Jupiter, 5.2 Astronomical Units from the Sun.[6][7][10] The main spacecraft would have been located at the center of the sail, equipped with a solar-electric ion engine for maneuvering and propulsion, especially for a possible sample-return trip to Earth.[4][6][7]

The spacecraft would have used solar sail technology initially developed for the successful IKAROS (Interplanetary Kite-craft Accelerated by Radiation of the Sun) that launched in 2010, whose solar sail was 14 m × 14 m in size.[6][15] As with the IKAROS, the solar angle of the sail would have been changed by dynamically controlling the reflectivity of liquid crystal displays (LCD) on the outer edge of the sail so that the sunlight pressure would produce torque to change its orientation.[16]

Ion engine

The ion engine intended for the mission was called μ10 HIsp. It was planned to have a specific impulse of 10,000 seconds, power of 2.5 kW, and a maximum thrust magnitude of 27 mN for each of the four engines.[17][18] The electric engine system would have been an improved version of the engine from the Hayabusa mission, used for maneuvering, and especially for an optional sample-return trip to Earth.[15][18] A study indicated the need for 191 kg of xenon propellant if it had been decided to bring a sample back to Earth.[18]




Mass ≤ 100 kg (220 lb)
Dimensions Cylindrical: 65 cm diameter
40 cm height
Power Non-rechargeable battery
(≤ 20 kg)
Sampling Pneumatic
Depth: ≤1 m

The mission concept considered several scenarios, targets, and architectures. The most ambitious scenario contemplated in situ analysis and a sample-return using a lander. This lander concept was a collaboration among the German Aerospace Center (DLR) and Japan's JAXA, starting in 2014.[3] The spacecraft would have deployed a 100 kg lander [4][1] on the surface of a 20–30 km Trojan asteroid to analyze its subsurface volatile constituents, such as water ice, using a 1-meter pneumatic drill powered by pressurized nitrogen gas. Some subsurface samples would have been transferred to the on board mass spectrometer for volatile analysis.[4] The lander's scientific payload mass, including the sampling system, would not have exceeded 20 kg. The lander would have been powered by batteries and was planned to perform an autonomous descent, landing, sampling and analysis.[3] Some samples were to be heated up to 1000 °C for pyrolysis for isotopic analysis. The conceptual payload for the lander would have included a panoramic camera (visible and infrared), an infrared microscope, a Raman spectrometer, a magnetometer, and a thermal radiometer.[20] The lander would have operated for about 20 hours using battery power.[1]

If a sample-return was to be performed, the lander would have taken off then, rendezvous and deliver the surface and subsurface samples to the mothership hovering above (at 50 km) for subsequent delivery to Earth within a reentry capsule.[5][3] The lander would have been discarded after the sample transfer.

Conceptual scientific payload

On the lander
On the spacecraft
Attached to the sail

GAP-2 and EXZIT were instruments for astronomical observations, and were not intended to be used for studying Trojan asteroids. The two would have conducted opportunistic surveys, taking advantage of the mission's trajectory. GAP-2 would have made it possible to locate the position of Gamma-ray bursts with high precision by pairing it with terrestrial observatories. EXZIT, as zodiacal light gets significantly weak beyond the asteroid belt, would have enabled the telescope to observe the cosmic infrared background. MGF-2 was a possible a successor of the MGF instrument on board the Arase satellite, and ALADDIN-2, GAP-2 were possible successors of the respective instruments onboard IKAROS.

See also


  1. ^ a b c d e f g SCIENCE AND EXPLORATION IN THE SOLAR POWER SAIL OKEANOS MISSION TO A JUPITER TROJAN ASTEROID 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)
  2. ^ a b c d e f g h INVESTIGATION OF THE SOLAR SYSTEM DISK STRUCTURE DURING THE CRUISING PHASE OF THE SOLAR POWER SAIL MISSION T. Iwata, T. Okada, S. Matsuura, K. Tsumura, H. Yano, T. Hirai, A. Matsuoka, R. Nomura, D. Yonetoku, T. Mihara, Y. Kebukawa, M. ito, M. Yoshikawa, J. Matsu-moto, T. Chujo, and O. Mori; 49th Lunar and Planetary Science Conference 2018 (LPI Contrib. No. 2083)
  3. ^ a b c d e f Direct Exploration of Jupiter Trojan Asteroid using Solar Power Sail Osamu Mori, Hideki Kato, et al. 2017
  4. ^ a b c d Sampling Scenario for the Trojan Asteroid Exploration Mission Archived 2017-12-31 at the Wayback Machine Jun Matsumoto, Jun Aoki, Yuske Oki, Hajime Yano; 2015
  5. ^ a b c Trajectory Design for Jovian Trojan Asteroid Exploration via Solar Power Sail Takanao Saiki, Osam Mori The Institute of Space and Astronautical Science (ISAS), JAXA 2017
  6. ^ a b c d e JAXA Sail to Jupiter's Trojan Asteroids Paul Gilster, Centauri Dreams 15 March 2017
  7. ^ a b c Huge sail will power JAXA mission to Trojan asteroids and back Shusuke Murai, The Japan Times 21 July 2016
  8. ^ Sasaki, Shio (2010). "Jupiter Magnetospheric Orbiter and Trojan Asteroid Explorer" (PDF). COSPAR. Retrieved 26 August 2015.
  9. ^ Roadmap 2017 — Fundamental Concepts for Promoting Large Scientific Research Projects 28 July 2017
  10. ^ a b The Solar Power Sail Mission to Jupiter Trojans Archived 2015-12-31 at the Wayback Machine The 10th IAA International Conference on Low-Cost Planetary Missions 19 June 2013
  11. ^ OKEANOS - Jupiter Trojan Asteroid Rendezvous and Landing Mission using the Solar Power Sail Okada, Tatsuaki; Matsuoka, Ayako; Ulamec, Stephan; Helbert, Jorn; Herique, M. Alain; Palomba, Ernesto; Jaumann, Ralf; Grott, Matthias; Mori, Osamu; Yonetoku, Daisuke; 42nd COSPAR Scientific Assembly Held 14–22 July 2018, in Pasadena, California, Abstract id. B1.1-65-18
  12. ^ System Designing of Solar Power Sail-craft for Jupiter Trojan Asteroid Exploration Osamu MORI, Jun MATSUMOTO, Toshihiro CHUJO, Hideki KATO, Takanao SAIKI, Junichiro KAWAGUCHI, Shigeo KAWASAKI, Tatsuaki OKADA, Takahiro IWATA, Yuki TAKAO; J-Stage doi:10.2322/tastj.16.328
  13. ^ Science exploration and instrumentation of the OKEANOS mission to a Jupiter Trojan asteroid using the solar power sail Tatsuaki Okada, Yoko Kebukawa, Jun Aoki; Planetary and Space Science Volume 161, 15 October 2018, Pages 99-106 doi:10.1016/j.pss.2018.06.020
  14. ^ ISAS Small Body Exploration Strategy Lunar and Planetary Laboratory The University of Arizona-JAXA Workshop (2017)
  15. ^ a b c IKAROS and Solar Power Sail - Craft Missions for Outer Planetary Region Exploration Archived 2017-01-26 at the Wayback Machine J. Kawaguchi (JAXA) 15 June 2015
  16. ^ Liquid Crystal Device with Reflective Microstructure for Attitude Control Toshihiro Chujo, Hirokazu Ishida, Osamu Mori, and Junichiro Kawaguchi Aerospace Research Central doi:10.2514/1.A34165
  17. ^ Lineup of Microwave Discharge Ion Engines JAXA
  18. ^ a b c Mission Analysis of Sample Return from Jovian Trojan Asteroid by Solar Power Sail Jun Matsumoto, Ryu Funase, et al. Trans. JSASS Aerospace Tech. Japan Vol. 12, No. ists29, pp. Pk_43-Pk_50, 2014
  19. ^ Science experiments on a Jupiter Trojan asteroid on the solar powered sail mission (PDF). O. Mori, T. Okada1, et al. 47th Lunar and Planetary Science Conference (2016).
  20. ^ Trojan asteroid probe (in Japanese) JAXA
  21. ^ EXZIT Telescope JAXA
  22. ^ Jupiter Trojan's shallow subsurface: direct observations by radar on board OKEANOS mission Alain Herique, Pierre Beck, Patrick Michel, Wlodek Kofman, Atsushi Kumamoto, Tatsuaki Okada, Dirk Plettemeier; EPSC Abstracts Vol. 12, EPSC2018-526, 2018 European Planetary Science Congress 2018