OKEANOS (Oversize Kite-craft for Exploration and Astronautics in the Outer Solar system) was a proposed mission concept to Jupiter trojan, 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 on spacecraft, 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.Sampling Scenario for the Trojan Asteroid Exploration Mission
Jun Matsumoto, Jun Aoki, Yuske Oki, Hajime Yano; 2015 OKEANOS was a finalist for Japan's Institute of Space and Astronautical Science (ISAS) 2nd Large Mission Class to be launched in 2026,JAXA Sail to Jupiter's Trojan Asteroids
Paul Gilster, ''Centauri Dreams'' 15 March 2017 and possibly return Trojan asteroid samples to Earth in the 2050s. The winning mission was LiteBIRD.

Overview

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. 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. 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.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'' There were several options for this mission, and the most ambitious one proposed to retrieve and send samples to Earth for extensive investigations. Had it been selected in April 2019 for development, the spacecraft would have launched in 2026, and may had offered some synergy with Lucy (spacecraft), ''Lucy'' spacecraft that will flyby multiple Jupiter Trojans in 2027.

Spacecraft

The spacecraft was projected to have a mass of about including a possible lander and would have been equipped with solar electric ion engines. 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. 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. 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. 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.

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. A study indicated the need for 191 kg of xenon propellant if it had been decided to bring a sample back to Earth.

Lander

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. The spacecraft would have deployed a 100 kg lander 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. 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. 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. The lander would have operated for about 20 hours using battery power. * Mass spectrometer * Hyperspectral imaging, Hyperspectral microscope * Hyperspectral panoramic imager * Optical navigation camera * Laser rangefinder * Magnetometer#Fluxgate magnetometer, Fluxgate 3-axis magnetometer * Alpha particle X-ray spectrometer (APXS) * Surface and subsurface sampler ;On the spacecraft: * Exo-Zodiacal Infrared telescope, Infrared Telescope (EXZIT) is a 10 cm-diameter telescope. * Gamma-ray burst polarimeter (GAP-2) * Monostatic radar to image the body's internal structures 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 ;Attached to the sail: * Arrayed Large-area Cosmic dust, Dust Detectors (ALDN-2) * Magnetic Field Experiment (MGF-2) is a fluxgate magnetometer 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), Arase satellite, and ALADDIN-2, GAP-2 were possible successors of the respective instruments onboard IKAROS.

References

{{Japanese space program Japanese space probes Jupiter trojans Missions to asteroids Missions to Jupiter Sample return missions Proposed space probes Solar sail spacecraft Solar sailing Japanese inventions