Trans. JSASS Aerospace Tech. Japan Vol. 10, No. ists28, pp. Tk_37-Tk_40, 2012 Topics The Jupiter Magnetospheric Orbiter and the Trojan Asteroid Explorer in EJSM (Europa Jupiter System Mission) 1) 2) 2) 2) 3) By Sho SASAKI , Masaki FUJIMOTO , Hajime YANO , Takeshi TAKASHIMA , Yasumasa KASABA , 4) 4) 2) 2) 2) Yukihiro TAKAHASHI , Jun KIMURA , Yuichi TSUDA , Ryu FUNASE , Osamu MORI 2) 2) Stefano CAMPAGNOLA , Yasuhiro KAWAKATSU 1)National Astronomical Observatory of Japan, Oshu, Japan 2)The Institute of Space and Astronautical Science, JAXA, Sagamihara, Japan 3)Tohoku University, Sendai, Japan 4)Hokkaido University, Sapporo, Japan (Received June 27th, 2011) EJSM (Europa Jupiter System Mission) is an international Jovian system mission with three spacecraft. Coordinated observation of Jovian magnetosphere is one of the important targets of the mission in addition to icy satellites, atmosphere, and the interior of Jupiter. JAXA will take a role on the magnetosphere spinner JMO (Jupiter Magnetospheric Orbiter), whereas ESA will launch JGO (Jupiter Ganymede Orbiter) and NASA will be responsible for JEO (Jupiter Europa Orbiter). One possibility is to combine JMO with a proposed solar sail mission of JAXA for Jupiter and one of Trojan asteroids. Since Trojan asteroids could be representing raw solid materials of Jupiter or at least outer solar system bodies, involvement of Trojan observation should enlarge the scope and enhance the quality of EJSM. Key Words:Jupiter, Jovian Magnetosphere, Trojan Asteroids, Europa, Ganymede 1. Introduction: EJSM to investigate the 3D spatial structure of magnetosphere, the multi-spacecraft mission is desiable1). From the beginning of Jupiter is the largest planet in the solar system. It is a EJSM (former Laplace), JAXA and Japanese members rapidly rotating gaseous body whose main composition is committed with the mission planning with ESA and European hydrogen and helium. Jupiter has various satellites, four of scientists. The initial plan was that JAXA will take a role on which were discovered by Galileo 400 years ago. Jupiter has the magnetosphere spinner JMO (Jupiter Magnetosphere 1) the strongest planetary magnetosphere in the solar system . Orbiter) and JMO would be launched and transported together And recent discoveries of exoplanets, especially hot jupiters, with ESA’s orbiter. The original plan was similar to the suggest that Jupiter should represent a body not only in the framework of the BepiColombo Mercury mission where ESA 2) solar system but in the universe . is responsible for the launcher and MPO (Mercury Planetary The Jupiter System, with Jupiter and its satellites, can be Orbiter) and JAXA provides MMO (Mercury Magnetosphere considered as a small planetary system. The Jupiter system Orbiter). EJSM (formerly "Laplace") was selected as one of was observed by several flyby missions such as Pioneer 10 future ESA mission candidates of L-class Cosmic Vision and 11, Voyager 1 and 2, Cassini, New Horizons and (2015-2025) 1). Then NASA with the Europa orbiter investigated by Galileo orbiter and its atmospheric probe. participated in the mission plan. ESA will take charge of However, data amount from Galileo spacecraft was very JGO (Jupiter Ganymede Orbiter) and NASA will be limited due to the malfunction of high-gain antenna. We responsible for JEO (Jupiter Europa Orbiter). However, due now have more information on the Saturnian System (being to the increase in the resource and mass of JGO, JAXA is provided by Cassini) than that on the Jupiter system. JUNO requested to launch JMO by a vehicle of its own. Then, we by NASA was launched in 2011 and will start observation of seek a possibility to combine JMO with a proposed solar Jupiter in 2016. Since the main target of JUNO is structure power sail mission of JAXA for Jupiter and one of Trojan and composition of Jupiter and JUNO takes polar orbits, asteroids. information of Jovian satellites would not increase. JUNO JAXA already started a study of a solar sail for deep space has a magnetometer and some plasma instruments but explorations in early 2000s. The ISAS (Institute of Space and preferable multi-satellite observation cannot be fulfilled. Astronautical Science) of JAXA once evaluated a mission EJSM (Europa Jupiter System Mission) is a planned Jovian proposal for a new engineering verification spacecraft, which system mission with three spacecraft aiming at coordinated is called the solar power sail, a hybrid propulsion system of observations of the Jovian satellites especially Europa and the solar sail and ion engines. It would demonstrate 1) magnetosphere, atmosphere and interior of Jupiter . In order technologies necessary to explore the outer planet region in Copyright© 2012 by the Japan Society for Aeronautical and Space Sciences and ISTS. All rights reserved. Tk_37 Trans. JSASS Aerospace Tech. Japan Vol. 10, No. ists28 (2012) the solar system. Together with a solar sail (photon to Jupiter’s rotation by the auroral current system, generation propulsion), it should have very efficient ion engines where of Jupiter’s intense radiation belts4). electric power is produced by very thin solar panels within the The Jovian magnetosphere is the most intense particle sail. JAXA has already experienced ion engine in the accelerator in the planetary system. Sulfur ions that came successful HAYABUSA mission 4). out of Io at the energy of less than 1 eV are somehow An engineering mission IKAROS (Interplanetary Kite-craft energized up to > 10 MeV within the magnetosphere. It is Accelerated by Radiation Of the Sun) 5) was launched in 2010 obvious that turbulence driven by the fast rotation of the together with Venus Climate Orbiter AKATSUKI 6). planet and magnetic reconnection in the magnetodisk are IKAROS was operated successfully where the folded sail playing crucial roles. (20m x 20m) was developed from the spin-stabilized satellite, Ganymede has an intrinsic magnetic field and occupies a and then it succeeded in utilizing the solar radiation pressure small magnetosphere in the huge Jovian magnetosphere7). for the navigation and in the tests of thin-film solar power Interaction of Jovian particles and Ganymedean panels. magnetosphere is another intriguing target of plasma science. From the experience of IKAROS, we consider that a It is desirable that JMO shall monitor the Jovian mission with a large (100m-scale) solar power sail can transfer magnetosphere while JGO is observing Ganymedean large payload mass to Jovian system. The original plan will environment. During the initial stage of orbital maneuver, take about 4-6 years to go to Jupiter, and the extend mission JMO by itself will flyby with Ganymede and observe its will reach to the Jovian L4 Trojan asteroids after using environment. As for JEO, JMO can monitor the Jovian gravitational swing-by with Jupiter 3). At present we are magnetosphere while JEO is observing Europa. However, studying a mission to Jupiter and one (or two) of Trojan because of strong radiation environment around Europa’s asteroids, which are primitive bodies with information of the orbits, JMO approach to Europa would be limited. early solar system as well as raw solid materials of Jovian system. JMO will be released and inserted to the orbit around Jupiter using a chemical thruster, before the main 3. Orbits and Instruments of JMO spacecraft flies by Jupiter to direct Trojan asteroid using gravity assist. Apoapsis of JMO around Jupiter will be During the initial periods of Jupiter observation phase of decreased by chemical thrusters and gravity assists by EJSM, the Jovian magnetosphere is investigated by the three satellites. The main spacecraft will cruise for about 5 years spacecraft. JMO will take the largest periapsis (> 100RJ: RJ to one of Trojan asteroids. being the radius of Jupiter). If possible, we set the periapsis as small as Io’s orbit (5.9RJ) to observe the role of particles from Io on the magnetosphere. After JEO and JGO enter 2. Jovian Magnetosphere orbits around Europa and Ganymede, respectively, JMO will take equatorial orbits with periapsis at Europa or The Jovian magnetosphere is driven by the fast rotation of Ganymede’s orbit and apoapsis around 100RJ. JMO will Jupiter and populated by ions coming mainly from its determine the outer boundary condition of when JEO and satellites, especially Io. Io has a lot of active volcanoes that JGO observe the satellite-magnetosphere interaction. In the supply SO2 particles and ions are distributed to form a torus final stage where JEO and JGO would have stopped along Io’s orbit. The jovian magnetosphere is the entrance to operation, using satellite flybys, we can increase the orbital the astro-plasma world. Explosive phenomena require inclination of JMO to observe off-equatorial characteristic of ideal-MHD to break down. How this can be done in an magnetosphere and polar regions of Jupiter. Numerical astro-plasma situation where the basic scale length is much simulations by Stefano Campagnola show that using multiple larger than the non-MHD characteristic scales (ion and gravity assists by Callisto the inclination of JMO can be electron scales) is not clear at all. This question cannot be enhanced up to 35deg in a half year and 55deg in two years8). answered without in-situ observation around the magnetically High inclination enables JMO to observe polar region of energetic planet Jupiter. Jupiber and off-equatorial (large volume in space) region of Important astrophysical plasma processes that can be Jovian magnetosphere. investigated in Jovian magnetosphere