DESTINY+ MISSION: FLYBY OF GEMINIDS PARENT ASTEROID (3200) PHAETHON AND IN-SITU
ANALYSES OF DUST ACCRETING ON THE EARTH . T. Arai1, M. Kobayashi1, K. Ishibashi1, F. Yoshida1, H.
Kimura1, K. Wada1, H. Senshu1, M. Yamada1, O. Okudaira1, T. Okamoto1, S. Kameda2, R. Srama3, H. Krüger4, M.
Ishiguro5, H. Yabuta6, T. Nakamura7, J. Watanabe8, T. Ito8, K. Ohtsuka8, S. Tachibana9, T. Mikouchi9, M. Komatsu10,K. Nakamura-Messenger11, S. Sasaki12, T. Hiroi13, S. Abe14, S. Urakawa15, N. Hirata16, H. Demura16, G. Komatsu1, 17,T. Noguchi18, T. Sekiguchi19, T. Inamori20, H. Yano21, M. Yoshikawa21, T. Ohtsubo21, T. Okada21, T. Iwata21, K.
Nishiyama21, H. Toyota21, Y. Kawakatsu21 and T. Takashima21, 1Planetary Exploration Research Center, Chiba Institute of Technology, Chiba 275-0016, Japan (tomoko.arai@it-chiba.ac.jp), 2Rikkyo University, Japan, 3Institut fürRaumfahrtsysteme, Stuttgart University. 4Max Planck Institute for Solar System Research, 5Seoul National University, South Korea, 6Hiroshima University, Japan, 7Tohoku University, Japan, 8National Astronomical Observatory ofJapan, 9The University of Tokyo, Japan, 10The Graduate University for Advanced Studies, Japan, 11NASA Johnson
Space Center, TX, U.S.A, 12Osaka University, Japan, 13Brown University, RI, U.S.A, 14Nihon University, Japan,15Japan Spaceguard Association, Japan, 16Aizu University, Japan, 17Università d'Annunzio, Italy, 18Kyushu University, Japan, 19Hokkaido University of Education, Japan, 20Nagoya University, Japan, 21ISAS, JAXA, Japan.
Introduction: About 40,000 metric tons per yearof extraterrestrial dust accrete onto the Earth [1]. Whilecarbonaceous meteorites are rare (less than 5%) amongmeteorite collection, interplanetary dust particles(IDPs) generally include carbon and organic materials
and their carbon contents are 5-10 times richer thanthose for carbonaceous meteorites. Dust particles arelikely major carriers of carbon and organic matters to
the Earth and potentially be precursors to the terrestrial
life. Extraterrestrial dust particles are derived either
from cosmic dust background or from meteor showers.
The former consists mostly of IDPs which originate
from miscellaneous comets and asteroids, with minor
interstellar dusts (Fig. 1). The latter are meteoroids
transported via dust trails or streams, where dust ejected from specific comets and asteroids, whose orbits
cross that of the Earth (Fig. 1).
Asteroid (3200) Phaethon is a parent body of Geminid meteor shower [e.g. 2], which is amongst the mostactive meteor showers. While parent bodies of meteor
showers are mostly comets, Phaethon is an Apollo typeasteroid with carbonaceous, B-type reflectance spectra[e.g. 3]. Recurrent dust ejection at its perihelion (0.14au) are reported [4-6], while no coma was observed
around 1.5 au [7]. The dust ejection mechanism of theactive asteroid remains unknown. Na depletion is reported for Geminid meteor shower [8] and higher dust
density (2.9g/cm3) is estimated [9], both of which hints
volatile depletion possibly by solar heating. Phaethon
is of great interest and significance because it is a carbonaceous asteroid providing dust to the Earth via dust
stream, has a break-up body, 2005 UD [10], is possiblya breakup from main-belt asteroid 2 Pallas [11], experiences extensive solar heating at a small perihelion
distance, and among the largest potentially hazardousbody. Due to its scientific importance, Phaethon was apotential target for previous missions, such as Deep
Impact and OSIRIS-REx. However, neither sample
return, nor impact experiment nor rendezvous are diffi-

cult for Phaethon with a large relative velocity due tothe large eccentricity and inclination. Only viable approach for Phaethon is flyby.
Mission overview: DESTINY+ (Demonstrationand Experiment of Space Technology for INterplanetary voYage, Phaethon fLyby and dUst Science) is a
mission proposed for JAXA/ISAS Epsilon class small
program, currently in the pre-project phase (Phase-A)
with a launch targeted for 2022.
DESTINY+ is a joint mission of technology
demonstration and scientific observation. It will
demonstrate high performance electric propelled vehicle technology and high-speed flyby exploration ofasteroid (3200) Phaethon. DESTINY+ aims to realize
high-resolution imaging during close proximity flyby,
high-accuracy navigation and wide-range observation,and these implemented for multiple small bodies (multi-flyby). Engineering challenges include proximity flyby navigation with adequate risk of collision, radiooptical hybrid navigation guidance and control, andautonomous imaging based on optical information fortarget tracking. System design of DESTINY+ is summarized in Table 1.

Fig. 1. Schematic diagram of delivery routes ofdust accreting onto the Earth.

Table. 1. System design of DESTINY+ spacecraft.

Science goal of DESTINY+ is to understand the natureand origin of cosmic dust brought to the Earth, in thecontext of exogenous contribution of carbon and organics to the origin of terrestrial life. The science mission objectives are to measure physical properties (velocity, orbit, mass) and chemical composition of interplanetary and interstellar dust particles around 1 auduring deep space cruising phase, and to conduct geological observation of Phaethon to understand dust
ejection mechanism of active asteroid and surface
compositional variation, and analyze dust particles
from Phaethon during high-speed flyby (33 km/sec).
Mission profile: DESTINY+ spacecraft is injected into an elliptical orbit around the Earth by an Epsilon launch vehicle and then the electric propulsion isused to raise the orbit to reach the moon. Subsequently,
it escapes from the Earth’s gravity sphere through multiple lunar gravity assists, and heads for Phaethon aftercruising by electric propulsion in deep space, and finally conducts flyby observation. A flyby point is arounddescending node of Phaethon with a geocentric distance of 1.72 au and a heliocentric distance of 0.87 au.
After Phaethon fly-by, DESTINY+ may head for another target asteroid such as 2005 UD, a breakup bodyof Phaethon, as an extended mission. The summary of
mission profile is shown in Table 2.
Table. 2. Mission profile of DESTINY+ .

Science payloads: DESTINY+ has three science
payloads, panchromatic telescopic camera (TCAP),
VIS-NIR multiband camera (MCAP) and dust analyser(DDA) for science observation. The three payloads in relation to science requirements areshown in Fig. 2. Dust
analyzer is developedwith a heritage of Cosmic
Dust Analyzer (CDA)
onboard Cassini and provided by a team led by
Stuttgart University [12].
TCAP and MCAP aredeveloped by a team led by Planetary Exploration Research Center, Chiba Institute of Technology. TCAP isequipped with a tracking mirror. The observation profile during flyby and the current design of the cameras
are presented by Ishibashi et al. [13].
Phaethon observation campaign: Phaethon approached the Earth as close as 10,000,000 km in December 2017. Variable observation of Phaethon, suchas photometric, spectroscopic, polarimetric and radarobservation were successfully conducted over theworld [e.g.14, 15]. These observation data are crucial
to better characterize Phaethon for further mission planand detailed payload design for DESTINY+.
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Fig. 2. Science requirements and payloads for DESTINY+ .