orbit determination of hayabusa spacecraft during close proximity phase

Paper number

IAC-08.C1.3.2

Author

Dr. Hitoshi Ikeda, Japan Aerospace Exploration Agency (JAXA), Japan

Coauthor

Prof. Jozef C. van der Ha, Kyushu University, Japan

Coauthor

Mr. Masatoshi Matsuoka, NEC Aerospace Systems, Ltd., Japan

Coauthor

Mr. Takafumi Ohnishi, Fujitsu Limited, Japan

Coauthor

Mr. Takashi Kominato, NEC Aerospace Systems, Ltd., Japan

Year

2008

Abstract

Recently, the interest in small celestial body exploration mission that target to asteroids and comets has increased. It is expected that small bodies are primitive bodies, and provide us significant information on the solar system formation process. Although a number of inherent difficulties must be considered to explore small bodies, theses mission provide us not only scientific knowledge but also important information on collisions of near Earth objects (i.e. spaceguard). 

Hayabusa mission is Japan's first sample return project from a near earth asteroid Itokawa. The Hayabusa spacecraft was launched by M-V rocket on 9 May 2003 from Uchinoura space center in Kagoshima prefecture. After the following subsequent Earth swing-by on 19 May 2004, Hayabusa had a rendezvous with asteroid 25143 Itokawa on 12 September 2005. As the result of various kinds of scientific analyses, a variety of physical parameters of Itokawa (e.g., size, volume, mass, and density) were derived. This mission provided us the first knowledge of the actual ”rubble-pile” structure asteroid. Before the Hayabusa mission, the National Aeronautics and Space Administration (NASA) / Johns Hopkins University Applied Physics Laboratory (JHU/APL) / Jet Propulsion Laboratory (JPL) Near Earth Asteroid Rendezvous (NEAR) mission to the asteroid Eros is the only case to investigate a small celestial body, and obtained the precise shape, mass, and gravity. In the case of NEAR mission, the spacecraft put into several sets of stable elliptic orbits with no orbital maneuvers for relatively long arcs. On the other hand, in the case of Hayabusa mission, the gravity of the asteroid Itokawa is too small to perform the stable orbit around the target body. Therefore, the spacecraft adopted a hovering approach (i.e. spacecraft was never put into orbit around Itokawa) for the scientific observations, and a unique method was used for the gravity estimation, which is different from the case of NEAR mission. 

During the rendezvous phase, there were five opportunities to descend to the surface or near the surface of the asteroid Itokawa. When Hayabusa moves near the asteroid’s surface, the orbit is strongly influenced by the gravity of Itokawa. Therefore, the distribution of Itokawa’s mass should be taken into account in the calculation. In order to consider the effect of the shape of Itokawa, the spherical harmonics gravity model and the polyhedron gravity model are adopted in the calculation. In addition, the effect of the thruster attitude control is another difficult point in evaluating the orbit of Hayabusa. Although, Hayabusa initially used three reaction wheels for attitude control, two of three reaction wheels had broken down by early October, and the bi-propellant chemical thrusters were used for the attitude control from then on. Unfortunately, this attitude control generated small unintended accelerations and affected the orbit of Hayabusa. In order to estimate the acceleration caused by the thruster attitude control, we adopted a simple thrust imbalance model. Through the evaluation of the actual data set, we confirmed that the acceleration model helped to perform the orbit determination of the Hayabusa spacecraft under thruster attitude control over a relatively long arc. The radiometric (2-way X-band Range and Doppler) data and optical (from optical navigation camera) data are used for the orbit determination of the Hayabusa spacecraft. In this paper, we will describe the results of orbit determination of the Hayabusa spacecraft under small accelerations (e.g., gravity of Itokawa, the effect of solar radiation pressure, the effect of thruster attitude control) during the close proximity phase. We will also mention about the gravity estimation of the asteroid Itokawa.

Abstract document

IAC-08.C1.3.2.pdf

Manuscript document

IAC-08.C1.3.2.pdf (🔒 authorized access only).

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