吉川 真

The HAYABUSA asteroid explorer successfully released its sample capsule to Australia on 2010 June 13. Since the Earth reentry phase of sample return was critical, many backup plans for predicting the landing location were prepared. This paper considers the reentry dispersion using ground-based optical observation as a backup observation for radiometric observation. Several scenarios were calculated and compared for the reentry phase of HAYABUSA to evaluate the navigation accuracy of the ground-based observation. The optical observation doesn't require any active reaction from a spacecraft, and thus these results show that optical observations could be a steady backup strategy even if a spacecraft had some trouble. We also evaluated the landing dispersion of HAYABUSA only with optical observation.

We present lightcurve observations and multiband photometry for 107P/Wilson-Harrington using five small- and medium-sized telescopes. The lightcurve has shown a periodicity of 0.2979 day (7.15 h) and 0.0993 day (2.38 h), which has a commensurability of 3:1. The physical properties of the lightcurve indicate two models: (1) 107P/Wilson-Harrington is a tumbling object with a sidereal rotation period of 0.2979 day and a precession period of 0.0993 day. The shape has a long axis mode (LAM) of L-1:L-2:L-3 = 1.0:1.0:1.6. The direction of the total rotational angular momentum is around lambda = 310 degrees, beta = -10 degrees, or lambda = 132 degrees, beta = -17 degrees. The nutation angle is approximately constant at 65 degrees. (2) 107P/Wilson-Harrington is not a tumbler. The sidereal rotation period is 0.2979 day. The shape is nearly spherical but slightly hexagonal with a short axis mode (SAM) of L-1:L-2:L-3 = 1.5:1.5:1.0. The pole orientation is around lambda = 330 degrees, beta = -27 degrees. In addition, the model includes the possibility of binary hosting. For both models, the sense of rotation is retrograde. Furthermore, multiband photometry indicates that the taxonomy class of 107P/Wilson-Harrington is C-type. No clear rotational color variations are confirmed on the surface. (C) 2011 Elsevier Inc. All rights reserved.

The Hayabusa spacecraft successfully recovered dust particles from the surface of near-Earth asteroid 25143 Itokawa. Synchrotron-radiation x-ray diffraction and transmission and scanning electron microscope analyses indicate that the mineralogy and mineral chemistry of the Itokawa dust particles are identical to those of thermally metamorphosed LL chondrites, consistent with spectroscopic observations made from Earth and by the Hayabusa spacecraft. Our results directly demonstrate that ordinary chondrites, the most abundant meteorites found on Earth, come from S-type asteroids. Mineral chemistry indicates that the majority of regolith surface particles suffered long-term thermal annealing and subsequent impact shock, suggesting that Itokawa is an asteroid made of reassembled pieces of the interior portions of a once larger asteroid.

Meteorite studies suggest that each solar system object has a unique oxygen isotopic composition. Chondrites, the most primitive of meteorites, have been believed to be derived from asteroids, but oxygen isotopic compositions of asteroids themselves have not been established. We measured, using secondary ion mass spectrometry, oxygen isotopic compositions of rock particles from asteroid 25143 Itokawa returned by the Hayabusa spacecraft. Compositions of the particles are depleted in (16)O relative to terrestrial materials and indicate that Itokawa, an S-type asteroid, is one of the sources of the LL or L group of equilibrated ordinary chondrites. This is a direct oxygen-isotope link between chondrites and their parent asteroid.

Regolith particles on the asteroid Itokawa were recovered by the Hayabusa mission. Their three-dimensional (3D) structure and other properties, revealed by x-ray microtomography, provide information on regolith formation. Modal abundances of minerals, bulk density (3.4 grams per cubic centimeter), and the 3D textures indicate that the particles represent a mixture of equilibrated and less-equilibrated LL chondrite materials. Evidence for melting was not seen on any of the particles. Some particles have rounded edges. Overall, the particles' size and shape are different from those seen in particles from the lunar regolith. These features suggest that meteoroid impacts on the asteroid surface primarily form much of the regolith particle, and that seismic-induced grain motion in the smooth terrain abrades them over time.

Noble gas isotopes were measured in three rocky grains from asteroid Itokawa to elucidate a history of irradiation from cosmic rays and solar wind on its surface. Large amounts of solar helium (He), neon (Ne), and argon (Ar) trapped in various depths in the grains were observed, which can be explained by multiple implantations of solar wind particles into the grains, combined with preferential He loss caused by frictional wear of space-weathered rims on the grains. Short residence time of less than 8 million years was implied for the grains by an estimate on cosmic-ray-produced (21)Ne. Our results suggest that Itokawa is continuously losing its surface materials into space at a rate of tens of centimeters per million years. The lifetime of Itokawa should be much shorter than the age of our solar system.

IKAROS (Interplanetary Kite-craft Accelerated by Radiation Of the Sun) is the world's first spacecraft to successfully demonstrate solar-sail technology in interplanetary space. The spacecraft is made of square shape of very thin membrane, whose diagonal dimension is 20m. By changing its attitude toward Sun, radiation pressure of solar photons can be used as propulsive force of the spacecraft. To determine the orbit under the continuous big influence of the nongravitational perturbative force (i.e. solar radiation pressure), Very Long Baseline Interferometry (VLBI) observation is effective because sky plane position of the spacecraft can be directly and instantaneously measured by VLBI observables without (or with less dependence on) a priori assumption for solar radiation pressure model. In order to effectively perform VLBI measurements, a signal generator of Differential One-way Range (DOR) tones, which consist of multiple tones whose spanning bandwidth is about 28MHz, was developed and installed to the spacecraft. A digital backend system for the ground stations which has maximum output performance of 4-Gbps had also developed to sample wideband DOR tones. A total number of 24 international VLBI experiments were carried out by using totally 15 antennas among 8 agencies during July and August in 2010. As a result of initial analysis, measurement accuracy of VLBI delay was confirmed to be 50 pico second level, which is 20 times improved precision compared to the JAXA's conventional deep space spacecraft such as Hayabusa and Akatsuki. © 2011 IEEE.

The Japanese asteroid explorer HAYABUSA launched in 2003 arrived at its target asteroid ITOKAWA in September, 2005. HAYABUSA has made amount of scientific discoveries and technological achievements during its stay at ITOKAWA and it came back to the Earth on June 13, 2010. Under this situation, the next asteroid exploration mission started. The spacecraft is called HAYABUSA-2. Although its design basically follows HAYABUSA, some new components are planned to be equipped in HAYABUSA-2 mission. A small carry-on impactor is one of the new challenges that were not seen with HAYABUSA. One of the most important scientific objectives of HAYABUSA-2 is to investigate chemical and physical properties of the internal materials and the internal structures in order to understand the formation history of small bodies. In order to achieve this objective, the impactor is required to remove the surface regolith and create an artificial crater on the surface of the asteroid. Ulis paper presents the overview of our small carry-on impactor system and impact operation of HAYABUSA-2 mission. And how to improve this impactor when it is applied to another small body exploration mission is also presented in this paper. Copyright ©2011 by the International Astronautical Federation. All rights reserved.

The Hayabusa spacecraft aiming at technology demonstration for the world's first sample and return from an extra-terrestrial object was launched by the fifth M-V rocket from Uchinoura Space Center, JAXA on May 9, 2003. It went through several troubles and hardships during totally 7 years of interplanetary flight. It successfully returned to the earth and completed the powered- flight by the ion thruster in the beginning of 2010. After successive trajectory correction maneuvers for the reentry, the mother spacecraft, Hayabusa successfully released a small sample-return capsule with asteroid Itokawa sample contained in the sample canister aboard. The capsule entered the earth atmosphere in the desert of Australia on June 13, 2010, and was successfully recovered by June 15. This paper overviews the return operation of the Hayabusa mother spacecraft and reentry flight and recovery operation of the sample return capsule. And the paper also will provide how these TCM and EDL activities were performed and some associated information regarding the Hayabusa mission.

The Hayabusa spacecraft aiming at technology demonstration for the world's first sample and return from an extra-terrestrial object was launched by the fifth M-V rocket from Uchinoura Space Center, JAXA on May 9, 2003. It went through several troubles and hardships during totally 7 years of interplanetary flight. It successfully returned to the earth and completed the powered-flight by the ion thruster in the beginning of 2010. After successive trajectory correction maneuvers for the reentry, the mother spacecraft, Hayabusa successfully released a small sample-return capsule with asteroid Itokawa sample contained in the sample canister aboard. The capsule entered the earth atmosphere in the desert of Australia on June 13, 2010, and was successfully recovered by June 15. This paper overviews the return operation of the Hayabusa mother spacecraft and reentry flight and recovery operation of the sample return capsule. And the paper also will provide how these TCM and EDL activities were performed and some associated information regarding the Hayabusa mission.

Spacecraft escape and capture trajectories from or to Halo orbits about the L1 or L2 points using impulsive maneuvers at periapsis of the manifolds for interplanetary transfers are analyzed in the restricted Hill three-body problem. This application is motivated by future proposals to place deep-space ports at the Earth and Mars L1 or L2 points. First, the feasibility of interplanetary trajectories between Earth Halo orbits and Mars Halo orbits is investigated. In this study, unstable and stable manifolds associated with the Halo orbits are used to approach the vicinity of the planet's surface, and use impulsive maneuvers at periapsis for escape and capture trajectories to and from Halo orbits. Interplanetary trajectories between Earth and Mars Halo orbits with reasonable A V and flight time are found. Next, applying these dynamics to an Earth Mars transportation system using spaceports on Earth and Mars Halo orbits, the system is evaluated in terms of the spacecraft mass of round-trip transfer. As a result, transfer between low Earth orbits and low Mars orbits via the planets' Halo orbits can reduce spacecraft wet mass compared with a direct round-trip transfer, by leaving propellant for the return.

We present the new method of detecting the asteroids quickly and automatically from a large volume of imaging data that are obtained by fully-depleted and undersampled CCD camera, by optimizing for a multi-core PC. The method detects the asteroids as faint as those detected by eyes *in much shorter time than eyes.

'Hayabusa' re-entry capsule was safely carried into the clean room of Sagamihara Planetary Sample Curation Facility in JAXA. After executing CT scanning, removal of heat shield, and surface cleaning of sample container, the sample container was enclosed into the clean chamber. After opening the sample container and residual gas sampling in the clean chamber, optical observation, sample recovery, sample separation for initial analysis is carried out. This curation work is continued with some selected member of Hayabusa Asteroidal Sample Preliminary Examination Team (HASPET) for several months. We report the 'Hayabusa' capsule recovery operation and current status of curation work for 'Hayabusa' sample.

This paper investigates the solar sail modeling and its estimation approach of solar power sail spacecraft IKAROS. Estimation of solar sail force model in space is the key factor for successful solar sail navigation because the solar sail have large uncertainty due to the flexible membrane. Since the sail wrinkles after the deployment and its surface will suffer from degradation, the solar sail force model is difficult to develop before the launch. In this paper, the spinning solar sail model is introduced considering the deformation of the sail. A practical analysis of estimating the solar sail force model from radiometric tracking data is investigated. The solar sail model estimation using the real tracking data is also demonstrated. Copyright ©2010 by the International Astronautical Federation. All rights reserved.

This paper investigates the solar sail modeling and its estimation approach of solar power sail spacecraft IKAROS. Estimation of solar sail force model in space is the key factor for successful solar sail navigation because the solar sail have large uncertainty due to the flexible membrane. Since the sail wrinkles after the deployment and its surface will suffer from degradation, the solar sail force model is difficult to develop before the launch. In this paper, a practical analysis of estimating the solar sail force model from radiometric tracking data is investigated. This is demonstrated by orbit determination including parameter estimation of generalized sail model.

This paper investigates the solar sail modeling and its estimation approach of solar power sail spacecraft IKAROS. Estimation of solar sail force model in space is the key factor for successful solar sail navigation because the solar sail have large uncertainty due to the flexible membrane. Since the sail wrinkles after the deployment and its surface will suffer from degradation, the solar sail force model is difficult to develop before the launch. In this paper, a practical analysis of estimating the solar sail force model from radiometric tracking data is investigated. This is demonstrated by orbit determination including parameter estimation of generalized sail model.

Marco Polo is a mission to return a sample from a near-Earth object of primitive type (class C or D). It is foreseen as a collaborative effort between the Japan Aerospace Exploration Agency (JAXA) and the European Space Agency (ESA). Marco Polo is currently in a Phase-A study (status as of summer 2009). This paper focuses on the scientific requirements provided to the industrial study consortia in Europe as well as the possible mission scenario at the target object in order to achieve the overall mission science objectives. The main scientific reasons for going to a near-Earth object are to...

Apollo-type near-Earth asteroid 3200 Phaethon, having a small perihelion distance of q similar to 0. 14 AU, is classified as F- or B-type, one of subclasses among the C-complex (C-, G-, B-, and F-types) asteroids. The F/B-type asteroids and dehydrated CI and CM carbonaceous chondrites, which are regarded as being linked to each other, underwent a thermal history of high-temperature heatings at more than hundreds of degrees and dehydration for a certain period of time after aqueous alteration in their parent bodies. However, their primary heating mechanism and its timing are less certain and still controversial. We have investigated solar-radiation heating effects on Phaethon at the present planetary-epoch. As a consequence, we have found that the effects on Phaethon, if it is still hydrated, might indeed be a likely candidate for the primary metamorphic heat source. We also found that solar-radiation heating on Phaethon is a function of the latitude, since Phaethon has a highly tilted polar axis. Thus, the northern hemisphere would be selectively more heated than the southern hemisphere. Therefore, we hypothesized that the northern hemisphere, especially the north pole-northern midlatitude region, would be more thermally metamorphosed and dehydrated, if solar-radiation heating is the primary metamorphic heat source of Phaethon. This may provide the latitude-dependent color variations on Phaethon's surface, although this has not been proven by the existing Phaethon's spectral data.

MARCO POLO is a joint European-Japanese sample return mission to a Near-Earth Object. This Euro-Asian mission will go to a primitive Near-Earth Object (NEO), which we anticipate will contain primitive materials without any known meteorite analogue, scientifically characterize it at multiple scales, and bring samples back to Earth for detailed scientific investigation. Small bodies, as primitive leftover building blocks of the Solar System formation process, offer important clues to the chemical mixture from which the planets formed some 4.6 billion years ago. Current exobiological scenarios for the origin of Life invoke an exogenous delivery of organic matter to the early Earth: it has been proposed that primitive bodies could have brought these complex organic molecules capable of triggering the pre-biotic synthesis of biochemical compounds. Moreover, collisions of NEOs with the Earth pose a finite hazard to life. For all these reasons, the exploration of such objects is particularly interesting and urgent. The scientific objectives of MARCO POLO will therefore contribute to a better understanding of the origin and evolution of the Solar System, the Earth, and possibly Life itself. Moreover, MARCO POLO provides important information on the volatile-rich (e.g. water) nature of primitive NEOs, which may be particularly important for future space resource utilization as well as providing critical information for the security of Earth. MARCO POLO is a proposal offering several options, leading to great flexibility in the actual implementation. The baseline mission scenario is based on a launch with a Soyuz-type launcher and consists of a Mother Spacecraft (MSC) carrying a possible Lander named SIFNOS, small hoppers, sampling devices, a re-entry capsule and scientific payloads. The MSC leaves Earth orbit, cruises toward the target with ion engines, rendezvous with the target, conducts a global characterization of the target to select a sampling site, and delivers small hoppers (MINERVA type, JAXA) and SIFNOS. The latter, if added, will perform a soft landing, anchor to the target surface, and make various in situ measurements of surface/subsurface materials near the sampling site. Two surface samples will be collected by the MSC using "touch and go" manoeuvres. Two complementary sample collection devices will be used in this phase: one developed by ESA and another provided by JAXA, mounted on a retractable extension arm. After the completion of the sampling and ascent of the MSC, the arm will be retracted to transfer the sample containers into the MSC. The MSC will then make its journey back to Earth and release the re-entry capsule into the Earth's atmosphere. © Springer Science+Business Media B.V. 2008.

Japanese two lunar and planetary missions, Kaguya (SELENE) and Hayabusa (MUSES-C) are returning vast amount of result to the Earth, and these data are planned to open to the public via the Internet. These are considered useful not only for scientists and engineers but also for the educators and students as a "real textbook". In space education, we can use several methods to facilitate students' interest. Here we describe some of our examples to promote space education. One is the event accompanying with the major conferences, and second is the video program describing the Hayabusa mission with very unique viewpoint, and the third is the website carefully designed for children. However, the application of mission results to the space education has some points which should be specific to these missions. This paper describes our current attempt of these application and future prospects for the promotion of space education.

In this paper, the estimation method of impact probability for Near-Earth Objects (NEOs) is investigated. The impact probability of NEOs has been calculated by a linear target plane analysis and a Monte-Carlo method. Since the collisions of NEOs with the Earth are quite sensitive problems, the calculations have to be confirmed by everal methods. A linear target plane analysis cannot be applied if the position uncertainty is too large since the uncertainty ellipsoid is not a good assumption in this case. A Monte-Carlo method can be used for a large position uncertainty, but the computational cost is high. The limitation of using a linear target plane analysis is investigated using the Monte-Carlo method for the close approach of 99942 Apophis (2004 MN4). The relation between impact probability and observation accuracy is investigated by analyzing the close approach of 2007WD5.

Spacecraft capture trajectories to Lyapunov/Halo periodic orbits of the L1 and L2 points in the restricted Hill three-body problem are analyzed. The specific focus is on transfer to these orbits from interplanetary trajectories. This application is motivated by future proposals to place "deep space ports" at the Earth and Mars L1 or L2 points. We use stable manifolds for capture trajectories to periodic orbits around the libration points. Numerical results show that the stable and unstable manifolds from periodic orbits around the libration points can intersect the surface of any of the planets of the solar system by changing the size of periodic orbits. Applying this to Earth-Mars transfers, the cost of capture,into a periodic orbit is reduced compared with direct capture into a parabolic orbit. Moreover, if a spaceport is built on a periodic orbit in the vicinity of a sun-Mars libration point and propellant can be supplied there to the spacecraft, the required A V for entry into a circular orbit about Mars from an interplanetary trajectory can be considerably reduced compared with a direct entry into a circular orbit.

Recent advances in the characterization of small body surfaces with stereophotoclinometry are & discussed. The principal data output is an ensemble of landmark maps (L-maps), high-resolution topography/albedo maps of varying resolution that tile the surface of the body. Because they can have a resolution comparable to the best images, and can be located on a global reference frame to high accuracy, L-maps provide a significant improvement in discriminatory power for studies of small bodies, ranging from regolith processes to interior structure. These techniques are now being used to map larger bodies such as the Moon and Mercury. L-maps are combined to produce a standard global topography model (GTM) with about 1.57 million vectors and having a wide variety of applications. They can also be combined to produce high-resolution topography maps that describe local areas with much greater detail than the GTM. When combined with nominal predictions from other data sources and available data from other instruments such as LIDAR or RADAR, solutions for the spacecraft position and camera pointing are the most accurate available. Examples are drawn from studies of Phobos, Eros, and Itokawa, including surface characterization, gravity analysis, spacecraft navigation, and incorporation of LIDAR or RADAR data. This work has important implications for potential future missions such as Deep Interior and the level of navigation and science that can be achieved. © The Meteoritical Society, 2008.

We explored the substantial spatial spread of the Quadrantid stream, based on the backward integration of orbital motions of the Quadrantids, impulsively perturbed by Jupiter. We found that the Jovian impulses can widely spread out them in the early twentieth century, especially their perihelia extended by a factor of ∼90 than those at the observed epoch. We regarded the spread as the intrinsic one of the Quadrantid stream itself. © Springer Science+Business Media B.V. 2007.

In September 2005, the Hayabusa (MUSES-C) spacecraft successfully accomplished a rendezvous with asteroid 25143 ltokawa. After arrival, Hayabusa performed detailed observations of the asteroid during its rendezvous phase of about three months duration. As the results of various scientific analyses, a variety of physical parameters of ltokawa (e.g. size, volume, mass, and density) were established. As to the orbit determination of Hayabusa during the cruise phase, the radiometric (i.e., 2-way X-band range and Doppler) measurements were used. On the other hand, during the approach phase or rendezvous phase, optical data from the star tracker and the optical navigation camera were available, so both the radiometric and the optical data were used for orbit determination. The present paper reports on the results of the orbit determination of Hayabusa during the close proximity phase. We also present the mass estimation of ltokawa performed in this period. This analysis uses 2-way the radiometric X-band Doppler data and the Hayabusa relative position data, which are calculated from the optical navigation camera observations. In addition to the large orbital maneuvers and the gravitational acceleration of ltokawa, the forces due to solar radiation pressure, and the effects of attitude control pulses are taken into account in the calculation. As to the gravity model of ltokawa, a spherical-harmonics gravity model and a polyhedron gravity model are used depending on the proximity to the asteroid.

We investigate spacecraft capture trajectories to the periodic orbits of the L1 and L2 points in the planar restricted Hill three-body problem are studied. The specific focus is on transfer to these vicinities from interplanetary trajectories. This application is motivated by future plan to use the Sun-Earth and Sun-Mars collinear libration points as space hub for Mars Mission. We utilize stable manifolds for capture trajectories to periodic orbits around the libration points. As a result, the cost of capture into a periodic orbit is also reduced relative to direct capture into a parabolic orbit. The way of linking between interplanetary transfer trajectories and the stable manifold is also discussed.

Spacecraft capture trajectories to Lyapunov/Halo of the L1 and L2 points in the restricted Hill three-body problem are analyzed. The specific focus is on transfer to these vicinities from interplanetary trajectories. This application is motivated by future proposals to place "deep space ports" at the Earth and Mars L1 or L2 points. We utilize stable manifolds for capture trajectories to periodic orbits around the libration points. Applying to Earth-Mars transfer, the way of linking interplanetary transfer trajectories and the stable manifold is discussed. As a result, the cost of capture into a periodic orbit is reduced compared with direct capture into a parabolic orbit. Moreover, if a spaceport is built on a periodic orbit in the vicinity of a Sun-Mars libration point and Propellant can be supplied there to the spacecraft, the required ?V for entry into a circular orbit about Mars from an interplanetary trajectory can be considerably reduced compared with a direct entry into a circular orbit.

Spacecraft space transportation systems using spaceports in the vicinity of libratoin points in the restricted Hill three-body problem are analyzed. This application is motivated by future proposals to place "deep space ports" at the Earth and Mars L1/L2 points. We utilize unstable and stable manifolds for escape and capture trajectories to/from periodic orbits around the libration points. Applying to Earth-Mars transfer, the way of linking interplanetary transfer trajectories with the unstable/stable manifold is discussed. As a result, if spaceports are built on each periodic orbit in the vicinity of Sun-Earth and Sun-Mars libration points so that payloads are transferred there from space vehicle exclusively used at Earth to interplanetary cargo ship and from interplanetary cargo ship to space vehicle exclusively used and at Mars, the propellant carried with payload from the Earth by the interplanetary vehicle for interplanetary transfer can be considerably reduced compared with a direct transfer case.

Spacecraft capture trajectories to the periodic orbits of the L1 and L2 points in the planar restricted Hill three-body problem are studied. The specific focus is on transfer to these vicinities from interplanetary trajectories. This application is motivated by future plan to use the Sun-Earth and Sun-Mars collinear libration points as space hub for Mars Mission. We utilize stable manifolds for capture trajectories to periodic orbits around the libration points. As a result, the cost of capture into a periodic orbit is reduced relative to direct capture into a parabolic orbit. However, the time of flight for capture trajectories is increased. Therefore, the way of reducing of the time of flight for capture trajectories is discussed based on using stable manifolds © 2008 by the American Institute of Aeronautics and Astronautics, Inc.

A team in JSPEC/JAXA has started a phase-A study and development for the high-speed reentry experiment called DASH-II. In the mission, a small capsule inserted into the geosynchronous orbit or a relevant orbit and conducts reentry flight at the super-orbital velocity after several orbital circulations. The main objective of the mission is to acquire and demonstrate the reentry/entry technologies associated with future planetary exploration missions and high-speed reentry from Moon and from farther small bodies such as Marco-Polo sample return. The present paper describes the DASH-II mission overview and recent development status. Copyright 2008 by the International Astronautical Federation. All rights reserved.

Spacecraft capture trajectories to Lyapunov/Halo of the L1 and L2 points in the restricted Hill three-body problem are analyzed. The specific focus is on transfer to these vicinities from interplanetary trajectories. This application is motivated by future proposals to place "deep space ports" at the Earth and Mars L1 or L2 points. We utilize stable manifolds for capture trajectories to periodic orbits around the libration points. Applying to Earth-Mars transfer, the way of linking interplanetary transfer trajectories and the stable manifold is discussed. As a result, the cost of capture into a periodic orbit is reduced compared with direct capture into a parabolic orbit. Moreover, if a spaceport is built on a periodic orbit in the vicinity of a Sun-Mars libration point and propellant can be supplied there to the spacecraft, the required AV for entry into a circular orbit about Mars from an interplanetary trajectory can be considerably reduced compared with a direct entry into a circular orbit.

We investigate spacecraft capture trajectories to the periodic orbits of the L1 and L2 points in the planar restricted Hill three-body problem are studied. The specific focus is on transfer to these vicinities from interplanetary trajectories. This application is motivated by future plan to use the Sun-Earth and Sun-Mars collinear libration points as space hub for Mars Mission. We utilize stable manifolds for capture trajectories to periodic orbits around the libration points. As a result, the cost of capture into a periodic orbit is also reduced relative to direct capture into a parabolic orbit. The way of linking between interplanetary transfer trajectories and the stable manifold is also discussed.

VSOP-2 is a next generation space-VLBI (SVLBI) mission for millimeter-wave VLBI astronomy. The VSOP-2 mission has a radio telescope satellite, ASTRO-G, as a space segment, which will be launched in JAXA's fiscal year 2012. The ASTRO-G satellite will be orbiting around the Earth with the apogee and perigee altitudes of 25000 and 1000 km, respectively. In VSOP-2, Precise Orbit Determination (POD) with an accuracy of 10 cm for ASTRO-G is required to conduct an advanced observation mode of phase referencing. To achieve the POD for such a highly elliptical orbit, two on-board instruments are proposed to be installed on ASTRO-G: one is a Global Navigation Satellite System (GNSS) receiver mainly used at lower altitudes, and another is a retroreflector array for Satellite Laser Ranging (SLR) at higher altitudes. In this paper, ASTRO-G's POD plan with the above two instruments are reported. POD simulations indicate that the proposed method is promising, while development of the acceleration model to treat non-gravitational perturbation is essential for the ASTRO-G's POD.

The effect of solar radiation on the near-term rotation rate of Asteroid Itokawa via the YORP effect is predicted using the detailed shape model, rotation pole, mass estimate, and optical properties derived from the Hayabusa mission to Itokawa. Based on these estimates Itokawa is decelerating at a rate which will halve its rotation rate in only 50-90 thousand years, a large deceleration that should be detectable in a future appartion. The implications of such a large deceleration for Itokawa's past history are discussed and related to possible seismic shaking. © 2007 Elsevier Inc. All rights reserved.

Spacecraft capture trajectories to the vicinity of the L1 and L2 points in the restricted Hill three-body problem are analyzed. The specific focus is on transfer to these vicinities from interplanetary trajectories. This application is motivated by future proposals to place "Deep Space" ports at the Earth and Mars L1 or L2 points. Numerical results show that the stable and unstable manifolds from periodic orbits around the libration points can intersect the surface of any of the planets of the solar system if the Jacobi value is large enough. Moreover, if a spaceport is built on a periodic orbit in the vicinity of a Sun-Mars libration point and propellant can be supplied there to the spacecraft, the required Delta V for entry into a circular orbit about Mars from an interplanetary trajectory can be considerably reduced compared with a direct entry into a circular orbit. The cost of capture into a periodic orbit is also reduced relative to direct capture into a parabolic orbit.

We present an overview of the laser altimeter(LIDAR) results for asteroid 25143 Itokawa. The trace of a 7 × 12-m elliptical beam spot made it possible to determine the local surface topography with an accuracy of a few meters in altitude, from a home position roughly 7 km above the surface. Sequential detection of the altitude of the spacecraft during two orbital spans of descent for sampling allowed determination of the asteroid mass as 3.58 × 10 kg ± 5% and 3.54 × 10 kg ± 6%, which are consistent with the most probable mass estimate of 3.51 × 10 kg ± 3% given by Fujiwara et al. [Fujiwara, A., Kawaguchi, J., Yeomans, D.K. et al., 2006. The rubble-pile asteroid Itokawa as observed by Hayabusa. Science 312, 1330-1334]. Together with the total volume of the asteroid deduced from a shape model (i.e., 1.84 × 10 m ± 3%), this estimate by LIDAR suggests that asteroid Itokawa has a low density of 1.9 g/cm ± 9% and a high bulk porosity of about 40%. © 2007 COSPAR. 10 10 10 7 3 3

This report describes the evaluation of Δ VLBI delay measurement accuracy for Spacecraft Navigation. At the epochs of Hayabusa's touchdown to asteroid Itokawa, we made Δ VLBI observation for Hayabusa with Japanese domestic VLBI stations. Since the orbit of Itokawa is accurately known, we could use this occasion for evaluation of the delay calibration accuracy by Δ VLBI. By using a calibration technique of modeling the excess delay with group delays of multiple reference sources, calibration accuracy in the order of several hundreds pico seconds are obtained. Further improvements are expected by using dual-band observation for reference sources. As another approach, phase delay data of reference radio sources were applied for calibration with expecting improved precision and temporal resolution, though it did not show significant improvement for calibration in this case. © 2007 SICE.

Spacecraft capture trajectories to the vicinity of the LI and L2 points in the restricted Hill three-body problem are analyzed. The specific focus is on transfer to these vicinities from interplanetary trajectories. This application is motivated by future proposals to place "Deep Space" ports at the Earth and Mars LI or L2 points. Numerical results show that the stable and unstable manifolds from periodic orbits around the libration points can intersect the surface of any of the planets of the solar system if the Jacobi value is large enough. Moreover, if a spaceport is built on a periodic orbit in the vicinity of a Sun-Mars libration point and propellant can be supplied there to the spacecraft, the required ΔV for entry into a circular orbit about Mars from an interplanetary trajectory can be considerably reduced compared with a direct entry into a circular orbit. The cost of capture into a periodic orbit is also reduced relative to direct capture into a parabolic orbit.

This report describes the evaluation of Delta VLBI delay measurement accuracy for Spacecraft Navigation. At the epochs of Hayabusa's touchdown to asteroid Itokawa, we made Delta VLBI observation for Hayabusa with Japanese domestic VLBI stations. Since the orbit of Itokawa is accurately known, we could use this occasion for evaluation of the delay calibration accuracy by A VLBI. By using a calibration technique of modeling the excess delay with group delays of multiple reference sources, calibration accuracy in the order of several hundreds pico seconds are obtained. Further improvements are expected by using dual-band observation for reference sources. As another approach, phase delay data of reference radio sources were applied for calibration with expecting improved precision and temporal resolution, though it did not show significant improvement for calibration in this case.

The spacecraft Hayabusa, which was launched in 2003, arrived at its destination, asteroid (25143) Itokawa in September 2005. The appearance of Itokawa, a small S-type near Earth asteroids, was totally unexpected. The surface is covered with a lot of boulders and there are only a few craters on it. It looks like a contact binary asteroid. The surface composition is quite similar to LL-chondrite. The estimated density is 1.9 0.13 (g/cm ), so the macro-porosity is about 40%. This means that Itokawa is a rubble pile object. In Itokawa, we may see such things that are very close to building blocks of asteroids. In this paper, we review the mission and the first scientific results. © 2007 International Astronomical Union. 3

Results of the Hayabusa mission to image and sample the asteroid Itokawa are summarized. © 2007 International Astronomical Union.

During the interval from September through early December 2005, the Hayabusa spacecraft was in close proximity to near-Earth asteroid 25143 Itokawa, and a variety of data were taken on its shape, mass, and surface topography as well as its mineralogic and elemental abundances. The asteroid's orthogonal axes are 535, 294, and 209 meters, the mass is 3.51 × 10 kilograms, and the estimated bulk density is 1.9 ± 0.13 grams per cubic centimeter. The correspondence between the smooth areas on the surface (Muses Sea and Sagamihara) and the gravitationally low regions suggests mass movement and an effective resurfacing process by impact jolting. Itokawa is considered to be a rubble-pile body because of its low bulk density, high porosity, boulder-rich appearance, and shape. The existence of very large boulders and pillars suggests an early collisional breakup of a preexisting parent asteroid followed by a re-agglomeration into a rubble-pile object. 10

After global observations of asteroid 25143 Itokawa by the Hayabusa spacecraft, we selected the smooth terrain of the Muses Sea for two touchdowns carried out on 19 and 25 November 2005 UTC for the first asteroid sample collection with an impact sampling mechanism. Here, we report initial findings about geological features, surface condition, regolith grain size, compositional variation, and constraints on the physical properties of this site by using both scientific and housekeeping data during the descent sequence of the first touchdown. Close-up images revealed the first touchdown site as a regolith field densely filled with size-sorted, millimeter- to centimeter-sized grains.

The ranging instrument aboard the Hayabusa spacecraft measured the surface topography of asteroid 25143 Itokawa and its mass. A typical rough area is similar in roughness to debris located on the interior wall of a large crater on asteroid 433 Eros, which suggests a surface structure on Itokawa similar to crater ejecta on Eros. The mass of Itokawa was estimated as (3.58 +/- 0.18) x 10(10) kilograms, implying a bulk density of (1.95 +/- 0.14) grams per cubic centimeter for a volume of (1.84 +/- 0.09) x 10(7) cubic meters and a bulk porosity of approximately 40%, which is similar to that of angular sands, when assuming an LL (low iron chondritic) meteorite composition. Combined with surface observations, these data indicate that Itokawa is the first subkilometer-sized small asteroid showing a rubble-pile body rather than a solid monolithic asteroid.

Aims: We have studied numerically the origin and dynamical evolution of the asteroid (25143) Itokawa on which a Japanese space probe landed and may have collected a sample. The return to Earth is planed in 2010. Methods: To estimate the most probable source of Itokawa, we have used the most recent model of the Near-Earth Object population, which allows us to relate the orbital parameters of a NEO to the different identified source regions of the NEO population. Results: The two source regions that are the most likely to transport an object to Itokawa's orbit are the v secular resonance in the main belt and at a lower level of probability the Mars-crosser population. This result is consistent with the spectral characteristics of Itokowa, identified as S-type, which is the dominant spectral type of objects in these sources. In a previous study, we had found that its most likely fate may be an impact with the Earth on a million year timescale. Here, we show that its evolution is consistent with the typical evolution of asteroids coming from the identified source and which are extracted in the Earth-crossing zone by planetary encounters. Conclusions: We conclude that Itokawa is a typical NEO, which probably arrived at its orbit from the main belt through the v channel. It belongs to the most common spectral-type in the inner Solar System. Therefore, unless this asteroid had a peculiar collisional history, the data obtained by the satellite Hayabusa will clarify some properties representative of the S-type NEO population. © ESO 2006. 6 6

Hayabusa was moving near Asteroid Itokawa for about three months in 2005. Using tracking and navigation data such as range, Boppler, distance from the asteroid, and optical images taken by navigation cameras, we estimated the mass of Itokawa for several orbital phases. The results are consistent in their error ranges. The estimated mass of Itokawa is 3.51 ± 0.105 (10 kg), from which the density of Itokawa is derived as 1.9 ± 0.13 (g/cm ). This is one of the important characteristics to understand the nature of Itokawa. We are also trying to investigate the accuracy of the ephemeris of this asteroid. Copyright © 2006 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. 10 3

The dynamical environment about and on Asteroid 25143 Itokawa is studied using the shape and rotation state model estimated during the close proximity phase of the Hayabusa mission to that asteroid. We first discuss the general gravitational properties of the shape model assuming a constant density. Next we discuss the actual dynamical environment about this body, both on the surface and in orbit, and consider the orbital dynamics of a Hayabusa-like spacecraft. Then we detail one of the approaches used to estimate the mass of the body, using optical and lidar imaging, during the close proximity phase.