吉川 真

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.

On 12 September 2005, Hayabusa (MUSES-C) spacecraft arrived at near-Earth asteroid (25143) Itokawa, and made various kinds of observations while hovering around the asteroid. At first Hayabusa hovered around "Gate position" at an altitude of about 20 km from the Itokawa's surface. After the initial observation of the asteroid, Hayabusa descended from Gate position to "Home Position" at an altitude of about 7 km from the Itokawa's surface. Since then Hayabusa made detailed observations of Itokawa and attempted to touch down on its surface. In this paper we mention about the motion of Hayabusa around Itokawa, especially in terms of the solar radiation pressure and the gravity of Itokawa. In order to evaluate these values, we have used radiometric and optical hybrid orbit determination method. As the results of analysis, we have estimated the solar radiation pressure with the error of 2% and the Itokawa's mass with the error of 4%.

The Japanese spacecraft Hayabusa is planed to reach the Asteroid Itokawa in September 2005, and to bring back some samples of its surface to Earth in 2007. We have studied the future possible evolution of this asteroid by integrating numerically over 100 Myr a set of 39 initially indistinguishable orbits (clones), obtained either by small variations of the nominal initial conditions, or by using different computers (introducing different round-off errors). The results indicate that an Earth impact of this 500-m-size asteroid is likely within a million years, which is only a factor of four larger than the average impact frequency of asteroids of this size. The mission Hayabusa may thus sample a good candidate for being among the next 500-m-size Earth impactors. © 2005 Elsevier Inc. All rights reserved.

The Bisei spaceguard Center started its space debris observations from February, 2000. At the beginning, we used two telescopes with apertures of 25cm and 50cn to find those detectability of different artificial and natural objects. The 50cm telescope showed its ability to detect even LEO objects additionally to GEO objects. From January, 2002, the 1m telescope started its operation. Although each telescope had to stop its operation time to time, because of initial problems of the telescope itself and large format CCD camera. Here, we will show some numbers of error evaluation during the last 2 years. The Japan Spaceguard Association has the main target to detect near-earth asteroids in order to detect them and to present a timely precaution of possible asteroid collision to the earth. To make this work efficient, the whole sky should be surveyed as quickly as possible, and therefore telescopes with wider field were built at the Bisei Spaceguard Center. Detail descriptions are given in different papers (Isobe et al, 2000) Three telescopes with apertures of 25cm, 50cm, and 1m have circular fields with diameters of 1.5, 2, and 3 degrees. These field sizes are also good for a survey work of space debris. At the BSGC, such works were started in 2000 under a collaboration between the JSGA and JAXA. Since our experiences of satellite and space debris observations in an optical wavelength range, we started to observe objects with well-determined orbital elements. During these test observing run, we detected some interesting objects (Isobe et al, 2001). Since our telescope fields are large, we could track some objects detected under a survey mode, where we fixed telescope position during 10 minutes. This long tracking observations can produce the first order orbital elements of the detected objects, which make those identification carried our several nights later possible (Figure 1, Bisei Team, 2004). Figures 2 and 3 are magnitude of each objects observed by 50cm and 1m telescopes, respectively. We can not see much limiting magnitude difference of both telescopes. This result is probably caused by a difference of stellar image sizes. Usually, we make 5 exposures at one telescope position with an exposure time of 6 seconds under an interval around 2 minutes, during which most of the geosynchronous orbit objects move about several ten seconds of arc and can be used single orbital elements. Using them, we evaluate standard deviations of right ascension, O-C (dAcosD) where A and D are right ascension and declination, respectively, for each set of 5 exposures (Figure 4). Figure 5 shows same as those for declination, O-C (dD). The standard deviations of both right ascension and declination were as large as 6 seconds of arc during time to the beginning of June, 2004. Since the telescopes were built to observe near-earth asteroid, it is not necessary to have a high accuracy of time and each observed time had been obtained in an accuracy of 1 second of time, which caused high value of the standard deviations. We changed our clock system with an accuracy down to 0.1 second of time on June 4, 2004, and then those standard deviation went down to an order of 1 second of arc. Considering our current stellar image size, these values are under a proper level, since those for asteroids are around 0.3 second of arc. If we could improve those stellar image sizes and also have clock accuracy of 0.1 second of time, much improvement of the standard deviation can be expected. After finding these results, we started to make a systematic survey work to detect unknown space debris, additionally to regular observations of some specific satellites.

Japanese first Mars explorer NOZOMI, which was launched in July 1998, suffered several problems during the operation period of more than five years. It could have reached near Mars at the end of 2003, but it was not put into the orbit around Mars. Although NOZOMI was not able to execute its main mission, it provided us a lot of good experiences from the point of the orbit determination of spacecraft. One of the most difficult works was the orbit determination for the period without the telemetry. In this period, for the most of the time the high gain antenna did not point to the earth because of a constraint of the attitude. Therefore, the quality of the tracking data was not good, and for some period it was impossible to get the tracking data at all. Under such critical condition, we managed to get the solution of the orbit, and in a near-miraculous way, we were able to control NOZOMI and execute two earth swingbys successfully. Other issues related to the orbit determination are the spin modulation, the solar radiation pressure, the small force related to the attitude change, and the solar conjunction. We tried to solve these issues by the conventional way using range and Doppler data. However, we also tried the new method, that is the orbit determination by using the Delta-VLBI method (VLBI: Very Long Baseline Interferometry). In addition to this, we tried optical observations of NOZOMI at the earth swingbys. © 2005 Elsevier Ltd. All rights reserved.

HAYABUSA, which was launched in May 2003, is the first asteroid sample return mission in the world. It has arrived at its destination, Asteroid (25143) Itokawa, at the beginning of September 2005 successfully. HAYABUSA has an ion engine system (IBS) as the main thrusting system and it makes difficult to carry out the orbit determination because of the continuous low acceleration. We have tried many attempts to estimate the acceleration by IES. However, the accuracy of the orbit determination is not good enough when IBS is working, so we make ballistic period of at least three passes once in three weeks or so. We carry out accurate orbit determination at the ballistic period, and we propagate the orbit by using the telemetry information of IBS with some correction by estimating the acceleration by IBS. By this way we have carried out the orbital operation of HAYABUSA. We summarize here the status of the estimation of IBS acceleration. There are several important phases for the orbit operation, such as the launch, the earth swingby, the solar conjunction, and the asteroid arrival. The earth swingby was done on 19 May 2004, and it was successful. We were able to put the spacecraft into the orbit that approach to Asteroid Itokawa. In July of 2005, the solar conjunction occurred and HAYABUSA was opposite side of the Sun. We were able to go through the solar conjunction without any problem, and after that we carried out the optical navigation by using the optical camera on board. In this paper, we also summarize the results of our orbit determination at the launch, the earth swingby, and the solar conjunction. The first result of the optical navigation is mentioned briefly.

We carried out a series of VLBI observations of Nozomi by using a dedicated narrow bandwidth VLBI system. The three carrier waves with frequency interval of 515 kHz were recorded in 3 channels of the system and correlated by a software method. As a result of the correlation, the residual fringe phases of the main carrier wave are obtained for every 1.3 seconds. We can also continuously track them for 100 minutes. The variation of the residual fringe phase is +/- 150 degrees. Moreover, we can derive succesively the group delay for every 100 seconds by using these three carrier waves. The RMS of the group delays is 13 nsec and its average is well accorded with the delay determined by the range and Doppler measurements within an error of 2 nsec. Consequently, we confirmed the validity of the narrow bandwidth VLBI system, and it could be expected that this system, in addition to range and Doppler measurements, can be applied to three-dimensional tracking of a spacecraft and the precise gravity measurement of the Moon and the planets. Copyright © The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS); The Seismological Society of Japan; The Volcanological Society of Japan; The Geodetic Society of Japan; The Japanese Society for Planetary Sciences.

The wide-field 1 m telescope with ten 2k×4k CCD chips was set up at the Bisei Spaceguard Center in Okayama prefecture, Japan. The Japan Spaceguard Association started to make space debris observations using this telescope in addition to the 50 and 25 cm telescopes. The 1 m telescope has a field of view of 2.5° by 3.0° and has the ability to detect space debris with a size of 30-50 cm in geosynchronous earth orbit. When the telescope's potential performance is reached, it will be one of the best telescopes to make space debris survey work. © 2004 COSPAR. Published by Elsevier Ltd. All rights reserved.

The infrared astronomical satellite ASTRO-F, which has a 67 cm cooled telescope, will be launched in early 2004 and it will carry out all sky survey observation. The obtained data will be used to study various fields of astronomy, such as formation and evolution of galaxies, star formation, interstellar matter, brown dwarf, and dark matter. In addition to these, ASTRO-F also observes objects in the solar system, such as asteroids, comets, and interplanetary dust. In this paper, we investigated the possible observation for Near-Earth Objects (NEOs), especially Near-Earth Asteroids (NEAs), by ASTRO-F. The definition of NEA is the asteroids whose perihelion distance is less than 1.3 AU. At the beginning of 2002, there were about 1750 NEAs. Among these NEAs, about 250 are numbered asteroids and about 1500 are unnumbered ones. At first we studied the number of NEAs that ASTRO-F can observe during the first survey period of six months in 2004. The result is that 140 NEAs (48 numbered and 92 unnumbered asteroids) will be observed if we assume that the limiting magnitude of the observation is 20 in V band. Next we checked infrared observations in the past for these 140 NEAs and found that most of them do not have infrared data. ASTRO-F has a capability to observe at 1.8-5, 5-12, 10-26, and 50-200 μm. Using these data, we can obtain the albedo and the size of these NEAs. We think that these data will be useful not only in the scientific researches but also in the hazard analysis of asteroid collision. © 2003 COSPAR. Published by Elsevier Ltd. All rights reserved.

As one of the potential candidates of the "post-MUSES-C" minor body exploration to be launched around 2010, we have investigated scientific justifications and feasible mission scenarios. Two mission types are focused on among many other proposed mission concepts. One is the multiple rendezvous and sample return mission to asteroids whose spectral type is already known. The other is the multiple fly-bys and sample return mission to an asteroid family. This paper reports the preliminary design results of these two proposed missions. © 2004 COSPAR. Published by Elsevier Ltd. All rights reserved.

A series of VLBI observations for spacecraft NOZOMI was performed in the period between the end of 2002 and July 2003 with aim of supporting the orbit determination. We have made astrometric analysis of the VLBI data for celestial coordinates estimation of the spacecraft with phase delay observables. Phase delay has potential to give 3-4 orders of improvement of delay resolution than group delay measurement, whereas main difficulty in using phase delay is ambiguity problem. We observed the spacecraft NOZOMI continuously for a long time with multiple VLBI stations, and we avoided the problem of phase ambiguity by connecting the phase delay. For correlation processing and analysis of VLBI data, relativistic VLBI delay model for finite distance radio source was developed, and it was used for the analysis. Coordinates of spacecraft in celestial sphere were estimated by least-square parameter fitting technique. © 2004 IEEE.

Japanese first Mars explorer NOZOMI, which was launched in July 1998, suffered several problems during the operation period of more than five years. It could have reached near Mars at the end of 2003, but it was not put into the orbit around Mars. Although NOZOMI was not able to execute its main mission, it provided us a lot of good experiences from the point of the orbit determination of spacecraft. One of the most difficult works was the orbit determination for the period without the telemetry. In this period, for the most of the time the high gain antenna did not point to the earth because of a constraint of the attitude. Therefore the quality of the tracking data was not good, and for some period it was impossible to get the tracking data at all. Under such critical condition, we managed to get the solution of the orbit, and in a near-miraculous way, we were able to control NOZOMI and execute two earth swingbys successfully. Other issues related to the orbit determination are the spin modulation, the solar radiation pressure, the small force related to the attitude change, and the solar conjunction. We tried to solve these issues by the conventional way using range and Doppler data. However, we also tried the new method, that is the orbit determination by using the Delta-VLBI method (VLBI: Very Long Baseline Interferometry). In addition to this, we tried optical observations of NOZOMI at the earth swingbys.

We present photometric observations of the near-Earth asteroid (25143) 1998 SF36 from the 2001 apparition campaign, and we discuss the corresponding physical model. The asteroid's photometric behaviour is consistent with an S-type object, it has a retrograde pole at λ = 355°, β = -84° ± 5°, and its sidereal rotation period is P = 12.132 ± 0.0005 hours. 1998 SF36 is elongated, with rough global dimension ratios a/b = 2.0, b/c = 1.3, but the elongation is not due to a bifurcated shape. The surface is not likely to contain major concavities. No significant albedo variegation was detected.

The Japanese Mars explorer NOZOMI was launched in July 1998. It was planed to arrive at Mars in October 1999. But a problem occurred when it left from the earth to Mars and it will reach Mars at the beginning of 2004. NOZOMI has several issues in its orbit determination, such as the spin modulation, the solar radiation pressure, the small force related to the attitude change, and the solar conjunction. We tried to solve these issues by using range and Doppler data. Recently, however, much more difficult problem has occurred. That is that the range and/or Doppler data cannot be obtained for some periods because we cannot turn the high gain antenna toward the earth due to the attitude constraint. Therefore we considered the orbit determination by using the Delta-VLBI method. In this paper, we summarize the issues of the orbit of NOZOMI up to now and show our recent activities on Delta-VLBI observations for NOZOMI.

Three short-duration "outbursts", in which more than 20-40 meteors appeared in a few seconds, have been reported during a recent Leonid storm. The meteors in these events were extremely localized within a few hundred km, which should be caused by clusters of meteoroids. The existence of such clusters indicates the fragmentation of meteoroids during orbital motion in interplanetary space. Considering the extent of the spatial distribution, the fragmentation should have occurred at around the perihelion passage of the meteoroids just before encountering the Earth. This may cause a possible enhancement of smaller meteoroids, even in old dust trails. A possible example of similar clusters in the past meteor storm of Giacobinids is also noted.

The orbital energies (a ) of released meteoroids (or fragments) from the periodic Comet 96P/Machholz must be slightly different from that of 96P. This results in the differences in their evolutional rates; therefore, the time-lags of the orbital evolutions should apparently occur in the course of time, stably holding the same amplitude in their orbital variations. In the present study, integrating the motion of 96P, we found that the orbital elements of 96P at epoch 2319 correspond to those of both the Arietids and the Marsden comet group, currently observed, and those of 96P at epoch 2408 agree with those of the Kracht comet group, similarly observable now. We also estimated a difference of the perihelion times, ΔT, as: ∼ 320 yr for 96P - Marsden comet group; ∼ 360 yr for 96P - Arietids; and ∼ 410 yr for 96P - Kracht comet group, respectively. These may indicate such time-lags of orbital evolutions between 96P and released meteoroids (or fragments) from 96P. As a consequence, we conclude that 96P, Arietids, the Marsden group, and the Kracht group are further possibly associated with each other now. -1

The Japanese Mars explorer NOZOMI was launched in July 1998. It was planed to arrive at Mars in October 1999. But a problem occurred when it left from the earth to Mars and it will reach Mars at the beginning of 2004. NOZOMI has several issues in its orbit determination, such as the spin modulation, the solar radiation pressure, the small force related to the attitude change, and the solar conjunction. We tried to solve these issues by using range and Doppler data. Recently, however, much more difficult problem has occurred. That is that the range and/or Doppler data cannot be obtained for some periods because we cannot turn the high gain antenna toward the earth due to the attitude constraint. Therefore we considered the orbit determination by using the Delta-VLBI method. In this paper, we summarize the issues of the orbit of NOZOMI up to now and show our recent activities on Delta-VLBI observations for NOZOMI.

The MIR re-entry brought much concern to Japanese government and public, because its final orbit had been announced to pass over Japanese populated area. We have carried out optical observations of the MIR space station from January 15 to March 11, 2001, when the MIR was visible from our observatory site and obtained enough accurate data for each observation night to determine its orbit. However, our observational capability is limited. It is necessary to develop a more accurate system and an idea is proposed. Using our data and NASA's two-line elements we were able to determine the MIR final reentry pass with sufficient accuracy and gave these information to the public through mass-media.

Japan Spaceguard Association (JSGA) carries out observations of asteroids and space debris at Bisei Spaceguard Center (BSGC) in Japan. Since the observations produce a lot of image data, we are considering to use them for education. One of the attempts is that we distribute the image data to school children and let them find asteroids. In order to find asteroids we developed software called "Asteroid Catcher B-612". This software is easy enough for children to handle. We are now distributing this software and image data to anybody who is interested in searching asteroids. We will supply image data by our web site, and then children can access much more recent data and can try to find asteroids. We call this next project "Spaceguard Detective Agency".