吉川 真

The near-Earth carbonaceous asteroid 162173 Ryugu is thought to have been produced from a parent body that contained water ice and organic molecules. The Hayabusa2 spacecraft has obtained global multicolor images of Ryugu. Geomorphological features present include a circum-equatorial ridge, east-west dichotomy, high boulder abundances across the entire surface, and impact craters. Age estimates from the craters indicate a resurfacing age of ≤ 106 years for the top 1-meter layer. Ryugu is among the darkest known bodies in the Solar System. The high abundance and spectral properties of boulders are consistent with moderately dehydrated materials, analogous to thermally metamorphosed meteorites found on Earth. The general uniformity in color across Ryugu's surface supports partial dehydration due to internal heating of the asteroid's parent body.

The Hayabusa2 spacecraft arrived at the near-Earth carbonaceous asteroid 162173 Ryugu in 2018.We present Hayabusa2 observations of Ryugu's shape, mass, and geomorphology. Ryugu has an oblate "spinning top" shape, with a prominent circular equatorial ridge. Its bulk density, 1.19 ± 0.02 grams per cubic centimeter, indicates a high-porosity (>50%) interior. Large surface boulders suggest a rubble-pile structure. Surface slope analysis shows Ryugu's shape may have been produced from having once spun at twice the current rate. Coupled with the observed global material homogeneity, this suggests that Ryugu was reshaped by centrifugally induced deformation during a period of rapid rotation. From these remote-sensing investigations, we identified a suitable sample collection site on the equatorial ridge.

The near-Earth asteroid 162173 Ryugu, the target of the Hayabusa2 sample-return mission, is thought to be a primitive carbonaceous object. We report reflectance spectra of Ryugu's surface acquired with the Near-Infrared Spectrometer (NIRS3) on Hayabusa2, to provide direct measurements of the surface composition and geological context for the returned samples. A weak, narrow absorption feature centered at 2.72 micrometers was detected across the entire observed surface, indicating that hydroxyl (OH)-bearing minerals are ubiquitous there. The intensity of the OH feature and low albedo are similar to thermally and/or shock-metamorphosed carbonaceous chondrite meteorites. There are few variations in the OH-band position, which is consistent with Ryugu being a compositionally homogeneous rubble-pile object generated from impact fragments of an undifferentiated aqueously altered parent body.

One of the primary operations in the Hayabusa2 mission is touchdown on the asteroid Ryugu, which was successfully performed on February 21st, 2019. Because of the abundance of boulders on the asteroid surface, it was challenging to guarantee a safe and secure landing. To identify a promising landing site and design a feasible landing trajectory even under such a situation, this research develops detailed site selection and dispersion analysis strategies. The dispersion of the landing points is computed by a Monte Carlo simulation. Moreover, the distributions of landing conditions, such as a surface contact angle and a clearance distance, are analyzed, validating the feasibility of the touchdown operation. Consequently, a circular area with a radius of 3 m was selected as a safe landing site, leading to the successful landing.

Most of NEOs (near-earth objects) from 10m to several 100m in diameter have not been discovered. These NEOs have more chances to collide with the Earth than lager NEOs and may cause significant localized damages. We have developed a new survey system for such small NEOs at extraordinary low cost in comparison with the current survey systems and discovered 10 NEOs since Jan 2017. Although the existing NEO search programs use 1-2m telescopes and large CCDs, our technology uses many CCD or CMOS frames from small telescopes of about 20cm to find out faint and fast moving NEOs in the frames. The FPGA board is used to implement the sophisticated image processing algorithm and reduce analysis time. We are considering applying the algorithm on the data taken with the spacecraft enabling us to discover NEOs which cannot be detected from ground-based sites. The ground test using the star simulator showed that NEOs of 20.7 magnitude are detectable using a 20cm-optics. 100kg class satellite will be able to accomplish our mission in sun-synchronous orbit of dawn-dusk. Power needed for the satellite is about 100W.

Hayabusa2 arrived at the C-type asteroid Ryugu in June 2018. During one and a half year of the Ryugu-proximity operation, we succeeded in two rovers landing, one lander landing, two spacecraft touchdown/sample collection, one kinetic impact operation and two tiny reflective balls and one rover orbiting. Among the two successful touchdowns, the second one succeeded in collecting subsurface material exposed by the kinetic impact operation. This paper describes the asteroid proximity operation activity of the Hayabuas2 mission, and gives an overview of the achievements done so far. Some important engineering and scientific activities, which have been done in synchronous with the spacecraft operations to tackle with unexpected Ryugu environment, are also described.

Imaging observations of faint meteors were carried out on April 11 and 14, 2016 with a wide-field CMOS mosaic camera, Tomo-e PM, mounted on the 105-cm Schmidt telescope at Kiso Observatory, the University of Tokyo. Tomo-e PM, which is a prototype model of Tomo-e Gozen, can monitor a sky of similar to 1.98deg(2) at 2 Hz. The numbers of detected meteors are 1514 and 706 on April 11 and 14, respectively. The detected meteors are attributed to sporadic meteors. Their absolute magnitudes range from +4 to +10 mag in the V-band, corresponding to about 8.3 x 10(-2) to 3.3 x 10(-4) g in mass. The present magnitude distributions we obtained are well explained by a single power-law luminosity function with a slope parameter r = 3.1 +/- 0.4 and a meteor rate log(10)N(0) = -5.5 +/- 0.5. The results demonstrate a high performance of telescopic observations with a wide-field video camera to constrain the luminosity function of faint meteors. The performance of Tomo-e Gozenis about two times higher than that of Tomo-e PM. A survey with Tomo-e Gozenwill provide a more robust measurement of the luminosity function.

Sample return from the near-Earth asteroid known as 25143 Itokawa was conducted as part of the Hayabusa mission, with a large number of scientific findings being derived from the returned samples. Following the Hayabusa mission, Hayabusa2 was planned, targeting sample return from a primitive asteroid. The primary target body of Hayabusa2 was asteroid 162173 Ryugu; however, it was also necessary to gather physical information for backup target selection. Therefore, we examined five asteroids spectroscopically, 43 asteroids spectrophotometrically, and 41 asteroids through periodic analysis. Hence, the physical properties of 74 near-Earth asteroids were obtained, which helped the Hayabusa2 backup target search, and also furthered understanding of the physical properties of individual asteroids and their origins.

There are hundreds of thousands of known asteroids, yet only 14 have been visited by spacecraft thus far, and 9 of those were targets of opportunity. The remaining five asteroids (Braille, Eros, Itokawa, Vesta, and Ceres) were visited by four missions dedicated to asteroid research (Deep Space 1, NEAR-Shoemaker, Hayabusa, and Dawn, respectively). In fact, of these five asteroids, Vesta and Ceres are perhaps better defined as protoplanets because of their sizes and the emerging evidence for their physical and chemical evolution. Two more near-Earth asteroids will be visited in 2018, followed by even more visits in 2023 and 2030. This asteroid mission chronology is listed in Table 1.1. This chapter will tell the story of these asteroid missions and visit each of them in turn to briefly review some of the exciting science results. The story begins with asteroid 951 Gaspra and continues down the list in Table 1.1, according to the target asteroid name presented in chronological order.

Tomo-e Gozen (Tomo-e) is a wide field optical camera for the Kiso 1.05 m f/3.1 Schmidt telescope operated by the University of Tokyo. Tomo-e is equipped with 84 chips of front-illuminated CMOS image sensors with a microlens array. The field of view is about 20 square degrees and maximum frame rate is 2 fps. The CMOS sensor has 2160x1200 pixels and a size of pixel is 19 microns, which is larger than those of other CMOS sensors. We have evaluated performances of the CMOS sensors installed in Tomo-e. The readout noise is 2.0 e(-) in 2 fps operations when an internal amplifier gain is set to 16. The dark current is 0.5 e(-)/sec/pix at room temperature, 290K, which is lower than a typical sky background flux in Tomo-e observations, 50 e(-)/sec/pix. The efficiency of the camera system peaks at approximately 0.7 in 500 nm.

The Tomo-e Gozen is a wide-field high-speed camera for the Kiso 1.0-m Schmidt telescope, with a field-of-view of 20.7-deg(2) covered by 84 chips of 2k x 1k CMOS image sensors with 19-mu m pixels. It is capable to take consecutive images at 2-fps in full-frame read with an absolute time accuracy of 0.2 millisecond. The sensors are operated without mechanical coolers owing to a low dark current at room temperature. A low read noise of 2-e(-) achieves higher sensitivity than that with a CCD sensor in short exposures. Big data of 30-TBytes per night produced in the 2-fps observations is processed in real-time to quickly detect transient events and issue alerts for follow-ups.

Near-Earth Objects (NEOs) impact hazard has become of great concern among the space communities as our NEO detection capability has been drastically improved over the last decades and numerous NEOs discovered. As of today, our discovery efforts resulted in discovering over 90% of NEOs greater than one kilometer in diameter and none of them has imminent impact threats to the Earth in the foreseeable future. However, the majority of the NEOs with 100-meter diameter or smaller, including potentially hazardous objects, are yet to be discovered. These objects are more frequent impactors and can cause local-scale damage if they impact over a populated area on the Earth although they are statistically more likely to impact over the ocean. In any case, impact hazard warning is important but impossible if we cannot find them. Conventional discovery efforts on the smaller NEOs with telescopes are suffering the following issues. First of all, since these objects are very small, they have to be close enough to the Earth and bright enough to be detected by telescope. Even if they come across the field of view of a telescope at close approaches when their apparent magnitude increases, their images are so faint that they are often buried in noise. This is not only due to their size but also their line-of-sight change rates during the exposure time. Secondly, those who approach from the sun-direction cannot be detected with ground-based telescopes. These issues have driven the planetary defense community to develop new detection techniques and study new survey mission concepts. The Japan Aerospace Exploration Agency is currently studying a new NEO detection mission concept consisting of a cluster of ground-based telescopes and a constellation of space-based telescopes in sun synchronous orbit (SSO). A state-of-art synthetic detection technique based on time delay integration is used to detect the small and fast-moving NEOs. In this work, the mission performance evaluation is conducted in terms the number of NEO discoveries by the mission through one-year observation simulations with the Granvik model-based NEO population, where the number of telescopes and the detectable apparent magnitude limit as a function of line-of-sight change rate are given as design variable. NEO detection capabilities with synthetic and non-synthetic detection approaches are compared. Finally, opportunities for post-detection actions such as followup observations are discussed. The observation simulations resulted in 40 ground-based telescopes could achieve 2,080 detections annually whereas 4 space-based telescopes in SSO could achieve 1,280 detections annually with 20 cm telescopes. The detectability of the NEOs based on the synthetic detection technique could be 3-5 times better than that based on a conventional non-synthetic detection technique. The maximum line-of-sight change rate of the fastest-moving NEO with absolute magnitude 24.1 was 13,865 arcmin/day at the detectable condition. It is also presented that some of the NEOs detected and tracked by the ground part of the proposed mission could be further tracked by follow-up observations of the space part of it, and vice versa.

The Japan Aerospace Exploration Agency (JAXA) is developing a new observation technology for Near Earth Objects (NEOs). The technology employs a very different process compared to existing NEO survey programs such as Pan-Starrs and CSS, and could possibly innovate the current NEO survey concept. It uses many CCD images in which to detect faint and fast moving NEOs. The FPGA (field programmable gate array) board is used to reduce analysis time. We discovered two NEOs using 18-cm telescopes in January 2017. This marked Japan's first discovery of NEOs in about nine years.

The Japan Aerospace Exploration Agency launched an asteroid sample return spacecraft "Hayabusa2" on December 3, 2014 by the Japanese H2A launch vehicle. Hayabusa2 aims at the round trip mission to the asteroid 162173 Ryugu. Hayabusa2 successfully conducted the Earth gravity assist on December 3, 2015, and now the spacecraft is flying toward Ryugu with the microwave discharge ion engine as the means of propulsion. As of September 2016, 1346 h of the ion engine operation has been achieved as planned. Three touch downs/sample collections, one kinetic impact/crater generation, four surface rovers deployment and many other in-situ observations are planned in the asteroid proximity phase. The operation team will perform extensive operation practice/rehearsal using a hardware-in-the-loop simulator in the year 2017 to be ready for the asteroid arrival in the summer 2018.

The Hayabusa2 mission journeys to C-type near-Earth asteroid (162173) Ryugu (1999 JU(3)) to observe and explore the 900 m-sized object, as well as return samples collected from the surface layer. The Haybusa2 spacecraft developed by Japan Aerospace Exploration Agency (JAXA) was successfully launched on December 3, 2014 by an H-IIA launch vehicle and performed an Earth swing-by on December 3, 2015 to set it on a course toward its target Ryugu. Hayabusa2 aims at increasing our knowledge of the early history and transfer processes of the solar system through deciphering memories recorded on Ryugu, especially about the origin of water and organic materials transferred to the Earth's region. Hayabusa2 carries four remote-sensing instruments, a telescopic optical camera with seven colors (ONC-T), a laser altimeter (LIDAR), a near-infrared spectrometer covering the 3-mu m absorption band (NIRS3), and a thermal infrared imager (TIR). It also has three small rovers of MINERVA-II and a small lander MASCOT (Mobile Asteroid Surface Scout) developed by German Aerospace Center (DLR) in cooperation with French space agency CNES. MASCOT has a wide angle imager (MasCam), a 6-band thermal radiator (MARA), a 3-axis magnetometer (MasMag), and a hyperspectral infrared microscope (MicrOmega). Further, Hayabusa2 has a sampling device (SMP), and impact experiment devices which consist of a small carry-on impactor (SCI) and a deployable camera (DCAM3). The interdisciplinary research using the data from these onboard and lander's instruments and the analyses of returned samples are the key to success of the mission.

Context. The JAXA Hayabusa2 mission will perform the first ever sample return from a primitive asteroid. The target near-Earth asteroid (162173) Ryugu will be reached in mid-2018 and its samples will be returned to the Earth by the end of 2020. Aims. We want to improve the current knowledge of the compositional and rotational properties of Ryugu, which are still presenting some uncertainties that might affect the mission operations and scientific return. Methods. We acquired high-quality photometric time-series data with the FORS2 instrument at the Very Large Telescope of the European Southern Observatory (ESO-VLT, Chile). We also acquired four FORS2 visible spectra and three X-shooter spectra in the 0.35-2.15 μm range, at different rotational phases. Results. We obtained the currently highest-quality visual light-curve of Ryugu. A best solution of ∼7.63 h is found for the rotational period, while a short-period solution (i.e., P - 3.8 h) is ruled out by the clearly non-symmetric light-curve. The obtained spectra are generally similar and featureless, but present a drop-off of the reflectance at <0.45 μm, suggesting the presence of aqueously altered minerals on Ryugu. The best meteorite analogs for Ryugu are represented by thermally altered CM carbonaceous chondrites. Conclusions. Our new photometric data help to refine the target reference model used by the Hayabusa2 team for the mission preparation and implementation, improving our knowledge of Ryugu's spin properties. Our new spectra constrain the compositional and geological context of the Ryugu's surface in order to prepare the planning of mission observations and support the working group for the selection of possible landing and sampling sites.

The Japan Aerospace Exploration Agency launched the asteroid sample return spacecraft "Hayabusa2" on December 3, 2014. Hayabusa2 will reach the C-type asteroid 1999 JU3 in 2018, and return back to the Earth in 2020. Sample collections from three sites, four surface rovers deployment and a 4 MJ-class kinetic impact crater generation are planned in the 1.5 years of the asteroid-proximity operation. The mission objective of Hayabusa2 has three aspects, science, engineering and exploration, all of which would be expanded by the successful round-trip journey. This paper describes the outline of the Hayabusa2 mission and the current flight status after the seven month of the interplanetary cruise. (C) 2016 IAA. Published by Elsevier Ltd. All rights reserved.

This paper reports the results of an analysis of the Mars impact probability for the Hayabusa-2 spacecraft to comply with the COSPAR planetary protection requirements. Since Hayabusa-2 is equipped with an ion engine system and its trajectory accommodates the non-ballistic trajectory, effective analysis methods are introduced. The results show that the Mars impact probability is sufficiently low for the Hayabusa-2 mission to fully comply with the COSPAR planetary protection requirements. (C) 2015 COSPAR. Published by Elsevier Ltd. All rights reserved.

Mitigation of hazardous Near Earth Objects (NEOs) has been discussed for the past few decades. The well-known Tunguska event occurred in Russia about 100 years ago, and the Chelyabinsk impact in 2013 reminded mankind that the threats of NEO impacts still exists on Earth. Although such harmful NEO impacts are relatively rare, those impacts have potential to bring severe damage to our society, and for the worst case scenario, destroy our civilization. The first international conference on the NEO hazard mitigation was convened in the United Nations in 1995, and the UN has established two organizations: International Asteroid Warning Network (IAWN) and Space Mission Planning Advisory Group (SMPAG) in 2013. The objective of this study is to propose a space-based NEO detection and impact warning system using an Artificial Equilibrium Point (AEP). In the natural equilibrium points such as Lagrange points, three kinds of forces are balanced i.e., the gravitational forces by the primary and secondary bodies and centrifugal force. The AEP, on the other hand, is literary, "artificial" equilibrium point where the residual acceleration is cancelled by low-thrust. Especially on 1 au circular orbit around the Sun, the AEP can be realized by very small acceleration, which enables to locate the space-telescope at an arbitrary fixed point relative to the Earth. Through some cases of numerical simulation, this paper presents the detectability of the virtual impactors estimated based on the debiased NEO distribution model developed by Bottke et al.

After the successful launch on the world first spacecraft, Sputnik 1 by the former Soviet Union in 1957, 58 years has passed. In 1960, Pioneer 5 of the United States escaped the Earth's gravity at the first time, and since then many interplanetary explorers had set to sail interplanetary. However, even in the present day, interplanetary voyages are not still easy. First, interplanetary missions require large amounts of delta-V, and second, the opportunity to get to the destination opens only every synodic period with the destination celestial body. For example, the synodic period with Mars is about 2 years, which means the opportunity to get to Mars opens every 2 years. For such circumstances, this paper proposes a new type of low-thrust orbit design method, "Interplanetary Parking Method" that realizes "anytime" launch of deep-space explorers. The proposed interplanetary parking method enables to make an Earth return orbit with an arbitrary time-of-flight connecting to the minimum energy transfer orbit to a destination. While the time-of-flight of the transfer orbit is fixed, the Earth return orbit with the arbitrary time-of-flight virtually eliminates the severe launch window constraint in interplanetary missions. As application of the proposed method, the paper demonstrates dual launch trajectory design of explorers to different destinations i.e., Mars and Venus. The proposed method will widen the scope of opportunity for interplanetary missions.

The Japan Aerospace Exploration Agency launched an asteroid sample return spacecraft "Hayabusa2" on December 3, 2014 by the Japanese H2A launch vehicle. Following the successful return back of Hayabusa from the asteroid 25143 Itokawa, Hayabusa2 aims at the round trip mission to the asteroid 162173 Ryugu. Ryugu is a near-Earth C-type asteroid, which is believed to contain organic and hydrated minerals. Thus it is expected that its successful sample return may provide fundamental information regarding the origin and evolution of terrestrial planets as well as the origin of water and organics delivered to the Earth. The spacecraft is equipped with four 10mN-class ion engines that provide a total delta-V of approximately 2km/s, which enables to realize the round-trip journey between the asteroid and the Earth. Some enabling technologies include the sample collection mechanism, optical navigation cameras, reentry capsule, four asteroid surface rovers and the impactor. The impactor is a kinetic impact device to create a 2m-class crater on the surface of the asteroid, enabling us to observe/collect not only the surface but also the sub-surface of the asteroid. Hayabusa2 is heavier than former Hayabusa by 100kg and has increased reliability and drastically more science capability as a sample-return spacecraft. Hayabusa2 will reach Ryugu in the middle of 2018 and perform an asteroid proximity operation for 1.5 years. Three touch downs for sample collection and one crater generation by a high-speed kinetic impact are planned during the asteroid proximity operation. The sample is to be brought back to the Earth by a re-entry capsule in December 2020. Hayabusa2 successfully conducted the Earth gravity assist (EGA) operation on December 3, 2015, passing above Hawaii islands at the altitude of 3090km, and increasing the interplanetary flight velocity by 1.6km/s. After the EGA, the spacecraft is planned to actuate the ion engine in March 2016 for the powered-cruise operation toward Ryugu rendezvous in 2018. This paper shows a brief introduction to the mission objective and spacecraft design, and then describes the first two year operation including launch, Earth gravity assist and ion engine-powered cruise operation. Finally the paper also provides a future operation plan for the asteroid proximity operation.

Hayabusa is the first asteroid sample return mission in the world, and Hayabusa2 is the second one. The purposes of these missions are to study the origin and evolution of the solar system and to develop the technologies that enable round-trip mission to asteroids. In addition to these "official" purposes, we have done many activities to enhance public interests in space. One of the successful activities was an emotional representation of Hayabusa mission. Spacecraft is a machine, so it does not have emotion. However, we described the mission of Hayabusa as if Hayabusa is a human. With a help of jazz music composed by a professional musician, the story of the mission becomes very emotional one. We were able to attract attention from the people who did not have interest in space missions. Thus this was successful to popularize the space activities to the people in Japan. Another example is the observation campaign of Hayabusa2 spacecraft when it approached to the Earth to perform the Earth swing-by. In this case, people who have a certain skill for star observation enjoyed the event by themselves, so this contributed science activities of public people. At the same time, we collaborated with public observatories in Japan to observe Hayabusa2, and people who do not have telescopes also could see Hayabusa spacecraft. These two are most noteworthy examples, and other than these we have done many things, such as the naming campaign of the target asteroid, putting people's names and messages on board, talk live show, and etc. These outreach activities have contributed to make public people have interests toward space and science. As a result, public people did some their own activities voluntarily. In this paper, we summarize what we have done for outreach activities in Hayabusa and Hayabusa2, and what happened as a consequence.

On February 15th, 2013, a meteor with size of about 20m in diameter entered the Earth's atmosphere over Chelyabinsk, Russia, and exploded at an altitude of about 20 km, damaging about 4,500 buildings and injuring about 1,500 residents. This incident widely invoked an interest in hazard mitigation caused by a NEO. Motivated by such interests, this study focuses on a new concept of NEO detection and impact warning system. In this concept, a space telescope is placed at the L1 point of the Sun-Earth system to intensively observe the NEOs in-coming from the noon-side, which ground-based observatories hardly detect because of the sunlight. Throughout some cases of simulations, this paper reveals the distributions of NEO directions at detection, V-infinity vectors at the Earth impact, and the NEO orbit determination precision are evaluated.

After the successful launch on the world first spacecraft, Sputnik 1 by the former Soviet Union in 1957, 58 years has passed. In 1960, Pioneer 5 of the United States escaped the Earth's gravity at the first time, and since then many interplanetary explorers had set to sail interplanetary. However, even in the present day, interplanetary voyages are not still easy. First, interplanetary missions require large amounts of delta-V, and second, the opportunity to get to the destination opens only every synodic period with the destination celestial body. For example, the synodic period with Mars is about 2 years, which means the opportunity to get to Mars opens every 2 years. For such circumstances, this paper proposes a new type of low-thrust orbit design method, "Interplanetary Parking Method" that realizes "anytime" launch of deep-space explorers. The proposed interplanetary parking method enables to make an Earth return orbit with an arbitrary time-of-flight connecting to the minimum energy transfer orbit to a destination. While the time-of-flight of the transfer orbit is fixed, the Earth return orbit with the arbitrary time-of-flight virtually eliminates the severe launch window constraint in interplanetary missions. As application of the proposed method, the paper demonstrates dual launch trajectory design of explorers to different destinations i.e., Mars and Venus. The proposed method will widen the scope of opportunity for interplanetary missions.

The Tomo-e Gozen camera is a next-generation extremely wide-field optical camera, equipped with 84 CMOS sensors. The camera records about a 20 square-degree area at 2 Hz, providing "astronomical movie data". We have developed a prototype of the Tomo-e Gozen camera (hereafter, Tomo-e PM), to evaluate the basic design of the Tomo-e Gozen camera. Tomo-e PM, equipped with 8 CMOS sensors, can capture a 2 square-degree area at up to 2 Hz. Each CMOS sensor has about 2.6 M pixels. The data rate of Tomo-e PM is about 80 MB/s, corresponding to about 280 GB/hour. We have developed an operating system and reduction softwares to handle such a large amount of data. Tomo-e PM was mounted on 1.0-m Schmidt Telescope in Kiso Observatory at the University of Tokyo. Experimental observations were carried out in the winter of 2015 and the spring of 2016. The observations and software implementation were successfully completed. The data reduction is now in execution.

The Tomo-e Gozen is an extremely wide-field optical camera for the Kiso 1.0-m Schmidt telescope. It is capable of taking consecutive frames with a field-of-view of 20 deg(2) and a sub-second time-resolution, which are achieved by 84 chips of 2k x 1k CMOS sensor. This camera adopts unconventional designs including a lightweight structure, a non-vacuumed and naturally-air cooled system, front-side-illuminated CMOS sensors with microlens arrays, a sensor alignment along a spherical focal plane of the telescope, and massive readout electronics. To develop technical components necessary for the Tomo-e Gozen and confirm a feasibility of its basic design, we have developed a prototype-model (PM) of the Tomo-e Gozen prior to the final-model (FM). The Tomo-e PM is equipped with eight chips of the CMOS sensor arranged in a line along the RA direction, covering a sky area of 2.0 deg(2). The maximum frame rate is 2 fps. The total data production rate is 80 MByte sec(-1) at 2 fps, corresponding to approximately 3 TByte night(-1). After laboratory testing, we have successfully obtained consecutive movie data at 2 fps with the Tomo-e PM in the first commissioning run conducted in the end of 2015.

In this study, we propose a flexible orbit design method that enables anytime launch of a deep-space explorer. Based on the Electric Delta-V Earth Gravity Assist (EDV-EGA) scheme, (Kawaguchi, 2001, 2002) [1,2] the proposed interplanetary parking method enables the explorer to make an Earth return orbit at an arbitrary time-of-flight by connecting to the minimum energy transfer orbit to destination. While the time-of-flight of the transfer orbit is fixed, the Earth return orbit with the arbitrary time-of-flight significantly alleviates the severe launch window constraint in interplanetary missions. We offer two case examples of applications of this method. The first is the dual launch of a Mars explorer with a geostationary transfer orbit (GTO) mission payload. The second is a dual launch of Mars and Venus explorers by a single launch vehicle. In the first case, we assume that a small Mars explorer is dual launched into a GTO for a secondary payload. With this assumption, the secondary payload cannot choose a desirable launch epoch for itself because the launch window to Mars is very narrow and opens only every 2 years. Moreover, the GTO, whose orbital period is approximately 10 h, repeatedly passes through the Van Allen belt wherein the radiation level is very high. Hence, the explorer has to escape from the GTO as soon as possible. However, our proposed interplanetary parking method enables the explorer to reach the destination within the limits of a practical mass resource, regardless of the Earth departure epoch. In the second case, the explorers traveling to different destinations, i.e., Mars and Venus, are dual launched by a single launch vehicle, and they fly to each destination via an interplanetary parking orbit. Our proposed method will widen the scope of opportunity for interplanetary missions. (C) 2015 IAA. Published by Elsevier Ltd. All rights reserved.

Hayabusa was the first asteroid sample return mission. It was launched in May 2003, and arrived at the target asteroid (25143) Itokawa in September 2005. The mission enabled us to see close up a very tiny asteroid in detail for the first time. Hayabusa observed Itokawa with its scientific instruments, and attempted to collect surface material. The mission experienced several serious problems, but successfully returned to Earth in June 2010. After retrieving the capsule, we found thousands of small grains that had been captured from the asteroid. We studied Itokawa in detail with both the remote sensing data and the returned samples, which revealed a great deal of new information to shed light on its origin. In this chapter, we review the Hayabusa mission and summarize the scientific results.

"Time-Delay Integration (TDI)" readout technique has been adopted to a mosaic CCD camera equipped with four fully-depleted CCDs. Optical distortion and image deformation due to the TDI operation are discussed. The manner and advantages of the TDI method in survey observations of geosynchronous orbit objects are summarized. We propose a new TDI application method of getting short-term light curves of artificial space objects. This method of detecting a short-term variability can be applied for a variety of objects, ranging from satellites to stars. It can also be used for the light-curve observations of transient objects which might show short-term variability and of which the precise time information is needed.

We investigated the magnitude-phase relation of (162173) 1999 JU3, a target asteroid for the JAXA Hayabusa 2 sample return mission. We initially employed the International Astronomical Union's H-G formalism but found that it fits less well using a single set of parameters. To improve the inadequate fit, we employed two photometric functions: the Shevchenko and Hapke functions. With the Shevchenko function, we found that the magnitude-phase relation exhibits linear behavior in a wide phase angle range (alpha = 5 degrees-75 degrees) and shows weak nonlinear opposition brightening at alpha < 5 degrees, providing a more reliable absolute magnitude of H-V = 19.25 +/- 0.03. The phase slope (0.039 +/- 0.001 mag deg(-1)) and opposition effect amplitude (parameterized by the ratio of intensity at alpha = 0 degrees.3 to that at alpha = 5 degrees, I(0 degrees.3)/I(5 degrees) = 1.31 +/- 0.05) are consistent with those of typical C-type asteroids. We also attempted to determine the parameters for the Hapke model, which are applicable for constructing the surface reflectance map with the Hayabusa 2 onboard cameras. Although we could not constrain the full set of Hapke parameters, we obtained possible values, w = 0.041, g = -0.38, B-0 = 1.43, and h = 0.050, assuming a surface roughness parameter <(theta)over bar> = 20 degrees. By combining our photometric study with a thermal model of the asteroid, we obtained a geometric albedo of p(v) = 0.047 +/- 0.003, phase integral q = 0.32 +/- 0.03, and Bond albedo A(B) = 0.014 +/- 0.002, which are commensurate with the values for common C-type asteroids.

This paper provides a unique data set representing the taxonomic type of near-Earth asteroids (NEAs) accessible by available spacecraft. The research on NEAs has entered upon a new phase, thanks to sample-return space explorations together with state-of-the-art large ground-based telescopes. We made observations of 13 asteroids with the Subaru, GEMINI-North, GEMINI-South, and Okayama 188cm telescopes. Twelve of them have low delta-v orbits with the potential to be investigated by manned/unmanned spacecraft. Also, ten subkilometer-sized bodies are included among them, and are one of remarkable characteristics in terms of their evolutionary scenario. We have found that eleven asteroids are classified as S-complex, and one asteroid as the V-type. Most S-complex asteroids (eight out of eleven, similar to 70%) have spectra similar to subgroups of Q- or Sq-type, suggesting that these objects are less matured by space weathering. We discuss the dominance of S-complex asteroids based on previous research.

The Planetary Material Sample Curation Facility of JAXA (PMSCF/JAXA) was established in Sagamihara, Kanagawa, Japan, to curate planetary material samples returned from space in conditions of minimum terrestrial contaminants. The performances for the curation of Hayabusa-returned samples had been checked with a series of comprehensive tests and rehearsals. After the Hayabusa spacecraft had accomplished a round-trip flight to asteroid 25143 Itokawa and returned its reentry capsule to the Earth in June 2010, the reentry capsule was brought back to the PMSCF/JAXA and was put to a series of processes to extract recovered samples from Itokawa. The particles recovered from the sample catcher were analyzed by electron microscope, given their ID, grouped into four categories, and preserved in dimples on quartz slide glasses. Some fraction of them has been distributed for initial analyses at NASA, and will be distributed for international announcement of opportunity (AO), but a certain fraction of them will be preserved in vacuum for future analyses.

Hayabusa2 is an asteroid exploration mission to return surface samples of a near-Earth C-type asteroid (162173) 1999 JU . Because asteroids are the evolved remnants of planetesimals that were the building blocks of planets, detailed observation by a spacecraft and analysis of the returned samples will provide direct evidence regarding planet formation and the dynamic evolution of the solar system. Moreover, C-type asteroids are expected to preserve the most pristine materials in the solar system, a mixture of minerals, ice, and organic matter that interact with each other. Space missions are the only way to obtain such pristine materials with geologic context and without terrestrial contamination. Hayabusa2 will launch off in 2014, arrive at 1999 JU in mid-2018, and fully investigate and sample the asteroid at three different locations during its 18-month stay. The concept and design of the Hayabusa2 sampler are basically the same as that on-board Hayabusa, and impact sampling with a 5-g Ta bullet will be made at three locations of the asteroid. The sample container has three separate chambers inside to store samples obtained at different locations separately. The spacecraft will return to Earth with samples in December 2020. Returned samples will be investigated by state-of-the-art analytical techniques in 2020 to understand the evolutionary history of the solar system from 4.56 Gyr ago to the present by combining results from laboratory examinations of the returned samples with remote-sensing datasets and comparing all results of observations of meteorites, interplanetary dust particles, and future returned samples. 3 3

Hayabusa2 is an asteroid sample return mission. It is the follow-on mission of Hayabusa, which was the first spacecraft in the world that brought back the surface material of an asteroid to the earth. Hayabusa2 is now almost ready to launch in 2014. The target asteroid of Hayabusa2 is (162173) 1999 JU3, which is a C-type asteroid. The scientific purpose is to study not only the formation and evolution of the solar system but also the organic matter and water, which existed in the early stage of the solar system. Since we have the experiences and heritages of Hayabusa, we modified the spacecraft in a lot of parts. Thus the spacecraft becomes much more robust and reliable with some new technological challenges. After the launch in 2014, it will arrive at the asteroid in the summer of 2018, stay there for one and half years, and it will come back to the earth at the end of 2020.

A hybrid estimation technique was applied to determine the solar radiation pressure (SRP) force acting on the solar sail spacecraft Interplanetary Kite-craft Accelerated by Radiation of the Sun (IKAROS). To evaluate the SRP force, only tracking data obtained during coast arcs are used. The orbit determination and SRP parameters estimation is implemented using batch weighted least squares. The observables are X/X band two-way Doppler and range measurements. The actually encountered solar radiation pressure acceleration of the IKAROS spacecraft is found to amount to only 88% of the value of the prelaunch simulations. Furthermore, the hybrid technique improves the accuracy of the solar radiation pressure acceleration estimation almost by a factor of five. These results underline the importance of applying a hybrid evaluation of not only the solar radiation pressure force but also the torque for navigation of a solar sail spacecraft.

The Japan Aerospace Exploration Agency is currently developing the second asteroid sample return mission, designated as Hayabusa 2. Following the successful return of Hayabusa from the asteroid "Itokawa", Hayabusa 2 is designed as a round-trip mission to the asteroid "1999 JU3". The 1999 JU3 is a C-type asteroid, which is believed to contain organic matter and hydrated minerals. Thus, it is expected that successful sample collection will provide additional knowledge on the origin and evolution of the planets and, in particular, the origin of water and organic matter. The current mission scenario will enable the spacecraft to reach 1999 JU3 in the middle of 2018 and perform an asteroid proximity operation for 1.5 years. Three touch downs for sampling and one 2-m-class crater generation by means of a high-speed impact operation are planned during the asteroid proximity operation. The samples are to be brought back to the Earth by a re-entry capsule. The present paper describes the system design of Hayabusa 2, some key technical challenges of the mission, and the development status. (C) 2013 IAA. Published by Elsevier Ltd. All rights reserved.

A Japanese spacecraft, Hayabusa2, the successor of Hayabusa, which came back from the Asteroid Itokawa with sample materials after its 7-year-interplanetary journeys, is a current mission of Japan Aerospace Exploration Agency (JAXA) and scheduled to be launched in 2014. Although its design basically follows Hayabusa, some new components are planned to be equipped in Hayabusa2 mission. A Small Carry-on Impactor (SCI), a small explosive device, is one of the challenges that were not seen with Hayabusa. An important scientific objective of Hayabusa2 is to investigate chemical and physical properties of the internal materials and structures. SCI creates an artificial crater on the surface of the asteroid and the mother spacecraft observes the crater and tries to get sample materials. High kinetic energy is required to creating a meaningful crater. The SCI would become complicated and heavy if the traditional acceleration devices like thrusters and rocket motors are used to hit the asteroid because the acceleration distance is quite large and guidance system is necessary. In order to make the system simpler, a technology of special type of shaped charge is used for the acceleration of the impact head. By using this technology, it becomes possible to accelerate the impact head very quickly and to hit the asteroid without guidance system. However, the impact operation should be complicated because SCI uses powerful explosive and it scatters high speed debris at the detonation. This paper presents the overview of our new small carry-on impact system and the impact operation of Hayabusa2 mission. (C) 2012 IAA. Published by Elsevier Ltd. All rights reserved.

This study aims to establish a flexible orbit design method which enables "any-time" launch of a deep-space explorer. In this study, it is assumed that a 500 kg deep-space explorer attached with a 300 kg small kick stage, designated as Earth Escape Stage, EES, is dual launched into a Geostationary Transfer Orbit, GTO, together with a primary payload, whereupon the EES is initiated at perigee to inject the deep-space explorer into an orbit whose orbital energy, C3, is almost zero. Then the on-board Ion Engine System, IES, accelerates the explorer through the Electric Delta-V Earth Gravity Assist, EDVEGA , scheme to increase the Earth relative velocity at the Earth reencounter point, which enables the explorer to inject into a transfer orbit to a deep-space destination after the Earth swing-by. In this assumption, the secondary payload i.e. the explorer cannot choose the "desired" launch epoch for itself, which is critical for deep-space missions. As a solution to this problem, this study suggests a flexible orbit design method utilizing a concept of "interplanetary parking orbit", which drastically alleviates the launch window constraints. The suggested method will open the door for deep-space mission designers to use dual launch opportunities of geostationary missions. 1,2

The Japanese asteroid explorer Hayabusa-2 will be launched in the mid-2010s to return samples from C-type near-Earth asteroid 1999JU3. During the rendezvous phase (i.e. proximity operation phase), we will conduct scientific observations to estimate physical parameters (e.g. gravity field, shape, pole direction, spin-rate, ephemeris) of the target body, which are crucial not only for its scientific investigation but also for spacecraft navigation. In particular, the mass is essential to perform a stable touchdown sequence to collect samples from the asteroids surface. We will attempt to estimate the gravity field of the target body using Earth-based radiometric tracking measurements (2-way Doppler and range) and spacecraft-based measurements (information from optical navigation cameras and laser altimeter) using a global parameter estimation technique. As the first step for gravity field estimation, we performed a simulation study on mass estimation under simple configuration and evaluated the relation between the quality and quantity of measurements and the accuracies of the estimation results. Subsequently, the detectability of the low degree and order gravity field coefficients was also studied. We will also present a method for ephemeris improvement of 1999JU3 using spacecraft relative position data and radiometric tracking measurements. © 2013 2013 California Institute of Technology.

The Japanese asteroid explorer Hayabusa-2 will be launched in the mid-2010s to return samples from C-type near-Earth asteroid 1999JU3. During the rendezvous phase (i.e. proximity operation phase), we will conduct scientific observations to estimate physical parameters (e.g. gravity field, shape, pole direction, spin-rate, ephemeris) of the target body, which are crucial not only for its scientific investigation but also for spacecraft navigation. In particular, the mass is essential to perform a stable touchdown sequence to collect samples from the asteroids surface. We will attempt to estimate the gravity field of the target body using Earth-based radiometric tracking measurements (2-way Doppler and range) and spacecraft-based measurements (information from optical navigation cameras and laser altimeter) using a global parameter estimation technique. As the first step for gravity field estimation, we performed a simulation study on mass estimation under simple configuration and evaluated the relation between the quality and quantity of measurements and the accuracies of the estimation results. Subsequently, the detectability of the low degree and order gravity field coefficients was also studied. We will also present a method for ephemeris improvement of 1999JU3 using spacecraft relative position data and radiometric tracking measurements.

本稿は,世界初のソーラー電力セイル実証機IKAROSが打ち上げられてからおよそ2年間という期間に実証された,ソーラーセイルの誘導・航法に関する成果をまとめたものである.世界初となるソーラーセイルの軌道上での実際の航法・誘導において,光圧加速度・光圧トルクのその類稀なる大きさから,一般的な手法だけでは評価しきれない点が少なからず存在し,そのため,IKAROSの誘導・航法技術に関しては,いくつかの工夫がなされた.ここでは,航法技術に関して,セイルによって発生する光圧加速度を精密に計測するための推定法,及び評価結果を,また,誘導技術に関しては,光圧トルクによって発生する姿勢のドリフト運動を考慮した誘導法,及びその評価結果について紹介する.また,航法技術に関連して,IKAROSに搭載されたDDOR用のトーン生成器によって得られたデータの評価結果についても紹介する.

This paper describes a newly designed wide-band optical filter. It is optimized for deep imaging of small solar-system bodies. The new filter, which we denote as Wi, is designed to reduce contamination by light pollution from street lamps, especially strong mercury and sodium emission lines. It is also useful for reducing unwanted scattered moonlight. Compared with the use of a commercially available long-wave cut wide-band filter, the signal-to-noise ratios in the detection of asteroids are improved by about 6% by using the Wi filter.

Records of micrometeorite collisions at down to submicron scales were discovered on dust grains recovered from near-Earth asteroid 25143 (Itokawa). Because the grains were sampled from very near the surface of the asteroid, by the Hayabusa spacecraft, their surfaces reflect the low-gravity space environment influencing the physical nature of the asteroid exterior. The space environment was examined by description of grain surfaces and asteroidal scenes were reconstructed. Chemical and O isotope compositions of five lithic grains, with diameters near 50 μm, indicate that the uppermost layer of the rubble-pile-textured Itokawa is largely composed of equilibrated LL-ordinary-chondrite-like material with superimposed effects of collisions. The surfaces of the grains are dominated by fractures, and the fracture planes contain not only sub-μm-sized craters but also a large number of sub-μm- to several-μm-sized adhered particles, some of the latter composed of glass. The size distribution and chemical compositions of the adhered particles, together with the occurrences of the sub-μm-sized craters, suggest formation by hypervelocity collisions of micrometeorites at down to nm scales, a process expected in the physically hostile environment at an asteroid's surface. We describe impact-related phenomena, ranging in scale from 10(-9) to 10(4) meters, demonstrating the central role played by impact processes in the long-term evolution of planetary bodies. Impact appears to be an important process shaping the exteriors of not only large planetary bodies, such as the moon, but also low-gravity bodies such as asteroids.

Microparticles recovered from the Asteroid 25143 Itokawa surface by the Hayabusa mission have been examined for the occurrence of soluble organic compounds. After five individual particles (∼50 to 100 μm in diameter) were rinsed with organic solvents on a diamond plate, two extracts were hydrolyzed with hydrochloric acid for amino acid analysis (AAA), and three extracts were combined for time of flight-secondary ion mass spectrometry (ToF-SIMS) to look for other organic compounds, including polycyclic aromatic hydrocarbons. The organic compounds detected by both methods have the same concentrations as those in blank levels, indicating that indigenous organic compounds are not found in this study. Based on the sensitivities of AAA and ToF-SIMS with the reference sample analyses, the concentrations of indigenous organics in the samples are below part-per-million (ppm), if present. Copyright © 2012 by The Geochemical Society of Japan.

Hayabusa was a JAXA sample-return mission to Itokawa navigated, in part, by JPL personnel. The spacecraft survived several near mission-ending failures at Itokawa yet returned to Earth with an asteroid regolith sample on June 13, 2010. This paper describes NASA/JPL's participation in the Hayabusa mission during the last 100 days of its mission, wherein JPL provided tracking data and orbit determination, plus verification of maneuver design and entry, descent and landing. © Copyright 2011 California Institute of Technology. Government sponsorship acknowledged.

JAXA's next asteroid investigator is now under development supposing a launch in 2014. The new mission is called HAYABUSA-2. It is a similar sample return mission to HAYABUSA, however its target asteroid is different from HAYABUSA. From the point of the scientific objective, 1999JU3 which is the asteroid with the primitive composition (C-type) is chosen as the target. HAYABUSA-2 is planned to be equipped with some new components. A small carry-on impactor (SCI) is one of the new challenges that were not seen with HAYABUSA. SCI is a small impact system for creating an artificial crater. One of the most important scientific objectives of HAYABUSA-2 is to investigate chemical and physical properties of the internal materials in order to understand the formation history of small bodies. The impact system is considered one of the most effective methods for investigating the inner structure of asteroids. We can extend our knowledge about asteroids by observing the diameter, depth and shape of the artificial crater. Additionally, the direct investigation of the inner materials of the asteroid becomes possible by sampling materials inside of the crater. This paper presents the development status of SCI and the results of its development tests. Copyright © (2012) by the International Astronautical Federation.

Context. The Hayabusa2 mission, which will be launched by JAXA in 2014, will return samples from the C-type near-Earth asteroid (162173) 1999 JU3. To better plan the mission, it is important to obtain as many physical characteristics of the asteroid as possible from ground-based observations. Moreover, these can then be calibrated with the in-situ and laboratory studies and be used to better understand other similar objects. Regarding the surface composition of the target asteroid, previous spectroscopic studies in the visible provided conflicting results for the possible presence of a deep absorption band, which is usually related to aqueous alteration processes. Aims. Our goal is to better understand the surface composition of asteroid (162173) 1999 JU3, and how it relates to the spectral differences observed by diverse authors at different epochs and telescopes. Moreover, to support the JAXA mission planning, we aim to constrain the level of aqueous alteration and thermal activity undergone by the object. Methods. The adopted methodology was to observe different regions of the surface of the asteroid that rotates around its axis. Spectroscopic observations that cover about 70% of its surface were therefore obtained at the SOAR telescope in Chile on 2012 July9-10. Results. Our results indicate that the surface of asteroid (162173) 1999 JU3 presents featureless spectra with very little variation. Conclusions. No sign of an absorption feature that could be related to aqueous alteration processes is detectable in the observed spectra. © © ESO, 2012.

"Akatsuki" mission has been launched on May 21, 2010 on an H-IIA booster from Tanegashima Space Center (TSC), Kagoshima, Japan, and arrived at Venus on December 6, 2010, without trouble, after cruising interplanetary approximately seven months. In this paper, the orbit determination result, the estimation strategy, and experiences during the period from the launch through the VOI (Venus Orbit Insertion) phase are discussed.

"Akatsuki" mission has been launched on May 21, 2010 on an H-IIA booster from Tanegashima Space Center (TSC), Kagoshima, Japan, and arrived at Venus on December 6, 2010, without trouble, after cruising interplanetary approximately seven months. In this paper, the orbit determination result, the estimation strategy, and experiences during the period from the launch through the VOI (Venus Orbit Insertion) phase are discussed.