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A new barbeled dragonfish, Eustomias shunyo sp. nov., is described based on three specimens [219.1–256.4 mm in standard length (SL)] collected at depths of 30–180 m from the Shatsky Rise in the western North Pacific. The new species is included in the subgenus Urostomias Regan and Trewavas 1930 and distinguishable from all congeners by the following combination of characters: 30 dorsal-fin rays; 48–49 anal-fin rays; 9–10 pectoral-fin rays; 7 pelvic-fin rays; 29–31 PV (photophores in ventral series between pectoral- and pelvic-fin insertions); 26–27 AC (photophores from dorsal to anal fin to end of row); 69–72 vertebrae; preanal length 63.7–65.3% SL; head length 9.7–10.1% SL; barbel length 12.2–13.7% SL; single luminous gland on upper margin of caudal fin; stem of barbel lacking external pigmentation except for its proximal portion, and melanophores sparsely scattered around small photophores on ventral side of stem; pale yellow patches arranged in 1 or 2 rows on dorsal and ventral sides of barbel stem; single or pared filaments on dorsal side of distal portion of barbel stem just before terminal bulb; single leaf-shaped dark patch on ventral side of barbel bulb. The revised diagnosis and a key to species of the subgenus Urostomias are presented. [ABSTRACT FROM AUTHOR]

Exploring the effects of water temperature on egg development in skipjack tuna (Katsuwonus pelamis) has substantial implications for evaluations of wild spawning habitats. In the present study, we examined the hatching success and duration as a function of temperature from 21 to 33°C under captive environments. A high hatching rate of over 50% between 23 and 31°C was observed, with the shortest hatching duration at 31°C. Because the egg period is vulnerable to predators, a shortened hatching duration with warming water would be ecologically advantageous for K. pelamis, as its main spawning grounds are located in tropical areas. [ABSTRACT FROM AUTHOR]

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 Hayabusa2 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. • JAXA launched the world-second asteroid sample return mission Hayabusa2 in 2014. • Hayabusa2 completed 1.5 years of the asteroid proximity operation with full success. • Surface and subsurface landings, 1 crater forming, landers delivery were conducted. • Adoptive mission re-planning and spacecraft reconfigurations were key to the success. • Hayabusa2 is now on the way back to the Earth with the collected Ryugu sample. [ABSTRACT FROM AUTHOR]

Abstract In the exploration of small bodies, the orbiting operation is very significant in terms of fuel consumption and scientific observation of small bodies. Although the force field around a small body is strongly perturbed, there is a family of stable orbits, called terminator orbits, that exist. However, although a terminator orbit is stable, it also has disadvantages. The orbital plane of a terminator orbit must always face the Sun and lacks flexibility in orbit design. Moreover, since the orbital plane lies in the night side because of the solar radiation pressure (SRP) shifting the equilibrium point, optical observation of the small body is extremely restricted. Therefore, the present study focuses on the perturbed terminator orbit, i.e., the quasi-terminator orbit (QTO), which is a stable orbit that does not suffer from impact with the surface or escape. The present study attempts to reveal the solution space and the usability of the QTO. We succeeded in analytically deriving the existence range of the long-term QTO and verified that the numerical and analytical solutions coincide well. As a result, the calculation time required for solving the existence range of the long-term stable QTO can be greatly shortened, and it becomes possible to quickly apply our findings to other missions by accounting for the gravity field and SRP of the mission-specific small body. Highlights • Quasi terminator orbit (QTO) is proposed for orbit operation around small bodies. • QTOis useful in terms of flexibility of orbit design and optical observability of the body. • Solution space of QTOis derived analytically and it coincides to the numerical results well. • The analytical solution becomes possible to quickly design QTOsto various missions. [ABSTRACT FROM AUTHOR]

Abstract The Japan Aerospace Exploration Agency launched the asteroid sample return spacecraft "Hayabusa2" on December 3, 2014. Hayabusa2 will reach the C-type asteroid 162173 Ryugu 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 forming 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. The objectives and technologies used in this mission is not a direct solution for the future planetary defense, but should contribute to this field by increasing general asteroid knowledge and enhancing human capabilities of small body-surface access/roving/sampling/impacting. This paper describes the outline of the Hayabusa2 mission, overviews the kinetic impact technology as an example of planetary defense-related technologies and the current flight status after the two and a half years of the interplanetary cruise. Highlights • JAXA successfully launched the world-second asteroid sample return mission Hayabusa2 in 2014. • Hayabusa2 is equipped with some key devices strongly related to planetary defense technologies. • The first 2.5 years of operation history are explained with major achievements. • The asteroid proximity operation plan is overviewed with preparation activities by the team. [ABSTRACT FROM AUTHOR]

We investigated the respective effects of the acute supplementation of valine, leucine, and isoleucine on metabolism-related markers by administering a swimming exercise test to rats. As a behavioral analysis, we evaluated the effect of valine and that of leucine on spontaneous activity after exercise. Acute supplementation of valine before exercise significantly suppressed the depression of the liver glycogen and the blood glucose after exercise, whereas leucine decreased the blood glucose and isoleucine had no effect. Valine or leucine supplementation significantly decreased the plasma corticosterone level after exercise, while isoleucine had no effect. In the behavioral analysis, valine significantly increased the spontaneous activity after exercise, whereas leucine had no effect. These results indicate that in rats, the acute supplementation of valine, not leucine or isoleucine, is effective for maintaining liver glycogen and blood glucose and increasing spontaneous activity after exercise, which could contribute to the reduction of fatigue during exercise. [ABSTRACT FROM AUTHOR]

The Hayabusa 2 mission is targeted to explore the asteroid (162173) 1999 JU 3 and return surface as well as sub-surface samples through a novel impactor. Upon its return, at the end of 2020, the spacecraft will release the capsule for Earth re-entry and drift away from the planet. Based on the current mission profile, the spacecraft is expected to retain 30 kg of xenon propellant for trajectory maneuvers after the capsule is released. This remaining fuel can be used to extend the mission and improve its scientific return by exploring a new target. Work herein outlines an extension plan for Hayabusa 2, detailing the target selection process and its subsequent trajectory design. Due to final Earth escape trajectory, considering the excess velocity and orbital geometry, the only available extension option is an asteroid flyby. One of the most important trajectory characteristic is to maximize the spacecraft's optical detection capabilities. As a result the asteroid 2001 WR 1 is identified as the most promising target candidate. The resulting trajectory uses all the available xenon with 100% duty cycle. Furthermore, the extension lasts for 932 days and offers 1.57 days of optical navigation time for a flyby on June 27, 2023. [ABSTRACT FROM AUTHOR]

The Hayabusa2 mission journeys to C-type near-Earth asteroid (162173) Ryugu (1999 JU) 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-μm 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This work presents a mission concept for in-orbit particle collection for sampling and exploration missions towards Near-Earth asteroids. Ejecta is generated via a small kinetic impactor and two possible collection strategies are investigated: collecting the particle along the anti-solar direction, exploiting the dynamical features of the L 2 Lagrangian point or collecting them while the spacecraft orbits the asteroid and before they re-impact onto the asteroid surface. Combining the dynamics of the particles in the Circular Restricted Three-Body Problem perturbed by Solar Radiation Pressure with models for the ejecta generation, we identify possible target asteroids as a function of their physical properties, by evaluating the potential for particle collection. • Novel mission concept for in-orbit sample collection at asteroids. • Identification and analysis of two possible collection strategies. • Ranking of most suitable targets among Near-Earth Asteroids. • Preliminary mission risk assessment from particle impacts. [ABSTRACT FROM AUTHOR]

Abstract: Vertical behavior of cultured chub mackerel, Scomber japonicus, in a net-cage was investigated using depth data logger and infrared video camera footage during the spawning and non-spawning seasons. Marked differences in the vertical distributions of spawning and non-spawning mackerel were observed. Non-spawning mackerel swam near the bottom of the net-cage during the daytime, coming up to shallow waters during night-time. However, spawning mackerel remained near the bottom of the net at all times except for brief, night-time visits to the surface for gamete release. Spawning events started with the school of fish whirling near the surface, before two or three fish, possibly the female followed by the males, darted upward and away from the school at high speed. Once away from the school, the fish swam in a tight circle two or three times before releasing their eggs and sperm. Estimation of the timing of spawning events based on back-calculations of egg development and then correlating these data with changes in vertical movements revealed that there were 26 events over a three-day period, and that most events occurred between sunset and midnight. Differences in the depth distribution between the spawning season and the non-spawning season could potentially be used as new indicator for the spawning period in chub mackerel reared under artificial conditions. These results could help us to better understand the spawning season in mackerel and allow us to increase the sustainability of the natural reproductive process in captivity. [Copyright &y& Elsevier]

The properties of hydrolyzed feather keratin ( HFK) were compared to those of hydrolyzed wool keratin ( HWK) with the aim of developing better ways to utilize feather keratin waste. Amino acid analysis showed that HFK contained more hydrophobic amino acids did than HWK. Although gel permeation chromatography indicated that HFK and HWK had more low-molecular weight peptides than their intact sources, Fourier transform infrared spectroscopy indicated that both hydrolyzed keratins retained their original secondary structure. The physical properties of HFK were evaluated by treating HFK to human hair fibers. HFK treatment enhanced significantly the surface hydrophobicity and strength of fibers, and HFK was more permeable into hair fibers. These results suggest that HFK is suitable for industrial applications to improve fibers. In addition, HFK may be suitable for raw material of products requiring both flexibility and hydrophobicity, such as films and biodegradable plastics. [ABSTRACT FROM AUTHOR]

Highlights: [•] We examined behaviors for Pacific bluefin tuna using animal-borne data-loggers. [•] We also reanalyzed published electronic tagging data for free-ranging dolphinfish. [•] Pacific bluefin tuna made frequent dives below the thermocline. [•] Dolphinfish remained near the surface and did not dive across the thermocline. [•] Dolphinfish extended their vertical depth ranges as thermocline depth increased. [ABSTRACT FROM AUTHOR]

Abstract: This paper describes achievements of the IKAROS project, the world''s first successful interplanetary solar power sail technology demonstration mission. It was developed by the Japan Aerospace Exploration Agency (JAXA) and was launched from Tanegashima Space Center on May 21, 2010. IKAROS successfully deployed a 20m-span sail on June 9, 2010. Since then IKAROS has performed interplanetary solar-sailing taking advantage of an Earth-Venus leg of the interplanetary trajectory. We declared the completion of the nominal mission phase in the end of December 2010 when IKAROS successfully passed by Venus with the assist of solar sailing. This paper describes the overview of the IKAROS spacecraft system, how the world''s first interplanetary solar sailer has been operated and what were achieved by the end of the nominal mission phase. [Copyright &y& Elsevier]

Abstract: Although full-cycle aquaculture of Pacific bluefin tuna, Thunnus orientalis, has been established by Kinki University, Japan, most juvenile die after transfer to net cages offshore due to the stress associated with fluctuations in environmental conditions. We examined the effect of environmental conditions on mortality of juvenile using a generalized liner model (GLM). Juveniles were reared for more than 300days in a net cage and number of dead fish was examined over time and in relation to water temperature, salinity, moon phase, and water transparency. Mortalities soon after transferring the fish from the indoor rearing tank to the net cage occurred independently of environmental factors and were considered to be due to the handling stress and lack of acclimation. In subsequent periods, fluctuations in water temperature were the most critical factor affecting juvenile survival. Our results showed that optimal water temperatures for juvenile bluefin tuna aquaculture are considered to range between 15 and 25°C. Salinity and lunar irradiance (half moon to full moon) fluctuations had less marked effects on juvenile survival. Juveniles in net cages cannot move to avoid those unfavorable environmental fluctuations and this inability to locate areas of optimal temperature may complicate their body temperature maintenance because the capacity for endothermy in juveniles is undeveloped. We propose that sites selected for culturing juvenile Pacific bluefin tuna have water temperatures ranging from 15 to 25°C with constant temperatures that avoid large fluctuations. [Copyright &y& Elsevier]

Abstract: This paper presents a method for approximating the state transition matrix for orbits around a primary body and subject to arbitrary perturbations. The primary objective of this method is to provide an accurate state transition matrix for orbits with realistic perturbations, which has a sufficiently simple form for implementation onboard spacecraft. The averaging method is employed to isolate the high and low frequency spectra of the perturbation terms, and construct a functional form of the approximate state transition matrix composed only of elementary analytic functions. In addition to the methodology of the approximation, it is shown that the symplectic property, which is a fundamental mathematical structure of Hamiltonian systems, can be incorporated into this method. This not only reduces the number of parameters required for approximations but also makes it possible to preserve the physically true structure of the state transition matrix. The resulting state transition matrix approximation is valid for tens of orbital revolutions without having to update the parameters. Numerical simulations show that this method is valid for arbitrary eccentricity orbits with semimajor axis ranging from LEO up to around 10 Earth radii when applied to Earth orbits. [Copyright &y& Elsevier]

A novel attitude control method to capture tumbling objects in space is discussed. The capturing procedure considered in this study is that the chaser satellite surrounds the target satellite and synchronizes its attitude to the target''s one so that the capturing operation can be conducted with small relative motion between the chaser and the target. To realize this idea, a novel control algorithm called free motion path method (FMPM) has been developed, which enables us to completely ignore a nonlinearity effect in the dynamics by taking advantage of the conservative quantities of the system. The FMPM aims for on-line control and forms a closed-loop system. With FMPM, we can explicitly limit the maximum control torque and can also implement a certain kind of optimality. Some theoretical analyses and the results of computer simulations are shown in this paper. [Copyright &y& Elsevier]

Ballistic landers enable orbiting asteroid missions to perform surface science at limited additional cost and risk. Due to asteroids' weak gravity and irregular terrain, lander deployment trajectories will consist of several chaotic bounces. Although impacts on regolith-covered asteroids are numerically expensive to model, impacts on rocky asteroids can be modeled with simpler, impulsive contact models. One such model is that by Stronge, which was successfully used in large-scale Monte Carlo studies of asteroid lander deployment. This model parameterizes impacts with (fixed) material restitution and friction coefficients, but has not been validated for the low-velocity regime of an assembled, nonspherical body. This paper uses an air-bearing setup to perform 2D experiments of a rectangular floating assembly impacting a concrete block with V ⩽ 25 cm/s. The impact velocity, assembly attitude, and block attitude are varied across 2,400 experimental runs of both normal and tangential impacts. Optical tracking is used to extract the pre- and post-impact velocities of the assembly. In a majority of cases, Stronge's model can be fit to the experiments to extract the corresponding restitution and friction coefficients. We find that the coefficients are not fixed with respect to the impact velocity and attitude, but that their variation is seemingly random. In some tangential impact cases, the model even fails to reproduce the observed behavior althogether. This suggests that there may not be a simple way to reconcile Stronge's fixed-material-coefficient model with reality, although it may retain practical use if the coefficients are randomly varied in each impact of a simulation. [ABSTRACT FROM AUTHOR]

The near-Earth asteroid 1998 KY26 is a rendezvous target of the Hayabusa2 extended mission, with a diameter as small as 20 – 40 m and a spin period as short as 10. 7 min. This research aims to develop a plan for Hayabusa2 operations around this particular asteroid constrained by the remaining spacecraft resources. The main part of this paper begins with the characterization of the orbital and surface dynamics about 1998 KY26. The analysis demonstrates that the orbital motion of the spacecraft in the microgravity environment is dominated by solar radiation pressure, while the centrifugal force due to the high spin rate plays a prominent role at the surface. The dynamical environment significantly differs from that of the original target Ryugu, for which Hayabusa2 was specifically designed, posing technical challenges in close-proximity operations. In particular, this article highlights the feasibility of two primary operations: hovering for station-keeping and controlled descent for close-up observations. The discussion is further extended to more advanced operations, such as those using the projectile and target marker aboard the spacecraft. Our research pushes the envelope to explore one of the smallest members of the Solar System. • Hayabusa2 ♯ target asteroid 1998 KY26 is a fast rotator with a diameter of ∼ 30 m. • Low gravity and rapid rotation form distinctive orbital and surface environments. • Station-keeping can be achieved by hovering 1 – 3 km above the asteroid. • Controlled descent to lower altitudes shows minimal guidance error and fuel cost. • Advanced options include operations using the projectile and the target marker. [ABSTRACT FROM AUTHOR]

Catch-and-effort data are among the primary sources of information for assessing the status of terrestrial wildlife and fish. In fishery science, elaborate stock-assessment models are fitted to such data in order to estimate fish-population sizes and guide management decisions. Given the importance of catch-and-effort data, we scoured a comprehensive dataset pertaining to albacore tuna (Thunnus alalunga) in the north Pacific Ocean for novel ecological information content about this commercially valuable species. Specifically, we used unsupervised learning based on finite mixture modelling to reveal that the north Pacific albacore-tuna stock can be divided into four pseudo-cohorts. We discovered that smaller body mass pseudo-cohorts inhabit relatively high—subtropical to temperate—latitudes, with hotspots off the coast of Japan. Larger body mass pseudo-cohorts inhabit lower—tropical to subtropical—latitudes, with hotspots in the western and central north Pacific. These results offer evidence that albacore tuna prefer different habitats depending on their body mass, and point to long-term migratory routes for the species that the current tagging technology is unlikely to capture in full. We discuss the implications of the results for data-driven modelling of albacore tuna in the north Pacific, as well as the management of the north Pacific albacore-tuna fishery. [ABSTRACT FROM AUTHOR]

Mars Moon eXplorer (MMX) is JAXA's next candidate flagship mission to be launched in the early 2020s. MMX will explore the Martian moons and return a sample from Phobos. This paper presents the mission analysis work, focusing on the transfer legs and comparing several architectures, such as hybrid options with chemical and electric propulsion modules. The selected baseline is a chemical-propulsion Phobos sample return, which is discussed in detail with the launch- and return-window analysis. The trajectories are optimized with the jTOP software, using planetary ephemerides for Mars and the Earth; Earth re-entry constraints are modeled with simple analytical equations. Finally, we introduce an analytical approximation of the three-burn capture strategy used in the Mars system. The approximation can be used together with a Lambert solver to quickly determine the transfer Δ v costs. [ABSTRACT FROM AUTHOR]

The motion of a spacecraft in proximity to a small body is significantly perturbed due to its irregular gravity field and solar radiation pressure. In such a strongly perturbed environment, the coupling effect of the orbital and attitude motions exerts a large influence that cannot be neglected. However, natural orbit-attitude coupled dynamics around small bodies that are stationary in both orbital and attitude motions have yet to be observed. The present study therefore investigates natural coupled motion that involves both a Sun-synchronous orbit and Sun-tracking attitude motion. This orbit-attitude coupled motion enables a spacecraft to maintain its orbital geometry and attitude state with respect to the Sun without requiring active control. Therefore, the proposed method can reduce the use of an orbit and attitude control system. This paper first presents analytical conditions to achieve Sun-synchronous orbits and Sun-tracking attitude motion. These analytical solutions are then numerically propagated based on non-linear coupled orbit-attitude equations of motion. Consequently, the possibility of implementing Sun-synchronous orbits with Sun-tracking attitude motion is demonstrated. [ABSTRACT FROM AUTHOR]

This work presents the model of an ejecta cloud distribution to characterise the plume generated by the impact of a projectile onto asteroids surfaces. A continuum distribution based on the combination of probability density functions is developed to describe the size, ejection speed, and ejection angles of the fragments. The ejecta distribution is used to statistically analyse the fate of the ejecta. By combining the ejecta distribution with a space-filling sampling technique, we draw samples from the distribution and assigned them a number of representative fragments so that the evolution in time of a single sample is representative of an ensemble of fragments. Using this methodology, we analyse the fate of the ejecta as a function of different modelling techniques and assumptions. We evaluate the effect of different types of distributions, ejection speed models, coefficients, etc. The results show that some modelling assumptions are more influential than others and, in some cases, they influence different aspects of the ejecta evolution such as the share of impacting and escaping fragments or the distribution of impacting fragments on the asteroid surface. • Development of an ejecta cloud distribution-based model. • Characterisation of asteroid ejecta fate via a representative fragments sampling. • Sensitivity analysis of ejecta fate to modelling techniques and assumptions. [ABSTRACT FROM AUTHOR]

This paper proposes an autonomous image-based navigation method for estimating the target-relative position of a spacecraft for distant small body exploration. The main focus is position estimation at high altitude where the outlines of a target body can be seen in images. The asteroid explorer Hayabusa2 touched down on the asteroid Ryugu with pin-point accuracy in February 2019. For this mission, the asteroid-relative position was estimated by ground operators from 20 km to 50 m above the surface of Ryugu. For the exploration of small bodies farther than the asteroid main belt, the delay of communication with Earth is unacceptably large for feedback guidance. This situation becomes worse for larger bodies because the time constant of the dynamics becomes smaller. Therefore, real-time autonomous navigation is required for distant small body exploration even at high altitude. To accomplish high-accuracy and real-time autonomous navigation, an autonomous position estimation method based on terrain-relative navigation (TRN) that estimates deviation by comparing nominal terrain information and actual terrain information is proposed. In addition to TRN, the vector code correlation (VCC) algorithm is used for the luminance comparison of terrain information. This algorithm is a type of correlation calculation method for template matching that finds the maximum correlated region in images. With the VCC algorithm, correlation can be calculated in real time via XOR operations suitable for FPGA. The estimation accuracy and processing time of the proposed method were evaluated with a comparison to those of other methods. The results show that a high estimation accuracy, similar to the image resolution, was accomplished in real time. Finally, an evaluation using flight data from Hayabusa2 shows that the estimation accuracy and processing time of the proposed method are suitable for a real mission environment. The proposed method will be a key technology for distant small body exploration. • Autonomous position estimation using vector code correlation algorithm is proposed. • Proposed method estimates positions with image-resolution accuracy in realtime. • Proposed method can be applied to a real mission environment such as Hayabusa2. • Proposed method will be a key technology for distant small body exploration. [ABSTRACT FROM AUTHOR]

This work studies periodic solutions applicable, as an extended phase, to the JAXA asteroid rendezvous mission Hayabusa 2 when it is close to target asteroid 1999 JU3. The motion of a spacecraft close to a small asteroid can be approximated with the equations of Hill's problem modified to account for the strong solar radiation pressure. The identification of families of periodic solutions in such systems is just starting and the field is largely unexplored. We find several periodic orbits using a grid search, then apply numerical continuation and bifurcation theory to a subset of these to explore the changes in the orbit families when the orbital energy is varied. This analysis gives information on their stability and bifurcations. We then compare the various families on the basis of the restrictions and requirements of the specific mission considered, such as the pointing of the solar panels and instruments. We also use information about their resilience against parameter errors and their ground tracks to identify one particularly promising type of solution. [ABSTRACT FROM AUTHOR]

Although chum salmon (Oncorhynchus keta) is an important fishery resource in Japan, acoustic methods cannot be applied to biomass estimation because the target strength (TS) is unknown. This study clarified the TS for each fork length (FL: 5.5–33.5 cm) of young chum salmon inhabiting the Japanese coastal area to the Bering Sea by measuring free-swimming fish. The size dependences of the TS values were TSmean = 20 log10 FL – 68.0, for both 38 and 120 kHz. This facilitated the estimation of biomass of young salmon using acoustic methods. [ABSTRACT FROM AUTHOR]

An improved weather-forecast-based link-budget design technique for space-to-Earth links is described. The aim is the stochastic optimization of both transmission symbol rate and received signal-to-noise ratio. The proposed radiometeorological operations prediction (RadioMetOP) model takes into account the forecast uncertainty by a space–time ensemble method exploiting the temporal evolution of the predicted radiometeorological variables over the weather-forecast spatial grid. The unique possibility of testing and validating the RadioMetOP model is presented, thanks to the $Ka$ -band downlink measurements available from the support of the European Space Agency’s antenna tracking network to deep-space Hayabusa-2 (HB2) mission, operated by the Japan Aerospace Exploration Agency. First, the RadioMetOP model accuracy is tested by comparing the signal-to-noise ratio, measured during the transmission periods, with the simulated one, properly scaled to the symbol rate operated by HB2, finding correlation values of 0.9 that confirm the effectiveness of the proposed approach. Second, the $a$ posteriori analysis of the optimization process is accomplished, showing that depending on the considered criteria for the link-budget optimization, the use of the RadioMetOP model would have allowed a transmitted data volume more than doubled and an average signal-to-noise ratio gain between 2.1 and 3.8 dB. [ABSTRACT FROM AUTHOR]

Hayabusa2 is the ongoing JAXA's sample and return mission to the asteroid Ryugu. In late 2018, Ryugu was in superior solar conjunction with the Earth. It is the first time that a spacecraft experiences the blackouts in the communication link with the Earth while hovering around a small celestial body. In this article, the design of the nominal conjunction trajectory flown by the Hayabusa2's spacecraft is presented. The requirements for the conjunction trajectory were (1) to guarantee a low fuel consumption, (2) to ensure the visibility of the asteroid by the spacecraft's wide angle camera ( 60 ∘ FoV), and (3) to increase the spacecraft altitude to a safety location (∼ 109 km ) from the nominal BOX-A operation of 20 km (Home Position - HP). Finally, (4) to return at BOX-A after the conjunction phase. Given the mission constraints, the designed conjunction trajectory appears to have a fish-shape in the Hill coordinates therefore we renamed it as "ayu" (sweetfish in Japanese) trajectory. The optNEAR tool was developed for the guidance (Δ V s planning) and navigation design of the Hayabusa2's conjunction mission phase. A preliminary sensitivity analysis in the Hill reference frame proved that the ayu trajectory is a good candidate for the conjunction operation of hovering satellite. The solution in the Hill coordinates is refined in the full-body planetary dynamics (optNEAR Tool) before flight. The ayu conjunction trajectory requires (a) two deterministic Δ V s at the Conjunction Orbit Insertion (COI) point and at the Home-position Recovery Maneuver (HRM) point respectively. (b) Two stochastic Δ V s , known as Trajectory Correction Manoeuvres (TCMs), before and after the deep conjunction phase are also required. The constraint linear covariance analysis in the full-body dynamics is here derived and used for the preliminary guidance and navigation planning. The results of the covariance analysis were validated in a nonlinear sense with a Monte Carlo approach which proved the validity of the semi-analytic method for the stochastic Δ V s planning derived in this paper. [ABSTRACT FROM AUTHOR]

Hayabusa2 is a Japanese interplanetary probe launched on December 3, 2014, which arrived at asteroid Ryugu on June 27, 2018. During its stay around Ryugu, it completed several challenging operations, including deploying two rovers and a lander, conducting two sample collections, and performing a kinetic impact experiment. The kinetic impact experiment was one of the biggest challenges of the Hayabusa2 mission. Investigating the physical and chemical properties of asteroid internal materials and structures is an important scientific objective for small body exploration. We developed a small kinetic impactor called the SCI (Small Carry-on Impactor) to achieve this objective. The SCI is a compact kinetic impactor designed to remove a small region of Ryugu's uppermost surface regolith layer and create an artificial crater. The spacecraft deployed the SCI on April 5, 2019, successfully creating an artificial crater with a diameter of 15 m. This paper describes the operational planning of the kinetic impact experiment and summarizes the operation results. • Sub-surface exploration is a new challenge for Hayabusa2. • A small kinetic impactor was developed to create an artificial crater. • The impactor created a 15m-class artificial crater on April 5, 2019. • The crater formation process was observed by a deployable camera. • The sub-surface sampling was completed during the touchdown operation on July 11, 2019. [ABSTRACT FROM AUTHOR]

Hayabusa2 is a Japanese sample return mission from the near-Earth asteroid Ryugu. The Hayabusa2 spacecraft was launched on December 3, 2014, and arrived at Ryugu on June 27, 2018. It stayed there until November 13, 2019 for in situ observation and soil sample collection, and will return to the Earth in November or December 2020. During the stay at the asteroid, the spacecraft performed a touchdown operation successfully for the first time in February 2019. Since the surface of Ryugu was rough and full of boulders, a targeted area finally found had a radius of only 3 m. There were several technical challenges to overcome including demanding guidance, navigation and control accuracy to realise the touchdown operation. In this paper, strategies and technical details of the guidance, navigation and control systems are presented. The flight results prove that the performance of the systems was satisfactory and largely contributed to the success of the operation. • Hayabusa2 is a Japanese sample return mission from the near Earth asteroid Ryugu. • Hayabusa2 touched down to Ryugu successfully in February 2019. • Ryugu's surface was rough; guidance, navigation and control accuracy were demanding. • Guidance, navigation and control systems and strategies realised pinpoint touchdown. • Flight results prove satisfactory performance and final position error of only 1 m. [ABSTRACT FROM AUTHOR]

Abstract This paper presents the robust planning of the Hayabusa2-Ryugu proximity operation and landing site selection process considering unknown asteroid environment and the spacecraft constraints. The proximity operation scenario is described together with the relationship between the selection process and the in-situ observation. The mission constraints are summarized for the possible asteroid environment, including the rotation state, thermal condition and gravity. Highlights • Hayabusa2 proximity operation and "joint" landing site selection process are summarized. • A strategy of Ryugu proximity operation is discussed for a surface sampling. • Joint landing site selection process is constructed for sampling and landing sites. [ABSTRACT FROM AUTHOR]

Behavior of adult Parahucho perryi was examined using bio-logging and acoustic telemetry concurrently in the Bekanbeushi River system, eastern Hokkaido, Japan, in 2009 and 2010. Based on 46.1-87.9 h data from five P. perryi (69.0-80.0 cm fork length) caught from Lake Akkeshi, they used upstream ( n = 2), midstream ( n = 3), and downstream ( n = 4) habitats. Large variability in diel activity and depth occupation existed in each stream habitat; however, fish in the downstream habitat tended to be more active than those in the upper habitats and mainly occupied shallower depths than mean bottom depth in this habitat. [ABSTRACT FROM AUTHOR]

We report results of a laser link experiment between a laser altimeter called light detection and ranging (LIDAR) aboard Hayabusa2 and ground-based satellite laser ranging stations conducted when the spacecraft was near the Earth before and after the gravity assist operation. Uplink laser pulses from a ground station were successfully detected at a distance of 6.6 million km, and the field of view direction of the receiving telescope of the LIDAR was determined in the spacecraft frame. The intensities of the received signals were measured, and the link budget from the ground to the LIDAR was confirmed. By detecting two successive pulses, the pulse intervals from the ground-based station were transferred to the LIDAR, and the clock frequency offset was thus successfully calibrated based on the pulse intervals. The laser link experiment, which includes alignment measurement of the telescopes, has proven to be an excellent method to confirm the performance of laser altimeters before they arrive at their target bodies, especially for deep space missions. [ABSTRACT FROM AUTHOR]

This study was designed to evaluate changes in auditory brainstem response (ABR) in the course of auditory disturbance in rats induced by Kanamycin (KM). KM was administered subcutaneously to 12 CD (SD) male rats aged 6 weeks for 10 days at a dose of 800 mg/kg. Death was observed in one male on day 8 and 2 males on day 10. It was thought that kidney damage was the cause of death from histopathological findings. ABR was recorded before KM treatment and on days 4, 8, 10 and 11 after KM treatment. The ABR changes after KM treatment in rats were as follows. On day 4, 6 rats showed an increase in amplitude of waves I and/or II and on day 8, among those, 4 rats still showed a high amplitude of waves I and/or II. On day 8, 2 rats showed an elevation of ABR threshold (15-40 dB SPL) and a decrease in amplitude of wave I and increase in amplitude of wave II at the same time. On day 11, 7 rats showed a decrease in amplitude of wave I. In addition, ABR threshold shifts(10-70 dB SPL) were observed in those rats. In ABR recording, KM-induced auditory disturbance model rats showed an increase in amplitude of waves I and/or II earlier than an ABR threshold shift. By analyzing temporal alteration of amplitude of the ABR components, we could detect precursory phenomenon of the auditory disturbance at an early phase of treatment. By following the pathway of click-ABR and tone pip-ABR examination, the auditory disturbance of low-frequency to high-frequency range could be analyzed at an early date in detail. [ABSTRACT FROM AUTHOR]

Abstract: This paper introduces a new attitude control system for a solar sail, which leverages solar radiation pressure. This novel system achieves completely fuel-free and oscillation-free attitude control of a flexible spinning solar sail. This system consists of thin-film-type devices that electrically control their optical parameters such as reflectivity to generate an imbalance in the solar radiation pressure applied to the edge of the sail. By using these devices, minute and continuous control torque can be applied to the sail to realize very stable and fuel-free attitude control of the large and flexible membrane. The control system was implemented as an optional attitude control system for small solar power sail demonstrator named IKAROS (Interplanetary Kite-craft Accelerated by Radiation Of the Sun). In-orbit attitude control experiments were conducted, and the performance of the controller was successfully verified in comparison with the ground-based analytical performance estimation. [Copyright &y& Elsevier]

The swimming path of a reared Pacific bluefin tuna, Thunnus orientalis, was measured in a submerged aquaculture net cage to understand how reared fish use the space in such a cage. A bluefin tuna (fork length, FL, 0.51 m) was captured by angling in the cage, and two micro data loggers (PD3GT, Little Leonardo; DST Comp-Tilt, Star-Oddi) were attached to its body. The fish was then released back into the net cage. The PD3GT measured its swimming speed and depth at 1-s intervals and recorded these in flash memory. The DST Comp-Tilt measured the magnetic field strength at 1-s intervals and recorded the heading estimated from the magnetic field strength in flash memory. The fish moved through the water in the cage at speeds of 0.7–0.8 m s-1 and attained a maximum speed of 3.6 m s-1. Burst swims exceeding 2 m s-1 were confirmed only after dark and a significant difference was found between the daytime and night-time swimming speeds (p < 0.001). The fish moved at depths between 2 and 22 m, swimming near the bottom during the day and at 10–15 m at night, with a significant difference in swimming depth between day and night (p < 0.001). The swimming path reconstructed by dead reckoning was visualised using night-time data. For this period, the absolute speed was corrected from 0.75 ± 0.09 m s-1 to 0.71 ± 0.15 m s-1 by removing the accumulated error from the reconstruction vector. This study allowed us to examine the behaviour of a tagged tuna in three dimensions and is the first to monitor the behaviour of a bluefin tuna in a submerged net cage. Although only one fish was analysed, this study provides useful information on the space use of reared fish in aquaculture net cages. Future studies must obtain sufficient data to understand the underlying generalities of tuna behaviour. [ABSTRACT FROM PUBLISHER]

Analysis of high-frequency depth-recording data of adult Japanese flounder Paralichthys olivaceus (Temminck & Schlegel) with depth/temperature logging tags, released in the Tsugaru Strait of northern Japan, has yielded new insights into behavioural differences on vertical movement. Here, we document diel differences in fine-temporal-scale swimming behaviour observed from six flounder released during the no-spawning season. While the flounder remained on the seabed for the majority of the recording period, fish occasionally left the seabed, swam into the water column and then swam back to the seabed. The mean swimming duration per tagged fish ranged from 44 ± 49 to 94 ± 164 s, with a maximum observed swimming duration of 44.5 min. Vertical movements included one or more clear ascent and descent phases highlighted by a distinct peak. Our results reveal that in the no-spawning season nocturnal swimming is more active and frequent than during the day. Our results provide important information about diel differences in swimming behaviour with respect to vertical movement and also show the vulnerability of Japanese flounder to capture by bottom-fishing gear (e.g. trawling) during the day. [ABSTRACT FROM AUTHOR]

The asteroid explorer Hayabusa2 was launched by Japan Aerospace Exploration Agency (JAXA) on December 3rd, 2014. The primary mission of the spacecraft is to sample pieces of the asteroid and return it to Earth for more advanced scientific analysis on the Earth. After three-year cruise phase, Hayabusa2 finally arrived at the asteroid Ryugu on June 28, 2018, and mission operations started. Hayabusa2 carries multiple rovers, separates them to land on the asteroid surface. One of these rovers, called MASCOT, was developed under the international cooperation between Deutsches Zentrum für Luft-und Raumfahrt (DLR) and Center National d'études Spatiales (CNES). This rover was planned to be separated to land on the surface of the asteroid and planned to perform several missions on the asteroid surface. In order to support these missions, the mother ship Hayabusa2 was requested to separate this rover at a very low altitude about 50 ​m, and to hover about 3 ​km after separation to achieve a reliable communication link with MASCOT. On October 2–5, 2018, we performed the operation for MASCOT release. In this paper, we introduce the flight results of the entire operation for the MASCOT release. The asteroid explorer Hayabusa2 carries multiple rovers, separates them to land on the asteroid surface. One of these rovers, called MASCOT, was developed under the international cooperation between DLR (Deutsches Zentrum für Luft-und Raumfahrt) and CNES (Center national d'études spatiales). Flying MASCOT and its shadow taken by navigation camera of Hayabusa2 © JAXA, University of Tokyo, Kochi University, Rikkyo University, Nagoya University, Chiba Institute of Technology, Meiji University, University of Aizu, and AIST. [Display omitted] • Hayabusa2 carries several rovers and one lander. • The lander, named MASCOT, was developed under the international cooperation between DLR and CNES. • Mission of MASCOT is to perform several science missions on the asteroid surface. • Hayabusa2 successfully delivered the MASCOT onto the asteroid surface. [ABSTRACT FROM AUTHOR]

Asteroid 162,173 Ryugu is a rubble-pile asteroid, whose top-shape is compatible with models of deformation by spin up. Rims of major craters on Ryugu have an east–west asymmetric profile; their western crater rims are sharp and tall, while their eastern crater rims are rounded and low. Although there are various possible explanations, we theoretically assess the effect of asteroid rotation as the possible reason for this east–west asymmetry. It is known that the trajectories and fates of ejecta are affected by the rotation. The Coriolis force and the inertial speed of the rotating surface are the factors altering the ejecta trajectories. Consequently, we found that the east–west asymmetric crater rims might be formed as a result of rotation, when the inertial speed of the rotating surface is nearly equal to the first cosmic velocity of the body. In other words, it is possible that the observed east–west asymmetric rims of the Urashima, Cendrillon, and Kolobok craters were formed when Ryugu's rotation period was ~3.6 h. • Major craters on Ryugu have east–west asymmetric rims. • Effect of rotation assessed as the possible cause of the east–west asymmetry. • The effect creates the E -W asymmetry only if rotation period was less than 3.6 h. [ABSTRACT FROM AUTHOR]

Hayabusa-2, a JAXA mission, reached C-type asteroid (162173) Ryugu in June 2018. Hayabusa2 carried MASCOT (Ho et al., 2016), a small lander developed by DLR and CNES. The goal of MASCOT was to perform in situ measurements on the surface of the asteroid by means of its four scientific instruments, substantially contributing in this way to the overall scientific return of Hayabusa2 mission. MASCOT landing occurred the October 3, 2018. After its release by Hayabusa2 spacecraft, the MASCOT lander experienced 17 ​min of descent and bounces. Then after stabilization it collected measurements during 17 ​h, visiting three slightly different sites. A comprehensive knowledge of MASCOT's attitudes on the various moment of its mission is essential for the understanding of the science data gathered by the scout. CNES flight dynamics team was involved in the reconstruction of MASCOT landing trajectory and attitude. This paper presents the attitude reconstruction of MASCOT during its descent and on its second landing site. The reconstruction used as inputs the housekeeping data generated by the 6 Photo Electric Cells of MASCOT, as well as the images acquired by Hayabusa2 ONC camera and the MASCAM camera. The assessment was very complex but we determined the attitude with a mean accuracy around 10° during descent and 8° when MASCOT was stable once the second landing site was successfully reached. Nevertheless, for the other phases - bounces, first landing site and last landing site-the lander attitude is still undetermined. Reconstruction of attitude of MASCOT during its landing on asteroid Ryugu: Comparison between the real MASCAM images (A1, B1, C1) and the corresponding ones using the reconstructed attitude (A2, B2, C2). Image 1 [ABSTRACT FROM AUTHOR]

MASCOT, the Mobile Asteroid Surface SCOuT, is a small lander jointly developed by the German and French space agencies [Ho et al., 2017], that travelled on board of the JAXA Hayabusa2 spacecraft for over 3 years to the C-type asteroid Ryugu. The goal of MASCOT was to perform in situ measurements on the surface of the asteroid by means of its four scientific instruments, substantially contributing in this way to the overall scientific return of Hayabusa2 mission. The objective of the paper is to provide a detailed overview of the Landing Site Selection Process (LSSP) for MASCOT, from the preliminary design phase that started several years before launch, up to the actual execution of the selection process and its operational implementation. The effort that was put on the LSSP by all the teams involved over all these years was one of the key elements, leading to the unprecedented success of this mission. [ABSTRACT FROM AUTHOR]

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 188 cm 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, ∼ 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. [ABSTRACT FROM AUTHOR]