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Abstract Ryugu is the C-type asteroid from which material was brought to Earth by the Hayabusa2 mission. A number of individual grains and fine-grained samples analysed so far for noble gases have indicated that solar wind and planetary (known as P1) noble gases are present in Ryugu samples with concentrations higher than those observed in CIs, suggesting the former to be more primitive compared to the latter. Here we present results of analyses of three fine-grained samples from Ryugu, in one of which Xe concentration is an order of magnitude higher than determined so far in other samples from Ryugu. Isotopically, this Xe resembles P1, but with a much stronger isotopic fractionation relative to solar wind and significantly lower 36Ar/132Xe ratio than in P1. This previously unknown primordial noble gas component (here termed P7) provides clues to constrain how the solar composition was fractionated to form the planetary components.

Abstract Returned samples from the carbonaceous asteroid (162173) Ryugu provide pristine information on the original aqueous alteration history of the Solar System. Secondary precipitates, such as carbonates and phyllosilicates, reveal elemental partitioning of the major component ions linked to the primordial brine composition of the asteroid. Here, we report on the elemental partitioning and Mg isotopic composition (25Mg/24Mg) of breunnerite [(Mg, Fe, Mn)CO3] from the Ryugu C0002 sample and the A0106 and C0107 aggregates by sequential leaching extraction of salts, exchangeable ions, carbonates, and silicates. Breunnerite was the sample most enriched in light Mg isotopes, and the 25Mg/24Mg value of the fluid had shifted lower by ~0.38‰ than the initial value (set to 0‰) before dolomite precipitation. As a simple model, the Mg2+ first precipitated in phyllosilicates, followed by dolomite precipitation, at which time ~76−87% of Mg2+ had been removed from the primordial brine. A minor amount of phyllosilicate precipitation continued after dolomite precipitation. The element composition profiles of the latest solution that interacted with the cation exchange pool of Ryugu were predominantly Na-rich. Na+ acts as a bulk electrolyte and contributes to the stabilization of the negative surface charge of phyllosilicates and organic matter on Ryugu.

Abstract Primordial carbon delivered to the early earth by asteroids and meteorites provided a diverse source of extraterrestrial organics from pre-existing simple organic compounds, complex solar-irradiated macromolecules, and macromolecules from extended hydrothermal processing. Surface regolith collected by the Hayabusa2 spacecraft from the carbon-rich asteroid 162173 Ryugu present a unique opportunity to untangle the sources and processing history of carbonaceous matter. Here we show carbonaceous grains in Ryugu can be classified into three main populations defined by spectral shape: Highly aromatic (HA), Alkyl-Aromatic (AA), and IOM-like (IL). These carbon populations may be related to primordial chemistry, since C and N isotopic compositions vary between the three groups. Diffuse carbon is occasionally dominated by molecular carbonate preferentially associated with coarse-grained phyllosilicate minerals. Compared to related carbonaceous meteorites, the greater diversity of organic functional chemistry in Ryugu indicate the pristine condition of these asteroid samples.

Abstract We report primordial aqueous alteration signatures in water-soluble organic molecules from the carbonaceous asteroid (162173) Ryugu by the Hayabusa2 spacecraft of JAXA. Newly identified low-molecular-weight hydroxy acids (HO-R-COOH) and dicarboxylic acids (HOOC-R-COOH), such as glycolic acid, lactic acid, glyceric acid, oxalic acid, and succinic acid, are predominant in samples from the two touchdown locations at Ryugu. The quantitative and qualitative profiles for the hydrophilic molecules between the two sampling locations shows similar trends within the order of ppb (parts per billion) to ppm (parts per million). A wide variety of structural isomers, including α- and β-hydroxy acids, are observed among the hydrophilic molecules. We also identify pyruvic acid and dihydroxy and tricarboxylic acids, which are biochemically important intermediates relevant to molecular evolution, such as the primordial TCA (tricarboxylic acid) cycle. Here, we find evidence that the asteroid Ryugu samples underwent substantial aqueous alteration, as revealed by the presence of malonic acid during keto–enol tautomerism in the dicarboxylic acid profile. The comprehensive data suggest the presence of a series for water-soluble organic molecules in the regolith of Ryugu and evidence of signatures in coevolutionary aqueous alteration between water and organics in this carbonaceous asteroid.

Abstract Extraterrestrial minerals on the surface of airless Solar System bodies undergo gradual alteration processes known as space weathering over long periods of time. The signatures of space weathering help us understand the phenomena occurring in the Solar System. However, meteorites rarely retain the signatures, making it impossible to study the space weathering processes precisely. Here, we examine samples retrieved from the asteroid Ryugu by the Hayabusa2 spacecraft and discover the presence of nonmagnetic framboids through electron holography measurements that can visualize magnetic flux. Magnetite particles, which normally provide a record of the nebular magnetic field, have lost their magnetic properties by reduction via a high-velocity (>5 km s–1) impact of a micrometeoroid with a diameter ranging from 2 to 20 μm after destruction of the parent body of Ryugu. Around these particles, thousands of metallic-iron nanoparticles with a vortex magnetic domain structure, which could have recorded a magnetic field in the impact event, are found. Through measuring the remanent magnetization of the iron nanoparticles, future studies are expected to elucidate the nature of the nebular/interplanetary magnetic fields after the termination of aqueous alteration in an asteroid.

The chirality of amino acids in extraterrestrial materials may provide an insight into the origin of the essential l-enantiopure amino acids in the terrestrial biosphere. In 2020, the Hayabusa2 mission succeeded in bringing back surface materials from the C-type asteroid (162173) Ryugu to the Earth. Amino acids were one of the targeted organic molecules to be studied in the Ryugu samples. To analyze the various structural isomers of amino acids, which were expected to be present, from the limited amount of the returned samples, the development of a highly-sensitive and selective analytical method was necessary. In the present study, a three-dimensional high-performance liquid chromatography (3D-HPLC) system has been developed for the enantioselective determination of five proteinogenic and three non-proteinogenic amino acids in the Ryugu samples, in which amino acids in the sample were separated by reversed-phase, anion-exchange and enantioselective columns after the fluorescence derivatization with 4-fluoro-7-nitro-2,1,3-benzoxadiozole. The applicability of the analytical system to the extraterrestrial samples was evaluated by analyzing several types of carbonaceous meteorites before applying the system to the Ryugu samples. In the analysis of the Ryugu samples, all of the target amino acids were successfully determined quantitatively. Non-proteinogenic amino acids including 2-amino-n-butyric acid, isovaline and norvaline, rarely present in the terrestrial environment, were found as almost racemic mixtures with 47.1 to 55.2%l.

Abstract The sample from the near-Earth carbonaceous asteroid (162173) Ryugu is analyzed in the context of carbonaceous meteorites soluble organic matter. The analysis of soluble molecules of samples collected by the Hayabusa2 spacecraft shines light on an extremely high molecular diversity on the C-type asteroid. Sequential solvent extracts of increasing polarity of Ryugu samples are analyzed using mass spectrometry with complementary ionization methods and structural information confirmed by nuclear magnetic resonance spectroscopy. Here we show a continuum in the molecular size and polarity, and no organomagnesium molecules are detected, reflecting a low temperature and water-rich environment on the parent body approving earlier mineralogical and chemical data. High abundance of sulfidic and nitrogen rich compounds as well as high abundance of ammonium ions confirm the water processing. Polycyclic aromatic hydrocarbons are also detected in a structural continuum of carbon saturations and oxidations, implying multiple origins of the observed organic complexity, thus involving generic processes such as earlier carbonization and serpentinization with successive low temperature aqueous alteration.

Abstract Returned samples from Cb-type asteroid (162173) Ryugu exhibit very dark spectra in visible and near-infrared ranges, generally consistent with the Hayabusa2 observations. A critical difference is that a structural water absorption of hydrous silicates is around twice as deep in the returned samples compared with those of Ryugu’s surface, suggesting Ryugu surface is more dehydrated. Here we use laboratory experiments data to indicate the spectral differences between returned samples and asteroid surface are best explained if Ryugu surface has (1) higher porosity, (2) larger particle size, and (3) more space-weathered condition, with the last being the most effective. On Ryugu, space weathering by micrometeoroid bombardments promoting dehydration seem to be more effective than that by solar-wind implantation. Extremely homogeneous spectra of the Ryugu’s global surface is in contrast with the heterogeneous S-type asteroid (25143) Itokawa’s spectra, which suggests space weathering has proceeded more rapidly on Cb-type asteroids than S-type asteroids.

Abstract Samples from the carbonaceous asteroid (162173) Ryugu provide information on the chemical evolution of organic molecules in the early solar system. Here we show the element partitioning of the major component ions by sequential extractions of salts, carbonates, and phyllosilicate-bearing fractions to reveal primordial brine composition of the primitive asteroid. Sodium is the dominant electrolyte of the salt fraction extract. Anions and NH4 + are more abundant in the salt fraction than in the carbonate and phyllosilicate fractions, with molar concentrations in the order SO4 2− > Cl− > S2O3 2− > NO3 − > NH4 +. The salt fraction extracts contain anionic soluble sulfur-bearing species such as S n -polythionic acids (n

Abstract In the samples collected from the asteroid Ryugu, magnetite displays natural remanent magnetization due to nebular magnetic field, whereas contemporaneously grown iron sulfide does not display stable remanent magnetization. To clarify this counterintuitive feature, we observed their nanoscale magnetic domain structures using electron holography and found that framboidal magnetites have an external magnetic field of 300 A m−1, similar to the bulk value, and its magnetic stability was enhanced by interactions with neighboring magnetites, permitting a disk magnetic field to be recorded. Micrometer-sized pyrrhotite showed a multidomain magnetic structure that was unable to retain natural remanent magnetization over a long time due to short relaxation time of magnetic-domain-wall movement, whereas submicron-sized sulfides formed a nonmagnetic phase. These results show that both magnetite and sulfide could have formed simultaneously during the aqueous alteration in the parent body of the asteroid Ryugu.

Abstract We performed in-situ analysis on a ~ 1 mm-sized grain A0080 returned by the Hayabusa2 spacecraft from near-Earth asteroid (162173) Ryugu to investigate the relationship of soluble organic matter (SOM) to minerals. Desorption electrospray ionization-high resolution mass spectrometry (DESI-HRMS) imaging mapped more than 200 CHN, CHO, CHO–Na (sodium adducted), and CHNO soluble organic compounds. A heterogeneous spatial distribution was observed for different compound classes of SOM as well as among alkylated homologues on the sample surface. The A0080 sample showed mineralogy more like an Ivuna-type (CI) carbonaceous chondrite than other meteorites. It contained two different lithologies, which are either rich (lithology 1) or poor (lithology 2) in magnetite, pyrrhotite, and dolomite. CHN compounds were more concentrated in lithology 1 than in lithology 2; on the other hand, CHO, CHO–Na, and CHNO compounds were distributed in both lithologies. Such different spatial distribution of SOM is likely the result of interaction of the SOM with minerals, during precipitation of the SOM via fluid activity, or could be due to difference in transportation efficiencies of SOMs in aqueous fluid. Organic-related ions measured by time-of-flight secondary ion mass spectrometry (ToF–SIMS) did not coincide with the spatial distribution revealed by DESI-HRMS imaging. This result may be because the different ionization mechanism between DESI and SIMS, or indicate that the ToF–SIMS data would be mainly derived from methanol-insoluble organic matter in A0080. In the Orgueil meteorite, such relationship between altered minerals and SOM distributions was not observed by DESI-HRMS analysis and field-emission scanning electron microscopy, which would result from differences of SOM formation processes and sequent alteration process on the parent bodies or even on the Earth. Alkylated homologues of CHN compounds were identified in A0080 by DESI-HRMS imaging as observed in the Murchison meteorite, but not from the Orgueil meteorite. These compounds with a large C number were enriched in Murchison fragments with abundant carbonate grains. In contrast, such relationship was not observed in A0080, implying different formation or growth mechanisms for the alkylated CHN compounds by interaction with fluid and minerals on the Murchison parent body and asteroid Ryugu. Graphical Abstract

Abstract Hayabusa2 spacecraft successfully collected rock samples from the surface of C-type near-Earth asteroid 162173 Ryugu through two touchdowns and brought them back to Earth in 2020. At the Extraterrestrial Sample Curation Center in JAXA, we performed initial description of all samples to obtain fundamental information and prepare the database for sample allocation. We propose morphological classifications for the returned samples based on the initial description of 205 grains described in the first 6 months. The returned samples can be distinguished by four morphological characteristics: dark, glossy, bright, and white. According to coordinated study to provide an initial description and detailed investigation by scanning electron microscopy and X-ray diffraction analysis in this study, these features reflect the differences in the degree of space weathering and mineral assemblages. The degree of space weathering of the four studied grain types is heterogeneous: weak for A0042 (dark group) and C0041 (white group); moderate for C0094 (glossy); and severe for A0017 (bright). The white phase, which is the mineral characteristic of the white group grains, is identified as large carbonate minerals. This is the first effort to classify Ryugu returned samples into distinct categories. Based on these results, researchers can estimate sample characteristics only from the information on the JAXA curation public database. It will be an important reference for sample selection for further investigation. Graphical Abstract

Uracil was identified in the sample returned from the asteroid Ryugu. Having been provided to the early Earth as a component in such asteroidal materials, these molecules might have played a role for prebiotic chemical evolution on the early Earth

Amino acid concentrations from 2 particles returned from different touchdown sites on the surface of Ryugu are reported. Differences in chemistry suggest different levels of aqueous alteration are recorded at the 2 sampled locations.

Abstract Evaluating the molecular distribution of organic compounds in pristine extraterrestrial materials is cornerstone to understanding the abiotic synthesis of organics and allows us to better understand the molecular diversity available during the formation of our solar system and before the origins of life on Earth. In this work, we identify multiple organic compounds in solvent extracts of asteroid Ryugu samples A0106 and C0107 and the Orgueil meteorite using two-dimensional gas chromatography and time-of-flight high resolution mass spectrometry (GC×GC–HRMS). Our analyses found similarities between the molecular distribution of organic compounds in Ryugu and the CI carbonaceous chondrite Orgueil. Specifically, several PAHs and organosulfides were found in Ryugu and Orgueil suggesting an interstellar and parent body origin for these compounds. We also evaluated the common relationship between Ryugu, Orgueil, and comets, such as Wild-2; however, until comprehensive compound-specific isotopic analyses for these organic species are undertaken, and until the effects of parent body processes and Earth’s weathering processes on meteoritic organics are better understood, their parent–daughter relationships will remain unanswered. Finally, the study of organic compounds in Ryugu samples and the curation practices for the future preservation of these unvaluable materials are also of special interest for future sample return missions, including NASA’s OSIRIS-REx asteroid sample return mission. Graphical Abstract

Chondrule-like objects and CAIs in the Ryugu samples are early generations of chondrules and possibly oldest solids in the Solar System. They were transported from the inner solar nebula to the formation location of the Ryugu original parent body.

Abstract A fundamental parameter-based quantification scheme for confocal XRF was applied to sub-micron synchrotron radiation X-ray fluorescence (SR-XRF) data obtained at the beamline P06 of the Deutsches Elektronen-Synchrotron (DESY, Hamburg, Germany) from two sections C0033-01 and C0033-04 that were wet cut from rock fragment C0033 collected from Cb-type asteroid (162173) Ryugu by JAXA’s Hayabusa2 mission. Trace-element quantifications show that C0033 bulk matrix is CI-like, whereas individual mineral grains (i.e., magnetite, pyrrhotite, dolomite, apatite and breunnerite) show, depending on the respective phase, minor to strong deviations. The non-destructive nature of SR-XRF coupled with a new PyMca (a Python toolkit for XRF data analysis)-based quantification approach, performed in parallel with the synchrotron experiments, proves to be an attractive tool for the initial analysis of samples from return missions, such as Hayabusa2 and OSIRIS-REx, the latter returning material from a B-type asteroid (101955) Bennu in 2023. Graphical Abstract

Abstract Millimetre-sized primordial rock fragments originating from asteroid Ryugu were investigated using high energy X-ray fluorescence spectroscopy, providing 2D and 3D elemental distribution and quantitative composition information on the microscopic level. Samples were collected in two phases from two sites on asteroid Ryugu and safely returned to Earth by JAXA’s asteroid explorer Hayabusa2, during which time the collected material was stored and maintained free from terrestrial influences, including exposure to Earth’s atmosphere. Several grains of interest were identified and further characterised to obtain quantitative information on the rare earth element (REE) content within said grains, following a reference-based and computed-tomography-assisted fundamental parameters quantification approach. Several orders of magnitude REE enrichments compared to the mean CI chondrite composition were found within grains that could be identified as apatite phase. Small enrichment of LREE was found for dolomite grains and slight enrichment or depletion for the general matrices within the Ryugu rock fragments A0055 and C0076, respectively. Graphical Abstract

The analysis of samples returned from the C-type asteroid Ryugu has drastically advanced our knowledge of the evolution of early solar system materials. However, no consensus has been obtained on the chronological data, which is important for understanding the evolution of the asteroid Ryugu. Here, the aqueous alteration age of Ryugu particles was determined by the Mn–Cr method using bulk samples, yielding an age of 4.13 + 0.62/−0.55 Myr after the formation of Ca–Al-rich inclusions (CAI). The age corresponds to 4563.17 + 0.60/−0.67 Myr ago. The higher ^55 Mn/ ^52 Cr, ε ^54 Cr, and initial ε ^53 Cr values of the Ryugu samples relative to any carbonaceous chondrite samples implies that its progenitor body formed from the least thermally processed precursors in the outermost region of the protoplanetary disk. Despite accreting at different distances from the Sun, the hydrous asteroids (Ryugu and the parent bodies of CI, CM, CR, and ungrouped C2 meteorites) underwent aqueous alteration during a period of limited duration (3.8 ± 1.8 Myr after CAI). These ages are identical to the crystallization age of the carbonaceous achondirtes NWA 6704/6693 within the error. The ε ^54 Cr and initial ε ^53 Cr values of Ryugu and NWA 6704/6693 are also identical, while they show distinct Δ' ^17 O values. This suggests that the precursors that formed the progenitor bodies of Ryugu and NWA 6703/6693 were formed in close proximity and experienced a similar degree of thermal processing in the protosolar nebula. However, the progenitor body of Ryugu was formed by a higher ice/dust ratio, than NWA6703/6693, in the outer region of the protoplanetary disk.

The nucleosynthetic isotope composition of planetary materials provides a record of the heterogeneous distribution of stardust within the early solar system. In 2020 December, the Japan Aerospace Exploration Agency Hayabusa2 spacecraft returned to Earth the first samples of a primitive asteroid, namely, the Cb-type asteroid Ryugu. This provides a unique opportunity to explore the kinship between primitive asteroids and carbonaceous chondrites. We report high-precision μ ^26 Mg* and μ ^25 Mg values of Ryugu samples together with those of CI, CM, CV, and ungrouped carbonaceous chondrites. The stable Mg isotope composition of Ryugu aliquots defines μ ^25 Mg values ranging from –160 ± 20 ppm to –272 ± 30 ppm, which extends to lighter compositions relative to Ivuna-type (CI) and other carbonaceous chondrite groups. We interpret the μ ^25 Mg variability as reflecting heterogeneous sampling of a carbonate phase hosting isotopically light Mg ( μ ^25 Mg ∼ –1400 ppm) formed by low temperature equilibrium processes. After correcting for this effect, Ryugu samples return homogeneous μ ^26 Mg* values corresponding to a weighted mean of 7.1 ± 0.8 ppm. Thus, Ryugu defines a μ ^26 Mg* excess relative to the CI and CR chondrite reservoirs corresponding to 3.8 ± 1.1 and 11.9 ± 0.8 ppm, respectively. These variations cannot be accounted for by in situ decay of ^26 Al given their respective ^27 Al/ ^24 Mg ratios. Instead, it requires that Ryugu and the CI and CR parent bodies formed from material with a different initial ^26 Al/ ^27 Al ratio or that they are sourced from material with distinct Mg isotope compositions. Thus, our new Mg isotope data challenge the notion that Ryugu and CI chondrites share a common nucleosynthetic heritage.

Rock fragments of the Cb-type asteroid Ryugu returned to Earth by the JAXA Hayabusa2 mission share mineralogical, chemical, and isotopic properties with the Ivuna-type (CI) carbonaceous chondrites. Similar to CI chondrites, these fragments underwent extensive aqueous alteration and consist predominantly of hydrous minerals likely formed in the presence of liquid water on the Ryugu parent asteroid. Here we present an in situ analytical survey performed by secondary ion mass spectrometry from which we have estimated the D/H ratio of Ryugu’s hydrous minerals, D/H _Ryugu , to be [165 ± 19] × 10 ^−6 , which corresponds to δ D _Ryugu = +59 ± 121‰ (2 σ ). The hydrous mineral D/H _Ryugu ’s values for the two sampling sites on Ryugu are similar; they are also similar to the estimated D/H ratio of hydrous minerals in the CI chondrites Orgueil and Alais. This result reinforces a link between Ryugu and CI chondrites and an inference that Ryugu’s samples, which avoided terrestrial contamination, are our best proxy to estimate the composition of water at the origin of hydrous minerals in CI-like material. Based on this data and recent literature studies, the contribution of CI chondrites to the hydrogen of Earth’s surficial reservoirs is evaluated to be ∼3%. We conclude that the water responsible for the alteration of Ryugu’s rocks was derived from water ice precursors inherited from the interstellar medium; the ice partially re-equilibrated its hydrogen with the nebular H _2 before being accreted on the Ryugu’s parent asteroid.

Both poles of asteroid Ryugu, the target of space mission Hayabusa2, preserve the least processed material by space weathering. Here, the authors show detection of 700 nm absorption band in the polar spectra of Ryugu, that allows to constrain the hydrothermal history of its spectrally blue parent body.

Abstract In this study, we determined the alignment of the laser altimeter aboard Hayabusa2 with respect to the spacecraft using in-flight data. Since the laser altimeter data were used to estimate the trajectory of the Hayabusa2 spacecraft, the pointing direction of the altimeter needed to be accurately determined. The boresight direction of the receiving telescope was estimated by comparing elevations of the laser altimeter data and camera images, and was confirmed by identifying prominent terrains of other datasets. The estimated boresight direction obtained by the laser link experiment in the winter of 2015, during the Earth’s gravity assist operation period, differed from the direction estimated in this study, which fell on another part of the candidate direction; this was not selected in a previous study. Assuming that the uncertainty of alignment determination of the laser altimeter boresight was 4.6 pixels in the camera image, the trajectory error of the spacecraft in the cross- and/or along-track directions was determined to be 0.4, 2.1, or 8.6 m for altitudes of 1, 5, or 20 km, respectively.

Abstract The precise orbit of the Hayabusa2 spacecraft with respect to asteroid Ryugu is dynamically determined using the data sets collected by the spacecraft’s onboard laser altimeter (LIght Detection And Ranging, LIDAR) and automated image tracking (AIT). The LIDAR range data and the AIT angular data play complementary roles because LIDAR is sensitive to the line-of-sight direction from Hayabusa2 to Ryugu, while the AIT is sensitive to the directions perpendicular to it. Using LIDAR and AIT, all six components of the initial state vector can be derived stably, which is difficult to achieve using only LIDAR or AIT. The coefficient of solar radiation pressure (SRP) of the Hayabusa2 spacecraft and standard gravitational parameter (GM) of Ryugu can also be estimated in the orbit determination process, by combining multiple orbit arcs at various altitudes. In the process of orbit determination, the Ryugu-fixed coordinate of the center of the LIDAR spot is determined by fitting the range data geometrically to the topography of Ryugu using the Markov Chain Monte Carlo method. Such an approach is effective for realizing the rapid convergence of the solution. The root mean squares of the residuals of the observed minus computed values of the range and brightness-centroid direction of the image are 1.36 m and 0.0270°, respectively. The estimated values of the GM of Ryugu and a correction factor to our initial SRP model are 29.8 ± 0.3 m3/s2 and 1.13 ± 0.16, respectively.

We present oxygen isotopic analyses of fragments of the near-Earth C _b -type asteroid Ryugu returned by the Hayabusa2 spacecraft that reinforce the close correspondence between Ryugu and CI chondrites. Small differences between Ryugu samples and CI chondrites in ${{\rm{\Delta }}}^{{\prime} 17}{\rm{O}}$ can be explained at least in part by contamination of the latter by terrestrial water. The discovery that a randomly sampled C-complex asteroid is composed of CI-chondrite-like rock, combined with thermal models for formation prior to significant decay of the short-lived radioisotope ^26 Al, suggests that if lithified at the time of alteration, the parent body was small (≪50 km radius). If the parent planetesimal was large (>50 km in radius), it was likely composed of high-permeability, poorly lithified sediment rather than consolidated rock.

Asteroid Explorer Hayabusa2 arrived at asteroid Ryugu in June of 2018. During its stay around Ryugu, Hayabusa2 will undertake several challenging missions such as collecting soil samples and deploying rovers, a lander, and an impactor. Before the spacecraft attempts these missions, our initial and most important work is to reveal the asteroid’s characteristics and properties. Science equipment is used to obtain data for use in making an asteroid model and for the landing site selection (LSS) of sample soil collection and rover/lander deployment. The LSS requires surface images taken from an altitude of around 5 km. Middle altitude observation was the operation needed to meet this requirement. This paper presents an overview of the operation, design, and study of hovering at a 5-km altitude from the surface, and specifically describes the RHC hovering method and Monte Carlo analysis of hovering trajectory and dV. It also describes the actual operation results. [ABSTRACT FROM AUTHOR]

This paper presents an overview of a guidance, navigation and control method used in descent operations of Hayabusa2. The method consists of on-board and on-ground guidance systems to control the spacecraft, and an image-based navigation technique using a shape model and ground control points of the asteroid. Hayabusa2 has performed descent operations 11 times as of mid-April 2019. Flight results of the operations demonstrate that the guidance, navigation and control system has satisfied accuracy requirements and shown an overall good performance. [ABSTRACT FROM AUTHOR]

Hayabusa2 is a Japanese asteroid explorer launched by the H-IIA rocket on Dec. 3, 2014. After the long cruising with the ion engine system, the spacecraft approached its target body, Ryugu, using optical navigation. It arrived at Home Position (HP), 20 km above the sub-Earth point, on Jun. 27, 2018. The spacecraft is now on its way back to Earth. It will reach the Earth by the end of 2020. During the 1.5-year asteroid proximity phase, we performed many kinds of science observations using the remote sensing instruments. We performed several numbers of descent operations to deploy and lander/rovers, to collect the surface samples, and to create an artificial crater using a new small kinetic impactor. Detailed operation planning of the asteroid proximity phase started after the launch, and lots of training for the proximity phase were conducted from one year before the arrival. This paper summarizes the overview of the asteroid proximity operation plan of Hayabusa2 and its preliminary results. [ABSTRACT FROM AUTHOR]

Hayabusa2 arrived at the asteroid Ryugu in June 2018, and as of April 2019, the mission succeeded in conducting two rovers landing, one lander landing, one spacecraft touchdown/sample collection and one kinetic impact operation. This paper describes the initial nine months of the asteroid proximity operation activity of the Hayabusa2 mission, and gives an overview of the achievements thus far. Some important engineering and scientific activities conducted synchronously with spacecraft operations in order to complete all planned operations in time against unexpectedly harsh environment of Ryugu are also described. [ABSTRACT FROM AUTHOR]

Hayabusa2 is a Japanese sample return mission from the asteroid Ryugu. The Hayabusa2 spacecraft was launched on 3 December 2014, arrived at Ryugu on 27 June 2018. It will stay in proximity of Ryugu until December 2019 for in situ observation and soil sample collection aiming to return to the Earth in December 2020 with the collected sample. During the 1.5-year asteroid proximity operation, the spacecraft performs several numbers of descent operation to deploy and land rovers, and to touchdown collecting soil sample. To obtain large amount of various data during asteroid proximity operation, data downlink from Hayabusa2 is realized using two high gain antennas (HGAs) which are designated to X-band (8GHz) downlink and Ka-band (32GHz) downlink respectively. This paper summarizes Ka-band capability of Hayabusa2 and its contribution to asteroid proximity operation including the Landing Site Selection (LSS) activity. Also, feedbacks for Ka-band equipped future deep space mission are extracted based on the comparison between X/Ka-band operation results. [ABSTRACT FROM AUTHOR]

Hayabusa2 is a current sample return mission spacecraft developed by JAXA. One of the most important scientific objectives of Hayabusa2 is to investigate the chemical and physical properties of the internal materials and structures of the asteroid Ryugu. To achieve this goal, we developed a new device called the small carry-on impactor (SCI). The SCI is a kinetic impactor that is being used to create an artificial crater on the surface of Ryugu. It has no attitude or orbit control device. The helical spring in the separation mechanism provides both separation force and spin torque to the SCI. The impact accuracy of the SCI depends heavily on the separation accuracy. Repeating a large number of separation tests is a straightforward approach to evaluate the separation accuracy. However, that is not realistic. Hence, first we performed several element tests to understand the separation dynamics. Then, the final separation accuracy was evaluated through a small number of separation tests, and this was followed by simulations that used the results of the element tests. This paper provides an overview of the separation mechanism, the results of development testing analyzed in detail, and a summary of the separation performance. [ABSTRACT FROM AUTHOR]

On-board orbit determination (OD) using directions of celestial bodies, planets and asteroids, in the Solar System for the Autonomous Navigation (AutoNav) is introduced in this paper. For deep space missions, OD has been performed by Range and Range- Rate (RARR), which is a traditional ground tracking approach by radio waves. RARR enables the higher accuracy of OD than other methods. However, such radio navigation has the inevitable problems, such as strength reduction of radio waves and the transmitter limitation. Furthermore, people must stay and operate the spacecraft on the ground station, which makes the operating cost and burden considerable. Therefore, there has been a growing interest in the autonomy of the spacecraft in recent years to avoid the above-mentioned problems. This paper considers on-board OD using directions of celestial bodies from spacecraft. In particular, the selection of target bodies to observe is focused on because it's important that the selection of such target bodies leads to the satisfaction of mission requirements or increment of scientific observation. Then, this paper presents the method for the target selection, which is computationally cheap and makes the target selection easy. [ABSTRACT FROM AUTHOR]

The Martian Moons eXplorer, the objective of which is to obtain a sample from a Martian moon, was presented by the Institute of Space and Astronautical Science and the Japan Aerospace Exploration Agency. For its trajectory design, some configurations of a propulsion system were considered using a comparison of the fuel efficiency and total mission time. The use of chemical and electric propulsion for its return trajectory was introduced in order to realize a fast and low-energy escape from Mars. In this configuration, the spacecraft departs from Mars using three-body dynamics with chemical propulsion and using electric propulsion for a v-infinity leveraging maneuver (VILM). In this paper, we first propose the modified all-three-body method, which constructs the escape and VILM trajectories using three-body dynamics to obtain the chemical-electric hybrid-propulsion return trajectory. We then propose the integrated three-and-two-body method, which uses three-body dynamics at the edge of the sphere of influence and integrates it into two-body dynamics in order to use a two-body-based low-thrust optimizer. A comparison of the integrated three-and-two-body methods and modified all-three-body method is performed. Furthermore, the patched conics method is used to compare the optimized solution obtained using the two-body and three-body dynamics. [ABSTRACT FROM AUTHOR]

The solar power sail is an original Japanese concept in which electrical power is generated by thin-film solar cells on the sail membrane. It can generate sufficient electric power to drive the high-specific ion engines in the outer planetary region. We propose a landing or sample return mission to explore a Jupiter Trojan asteroid directly using solar power sail. After rendezvousing with a Trojan asteroid, a lander separates from the solar power sail-craft to collect surface and underground samples, and perform an in-situ analysis in Plan-A/B. In addition, the lander delivers samples to the solar power sail-craft to return the sample in Plan-B. This paper shows a system design for the solar power sail-craft and introduces the latest mission analysis. [ABSTRACT FROM AUTHOR]

This paper describes a method of modeling general attitude dynamics of a nonspinning momentum-biased spacecraft under strong influence of solar radiation pressure. This model, called the "generalized sail dynamics model," can be applied to realistic solar sail spacecraft with nonflat surfaces and nonuniform optical reflectance. A coarse sun-pointing momentum-biased spacecraft is especially of interest, for which an approximate solution of the equations of motion is analytically derived. Stability and fundamental characteristics of momentum-biased spacecraft dynamics as well as theoretical relations with past dynamics models are discussed in detail. Furthermore, unique attitude motion predicted by the novel model is verified with flight data of the Japanese interplanetary probe, Hayabusa 2. [ABSTRACT FROM AUTHOR]

The solar power sail can generate sufficient electric power to drive the high specific ion engine in the outer planetary region by thin-film solar cells attached to the entire surface of the spin-type solar sail. This paper proposes the direct exploration of the outer planetary region using solar power sail-craft. The target is an unexplored D/P-type Jovian Trojan asteroid. A lander is separated from the solar power sail-craft to collect surface and underground samples of the Trojan asteroid and perform in-situ analysis. The lander delivers samples to the solar power sail-craft for sample return to Earth as optional goal. Scientific observations during the interplanetary cruise are also implemented. [ABSTRACT FROM AUTHOR]

This paper presents the extended missions of the IKAROS solar sail interplanetary spacecraft. IKAROS entered an extended operation phase at the beginning of 2011. During this phase, its spin rate was reduced to observe deformation of the sail membrane under low centrifugal forces, and on Oct. 18, 2011 the spin was reversed to enhance knowledge of the membrane’s stiffness against solar radiation pressure. We also investigated changes in IKAROS's attitude motions under reverse spin conditions. At the end of 2011, IKAROS switched to hibernation mode due to an increased Sun angle reducing on-board electricity generation. We later searched for IKAROS considering its attitude and orbital motion during hibernation, and on Sep. 6, 2012, we succeeded in locating the spacecraft, which came out of hibernation. A solar power sail can be part of a hybrid propulsion system, with electrical power generated by thin-film solar cells on a solar sail membrane being used to operate ultra-high specific impulse ion engines. This paper also introduces a follow-on mission to IKAROS, a round trip to the Trojan asteroid using hybrid electric photon propulsion. [ABSTRACT FROM AUTHOR]

A kinetic impact to the asteroid 1999 JU3 by a 300kg-class impactor spacecraft is studied. This study is a part of conceptual studies conducted within the mission design of “Hayabusa-2”, the second Japanese asteroid sample-return mission. In contrast with the finally selected “Small Carry-on Impactor(SCI)” concept, the present paper shows a feasibility of a different option, the kinetic impact by a 300kg class dedicated spacecraft. This option is valuable in terms of its scientific outcome, as the impact energy is 100 times larger than the current SCI concept. This paper discusses the feasibility of the terminal impact guidance and navigation using an onboard optical telescope. The study assumes a ground operator-in-the-loop guidance scheme, which is deemed to be the lowest development risk within the limited schedule before launch. It is shown that the ground-based terminal guidance is achievable with the accuracy of 200-300m with a realistic amount of fuel and operational load. [ABSTRACT FROM AUTHOR]

An attitude model for a general spinning solar sail spacecraft under the influence of solar radiation pressure is presented. This model, called "Generalized Spinning Sail Model", can be applied to realistic sails with nonflat surfaces that have nonuniform optical properties. The unique behaviors predicted by the generalized spinning sail model are verified by actual operation of the Japanese spinning solar sail spacecraft IKAROS. It is shown how imperfections in the sail surface affect the attitude motion of spinning sails, and a compact mathematical model that can precisely reproduce the spin-averaged motion of the spinning sails is derived. The stability conditions and a reduced model that preserves the key characteristics of the generalized spinning sail model are also derived to reveal the unique properties of the attitude behavior of spinning sails. [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]

This paper describes the modeling, dynamical characteristics, and implementation of an attitude control method that actively uses solar radiation pressure. The theory behind this control method is called the generalized sail dynamics model, which was developed by the authors and successfully applied to Hayabusa2, which is a Japanese asteroid explorer launched in 2014. The quasi-stable property of the dynamics is proved, which enables the implementation of a fuel-free sun-tracking attitude using only one reaction wheel. As of August 2016, the attitude of Hayabusa2 was maintained within 10 deg offset from the sun direction for 193 days in total without consuming any fuel. The auto-sun tracking, single-wheel, and fuel-free features were distinctive as compared to any other conventional control methods, such as three-axis stabilization, and brought many merits to practical spacecraft operations. The theoretical background, the prelaunch evaluation based on a finite element model analysis, the identification process of the dynamics model carried out for the Hayabusa2 mission operation, and their effectiveness are presented in this paper. [ABSTRACT FROM AUTHOR]

Deployable payloads have been used to expand mission opportunities and enable autonomous navigation and guidance under uncertain terrain conditions. A spacecraft may deploy an artificial marker toward the surface of the target body. An estimation of the deployment trajectory of markers can provide important information for guidance and navigation. We propose a method estimating the deployment trajectory using only images and evaluate its accuracy and reliability. In addition, to determine the spacecraft's relative attitude with respect to the asteroid surface, we introduce an attitude estimation method using the spacecraft's own shadow. The results shown in this paper confirm that the estimated trajectory is sufficiently accurate and thus the proposed method is a viable option for future missions for determining the trajectory of deployable payloads using only images of a deployment. [ABSTRACT FROM AUTHOR]

This research focuses on the design and reconstruction of the first touchdown of Hayabusa2 on the asteroid Ryugu. Because of the plethora of boulders, the landing operation required high accuracy to ensure spacecraft safety. This paper therefore investigates a pinpoint touchdown sequence using a retroreflective marker as an artificial landmark. First, the dynamical environment in the vicinity of Ryugu is explored for precise trajectory analyses; particularly, the irregular gravitational field around Ryugu is computed, which has an impact on the spacecraft motion. Based on the dynamics model, the touchdown trajectory used to land on the selected landing site with a radius of 2.8 m is designed. This process is followed by landing dispersion analyses, validating the feasibility of the touchdown sequence. As a result, the Hayabusa2 spacecraft successfully landed on the asteroid Ryugu on 21 February 2019. This paper further provides trajectory reconstruction results based on actual flight data, revealing that the achieved landing accuracy was 1 m. Consequently, this work demonstrates the performance of the proposed precision landing strategy and expands the capabilities of small-body missions. [ABSTRACT FROM AUTHOR]