Japan Aerospace Exploration Research Articles

The noble gas and nitrogen relationship between Ryugu and carbonaceous chondrites

Carbonaceous chondrites are considered to have originated from C-type asteroids and represent some of the most primitive material in our solar system. Furthermore, since carbonaceous chondrites can contain significant quantities of volatile elements, they may have played a crucial role in supplying volatiles and organic material to Earth and other inner solar system bodies. However, a major challenge of unravelling the volatile composition of chondritic meteorites is distinguishing between which features were inherited from the parent body, and what may be a secondary feature attributable to terrestrial weathering. In December 2020, the Hayabusa2 mission of the Japan Aerospace Exploration Agency (JAXA) successfully returned surface material from the C-type asteroid (162173) Ryugu to Earth. This material has now been classified as closely resembling CI-type chondrites, which are the most chemically pristine meteorites. The analysis of material from the surface of Ryugu therefore provides a unique opportunity to analyse the volatile composition of material that originated from a CI-type asteroid without the complications arising from terrestrial contamination. Given their highly volatile nature, the noble gas and nitrogen inventories of chondrites are highly sensitive to different alteration processes on the asteroid parent body, and to terrestrial contamination. Here, we investigate the nitrogen and noble gas signature of two pelletized grains collected from the first and second touchdown sites (Okazaki et al., 2022a), to provide an insight into the formation and alteration history of Ryugu. The concentration of trapped noble gas in the Ryugu samples is greater than the average composition of previously measured CI chondrites and are primarily derived from phase Q, although a significant contribution of presolar nanodiamond Xe-HL is noted. The large noble gas concentrations coupled with a significant contribution of presolar nanodiamonds suggests that the Ryugu samples may represent some of the most primitive unprocessed material from the early solar system. In contrast to the noble gases, the abundance of nitrogen and δ15N composition of the two Ryugu pellets are lower than the average CI chondrite value. We attribute the lower nitrogen abundances and δ15N measured in this study to the preferential loss of a 15N-rich phase from our samples during aqueous alteration on the parent planetesimal. The analyses of other grains returned from Ryugu have shown large variations in nitrogen concentrations and δ15N indicating that alteration fluids heterogeneously interacted with material now present on the surface of Ryugu. Finally, the ratio of trapped noble gases to nitrogen is higher than CI chondrites, and is closer to refractory phase Q and nanodiamonds. This indicates that Ryugu experienced aqueous alteration that led to the significant and variable loss of nitrogen, likely from soluble organic matter, without modification of the noble gas budget, which is primarily hosted in insoluble organic matter and presolar diamonds and is therefore more resistant to aqueous alteration.

Characterization of oscillation modes in levitated droplets using image and non-image based techniques

The dynamics of levitated liquid droplets can be used to measure their thermophysical properties by correlating the frequencies at which normal modes of oscillation most strongly resonate when subject to an external oscillatory force. In two preliminary works, it was shown via electrostatic levitation and processing of various metals and alloys that (1) the resonance of the first principal mode of oscillation (mode n = 2) can be used to accurately measure surface tension and (2) that so-called “higher-order resonance” of n = 3 is observable at a predictable frequency. It was also shown, in the context of future space-based experimentation on the Electrostatic Levitation Furnace (ELF), a setup on the International Space Station (ISS) operated by Japan Aerospace Exploration Agency (JAXA), that while the shadow array method in which droplet behavior is visualized would be challenging to identify the n = 3 resonance, the normal mode n = 4 was predicted to be more easily identifiable. In this short communication, experimental evidence of the first three principal modes of oscillation is provided using molten samples of Tin and Indium and it is subsequently shown that, as predicted, an “image-less" approach can be used to identify both n = 2 and n = 4 resonances in levitated liquid droplets. This suggests that the shadow array method may be satisfactorily used to obtain a self-consistent benchmark of thermophysical properties by comparing results from two successive even-mode natural frequencies.

Evaluating the effect of the incidence angle of ALOS-2 PALSAR-2 on detecting aquaculture facilities for sustainable use of coastal space and resources.

Driven by the growing world population, aquaculture plays a key role in meeting the increasing demand for food. However, aquaculture facilities in Japan are widely installed in coastal waters where natural disasters, such as typhoons and tsunamis, might wash these facilities away, thereby interfering with maritime navigation safety. Therefore, it is imperative to efficiently monitor the state of aquaculture facilities daily, particularly after a disaster in real time. To this end, several new space-borne L-band synthetic aperture radars (SARs) continue to be launched now and in the future, whose utilizations are expected to increase nationally and internationally. An example is the Japan Aerospace Exploration Agency, currently operating a SAR that can be operated day and night, and even under cloudy conditions, called ALOS-2 PALSAR-2. Based on the above facts, this study evaluated the effect of the incidence angle of ALOS-2 PALSAR-2 HH single-polarization data, using 3 m spatial resolution, on aquaculture raft detection. As the study site, we selected Ago Bay, located on the Pacific coast of Mie Prefecture in central Japan since the Nankai Trough Megathrust Earthquake and tsunamis have been predicted to occur in the future around this area. Then, we analyzed the sigma zero (backscattering coefficient) of aquaculture rafts and their surrounding sea surfaces, including the relationships between satellite orbits and aquaculture raft directions. Investigations revealed that the optimum incidence angle for detecting aquaculture rafts in this study was 33.8°-45.1°. Differences in the sigma zero values existed between the ascending and descending orbits. However, the incidence angles differed on the orbits. Then, differences in the median sigma zero values across a range of incidence angles were evaluated under the descending orbit. In addition, when the directions of the aquaculture rafts were closely perpendicular to the satellite orbit, aquaculture rafts tended to show the highest values of sigma zero due to Bragg resonance scattering. Hence, this knowledge may allow for the rapid detection of aquaculture rafts during an emergency without going on-site.

Flight-to-Wind-Tunnel Correlation Study using JAXA’s Flying Test Bed “Hisho”

Predicting aircraft flight performance using ground tests is important for development but difficult, and flight-to-wind-tunnel correlation methods have been developed and improved over many years. This paper examines the flight-to-wind-tunnel correlation of the aerodynamic characteristics of the Japan Aerospace Exploration Agency’s (JAXA) “Hisho” Flying Test Bed by applying typical methods to flight test data. It was found that the minimum drag coefficient of a business jet geometry test model follows the gradient of the Schoenherr equation well for forced turbulent flows. After that, the reference condition for the correlation was set, but discrepancies in the lift and drag coefficients remained between the flight and wind tunnel tests. A preliminary study identified force differences parallel to the axis of the engine nacelle as being caused by spillage drag due to the difference in the capture area ratio (CAR) between the flight and wind tunnel tests. However, the test data were insufficient to reasonably attribute the difference in the normal force component to lift yielded by the engine nacelle. This was due to the fact that the flight test parameters showed an interdependency and the effects of relevant parameters were not fully investigated in wind tunnel tests.

Mapping Australia’s precipitation: harnessing the synergies of multi-satellite remote sensing and gauge network data

ABSTRACT Coverage, resolution, and accuracy in the spatial and temporal estimates of remotely sensed precipitation from space satellites, along with the number of instruments deployed to deliver these observations, are increasing. Of key interest in this study is the unsurpassed opportunity offered by their broad and continuous coverage to complement sparse, but more accurate, in situ rain gauge measurements for building climate resilience at the local, regional, and global scales. For many parts of the globe, this opportunity remains untapped. Australia is no exception and provides a unique challenge, given the small fraction of the continent that has rain gauges, the highly diverse climate due to its large size, and the apparent worsening of extreme weather events in both frequency and intensity. Notwithstanding this great impetus, a continent-wide record of multi-satellite-gauge fused precipitation data for Australia remains lacking. This missing data asset is a prerequisite for understanding the emerging spatiotemporal dynamics of precipitation, without which reliable forecasts would be difficult if not impossible. This study seeks to address this need. Here, we develop a method which can synergistically fuse precipitation data from different sources. More specifically, the aim of this study is to develop Precipitation Profiler-Observation Fusion and Estimation (PPrOFusE), a tool to deliver high-quality gauge and multi-satellite fused precipitation data. We test and apply this tool for Australia, but it is by no means limited in scope to this region. By design, PPrOFusE has a built-in capability to assess the strengths and weaknesses of each platform. In this case study, we fused data for a period of 22 years (2000–2022) using the rain gauge network data from the Australian Bureau of Meteorology (BOM) together with satellite data from the Japan Aerospace Exploration Agency’s (JAXA) Global Satellite Mapping of Precipitation (GSMaP) and National Oceanic and Atmospheric Administration’s (NOAA) Climate Prediction Center Morphing technique (CMORPH). Our proposed precipitation data fusion method consists of two steps. Step 1, the relationship among the three sources of data is modeled by multiple linear regression at each rain gauge location, returning the least squares estimates for the associated regression coefficient vector. Step 2, such regression coefficient vector estimates for all rain gauge locations are fitted by a spatial autoregression model, whereafter the multiple linear regression coefficient vectors for those locations void of rain gauges are predicted by spatial interpolation. Key findings are twofold. First, CMORPH is more accurate for most regions of Australia than GSMaP. Second, a clustering analysis of the fused precipitation over the last 20 years suggests two key trends on Australia’s changing climate, relative to BOM’s six major climate zones, from the previous century: (a) increased spatial variability to the north, consistent with meteorological expectations, amid a southwards expansion of the wet summer dominant zones across the continent; (b) the edge of the arid region shifts southwards and pushes out Mediterranean climate and winter dominant rainfall zones across southern Australia.

Control algorithm for a 6 kW hall thruster

This paper presents a control algorithm for ensuring the stable operation of a 6 kW Hall thruster. The Japan Aerospace Exploration Agency is developing a “wide-range” power processing unit (PPU) to power a 6 kW Hall thruster system, a candidate for all-electric satellites. The PPU provides discharge oscillation, power, and discharge current control. The increments in the control loop are fixed, so the PPU digital controller does not need to calculate them, and the algorithm’s computational complexity is minimal. Results of integration tests on the 6 kW Hall thruster and the PPU breadboard model showed that the three control functions run correctly. The total controlled PPU power was adjusted in the range of 3.45–3.55 kW under constant power control with a target of 3.5 kW. Oscillations of ± 0.05 kW around the target power are acceptable. 70% of the peaks in the discharge current acquired for 100 ms exceeded the limit of 1.5A. Discharge oscillation control varied the coil magnetic field and reduced them to 0%. The PPU successfully controlled the coil current, reducing the discharge current from 13.7 A to 13 A. The propulsion efficiency increased from 59% to 60.5%.

Performance assessment of RTPPP positioning with SSR corrections and PPP-AR positioning with FCB for multi-GNSS from MADOCA products

The state-space representation (SSR) product of satellite orbit and clock is one of the most essential corrections for real-time precise point positioning (RTPPP). When it comes to PPP ambiguity resolution (PPP-AR), the fractional cycle bias (FCB) matters. The Japan Aerospace Exploration Agency (JAXA) has developed a multi-GNSS (i.e., global navigation satellite system) advanced demonstration tool for orbit and clock analysis (MADOCA), providing free and precise orbit and clock products. Because of the shortage of relevant studies on performance evaluation, this paper focuses on the performance assessment of RTPPP and PPP-AR by real-time and offline MADOCA products. To begin with, the real-time MADOCA products are evaluated by comparing orbit and clock with JAXA final products, which gives an objective impression of the correction. Second, PPP tests in static and simulated kinematic mode are conducted to further verify the quality of real-time MADOCA products. Finally, the offline MADOCA products are assessed by PPP and PPP-AR comparisons. The results are as follows: (1) Orbit comparisons produced an average error of about 0.04–0.13 m for the global positioning system (GPS), 0.14–0.16 m for the global navigation satellite system (GLONASS), and 0.07–0.08 m for the quasi-zenith satellite system (QZSS). The G15 satellite had the most accurate orbit, with a difference of 0.04 m between the JAXA orbit products and MADOCA’s counterpart, while the R07 satellite had the least accurate orbit with a difference of 0.16 m. Clock products had an accuracy of 0.4–1.3 ns for GPS, 1.4–1.6 ns for GLONASS, and 0.7–0.8 ns for QZSS in general. The G15 satellite had the most accurate clock with a difference of only 0.40 ns between the JAXA clock products and MADOCA products, and the R07 satellite had the least accurate clock with a difference of 1.55 ns. The orbit and clock products for GLONASS performed worse than those of GPS and QZSS. (2) After convergence, the positioning accuracy was 3.0–8.1 cm for static PPP and 8.1–13.7 cm for kinematic PPP when using multi-GNSS observations and precise orbit and clock products. The PFRR station performed the good performance both in static and kinematic mode with an accuracy of 2.99 cm and 8.08 cm, respectively, whereas the CPNM station produced the worst static performance with an error of 8.09 cm, and the ANMG station produced the worst kinematic performance with a counterpart of 13.69 cm. (3) The PPP-AR solution was superior to the PPP solution, given that, with respect to PPP, post-processing PPP-AR improved the positioning accuracy and convergence time by 13–32 % (3–89 %) in GPS-only mode by 2–15 % (5–60 %) in GPS/QZSS mode. Thus, we conclude that the current MADOCA products can provide SSR corrections and FCB products with positioning accuracy at the decimeter or even centimeter level, which could meet the demands of the RTPPP and PPP-AR solutions.

Probing cosmic inflation with theLiteBIRDcosmic microwave background polarization survey

AbstractLiteBIRD, the Lite (Light) satellite for the study of B-mode polarization and Inflation from cosmic background Radiation Detection, is a space mission for primordial cosmology and fundamental physics. The Japan Aerospace Exploration Agency (JAXA) selected LiteBIRD in May 2019 as a strategic large-class (L-class) mission, with an expected launch in the late 2020s using JAXA’s H3 rocket. LiteBIRD is planned to orbit the Sun–Earth Lagrangian point L2, where it will map the cosmic microwave background polarization over the entire sky for three years, with three telescopes in 15 frequency bands between 34 and 448 GHz, to achieve an unprecedented total sensitivity of $2.2\, \mu$K-arcmin, with a typical angular resolution of 0.5○ at 100 GHz. The primary scientific objective of LiteBIRD is to search for the signal from cosmic inflation, either making a discovery or ruling out well-motivated inflationary models. The measurements of LiteBIRD will also provide us with insight into the quantum nature of gravity and other new physics beyond the standard models of particle physics and cosmology. We provide an overview of the LiteBIRD project, including scientific objectives, mission and system requirements, operation concept, spacecraft and payload module design, expected scientific outcomes, potential design extensions, and synergies with other projects.

Overview of H-II Transfer Vehicle (HTV) and HTV-X safety design considering common-cause software failure

The Japan Aerospace Exploration Agency (JAXA) is now developing the HTV-X, the successor to the H-II Transfer Vehicle (HTV). The HTV, also known as the Kounotori, was an unmanned cargo vehicle that transferred supplies to the International Space Station (ISS) with the largest spacefaring cargo capacity in the world. The HTV-X has improved transport capability and operability based on the expertise and technologies gained through the R and D and mission operation of earlier HTVs.During HTV-X development, JAXA encountered several challenges regarding ISS safety, but JAXA overcame them and enhanced the safety design. One example of the design enhancement is the countermeasure against Common-Cause Software Failure (CCSF).Hence this paper presents an overview of the HTV and HTV-X safety design, the trend of the discussion on the safety panels of the HTV through the HTV-X, and the feedback from the technical coordination incorporated into ongoing HTV-X safety design, taking countermeasure to manage CCSFs for example.

Similarities between Disaster Food and Space Food.

Disaster and space environments are similar in that they are closed environment, with limited lifelines. Here, we examined the similarity between disaster food and space food, to explore interactive problem-solving of food support for disaster and space environments. The Japan Disaster Food Certification Standards (Japan Disaster Food Society) and the Japanese Space Food Certification Standards (Japan Aerospace Exploration Agency) requirements and certified products, which were posted on the websites as of June 16, 2021, were compared. Certified products were classified into "staple foods," "main and/or side dishes," "milk and dairy products," "fruits," "confectionery and favorite beverages," "condiments," "dietary supplements," and "sets." Certification standards involved six items for Japan Disaster Food and eight items for Japanese Space Food. Most standards were similar. Concretely, both standards demanded room temperature storage, tough packaging and hygiene management in facilities. Both emphasized habitual food and easy eating. However, the best-by date was ≥6 mo for Japan Disaster Food, but ≥1.5 y for Japanese Space Food. In addition, Japanese Space Food required noted nutritious, food hygienic, eatable in space, cookable by specific equipment, endurable pressure by launch, and domestically produced food. There were 171 and 47 products of Japan Disaster Food and Japanese Space Food, respectively. Staple foods (pregelatinized rice, etc.) and main and/or side dishes were commonest among Japan Disaster Foods and Japanese Space Foods, respectively. It is possible to utilize of Space Food as Disaster Food, but there are some issues that must be cleared before "utilization of Disaster Food as Space Food."

Comparison of Satellite Precipitation Products: IMERG and GSMaP with Rain Gauge Observations in Northern China

Extreme precipitation events have increasingly happened at global and regional scales as the global climate has changed in recent decades. Accurate quantitative precipitation estimation (QPE) plays an important role in the warning of extreme precipitation events. With hourly rain gauge observations as a reference, this study compares the performance of Integrated Multi-satellitE Retrievals for Global Precipitation Measurement (GPM) mission (IMERG) and Global Satellite Mapping of Precipitation (GSMaP) quantitative precipitation estimation (QPE) products over Northern China in 2021. The Probability of Detection (POD), Relative Bias (RB), Root-Mean-Squared Error (RMSE), and Fractional Standard Error (FSE) are among the assessment metrics, as are the Probability of Detection (POD), False Alarm Ratio (FAR), and Critical Success Index (CSI). We examined the spatial distribution of cumulative precipitation and the temporal distribution of hourly average precipitation for three severe precipitation occurrences using these assessment metrics. The IMERG products capture strong precipitation centers that are compatible with the gauge observations, especially in extreme precipitation events in areas with relatively flat terrain and low-altitude (≤1000 m). Both IMERG (National Aeronautics and Space Administration, NASA) and GSMaP (Japan Aerospace Exploration Agency, JAXA) satellite-based QPE products have precipitation peaks in advance (2–4 h) and generally underestimate (overestimate) precipitation when the actual precipitation is heavy (light). The satellite-based QPE products generally overestimate the heavy rainfall caused by non-typhoons and underestimate the heavy rainfall caused by typhoons. The GSMaP products may have the capacity to detect short-term rainstorm events. The accuracy of satellite-based QPE products may be influenced by precipitation intensity, sensors, terrain, and other variables. Therefore, in accordance with our recommendations, more ground rainfall stations should be used to collect actual precipitation data in regions with high levels of spatial heterogeneity and complex topography. The data programmers should strengthen the weights computation retrieval technique and fully utilize infrared (IR)-based data. Furthermore, this study is expected to give helpful feedback to the algorithm developers of IMERG and GSMaP products, as well as those researchers into the use of IMERG and GSMaP satellite-based QPE products in applications.

Global Mangrove Extent Change 1996–2020: Global Mangrove Watch Version 3.0

Mangroves are a globally important ecosystem that provides a wide range of ecosystem system services, such as carbon capture and storage, coastal protection and fisheries enhancement. Mangroves have significantly reduced in global extent over the last 50 years, primarily as a result of deforestation caused by the expansion of agriculture and aquaculture in coastal environments. However, a limited number of studies have attempted to estimate changes in global mangrove extent, particularly into the 1990s, despite much of the loss in mangrove extent occurring pre-2000. This study has used L-band Synthetic Aperture Radar (SAR) global mosaic datasets from the Japan Aerospace Exploration Agency (JAXA) for 11 epochs from 1996 to 2020 to develop a long-term time-series of global mangrove extent and change. The study used a map-to-image approach to change detection where the baseline map (GMW v2.5) was updated using thresholding and a contextual mangrove change mask. This approach was applied between all image-date pairs producing 10 maps for each epoch, which were summarised to produce the global mangrove time-series. The resulting mangrove extent maps had an estimated accuracy of 87.4% (95th conf. int.: 86.2–88.6%), although the accuracies of the individual gain and loss change classes were lower at 58.1% (52.4–63.9%) and 60.6% (56.1–64.8%), respectively. Sources of error included misregistration in the SAR mosaic datasets, which could only be partially corrected for, but also confusion in fragmented areas of mangroves, such as around aquaculture ponds. Overall, 152,604 km2 (133,996–176,910) of mangroves were identified for 1996, with this decreasing by −5245 km2 (−13,587–1444) resulting in a total extent of 147,359 km2 (127,925–168,895) in 2020, and representing an estimated loss of 3.4% over the 24-year time period. The Global Mangrove Watch Version 3.0 represents the most comprehensive record of global mangrove change achieved to date and is expected to support a wide range of activities, including the ongoing monitoring of the global coastal environment, defining and assessments of progress toward conservation targets, protected area planning and risk assessments of mangrove ecosystems worldwide.

Sliding mode observers for robust fault estimation in linear parameter varying systems

AbstractA linear parameter varying sliding mode fault reconstruction scheme is proposed. Compared with other conventional sliding mode observer designs, the estimate emerges quite naturally from the equations governing the sliding motion, and although the process may be viewed as a filtering of the discontinuous injection, there is no phase lag introduced in the process. A semi‐analytic solution to the proposed linear parameter varying sliding mode observer is first discussed. This motivates the structure of the linear matrix inequality formulation which is proposed, and clarifies the class of systems to which the approach is applicable. The linear matrix inequality problem set up minimizes the induced gain between the fault estimate and external disturbances, whilst ensuring linear quadratic performance of the underpinning sliding motion. The proposed scheme has been validated using the Japan Aerospace Exploration Agency's Multi‐Purpose Aviation Laboratory aircraft‐in‐the‐loop platform to demonstrate the design efficacy.

Study on low gravity effect on bearing capacity and slope stability of a new lunar highland soil simulant (LSS-ISAC-1) for futuristic moon habitation

The future lunar missions of the space research organizations (SRO) such as the (US) National Aeronautics and Space Administration (NASA), the China National Space Administration (CNSA), the European Space Agency (ESA), the Indian Space Research Organisation (ISRO), the Japan Aerospace Exploration Agency (JAXA), and the Russian Federal Space Agency (RFSA or Roscosmos), etc., comprise extended stay on Moon, making the lunar surface a launchpad for the interplanetary missions and Moon habitation. These are the most challenging task for the space research organizations (SRO) and the researchers, which needs all engineering disciplines. Also, the distinct difference in the environment between the lunar surface (lunar gravity, moonquakes, high temperature, etc.) and the Earth forced the SROs and the researchers to study the geotechnical properties such as specific gravity, particle size distribution, density, shear strength, and bearing capacity of the lunar soils. In this, the lunar gravity (1/6g) significantly influences the bearing capacity of the lunar soil, which is the predominant property for the design and analysis of foundation systems of the lunar structures. Assessing the bearing capacity under the reduced lunar gravity will enhance the evaluation of design criteria for the lunar structures and their foundation systems. In this respect, this paper explains the low gravity effect on the bearing capacity of the new lunar highland soil simulant LSS-ISAC-1 developed to represent the geotechnical properties of the highland soils of the lunar surface. The bearing capacity of the simulant for both the lunar and Earth gravity was evaluated and compared with the lunar soils and lunar simulants. The plate load test and single wheel load tests were performed to determine the sinkage property (compression/settlement) of the LSS-ISAC-1. The slope stability and self-standing height of the LSS-ISAC-1 were also determined for a better understanding of stability. Overall, the comparison results state that the new simulant LSS-ISAC-1 is more than sufficient to support virtually any conceivable structures based on the results.

Wide-Output Range Power Processing Unit for 6-kW Hall Thruster

The Japan Aerospace Exploration Agency (JAXA) has developed a power processing unit (PPU) for a 6 kW Hall thruster system. The PPU is a candidate for future mission applications, such as all-electric satellites, exploration vehicles, and orbital transfer services. The PPU has to be small and still provide a wide output range of outputs, consider the in orbit and launch environments, and manage any instability in the Hall thruster's discharge. Specifically, the four converters that make up the anode power supply of the PPU is digitally controlled to reduce the size of the control circuit. It must operate stably despite small output capacitors and long dead times. This article clarifies the design criteria for the power supply, focusing on the size of capacitors and the PI control parameters to solve these problems. The result is a compact, high-performance PPU for the 6 kW Hall thruster. The power supply meets stringent design criteria and operates the thruster stably with an output voltage that can be varied between 200 and 730 V, provide a maximum power of 5.9 kW, and offer a maximum efficiency of 96.1% in the coupling test for the 6 kW Hall thruster. The proposed PPU, including the anode power supply, achieves a power density of 0.3 kW/kg, significantly higher than that of comparable PPUs.

Urbanization and land use change: A study in Vietnam

Abstract Land-use change is a human process aimed at transforming the natural landscape and emphasizing the role and function of land for socio-economic activities. However, we do not know how the land transition in Vietnam has been proceeding recently. Thus, this article aims to examine the current urbanization process of land conversion in Vietnam. To explore the current situation and recent change of land use, the author analyzed standardized databases and maps from reports of the Ministry of Natural Resources and Environment of Vietnam (MoNRE), the General Statistics Office of Vietnam (GSO), and the land cover map of Japan Aerospace Exploration Agency (JAXA). Research results show that the land transition in Vietnam has been similar to the world trend. The highest land conversion rate occurs in the North Central and Central Coast regions, but conversion of agricultural land for urbanization is mainly in the Red River Delta and Southeast. The study also noted some negative socio-economic impacts of land conversion on the lives of suburban residents.

Flight Evaluation of an LPV Sliding Mode Observer for Sensor FTC

This brief develops a sliding mode sensor fault-tolerant control scheme for a class of linear parameter varying (LPV) systems. It incorporates a sliding mode observer that reconstructs the unknown sensor faults based on only the system inputs and outputs. The reconstructed sensor faults are used to compensate for the corrupted sensor measurements before they are used in the feedback controller. Provided accurate fault estimates can be computed; near nominal control performance can be retained without any controller reconfiguration. Furthermore, the closed-loop stability of the fault-tolerant control (FTC) scheme, involving both a sliding mode controller and a sliding mode observer, is rigorously analyzed. The proposed scheme is validated using the Japan Aerospace Exploration Agency&#x2019;s Multipurpose Aviation Laboratory (MuPAL-<inline-formula> <tex-math notation="LaTeX">$\alpha $ </tex-math></inline-formula>) research aircraft. These flight tests represent the first validation tests of a sliding mode sensor FTC scheme on a full-scale aircraft.

Review for Examining the Oxidation Process of the Moon Using Generative Adversarial Networks: Focusing on Landscape of Moon

Japan Aerospace Exploration Agency (JAXA) has collected and studied the data observed by the lunar probe, SELenological and ENgineering Explorer (SELENE), from 2007 to 2017. JAXA discovered that the oxygen of the upper atmosphere of the Earth is transported to the moon by the tail of the magnetic field. However, this research is still in progress, and more data are needed to clarify the oxidation process. Therefore, this paper supplements the insufficient observation data by using Generative Adversarial Networks (GAN) and proposes a review paper focusing on the methodology, enhancing the level of completion of the preceding research, and the trend of examining the oxidation process and landscape of the moon. We propose using Anokhin’s Conditionally-Independent Pixel Synthesis (CIPS) as a model to be used in future experiments as a result of the review. CIPS can generate pixels independently for each color value, and since it uses a Multi-Layer Perceptron (MLP) network rather than spatial convolutions, there is a significant advantage in scalability. It is concluded that the proposed methodology will save time and costs of the existing research in progress and will help reveal the causal relationship more clearly.

Asteroid Flyby Cycler Trajectory Design Using Deep Neural Networks

Asteroid exploration has been attracting more attention in recent years. Nevertheless, we have just visited tens of asteroids, whereas we have discovered more than 1 million bodies. As our current observation and knowledge should be biased, it is essential to explore multiple asteroids directly to better understand the remains of planetary building materials. One of the mission design solutions is utilizing asteroid flyby cycler trajectories with multiple Earth gravity assists. An asteroid flyby cycler trajectory design problem is a subclass of global trajectory optimization problems with multiple flybys, involving a trajectory optimization problem for a given flyby sequence and a combinatorial optimization problem to decide the sequence of the flybys. As the number of flyby bodies grows, the computation time of this optimization problem expands maliciously. This paper presents a new method to design asteroid flyby cycler trajectories utilizing a surrogate model constructed by deep neural networks approximating trajectory optimization results. Because one of the bottlenecks of machine learning approaches is the heavy computation time to generate massive trajectory databases, we propose an efficient database generation strategy by introducing pseudo-asteroids satisfying the Karush–Kuhn–Tucker conditions. The numerical result applied to Japan Aerospace Exploration Agency’s mission shows that the proposed method is practically applicable to space mission design and can significantly reduce the computational time for searching asteroid flyby sequences.

Wind Tunnel Installation Effects on Japan Aerospace Exploration Agency’s Standard Model

This paper investigates the interference effects of wind tunnel floor and walls on the Japan Aerospace Exploration Agency’s High-Lift Configuration Standard Model (JSM) as an extension to a paper published in the Journal of Aircraft, Vol. 56, No. 3, May–June 2019, pp. 1080–1098. An unstructured hybrid grid generator, MEGG3D, was applied to JSM wing–body and wing–body–nacelle–pylon configurations to generate grids for free-air flow conditions. These grids were then reused in an investigation of the interference effects of Japan Aerospace Exploration Agency’s low-speed wind tunnel walls to better compare the computational results, both with each other and with experiment. The geometry of the wind tunnel used in our computational simulations is described in detail so that they can be reproduced. A Reynolds-averaged Navier–Stokes flow solver for unstructured hybrid grids, the Tohoku University Aerodynamic Simulation (TAS) code, was used for the simulations. The computational results indicated that the standoff and test section floor boundary layer significantly affected the aerodynamics of the JSM at high angles of attack. Better agreement with experiment was observed for the wing–body configuration in the aerodynamic characteristics near maximum lift if the effects of the standoff and floor boundary layer were considered.