Japan Aerospace Exploration Research Articles

Sensitivity analysis of landing and takeoff noise for conceptual low-boom supersonic aircraft using variable noise reduction system

This paper presents the results of an analysis of the sensitivity of the use of a variable noise reduction system (VNRS), considered in the new landing and takeoff (LTO) noise standard for supersonic aircraft, using a Japan Aerospace Exploration Agency (JAXA)-designed 66-ton twin-engine conceptual low-boom supersonic airliner as an example. The analysis was conducted using a tool developed by JAXA and examined the sensitivity of low-speed aerodynamic performance, the sensitivity of takeoff reference speed, the sensitivity of thrust control and flap control duration time ranges, and the sensitivity of noise level to takeoff profile uncertainty. The analyses showed that improving low-speed aerodynamic performance and increasing the takeoff reference speed significantly impact noise levels and the use of VNRS could reduce noise by 2.1 EPNLdB while maintaining the performance of the aircraft. Because the effective noise reduction method by changing the takeoff procedure considered differs for each noise measurement point, it is important to design a takeoff procedure that incorporates an appropriate VNRS. Uncertainty of the takeoff profile was also investigated using Monte Carlo simulations, and it was shown that noise reduction by VNRS is effective even with the assumed uncertainty in the takeoff profile.

Observation of Superposition of Cavitation Instability in Liquid Rocket Inducer by Multi-point Pressure Measurement

Abstract The purpose of this study is to investigate the relationship between the growth and contraction processes of each blade cavity and cavitation instability, and to conduct multi-point pressure measurement tests. The experiments will be conducted using cavitation water flow tunnels installed at the Kakuda Space Center of the Japan Aerospace Exploration Agency (JAXA). In the multi-point pressure measurement experiment, a number of pressure sensors are installed in the inducer casing, and the cavity area can be estimated and the cavity length can be obtained by creating a pressure distribution between the blades during the depressurization experiments. This method makes it possible to continuously determine cavity length variation during inducer experiments and to investigate the cavity growth process. In addition, cavity length variation can be obtained with higher time resolution than in visualization experiment, allowing more detailed investigation of the unsteady cavity behaviour during cavitation instability. And two types of superposition cavitation instability were found in this study: one is Super-S R.C. and C.S., the other is Sync R.C. and C.S..

Spatial resolution of sea surface temperature observed by AMSR2 on GCOM-W satellite

ABSTRACT This study developed a method to evaluate the effective spatial resolution of sea surface temperature (SST) data produced from observations of a microwave radiometer on satellites. The method was applied to 7-year SST data from the Advanced Microwave Scanning Radiometer 2 (AMSR2) on the Japan Aerospace Exploration Agency’s (JAXA) Global Change Observation Mission-Water (GCOM-W) satellite. JAXA has produced three SST products from AMSR2 observations: standard SST, 10-GHz SST, and multi-band SST. They differ in spatial resolution because the frequency used to retrieve the SST has different footprint sizes, although the resolution has not been evaluated so far. We utilized high-resolution infrared SST data from the geostationary meteorological satellite Himawari-8. The Himawari SST was spatially smoothed by a Gaussian function to identify the smoothing scale that most accurately reproduces the AMSR2 SST gradient fields in the same area and time. The similarities between the Himawari and AMSR2 SST gradient fields were assessed using three metrics. The correlation coefficient provided a stable and robust estimate against the noise included in the AMSR2 SSTs. As a result, the effective resolution was estimated at 67 km for the standard SST, 52 km for the 10-GHz SST, and 63 km for the multi-band SST. These are all larger than the nominal resolution expected from the AMSR2 footprint size. The 10-GHz and multi-band SSTs had significantly higher resolutions than the standard SST.

HEMLAB Algorithm Applied to the High-Lift Japan Aerospace Exploration Agency Standard Model

The high-lift Japan Aerospace Exploration Agency (JAXA) standard model (HL-JSM) has been numerically analyzed in order to further validate the HEMLAB code for realistic aircraft configurations. The numerical algorithm is based on highly efficient edge-based data structure for a vertex-based finite volume algorithm on hybrid meshes. The data pattern is arranged to meet the requirements of a vertex-based finite volume algorithm by considering data access patterns and cache efficiency. A fully implicit version of the numerical algorithm has also been implemented based on the Portable, Extensible Toolkit for Scientific Computation (PETSc) library in order to improve the robustness of the algorithm. The resulting algebraic equations, including the one-equation Spalart–Allmaras, are solved in a monolithic manner using the restricted additive Schwarz preconditioner combined with the flexible generalized minimal residual method [FGMRES(m)] Krylov subspace algorithm. The numerical method is also combined with the metric-based anisotropic mesh refinement library Python Adaptive Mesh Geometry Suite–INRIA (pyAMG) from National Institute for Research in Digital Science and Technology in order to improve the numerical accuracy. The numerical algorithm is initially applied to the two-dimensional L1T2 (National High Lift Programme) high-lift system, and then the calculations around the HL-JSM are carried out at relatively high angles of attack. The numerical results with the anisotropic mesh refinement library pyAMG indicate significant improvements in numerical accuracy.

The Greenhouse gas Observations of Biospheric and Local Emissions from the Upper sky (GOBLEU): a mission overview, instrument description, and results from the first flight

BackgroundThe Greenhouse gas Observations of Biospheric and Local Emissions from the Upper sky (GOBLEU) is a new joint project by Japan Aerospace Exploration Agency (JAXA) and ANA HOLDING INC. (ANAHD), which operates ANA flights. GOBLEU aims to visualizes our climate mitigation effort progress in support of subnational climate mitigation by collecting greenhouse gas (GHG) data as well as relevant data for emissions (nitrous dioxide, NO2) and removals (Solar-Induced Fluorescence, SIF) from regular passenger flights. We developed a luggage-sized instrument based on the space remote-sensing techniques that JAXA has developed for Japan’s Greenhouse gas Observing SATellite (GOSAT). The instrument can be conveniently installed on a coach-class passenger seat without modifying the seat or the aircraft.ResultsThe first GOBLEU observation was made on the flight from the Tokyo Haneda Airport to the Fukuoka Airport, with only the NO2 module activated. The collected high-spatial-resolution NO2 data were compared to that from the TROPOspheric Monitoring Instrument (TROPOMI) satellite and surface NO2 data from ground-based air quality monitoring stations. While GOBLEU and TROPOMI data shared the major concentration patterns largely driven by cities and large point sources, regardless of different observation times, we found fine-scale concentration pattern differences, which might be an indication of potential room for GOBLEU to bring in new emission information and thus is worth further examination. We also characterized the levels of NO2 spatial correlation that change over time. The quickly degrading correlation level of GOBLEU and TROPOMI suggests a potentially significant impact of the time difference between CO2 and NO2 as an emission marker and, thus, the significance of co-located observations planned by future space missions.ConclusionsGOBLEU proposes aircraft-based, cost-effective, frequent monitoring of greenhouse emissions by GOBLEU instruments carried on regular passenger aircraft. Theoretically, the GOBLEU instrument can be installed and operated in most commercially used passenger aircraft without modifications. JAXA and ANAHD wish to promote the observation technique by expanding the observation coverage and partnership to other countries by enhancing international cooperation under the Paris Agreement.

Development of 1400°C(2552°F) class Ceramic Matrix Composite Turbine Shroud and Demonstration Test with JAXA F7 Aircraft Engine

Abstract The Authors developed 1400°C(2552°F) class CMC material system which consist of SiC fibers and SiC matrix and ytterbium silicate base matrix, aiming for higher temperature capability. Then they designed and manufactured high pressure turbine shrouds for aircraft engines using that 1400°C class material system, and they conducted strength tests and thermal cycle tests for turbine shroud components. After that they conducted engine tests for the CMC turbine shrouds demonstration in the actual engine environment jointly with the Japan Aerospace Exploration Agency (JAXA) in 2021. The engine test was conducted for over 75 hours including over 35 hour hot time. After the test teardown inspection was conducted. No spallation of EBC, no recession and no wear on CMC turbine shrouds were found. As the result of the microstructure observation for cut faces of CMC turbine shrouds, no oxidation in SiC fibers, no chemical reaction in matrix, and no microcrack in matrix were found, but, some oxidation in fiber interface coating and microcrack in EBC were found. Bending strength tests with specimens cut out from CMC turbine shrouds were conducted in order to survey the degradation of material. As the result of bending test, the strength of the specimens cut out from engine tested shrouds were equivalent to the strength of the specimens cut out from unused shrouds. The CMC turbine shrouds after engine test were determined to be serviceable, therefore the developed 1400°C class CMC shrouds was proven to be sound in an actual engine environment.

AERODYNAMIC IMPACT OF SECONDARY AIR INJECTION FLOWRATES ON THE MAIN ANNULUS FLOW FIELD FOR A TRANSONIC HIGH-PRESSURE TURBINE STAGE

Abstract In this study, the influence of secondary air blowing on the main annulus flow field of a transonic high-pressure turbine (HPT) was investigated experimentally and numerically. The experimental setup was a single-stage, unshrouded turbine with a blading consistent with modern HPTs. The entire testing campaign was conducted in a full annular, rotating, continuous turbine test rig at the Japan Aerospace Exploration Agency (JAXA), which realized the most faithful matching unrivalled of both the primary and secondary stream similarity parameters to reality. An elaborate secondary air system implemented in the hardware enabled it to mimic all the dominant coolant/purge streams representative of advanced hot sections: the full coverage film-cooling on stator and rotor airfoils, disk wheelspace purge air blown forward and aft of the rotor, and coolant injection through the over-tip casing. Detailed three-dimensional flow field measurements for various secondary air flowrates were performed by traversing a pneumatic thermometric combination probe downstream of the rotor. A complete set of numerical simulations was run concurrently with the testing to determine how well they captured the flow physics, particularly the interaction of the ejected secondary streams with the primary flow. The JAXA in-house code, UPACS, and its best practice settings, based on past verification and validation efforts, were employed and not intentionally tuned to better fit the data.

Performance evaluation of rebound damping of target marker

For small body missions, autonomous guidance is crucial for landing. The Japan Aerospace Exploration Agency’s Hayabusa and Hayabusa2 spacecraft thus placed a target marker on an asteroid’s surface for approach and landing maneuvers. Because of the microgravity environment of an asteroid, even a low-velocity impact can result in a high rebound. In order to reduce rebound motion, a target marker is composed of a shell and a large number of inner particles. The inner particles collide with each other in the shell, reducing the coefficient of restitution of the whole system. Since the settling position of the target marker is directly related to landing accuracy, understanding the target marker’s coefficient of restitution is crucial. This work explains the damping mechanism and develops a theory that can be used to evaluate damping performance based on the number and radius of inner particles. The proposed model is validated by a comparison with the results of a numerical simulation based on the discrete element method. The results of this study will contribute to future small body missions, whose success can depend on mitigating rebound on an asteroid surface. Since particle dampers can be applied to a wide variety of payloads, the results of this study are useful for designing separable payloads for future small body missions.

Performance of GNSS positioning in PPP mode using MADOCA precise products

The Global Navigation Satellite System (GNSS) is widely utilized for accurate positioning. One commonly applied method to obtain precise coordinate estimates is by implementing the relative positioning in network mode. However, this approach can be complex and challenging. Fortunately, The Japan Aerospace Exploration Agency (JAXA) offers freely available satellite orbit and clock correction products called Multi-GNSS Advanced Demonstration Tool for Orbit and Clock Analysis (MADOCA), which can enhance positioning accuracy through the precise point positioning (PPP) method. This study focuses on evaluating PPP static mode positioning using MADOCA products and comparing the results with the highly precise relative positioning method. By analyzing a network of 20 GNSS stations in Indonesia, we found that the PPP method using MADOCA products provided favorable positioning estimates. The median discrepancies and the corresponding median absolute deviation (MAD) for easting, northing, and up components were estimated as 9 ± 18 mm, 10 ± 9 mm, and 3 ± 40 mm, respectively. These results indicate that PPP with MADOCA products can be a reliable alternative for establishing Indonesia's horizontal control networks, particularly for orders 0, 1, 2, and 3, and for a broad spectrum of geoscience monitoring activities. However, considerations such as epoch transformations and seismic activities should be taken into account for accurate positioning applications that comply with the definition of the national reference framework.

A second space age spanning omics, platforms and medicine across orbits.

The recent acceleration of commercial, private and multi-national spaceflight has created an unprecedented level of activity in low Earth orbit, concomitant with the largest-ever number of crewed missions entering space and preparations for exploration-class (lasting longer than one year) missions. Such rapid advancement into space from many new companies, countries and space-related entities has enabled a 'second space age'. This era is also poised to leverage, for the first time, modern tools and methods of molecular biology and precision medicine, thus enabling precision aerospace medicine for the crews. The applications of these biomedical technologies and algorithms are diverse, and encompass multi-omic, single-cell and spatial biology tools to investigate human and microbial responses to spaceflight. Additionally, they extend to the development of new imaging techniques, real-time cognitive assessments, physiological monitoring and personalized risk profiles tailored for astronauts. Furthermore, these technologies enable advancements in pharmacogenomics, as well as the identification of novel spaceflight biomarkers and the development of corresponding countermeasures. In this Perspective, we highlight some of the recent biomedical research from the National Aeronautics and Space Administration, Japan Aerospace Exploration Agency, European Space Agency and other space agencies, and detail the entrance of the commercial spaceflight sector (including SpaceX, Blue Origin, Axiom and Sierra Space) into aerospace medicine and space biology, the first aerospace medicine biobank, and various upcoming missions that will utilize these tools to ensure a permanent human presence beyond low Earth orbit, venturing out to other planets and moons.

Geostationary aerosol retrievals of extreme biomass burning plumes during the 2019–2020 Australian bushfires

Abstract. Extreme biomass burning (BB) events, such as those seen during the 2019–2020 Australian bushfire season, are becoming more frequent and intense with climate change. Ground-based observations of these events can provide useful information on the macro- and micro-physical properties of the plumes, but these observations are sparse, especially in regions which are at risk of intense bushfire events. Satellite observations of extreme BB events provide a unique perspective, with the newest generation of geostationary imagers, such as the Advanced Himawari Imager (AHI), observing entire continents at moderate spatial and high temporal resolution. However, current passive satellite retrieval methods struggle to capture the high values of aerosol optical thickness (AOT) seen during these BB events. Accurate retrievals are necessary for global and regional studies of shortwave radiation, air quality modelling and numerical weather prediction. To address these issues, the Optimal Retrieval of Aerosol and Cloud (ORAC) algorithm has used AHI data to measure extreme BB plumes from the 2019–2020 Australian bushfire season. The sensitivity of the retrieval to the assumed optical properties of BB plumes is explored by comparing retrieved AOT with AErosol RObotic NETwork (AERONET) level-1.5 data over the AERONET site at Tumbarumba, New South Wales, between 1 December 2019 at 00:00 UTC and 3 January 2020 at 00:00 UTC. The study shows that for AOT values > 2, the sensitivity to the assumed optical properties is substantial. The ORAC retrievals and AERONET data are compared against the Japan Aerospace Exploration Agency (JAXA) Aerosol Retrieval Product (ARP), Moderate Resolution Imaging Spectroradiometer (MODIS) Deep Blue over land, MODIS MAIAC, Sentinel-3 SYN and VIIRS Deep Blue products. The comparison shows the ORAC retrieval significantly improves coverage of optically thick plumes relative to the JAXA ARP, with approximately twice as many pixels retrieved and peak retrieved AOT values 1.4 times higher than the JAXA ARP. The ORAC retrievals have accuracy scores of 0.742–0.744 compared to the values of 0.718–0.833 for the polar-orbiting satellite products, despite successfully retrieving approximately 28 times as many pixels over the study period as the most successful polar-orbiting satellite product. The AHI and MODIS satellite products are compared for three case studies covering a range of BB plumes over Australia. The results show good agreement between all products for plumes with AOT values ≤ 2. For extreme BB plumes, the ORAC retrieval finds values of AOT > 15, significantly higher than those seen in events classified as extreme by previous studies, although with high uncertainty. A combination of hard limits in the retrieval algorithms and misclassification of BB plumes as cloud prevents the JAXA and MODIS products from returning AOT values significantly greater than 5.

Effects of long-term storage on properties of perovskite solar cells

The Japan Aerospace Exploration Agency (JAXA) is planning a Space photovoltaics Demonstration eXperiment (SDX) to reveal the tolerance to the space environment of the next-generation solar cells. One of the next-generation solar cells mounted on SDX is a perovskite solar cell (PSC), which is cost-effective and has the potential for high specific power and radiation tolerance. It is necessary to clarify the long-term stability to analyze the characteristics of PSCs in orbit because SDX will be stored for months before and after launch. Therefore, we conducted three storage tests (in air, nitrogen, and low pressure) using encapsulated PSCs. Their performance was evaluated by Light I–V, Dark I–V, and EQE measurements. As a result, almost no degradation was observed at EOL (after 400 days) under all storage conditions. We found that the encapsulated PSCs mounted on SDX are highly stable. We also found that the slight degradation of Pmax within 4 % was due to an increase in series resistance.

JASMINE: Near-infrared astrometry and time-series photometry science

Abstract The Japan Astrometry Satellite Mission for INfrared Exploration (JASMINE) is a planned M-class science space mission by the Institute of Space and Astronautical Science, the Japan Aerospace Exploration Agency. JASMINE has two main science goals. One is Galactic archaeology with a Galactic Center survey, which aims to reveal the Milky Way’s central core structure and formation history from Gaia-level (∼25 ${\mu} $as) astrometry in the near-infrared (NIR) Hw band (1.0–1.6 ${\mu} $m). The other is an exoplanet survey, which aims to discover transiting Earth-like exoplanets in the habitable zone from NIR time-series photometry of M dwarfs when the Galactic Center is not accessible. We introduce the mission, review many science objectives, and present the instrument concept. JASMINE will be the first dedicated NIR astrometry space mission and provide precise astrometric information on the stars in the Galactic Center, taking advantage of the significantly lower extinction in the NIR. The precise astrometry is obtained by taking many short-exposure images. Hence, the JASMINE Galactic Center survey data will be valuable for studies of exoplanet transits, asteroseismology, variable stars, and microlensing studies, including discovery of (intermediate-mass) black holes. We highlight a swath of such potential science, and also describe synergies with other missions.

New smart twisting active rotor (STAR): pretest predictions

A Mach-scaled model rotor with an active twist capability is in preparation for a wind tunnel test in the large low-speed facility of the German-Dutch wind tunnel (DNW) with international participation by the German Aerospace Center (DLR), US Army Combat Capabilities Development Command (DEVCOM) Aviation & Missile Center, National Aeronautics and Space Administration, French Aerospace Lab (ONERA), Korea Aerospace Research Institute, Konkuk University, Japan Aerospace Exploration Agency, Glasgow University, and DNW. To get the maximum benefit from the test and the most valuable data within the available test time, the tentative test matrix was covered by predictions of the partners, active twist benefits were evaluated, and support was provided to the test team to focus on the key operational conditions.

Mitigating underestimation of fire emissions from the Advanced Himawari Imager: A machine learning and multi-satellite ensemble approach

The accurate estimation of biomass burning emissions has played a crucial role in air quality and climate forecast modeling. Satellite-based fire radiative power (FRP) has proven effective for calculating biomass burning emissions. However, FRP-based emission estimations in East Asia often rely on polar-orbiting satellites owing to the unstable performance of Japan Aerospace Exploration Agency Advanced Himawari Imager (JAXA AHI) from poor detection capability and unproper FRP retrieval method. To address this, we improve the FRP by machine learning based on mid-infrared (MIR) radiance method, leveraging the superior fire detection model developed in our previous study. In addition, we propose a multi-satellite distance-based weighted ensemble FRP estimation method. Compared to traditional MIR radiance methods, the machine learning-based FRP estimation model exhibited promising performance (correlation coefficient: 1, mean bias error: 0.2, mean absolute percentage error: 1.9%). The integration of machine learning-based FRP estimation and fire detection model dramatically mitigated the underestimation issues from the JAXA AHI. The machine learning-based FRP was combined with the Moderate Resolution Imaging Spectroradiometer FRP to create a multi-satellite ensemble FRP. Comparative assessments using the TROPOspheric Monitoring Instrument and conventional bottom-up method demonstrated that the proposed method produced reliable output. Furthermore, impact analysis revealed that missing peaks or underestimated burn scars could lead to fatally low emissions; however, the proposed method was relatively robust against missing data owing to its multi-satellite ensemble. By identifying potential FRP problems and their impact on emission estimations, this study provides valuable insights for FRP-based emission estimation studies.

Acoustic Liners Combined with Fine Perforated Film

The presence of grazing flow can alter the noise reduction performance of resonant liner panels. One possible cause is the flow entering the liner opening. In this study, a fine perforated film was applied to the surface of acoustic liners to prevent such flow effects. Three types of liner samples were fabricated and tested in a flow duct rig at the Japan Aerospace Exploration Agency. The first sample was a conventional resonant liner (“baseline”), the second sample had a fine perforated film directly attached to the baseline liner surface (“direct fine perforated film”), and the third sample had a gap fixed between the film and the liner surface (“fine perforated film with a gap”). The impedance eduction results show that the fine perforated film with a gap was effective in separating grazing flow from the liner openings and in reducing the effect of the flow on the impedance. The transmission loss in the duct improved. However, the effectiveness of the direct fine perforated film was limited. The fine perforated film with a gap structure showed potential to facilitate the design of high-efficiency liners under grazing flow conditions.

Performance test results of a helium Dewar for the Resolve instrument onboard the XRISM

The X-ray imaging and spectroscopy mission (XRISM) is an X-ray astronomy satellite developed by the Japan Aerospace Exploration Agency (JAXA) and the National Aeronautics and Space Administration (NASA) to explore the evolution of the universe and its physical phenomena as the replacement for ASTRO-H. One of the primary scientific instruments of the XRISM is the Resolve, which utilizes an X-ray microcalorimeter array. This detector array is required to be cooled down to 50 mK using a complex cryogenic system with a multistage adiabatic demagnetization refrigerator (ADR) developed by NASA and a cryogenic system developed by Sumitomo Heavy Industries, Ltd. (SHI). The cryogenic system is required to cool the heat sink of the ADR to a temperature below 1.5 K in orbit for at least 3 years. To meet the specific requirements, we developed a hybrid cryogenic system consisting of a liquid helium tank, a 4K Joule–Thomson cooler, and two two-stage Stirling coolers. As a result, the specific requirements were verified by ground tests. This paper describes the design, including the major changes from ASTRO-H, fabrication, and results of the ground tests of the helium Dewar of the Resolve instrument.

Transcriptome Analysis by RNA Sequencing of Mouse Embryonic Stem Cells Stocked on International Space Station for 1584 Days in Frozen State after Culture on the Ground.

As a space project, in "Stem Cells" by the Japan Aerospace Exploration Agency (JAXA), frozen mouse ES cells were stored on the International Space Station (ISS) in the Minus Eighty Degree Laboratory Freezer for ISS (MELFI) for 1584 days. After taking these cells back to the ground, the cells were thawed and cultured, and their gene expressions were comprehensively analyzed using RNA sequencing in order to elucidate the early response of the cells to long-time exposure to space radiation consisting of various ionized particles. The comparisons of gene expression involved in double-stranded break (DSB) repair were examined. The expressions of most of the genes that were involved in homologous recombination (HR) and non-homologous end joining (NHEJ) were not significantly changed between the ISS-stocked cells and ground-stocked control cells. However, the transcription of Trp53inp1 (tumor protein 53 induced nuclear protein-1), Cdkn1a (p21), and Mdm2 genes increased in ISS-stocked cells as well as Fe ion-irradiated cells compared to control cells. This suggests that accumulated DNA damage caused by space radiation exposure would activate these genes, which are involved in cell cycle arrest for repair and apoptosis in a p53-dependent or -independent manner, in order to prevent cells with damaged genomes from proliferating and forming tumors.

Application of Mass Particle Methods in the Shape Design for Scientific Balloons

This paper proposes a dynamic simulation method for solving balloon shapes. The mass-spring-damping model is used to discretize two-dimensional generatrixes and three-dimensional membrane surfaces, respectively. We solve two-dimensional/three-dimensional ascent shapes at different zero-pressure heights and numerically simulate mushroom cloud shapes that occur during the balloon ground launch. The typical rapid transition feature of the mushroom cloud shape at the waist is depicted. In addition, a preliminary numerical simulation study was conducted for the pumpkin superpressure balloon deployment instability problem. The Calladine instability critical curve for constant angle design lobes is compared and validated for different gore numbers and lobe angles. Further, simulations were carried out on fully inflated shapes of two derived superpressure balloon designs developed by the Japan Aerospace Exploration Agency/Institute of Space and Astronautical Science, namely, the Tawara intermediate cylindrical segment balloon and the diamond-shaped tendon balloon. We verify the ISAS conclusion that the diamond-shaped tendon balloon has a cylindrical shape when fully inflated. Finally, a preliminary simulation study was carried out on the deployment shape of four ballonet architectures in the superpressure balloon. The proposed method for solving various types of balloon shapes based on the mass particle method is simple and efficient, and it has been well applied in our actual balloon engineering.

Mechanical strength distribution in Geminid meteoroids derived via fireball modeling

Context. Geminids are the most active annual meteor shower observed on Earth. Their parent is an active asteroid, (3200) Phaethon, which is a target of the planned DESTINY+ mission of the Japan Aerospace Exploration Agency (JAXA). The exact physical nature of (3200) Phaethon and Geminids is still debated. Aims. This paper is devoted to fragmentation modeling of bright Geminid fireballs, which should reveal information about the structure of centimeter-sized Geminid meteoroids. These fireballs were observed by the European Fireball Network (EN) over the past few years. We aim to describe their disintegration cascade in the atmosphere and their mechanical properties, and to derive their precise initial masses and velocities. Methods. We used a semi-empirical fragmentation model that employs an automatic procedure based on parallel genetic algorithms to determine the aerodynamic pressures at which a meteoroid and its parts fragment. This serves as a proxy for the mechanical strength of the body and its subsequent fragments. It enabled us to derive the minimum, median, and maximum mechanical strength and the strength distribution inside the meteoroid and reveal its internal structure. Results. We find that the Geminids begin to crumble at pressures 1–100 kPa, with the strongest parts reaching pressures of between 0.4 and 1.55 MPa before fragmenting. Knowing the spectral type of (3200) Phaethon (a B-type asteroid, part of the C complex), we conclude that the Geminids are made of compact and coherent carbonaceous material. We also find that the minimum aerodynamic pressure that causes the fragmentation of Geminids increases with increasing entry mass of Geminids. In contrast, the median aerodynamic pressure decreases as their entry mass increases. The spectra of all the observed Geminid fireballs show normal content and little variation in terms of sodium.