In-orbit Demonstration of Reaction Control System for Orbital Altitude Change of Micro-Satellite ALE-2

This research presents the results of an in-orbit test of the orbital altitude control for a micro-satellite equipped with the first space-demonstrated high-density small cold gas jet thruster. In the field of micro-satellites, the application of thrusters to practical missions has not yet progressed due to their high cost, mechanical and electrical incompatibility with the satellite bus system, and increased operational risks. By contrast, the demand for orbit control functions has been increasing in recent years with the expansion of micro-satellite applications. The76kg satellite ALE-2 , which was jointly developed by Tohoku University and ALE Co., Ltd., has the world\u27s first challenging mission to artificially generate shooting stars by ejecting small substances (meteor source) from the ejection device fixed on the satellite body. To avoid collision of the ejected meteor source with other flying objects, the mission must be performed in a sun-synchronous orbit at an altitude of less than 400 km, which is lower than that of the International Space Station. However, it is required to maintain the mission orbit autonomously because the orbit decay is large due to the effect of atmospheric drag. In addition, to release the meteor source at an arbitrary orbital position, it is essential to manipulate the ground track by raising and lowering the orbital altitude. Therefore, ALE-2 needs to control the orbit altitude actively and with arbitrary amount of change. In this study, the reaction control system (RCS), which satisfies the orbit change capability, mission requirements, and compatibility with the satellite bus system, is installed on ALE-2 to perform space demonstrations of orbit control and to evaluate the operational performance of the thruster. ALE-2 will be the first to be equipped with a cold gas jet thruster developed by Patched conics, LLC. It is estimated that the thruster is capable of changing altitude more than 1 km by continuous drive for one orbital period. Using this RCS, the following three criteria were set as the evaluation criteria: (Minimum) the orbit altitude can be actively changed by the thruster, (Full) the orbit altitude can be controlled by an arbitrary amount of operation and can be increased more than 1 km per orbit, and (Extra) the mission orbit can be transferred according to the meteor source release plan. ALE-2 was launched on December 6, 2019, and the in-orbit test of the RCS started four months later. Although the RCS was not able to achieve its initial orbit change capability due to an anomaly in the power supply system, various kinds of tests were conducted under conditions that allowed continuous thruster operation. It was confirmed that the orbit altitude was increased by 0.4 km per orbit. In addition, the fault detection, isolation and recovery (FDIR)function was effectively performed against any kinds of anomalies of RCS during in-orbit operation. Therefore, a sustained orbital altitude of 400 km was expected to be achievable using the onboard RCS

Development of an Operating Strategy for On-Demand Earth Observation Missions of the Diwata-2 Microsatellite

Diwata-2 is the Philippines’ 2nd microsatellite developed by Tohoku University, Hokkaido University, University of the Philippines, and the Philippine Department of Science and Technology. Its primary purpose is gathering remote sensing data through imaging areas of interest for the Philippines. This paper presents the study of Diwata-2’s initial Earth observation pointing performance, investigation of its Attitude Determination and Control System, the tuning of its Star Tracker sensor parameters, the in-flight target pointing calibration, and the sequential scheduling of its components forming an operation strategy for an effective on-demand earth observation mission. This operation strategy has managed to improve the satellite’s pointing performance from the initial 2.88°±2.06° RMS pointing error to having an accuracy of 0.204°±0.12° RMS for its High Precision Telescope payload. This strategy has been implemented to the university-built microsatellite for over 400 successful Earth observation missions and has covered about 82.8% of the Philippine’s land area with its Spaceborne Multispectral Imager payload

Spectral evolution of GRB 060904A observed with Swift and Suzaku -- Possibility of Inefficient Electron Acceleration

We observed an X-ray afterglow of GRB 060904A with the Swift and Suzaku satellites. We found rapid spectral softening during both the prompt tail phase and the decline phase of an X-ray flare in the BAT and XRT data. The observed spectra were fit by power-law photon indices which rapidly changed from $\Gamma = 1.51^{+0.04}_{-0.03}$ to $\Gamma = 5.30^{+0.69}_{-0.59}$ within a few hundred seconds in the prompt tail. This is one of the steepest X-ray spectra ever observed, making it quite difficult to explain by simple electron acceleration and synchrotron radiation. Then, we applied an alternative spectral fitting using a broken power-law with exponential cutoff (BPEC) model. It is valid to consider the situation that the cutoff energy is equivalent to the synchrotron frequency of the maximum energy electrons in their energy distribution. Since the spectral cutoff appears in the soft X-ray band, we conclude the electron acceleration has been inefficient in the internal shocks of GRB 060904A. These cutoff spectra suddenly disappeared at the transition time from the prompt tail phase to the shallow decay one. After that, typical afterglow spectra with the photon indices of 2.0 are continuously and preciously monitored by both XRT and Suzaku/XIS up to 1 day since the burst trigger time. We could successfully trace the temporal history of two characteristic break energies (peak energy and cutoff energy) and they show the time dependence of $\propto t^{-3} \sim t^{-4}$ while the following afterglow spectra are quite stable. This fact indicates that the emitting material of prompt tail is due to completely different dynamics from the shallow decay component. Therefore we conclude the emission sites of two distinct phenomena obviously differ from each other.Comment: 19 pages, 9 figures, accepted for publication in PASJ (Suzaku 2nd Special Issue

Induction and Enhancement of Cardiac Cell Differentiation from Mouse and Human Induced Pluripotent Stem Cells with Cyclosporin-A

Induced pluripotent stem cells (iPSCs) are novel stem cells derived from adult mouse and human tissues by reprogramming. Elucidation of mechanisms and exploration of efficient methods for their differentiation to functional cardiomyocytes are essential for developing cardiac cell models and future regenerative therapies. We previously established a novel mouse embryonic stem cell (ESC) and iPSC differentiation system in which cardiovascular cells can be systematically induced from Flk1+ common progenitor cells, and identified highly cardiogenic progenitors as Flk1+/CXCR4+/VE-cadherin− (FCV) cells. We have also reported that cyclosporin-A (CSA) drastically increases FCV progenitor and cardiomyocyte induction from mouse ESCs. Here, we combined these technologies and extended them to mouse and human iPSCs. Co-culture of purified mouse iPSC-derived Flk1+ cells with OP9 stroma cells induced cardiomyocyte differentiation whilst addition of CSA to Flk1+ cells dramatically increased both cardiomyocyte and FCV progenitor cell differentiation. Spontaneously beating colonies were obtained from human iPSCs by co-culture with END-2 visceral endoderm-like cells. Appearance of beating colonies from human iPSCs was increased approximately 4.3 times by addition of CSA at mesoderm stage. CSA-expanded human iPSC-derived cardiomyocytes showed various cardiac marker expressions, synchronized calcium transients, cardiomyocyte-like action potentials, pharmacological reactions, and ultra-structural features as cardiomyocytes. These results provide a technological basis to obtain functional cardiomyocytes from iPSCs

Impact of the Boreholes on the Surrounding Ground

The infrastructures that were constructed decades ago do not meet the present structural benchmark, and they need to be demolished. In order to reclaim these lands, the existing pile foundations must be removed; otherwise, the land will lose its value. Since the piles are pulled out, vacant spaces are created in the ground. This causes the surrounding ground to experience settlement, jeopardizing its stability. The degree of influence depends upon the number of boreholes, the saturated condition of the ground, the time period of the vacant condition, the presence of loading, etc. It is important to understand the scope of the probable settlement under various situations. This study focused on determining the amount of displacement and its range for three different saturated soil types under loaded and unloaded conditions using the finite element method (FEM) analysis. It was observed that stiff ground underwent maximum deformation, while soft ground experienced the maximum influence from external factors. Moreover, the presence of loading not only increased the displacement amount and range, but it also caused a change in the location of the maximum displacement