In this study, the micro-topographical classification on the basis of extraction of geomorphological feature information such as sand dune, terrace and former river bed was carried out through the integrated analysis of LANDSAT-8/OLI mosaic data, ALOS-2/PALSAR-2 data, and the existing DSM in the delta area along the Ili River of Balkhash Lake. The study result showed the possibilities of the classification with six categories including the oldest delta in the object area and its vicinity through the analysis of the sand dune distribution by filtering operation for DSM, the PALSAR-2 ScanSAR intensity data, and the vegetation covering and high soil moisture area distribution by NDVI and NDWI derived from OLI data.
The various devices used in lunar activities are exposed to a constant hazard-moon dust. Consequently, appropriate measures must be taken to protect anything with moving parts from a large amount of lunar dust particulates, called regolith, so the development of better seals to protect mechanical components from dust particles is very important. Further, there are considerations such temperature that must be taken into account. This study focuses on face seals such as mechanical seal instead of radial seals because face seals can easily get lower torque than the radial seals since rotational torque is hardly affected by temperature. Mechanical seals were evaluated for use with a main shaft with respect to their effectiveness in protecting motors, gears, and bearings from dust particles. First, a ring-on-ring friction test was carried out to find a suitable material and combination to use as sliding materials. SiC against SiC had good tribological properties in various material combinations. Using a SiC/SiC combination as the sliding materials, mechanical seals were evaluated in a vacuum and under heavy-dust conditions. This paper reports the results of testing seal properties and torque.
In a ground test facility (vacuum chamber), propellant particles emitted from an electric propulsion thruster are reflected from chamber wall surfaces. They remain within the chamber until evacuation by vacuum pumps. Some particles return to the original thruster. To measure horizontal and vertical rarefied particle flow, a rarefied flow vector detector (RFVD) using an extra-fine thin optical fiber was developed for this study. It was redesigned as described herein. Multi-point measurement results confirmed that both reflection from the chamber wall surface and evacuation using the vacuum pump strongly influence the propellant particle flow. Adequate vacuum pump and thruster locations are discussed for thruster performance evaluation.
Over the past few years, the number of Japanese astronauts recruited for a long-term stay in the International Space Station (ISS) has increased. Being on a prolonged mission with the same people, in the same room, should impose psychosocial stress on the astronauts, possibly causing feelings of “psychological suffocation”. Several confinement studies have been conducted to simulate the conditions of the ISS, the Mir space station, and potential habitats on Mars, and to survey psychological interpersonal communication between the crew in a confined environment, including the Isolation Study for European Manned Space Infrastructure, Experimental Campaign for the European Manned Space Infrastructure, Simulation of Flight of International Crew on Space Station, Human Behavior in Extended Spaceflight, Mars-500, and Hawaii Space Exploration Analog and Simulation. Here, the findings from these studies were integrated into a structured review according to an evidence-based set of items for reporting in systematic reviews and meta-analyses. The results indicated that metaanalyses would not always be appropriate because it is difficult to design a research protocol with a high level of evidence in this field. Therefore, future research in this field should be focused on the following three points: 1) developing more accurate parameters for monitoring stress levels in long-term confinement environments; 2) analyzing stress levels in such situations with higher precision; and 3) accumulating and assembling existing and future data from long-term confinement environments.
Nano/microsatellites play a significant role in Earth observation with the emerging constellation of high spatial resolution satellites. However, there are technological limitations in their spectral resolution. In this paper, we present an overview of a high spatial resolution multispectral sensor, the High-Precision Telescope (HPT), which was developed originally for the RISING-2 microsatellite and subsequently improved for the Rapid International Scientific Experiment Satellite (RISESAT) microsatellite. The HPTs were also installed on the DIWATA-1 and DIWATA-2 microsatellites, but they are different from those in the RISING-2 and RISESAT microsatellites in terms of number of spectral bands. The HPT on the RISESAT has the largest number of spectral bands in a series of the high spatial resolution multispectral sensors. The RISESAT was successfully launched by the Epsilon-4 launch vehicle on 18 January 2019. The preliminary results obtained in the commissioning phase of the operation demonstrate the expected performance of the HPT.
The NICT is currently researching and developing an array-fed reflector antenna that flexibly changes the coverage area using a DBF and improves the frequency utilization efficiency using a DC for next-generation communication satellites in the Ka-band. The systematic error calibration of an array feed is very important because the influence of phase errors appears prominently in the characteristics of the antennas. We propose a self-calibration system for an array feed using a pickup antenna and gating process to realize a more accurate systematic error calibration for array-fed reflector antennas. The calibration values for the array feed are obtained from the coupling characteristics using a pickup antenna from which the noise is removed by a gating process. This paper shows the proposed method, procedure, and calibration results of the radiation pattern in an anechoic chamber. In order to determine the measurement parameters of the proposed method by parametric study, only the characteristics of the array feed were measured and evaluated. The calibration values, with gating a width of 0.01 μs, were almost the same compared with reference values. The calibrated radiation pattern using the proposed method was compared with a simulated radiation pattern, and the deviation in the H- and V-planes within a ± 6-degree range was about ±1.0 and ±0.6 dB, respectively. This paper shows that the proposed self-calibration using a pickup antenna and gating process is effective for a DBF array feed.
As the number of small satellites keeps increasing due to the low-cost development and fast delivery duration, there is a demand for higher capacity and capability of the ground station tracking system. Generally, the existing ground station tracking system faces major performance degradation while tracking satellites because of signals interference and multi-path fading. These problems motivate researchers to come out with interesting solution to mitigate the degradation performance. This paper describes the implementation of adaptive beam forming algorithm of phased array antenna for ground station tracking system. The adaptive antenna array demonstrates electronically self-steering radiation pattern capability towards satellites signals, suppress interferences and multi-path signals. This can be achieved by adapting the Least Mean Square (LMS) algorithm by varying the number and phase of the array antenna elements and the angle of beam steering to determine the Direction of Arrival (DOA) of incoming signals. The performance of adaptive LMS algorithm is investigated in MATLAB software by analyzing the radiation patterns for different number of array antenna elements, phases and beam steering angle. The purpose of LMS algorithm implementation in the Adaptive Array Antenna (AAA) system is to control weights adaptively, optimize the Signal to Noise Ratio (SNR) of the desired signal and minimize the Mean Square Error (MSE).
Recently, various unmanned and manned Mars exploration programs have been proposed. To send a space vehicle safely to the ground of Mars, the vehicle needs to be protected from the aerodynamic heating. The accurate prediction of the aerodynamic heating is important for the design of safe and light-weight thermal protection system. For the accurate prediction, it is necessary to simulate the plasma generated behind the shock wave and to clarify its internal state. To investigate the state of the plasma, spectroscopic measurement is useful. We performed the spectroscopic measurements of carbon dioxide (CO2) plasma generated using microwave discharge under the pressure condition during Mars entry. To investigate the basic characteristics of microwave-discharged CO2 plasma, the spectra of the radiation were obtained in the wavelength region of 200 to 800 nm. As a result, carbon monoxide (CO) fourth positive bands, CO third positive bands, CO Ångström bands, and atomic oxygen lines were observed. Electronic excitation temperature was also estimated by the Boltzmann plot method for the atomic oxygen lines.
A huge fire occurred on December 22, 2016 in Itoigawa, Niigata. Records show that instantaneous wind speeds reached 27.2 m/s, whereas 120 houses were burnt down, 147 houses were damaged, and an area of approximately 4 ha was affected. The city has been promoting the recovery of infrastructure from September 2017. In this study, the recovery was evaluated based on the Landsat-8 time series data by using urban indices. By comparing the indices in damaged and non-damaged areas, the authors investigated the relationship between the recovery status and index values. The urban index (UI), built-up area (BA) and Grain Size Index (GSI) were used in this study. The UI is calculated based on the difference/sum of bands 7 and 5. The BA is determined by the difference between the Normalized Difference Built-up Index (NDBI) and the Normalized Difference Vegetation Index (NDVI), which are calculated by the difference/sum of bands 6 and 5, and by the difference/sum of bands 5 and 4, respectively. Changes in each index in the damaged and non-damaged areas were recognized from the Landsat data collected for two years. However, sufficient time is required to initiate a restoration plan, and, therefore, the present status is limited to the planning stage. This is one of the reasons why changes in the indices were not so clearly visible. Moreover, as indices are influenced by seasonality, it should be compared between the images observed during the same season.
Smart Lander for Investigating Moon (SLIM) is a lunar lander that demonstrates pinpoint guidance to the target site. From mission requirements such as landing on rough terrain and slopes, SLIM adapt a landing method called the two-step landing. In this study, we explored landing leg arrangements suitable for the constraints from launch to touchdown in the SLIM mission and then realized stable touchdown on the lunar surface. For this challenge, simulation was constructed for the touchdown dynamics of SLIM, and Monte Carlo analysis was conducted to understand the tendencies. Moreover, the obtained leg arrangement was confirmed as making stable touchdown possible within the range guided by the guidance and navigation control system. In the process of these studies, we also revealed that it is possible to analyze touchdown dynamics efficiently by focusing and considering the critical results derived from a statistical analysis using the Monte Carlo method even in complex boundary conditions for the realistic spacecraft.
The development of the MEMS (Micro Electro Mechanical System) technology makes the COTS (Commercial Off-The-Shelf) attitude sensor smaller, enables lower power consumption, and improves the attitude determination and stabilization performance of the CubeSat. However, their performance has a temperature dependence. Verification and evaluation need certain development duration and costs. In addition, in CubeSat thermal design, the contact thermal conductance between the components can be varied with the system integration uncertainties and the thermal interfaces are difficult to standardize. Their heat capacities are small and the temperature of the component is easy to be influenced by the thermal environment changes mainly corresponding to their attitude. This paper proposes the temperature stabilization system for MEMS attitude sensor for maintaining performance. The system mitigates temperature change by increment the heat capacity around the target temperature. The novel solid-solid phase change heat storage materials are introduced and evaluated for this purpose. In addition, the suitable insulator and heat transportation materials are designed and equipped to reduce the contact thermal conductance variation range. The effectiveness of the proposed system is confirmed through numerical analysis and some typical experiment, considering practical on-orbit condition. The thermal-mathematical model of the proposed system is also constructed through the discussions.
This paper presents expansion tube specifications and characteristics using high-speed imaging, the emission intensity of flow, and the pressure probe using a 35 mm square bore and 15 m total length expansion tube in ISAS/JAXA. To elucidate test gas acceleration processes, several visible windows can be used to observe flow static pressure and emission intensity. Results show that the shock wave and test flow velocities, flow density, and flow temperature were, respectively, 7.8 km/s, 7.2 km/s, 0.02 kg/m3, and 5922 K with 44 μs test time duration. This study obtained characteristics of expansion tube flow which can be compared with numerical calculation or more accumulated measurements.
This study aims at improving the actuator which has hold-down and releases mechanism using Shape Memory Alloy (SMA). The SMA actuator, which is discussed in this study, consists of an SMA tube, a restraint, and a heater. These kinds of actuators can achieve high power density; however, their force generation trajectories are affected by the environmental temperature variation because of their huge heat capacity. This paper discusses the method to track the required force trajectories for drive timing improvement. First, previous studies are introduced. Then, this paper points out the problems in previous research and describes the details of the modeling to improve simulation accuracy. The hysteresis model of SMA is introduced and the system identification method used in this study is shown. Finally, the experiment is performed to identify the hysteresis characteristics of SMA. The result was consistent with the trend of the detailed model. Moreover, the constraints for the system identification were derived from the experiment results.
This paper proposes a method to design a rendezvous trajectory of Earth orbiting satellite that is energy-saving and robust against parameter variation. In order to obtain inputs that generate robust trajectories, we evaluate the effect of the parameter variations by using the variational system, which considers the variation of the state. We have introduced the variational system of the discrete-time model so that we can apply L1-optimal control. By using Kalman's canonical decomposition, a sufficient condition to suppress the effect of the parameter variation is obtained. Numerical examples exhibit how the proposed method works in suppressing the effect of the parameter variation.
A key technological requirement for realizing a supersonic combustion ramjet (scramjet) engine is supersonic mixing enhancement. Streamwise vortices, which have larger circulation and break down more quickly into small-scale turbulent eddies, can be effectively used for supersonic mixing enhancement. In the present study, to clarify the condition for mixing transition in supersonic streamwise vortices, we performed visualization by the schlieren method as well as particle image velocimetry and hot-wire anemometry measurements of a supersonic mixing field that introduced streamwise vortices at the freestream Mach number M∞ = 1.8. It was confirmed that the mixing transition state of streamwise vortices was spread over the whole vortex region owing to the shear layer instability at the outer edge and the unstable swirling motion of the streamwise vortices.
In this paper, we introduce a concept for the utilization of Data over Power Line (DoP) for space applications to extend the currently available networking between components and subsystems and to benefit from the resulting harness reduction. DoP makes use of the already existing power lines in a spacecraft (S/C), since each of the electronics needs to be powered. The proposed system uses a commercially available DoP modem to convert between digital signals and a modulated carrier that is superimposed onto the DC power lines. The utilization of this technique also needs to pass significant challenges whereas solutions are presented in this paper. For this reason, we introduce possible network topologies which can be used in spacecraft systems. Furthermore, we give an insight into the development of the end-to-end communication demonstrator and illustrate the use cases for our latest spacecraft projects, i.e. CompactSat or S2TEP satellite platforms. We also explain the modes of operation, and we will present the results of the electromagnetic compatibility (EMC) tests, which is one of the most challenging concerns, when using DoP in a spacecraft. Finally, we conclude the harness reduction potential that we expect for a reference DLR spacecraft mission.
LSP (Laser Sustained Plasma) has a higher temperature than arc discharge plasma without electrodes. So, the LSP is a promising heat source of electrothermal type thruster, which has a higher specific impulse and longer lifetime than those of arcjet thrusters. In this study, we tried to generate methane, methane–argon and methane–xenon LSPs using 1 kW class diode laser. As a result, the LSP could not be generated for the methane and methane–argon gases though the emission intensity increased with the laser irradiation. In the case of methane–xenon gases, the LSP could be generated at the xenon pressure of 0.10 MPa, and the methane pressure ranged from 0.02 MPa to 0.06 MPa. The threshold power was around 850 W, which is lower than the pure xenon condition.
Space debris smaller than 2 mm that cannot be detected by ground-based observations may lead to a spacecraft's mission end. Therefore, multiple institutes and organizations have conducted in-situ measurement projects including the IDEA (In-situ Debris Environmental Awareness) project, which has been initiated at Kyushu University. The previous research has proposed a statistical method that estimates the environment of sub-millimeter-size debris sequentially utilizing in-situ measurements. This paper aims to improve accuracy of the estimation result by a “feedback estimation” method that utilizes the measurement data multiple times. Furthermore, this paper also calculates “total likelihood” to evaluate the accuracy of estimation results quantitatively so that effectiveness of the feedback estimation can be discussed. The evaluation with the total likelihoods suggests that the feedback estimation method can increase the accuracy of the environmental estimation. In conclusion, this paper contributes the improvement in the environmental estimation on sub-millimeter-size debris utilizing in-situ measurement.
In this study, cheap and easy-to-use CubeSat educational materials are developed for students studying satellite development, for the first time. The developed model CubeSat is slightly larger than 1U size, and comprises multiple subsystems similar to a real satellite. In addition, model CubeSat competitions on the power supply, communication, and attitude are designed and conducted, where the respective subsystems are applied. The questionnaire results indicate that the model CubeSat assembly course and competition are popular and beneficial for the students.