In this paper, among the technological innovations for sustainable development of future space transportation, the safety aspects of rocket propulsion are discussed to show that the achievement of fail-safety or fail-tolerance is equivalent to the realization of safety resilience in the space transportation system. Further, it is shown that such realization is extremely difficult with the conventional essentially explosive propulsion systems (EEPS) and that essentially non-explosive propulsion systems (ENEPS) are indispensable to obtain the required safety characteristics in space transportation systems. Specifically, the safety characteristics of the EEPS and ENEPS are analyzed under both the current Safety-I and the Safety-II conditions advocated by Hollnagel. As a result, it is shown that the safety characteristics of EEPS are in the category of Safety-I, and it is difficult to shift to Safety-II, while the safety characteristics of ENEPS allow achieving the category of Safety-II. The technical challenges of hybrid rockets, which are representative of ENEPS, are expected to be overcome by devising the Altering-Intensity Swirling-Oxidizer-Flow-Type method or similar ones. Thus, ENEPS will pave the way for future failure tolerance of space transportation.

In this study, the authors conducted four experiments to investigate the response time of axial-injection end-burning hybrid rockets under throttling operations. Oxidizer mass flow rate and chamber pressure were throttled by two methods, by actuating valves in a fluid circuit consisting of two oxidizer supply lines and by motor control. Chamber pressure and oxidizer mass flow rate were measured during each firing. The results show that a chamber pressure response time was observed when oxidizer mass flow rate was increased (turn-up operation). The chamber pressure response time increases as the rate of change of oxidizer mass flow rate increases. In addition, the chamber pressure response time also increases as the difference in the oxidizer port velocity before and after throttling increases. Therefore, it is considered that the chamber pressure response time is the time that it takes for the diffusion flame to achieve a steady-state stand-off distance in response to a change in oxidizer port velocity.

In order to check the operation of a parachute deployment subsystem under the environment equivalent to dynamic pressure of Mars entry, to validate the mechanical strength of a supersonic parachute, and to obtain the opening shock and aerodynamic coefficients of parachute under free flight condition, flight test of the supersonic parachute was carried out by using the JAXA’s research helicopter at the Taiki aerospace research field. In the test, the test vehicle equipped with the supersonic parachute was suspended below the helicopter, and was dropped from 600m altitude at sea area 7km offshore of Hamataiki. A supersonic parachute was then deployed automatically after the 3.5 s free flight. The release of parachute was attained by igniting an automobile airbag inflator. A disc-gap-band type parachute was employed as the supersonic parachute in this study. During the flight, flight dynamics of the test vehicle was analyzed by using 3D accelerometers. The tension in parachute riser lines were measured by using load cells. After 22 s flight, the test vehicle splashed down in the ocean, and was recovered by fishing boats.

In order to predict the flammability limit of thin materials in microgravity environments without conducting microgravity experiments, we developed a simplified model for flame spread in an opposed flow by introducing two non-dimensional parameters which represent radiative quenching and blow-off extinction. Thin PMMA sheet and NOMEX HT90-40 fabric were used as the sample. For predicting the blow-off limiting curve, the pre-exponential factor and the activation energy are required, however, these properties are hardly available in the literature. Hence, we proposed a novel blow-off test in a forced flow to obtain empirical parameters which reproduce the actual blow-off phenomena correctly. Although the properties of NOMEX are unknown, the limiting curves of NOMEX with these empirical parameters well agreed with the results of the parabolic flights, and the obtained minimum oxygen concentration was also close to the experimental value.

In satellite-to-ground optical communications, it can be assumed that the link will be established if site diversity is performed among two or more ground stations connected with the terrestrial network. But by storing the data based on weather survey data quantitatively and statistically, and carrying out analysis processing needs to show the validity. Therefore, the data from ten environmental-data collection stations throughout Japan has been collected and analyzed for a statistically-long time. This paper shows the overview of this system and the analyzed site diversity effect.

Frequent monitoring of the urban changes is important for urban and economic development planners. Satellite imageries provide chance for mapping the rapid urban expansions and can be effectively used for monitoring the urban changes. This study highlights the automatic extraction methodology of generating land cover maps from single-polarization SAR imageries of TerraSAR-X (HH) of the developing regions in Southeast Asia such as Indonesia and the Philippines by utilizing deep learning algorithm. As single-polarization SAR imageries have difficulty of classification of water areas, the water areas are extracted from optical satellite imagery of Landsat and Sentinel-2. After generating land cover maps, urban areas are extracted. By analyzing time series of satellite imageries in the proposed methodology revealed that there are fast developments of the urban areas in the developing countries. The results were validated by the existing facts of development plans for each country. This study demonstrated about the value of combining SAR and optical satellite imageries for urban change monitoring by utilizing deep learning technique.

We are developing an image based adaptive optics system using a micro electro mechanical system (MEMS) deformable mirror for earth observing sensors. We proposed two algorithms for control of the deformable mirror, a stochastic parallel gradient descent (SPGD) optimization and a deformable mirror diversity estimation. We developed an adaptive optics system testbed using a commercial astronomical telescope and a MEMS deformable mirror. We observed a distant building pattern from our laboratory, then controlled the deformable mirror to compensate the wavefront aberration. Experimental results show that misalignments and wavefront aberrations are compensated and image qualities are improved.

Long-term manned space flights are dependent on bio-regenerative life support systems (BLSS). Plants in BLSS will be important for food production, CO₂/O₂ conversion, and water purification. Stem sap flow is an important indicator of transpiration and growth of plants. In the present study, we created three low gravity levels in parabolic airplane flights and investigated stem sap flow of sweetpotatoes, which are candidate crops in space agriculture. We observed that stem sap flow with forced air movements was promoted at gravity levels lower than 1 g. Air movement around the plants is very important in order to develop BLSS that is able to maintain healthy plant growth with high yields for long-term periods.

The characteristics of a CFRP deformable reflector system were investigated through experiments and numerical simulations. The CFRP reflector was mounted on an actuation system and deformed by three actuators, which were placed one each on three concentric lines that were 120° away from each other. In the experiments, three types of reflector deformation were achieved by operating each actuator individually, and the deformations were measured by a photogrammetric measurement system. The deformations were analyzed and compared using Zernike polynomials. The apparent anisotropic deformations of the quasi-isotropic CFRP shell were observed, and the tilt and astigmatism modes were determined to be outstanding. In order to investigate the effects of actuator stiffness, a few numerical simulations with higher stiffness of the actuators were performed. The results reveal that with the increased actuator stiffness, deformations became larger, while the outstanding modes did not vary.

A field emission cathode (FEC) using a carbon nanotube was developed for an electrodynamic tether experiment on H-II transfer vehicle 6 (HTV-6). The mission is called the Kounotori Integrated Tether Experiment (KITE). Development of the FEC began at the beginning of 2013 and was completed in the spring of 2016. KITE began in January 2017 and the FEC worked well, with various types of on-orbit data being obtained despite unsuccessful tether deployment. All eight cathode units operated without any critical trouble throughout the experiment period. The total operation time reached 50 hours and the maximum emission current was approximately 5.8 mA, and thus exceeded expectations based on ground experiments. The electrical current loop via an ambient space plasma without the tether was probably formed due to the collection of electrons on the anodic parts of the HTV’s solar cells.

The thrust performance of a steady-state, applied-field magnetoplasmadynamics (MPD) thruster has been improved by increasing a discharge current was increased from 20 A to 60 A using a lanthanum hexaboride (LaB₆) hollow cathode. The experimentally obtained thrust characteristics were consistent with that of electromagnetic acceleration. Using argon as the propellant, a thrust efficiency of 25.5% and a thrust/power ratio of 17.0 mN/kW were obtained with an applied magnetic field of 265 mT, discharge current of 30 A, propellant mass flow rate of 2.1 mg/s and discharge voltage was 121 V.

Satellite dynamics is described by a nonlinear differential equation. Most recent studies about attitude control have used nonlinear controllers. However, with these controllers, control performance is ignored in most cases. To overcome this problem, this paper applies the linear parameter-varying (LPV) control theory to the attitude control for a spacecraft with reaction wheels (RWs). The LPV control theory can provide a gain-scheduled (GS) controller by using linear matrix inequalities (LMIs) for the mixed H₂/H_∞ control which guarantees optimality and robustness at the same time. Besides, two types of regional pole placement (RPP) constraints are considered. Through some numerical examples, the effectiveness of these two types of RPP constraints are demonstrated.

Nitrous oxide is in a gas-liquid equilibrium state at room temperature, and its vapor pressure is very useful concerning devices such as a pressure-fed hybrid rocket engine systems. However, it is not easy to estimate the flow history of the equilibrium flow. The vapor pressure and the latent heat of the vaporization of nitrous oxide strongly depend on its temperature. Though many models have been proposed, we used a simple equilibrium model and examined important parameters and negligible parameters considering experimental results. Experimental results displayed a substantial difference between the top and bottom tank temperatures, and that the tank pressure greatly matched the saturated vapor pressure at the liquid-phase temperature. A simple analysis showed that the determination of initial temperature was the most important factor and the heat transfer from the tank wall to the nitrous oxide was negligible.

Certain combinations of ammonium dinitramide (ADN, melting point = 93 °C) and additives such as methylamine nitrate (MMAN) (melting point = 110 °C) and urea (melting point = 133 °C), form stable ionic liquids, even below room temperature. These mixtures, referred to as energetic ionic liquid propellants (EILPs), can be highly energetic, and yet are easy to handle. Improving the performance of EILPs will require an understanding of the effects of the additives on the melting point and reaction mechanism for ADN. Therefore, the present work examined the melting point and thermal decomposition and ignition processes for EILPs based on ADN and various amine nitrates. Some EILPs made with low molecular weight amines were found to exhibit a reduced melting point, and high speed photography demonstrated that ignition of these mixtures took place following thermal decomposition of the condensed phase. The thermal behavior and gas evolution for EILPs during heating were assessed by thermal analysis combined with spectrometry and the results showed that the decomposition products were not affected by the specific amine nitrate used in the mixture. The data also suggested that variations in the heat release and reactivity for these mixtures during thermal decomposition can influence the ignitability of the EILPs.

Gel propellants have been recognized as future propulsion systems. Gel propellants are liquid fuels such as hydrazine, of which the rheological properties have been altered by the addition of gelation agents. Ammonium dinitramide (ADN) based energetic ionic-liquid propellants (EILPs) are expected to be used as replacements for hydrazine, which has high toxicity, and also for ionic liquid gel propellants (ILGPs). However, there have been few studies conducted on ADN based ILGPs. Here, ADN based ILGPs were prepared to obtain a better understanding of their thermal properties. The thermal behavior of the ADN based ILGP samples were measured using differential scanning calorimetry and the evolved gases were analyzed using thermogravimetry–differential thermal analysis with mass spectrometry. An ADN based ionic liquids (ILs) formed a gel using gelation agents of agarose and hydroxypropyl cellulose. The gas evolved from ADN based ILGPs was determined to be different from that from ADN based ILs due to reaction between the IL and the gelation agents.