The Space Debris Mitigation Guidelines of the Scientific and Technical Subcommittee of the United Nations Committee on the Peaceful Uses of Outer Space consist of seven guidelines to be considered for the mission planning, design, manufacturing and operational (launch, mission and disposal) phases of spacecraft and launch vehicle orbital stages. In order to compare small satellites with large satellites in terms of impact on the orbital debris environment, this paper focuses on guideline 3 in the mitigation guidelines, which limit the probability of accidental collision in orbit. The probability of accidental collision is a function of the effective cross-sectional area. Large satellites have a larger effective cross-sectional area in comparison to small satellites, so that large satellites specify a higher probability of accidental collision than small satellites do. The number of fragments to be generated by a collision is a function of mass. Therefore, in the comparison to small satellites, large satellites also generate more fragments and add them to the environment.

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A numerical and experimental study on the aerodynamic heating inside a gap in a hypersonic laminar boundary layer on a flat plate is conducted at a unit Reynolds number of 6.1 × 10⁶ m^-1 and a Mach number of 8.1. In this study, two cases: a side-open gap and a side-closed gap are investigated. As a result, It is found that in both cases, the heat flux at the back wall of the gap is predominant only in the upper region of the gap depth. The difference between the side-open gap and the side-closed gap appears only in the side region. In the former case, a free shear layer comes into the gap from outside, which generates a heat flux peak at the side wall edge, while in the latter case such a phenomenon is not observed. In addition, the two cases have similar distributions of heat flux except in the side region. Furthermore, the peak value of heat flux at the back wall is 3-4 times as large as that on the flat plate without a gap at the same location. On the other hand, the heat flux at the side wall of the gap in the case of side-closed gap becomes smaller than that at the back wall; it is less than half as large.

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The aerodynamic characteristics and the effects of tip plates of a tapered supersonic biplane wing during the starting process were investigated by experimental and computational fluid dynamics (EFD/CFD). Three types of wing models were used: one with a tip plate covering only the aft-half of the wing tip (type-A); one with a tip plate covering the entire wing tip (type-B); and one without a tip plate (type-N). Experiments were conducted in a supersonic blowdown wind tunnel 600 × 600 mm in cross-section located at the high-speed wind tunnel facility of the Institute of Space and Astronautical Science (ISAS/JAXA). The flow conditions ranged from M_∞ = 1.5 to 1.9 in increments of 0.1. Pressure-sensitive paint was applied to measure the pressure distributions on the wing surface. CFD simulations were conducted for comparison with the experimental results and for detailed investigation of the effects of the Mach number. The tapered biplane wing without a tip plate is found to start between M_∞ = 1.8 and 1.9. The difference in starting Mach number between type-N and type-A is small. On the other hand, the starting Mach number of type-B is approximately 0.05 higher than that of type-N.

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In this paper, the behavior of flexible membranes is investigated via numerical simulations using the multi-particle method (MPM) in which the membrane is replaced by a spring, damper and mass. To verify the model, some experiments on membrane vibration using a vacuum chamber are carried out. These results are compared with the results of numerical simulations using the MPM, and then the membrane structural model based on the MPM is refined to accurately simulate the behavior of membranes in experiments.

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In the present study the supersonic flow over rigid parachute models is studied by numerically solving the three-dimensional compressible Navier-Stokes equations at a free stream Mach number of 2. The parachute system employed here consists of a capsule and a canopy. Two models are considered: model A and model B. The former is the same model as the experiment, where the canopy is connected with the capsule by a rod, and the whole system is supported by another rod, while the latter does not have these rods. The objective of the present study is to examine the flow field produced by these models, and analyze the effects of aerodynamic interaction such as shock/shock and wake/shock interactions on it. The numerical results show good agreement with the experimental data in the case of model A. In addition, it is found that the difference of flow features between models A and B is rather small. The unsteady flow pulsation phenomenon observed in this study can be demonstrated using three processes; the bow shock formed ahead of the capsule periodically inflates and laterally expands, which is caused by upstream propagation and lateral expansion of the complicated wake/rear shock and fore shock/rear shock interaction systems.

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This study elaborates on system identification of flight characteristics of small unmanned aerial vehicles (UAVs), which are defined as fixed-wing aircraft with wingspan of approximately 1 m and gross weight of 1 kg. Although system identification is well-established as a method to acquire flight characteristics of large aircraft, few cases apply this method to small UAVs. Therefore, the goal is to examine whether techniques for large aircraft are applicable to small UAVs. This study focuses on two obstacles: 1) An avionics device that obtains the required data to perform system identification must be far lighter and smaller than the existing ones for installation into small UAVs, and 2) an appropriate analytical method must be used to obtain accurate results because small UAV flight differs significantly from large aircraft flight, such as in terms of low gust resistance. For the first problem, new small and lightweight avionics utilizing micro electro-mechanical system (MEMS) sensors are proposed. The second obstacle is studied by applying four sophisticated analytical methods and the results show that unscented Kalman filter (UKF) is superior to recursive least square (RLS), Fourier transform regression (FTR), and filter error method (FEM).

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The mechanisms of drag reduction in a Mach 2 supersonic flow induced by repetitively deposited laser pulse energy are investigated through computational fluid dynamics based on Navier-Stokes equations for an axis-symmetric flow. The effectively deposited energy into the flow is determined by fitting a measured stagnation pressure history. With the repetition frequency lower than 20 kHz, the experimental flow-field, the residence time of baroclinically-generated vortex rings in the shock layer and drag reduction characteristics are well simulated by the axis-symmetric computation. At the lower frequency below 5 kHz, the low-density bubbles successively generated by energy depositions behave in an almost independent manner, so the drag reduction can be estimated by superimposing single pulses. At a middle frequency from 5 to 14 kHz, there is weak interaction among the successive vortex rings, but the behavior can be assumed to be almost independent. At even higher frequency, a quasi-stationary vortex ring is observed in the shock layer and grows according to frequency increases and the shape of the shock transit from the bow shock to the oblique one. The drag reduction is related to the number and the residence time of the vortex rings.

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In this paper, the flow field and aerodynamic characteristics of a quadrotor are studied via three cases of numerical simulations: First, the flow field around a hovering quadrotor is simulated; second, the case with a side wind is simulated; finally, the flow around the quadrotor and its motion are simulated via motion-coupled flow computation. In the first case, it is found that the downwash generated by each blade is strengthened mutually and that the Cp distributions on the blade upper surface vary according to the blade position, causing periodic, 5% of thrust oscillations. In the second case, it is found that the positive pitching moment acts on the body. This moment is partly created by reduced thrust from downstream rotors that receive flows already directed downward at upstream rotors, and hence, having effectively decreased angles of attack. The final case shows that, due to the pitching, the quadrotor is unstable in the side wind condition until it reaches an almost vertical attitude. It is demonstrated that the present motion-coupled flow simulation serves as a powerful tool to reproduce and understand behaviors of quadrotor flights.

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One nodal thermal analysis of nano and micro cubic satellites pointing to the Earth on sun-synchronous and circular orbits is carried out. The altitudes of the orbits are from 300 to 1,000 km. The local time of descending node is from 6 to 12. The combinations of the solar absorptivity and the infrared emissivity on the surface of the satellite in which the satellite satisfies the allowable temperature range, from 0 to 40 deg. C., are clarified for each of the above orbits. As the parameter of heat capacity of the satellite over one surface area of the satellite increases, the choice of combinations of the solar absorptivity and the infrared emissivity increases. The number of combinations in the case of the orbits without the shadow region is much larger than that with the shadow region. The number of combinations in the orbits without the shadow region increases with higher altitude and larger projected area with respect to the sun. The number of combinations in the orbits with the shadow region increases with higher altitude, larger projected area and smaller angle of the shadow region.

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This paper quantitatively evaluates the accuracy of the base of aircraft data (BADA) model by comparing calculated fuel flow and total fuel consumption with flight data recorded by airliners' quick access recorder systems. For future more efficient air transportation system research, it is necessary to derive fuel consumption for an arbitrary flight trajectory with good accuracy. BADA, the European Organization for the Safety of Air Navigation (EUROCONTROL) aircraft performance model is widely used for such purposes, but there is only a small number of papers which discuss its accuracy with actual flight data. The purpose of this paper is to investigate whether the BADA model has sufficient accuracy to deal with the study of air transportation systems. As a result of comparison conducted for a single fleet of twin engine wide-body jet passenger aircraft, calculated fuel flow showed good agreement with the flight data in the cruise phase and it was found that the error between the BADA model and flight data falls within plus or minus 5 [%] for a whole flight.

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The purpose of this research is to characterize the thermochemical states of CO₂ and CO₂-N₂ arc plasma flows via temperature measurements. To do this, radiation from the stagnation streamline around a disk model is measured using the newly developed multipoint spectroscopic measurement system and temperatures are deduced by applying the spectrum fitting method to the measured spectra. It is found that the vibrational temperature is nearly constant and higher than the rotational temperature along the stagnation streamline, showing the vibrational nonequilibrium process. The rotational temperature is also nearly constant and does not increase in the shock layer. This may be caused by the fact that measured temperatures are averaged temperatures along the line-of-sight (LOS). In conclusion, the thermochemical states of CO₂ and CO₂-N₂ arc plasma flows are vibrational nonequilibrium states in the free stream region. However, the thermochemical state in the shock layer cannot be clarified accurately using LOS averaged temperatures. In the future, LOS effects should be examined using spectroscopic measurements along a radial direction.

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Fuel-efficient flight is in strong demand due to environmental concerns and skyrocketing fuel prices. This paper analyzes airliner flight trajectory from the perspective of fuel efficiency through comparison with the optimal trajectory. Since the optimal trajectory gives the maximum achievable performance without any constraint of air traffic control, it introduces reference data for quantitative merit of the ideal flight. Dynamic programming is adopted to calculate the optimal trajectory. Examples show that considerable reduction in the fuel consumption from the estimated values for actual flights could be achieved by the trajectory optimization, where wind conditions are taken into account as well.

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In the present study, the supersonic flow over a three-dimensional flexible parachute system is numerically simulated using a simple "immersed boundary method" together with the weak fluid-structure coupling scheme. The parachute system employed here consists of a capsule and a canopy. The mass-spring-damper model is applied to solve the structural dynamics of the flexible parachute system. The objective of this study is to analyze the effects of aerodynamic interaction such as wake/shock interaction on the dynamics of the canopy behavior, and clarify the performance of the flexible parachute system in terms of Mach number, the ratio of a capsule to a canopy diameter, and the trailing distance between the capsule and canopy. As a result, it is found that there are two key factors for the dynamics of the parachute system: one is the unsteady change in canopy shape and the other the aerodynamic interference between the capsule wake and the canopy shock. As the trailing distance increases reasonably, the area oscillation of the canopy shape is observed. However, by reducing the canopy size in the certain smaller trailing distance case, the canopy deformation is improved. Moreover, it is found that the free stream Mach number has a big impact on the canopy behavior in the smaller Mach number case, where the canopy undergoes smaller deformation, leading to a larger drag coefficient.

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The presence of orbital debris is a potential risk for sustainable space development and its utilization for humankind. Prevention of large-scale spacecraft breakup events is a crucial part of countermeasures against orbital debris, and one of the key related technologies is the collision avoidance maneuver. Current observations are insufficient to track objects smaller than 10 cm, which are still large enough to cause catastrophic damage to primary spacecraft. The final goal of this study is to track debris 1 cm and larger in the low Earth orbit region. This paper proposes a space-based optical measurement system as a new promising solution. There are three points to be followed: 1) observation opportunity, 2) orbit determination accuracy and 3) tracking capability. As the first step, this paper focuses on assessing observation opportunity using a newly developed space-based observation simulator. This paper summarizes assessment results in terms of the number of passing objects, imaged objects, image moving velocity in pixels, apparent magnitude, observation occurrence frequency with respect to the observer's true anomaly, and the relationship between the observation count and interval.

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