The Japan Aerospace Exploration Agency (JAXA) has developed an airborne turbulence detection system based on coherent Doppler lidar (CDL) as a way to reduce the number of turbulence-induced accidents. A flight experiment with a jet aircraft measured and compared how the aerosol particle concentration in the atmosphere correlated with the laser backscatter coefficient and maximum observation range at different altitudes. Although we verified that the turbulence detection range of the CDL was sufficient to be able to issue go-around advisories to avoid windshear during approach, its short range at high altitudes is likely to limit its effectiveness at providing advance warning of turbulence when cruising. In order to mitigate turbulence-induced accidents, it is possible to use CDL as a sensor to acquire preview information for gust alleviation control. However, there are still technical issues to be solved in general control by control surfaces, so automatic deceleration is a more realistic control method. Generally, deceleration reduces the severity of aircraft motions induced by turbulence. Based on these results, we propose the basic specifications of a CDL that will be effective in mitigating turbulence accidents and its practical use.
Modern aircraft can generate their optimal flight profile via a flight management computer. The optimality considers both time and fuel costs, and the pilot can set the relative weight factor called a cost index (CI). However, sometimes the flight profile should be updated during flight due to various reasons e.g. passenger boarding delay and airport congestion, and pilots often change the flight profile by changing the CI. Since CI is a relative factor, it is difficult to set the optimal CI in every situation and flight stage. This paper proposes a decision-support algorithm aimed at 1) providing pilots with information on the most appropriate range of CI or flight speed (climb/cruise/descent) and 2) clarifying the relationship between the timing of changing the flight profile and its effect. As for 1), in order to provide the appropriate range of CI or speed, a new metric of direct operating cost bound is introduced. As for 2), it is revealed that descent speed is the most effective parameter to change the flight time and fuel consumption, but the appropriate CI varies with flight phases. The results obtained in this research will help pilots change the flight profile flexibly to achieve greater efficiency.
To solve the complicated scheduling problem of many observations in earth-observing satellites, we propose an effective multi-objective combinatorial optimization method using a genetic algorithm (GA) to maximize speed, visibility, and the number of adoptions of target points according to the priority. A characteristic of the proposed method is the constraint of “one observation per point.” Another is that conflict between the observation tasks is considered. To determine the conflicts, the attitude maneuver time is calculated by assuming a triangular or trapezoidal linear angular velocity profile in order to reduce the computation time and obtain an actual control time that is as close as possible. The simulation results indicate that the proposed method can adopt more target points than the comparative method without considering the attitude maneuvering time. Moreover, the Nankai-Trough earthquake demonstration shows the effectiveness of disaster monitoring.
This paper proposes an algorithm to determine the convergence of angular rate by using B-dot measurements from a 3-axis magnetometer based on a probabilistic approach. The probability distribution of the sum of the square of B-dot is analytically derived when the CubeSat has a zero angular rate. The probability distribution when the CubeSat has a non-zero angular rate is derived based on simulations. In addition, by choosing two probability distributions and setting a threshold between them, the convergence probability of the angular rate is calculated using Bayes’ theorem assuming that CubeSat obtains consecutive magnetic measurements in real-time. Finally, the proposed algorithm is verified through Monte Carlo simulations and detailed discussions are presented along with comparisons with previous research and methods.
The effects of roughness parameters, including height, diameter, and spacing of the cylindrical roughness elements, on turbulent transition are investigated in a three-dimensional boundary layer using direct numerical simulation. There are two types of transition process, classified as gradual and forced. The former is caused by a linear development of crossflow vortices and their secondary instability, while the latter is an immediate breakdown to turbulence behind the roughness without any crossflow vortex. These processes are only demarcated by the roughness height. The diameter and the spacing affect the initial creation processes of the crossflow vortex as well as the onset of the secondary instability in the gradual transition. With a fixed roughness volume, the greater height induces larger initial disturbances and causes earlier transition than a larger diameter. The aforementioned observations apply when the most unstable crossflow mode is induced. When the unstable mode is absent or is secondarily induced, the disturbance decays or the transition point shifts downstream. Therefore, when considering the critical parameter between the gradual and forced transitions, only the height is crucial. However, for a gradual transition, roughness parameters affect the transition point and we should consider the flow alternation caused by the roughness.
Majority of spacecrafts rely on solar power as the main source of energy. The search for a lightweight and cost-efficient energy source with high power conversion efficiency (PCE) led to the development of organic-inorganic metal halide Perovskite solar cells (PSCs). In this paper, the performance of PSCs with different hole-transport material (HTM) prepared for in-orbit demonstration mission onboard CubeSats are compared under simulated space environment such as thermal cycling stress, high-vacuum, UV radiation and vibration. Results show that even though organic and inorganic HTM display superior initial PCE, Carbon HTM PSCs trumps them in terms of stability and is more practical for use in space. The paper also discusses the satellite mission and developed hardware for the first demonstration of Perovskite solar cells on-board a satellite to gather in-orbit information on the performance of Perovskite solar cells in low-earth orbit and how the ground test results would be verified.