During Solar Cycle 24, the passive spherical satellites LARES and Ajisai, placed in nearly circular orbits with mean geodetic altitudes between 1450 and 1500 km, were used as powerful tools to probe the neutral atmosphere density and the performances of six thermospheric models in orbital regimes for which the role of dominant atomic species is contended by hydrogen and helium, and accurate satellite measurements are scarce. The starting point of the analysis was the accurate determination of the secular semi-major axis decay rate and the corresponding neutral drag acceleration in a satellite-centered orbital system. Then, for each satellite, thermospheric model and solar activity level, the drag coefficients capable of reproducing the orbital decay observed were found. These coefficients were finally compared with the physical drag coefficients computed for both satellites in order to assess the biases affecting the thermospheric density models. None of them could be considered unconditionally the best; the specific outcome depending on solar activity and the regions of the atmosphere crossed by the satellites. During solar maximum conditions, an additional density bias linked to the satellite orbit inclination was detected.
As the amount of debris in orbit increases, so does the risk of collisions and their seriousness. All nations involved with space operations acknowledge this growing threat. One solution receiving increased attention is active debris removal. The first step in a debris removal mission would be to approach the debris. In this phase, it is important to ensure passive abort safety and to guarantee the robustness against collisions in the case of off-nominal thruster burns, that may be caused by spacecraft anomalies such as navigation sensor or actuator failures. This paper compares two types of passive abort safe trajectories –the V-bar hopping and spiral approaches– considering the ΔV budget, the duration of operations, and variation in the line-of-sight vector to the target. This paper also proposes design strategies for determining the parameters in the two candidate trajectories, considering passive abort safety. The robustness of the trajectories against collisions due to off-nominal thruster burns is also demonstrated through Monte Carlo simulations. The paper investigates which trajectories are suitable for an active debris removal mission to a non-cooperative target.
The objective of this study is to determine the two-dimensional unsteady aerodynamic forces and moment acting on a heaving wing in a uniform flow using a wind tunnel. However, it is difficult to measure the aerodynamic forces acting on the heaving wing due to measuring device oscillation and the large inertial force of the wing model. In this study, a new type of wind tunnel test, named ` `heaving wind tunnel,' ' was developed. Here, the wing model remains stationary as the wind tunnel oscillates with a heaving motion. The advantage of this experimental method is that the measurement results are unaffected by the large inertial force acting on the oscillating wing model. Therefore, the wing model can be used in the same way as in steady state experiments. The normal force, thrust and pitching moment coefficients of a heaving airfoil were measured using the heaving wind tunnel test developed in this study. Through flow visualizations and pressure measurements, we found that the rapid drop in normal force coefficient after it reached its maximum value was due to a large growing leading-edge vortex.
We have developed a low-density wind tunnel that simulates Martian atmospheric flight on the ground. This wind tunnel employs a supersonic ejector-drive system to realize high-speed flow under low-density conditions. This study presents a general evaluation method for the ejector driver of the wind tunnel under low-pressure conditions. As an evaluation parameter for the pressure-recovery ratio, which is a representative value of the driving performance, the ejector-drive parameter (EDP) determined from the design and operating conditions is applied, verifying its effectiveness under atmospheric conditions. Accordingly, we investigate the effectiveness of the EDP at low pressures and its scalability to complex multiple supersonic nozzles. Our results suggest that the pressure-recovery ratio is correlated with the EDP even when the ambient pressure, system configuration, and operational conditions change. The EDP allows us to predict the Mach number, and can provide us with an appropriate framework for ejector design optimization.
This paper conducts a safety assessment for reduced route spacing for RNP 2 aircraft under a radar environment. Although the criteria for 15 NM separation standards exist, past safety assessment did not consider the surveillance environment. This consideration may reduce the possible route spacing. Here, to account for the surveillance environment, the recently developed ASEPS model is applied. Since this model was intended for deployment on oceanic route systems, the model parameters are modified appropriately while keeping the consistency of the past safety analysis and data analysis. In particular, the parameter of occupancy is set based on one-year flight data in Japanese airspace, and the calculation of action time to resolve the conflict is modified to estimate the collision probability more accurately. The results show that 8 NM route spacing satisfies the safety criteria.
This paper introduces a novel filter for hybrid attitude and orbit estimation of spacecraft using geomagnetic measurements and their time-differential information. Geomagnetic measurements can be used to simultaneously estimate attitude and orbit of spacecrafts. In practice, the attitude estimation from a single magnetometer is achieved by fusing the magnetometer readings and their time derivatives together. The orbit can also be estimated using the relationship between the geomagnetic model and spacecraft coordinates in the Earth geodetic frame. However, the magnetic time derivatives have not been utilized in estimating the orbit elements. According to the mathematical structures of the geomagnetic models, the time-differential feedback can effectively enhance estimation of the velocity and can therefore provide better performance for the position loop. This paper first introduces direct feedback and formulates a new filter with better characteristics. The simulation study of a medium Earth orbit (MEO) Nadir-pointing satellite mission shows that the proposed filter achieves faster convergence and lower estimation errors.
We propose a tangential blowing cylinder, a type of circulation control wing, to control the direction of a jet replacing a blade or a cascade. Flow characteristics including deflection are experimentally investigated. Specifically, visualization observations, velocity distribution measurements, and the effects of momentum ratio, injection angle, and location of the cylinder on the deflection angle of the jet are analyzed. The stalling at an angle-of-attack above 20° with a single blade impedes direction control for such large angles. However, the jet may be bent to approximately 90° by using the proposed tangential blowing cylinder. The optimal injection angle for controlling the jet direction and the unsteady characteristics downstream of the tangential blowing cylinder are also determined.
An expansion tube is a promising facility to simulate atmospheric entry conditions, although its flow conditions have not been completely characterized mainly owing to its short operation time. In this study, laser absorption spectroscopy was applied to diagnose HEK-X expansion tube flow in the Kakuda Space Center. The target is an absorption line of an oxygen molecule at 763 nm. To increase the sensitivity, optical path length was extended by five times using mirrors. Consequently, an absorption profile with a fractional absorption of 2.4 ± 0.3% was detected at a shock velocity of 7.65 ± 0.05 km/s. The estimated translational temperature from the Voigt fitting was 2750 ± 450 K.