The solution domain of the Earth-Moon quasi-symmetric free-return orbits (EMQSFRO) is analyzed using a novel strategy proposed in this paper applying the Jet Propulsion Laboratory (JPL) ephemeris dynamic model. EMQSFRO is constrained by altitude at the time of trans-lunar injection (TLI), lunar swing-by altitude and Earth atmosphere re-entry angle. A vehicle on such an orbit can return to Earth without need of additional impulse after TLI. The present research on EMQSFRO and its technical applications are first summarized. Then a novel direct design strategy for EMQSFRO is proposed using a sequential quadratic programming algorithm, which applies the orbital parameters in the Moon perilune inertial coordinate system as design variables, and computes the objective orbital parameters in the TLI and re-entry time using the forward and backward numerical integral method. A simulation example indicates that the method has excellent convergence performance and precision. According to further simulation results, the solution domain cross-profile characteristics of four kinds of the EMQSFRO are discovered, which can give a deeper insight into the dynamic principle of EMQSFRO generation and supply references to the orbit design of aerospace missions.
Human error is considered a causal or contributory factor in a major part of aviation incidents. It's also known from relevant research and reports that even the smallest error made by a person can cause fatal results in the aviation sector. In this study, the relationship between factors that contribute to trainee error based on scores achieved in pilot training, such as personality traits, psychomotor abilities, audio-visual memory capacity and quantitative skills of pilots, are determined by means of a multiple regression analysis. In the study, the total number of errors that a sample of 24 civilian student pilots made in initial and advanced flight training was evaluated. According to the results of the regression analysis, it was determined that the errors student pilots made during these flight training periods had a close relationship to their personality traits. For this reason, while selecting student pilots, it's necessary to predict a student pilot's personality traits. Additionally, by taking the factors that are the focus of this study into consideration, the selection of suitable student pilots having a low probability of making errors is possible.
Meteorological phenomena involving strong gusts, such as dust devils, occur frequently on Mars. The wind distribution on Mars is essential information for both scientific and engineering research fields. Although landers and rovers have performed weather observations near the surface, the wind has not been measured directly at high altitudes. In this research, a wind structure exploration mission using an airplane is proposed. The flight profiles and the algorithm to estimate the statistical parameters of an atmospheric turbulence model are shown. Additionally, the wind profile model of a dust devil is constructed and is employed for simulating the dynamics of the Mars airplane. The frequency of occurrence of dust devils is calculated from the observation data of past exploration missions. Flight feasibility studies were carried out, and it was revealed that the probability of success of a flight on Mars with an acceptable load factor of 5 is 89%.
The global navigation satellite system (GNSS) can potentially provide centimeter-level positioning using real-time kinematic (RTK) positioning. However, in static positioning, such as for surveying, receivers easily receive multipath signals continuously. Our goal was to improve the performance of instantaneous RTK-GNSS in multipath environments. Two conventional satellite selection methods based on the idea of correctly removing multipath signals, which allows more reliable solutions, were evaluated in this study. The first method is based on using signal-to-noise ratio (SNR) observations to mask measurements having degraded quality. In the second method, a mask of sky obstacles is generated using a fisheye view lens camera to detect non-line-of-sight (NLOS) signals. In this study, several static tests were performed to evaluate these conventional methods. The results show that both methods can efficiently improve availability. Furthermore, the performance when using a fisheye view mask was slightly better than that when using the SNR method, in particular for situations where a powerful reflected signal by NLOS was received. Based on these results, an improved SNR-based satellite selection method that uses the SNR fluctuation magnitude for a certain period is proposed. The results show that this method effectively improves the performance as compared with the conventional SNR mask.
A cavitation test was carried out for a fuel pump designated for a liquid rocket engine. The fuel enters the pump perpendicular to the direction of the shaft. Cavitation instabilities were investigated using an accelerometer installed on the pump casing and pressure transducers placed at the inlet and the outlet of the pump. Rotating cavitation appeared at a frequency faster than the pump rotational frequency, and cavitation surge appeared at a slower frequency. Cavitation surge appeared within the range of cavitation coefficients where rotating cavitation occurred. The frequencies of the rotating cavitation and the cavitation surge decreased as the cavitation coefficient and flow rate decreased, and were proportional to the rotational speed.
This paper proposes a new type of super-low-altitude flight governed by aerodynamic lift and gravitational forces. A general trajectory generation algorithm is proposed to create combined aerodynamic and orbital (CAO) trajectories, including spaceship reentry and missile boost-glide trajectories. The relationship between the number of hops per day and the aerodynamic coefficients are then presented for them. Analytical and numerical simulations conducted reveal that the changing argument of perigee caused by the lift component can essentially characterize the hops. A control strategy that use the on-orbit time-dependent change in angle of attack is developed, yielding an extended CAO trajectory with time-dependent hops, which is more difficult to track and predict. The partial drag-free flight addressed in this paper has potential applications in some stealth military missions.
The attenuation of wingtip/blade vortices has been one of the primary concerns in aviation safety and blade-vortex noise. In an effort to effectively dissipate the vortex intensity, a trailing-edge (TE) chipped wing concept was suggested. In this study, to exploit the potential of the chipped wingtip concept for alleviating the tip vortex, a series of numerical simulations are conducted. The numerical simulations are performed using open source code, OpenFOAM. The wake structures are measured for different wingtip shapes. The chip depth and location are varied to evaluate the vortex alleviation rate and aerodynamic characteristics. As a result of numerical simulation, it is confirmed that the vortex dissipation rate of the tip-chipped wing is higher than that of a TE-chipped wing. For the tip-chipped wing, the counter-rotating vortex is found to be strong enough to weaken the primary vortex. The dissipation rate increases as the location of the chip gets closer to the leading-edge, and as the depth of the chip increases. A trade-off relationship between vortex alleviation and an increase in drag is confirmed. For example, the MID D3 attenuates the strength of the wingtip vortex by 51%, while the drag is increased within 5%.