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221.
航空发动机滑油系统发现金属末意味着这发动机部件之间出现了过度磨损,这类故障严重影响飞行安全,必须查明故障原因并纠正。本文根据多次发动机热端部件检查的实践经验,对一起由于安装不当造成发动机轴承磨损的故障进行了分析,并总结了FJ44-1A发动机热端部件装配的若干经验。 相似文献
222.
The development of a fiber based laser architecture will enable novel applications in environments which have hitherto been impossible due to size, efficiency and power of traditional systems. Such a new architecture has been developed by the International Coherent Amplification Network (ICAN) project. Here we present an analysis of utilizing an ICAN laser for the purpose of tracking and de-orbiting hyper-velocity space debris. With an increasing number of new debris from collisions of active, derelict and new payloads in orbit, there is a growing danger of runaway debris impacts. Due to its compactness and efficiency, it is shown that space-based operation would be possible. For different design parameters such as fiber array size, it is shown that the kHz repetition rate and kW average power of ICAN would be sufficient to de-orbit small 1–10 cm debris within a single instance via laser ablation. 相似文献
223.
Sébastien E. Wailliez 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
In the two-body model, time of flight between two positions can be expressed as a single-variable function and a variety of formulations exist. Lambert’s problem can be solved by inverting such a function. In this article, a method which inverts Lagrange’s flight time equation and supports the problematic 180° transfer is proposed. This method relies on a Householder algorithm of variable order. However, unlike other iterative methods, it is semi-analytical in the sense that flight time functions are derived analytically to second order vs. first order finite differences. The author investigated the profile of Lagrange’s elliptic flight time equation and its derivatives with a special focus on their significance to the behaviour of the proposed method and the stated goal of guaranteed convergence. Possible numerical deficiencies were identified and dealt with. As a test, 28 scenarios of variable difficulty were designed to cover a wide variety of geometries. The context of this research being the orbit determination of artificial satellites and debris, the scenarios are representative of typical such objects in Low-Earth, Geostationary and Geostationary Transfer Orbits. An analysis of the computational impact of the quality of the initial guess vs. that of the order of the method was also done, providing clues for further research and optimisations (e.g. asteroids, long period comets, multi-revolution cases). The results indicate fast to very fast convergence in all test cases, they validate the numerical safeguards and also give a quantitative assessment of the importance of the initial guess. 相似文献
224.
Antonio F.B.A. Prado 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
The present paper has the goal of mapping orbits, with respect to the perturbations, for a spacecraft traveling around the asteroid 2001SN263. This asteroid is a triple system, which center of mass is in an elliptic orbit around the Sun. The perturbations considered in the present model are the ones due to the oblateness of the central body, the gravity field of the two satellite bodies (Beta and Gamma), the Sun, the Moon, the asteroids Vesta, Pallas and Ceres and all the planets of the Solar System. This mapping is important, because it shows the relative importance of each force for a given orbit for the spacecraft, helping to make a decision about which forces need to be included in the model for a given accuracy and nominal orbit. Another important application of this type of mapping is to find orbits that are less perturbed, since it is expected that those orbits have good potential to require a smaller number of station-keeping maneuvers. Simulations under different conditions are made to find those orbits. The main reason to study those trajectories is that, currently, there are several institutions in Brazil studying the possibility to make a mission to send a spacecraft to this asteroid (the so-called ASTER mission), because there are many important scientific studies that can be performed in that system. The results showed that Gamma is the main perturbing body, followed by Beta (10 times smaller) and the group Sun–Mars-oblateness of Alpha, with perturbations 1000 times weaker than the effects of Gamma. The other bodies have perturbations 107 times smaller. The results also showed that circular and polar orbits are less perturbed, when compared to elliptical and equatorial orbits. Regarding the semi-major axis, an internal orbit is the best choice, followed by a larger external orbit. The inclination of the orbit plays an important role, and there are values for the inclination where the perturbations show minimum and maximum values, so it is important to make a good decision on those values. 相似文献
225.
S. Dasso A.M. Gulisano C.H. Mandrini P. Dmoulin 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2005,35(12):2172-2177
Magnetic clouds are the interplanetary manifestation of coronal mass ejections, which are transient expulsions of major quantities of magnetized plasma, from the Sun toward the heliosphere. The magnetic flux and helicity are two key physical magnitudes to track solar structures from the photosphere-corona to the interplanetary medium. To determine the content of flux and helicity in magnetic clouds, we have to know their 3D structure. However, since spacecrafts register data along a unique direction, several aspects of their global configuration cannot be observed. We present a method to estimate the magnetic flux and the magnetic helicity per unit length in magnetic clouds, directly from in situ magnetic observations, assuming only a cylindrical symmetry for the magnetic field configuration in the observed cross-section of the cloud. We select a set of 20 magnetic clouds observed by the spacecraft Wind and estimate their magnetic flux and their helicity per unit length. We compare the results obtained from our direct method with those obtained under the assumption of a helical linear force-free field. This direct method improves previous estimations of helicity in clouds. 相似文献
226.
227.
M. Murawiecka A. Lemaitre 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2018,61(3):935-940
The Yarkovsky-Schach effect is a small perturbation affecting Earth satellites and space debris illuminated by the Sun. It was first applied to the orbit of LAGEOS satellites as an explanation of the residuals in orbital elements. In this work, we carry out several numerical integration tests taking into consideration various orbit and rotation parameters, in order to analyse this effect in a broader context. The semi-major axis variations remain small and depend on the spin axis attitude with respect to the Sun. We show that the force amplitude is maximised for orbits inclined with ?20–30°. We also observe the influence on other orbital elements, notably on the orbit inclination. However, these effects are clearly observed only on long timescales; in our simulations, we propagated the orbits for 200?y. The Yarkovsky-Schach effect is thus confirmed to have a minuscule magnitude. It should be taken into account in studies requiring high-precision orbit determination, or on expanded timescales. 相似文献
228.
Roberto Armellin Juan F. San-Juan 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2018,61(4):1097-1120
Nowadays there is international consensus that space activities must be managed to minimize debris generation and risk. The paper presents a method for the end-of-life (EoL) disposal of spacecraft in Medium Earth Orbit (MEO). The problem is formulated as a multiobjective optimisation one, which is solved with an evolutionary algorithm. An impulsive manoeuvre is optimised to reenter the spacecraft in Earth’s atmosphere within 100?years. Pareto optimal solutions are obtained using the manoeuvre and the time-to-reentry as objective functions to be minimised. To explore at the best the search space a semi-analytical orbit propagator, which can propagate an orbit for 100?years in few seconds, is adopted. An in-depth analysis of the results is carried out to understand the conditions leading to a fast reentry with minimum propellant. For this aim a new way of representing the disposal solutions is introduced. With a single 2D plot we are able to fully describe the time evolution of all the relevant orbital parameters as well as identify the conditions that enables the eccentricity build-up. The EoL disposal of the Galileo constellation is used as test case. 相似文献
229.
Hou-Yuan Lin Chang-Yin Zhao 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2018,61(1):182-188
The rotational state of Envisat is re-estimated using the specular glint times in optical observation data obtained from 2013 to 2015. The model is simplified to a uniaxial symmetric model with the first order variation of its angular momentum subject to a gravity-gradient torque causing precession around the normal of the orbital plane. The sense of Envisat’s rotation can be derived from observational data, and is found to be opposite to the sense of its orbital motion. The rotational period is estimated to be , where t is measured in days from the beginning of 2013. The standard deviation is 0.760?s, making this the best fit obtained for Envisat in the literature to date. The results demonstrate that the angle between the angular momentum vector and the negative normal of the orbital plane librates around a mean value of with an amplitude from about (in 2013) to (in 2015), with the libration period equal to the precession period of the angular momentum, from about 4.8?days (in 2013) to 3.4?days (in 2015). The ratio of the minimum to maximum principal moments of inertia is estimated to be , and the initial longitude of the angular momentum in the orbital coordinate system is . The direction of the rotation axis derived from our results at September 23, 2013, UTC 20:57 is similar to the results obtained from satellite laser ranging data but about closer to the negative normal of the orbital plane. 相似文献
针对日益增长的空间碎片污染太空环境问题,建立了天基激光能量清除空间碎片的降轨模型。重点讨论了速度增量与空间碎片速度的夹角对近地点高度降低的影响,并考虑到天基平台与空间碎片作用距离的影响,从能量利用率的角度出发,提出了能量分配系数(CEA)的概念。基于CEA,设计出关于脉冲激光能量分配的策略,并与脉冲激光能量平均方式清除空间碎片的方式进行对比分析,说明了脉冲激光能量分配策略的有效性,提高了天基激光能量利用能力,达到了高效清除空间碎片的目的。 相似文献