Inter-orbital low-thrust transfers in an arbitrary field of forces

Low-thrust transfers between preset orbits are considered in the presence of perturbations of different origin. A simple method of finding the transfer trajectory is suggested, based on linearization of motion near reference orbits. The required accuracy of calculations is achieved by way of increasing the number of reference orbits. The method can also be used in the case of a large number of revolutions around the attracting center: no averaging of motion is required in this case. The suggested method is applicable as well, when the final orbit is specified partially and when there are constraints on the thrust direction. The optimal solution to the linearized problem is not optimal for the original problem; closeness of solutions to these two problems is estimated using a numerical example. Capabilities of the method are also illustrated by examples.     

Orbital debris - status and possibilities for control

This article is a shortened version of a position paper on orbital debris compiled by an Ad hoc Expert Group of the International Academy of Astronautics' Committee on Safety, Rescue and Quality. Its objectives were to elaborate on the need and urgency for action and to indicate ways for its implementation. The article reviews debris control options and methods ranging from those requiring no technology development to those which require new and thus far untried developments.     

Spacecraft Injection into a Heliocentric Terrestrial Orbit

We consider the problem of injection of a spacecraft into the heliocentric Earth's orbit ahead and/or behind the Earth by 60° and 120° in heliographic longitude. The range of solar and astrophysical problems for which these orbits are necessary is reviewed. The variants of injection into heliocentric orbits work from a low around-Earth orbit with one turn-on of the engine in this orbit and one turn-on at the end of the injection trajectory. In this case, it turns out to be more profitable to put spacecraft into orbit for three or even four revolutions of the Earth about the Sun. The velocities necessary for the start from a low around-Earth orbit, the velocities at the final point of injection, and the fuel mass (relative to the spacecraft mass) necessary for injection are estimated. The problems for which injection to similar orbits is executed, using the low-thrust engine and with a combined regime of injection, are also considered.     

Analysis of heterogeneous recombination of oxygen atoms on aluminum oxide by methods of quantum mechanics and classical dynamics

To analyze the catalytic properties of heat shield materials of space vehicles, the cluster models of the adsorption of oxygen atoms on aluminum oxide are constructed and the corresponding potential energy surface is calculated on the basis of the density functional theory. Quantum-mechanical calculations showed that it is necessary to take into account the relaxation of the surface monolayers. Using this surface in molecular dynamics, calculations made it possible to obtain the probabilities of the heterogeneous recombination of oxygen atoms on the α-Al₂O₃ surface, which are in good agreement with experimental data. The calculations performed substantially decrease the amount of experimental investigations necessary reliably to describe the heterogeneous catalysis on promising reusable heat shield coatings for analyzing heat transfer during spacecraft entry into the atmosphere.     

On autonomous tracking of a minor celestial body

There is suggested an algorithm of the autonomous tracking of a minor celestial body (comet, asteroid or satellite) by the photo-TV-camera of the spacecraft during its flyby in the vicinity of the celestial body, investigated by the data of images obtained by this camera. This algorithm allows prediction of the celestial body angular position in order to point the onboard camera to the body. The field of applicability for the suggested algorithm taking into account various errors is being investigated. The problems of the optimization of the program of the autonomous tracking in order to decrease the prediction errors or to increase the prediction time interval are considered. The results obtained are illustrated by the example of the autonomous tracking of Halley's comet nucleus.     

利用PIV方法测量半浮区液桥热毛细对流的速度场

利用PIV法对硅油液桥热毛细对流的定常速度场进行了实时测量。为了便于测量,液桥上桥端面采取了铜环中嵌透明材料的方法,从液桥的顶部进行观测。当液桥上下桥有温差时,热毛细对流出现;本实验对于不同上下桥的温差,对液桥横剖面内的速度场分别进行了测量,研究外加温差对于流场速度分布的影响;并且在液桥中取了几个典型横截面进行测量,以期对大Pr数液桥的定常速度场有比较全面的定量测量。此外,实验结果也可作为数值模拟计算结果的验证。