基于X射线脉冲星的航天器自主导航算法分析

脉冲星自转非常稳定,可以用作时间标准,许多脉冲星的空间位置、自行、距离、自转周期及其导数等天体测量参数和天体物理参数都能被精确测定.由于脉冲星能够同时提供时间信号和空间位置坐标,安装在航天器上的脉冲星导航系统能够实现航天器的自主导航.首先根据航天器轨道动力学方程预测航天器的位置,再通过航天器上观测的脉冲到达时间和预报的脉冲到达时间之差,应用Kalman滤波计算航天器位置估计的误差,从而对航天器的位置进行修正.最后,分析初始误差、脉冲到达时间测量精度、脉冲星个数对导航精度的影响.     

Algorithm Analysis of Autonomous Navigation of Spacecraft Based on X-ray Pulsars

A pulsar has the very stable rotation and can be used as the time standard. The astrometric parameters and astrophysical parameters of many pulsars, such as the spatial position, proper motion, distance, rotation period and its derivative, etc., can be all accurately determined. Since the pulsar can provide the time signal and the coordinates of its spatial position simultaneously, the pulsar navigation system installed on a spacecraft enables the autonomous navigation of the spacecraft to be realized. Firstly, the position of the spacecraft is predicted based on the equation of orbit dynamics of the spacecraft and then the Kalman filtering is applied to calculating the estimation error of the spacecraft position through the difference between the pulse arrival time observed on the spacecraft and the predicted pulse arrival time, thereby modifying the position of the spacecraft. Finally, the effects of the initial error, measuring accuracy of the pulse arrival time and number of pulsars on the navigation accuracy are analyzed.     

Optimal Control of a Spacecraft During Descent in the Martian Atmosphere

The way for optimal controlling a spacecraft under its motion in the Martian atmosphere is examined. The minimum final velocity is taken as an optimality criterion. A procedure for calculating the spacecraft trajectories is developed based on the formalism of the Pontryagin maximum principle. The high efficiency of two-parameter control of the spacecraft is shown. The results can be used for exploring Mars and other planets.     

Analytical Study of The Resonance Caused by Solar Radiation Pressure on a Spacecraft

The resonance terms produced by the effect of direct solar radiation pressure on the motion of a spacecraft in the oblate field of the earth are analyzed. The spacecraft was assumed axially symmetric with a despun antenna and solar panels. A canonical transformation technique is developed, based on the Bohlin technique of expansion in fractional powers, using Lie series and transformation as well as the concept of the Delaunay anomaly. The developed technique, applied to the problem averaged over the mean anomaly, is suitable in the presence of more than one resonant vector.     

用脉冲星钟作航天器时间标准

在介绍参考坐标系和时间标准的基础上,讨论了用脉冲星为航天器导航的时间标准问题。利用X射线脉冲星实现航天器自主导航,星载钟的任何误差都会直接影响航天器位置测量。脉冲星钟具有较高的长期频率稳定度,适合用作各类航天器的时间标准。重点讨论了时间标准误差对航天器定位的影响;给出了用脉冲星钟作航天器时间标准的物理实现方法。     

Symmetric theory of probe-plasma interactions

The theory of interactions between a probe and the surrounding plasma at rest is developed in a spherically and in a cylindrically symmetric model (probe theory). The theory is based on the Vlasov-Poisson system; a general numerical program was developed to solve this system by means of an iterative procedure. Various ambient plasma and charged particle emission properties are described by the complete set of boundary conditions for the distribution functions in the phase space. By use of this numerical method, potential and space charge density in the whole surroundings of the probe as well as the current densities of all plasma constituents are calculated self-consistently.Furthermore, the regions of the phase space with particle trajectories of the same kind can be approximated depending on the plasma properties. Then, the current densities can be estimated analytically. This approach to the problem yields self-consistent approximations and is the only stringent derivation of the thick sheath and of the thin sheath approximation of the classical Langmuir theory. These approximations are generalized with respect to the charged particle emission from the surface.The symmetric probe theory is applied to the following problems of spacecraft environment and spacecraft charging: (i) a spacecraft in the ionosphere with very negative surface potential, (ii) a spacecraft in the solar wind with strong photoelectron emission, and (iii) a spacecraft in the transition region of comet Halley with very strong secondary plasma emission.     

基于脉冲星计时的航天器自主定位误差估计方法

目前很多学者希望从"X射线脉冲星自主导航"的导航算法研究入手,利用数据分析或仿真进行验证.其中关于航天器自主定位的误差估计方法、误差量级和各种影响因素的讨论,并没有在给定详细初始条件的基础上系统性地说明问题.为了分析上述问题,需从天体测量学的角度出发,对自主定位的各种误差源及其影响因素进行探讨和误差量级的估计.首先,由...     

Organization of tests of integrated on-board spacecraft control system

The experience accumulated by a test organization of integrated on-board control systems of spacecraft for scientific purposes, which became the basis for all the latest developments at Lavochkin Research and Production Association in the implementation of advanced space programs, is analyzed. At this enterprise, the proposed methods of test organization have made it possible to take a step toward developing the technology of scientific spacecraft testing based on new principles of the modern development of electronic and software systems used as block and unit devices (BUDs) and separate on-board systems.     

Engineering Methodology for Assessment оf Spacecraft Structure Shock Load Levels During Pyromechanical Separation

In this paper, we consider an algorithm for estimating the dynamic shock loads on sensitive units, assemblies, systems, and payloads of a spacecraft, as well as on precision elements of its construction occurring near separation belts that are based on linear cumulative and noncumulative pyromechanisms.     

Assessing the Effect of Spacecraft Motion on Single-Spacecraft Solar Wind Tracking Techniques

Recent advances in wide-angle imaging by the Solar Mass Ejection Imager (SMEI) on board the Coriolis spacecraft and more recently by the Heliospheric Imagers (HI) aboard NASA’s Solar TErrestrial RElations Observatory (STEREO), have enabled solar wind transients to be imaged and tracked from the Sun to 1 AU and beyond. In this paper we consider two of the techniques that have been used to determine the propagation characteristics of solar wind transients based on single-spacecraft observations, in particular propagation direction and radial speed. These techniques usually assume that the observing spacecraft remains stationary for the duration of observation of the solar wind transient. We determine the inaccuracy introduced by this assumption for the two STEREO spacecraft and find that it can be significant, and it can lead to an overestimation of the transient velocity as seen from STEREO-A and an underestimation as seen by STEREO-B. This has implications for the prediction or solar wind transients at 1 AU and hence is important for the study of space weather.     

Exploiting Unstable Periodic Orbits of a Chaotic Invariant Set for Spacecraft Control

The purpose of this work is to show that chaos control techniques (OGY, in special) can be used to efficiently keep a spacecraft around another body performing elaborate orbits. We consider a satellite and a spacecraft moving initially in coplanar and circular orbits, with slightly different radii, around a heavy central planet. The spacecraft, which is the inner body, has a slightly larger angular velocity than the satellite so that, after some time, they eventually go to a situation in which the distance between them becomes sufficiently small, so that they start to interact with one another. This situation is called as an encounter. In previous work we have shown that this scenario is a typical situation of a chaotic scattering for some well-defined range of parameters. Considering this scenario, we first show how it is possible to find the unstable periodic orbits that are located in the chaotic invariant set. From the set of unstable periodic orbits, we select the ones that can be combined to provide the desired elaborate orbit. Then, chaos control technique based on the OGY method is used to keep the spacecraft in the desired orbit. Finally, we analyze the results and make considerations regarding a realistic scenario of space exploration.     

脉冲星在空间飞行器定位中的应用

利用脉冲星钟模型能高精度地预报脉冲星脉冲到达太阳系质心的时间。基于脉冲星时、空参考架可实现各类空间飞行器的自主导航。讨论了脉冲星钟的模型和脉冲星导航系统的框架结构,描述了脉冲星导航的基本原理和算法。指出脉冲星导航系统对脉冲星脉冲到达探测器时刻的测量精度,是决定空间飞行器位置解算精度的关键因素。脉冲星导航观测采用的原子钟如果足够稳定,则空间飞行器位置的解算方法可以简化。在脉冲星导航系统计时观测精度达到或优于几十微秒量级时,脉冲星视差、相对论效应的影响是不可忽略的。对脉冲星导航系统开发设计中的关键技术和进一步研究的主要问题进行了初步分析和讨论。     

First evidence of IMF control of Jovian magnetospheric boundary locations: Cassini and Galileo magnetic field measurements compared

The Cassini spacecraft, en route to Saturn, passed close to Jupiter while the Galileo spacecraft was completing its 28th and 29th orbits of Jupiter, thus offering a unique opportunity for direct study of the solar wind-Jovian interaction. Here evidence is given of response of the Jovian magnetopause and bow shock positions to changes of the north-south component of the solar wind magnetic field, a phenomenon long known to occur in equivalent circumstances at Earth. The period analyzed starts with the passage over Cassini of an interplanetary shock far upstream of Jupiter. The shock's arrival at Galileo on the dusk-flank of the magnetosphere caused Galileo to exit into the solar wind. Using inter-spacecraft timing based on the time delay established from the shock arrival at each spacecraft, we point out that Galileo's position with respect to the Jovian bow shock appears to correlate with changes in the disturbed north-south reversing field seen behind the shock. We specifically rule out the alternative of changes in the shape of the bow shock with rotations of the interplanetary magnetic field as the cause.     

A new generation of spacecraft pyroautomatic systems as a result of a successful cooperation

A new generation of spacecraft pyroautomatic systems is developed as a result of a long-term cooperation of NPO Lavochkin, St. Petersburg State Technological Institute (Technical University), and the Special Design and Technological Bureau (Technolog). Separation systems based on elastic explosives have proven their high efficiency and reliability in a number of Russian and international interplanetary and astrophysical space projects. Advanced devices based on new pyrotechnic compositions are developed.     

On one technique for determining the spacecraft attitude prom the sun

A variant to implement a spacecraft (SC) spatial attitude system with respect to the Sun is discussed. The sunward direction and the solar rotation axis are used as reference points. The system is based on measuring spectral line Doppler shift by scanning the solar image along the limb and is self-adjusting for relative spectral line shifts and instrument band shifts. The first harmonic of the signal serves as a basis for accurate adjustment of filter band. The second harmonic phase is used to measure the spacecraft attitude. The application of this method holds the greatest promise when the SO is stabilized by the sunward spinning because this ensures continuous monitoring of the spacecraft attitude.In addition, the method provides information on the precise coordinates of solar surface details during space-borne observations.     

New Challenges to Trajectory Design by the Use of Electric Propulsion and Other New Means of Wandering in the Solar System

The design of spacecraft trajectories is a crucial part of a space mission design. Often the mission goal is tightly related to the spacecraft trajectory. A geostationary orbit is indeed mandatory for a stationary equatorial position. Visiting a solar system planet implies that a proper trajectory is used to bring the spacecraft from Earth to the vicinity of the planet. The first planetary missions were based on conventional trajectories obtained with chemical engine rockets. The manoeuvres could be considered 'impulsive' and clear limitations to the possible missions were set by the energy required to reach certain orbits. The gravity-assist trajectories opened a new way of wandering through the solar system, by exploiting the gravitational field of some planets. The advent of other propulsion techniques, as electric or ion propulsion and solar sail, opened a new dimension to the planetary trajectory, while at the same time posing new challenges. These 'low thrust' propulsion techniques cannot be considered 'impulsive' anymore and require for their study mathematical techniques which are substantially different from before. The optimisation of such trajectories is also a new field of flight dynamics, which involves complex treatments especially in multi-revolution cases as in a lunar transfer trajectory. One advantage of these trajectories is that they allow to explore regions of space where different bodies gravitationally compete with each other. We can exploit therefore these gravitational perturbations to save fuel or reduce time of flight. The SMART-1 spacecraft, first European mission to the Moon, will test for the first time all these techniques. The paper is a summary report on various activities conducted by the project team in these areas.     

Space astronomy for the mid‐21st century: Robotically maintained space telescopes

The historical development of ground based astronomical telescopes leads us to expect that space‐based astronomical telescopes will need tobe operational for many decades. The exchange of scientific instruments in space will be a prerequisite for the long lasting scientific success of such missions. Operationally, the possibility to repair or replace key spacecraft components in space will be mandatory. We argue that these requirements can be fulfilled with robotic missions and see the development of the required engineering as the main challenge. Ground based operations, scientifically and technically, will require a low operational budget of the running costs. These can be achieved through enhanced autonomy of the spacecraft and mission independent concepts for the support of the software. This concept can be applied to areas where the mirror capabilities do not constrain the lifetime of the mission (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Perturbation of an electrostatic probe by a spacecraft at small speed ratios

The disturbance of an electrostatic probe, by the spacecraft carrying it, in the intermediate altitude regime from about 3000 km to the plasmapause, is discussed. Three kinds of disturbance are studied: loss of symmetry of the probe sheath due to the presence of the spacecraft; creation of potential barriers around the probe; and particle removal, or shadowing, by the spacecraft. The first of these effects is shown to be nonexistent for a spherical probe if it is operated under orbit-limited conditions. Methods are given for estimating the magnitudes of the other two effects in any given situation. The electrostatic probe experiment on the Explorer 31 spacecraft is discussed as an example.     

Bounded relative motions for formation flying in displaced orbits by low-thrust propulsion

This paper discusses a numerical searching approach for the relative motion of formation flying in displaced orbits by spacecraft with low-thrust propulsion. The nonlinear dynamical model of spacecraft is established in a two-body rotating reference frame with arbitrary polar component of momentum and thrust-induced acceleration. Motions near the stable equilibria are distinguished from each other by means of five-dimensional variables, which can then be compressed uniquely into two-dimensional mapping images characterized by the crossing interval and the angle drifts. The surjective but not injective mapping makes the generation of three configurations of the relative motions possible. The corresponding relative orbits for three kinds of two-spacecraft formation flying are searched and exemplified based on the formation conditions formulized as functions of the crossing interval and the angle drifts. Furthermore, based on the assignment of displaced relative orbits to five-dimensional vector, the working orbit of the deputy for a specific chief can also be searched via the optimization algorithm to generate the bounded relative motion with the minimum thrust acceleration magnitude, which is of certain significance in reducing fuel consumption of formations.     

The Relation Between Magnetic Fields and X-ray Emission for Solar Microflares and Active Regions

Solar Physics - We develop an approach of the Grad–Shafranov (GS) reconstruction for toroidal structures in space plasmas, based on in situ spacecraft measurements. The underlying theory is...