共查询到20条相似文献,搜索用时 15 毫秒
1.
2.
3.
《Acta Astronautica》1987,15(8):567-571
The analytical solution for the different shapes that a bidimensional liquid bridge in a gravity field may adopt is reviewed, criticizing the well-known limit of Heywang. The work is shown in the context of a wider-scope program to model the fluid-mechanical behaviour of molten bridges in the floating zone and related techniques of crystal growth, which has blossomed with the advent of microgravity platforms. 相似文献
4.
A method for determination of internal gravity wave (IGW) parameters from a single vertical temperature or density profile
measurement in the Earth’s atmosphere has been developed. This method may be used for the analysis of profiles measured by
any techniques in which the accuracy is enough to measure small (∼1%) amplitudes of the temperature or density fluctuations
in the atmosphere. The criterion for the IGW identification has been formulated and argued. In the case when this criterion
is satisfied then analyzed fluctuations can be considered as wave-induced. The method is based upon the analysis of relative
amplitude thresholds of the temperature or density wave field and upon linear IGW saturation theory in which amplitude thresholds
are restricted by dynamical instability processes in the atmosphere. In order to approbate the method we have used data of
simultaneous radiosonde measurements of the temperature and wind velocity in the Earth’s stratosphere where the saturated
IGW propagation has been detected. It is shown that the application of the method to radio occultation temperature data gives
the possibility to identify IGWs in the Earth’s lower stratosphere and to determine values of key wave parameters. 相似文献
5.
V. I. Abrashkin K. E. Voronov I. V. Piyakov Yu. Ya. Puzin V. V. Sazonov N. D. Syomkin S. Yu. Chebukov 《Cosmic Research》2016,54(5):375-387
The mathematical model, which allowed us to reconstruct the rotational motion of the Bion M-1 and Foton M-4 satellites by processing the measurements of onboard magnetometers and the angular velocity sensor, is sufficiently detailed and accurate. If we slightly lower the requirements for accuracy and transfer to a rougher model, i.e., we will not update the biases in measurements of the angular velocity component, then the measurement processing technique can be significantly simplified. The volume of calculations in minimizing the functional of the least-square technique is reduced; the most complicated part of calculations is performed using the standard procedure of computational linear algebra. This simplified technique is described below, and the examples of its application for reconstructing the rotational motion of the Foton M-4 satellite are presented. A noticeable distinction in the reconstructions of motion, constructed by simplified and more exact techniques, is revealed in processing the measurements over time intervals longer than 4 hours. 相似文献
6.
V. K. Saul’skii 《Cosmic Research》2017,55(4):275-289
Satellite systems for the periodic survey of a given range of the Earth’s latitudes have been analyzed. As a rule, the efficiency of the satellite systems is estimated based on the maximum interruption, i.e., the maximum time interval that appears when surveying. However, this performance cannot serve as a full criterion for the quality of the survey, since it does not reflect all survey interruptions with their frequencies. To adequately analyze the operation of the satellite system, it is necessary to use the frequency distribution function of the survey interruptions; its determination is a complex problem and has not yet been solved in the general case. In this paper, we propose a method for calculating the set of all interruptions and frequencies suitable for any multisatellite systems with an arbitrary structure. The method is based on the vector model of the Earth’s survey. To estimate the efficiency of the satellite system operation, a complex criterion has been recommended that takes into account all survey interruptions and their frequencies. Two examples of the application of the developed method have been presented. 相似文献
7.
The paper has studied the accuracy of the technique that allows the rotational motion of the Earth artificial satellites (AES) to be reconstructed based on the data of onboard measurements of angular velocity vectors and the strength of the Earth magnetic field (EMF). The technique is based on kinematic equations of the rotational motion of a rigid body. Both types of measurement data collected over some time interval have been processed jointly. The angular velocity measurements have been approximated using convenient formulas, which are substituted into the kinematic differential equations for the quaternion that specifies the transition from the body-fixed coordinate system of a satellite to the inertial coordinate system. Thus obtained equations represent a kinematic model of the rotational motion of a satellite. The solution of these equations, which approximate real motion, has been found by the least-square method from the condition of best fitting between the data of measurements of the EMF strength vector and its calculated values. The accuracy of the technique has been estimated by processing the data obtained from the board of the service module of the International Space Station (ISS). The reconstruction of station motion using the aforementioned technique has been compared with the telemetry data on the actual motion of the station. The technique has allowed us to reconstruct the station motion in the orbital orientation mode with a maximum error less than 0.6° and the turns with a maximal error of less than 1.2°. 相似文献
8.
9.
某遥感卫星平台的微振动试验研究 总被引:1,自引:2,他引:1
为了研究动量轮/控制力矩陀螺造成的微小振动在卫星结构内的传递规律,文章利用某遥感卫星平台在国内首次开展了气浮和悬吊两种状态下的卫星微振动对比研究试验。分别在两种边界下进行了背景噪声测试及模态试验,分析了两种边界条件对试验结果的影响;测量了动量轮/控制力矩陀螺工作造成的微振动响应。通过对试验结果的分析,总结了典型微振动源的主要扰动成分及其传播规律。研究表明:两种边界引入的噪声对试验结果的影响均较小,微振动响应在传播过程中会大幅衰减;动量轮及控制力矩陀螺工作时引起的扰动响应从总体上看受边界的影响不大。 相似文献
10.
11.
在世界各大卫星制造商竞争商业通信卫星市场的同时,全球对地观测卫星市场也渐入激烈的市场竞争阶段。在对地观测卫星市场中,按照技术特性又分为载有被动式光学载荷和主动式合成孔径雷达载荷的 相似文献
12.
It is assumed that the gravitational interaction is carried out by material agents, and it is affected by the relativistic squeezing. With only this assumption, the solution of the problem of a photon path deviation in the Sun gravity field conforms with the experiment. 相似文献
13.
14.
针对空间辐射环境影响下近地卫星某器件单粒子锁定(SEL)事件频发现象,在分析卫星轨道根数演变的基础上,详细讨论SEL事件时空分布特征。结果表明,SEL事件的星下点分布具有明显地域特征,其在南大西洋区域、南北两极区域、其他区域的比例接近于3∶2∶1;器件SEL事件平均发生率略高于0.134 d-1,太阳活动较强时的发生率不足0.103 d-1,而太阳活动较弱时则接近0.165 d-1;近日点附近时的发生率达到0.200 d-1,远日点附近时约为0.072 d-1。在测控中,针对SEL事件进行遥控作业自动识别与处理,操控时长平均为130 s。 相似文献
15.
The concept of a European remote sensing satellite (ERDSAT) launched by ARIANE is characterized by a model payload, consisting of a synthetic aperture radar (SAR) and an optical multispectral scanner with 9 channels, for land applications or coastal zone missions. The mission goal of ERDSAT is based on European user requrements where a strong need for optical and microwave sensor operation on board the same satellite in a simultaneous or sequential mode is expressed. A data collection system is included. The proposed spacecraft is three-axes-stabilized and has a Sun-synchronous, near polar circular orbit with 750 km altitude. The selected configuration separates payload module and bus module. A thermostable carbon fibre grating structure is the central framework of the satellite. Each major subsystem is housed in a separate compartment and can be integrated and tested individually. First mass estimates resulted in 450 kg for the payload and 880 kg for the bus. The maximum power needed is 1750 W (for 6 min three times a day), which will be provided by a 1330 W solar array and two batteries. A “low cost” model philosophy is defined; the time schedule envisages a program start in late 1980 and a launch possibility end of 1985. 相似文献
16.
Ahmed Bounfour 《Space Policy》1994,10(4):290-306
This paper refers to a study (specificaly to its chapter 7)1 carried out by Euroconsult for ESA on the key characteristics of European R&D in the satellite communications user Earth segment. The study was initiated by the Working Group on Satellite Communications Policy2 of the Joint Board on Communications Satellite Programmes (JCB), which was established by the Director General of ESA in July 1990 to contribute to the European agency's response to the EC Green Paper. The working group specifically expresses the European space communications industry's point of view. 相似文献
17.
18.
This paper describes a computer simulation study that was undertaken to determine how well long-wavelength variations in the Earth's gravitational field can be recovered using data from the Dedicateditational ellite (GRAVSAT) mission. This mission is to consist of two low altitude (160 km) spacecraft in essentially the same orbit but separated in phase by 100–300 km. Geodetic data are measurements of the relative range rate to an accuracy of about 1 μm/s at 4 sec intervals. Specifically, a Bayesian covariance simulation was used to investigate simultaneous recovery of the spacecraft ephemerides and a global distribution of 20° × 20° mean gravity anomaly blocks. Sources of errors considered were tracking station positions, gravitational constant, Earth body tides, tropospheric modeling and measurement noise. It should be noted that this simulation does not include as an error source variations in the gravity field that have a character different from what was modeled. Consequently, this study demonstrates the potential of the low-low system as configured to recover the long-wavelength variations in the gravity field.Using only one days worth of data, the mean of the standard deviations of the 162 20° × 20° gravity anomaly blocks is about 1 μgal. For a 6 month mission (assuming a reduction proportional to the square root of the data intervals) this projects to < 0.1 μgal. Because of the potential of increased measurement precision at shorter separation distances, and the relative insensitivity of the recovery process to separation distance, it should be possible to recover both long and short wavelength variations with a modest distribution of separation distances tailored primarily to the short wavelength recovery. Effects of the uncertainty in the gravitational constant and Love's numbers are negligible. In a simulation not reported on, increasing the altitude of the orbit to 200 km from 150 km, degraded, as expected, the accuracy of the recovered parameters by only 7%. 相似文献
19.
20.
Eliot Christian 《Space Policy》2005,21(2):274-109
The Group on Earth Observations was established to promote comprehensive, coordinated, and sustained Earth observations. Its mandate is to implement the Global Earth Observation System of Systems (GEOSS) in accord with the GEOSS 10-Year Implementation Plan and Reference Document. During the months over which the GEOSS Implementation Plan was developed, many issues surfaced and were addressed. This article discusses several of the more interesting or challenging of those issues—e.g. fitting in with existing organizations and securing stable funding—some of which have yet to be resolved fully as of this writing. Despite the relatively short period over which the Implementation Plan had to be developed, there is a good chance that the work undertaken will be influential for decades to come. 相似文献