高速飞行器非视距短波通信的可行性验证飞行试验

当高速飞行器处于失稳失控等紧急情况时，现有航天器测控方法可能面临地面站天线无法及时跟踪和对准飞行器的问题，这将导致测控通信链路的中断，无法传输紧急的安控遥控指令。为了在飞行器失稳失控、非视距通信时与地面站维持通信，提出将短波通信应用于高速飞行器测控通信系统的应急通信，并进行非视距短波通信的飞行试验以验证方法的可行性。在试验中，地面站发射7 MHz的短波信号，高速飞行器内部安装的交流磁场计用于接收短波信号，获得了短波的磁场强度与飞行环境的本底噪声。试验结果表明，随着飞行器海拔的增加，磁场强度减小，高速飞行器始终能在非视距和天线不对准的情况下接收到短波信号，证实了短波应用于高速飞行器应急通信的可行性。试验是进一步验证高速飞行器在远距离、超视距以及拒止环境下应急通信的技术基础，同时，也为高速飞行器短波通信系统的研制提供重要的数据支撑。     

Inter-satellite links for satellite autonomous integrity monitoring

A new integrity monitoring mechanisms to be implemented on-board on a GNSS taking advantage of inter-satellite links has been introduced. This is based on accurate range and Doppler measurements not affected neither by atmospheric delays nor ground local degradation (multipath and interference). By a linear combination of the Inter-Satellite Links Observables, appropriate observables for both satellite orbits and clock monitoring are obtained and by the proposed algorithms it is possible to reduce the time-to-alarm and the probability of undetected satellite anomalies.     

Interplanetary Origin of Intense,Superintense and Extreme Geomagnetic Storms

We present a review on the interplanetary causes of intense geomagnetic storms (Dst≤−100 nT), that occurred during solar cycle 23 (1997–2005). It was reported that the most common interplanetary structures leading to the development of intense storms were: magnetic clouds, sheath fields, sheath fields followed by a magnetic cloud and corotating interaction regions at the leading fronts of high speed streams. However, the relative importance of each of those driving structures has been shown to vary with the solar cycle phase. Superintense storms (Dst≤−250 nT) have been also studied in more detail for solar cycle 23, confirming initial studies done about their main interplanetary causes. The storms are associated with magnetic clouds and sheath fields following interplanetary shocks, although they frequently involve consecutive and complex ICME structures. Concerning extreme storms (Dst≤−400 nT), due to the poor statistics of their occurrence during the space era, only some indications about their main interplanetary causes are known. For the most extreme events, we review the Carrington event and also discuss the distribution of historical and space era extreme events in the context of the sunspot and Gleissberg solar activity cycles, highlighting a discussion about the eventual occurrence of more Carrington-type storms.     

削尖三角翼涡破裂前后的气动弹性特性对比研究

大迎角气动弹性分析是现代飞行器设计中非常引人瞩目并且复杂的研究课题.采用Navier-Stokes方程求解非定常流场,耦合结构运动方程,在状态空间内实现了70°削尖三角翼涡破裂前后的气动弹性时域模拟.研究显示,前缘分离涡破裂后,流动的非定常脉动特性非常明显,这种非定常效应对机翼气动弹性特性的影响不可忽略.涡破裂前,气动...     

Martian obstacle and bow shock: origins of boundaries anisotropy

The origin of the anisotropy in the shape of the Martian obstacle and bow shock is analyzed using Mars Global Surveyor observations. The influence of MHD or ion pick-up effects on Martian obstacle position was to be small found, however, localized Martian crustal magnetization increases the thickness of the downstream planetary magnetotail by 500–1000 km in agreement with earlier Phobos 2 observations. A new analytical model is presented for Martian obstacle shape variation for different solar wind ram pressure. Elongation of the Martian BS cross-section in the direction perpendicular to IMF was confirmed while the shift of this cross section in the +Y direction of Martian interplanetary medium reference frame was discovered. The shift of BS cross section in the direction of interplanetary electric field was not revealed thus not conforming the idea that mass-loading play some role in BS control.     

一种火箭发射场坪流场的环形线汇描述方法

针对火箭发射场坪流场分布规律，基于势流法提出环形线汇描述方法，推导了环形线汇流场的速度势和速度的计算公式，建立了流场的FLUENT仿真模型并进行计算，将环形线汇理论计算结果与仿真结果进行对比。结果表明，不同火箭半径和入口流速对环形线汇和FLUENT仿真两种方法计算结果的相关性没有影响，随着箭井间隙增大，两种方法计算结果的相关度减小；环形线汇方法能够描述发射场坪流场变化趋势，在箭井间隙较小且误差允许时可以作为发射场坪流场的简化描述方法。     

适应多样化军事任务需要 提高直升机维修保障能力

分析了新形势下直升机在多样化军事行动中的使命任务,总结了目前多样化军事行动中直升机维修保障存在的问题。为适应多样化军事任务需要,提出了提高直升机维修保障能力的措施。     

Low-frequency Periodic Error Identification and Compensation for Star Tracker Attitude Measurement

The low-frequency periodic error of star tracker is one of the most critical problems for high-accuracy satellite attitude determination.In this paper an approach is proposed to identify and compensate the low-frequency periodic error for star tracker in attitude measurement.The analytical expression between the estimated gyro drift and the low-frequency periodic error of star tracker is derived firstly.And then the low-frequency periodic error,which can be expressed by Fourier series,is identified by the frequency spectrum of the estimated gyro drift according to the solution of the first step.Furthermore,the compensated model of the low-frequency periodic error is established based on the identified parameters to improve the attitude determination accuracy.Finally,promising simulated experimental results demonstrate the validity and effectiveness of the proposed method.The periodic error for attitude determination is eliminated basically and the estimation precision is improved greatly.     

Cycle-slip Detection of GPS Carrier Phase with Methodology of SA4 Multi-wavelet Transform

That cycle-slips remain undetected will significantly degrade the accuracy of the navigation solution when using carrier phase measurements in global positioning system (GPS). In this paper, an algorithm based on length-4 symmetric/anti-symmetric (SA4) orthogonal multi-wavelet is presented to detect and identify cycle-slips in the context of the feature of the GPS zero-differential carrier phase measurements. Associated with the local singularity detection principle, cycle-slips can be detected and located precisely through the modulus maxima of the coefficients achieved by the multi-wavelet transform. Firstly, studies are focused on the feasibility of the algorithm employing the orthogonal multi-wavelet system such as Geronimo-Hardin-Massopust (GHM), Chui-Lian (CL) and SA4. Moreover, the mathematical characterization of singularities with Lipschitz exponents is explained, the modulus maxima from wavelet to multi-wavelet domain is extended and a localization formula is provided from the modulus maxima of the coefficients to the original observation. Finally, field experiments with real receiver are presented to demonstrate the effectiveness of the proposed algorithm. Because SA4 possesses the specific nature of good multi-filter properties (GMPs), it is superior to scalar wavelet and other orthogonal multi-wavelet candidates distinctly, and for the half-cycle slip, it also remains better detection, location ability and the equal complexity of wavelet transform.     

单边膨胀喷管膨胀型面的非线性缩短设计

对单边膨胀喷管(SERN)型面进行非线性缩短设计,采用CFD技术分析了非线性缩短SERN性能。与理想喷管、线性缩短理想喷管性能对比发现:非线性缩短理想喷管的推力性能优于直接线性缩短理想喷管;NPR较大范围内,较理想喷管推力性能下降很小,最好时不足0.04%。非线性缩短SERN设计方法应用于截短理想喷管并与RAO喷管推力性能对比发现:完全膨胀时推力性能较RAO喷管只低0.7%;严重过膨胀状态NPR=40时,推力性能较RAO喷管高15.6%。