Alternative transfer to the Earth–Moon Lagrangian points L4 and L5 using lunar gravity assist

Lagrangian points L4 and L5 lie at 60° ahead of and behind the Moon in its orbit with respect to the Earth. Each one of them is a third point of an equilateral triangle with the base of the line defined by those two bodies. These Lagrangian points are stable for the Earth–Moon mass ratio. As so, these Lagrangian points represent remarkable positions to host astronomical observatories or space stations. However, this same distance characteristic may be a challenge for periodic servicing mission. This paper studies elliptic trajectories from an Earth circular parking orbit to reach the Moon’s sphere of influence and apply a swing-by maneuver in order to re-direct the path of a spacecraft to a vicinity of the Lagrangian points L4 and L5. Once the geocentric transfer orbit and the initial impulsive thrust have been determined, the goal is to establish the angle at which the geocentric trajectory crosses the lunar sphere of influence in such a way that when the spacecraft leaves the Moon’s gravitational field, its trajectory and velocity with respect to the Earth change in order to the spacecraft arrives at L4 and L5. In this work, the planar Circular Restricted Three Body Problem approximation is used and in order to avoid solving a two boundary problem, the patched-conic approximation is considered.     

Robust Kalman filter design for predictive wind shear detection

Severe low-altitude wind shear is a threat to aviation safety. Newly developed airborne sensors measure the radial component of wind along a line directly in front of an aircraft. The authors use optimal estimation theory to define a detection algorithm to warn of hazardous wind shear from these sensors. To achieve robustness, a wind shear detection algorithm must distinguish threatening wind shear from less hazardous gustiness, despite variations in wind shear structure. Statistical analysis methods to refine wind shear detection algorithm robustness are presented. Computational methods predict the ability to warn of severe wind shear and avoid false warning. Comparative capability of the detection algorithm as a function of its design parameters is determined, identifying designs that provide robust detection of severe wind shear     

Adaptive Pulse Doppler Ambiguity Resolution

This paper demonstrates and tests a new algorithm for extracting velocity information from a pulse Doppler radar signal. The system is adaptive and performs weil in the presence of target scintillation. This paper also shows a special steady-state version of the adaptive algorithm. lt is computationally attractive and produces near optimal velocity estimates.     

How Operational Oceanography Can Benefit from Dynamic Topography Estimates as Derived from Altimetry and Improved Geoid

With a precise geoid, GOCE will allow an estimation of absolute dynamic topography from altimetry. The projected benefits to operational oceanography and its applications are analyzed herein. After a brief overview of operational oceanography, we explain how the new geoids will be used in the future to improve real time altimeter products and to better constrain modelling and data assimilation systems. A significant impact is expected both for mesoscale (e.g. better estimations and forecasts of currents for pollution monitoring, marine safety, offshore industry) and climate (better initialization of coupled ocean/atmosphere models) applications. This revised version was published online in August 2006 with corrections to the Cover Date.     

Langmuir Turbulence and Solar Radio Bursts

Langmuir waves and turbulence resulting from an electron beam-plasma instability play a fundamental role in the generation of solar radio bursts. We report recent theoretical advances in nonlinear dynamics of Langmuir waves. First, starting from the generalized Zakharov equations, we study the parametric excitation of solar radio bursts at the fundamental plasma frequency driven by a pair of oppositely propagating Langmuir waves with different wave amplitudes. Next, we briefly discuss the emergence of chaos in the Zakharov equations. We point out that chaos can lead to turbulence in the source regions of solar radio emissions. This revised version was published online in August 2006 with corrections to the Cover Date.     

Imaging the solar corona in the EUV

The SOHO (SOlar and Heliospheric Observatory) satellite was launched on December 2nd 1995. After arriving at the Earth-Sun (L1) Lagrangian point on February 14th 1996, it began to continuously observe the Sun. As one of the instruments onboard SOHO, the EIT (Extreme ultraviolet Imaging Telescope) images the Sun's corona in 4 EUV wavelengths. The He II filter at 304 Å images the chromosphere and the base of the transition region at a temperature of 5 − 8 × 10⁴ K; the Fe IX–X filter at 171 Å images the corona at a temperature of 1.3 × 10⁶ K; the Fe XII filter at 195 Å images the quiet corona outside coronal holes at a temperature of 1.6 × 10⁶ K; and the Fe XV filter at 284 Å images active regions with a temperature of 2.0 × 10⁶ K. About 5000 images have been obtained up to the present. In this paper, we describe also some aspects of the telescope and the detector performance for application in the observations. Images and movies of all the wavelengths allow a look at different phenomena present in the Sun's corona, and in particular, magnetic field reconnection.     

基于非交错有限体积格式和 k-ω 湍流模型模拟叶栅湍流分离流动

发展了一种求解任意坐标系下二维Ｎ－Ｓ方程的非交错有限体积法和一种高阶ＴＶＤ对流格式。采用一种ｋ－ω湍流模型和几种不同的ｋ－ω模型对叶栅湍流分离流动进行了详细的分析。数值结果与得到的实验结果比较表明,此方法不仅精度高,而且具有较好的数值稳定性。     

The variable X-ray spectrum of Cyg XR-1

The variability of the X-ray spectrum of the discrete source Cyg XR-1 (α = 19^h 56^m δ = +35°.1) is reviewed. The variations observed in the energy region accessible to balloon borne detectors (energies greater than 20 keV) can be explained by assuming them to be caused by the eclipsing properties of a binary system. It is suggested that the system is composed of a source of small angular extent having a spectrum similar to that of a black body at approximately 1.5 × 10⁸ K (kT= 12.5 keV) and a non X-radiating companion which eclipses it at intervals of 2.9850 days. The system would be surrounded by an X-radiating plasma whose photon flux between 1 and 100 keV can be approximated by a power law spectrum whose exponent is — 1.7.