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.     

Analysis of an adaptive algorithm for unbiased multipath time delay estimation

The multipath equalization time delay estimator (METDE) provides an adaptive approach for estimating the difference in arrival times of a signal received at spatially separated sensors as well as the multipath channel characteristics. However, the parameter estimates of the METDE are biased in the presence of noise. The METDE algorithm is improved for unbiased parameter estimation via minimizing a modified cost function. Convergence behaviors and variances of the system variables of the amended method are derived. Computer simulations are included to corroborate the theoretical analysis and to evaluate the adaptive multipath delay estimation performance of the proposed algorithm.     

Galileo Probe Nephelometer experiment

The objective of the Nephelometer Experient aboard the Probe of the Galileo mission is to explore the vertical structure and microphysical properties of the clouds and hazes in the atmosphere of Jupiter along the descent trajectory of the Probe (nominally from 0.1 to > 10 bars). The measurements, to be obtained at least every kilometer of the Probe descent, will provide the bases for inferences of mean particle sizes, particle number densities (and hence, opacities, mass densities, and columnar mass loading) and, for non-highly absorbing particles, for distinguishing between solid and liquid particles. These quantities, especially the location of the cloud bases, together with other quantities derived from this and other experiments aboard the Probe, will not only yield strong evidence for the composition of the particles, but, using thermochemical models, for species abundances as well. The measurements in the upper troposphere will provide ground truth data for correlation with remote sensing instruments aboard the Galileo Orbiter vehicle. The instrument is carefully designed and calibrated to measure the light scattering properties of the particulate clouds and hazes at scattering angles of 5.8°, 16°, 40°, 70°, and 178°. The measurement sensitivity and accuracy is such that useful estimates of mean particle radii in the range from about 0.2 to 20 can be inferred. The instrument will detect the presence of typical cloud particles with radii of about 1.0 , or larger, at concentrations of less than 1 cm³.Deceased.     

Massive stars: Setting the stage

The paper gives a summary of the situation mid-1993 of theory and observations regarding massive stars. I describe: stellar mass loss and its implications, pre-main-sequence evolution, the main sequence, problems of atmospheric instability, Luminous Blue Supergiants, Yellow Hypergiants, Wolf-Rayet stars and supernovae.     

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.     

Using sunshine for elementary space science education: A model for IHY scientist–teacher partnerships

An elementary science education professional development partnership between Culver City Unified School District teachers and UCLA has been formed. The project was designed to assist teachers to comfortably present introductory space science concepts, to support them in their efforts, and to aid them in encouraging their students to develop inquiry skills related to space sciences. The project encourages teacher use of observational science techniques in their classrooms, the use of NASA solar mission images and enhanced use of astronomical observation to facilitate discovery learning. The integrated approach of the project has fostered collegial learning activities among the participating teachers and offered them opportunities for continued renewal and professional development of teacher competencies in astronomy and space science. The activities used in the classroom were developed by others, classroom tested, and specifically address National Science Education and California Science Content Standards. These activities have been sustained through on-going collaboration between the scientist and the teachers, a summer Research Experience for Teachers program, and on-going, grade-specific, district-sponsored workshops. Assessment of the value of the program is done by the school district and is used to continuously improve each workshop and program component. Culver City (California) Unified School District is a small urban school district located on the Westside of Los Angeles. This paper describes the program and the plans for incorporating IHY-themed science into the classroom.