Cosmic ray investigation for the Voyager missions; energetic particle studies in the outer heliosphere—And beyond

A cosmic-ray detector system (CRS) has been developed for the Voyager mission which will measure the energy spectrum of electrons from 3–110 MeV and the energy spectra and elemental composition of all cosmic-ray nuclei from hydrogen through iron over an energy range from 1–500 MeV/nuc. Isotopes of hydrogen through sulfur will be resolved from 2–75 MeV/nuc. Studies with CRS data will provide information on the energy content, origin and acceleration process, life history, and dynamics of cosmic rays in the galaxy, and contribute to an understanding of the nucleosynthesis of elements in the cosmic-ray sources. Particular emphasis will be placed on low-energy phenomena that are expected to exist in interstellar space and are known to be present in the outer Solar System. This investigation will also add to our understanding of the transport of cosmic rays, Jovian electrons, and low-energy interplanetary particles over an extended region of interplanetary space. A major contribution to these areas of study will be the measurement of three-dimensional streaming patterns of nuclei from H through Fe and electrons over an extended energy range, with a precision that will allow determination of anisotropies down to 1%. The required combination of charge resolution, reliability and redundance has been achieved with systems consisting entirely of solid-state charged-particle detectors.Principal Investigator of the Voyager Cosmic Ray Experiment.     

A Sequential Implementation of Optimal Array Processors

A sequential implementation of the likelihood ratio for doubly composite hypothesis array processing problems is presented in which the likelihood ratio is realized by an appropriate combination ion of single frequency components. The array processos decomposed in such a way that the actual a priori parameter knowledge dge need not be introduced until after a significant portion of the data processing has taken place.     

Analysis of a Signal Processor for an Antenna Array

A signal processor that provides ratio-squared predetection combining, has been investigated for application in an adaptive antenna array. The analysis and experimental data presented here pertain to the signal processing gain when the antenna array is illuminated by a coherent signal source and a partially coherent noise source. For a noise source which is coherent, the processing gain depends on relative strength of the signal and noise, relative directions of arrival, and the usual "array factor." The array exhibits capturing effects much as in an FM receiver. The effective antenna pattern is a superposition of two beams of different magnitudes, one directed to the signal source and the other to the noise source. When the noise is partially coherent, the behavior of the signal processor is quite complex. Analytical prediction and experimental simulation measurement on a four-channel system indicate that the partially coherent noise may be regarded as the source of an incoherent noise component plus a coherent noise component with the magnitude of the latter determined by the coherence coefficient for the noise source.     

多股射流横向喷入有约束管流过程的模拟

用基于控制体的有限差分方法对一排射流横向喷入管流的流场进行了数值分析，以建立流场温度分布和上游流动条件及几何参数的关系，可变的参数包括：喷嘴直径，喷嘴数，圆柱管半径，射流与主流的体积流量比，温度比和动压比，结果发现，动压比，喷嘴个数和喷嘴间距是三个重要变量，通过对模拟结果的函数拟合，发现射流喷射深度与动压比除以喷嘴数的平方之间的关系可用一个对数函数很好地描述，给出了适用最佳混合的喷射深度和喷嘴间距，提出了可用于结构实设计的程序。     

Space-time registration of radar and ESM using unscented Kalman filter

Space and time alignments are the prerequisites for the successful fusion of multiple sensors. A space-time registration model is proposed to estimate the system biases and to perform time synchronization together for mobile radar and electronic support measure (ESM) systems. A space-time registration model for radar and ESM is first developed, and an unscented Kalman filter (UKF) is proposed to estimate the space-time biases and target states simultaneously. The posterior Cramer-Rao bounds (PCRBs) are derived for the proposed UKF registration algorithm for ESM detection probability less than or equal to one. Theoretical analyses are performed to evaluate the accuracy and robustness of the proposed method. Computer simulations show that the UKF registration algorithm is indeed effective and robust for different radar and ESM tracking scenarios.     

Radar: The Cassini Titan Radar Mapper

The Cassini RADAR instrument is a multimode 13.8 GHz multiple-beam sensor that can operate as a synthetic-aperture radar (SAR) imager, altimeter, scatterometer, and radiometer. The principal objective of the RADAR is to map the surface of Titan. This will be done in the imaging, scatterometer, and radiometer modes. The RADAR altimeter data will provide information on relative elevations in selected areas. Surfaces of the Saturn’s icy satellites will be explored utilizing the RADAR radiometer and scatterometer modes. Saturn’s atmosphere and rings will be probed in the radiometer mode only. The instrument is a joint development by JPL/NASA and ASI. The RADAR design features significant autonomy and data compression capabilities. It is expected that the instrument will detect surfaces with backscatter coefficient as low as −40 dB.RADAR Team LeaderThis revised version was published online in July 2005 with a corrected cover date.     

The Electron and ion Plasma Experiment for Fast

The ion and electron plasma experiment on the Fast Auroral Snapshot satellite (FAST) is designed to measure pitch-angle distributions of suprathermal auroral electrons and ions with high sensitivity, wide dynamic range, good energy and angular resolution, and exceptional time resolution. These measurements support the primary scientific goal of the FAST mission to understand the physical processes responsible for auroral particle acceleration and heating, and associated wave-particle interactions. The instrument includes a complement of 8 pairs of `Top Hat' electrostatic analyzer heads with microchannel plate (MCP) electron multipliers and discrete anodes to provide angle resolved measurements. The analyzers are packaged in four instrument stacks, each containing four analyzers. These four stacks are equally spaced around the spacecraft spin plane. Analyzers mounted on opposite sides of the spacecraft operate in pairs such that their individual 180° fields of view combine to give an unobstructed 360° field of view in the spin plane. The earth's magnetic field is within a few degrees of the spin plane during most auroral crossings, so the time resolution for pitch-angle distribution measurements is independent of the spacecraft spin period. Two analyzer pairs serve as electron and ion spectrometers that obtain distributions of 48 energies at 32 angles every 78 ms. Their standard energy ranges are 4 eV to 32 keV for electrons and 3 eV to 24 keV for ions. These sensors also have deflection plates that can track the magnetic field direction within 10° of the spin plane to resolve narrow, magnetic field-aligned beams of electrons and ions. The remaining six analyzer pairs collectively function as an electron spectrograph, resolving distributions with 16 contiguous pitch-angle bins and a selectable trade-off of energy and time resolution. Two examples of possible operating modes are a maximum time resolution mode with 16 angles and 6 energies every 1.63 ms, or a maximum energy resolution mode with 16 angles and 48 energies every 13 ms. The instrument electronics include mcp pulse amplifiers and counters, high voltage supplies, command/data interface circuits, and diagnostic test circuits. All data formatting, commanding, timing and operational control of the plasma analyzer instrument are managed by a central instrument data processing unit (IDPU), which controls all of the FAST science instruments. The IDPU creates slower data modes by averaging the high rate measurements collected on the spacecraft. A flexible combination of burst mode data and slower `survey' data are defined by IDPU software tables that can be revised by command uploads. Initial flight results demonstrate successful achievement of all measurement objectives.     

Role of ionospheric effects and plasma sheet dynamics in the formation of auroral arcs

At the ionospheric level, the substorm onset (expansion phase) is marked by the initial brightening and subsequent breakup of a pre-existing auroral arc. According to the field line resonance (FLR) wave model, the substorm-related auroral arc is caused by the field-aligned current carried by FLRs. The FLRs are standing shear Alfvén wave structures that are excited along the dipole/quasi-dipole lines of the geomagnetic field. The FLRs (that can cause auroral arc) thread from the Earthward edge of the plasma sheet and link the auroral arc to the plasma sheet region of 6–15 R _E. The region is associated with magnetic fluctuations that result from the nonlinear wave-wave interactions of the cross-field current-instability. The instability (excited at the substorm onset) disrupts the cross-tail current which is built up during the growth phase of the substorms and results in magnetic fluctuations. The diversion of the current to polar regions can lead to auroral arc intensification. The current FLR model is based on the amplitude equations that describe the nonlinear space-time evolution of FLRs in the presence of ponderomotive forces exerted by large amplitude FLRs (excited during substorms). The present work will modify the FLR wave model to include the effects arising from magnetic fluctuations that result from current disruption near the plasma sheet (6–15 R _E). The nonlinear evolution of FLRs is coupled with the dynamics of plasma sheet through a momentum exchange term (resulting from magnetic fluctuations due to current disruption) in the generalized Ohm's law. The resulting amplitude equations including the effects arising from magnetic fluctuations can be used to study the structure of the auroral arcs formed during substorms. We have also studied the role of feedback mechanism (in a dipole geometry of the geomagnetic field) in the formation of the discrete auroral arc observed on the nightside magnetosphere. The present nonlinear dispersive model (NDM) is extended to include effects arising from the low energy electrons originating from the plasma sheet boundary layer. These electrons increase the ionospheric conductivity in a localized patch and enhance the field-aligned current through a feedback mechanism. The feedback effects were studied numerically in a dipole geometry using the the NDM. The numerical studies yield the magnitude of the field-aligned current that is large enough to form a discrete auroral arc. Our studies provide theoretical support to the observational work of Newell et al. that the feedback instability plays a major role in the formation of the discrete auroral arcs observed on the nightside magnetosphere.     

Analytical parametric identification in dynamic wind-tunnel tests

The dynamic wind-tunnel tests of a functional model of a flight vehicle being developed make it possible to obtain more reliable data on aerodynamic and structural characteristics and, hence, improve the design quality and increase reliability in the finished product operation. The objective stated is achieved by formation of angular model motions, the parameters of which are measured and compared with angular parameters calculated using the analytical solutions of differential equations of motions being formed. We considered two media of the incoming flow with the resistance proportional to speed and the square of speed. The results can be used in flight vehicle design, development of onboard control algorithms and subsequent identification of other parameters.     

Possible Role of ion Demagnetization in the Plasma Sheet in Auroral arc and Substorm Generation

Ion demagnetization in the plasma sheet causes the formation of field-aligned current that can trigger a magnetosphere-ionosphere coupling feedback instability, which may play an important role in substorm and auroral arc generation. Since field-aligned currents close ionospheric currents, their magnitude is controlled by ionospheric conductivity. The cause of instability is the impact of increasing upward field-aligned currents on ionospheric conductivity, which in turn stimulates an increase in the field-aligned currents. When the magnitude of these currents becomes sufficiently large for the acceleration of precipitating electrons, a feedback mechanism becomes possible. Upward field-aligned currents increase the ionospheric conductivity that stimulates an explosion-like increase in field-aligned currents. It is believed that this instability may be related to substorm generation. Demagnetization of hot ions in the plasma sheet leads to the motion of magnetospheric electrons through a spatial gradient of ion population. Field-aligned currents, because of their effect on particle acceleration and the magnitude of ionospheric conductivity, can also lead to another type of instability associated with the breaking of the earthward convection flow into convection streams. The growth rate of this instability is maximum for structures with sizes less than the ion Larmor radius in the equatorial plane. This may lead to the formation of auroral arcs with widths of the order of 10 km. This instability is able to explain many features of auroral arcs, including their conjugacy in opposite hemispheres. However, it cannot explain very narrow (less than 1 km) arcs.