Microinstabilities associated with a high Mach number,perpendicular bow shock

The instabilities associated with a high Mach number perpendicular shock are reexamined in light of recent enhanced understanding of the Earth's bow shock. The insights provided by both the ISEE observations and hybrid simulations are reviewed and subsequently incorporated into the instability analyses. The discussion of the instabilities is divided according to their location in the shock layer. In the regions in front of and at the shock transition the cross-field instabilities are subdivided into low frequency modes (e.g. ion-ion streaming, kinetic cross-field streaming, drift lower hybrid instabilities) and high frequency modes (electron cyclotron drift, ion sound and electron whistler instabilities). Further downstream various ion ring-like and anisotropy driven instabilities are considered. In each case the instability analysis is reviewed and recent developments are emphasized. Implications of these results concerning the wave signatures and plasma heating and acceleration are also discussed.     

Magnetosphere–Ionosphere Convection as a Compound System

Convection is the most fundamental process in understanding the structure of geospace and disturbances observed in the magnetosphere–ionosphere (M–I) system. In this paper, a self-consistent configuration of the global convection system is considered under the real topology as a compound system. Investigations are made based on the M–I coupling scheme by analyzing numerical results obtained from magnetohydrodynamic (MHD) simulations which guarantee the self-consistency in the whole system under the Bv (magnetic field and velocity) paradigm. It is emphasized in the M–I coupling scheme that convection and field-aligned current (FAC) are different aspects of same physical process characterizing the open magnetosphere. Special attention is given in this paper to the energy supplying (dynamo) process that drives the FAC system. In the convection system, the dynamo must be constructed from shear motion together with plasma population regimes to steadily drive the convection. Convection patterns observed in the ionosphere are also the manifestation of achievement in global self-consistency. A primary approach to apply these concepts to the study of geospace is to consider how the M–I system adjusts the relative motion between the compressible magnetosphere and the incompressible ionosphere when responding to given solar-wind conditions. The above principle is also applicable for the study of disturbance phenomena such as the substorm as well as for the study of apparently unique processes such as the flux transfer event (FTE), the sudden commencement (SC), and the theta aurora. Finally, an attempt is made to understand the substorm as the extension of enhanced convection under the southward interplanetary magnetic field (IMF) condition.     

A numerical study of the charge diameter effect on unsteady detonation

A numerical study for the unsteady detonation of an unconfined tetryl charge of small diameter, which is assumed to be homogeneous, was performed by using the two-dimensional Lagrangian hydrodynamic computer code, 2 DL, with the first order Arrhenius equation of reaction rate. Becker-Kistiakowsky-Wilson (BKW) and Kihara-Hikita (KH) equations of state have been applied to the detonation products.In the case of BKW, it is shown that the rarefaction waves propagating inward from the lateral surface make the reaction rate slow and give a curvature to the front. Then after an induction time, a strong initiation occurs in the reaction zone near the lateral surface and higher pressure zone moves to the axis. This higher pressure accelerates the detonation propagation near the lateral surface and the curvature of detonation front is reduced. Then, the reaction at the lateral surface again begins to decay by the rarefaction waves. Such a sequence of process is repeated periodically.The possibility of the occurrence of the strong initiation depends on the pressure and temperature in the shocked zone near the surface. In a small diameter charge, the delayed explosion becomes weaker near the surface, while its frequency increases. No shock interaction occurs because the direction of the particle flow is always divergent.In the case of KH equation of state, the temperature of detonation is higher than that obtained by BKW and the behaviour of instability becomes rather different from the previous result, i.e. in the axis the pressure oscillates repeating the overdriven and underdriven detonation similar with the case of BKW.     

A Simple Method for Evaluating the System Observability in Satellite Orbit Determination

A method is described for evaluating the system observability in satellite orbit determination. The method is simple and rapid in computation time, because it uses the calculation of the mutual orthogonality between the observation partial vectors rather than the calculation of eigenvalues of the Grammian matrix.     

Application of an MHD simulation to the study of substorms

The substorm mechanism is studied by the numerical solutions obtained from a resistive magnetohydrodynamic (MHD) simulation. After a southward turning of the interplanetary magnetic field (IMF), the simulation results reproduce observed features of the growth phase. The numerical solutions show that the plasma sheet thinning during the growth phase is formed under the dynamic balance between the flux pileup from the midtail and the flux removal toward the dayside controlled by the convection in the magnetosphere-ionosphere (M-I) coupling system. After the growth phase, dipolarization is generated in the near-earth tail accompanied by a plasma injection into the inner magnetosphere, the formation of plasmoid in the midtail, and the enhancement of the nightside field-aligned currents (FACs). The direct cause of this onset is the state (phase space) transition of the convection system from a thinned state to a dipolarized state associated with a self-organization in the nonlinear system.     

Overview of Differential VLBI Observations of Lunar Orbiters in SELENE (Kaguya) for Precise Orbit Determination and Lunar Gravity Field Study

The Japanese lunar explorer SELENE (Kaguya), which was launched on September 14th, 2007, was the target of VLBI observations over the period November 2007 to June 2009. These observations were made in order to improve the lunar gravity field model, in particular the lower degree coefficients and the model near the limb. Differential VLBI Radio sources, called VRAD instruments, were on-board the subsatellites, Rstar (Okina) and Vstar (Ouna), and the radio signals were observed by the Japanese VERA (VLBI Exploration of Radio Astrometry) network, and an international VLBI network. Multi-frequency and same-beam VLBI techniques were utilized and were essential aspects of the successful observing program. Multi-frequency VLBI was employed in order to improve the accuracy of the orbit determination obtained from the phase delay from the narrow-band satellite signals, while the same-beam VLBI method was used to resolve the cycle ambiguity which is inherent in the multi-frequency VLBI method. The observations were made at three S-band frequencies (2212, 2218 and 2287 MHz), and one X-band frequency (8456 MHz). We have succeeded in correlating the recorded signals from Okina/Ouna, and we obtained phase delays with an accuracy of several pico-seconds at S-band.     

In-flight Performance and Initial Results of Plasma Energy Angle and Composition Experiment (PACE) on SELENE (Kaguya)

MAP-PACE (MAgnetic field and Plasma experiment—Plasma energy Angle and Composition Experiment) on SELENE (Kaguya) has completed its ～1.5-year observation of low-energy charged particles around the Moon. MAP-PACE consists of 4 sensors: ESA (Electron Spectrum Analyzer)-S1, ESA-S2, IMA (Ion Mass Analyzer), and IEA (Ion Energy Analyzer). ESA-S1 and S2 measured the distribution function of low-energy electrons in the energy range 6 eV–9 keV and 9 eV–16 keV, respectively. IMA and IEA measured the distribution function of low-energy ions in the energy ranges 7 eV/q–28 keV/q and 7 eV/q–29 keV/q. All the sensors performed quite well as expected from the laboratory experiment carried out before launch. Since each sensor has a hemispherical field of view, two electron sensors and two ion sensors installed on the spacecraft panels opposite each other could cover the full 3-dimensional phase space of low-energy electrons and ions. One of the ion sensors IMA is an energy mass spectrometer. IMA measured mass-specific ion energy spectra that have never before been obtained at a 100 km altitude polar orbit around the Moon. The newly observed data show characteristic ion populations around the Moon. Besides the solar wind, MAP-PACE-IMA found four clearly distinguishable ion populations on the dayside of the Moon: (1) Solar wind protons backscattered at the lunar surface, (2) Solar wind protons reflected by magnetic anomalies on the lunar surface, (3) Reflected/backscattered protons picked-up by the solar wind, and (4) Ions originating from the lunar surface/lunar exosphere.     

Introduction to Japanese exploration study to the moon

The Japan Aerospace Exploration Agency (JAXA) views the lunar lander SELENE-2 as the successor to the SELENE mission. In this presentation, the mission objectives of SELENE-2 are shown together with the present design status of the spacecraft. JAXA launched the Kaguya (SELENE) lunar orbiter in September 2007, and the spacecraft observed the Moon and a couple of small satellites using 15 instruments. As the next step in lunar exploration, the lunar lander SELENE-2 is being considered. SELENE-2 will land on the lunar surface and perform in-situ scientific observations, environmental investigations, and research for future lunar utilization including human activity. At the same time, it will demonstrate key technologies for lunar and planetary exploration such as precise and safe landing, surface mobility, and overnight survival. The lander will carry laser altimeters, image sensors, and landing radars for precise and safe landing. Landing legs and a precisely controlled propulsion system will also be developed. A rover is being designed to be able to travel over a wide area and observe featured terrain using scientific instruments. Since some of the instruments require long-term observation on the lunar surface, technology for night survival over more than 2 weeks needs to be considered. The SELENE-2 technologies are expected to be one of the stepping stones towards future Japanese human activities on the moon and to expand the possibilities for deep space science.     

An AO-free coronagraph experiment in vacuum with a binary-shaped pupil mask

We present our first results from laboratory experiments on a binary-shaped checkerboard mask coronagraph that was fitted inside a vacuum chamber for the development of skills to the direct observation of extra-solar planets. The aim of this work was to utilize a vacuum chamber for our coronagraph experiments in order to achieve an environment with higher thermal stability and which is free from air turbulence. We also aimed to evaluate and improve the performance of such a system consisting of a vacuum chamber with a coronagraph set inside the chamber. Both the raw contrast and the contrast after point spread function (PSF) subtraction are evaluated. We sited the vacuum chamber in a clean room, and we installed an optical fiber coupled to a visible He–Ne laser, appropriate coronagraph optics, a temperature sensor and heaters in the chamber. This provided a vacuum environment and a temperature-controlled environment with a visible light source, and was shown to improve the stability of the coronagraph. A contrast of 1.7×10^-7$1.7\times {10}^{-7}$ was achieved for the raw coronagraphic images by analyzing the areal mean of all of the observed dark regions. A contrast of 7.3×10^-9$7.3\times {10}^{-9}$ was achieved for the PSF subtraction by areal variance (1σ) of all of the observed dark regions. Speckles were a major limiting factor throughout the dark regions of both the raw images and the PSF subtracted images. The application of PSF subtraction for the Space Infrared telescope for Cosmology and Astrophysics (SPICA) and for other platforms is discussed.