Japan Aerospace Exploration Agency

About: Japan Aerospace Exploration Agency is a facility organization based out in Tokyo, Japan. It is known for research contribution in the topics: Galaxy & Telescope. The organization has 4327 authors who have published 12054 publications receiving 208330 citations.

On New Simple Low-Dissipation Scheme of AUSM-Family for All Speeds

Abstract: Compressible CFD methods for all speeds that can compute very low Mach number flows with low dissipation, as well as strong shock and expansion waves in high Mach number flows, are very attractive for aerospace applications such as sound generation by supersonic plume, flows in a rocket engine combustor, and cavitating gas-liquid flows. We present here such a new simple numerical flux of AUSM-family for all speeds with no tunable parameters, named SLAU (Simple Low-dissipation AUSM), along with its formulation. This scheme features low dissipation in low Mach number regime, while keeping robustness and non-oscillating nature at high Mach numbers, i.e., stabilities against shock-induced anomalies such as the carbuncle phenomenon. Furthermore, although this method does not use nor rely on scaling of numerical viscosity by the preconditioning matrix, its combination with the time derivative preconditioning is proved to be quite effective for fast convergence in low Mach number flows. These advantages of the present scheme will be demonstrated in applications to flow computations of wide-ranging Mach numbers.

The ARASE (ERG) magnetic field investigation

Abstract: The fluxgate magnetometer for the Arase (ERG) spacecraft mission was built to investigate particle acceleration processes in the inner magnetosphere. Precise measurements of the field intensity and direction are essential in studying the motion of particles, the properties of waves interacting with the particles, and magnetic field variations induced by electric currents. By observing temporal field variations, we will more deeply understand magnetohydrodynamic and electromagnetic ion-cyclotron waves in the ultra-low-frequency range, which can cause production and loss of relativistic electrons and ring-current particles. The hardware and software designs of the Magnetic Field Experiment (MGF) were optimized to meet the requirements for studying these phenomena. The MGF makes measurements at a sampling rate of 256 vectors/s, and the data are averaged onboard to fit the telemetry budget. The magnetometer switches the dynamic range between ± 8000 and ± 60,000 nT, depending on the local magnetic field intensity. The experiment is calibrated by preflight tests and through analysis of in-orbit data. MGF data are edited into files with a common data file format, archived on a data server, and made available to the science community. Magnetic field observation by the MGF will significantly improve our knowledge of the growth and decay of radiation belts and ring currents, as well as the dynamics of geospace storms.

First Star Signature in Infrared Background Anisotropies

Abstract: Recent cosmic microwave background anisotropy results from the Wilkinson Microwave Anisotropy Probe suggest that the universe was reionized at a redshift around 20 with an optical depth for Thomson scattering of 0.17 ± 0.04. Such an early reionization could arise through the ionizing radiation emitted by metal-free Population III stars at redshifts of 10 and higher. We discuss infrared background (IRB) surface brightness spatial fluctuations from such a generation of early star formation. We show that the spatial clustering of these stars at tens of arcminute scales generates a contribution to the angular power spectrum of the IRB anisotropies at the same angular scales. This excess can be potentially detected when resolved foreground galaxies out to a redshift of a few are removed from the clustering analysis. We do not expect faint galaxies at redshifts of ~3, with magnitudes less than 20 in the K band, to be a source of strong confusion, since the fractional contribution to the IRB from these galaxies is at a level less than a few percent, while the expected contribution from first stars can be 50% or more. Additionally, assuming a Population III stellar spectrum, we suggest that the clustering excess related to the first generation of stars can be separated from brightness fluctuations resulting from other foreground sources and galaxies using multifrequency observations in the wavelength range of ~1-5 μm. In addition to identifying the IR clustering associated with low-redshift galaxy population, the multifrequency data are essential to account for certain foreground contaminants such as zodiacal light, which, if varying spatially over degree scales, can be a significant source of confusion for the proposed study. Using various instruments, we study the extent to which spatial fluctuations of the IRB can be studied in the near future.

Pole and Global Shape of 25143 Itokawa

Abstract: The locations of the pole and rotation axis of asteroid 25143 Itokawa were derived from Asteroid Multiband Imaging Camera data on the Hayabusa spacecraft. The retrograde pole orientation had a right ascension of 90.53 degrees and a declination of -66.30 degrees (52000 equinox) or equivalently 128.5 degrees and -89.66 degrees in ecliptic coordinates with a 3.9 degrees margin of error. The surface area is 0.393 square kilometers, the volume is 0.018378 cubic kilometers with a 5% margin of error, and the three axis lengths are 535 meters by 294 meters by 209 meters. The global Itokawa revealed a boomerang-shaped appearance composed of two distinct parts with partly faceted regions and a constricted ring structure.