Ground-to-satellite laser communication experiments

Ground-to-satellite laser communication experiments between the optical ground station located in Koganei, central Tokyo, and a low earth orbit (LEO) satellite were jointly performed by the Japan Aerospace Exploration Agency and the National Institute of Information and Communications Technology. In 18 trials during three non-consecutive months, the satellite was acquired and tracked 61 % of the time, when clear or partly-clear conditions were predominant. The optical link was maintained for about 6 minutes when the satellite was visible in spite of the high angular velocity of the satellite. In 3 of the 18 trials, the link was not interrupted due to clouds during the six-minute transit. The failures (39% of the time) occurred when cloudy or rainy conditions were predominant. Fluctuation in the uplink received signal power was minimized by using multiple laser beam transmissions. The measured uplink and downlink bit error ratios were 10^-7-10^-4. These results demonstrate the applicability of free-space laser communication for not only geostationary earth orbit-LEO optical links but also ground-to-LEO optical links.     

Interrelation between VLF and ULF emissions

Observations and theoretical works so far made are reviewed in regard to the interrelation of VLF and ULF emissions. Quasi-periodic VLF emissions are one of the typical examples showing the interrelation between the two phenomena. The term modulation may be more appropriate to explain these phenomena. Tentative interpretations will be given of the VLF and ULF emissions which are closely associated through a modulation of the electron distributions.     

JUXTA: A new probe of X-ray emission from the Jupiter system

For the future Japanese exploration mission of the Jupiter’s magnetosphere (JMO: Jupiter Magnetospheric Orbiter), a unique instrument named JUXTA (Jupiter X-ray Telescope Array) is being developed. It aims at the first in-situ measurement of X-ray emission associated with Jupiter and its neighborhood. Recent observations with Earth-orbiting satellites have revealed various X-ray emission from the Jupiter system. X-ray sources include Jupiter’s aurorae, disk emission, inner radiation belts, the Galilean satellites and the Io plasma torus. X-ray imaging spectroscopy can be a new probe to reveal rotationally driven activities, particle acceleration and Jupiter–satellite binary system. JUXTA is composed of an ultra-light weight X-ray telescope based on micromachining technology and a radiation-hard semiconductor pixel detector. It covers 0.3–2 keV with the energy resolution of <100 eV at 0.6 keV. Because of proximity to Jupiter (∼30 Jovian radii at periapsis), the image resolution of <5 arcmin and the on-axis effective area of >3 cm² at 0.6 keV allow extremely high photon statistics and high resolution observations.