A simulation study for anticipated accuracy of lunar gravity field model by SELENE tracking data

Results of numerical simulations are presented to examine the global gravity field recovery capability of the Japanese lunar exploration project SELENE (SELenological and ENgineering Explorer) which will be launched in 2007. New characteristics of the SELENE lunar gravimetry include 4-way satellite-to-satellite Doppler tracking of main orbiter and differential VLBI tracking of two small free-flier satellites. It is shown that the proposed satellite constellation will provide the first truly global satellite tracking data coverage. The expected results from these data are; (1) drastic reduction in far-side gravity error, (2) estimation of many gravity coefficients by the observation, not by a priori information, and (3) one order of magnitude improvement over existing gravity models for low-degree field.     

Studying the Lunar Ionosphere with SELENE Radio Science Experiment

Radio occultation observations of the electron density near the lunar surface were conducted during the SELENE (Kaguya) mission using the Vstar and Rstar sub-satellites. Previous radio occultation measurements conducted in the Soviet lunar missions have indicated the existence of an ionosphere with peak densities of several hundreds of electrons per cubic centimeters above the dayside lunar surface. These densities are difficult to explain theoretically when the removal of plasma by the solar wind is considered, and thus the generation mechanism of the lunar ionosphere is a major issue, with even the validity of previous observations still under debate. The most serious error source in the measurement is the fluctuation of the terrestrial ionosphere which also exists along the ray path. To cope with this difficulty, about 400 observations were conducted using Vstar to enable statistical analysis of the weak signal of the lunar ionosphere. Another method is to utilize Vstar and Rstar with the second one being used to measure the terrestrial ionosphere contribution. The observations will establish the morphology of the lunar ionosphere and will reveal its relationship with various conditions to provide possible clues to the mechanism.     

Single-event upset in geostationary transfer orbit during solar-activity maximum period measured by the Tsubasa satellite

This paper reports single-event upset (SEU) occurrence related to the space radiation environment in geostationary transfer orbit during solar-activity maximum period measured by the Tsubasa satellite. Most SEUs are measured in the inner radiation belt, indicating that they are mainly caused by trapped protons. Thus, the spatial distribution and the temporal variation of the SEU count correlate well with those of trapped protons. The peak SEU rate appears around L = 1.4. The transition point from SEUs caused by trapped protons to those caused by galactic cosmic rays is around L = 2.6. During the experiment period, increased SEU count was sometimes detected due to solar and geomagnetic events outside the inner radiation belt.     

Coherent nonlinear effects on electromagnetic wave-particle interactions

In many particle simulations and space experiments, the knowledge of nonlinear characteristics of both waves and particles in plasmas is very helpful in the data analysis phase. Such knowledge is needed even more in the designing phase of appropriate diagnostics and probings in both simulations and space experiments. In this tutorial lecture, I will attempt to provide a basic introduction to the fundamental features of coherent nonlinear wave-particle and wave-wave interactions in magnetized plasmas. The present lecture covers only some of the important and basic characteristics in the coherent nonlinear interactions. The main subjects are: (1) trapping dynamics in the electrostatic wave, (2) nonlinear phase trapping and phase bunching in electromagnetic wave both in homogeneous and inhomogeneous plasmas, and (3) coherent three wave interactions.     

Comparison of gradual and rapid onset runs in a short-arm centrifugation

A gradual onset run (GOR) in a short-arm centrifugation was performed on ten healthy students. The centrifuge had a 1.8 m radius, and the subjects sat on a chair in a cabin. The Gz force increased to 2.2 Gz at 0.1 °/sec² for 32 min. and the same Gz-level was maintained for 20 min. Three out of ten subjects completed the whole protocol; the load on the others was terminated because of symptoms or increased heart rate. There were few symptoms such as vertigo, that was a common problem with a rapid onset run (ROR) in former experiments, due to the short-arm centrifugation. The changes of the flicker test after the load were much less in the GOR protocol than in the ROR protocol, even in the terminated group. GOR seemed preferable to ROR in preventing vertigo even though it took longer to reach the necessary G load.     

The simulation of lunar gravity field recovery from D-VLBI of Chang’E-1 and SELENE lunar orbiters

The lunar gravity field is a foundation to study the lunar interior structure, and to recover the evolution history of the Moon. It is still an open and key topic for lunar science. For above mentioned reasons, it becomes one of the important scientific objectives of recent lunar missions, such as KAGUYA (SELENE) the Japanese lunar mission and Chang’E-1, the Chinese lunar mission. The Chang’E-1 and the SELENE were successfully launched in 2007. It is estimated that these two missions can fly around the Moon longer than 6 months simultaneously. In these two missions, the Chinese new VLBI (Very Long Baseline Interferometry) network will be applied for precise orbit determination (POD) by using a differential VLBI (D-VLBI) method during the mission period. The same-beam D-VLBI technique will contribute to recover the lunar gravity field together with other conventional observables, i.e. R&RR (Range and Range Rate) and multi-way Doppler. Taking VLBI tracking conditions into consideration and using the GEODYNII/SOVLE software of GSFC/NASA/USA [8 and 10], we simulated the lunar gravity field recovering ability with and without D-VLBI between the Chang’E-1 and SELENE main satellite. The cases of overlapped flying and tracking period of 30 days, 60 days and 90 days have been analyzed, respectively. The results show that D-VLBI tracking between two lunar satellites can improve the gravity field recovery remarkably. The results and methods introduced in this paper will benefit the actual missions.     

Statistical study of electrostatic solitary waves associated with reconnection: Geotail observations

The role of waves in the dynamics of the magnetotail has long been a topic of interest in magnetospheric physics. The characteristics of Electrostatic Solitary Waves (ESWs) associated with reconnection have been studied statistically in the magnetotail by surveying the large amounts data obtained from Waveform Capture (WFC) which is an important component of Plasma Wave Instrument (PWI) on the Geotail spacecraft. About 150 reconnection events with WFC data available are selected, and approximately 10 thousands of ESW waveforms are picked up by hands for statistical study. The ESWs are observed near diffusion region and near the plasma sheet boundary layer (PSBL). Two kinds of waveforms of ESWs are observed: bi-polar and tri-polar pulses. It is found that the pulse width of the ESWs is in the order of 1–5 ms and the peak-to-peak amplitude is in the order of 0.1–5 mV/m. The amplitudes of ESWs are larger in the near-earth tail region than that in deep tail region. ESWs have been observed with or without guide magnetic field 〈By〉. The characteristics of ESWs in different reconnection region and under different strength of guild magnetic field, their possible generation mechanism will be discussed.     

The development of compression long-period pulsations on the recovery phase of the magnetic storm on May 23, 2007

The features of the excitation of spatially localized long-period (10–15 min) irregular pulsations with a maximum amplitude of ~200 nT at a geomagnetic latitude of 66° in the morning sector 5 MLT are considered. Fluctuations were recorded against the background of substorm disturbances (maximum AE ~ 1278 nT). Antiphase variations of plasma density and magnetic field accompanied by vortex disturbances of the magnetic field both in the magnetosphere and the ionosphere have been recorded in the magnetosphere in this sector. Compression fluctuations corresponding to a slow magnetosonic wave have been recorded in the interplanetary medium in the analyzed period. It is assumed that pulsations have been excited in the localization of the cloud of injected particles in the plasma sheet by compression fluctuations caused by variations of the dynamic pressure of solar wind.     

Rocket observation of the near-infrared extragalactic background radiation

Near-infrared diffuse radiation at 1 μm – 5 μm was observed using cold optics on board a sounding rocket. The observed surface brightness is too bright to be explained by known diffuse sources and its significant part is possibly attributed to the cosmic origin. Extragalactic background radiation thus obtained is brighter than theoretically estimated so that new energy sources at an early epoch of the universe are required.