Toshimichi Otsubo

VLBI, SLR and GPS observations in the Key Stone Project

A space geodetic observation network has been established around Tokyo, Japan under a project name of Key Stone Project by Communications Research Laboratory. Three space geodetic methods, i.e. Very Long Baseline Interferometry, Satellite Laser Ranging, and Global Positioning System, are involved in the project. As of September, 1997, VLBI and GPS observation facilities at all four stations are operational, whereas developments of SLR observation facilities are in course of final alignment procedures. Daily VLBI observations began in January 1995 with a single baseline between Koganei and Kashima, and the full network observations with four stations began in September 1996. Observations and data analysis of VLBI measurements are fully automated and the analysis results are produced shortly after all observations of an experiment session finished. GPS observations at four sites began in July 1997 and the automatic data collection and analysis system are under developments.

Optical response of the H2A-LRE satellite

We designed the arrangement of the corner cube reflectors to be carried on the H2A-LRE satellite. There are 126 reflectors on its quasi-spherical surface; 66 are made of fused silica and the others are made of BK7 glass. Fused silica remains active for more than a few decades, while BK7 degrades in a short time. The reflectors are arranged on the body faces so that the satellite can respond most angles of incidence and so that the optical response does not change significantly after the BK7 reflectors degrade. The optical response from the H2A-LRE satellite was simulated based on the measured position of all its reflectors. The centre-of-mass corrections for multi-photon systems were calculated at 215.3 mm while the BK7 was active and at 210.5 mm after it totally degraded. For single-photon systems, the corrections were 208.5 mm before degradation and 204.7 mm after degradation.

Laser reflector arrangement on H2A-LRE satellite for monitoring spin rate and optical degradation

We devised a unique array of cube-corner reflectors on a spherical satellite so that laser ranging could be used to detect the spin rate and the optical degradation. On the H2A-LRE satellite, there are reflectors made of synthetic silica and ones made of BK7 glass. We report that the degradation of the BK7 reflectors, as well as the spin rate of the satellite, can be monitored through a spectral analysis of laser-ranging data. The center-of-mass correction of the Laser Ranging Equipment satellite was calculated at 210 +/- 10 mm for all possible systems and throughout the degradation process of the BK7 reflectors.

Satellite signature effects by ranging system and satellite attitude

Residuals of AJISAI ranging data are investigated for single-photon detection and multi-photon detection by comparing our simulation model with actual range data. The simulated distribution histogram for a single-photon system based on our model agrees well with that obtained by the Herstmonceux station. We also found the variations in the AJISAIs center-of-mass correction for multi-photon systems was linked to the satellite attitude as a result of doing a spectral analysis of the Orroral stations data.