岩田 隆浩

The solar radiation pressure model for the sub-satellites RSAT and VSAT in the SELENE project is improved to correct the mean acceleration due to an evolving tip-off of the spin during the life time of satellites. The shape of the satellites is assumed to be a regular octagonal pillar. Solar radiation pressure force components acting on each surface element of the satellite are calculated independently and summed vectorially during a total period of Euler's free nutation of the satellite to obtain the mean acceleration of the satellite center of mass. The Doppler tracking data reduction process for the RSAT is simulated after incorporating the modified model into the orbit analysis software. Comparing with two other types of solar radiation pressure models, the standard cannonball model and a non tip-off model, it is found that when the tip-off becomes larger than 5°/s, the orbit determination result of using the modified model is better than the results of using other ones.

In the SELenological and ENgineering Explorer (SELENE) project which is the Japanese lunar program to be launched in 2003 by the Institute of Space and Astronautical Science (ISAS) and National Space Development Agency of Japan (NASDA), we measure angular distance between a radio transmitter on a relay satellite, that on the Moon and quasars by differential VLBI and determine amplitudes of the physical Librations, gravitational harmonic coefficients of the Moon and lunar ephemeris with an accuracy one or two orders higher than before in cooperation with 4-way Doppler measurements and two-way Doppler and ranging m(e)asurements using the lunar orbiter and the relay satellite. We are proposing another selenodetic mission, In situ Lunar Orientation Measurement (ILOM) to study lunar rotational dynamics by direct observations of the lunar physical libration from the lunar surface with an accuracy of 1 milliarcsecond in a post-SELENE project which will be launched about three years after SELENE. Year-long trajectories of the stars provide information on various components of the physical librations and we will also try to detect the lunar free librations in order to investigate the lunar mantle and the liquid core.

Nutrient distributions (NO3-, NO2-, PO43-, SiO2) were measured in Kuroshio Warm-Core Ring (WCR) during the Hakuho-maru cruise KH-97-3. WCR is occurring as a transit zone between the Kuroshio and Oyashio. In generally, it is thought that organic production is much greater at the edge of WCR than at the center of that. Concentration of chlorophyll-a is also higher at the edge of WCR than center of that. But, We have no clear interpretation about the mechanism of nutrient supply, especially to the edge of WCR. We had studied hydrographic of WCR structure using potential T, S, σ(θ) and nutrient. Consequently, I had gotten new hypothesis on WCR structure: The edge of WCR has lower than sea surface and mulchlayered structure from surface to bottom of WCR. This WCR structure will bring to the small scales upwelling around top of edge, which supplies nutrient to the edge of WCR, and maintains the higher organic production at the edge.