One of the promising technology to economize satellite communication system is the multi-beam system. The multi-beam satellite communication system requires large diameter satellite antenna. In order to satisfy several requirements, the large antenna learns to have low natural frequencies of about 1-2Hz or lower. The effects of the low frequency structural vibration on satellite attitude control have been discussed. In those effects the coupling coefficients, which shows the coupling between the rigid motion and the vibration, are important. But most of them are dealing with the flexible appendages which are connected to the satellite main body at one point. So those formulations of flexible satellite can be applied to a satellite with one-point connection. However, from the point of structural stability, it is desirable that the communication antenna reflector has multiple connection points to the main body. Using Lagrange multiplier, we revealed that the coupling coefficients are derived only by modal momentum and modal angular momentum regardless of the number of connecting points.
Aiming at precise orbit determination of a geosynchronous satellite, a VLBI experiment was conducted to observe the 2GHz band telemetry signal of the DSCS-II satellite stationed at 180deg, East. A differential VLBI method was used, where the satellite and quasars with well-known positions were alternatively observed over 24 hours using stations in Japan, United States and Australia. It was confirmed that a few meter position accuracy of the satellite in an inertial frame referring to the quasars was achieved in orbit determinations and covariance analysis considering observation errors, quasar position errors, and modeling errors in the observation system and satellite dynamics.
Experimental studies were made of combustion and evaporation of fuel droplets in high pressure environments. The burning rate constant, evaporation constant, life time and droplet temperature were measured for various kinds of liquid hydrocarbon fuels. As results, with increasing ambient pressure the burning rate constant increases and reaches the maximum value in the vicinity of the critical pressure of the fuel, and then decreases as the pressure increases further. From the comparison between the pressure dependences of the burning rate constant and the evaporation constant at various ambient temperatures, it is suggested that the evaporation phenomena during both combustion and evaporation in a high temperature environment are similar to each other.
A study is performed on the feasibility of DME-based RNAV system in Japan, where the usage of such an airborne equipment is not authorized. It is proposed here a navigation method that utilizes three DME stations (responders) and the airborne altimeter to obtain the positional information of an aircraft. Through computations, it is invesigated how the navigation system shows its effectiveness in Japan with her actual DME fascilities (counting a little more than a hundred). The HDOP is used as the evaluation parameter. Obtained results show that the DME-based navigation would exhibit adequate characteristics on the en-route area all over Japan and her vicinity; except Okinawa region where the geographical condition refuses to possess the favourable configuration of DME stations.
This note presents a difficulty encountered in random vibration testing of a satellite as well as the cause. The vibration testing system did not work because of intermittent unusual vibration of the shaker. It was found to be caused by a biharmonic signal introduced in the driving signal by “3σ clipping” of nallow-band random driving signal because a resonance frequency of the mounting adapter and the shaker was twice an anti-resonance frequency and the resonance amplitude ratio was very large. The importance of carefull design of mounting adapter was renoted.