This research is being conducted in the Mechanical Engineering Sciences department of the Tokyo Institute of Technology under the supervision of Dr. Yoshiaki Ohkami. The project is supported by a small company in California that manufactures actively stabilized antenna platforms. Such antenna platforms are used onboard moving vehicles, such as ships, so that the antenna can be made to point toward a given satellite despite undulating motions of the boat or vehicle. The goal of the project is to modify one of the company�fs existing tracking systems so as to achieve more precise control and pointing accuracy of the antenna platform. The system provided by the US company is currently being used by customers onboard large shipping vessels to track INMARSAT geostationary satellites. Such an application requires a pointing accuracy of approximately 5 [deg], and the current system is capable of achieving this despite relatively large motions of the ship. In the future, however, the same system will be required for higher communications bandwidth applications, such as Ku and even Ka band, and the laboratory at TIT has been asked to improve the current system so as to enable it to track more narrow beam widths. The laboratory, which specializes in the dynamics and control of multibody system, was deemed qualified to handle this research as the control of the antenna platform can be treated as a classic robotics problem.

The project was begun in June of 1997 and is being carried out by a team consisting of one 1st-year doctoral student, one 4th-year undergraduate student, and me, who was assigned as project team leader. As part of the first phase of the research, the laboratory was responsible for identifying specific areas of the system that will require improvement in order to achieve the higher bandwidth tracking. As INMARSAT receivers were not readily in hand, the lab chose to conduct evaluation tests outdoors using a satellite dish/tuner package compatible with the reception from a Japanese BS satellite flying over Tokyo. Note that tracking of a broadcast satellite (C-band) represents a more severe problem than tracking of the L-band INMARSAT signal. Additional tests were carried out onboard a small yacht to test the tracking capabilities of the system in the presence of swaying motions of the antenna base. One major finding was that the current system lacks proper structural rigidity in the antenna mount, resulting in a non-collocated control problem due to the flexing of the antenna post. The lab has also identified several problems related directly to limitations in the accuracy of the sensors used to detect the swaying motions of the antenna base (or ship). Here, the laboratory is attempting to replace the existing sensors with better, more accurate sensors.

The second phase of the research will involve implementation of the laboratory's own control algorithms, which have been specifically designed to overcome the current system's shortcomings and thus to demonstrate improved performance. It is expected that all improvements made through this research will be directly translated into future generations of this tracking platform, thus representing a direct contribution to the success of the US company.