L-Band Maritime Experiments

Abstract

The authors have directed the technical portion of the MARAD maritime communications experiments using the NASA ATS-6 satellite. The MARAD experiments were conducted with satellite terminals placed on two commercial ships for evaluation of the communication service similar to that which will be available with the maritime commercial satellite system. These experiments also evaluated the benefits to fleet management through utilization of the communications services. Furthermore, evaluation of position determination using satellites was also made. These experiments were conducted from the MARAD earth station located at Kings Point, N. Y., and the NASA earth station at Rosman, N. C. Three modems having voice and digital data and a stabilized shipboard L-band antenna system were evaluated. Present results indicate that future commercial communications satellite systems will provide the expected high-quality service, particularly when attention is given to improving the reliability of components, such as the vertical reference system used by the shipboard antenna. The results of the experiments conducted indicate that the ship antenna demonstrated successful tracking of the satellites for test period intervals of 4 to 6 hours without the need for operator adjustment. The ship position determination tests show good measurement repeatability, but with significant bias errors which may result from satellite ephemeris. Finally, the data analyzed demonstrated the ability of future commercial satellite systems to achieve a probability of bit error of better than 10-5. Further data analysis is needed to completely confirm these digital data results.