Airborne protected Military Satellite Communications: Analysis of open-loop pointing and closed-loop tracking with noisy platform attitude information

U.S. military assets' increasing need for secure global communications has led to the design and fabrication of airborne satellite communication terminals that operate under protected security protocol. Protected transmission limits the closed-loop tracking options to eliminate pointing error in the open-loop pointing solution. In an airborne environment, aircraft disturbances and noisy attitude information affect the open-loop pointing performance. This paper analyzes the open-loop pointing and closed-loop tracking performance in the presence of open-loop pointing error and uncertainty in the received signal to assess hardware options relative to performance requirements. Results from the open-loop analysis are characterizations of the pointing error based on plant definition, aircraft motion, the control system, and a non-ideal GPS/INS. The closed-loop tracking analysis shows several results. The distribution of the noise power dominates (over the received signal power) the SNR distribution. The defined step-tracking algorithm reduces pointing error in the open-loop pointing solution for a pedestal experiencing aircraft disturbances and random errors from the GPS/INS. For initial pointing off-boresight, the performance of the step tracking algorithm depends on the antenna aperture size and the GPS/INS unit. The closed-loop tracking performance is primarily a function of the number of SNR samples and is for the most part independent of the hardware selection.