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.