Continuity improvements via inertial augmentation of GPS-based landing system

The role of inertial backup of GPS-based landing systems in the improvement of continuity is investigated. The purpose is to understand the relationship between the grade of inertial system and the system accuracy during various GPS discontinuity scenarios. GPS outages are considered at various locations on the approach. For systems that included pseudolites (PLs), outages are considered before entering the PL range of coverage (the “bubble”) and after exiting the bubble. The inertial systems are assumed to be calibrated by GPS during the enroute portion of flight. Linear covariance analysis and Monte Carlo techniques are used to determine the navigation accuracy at the runway threshold to determine whether the system meets the various levels of Required Navigation Performance (RNP). It was found that in the event of a total loss of satellite GPS signals prior to bubble entrance, a navigation grade INS could be calibrated by 3 suitably placed PLs sufficiently accurately to provide an RNP that allowed the most stringent landing minimums (Category III). Other less drastic outage scenarios all indicated that substantial improvements in continuity can be achieved with inertial system augmentation. Except for GPS outages within 50 seconds of touchdown, navigation grade inertial systems were required for useful improvements. Conditions that allow tactical missile grade inertial systems for CAT III RNP for the case of a GPS outage within 50 seconds from touchdown are specified