Service outages in GPS associated with satellite failures

The planned NAVSTAR/GPS satellite constellation of 18 satellites plus 3 active spares will provide excellent coverage over the CONUS if all are operating properly. This report examines the coverage under conditions of one satellite failure. It turns out that the failure of any satellie results in service outages of up to half an hour somewhere in the CONUS. While altimeter aiding eliminates most of these outages, there still remain 14 outage events each day. Furthermore, 'coasting' the navigation solution with a stable clock is not effective in handling these outages. The one technique that does appear effective is using a mask angle of 5 degrees or less.