precision distance Measuring Equipment (DME) aiding the onboard inertial navigation can be used to meet the stringent landing navigation requirements of the Space Shuttle. The required accuracy is achieved by using a 10-state-variable Kalman filter to process the measured range and delta-range data from the DME. Contributing to the success of the Kalman filter design are the satisfactory choice of a low number of critical state variables and proper modeling of all significant sources of navigation error as process and measurement noises. Three DME transponders are required to meet the accuracy requirements: two are deployed under the final approach path and one is deployed to the side. Failure considerations require deployment of additional redundant transponders. Initialization of the landing navigation after hypersonic entry is accomplished using the transponders at the airport. No additional distant transponders are required. A satisfactory performance margin exists to tolerate somewhat degraded DME or inertial system performance.