A method to calculate position of a platform using a detection and ranging system coupled to the platform to transmit a signal to space object having a known ephemeris. The detection and ranging system receives the reflected signal from the space object. Taking the range of the platform from the space object using a time delay between transmission of the signal and receipt of the reflected signal and the range-rate using a Doppler frequency shift between the transmission of the signal and the receipt of the reflected signal makes it possible to calculate a position fix of the platform using the determined range, the determined range-rate, an altitude of the platform, and the known ephemeris of the space object.