En-route alignment and calibration of SINS by celestial observation and distinctiveness of free fall trajectory

Celestial observations provide information about angular orientation of a flight vehicle in inertial space, wherein the distant stars are predetermined reference points infinitely apart from the observer. No information about velocity and position of the observer in inertial space can be extracted from celestial observation alone. Attitude information obtained through celestial observations, however, may be fused with the navigation output of strapdown inertial navigation system (SINS) and the time dependent departure of SINS output due to sensors ' errors from the true navigation solution thus can be significantly reduced. During the free fall trajectory accelerometers' biases can be measured and compensated for. A scheme for integration of celestial navigation with SINS is discussed and improvement in navigation solution achieved through numerical simulation is presented. A comparison of GPS aided and CNS aided INS is carried out.