This paper verifies an observer system of satellite attitude estimation via Extended Kalman Filter. This work can contribute as a backup or an alternative system during unavailable sensor measurements due to malfunction sensor or for cost reduction by reducing the number of sensors for future mission. In this work, the observability test for any possible combination of output measurements is carried out using Lie derivative technique. Then, verification of the observer system is performed through full state observer by using real in-flight telemetry data of RazakSAT.
