An integrated communications, navigation and surveillance system includes a plurality of satellites in communication with one another and broadcasting navigation signals. The satellites are capable of bi-directional communication and of receiving and relaying surveillance signals. A user segment includes at least one mobile user device operable to communicate with the satellites and to broadcast a surveillance signal to the satellites. The user device is also operable to compute its position based upon received navigation signals. The system uses the surveillance signal broadcast by the user device to monitor a position of the user device. The position of the user device determined by the system and by the user device can be shared to provide backup surveillance and backup navigation capabilities.