Challenges and software design modifications in GNSS Receiver for tackling signal strength variations under High Rate Conditions for ISRO’s re-entry Vehicles

Global Navigation Satellite System (GNSS) receivers have become a de-facto standard in all launch vehicles/re-entry vehicles globally for precise navigation applications. ISRO’s launch vehicle Navigation, Guidance and Control (NGC) system also houses an indigenously developed GNSS receiver capable of acquiring GPS and NavIC satellite signals and generating position, velocity and timing (PVT) information. Launch Vehicle (LV) GNSS receivers are generally designed for high dynamic applications with high acceleration, velocity and jerk requirements. These are defined in terms of linear dynamic specifications. The challenge in designing a GNSS receiver for re-entry vehicles is to tackle high rotational body rates which can result in reduced satellite signal strength as well as loss of satellite visibility. This paper describes the challenges and software design improvements done in GNSS Receiver for tackling signal strength variations under High Rate Conditions for ISRO’s re-entry vehicles.