A Robust and Effective GNSS/INS Integration Optimizing Cost and Effort Michael Felux 1,2 , Markus Rippl 1 , Anja Grosch 1 ( 1 German Aerospace Center (DLR), Munich, Germany 2 Technische Universit¨at M¨ unchen, Munich, Germany) (Email: michael.felux@dlr.de) Meeting all requirements for flying approaches in bad weather conditions is one of the most demanding and challenging aspects of present day airborne navigation. Stand-alone satellite navigation has not yet reached the point of being sufficiently robust and accurate in order to reach certification level. Therefore, in this work the performance of an integrated satellite/inertial navigation system (GNSS/INS) is investigated in order to cope with short term losses of GNSS signals. We consider a low-cost Micro Electronic Mechanical System (MEMS) INS which is constantly reinitialized with information coming solely from GNSS. It takes over navigational responsibility when a loss of signal occurs or other failures in the satellite navigation system are detected. For the GNSS to provide all information necessary to initialize an INS, a minimum of three antennas is needed to measure the aircraft’s attitude along with its speed and position. Error models for positioning, speed and attitude estimation are used to create a model for initialization uncertainties. Together with error models for the accelerometers and gyros in the Inertial Measurement Unit (IMU), the behavior of the whole proposed architecture is determined via performance simulations. As a maximum allowable error 15.3 meters (which corresponds to the CAT III horizontal alert limit for GNSS approaches) are taken. Our simulations show that this limit is not exceeded for at least 14 seconds after the take-over of navigational responsibility by the INS. key words 1. GNSS 2. INS integration 3. Continuity improvement 1. Introduction and definition of terms Flying approaches in low visibility condi- tions is the remaining challenge today when relying on satellite navigation in aviation. Very stringent requirements are imposed when safety critical issues, like landing an airplane, are involved. One of the biggest threats to continuity of the service is a loss of signal from one or more satellites, especially if the number of visible satellites is low. This can be the case during a maneuver where the antenna points away from satellites which were previously used for navigation. Mountains surrounding an airport or airports in polar regions with limited satel- lite visibility can increase this problem. Figure 1 shows the number of tracked satellites in a tight curve during a flight test performed in 2008 by the Institute of Communications and 1