AGILE QUATERNION BASED ATTITUDE DETERMINATION AND CONTROL TO SUPPORT NEAR-SPACE VEHICLE OPERATIONS

Near-space is becoming more and more important both for space vehicle experimentation and for Earth surveillance applications. Flight conditions in near-space region emulate closely those of an extra-atmospheric space vehicle especially for its re-entry flight phase. European Space Agency is using near-space operations to perform critical test flights intended for validation of attitude control of space vehicles such as Space Rider. Here the issue of attitude control of a vehicle for operation in near-space conditions is addressed. A 6 DOF model has been developed to provide the framework for the quaternion based attitude control. The model was programmed on a dedicated autopilot installed onboard a dedicated and unique flying wing designed to be operated in near-space conditions. Autopilot uses a microcontroller, HEMS gyroscopes and accelerometers to provide a stable real-time attitude and trajectory solution. The attitude determination and control is performed using quaternions and their time derivatives instead of the usual Euler angles, allowing a stable attitude solution without the gimbal lock problems of a typical Euler formulation. A high altitude test flight has been performed from Cape Midia firing range which proved that the attitude determination and control system successfully allowed accurate control both of the roll and pitch angles.