In October 2005 the first version of DLR’s hypersonic SHarp Edge Flight EXperiment (SHEFEX) program was successfully launched from the Andøya Rocket Range in northern Norway. The mission investigated new shape possibilities for future launch or reentry vehicles, using a reentry vehicle body with facetted surfaces and sharp edges. The next generation experiment, SHEFEX II, will launch in 2010. This mission will focus on hypersonic flight control, using controllable canard fins, and will include experiments for new thermal protection system concepts.
Accurate control of the vehicle requires precise knowledge of the approach angle and the side slip angle. Both of these are derived from the flight path and vehicle attitude. A hybrid navigation system supplies this information by combining measurements from several sensors. The sensors that are used are an IMU, a GPS and a star tracker.
The Inertial Measurement Unit (IMU) is used to capture high dynamics. But it is subject to instrument errors that can cause the error in the navigation solution to grow exponentially, if not corrected. The Global Positioning System (GPS) receiver provides position and velocity measurements with bounded errors but only at a low rate. The strengths of these two instruments are combined to provide a high rate navigation solution with better accuracy, which can not be achieved by using only one of the two instruments separately.
To provide further attitude accuracy, an experimental star tracker will also be integrated together with the IMU and GPS. The star tracker measures the attitude of the vehicle with respect to the stars with bounded errors and at a low rate. The attitude solution is combined with the IMU and GPS data by the navigation filter to compute a full navigation solution consisting of position, velocity, and attitude.
The Simulation and Software Technology accompanies the development of the hybrid navigation system in the area of software quality assurance and software development. The developers of the navigation algorithms stage the tasks of the software development on the real-time operating system QNX. QNX encompasses preparation of general software architecture, assignment of serial bus drivers, and the general services for commanding, telemetry, and the recording of the experiment data in the bulk storage of the hardware platform.