ITEE Innovation Expo 2008 : Project Details

Terrestrial Optical Attitude Determination System (TOADS)

Scramjets are air breathing hypersonic jet engines which have been a major focus of Australian research. Recent scramjet test flights have been launched into the outer atmosphere in a parabolic flight path. Upon returning into the Earth’s atmosphere the payload reaches speeds suitable for the scramjet engines to begin combustion. Around the top of the flight path (the apogee) the scramjet must undertake a critical turning manoeuvre before re-entering the atmosphere. During this turning manoeuvre determinable and controllable attitude is crucial to mission success. The Terrestrial Optical Attitude Determination System (TOADS) is a new attitude determination system in development for HIFiRE scramjet test flights. TOADS uses digital images of the Earth’s horizon and models this horizon as a circle in order to determine the attitude of a scramjet in real-time during flight. TOADS uses wide-angle camera lenses in order to capture as much of the horizon as possible. The primary goal of this thesis is to provide the grounding theoretical work for TOADS. Image processing techniques relevant to horizon capturing are explored and evaluated. This begins with fisheye distortion unwrapping techniques based on work from endoscopic imaging. Several circle detection techniques are introduced and compared for the purpose of real-time horizon sensing. Evaluated techniques include Hough Transform, Least Squares Fit, Random Sampling Consensus (RANSAC), and Phase-Coded Annulus. Evaluation is based on ideal images of circles and images of the Earth; comparisons are made in terms of run-time, computational complexity, accuracy and robustness. The secondary goal of this thesis is to describe and evaluate models which could be used to test prototyped hardware systems. A simple model using a large inflatable globe and a monochromatic camera equipped with a fisheye lens is introduced; promising results of the prototyped horizon capturing system are shown. Other potential testing models are hypothesised and described. This thesis concludes by making recommendations for a hardware platform for TOADS and recommended future work in order to improve the work already undertaken.