Analytical entry guidance for no-fly-zone avoidance

This paper is devoted to designing an analytical entry guidance for steering a hypersonic glide vehicle of high Lift-to-Drag ratio (L/D) in the presence of numerous No-Fly Zones (NFZs). The NFZ constraints pose serious challenges to the guidance design: (1) because there is no engine to provide thrust, the vehicle needs to manage the energy of motion carefully and cannot perform avoidance maneuvers arbitrarily; (2) due to disorder distribution of NFZs, there are multitudinous complicated cases to consider. As the basis of the guidance, the adopted 3-D analytical glide formulae are improved by posing a more accurate Earth-rotation compensation model. Then, the guidance uses the new downrange formula to plan longitudinal reference profile according to the energy-management requirement, and mainly employs the new crossrange formula to schedule proper bank reversals under the NFZ and terminal-position constraints. Here, a complex but rigorous scheme is proposed for fast planning bank-reversal sequence based on six analytical iteration algorithms, which are designed to search the nearest trajectory point to NFZ, to adjust the existing bank reversals or add a new one for NFZ avoidance, and to regulate the last bank reversals for eliminating terminal crossrange error, respectively. The scheme begins with two bank reversals and then gradually adds more bank reversals according to the needs of avoiding the NFZs. As the scheme prefers to adjust the existing bank reversals to address the NFZ constraints, it commonly requires only a few bank reversals. The superior performance of the guidance is verified by sufficient trajectory simulations in disturbed environments.