Adaptive entry guidance with time and full state constraints using analytical drag-vs-energy profile

Advanced entry vehicles need to satisfy both flight time and full state constraints in the specific global transportation and cooperative rendezvous missions. This paper mainly proposes an adaptive entry guidance algorithm with time and terminal full state constraints. The algorithm is composed of three parts: longitudinal analytical guidance, lateral guidance and three-degree-of-freedom (3DOF) guidance. In the longitudinal analytical guidance, a smooth drag acceleration-vs-energy profile is represented as five piecewise polynomials by using the double-parameter interpolation between upper and lower boundary of entry corridor first. A high-precision analytical prediction algorithm for time and range to-go is derived over a spherical and rotating Earth, and the double-parameter of the profile can be corrected using double-objective iterative method to satisfy terminal height, velocity, flight-path angle, range, and time constraints. Secondly, an online adaptive analytical update strategy for the profile based on the double/single parameter sequential solving mode is proposed to improve the robustness of the algorithm. In the lateral part, a double-stage adaptive lateral guidance algorithm based on heading adjustment and maintaining is put forward, which is enabled to plan and update the bank-reversal sequence according to the terminal position and heading angle constraints. Finally, a real-time 3DOF entry guidance algorithm for the wide range heading adjustment is proposed to achieve the generation of the 3DOF guidance commands online rapidly. Simulations with the CAV-H model show that the presented approach is capable of satisfying all path constraints, terminal time and full state constraints, robust to typical entry dispersions, and adaptive for various entry missions with high real-time performance. The advantage of the guidance strategy is also verified by comparisons.