Terminal Velocity Constraints Research Articles

Prescribed-time integrated guidance and control for bank to turn reentry vehicle

In this paper, a novel prescribed-time integrated guidance and control (IGC) with spiral maneuvering deceleration (SMD) method is developed for bank to turn (BTT) reentry vehicle with the consideration of elevation angle and terminal velocity constraints. First, a strict feedback form IGC model is established for BTT reentry vehicle under multiple constraints. Second, a prescribed-time sliding mode controller (SMC) based on prescribed-time extended state observer (ESO) is designed to hit the ground fixed target with the desired line of sight (LOS) elevation angle. Then in order to make the reentry vehicle achieve a better strike effect, it is necessary to constrain the terminal velocity of the reentry flight, a SMD scheme is proposed to achieve the desired terminal velocity. Finally, the efficiency of the proposed scheme is verified by six–degree–of–freedom (6DoF) numerical simulations.

A parametric study of fixed-wing aircraft perching maneuvers

This paper presents a trajectory optimization-based study for identifying the influences of different fixed-wing aircraft parameters on perching maneuvers. Perching trajectories, which involve climbing for landing with a near-zero speed, are optimized to minimize the unwanted altitude gain, herewith referred to as undershoot. Undershoot has a complex relationship not only with the control inputs, but also with the aircraft geometry and features, such as stability characteristics, controllability, and thrust available. To facilitate this parametric study, an aerodynamic modeling tool is developed, which combines a nonlinear vortex correction method with the Leishman's state-space form of Wagner's unsteady model. This tool is used for in-flight aerodynamics evaluation during the optimization of the perching maneuvers. The perching solutions – minimum undershoot and trajectory length – are then computed, and the effects of key parameters of the maneuver are studied. It is found that a high aspect ratio, high thrust available, optimal placement of the center of gravity, relaxed terminal velocity constraints, low zero-lift drag, and headwind reduce the spatial requirements for the maneuver. Furthermore, it is confirmed that a high angle-of-attack maneuver is not critical for very low speed perching.

Geometrical Guidance Algorithm for Soft Landing on Lunar Surface

Abstract Augmented design of a guidance algorithm previously developed for intercepting target in a missile-target engagement scenario, but catering to powered descent soft landing on lunar surface is the main focus of this paper. When it comes to lunar soft landing guidance formulation, it is required that the Lander reach the desired position with terminal velocity constraints. An existing circular guidance law developed for missile guidance is modified to be applied for the fine braking phase of lunar powered descent. Presently in the algorithm, at the beginning of each guidance cycle, there will be an assumed varying circular path from missile to target and the guidance solution lies in finding the acceleration towards the centre of the circle so that the missile moves towards the target. The design augmentation proposed for lunar landing introduces a quadratic acceleration term opposite to the instantaneous tangential velocity vector to ensure terminal conditions. Coefficients of the quadratic acceleration profile are determined by the length of the circle as well as the magnitude of instantaneous tangential velocity. Finally a simple compensation scheme based on comparison of actual velocity from sensors and expected velocity from the algorithm is also proposed to take care of the variation in gravity and error in initial mass estimate.

Linear quadratic pursuit-evasion games with terminal velocity constraints

Linear quadratic pursuit-evasion games with terminal velocity constraints