Reentry Guidance for Generic RLV Using Optimal Perturbations and Error Weights

Abstract

The present paper describes a simple guidance strategy for the reentry mission of a generic Reusable Launch Vehicle. The guidance computation starts with a nominal feasible trajectory, which gets updated during actual reentry based on onboard measurements, using both incremental angle of attack and bank angle parameters. An analytical formulation for a modified predictor-corrector algorithm is developed, using angle of attack profile and bank angle reversal strategy. The guidance solution is arrived at under the heating rate and equilibrium glide constraints and the control actuation is implemented through the aerodynamic control surfaces. A scheme to improve the overall performance of the predictor-corrector algorithm is evolved, which is based on the determination of optimum perturbation levels of control variables. In addition, the control vector formulation is provided with a weighting option, for improving the overall terminal interface accuracy. Numerical results are obtained for the time histories of control variables and performance parameters, for a typical nominal trajectory, which show that proposed guidance scheme works well for a specified reentry mission. Results are also obtained for the optimum perturbation levels for the control parameters, which are used for estimating the sensitivity coefficients required in corrector algorithm. Lastly, the results are obtained for the trajectory parameters, by considering dispersions in the aerodynamic drag and lift coefficients, for establishing its robustness. The results clearly bring out the fact that the proposed reentry guidance algorithm is able to achieve the required terminal conditions, even in the presence of large perturbations in the aerodynamic coefficients.