The accuracy of predictor-corrector entry guidancealgorithms relies heavily on the accuracy of the onboard atmospheric density model. Existing approaches, such as fading-memory filters, assume a constant bias in the ...
详细信息
The accuracy of predictor-corrector entry guidancealgorithms relies heavily on the accuracy of the onboard atmospheric density model. Existing approaches, such as fading-memory filters, assume a constant bias in the density profile from the current state in the entry trajectory to the terminal condition which does not capture the geospatial variation of atmospheric density. In this work, a deep-learning approach to estimate atmospheric density profiles for use in planetary entry guidance problems is developed. A long short-term memory (LSTM) neural network is trained to learn the mapping between measurements available onboard an entry vehicle and the density profile through which it is flying. Measurements include the spherical state representation, Cartesian sensed acceleration components, and a surface-pressure measurement. Training data for the network are initially generated by performing a Monte Carlo analysis of an entry mission at Mars using the fully numerical predictor-corrector guidance (FNPEG) algorithm that uses an exponential density model, while the truth density profiles are sampled from MarsGRAM. An iterative curriculum-learning procedure is developed to refine the LSTM network's predictions for integration within the FNPEG algorithm. The trained LSTM is capable of accurately predicting both the density profile through which the vehicle will fly and reconstructing the density profile through which it has already flown. The performance of the FNPEG algorithm is assessed for three different density estimation techniques: an exponential model, an exponential model augmented with a first-order fading-memory filter, and the LSTM network. Results demonstrate that using the LSTM model results in an order of magnitude increase in terminal accuracy compared to the other two techniques when considering both noisy and noiseless measurements.
A fast trajectory optimization/guidance algorithm in the presence of path constraints for a multistage launch vehicle is presented in this work. The optimization problem is to maximize the payload to be injected into ...
详细信息
A fast trajectory optimization/guidance algorithm in the presence of path constraints for a multistage launch vehicle is presented in this work. The optimization problem is to maximize the payload to be injected into a geostationary transfer orbit with constraints on argument of perigee, second-stage impact point longitude, and heat flux constraint on the third stage that flies a low-altitude trajectory. These constraints constitute a unique set of equality and inequality constraints as they are contradictory in nature. Most of the gradient-based trajectory optimization schemes require an initial guess close enough to the optimal value for assured convergence. In addition, the rate of convergence deteriorates in the presence of inequality constraints. These issues are addressed by providing a solution to the optimization problem with low sensitivity to the initial guess profiles. A self-starting optimization scheme that can generate initial guess profiles automatically from boundary conditions is the major contribution of this work. The proposed method presented in this paper also gives a methodology for real-time implementation of the optimization scheme in the onboard computer. The sensitivity to initial guess in a gradient-based optimization procedure, in the presence of inequality constraints, is clearly brought out as part of this work by studying the convergence from random sets of initial guess profiles. The real-time implementation of the algorithm is validated with various initial conditions in deterministic as well as Monte Carlo sense to establish the robustness of the algorithm.
During powered descent of a crewed lunar landing mission, the ability to abort and ascend into a clear pericynthion orbit is critical in case any contingency renders the landing infeasible or excessively risky. In suc...
详细信息
During powered descent of a crewed lunar landing mission, the ability to abort and ascend into a clear pericynthion orbit is critical in case any contingency renders the landing infeasible or excessively risky. In such a case, it is incumbent upon the guidance system to determine autonomously a safe abort trajectory and the associated guidance command. To accomplish this task reliably, a novel two-phase abort guidance strategy is proposed in this paper where a pull-up maneuver redirects the velocity vector to help mitigate any ground collision risk and achieve an appropriate initial ascent condition, followed by a fuel-optimal ascent guidance algorithm to insert the spacecraft into a predefined safe orbit around the moon. Development of the pull-up guidance laws and a description of the fuel-optimal ascent guidance based on the indirect method of optimal control are presented. In-depth investigation is conducted to provide a full understanding of the validity of the abort solutions. The solutions and fuel efficiency of the proposed guidance strategy are independently verified by using a direct method of optimal control. Monte Carlo closed-loop simulations demonstrate the effectiveness and robustness of this method throughout the entire powered descent.
In this paper, a nature-inspired guidance algorithm based on the panel method is proposed. The panel method is a numerical tool borrowed from the aerodynamics domain to calculate the potential field of a fluid flow ar...
详细信息
In this paper, a nature-inspired guidance algorithm based on the panel method is proposed. The panel method is a numerical tool borrowed from the aerodynamics domain to calculate the potential field of a fluid flow around arbitrarily shaped objects. The proposed algorithm has little computational load and generates guidance vectors in real time that can guide multiple vehicles through smooth and collision-free paths. Panel-method-based guidance is a promising candidate for air mobility applications in urban environments where multiple aerial vehicles are expected to operate simultaneously without colliding with architectural structures and other vehicles in the airspace. In this study, the effectiveness and feasibility of the proposed guidance method is evaluated through a test campaign conducted in Toulouse, France, using multiple quadrotors in a scaled urban environment. Furthermore, the robustness of the guidance method under wind disturbances is tested in both indoor and outdoor experiments. Experimental results suggest that the panel-method-based guidance algorithm is an effective and robust tool for real-time, collision-free guidance of multiple aerial vehicles in complex urban environments.
A robust trajectory optimization approach for guidance algorithm gain and target vector selection for powered descent and landing is developed. A genetic algorithm is used to determine optimized guidance algorithm par...
详细信息
A robust trajectory optimization approach for guidance algorithm gain and target vector selection for powered descent and landing is developed. A genetic algorithm is used to determine optimized guidance algorithm parameters to minimize the impact of initial condition, environment, navigation, and vehicle property uncertainty on flight performance for a given sensor suite. Vehicle state uncertainties are computed efficiently using linear covariance analysis techniques. When implemented in the guidance algorithm, the optimized gains and target vectors shape a trajectory that has more favorable conditions for a given navigation sensor suite, resulting in improved flight performance. As a demonstration of this method, the optimized guidance parameters are found for a multiphase trajectory from powered descent initiation to touchdown for a robotic lunar landing mission. Single-objective optimization results demonstrate a reduction in uncertainty and an improvement in nominal performance. Multi-objective optimization results showing the tradeoff between terminal position uncertainty and total propellant usage are presented for multiple sensor suite compositions. Further, guidance parameters selected using the developed robust trajectory design approach may enable acceptable flight performance with fewer and/or lower-quality sensors. The resulting Pareto fronts present the optimal trade space early in the mission design process to enable informed decision-making.
The propellant-optimal powered descent solution requires a bang-bang thrust magnitude profile that switches instantaneously between the upper and lower bounds of the engine thrust. Implementing a bang-bang thrust patt...
详细信息
The propellant-optimal powered descent solution requires a bang-bang thrust magnitude profile that switches instantaneously between the upper and lower bounds of the engine thrust. Implementing a bang-bang thrust pattern for guidance can be challenging for the engine and may cause practical and operational difficulties. Motivated by the observation that excellent propellant performance does not appear to be predicated on necessarily having a bang-bang thrust structure, a new powered descent guidance method is proposed in this work. The foundation lies in a propellant-optimal problem in which the thrust magnitude is parameterized by a user-prescribed continuous function of time. In particular, constant and linear functions are considered. The solution determines the optimal thrust direction, time of flight, and design parameters defining the thrust function. An indirect-method-based guidance algorithm is developed to solve this problem rapidly and reliably. Substantial evidence is provided to demonstrate that the solutions proposed in this paper in general yield a propellant consumption very close to that of the optimal bang-bang solution. Given its comparable propellant performance, implementability, and robustness, this paper makes a strong case that the proposed propellant-optimal powered descent guidance approach is preferred to the long-standing bang-bang guidance approach.
暂无评论