8,327 research outputs found
Prescribed performance-based powered descent guidance for step-shaped hazardous terrains
No full textThe planetary powered descent guidance problem for step-shaped hazardous terrains is investigated in this article based on prescribed performance function (PPF) methodology. Initially, the distances between the lander and step-shaped terrains around the landing site have been formulated in a new form boundaryfunction using PPF, in which a new step-shaped boundary PPF is specifically designed to constrain the lateral motion. Furthermore, a fixed-time convergent PPF is chosen to coordinate the vertical motion. Next, to avoid the collision with step-shaped terrains and planetary surface, a feedback guidance algorithm is proposed based on the backstepping method. Considering a large guidance gain is beneficial for the lander to move away from the boundary PPF, but excessive control acceleration will be generated when the landing error is large. To solve this problem, an adaptive guidance gain is designed using Gaussian function. Finally, the feasibility and effectiveness of the proposed algorithm have been verified through typical numerical simulations inspired by realistic Martian terrains. Moreover, this attempt using PPF methodology here can be easily reformulated to adjust the powered descent problem with collision avoidance for a flat surface or glide-slope constraint.</p
Barrier Lyapunov function-based planetary landing guidance for hazardous terrains
No full textThe landing guidance based on the barrier Lyapunov function (BLF) for hazardous terrains is investigated. Three suitable spatial geometric shapes (frustum-shape, cone-shape, and <formula><tex></tex></formula>-step-shape) have been chosen to describe the possible obstacles on the planetary surface. Next, a novel and general form of the barrier function (BF) has been developed using selected spatial geometric shape information, specifically designed to constrain the lateral motion. For these three different spatial geometric shapes, only the segment number of BF is different, and the segment number is determined by the spatial geometric shape. Furthermore, a fixed-time convergent function is selected as the upper boundary to coordinate the vertical motion, guaranteeing that the lander completes the landing mission within the predefined time. Next, a new nonlinear feedback guidance is designed using the asymmetric BLF constructed by the BF, keeping the lander from colliding with the obstacle and achieving the pinpoint soft landing. Finally, numerical simulations with different hazardous terrains are performed to verify the feasibility and effectiveness of the proposed algorithms
Mars powered descent phase guidance law based on reinforcement learning for collision avoidance
No full textThis paper proposes a reinforcement learning-based guidance law for Mars pow- ered descent phase, which is an effective online calculation method that handles the nonlinearity caused by the mass variation and avoids collisions. The reinforcement learning method is designed to solve the constrained nonlinear optimization problem by using a critic neural network. Specifically, to cope with the position constraint (i.e. glide-slope constraint) and the thrust force limit constraint, a modified cost function is proposed, and the associated Hamilton-Jacobi-Bellman equation is solved online without using an actor neural network, which significantly reduces the computational burden. The convergence of the critic neural network is proven. Simulation results show the effectiveness of the proposed method
Model predictive control guidance for constrained mars pinpoint landing
No full textIn order to achieve pinpoint landing under various constraints during powered descent phase of landing on Mars, model predictive control (MPC) is employed in this paper by designing a novel performance index. Its main advantage is that it can ensure the pinpoint landing with online calculation and handle constraints as well, both of which are important in practical engineering missions. Detailed derivational process is given. Simulation results show the effectiveness of the proposed guidance
Multi-power sliding mode guidance for Mars powered descent phase
No full textTo reach and keep tracking the desired Mars landing trajectory rapidly under various uncertainties and unexpected wind, a power reaching law based sliding mode tracking guidance algorithm is proposed in this paper. The proposed guidance law is composed of three exponential terms, its main improvement is that it can ensure that the lander track the reference trajectory in finite time without chattering. Theoretical proofs are presented to prove its existence, reachability and stabilization characteristics. Compared with existing exponential reaching law, single power reaching law and double power reaching law, simulation results show the effectiveness of the proposed guidance law with a typical Mars powered descent landing scenari
Fixed-time pinpoint mars landing using two sliding-surface autonomous guidance
No full textAutonomous powered-descent guidance algorithm for the pinpoint Mars landing in the presence of various disturbances and uncertainties is necessary for next-generation Mars exploration rover mission. This paper proposes a novel two sliding-surfaces guidance scheme based on fixed-time stabilization technique, which is robust against unknown Martian atmospheric disturbances (with known upper bound). For a fixed-time pinpoint landing mission, the main advantage of the proposed guidance is that the landing mission reliability can be ensured that Martian surface collision would never encounter. The fuel efficiency can be guaranteed in the comparison with the offline fuel optimal solution. The capacity of avoiding collisions is guaranteed by the monotonic convergence design of the proposed sliding modes. Lyapunov stabilization theory is adopted to prove the global stability of the proposed guidance. Monte Carlo numerical simulations are implemented in a realistic scenario and the results confirm the collision avoidance capability, the fuel efficiency and the robustness of the proposed guidance
Collision avoidance ZEM/ZEV optimal feedback guidance for powered descent phase of landing on Mars
No full textA novel zero-effort-miss (ZEM)/zero-effort-velocity (ZEV) optimal feedback guidance is proposed in order to rule out the possibility of Martian surface collision caused by the classical ZEM/ZEV optimal feedback guidance. The main approach is to add a collision avoidance term, which has self-adjustment capacity to ensure the near fuel optimality. Its main improvement is that it can not only successfully avoid collisions with the thruster constraint but also guarantee the near fuel optimality, and both of them are pivotal performances in Mars landing missions. Simulations are made to show the effectiveness of the proposed guidance and the parameters effects are simulated as well to analyze the properties of the proposed guidance
Applicability of Phase-Function Normalization Techniques for Radiation Transfer Computation
No full textThe applicability of recently-developed four phase-function (PF) normalization techniques for modeling radiation transfer in strongly anisotropic scattering media is intensively examined using the discrete-ordinate method. The three simple techniques via normalization of only the forward- and/or backward-scattering directions were shown to reduce normalization complexity whilst retaining diffuse radiation computation accuracy for Henyey-Greenstein (HG) PFs. For Legendre PFs, however, such simple techniques are found to result in unphysical negative PF value at one or few correction direction in some cases. Additionally, negative PF values can occur for these simple techniques for ballistic radiation transfer for both HG and Legendre PF types. If negative-intensity correction is applied, however, radiative heat transfer calculation can still converge regardless of the appearance of negative PF values. The relatively complex Hunter and Guo 2012 technique, in which normalization is realized through a correction matrix covering all discrete directions, is shown to be applicable for diffuse and ballistic radiation for both PF types.Peer reviewed
Adaptive pseudospectral successive convex optimization for six-degree-of-freedom powered descent guidance
No full textGuidance for six-degrees-of-freedom powered descent is more challenging due to its stronger nonlinearity
compared to three-degrees-of-freedom. The standard convex programming algorithm has been difficult to
effectively address this problem. To enhance the performance of successive convex programming in terms of both
optimality and accuracy, an adaptive pseudospectral successive convex optimization algorithm is proposed in this
paper. First, it transforms the nonlinear optimal control problem into a convex subproblem by integrating global
pseudospectral discretization with local linearization. Second, a parameter-adaptive successive convexification
algorithm is proposed, which adaptively adjusts the trust region size based on the update rate of the optimal
trajectory. Last, the global error and local error are accurately calculated based on the pseudospectral method.
To tackle the issue of excessively large local errors caused by nonlinearity, an adaptive grid method is proposed
to refine the mesh grid. Simulation results demonstrate the efficacy of the proposed pseudospectral convex
optimization method and adaptive mesh grid method in reducing local errors and improving solution accuracy.
Furthermore, the proposed parameter-adaptive successive convex optimization algorithm exhibits adaptability
and optimality across different initial conditions, while also improving solution accuracy
Robust powered descent guidance considering mass and fuel consumption uncertainties: A convex optimization approach
No full textThis paper addresses the challenge of mass uncertainty during the powered descent phase of a Mars lander and proposes a robust powered descent guidance algorithm that accounts for uncertainties in mass and fuel consumption. First, the traditional trajectory optimization method based on convex optimization is improved by developing a fast and accurate solution approach using sequential convex optimization. Second, the effects of mass uncertainty on position are modeled and analyzed, with corresponding computational methods provided for different scenarios. Third, the worst-case scenario under mass uncertainty is analyzed through both geometric and theoretical approaches, and a modified glide-slope constraint method is proposed to ensure safe landing even in adverse conditions. Moreover, a closed-loop receding horizon based guidance is developed to further mitigate the effects of mass uncertainty and improve terminal landing accuracy. Finally, the proposed improved convex optimization algorithm and robust trajectory optimization algorithm are validated through simulation cases and compared with a probabilistic approach. The simulations further test various initial positions, velocities, and glide-slope angles, demonstrating that the solutions are both accurate and robust
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