1,721,139 research outputs found
Model Predictive Static Programming for Bang-off-Bang Low-Thrust Neighboring Control Law Design
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An optimal h6 scheme for solving TPBVP in astrodynamics
No full textThe present paper presents an accurate scheme for the solution of boundary value problems with two-point nonlinear boundary conditions. The proposed scheme is a linear multi-point method of sixth-order accuracy successfully used in uid dynamics and here implemented for the rst time in astrodynamics applications. It is an optimal scheme since a discretization molecule made up of just four grid points assures an h6 order of accuracy. This kind of discretization allows to attain an accuracy beyond the rst Dahlquist's stability barrier and simultaneously has a simple formulation and numerical e ciency. Astrodynamics applications concern the computation of libration point halo orbits, in the restricted three- and four-body models, and the design of an optimal control strategy for a low thrust libration point mission
Orbit Determination for X-Ray Pulsar Navigation with the Aid of Artificial Neural Networks
Full text linkA flow-informed strategy for ballistic capture orbit generation
Full text linkBallistic capture is a phenomenon by which a spacecraft approaches its target body, and performs a number of revolutions around it, without requiring manoeuvres in between. Capture orbits are characterized by specific dynamics, defining regions that guide transport phenomena. Because of the limitations associated with existing approaches, the development of heuristics informed by Lagrangian Coherent Structures appears desirable. In fact, such structures identify transport barriers in dynamical systems, separating regions with qualitatively different dynamics. In this work, different flow-informed approaches are presented, and their relations with ballistic capture are discussed. A new heuristic, the time-varying strainline, is introduced. This new tool is applied to compute ballistic capture orbits around Mars. Different degrees of model fidelity have been investigated, mainly in order to test the robustness of the proposed technique with respect to different features of the underlying dynamical model. We show that time-varying strainlines are useful in identifying ballistic capture orbits
Optimal Beacons Selection for Deep-Space Optical Navigation
Full text linkDeep-space optical navigation is among the most promising techniques to autonomously estimate the position of a spacecraft in deep space. The method relies on the acquisition of the line-of-sight directions to a number of navigation beacons. The position knowledge depends upon the tracked objects. This paper elaborates on the impact of the observation geometry to the overall performances of the method. A covariance analysis is carried out considering beacons geometry as well as pointing and input errors. A performance index is formulated, and criteria for an optimal beacons selection are derived in a scenario involving two measurements. A test case introducing ten available beacons pairs is used to prove the effectiveness of the developed strategy in selecting the optimal pair, which leads to the smallest achievable error
Embedded Homotopy for Convex Low-Thrust Trajectory Optimization with Operational Constraints
Full text linkComputation of Invariant Tori in the Hill Restricted Four-Body Problem via Collocation
Full text linkAn Algorithm to Engineer Autonomous Ballistic Capture at Mars
Full text linkCurrent deep-space missions heavily count on ground-based operations. Although reliable, ground slots will saturate soon, so hampering the current momentum in space exploration. EXTREMA, a project awarded an ERC Consolidator Grant in 2019, enables self-driving spacecraft, challenging the current paradigm and aiming, among others, at autonomously engineering ballistic capture. This work presents an autonomous ballistic capture algorithm suitable for spacecraft with limited control authority and onboard resources. The algorithm is applied to construct BC corridors at Mars, time-varying manifolds supporting capture that can be targeted far away from the planet. The algorithm envisaged a novel methodology to generate families of ballistic capture orbits characterized by succeeding capture epochs. The families are built by correcting in sequence the initial conditions of ballistic capture orbits provided that they are enough regular. New orbits are obtained solving a well-posed three-point boundary value problem exhibiting 8 boundary conditions. The conditions are linearized, and the problem is solved for a finite set of variables with the multiple shooting technique. The computationally demanding problem of finding ballistic capture orbits through stable sets manipulation is unburdened by just solving a linear system, making the algorithm compatible with CubeSats onboard resources. An overview of the autonomous BC algorithm and the details of the correction procedure are provided. The methodology is applied to generate families of orbits belonging to capture sets C−11 and C−16 starting from the same baseline capture orbit. In both cases, the method constructs sequences of initial conditions spanning more than 100 days. The algorithm performance is assessed and its limitations are discussed. Results are inspected against the solar gravity gradient field to get insight about how the methodology acts when it corrects a reference solution into a new capture orbit
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