Astrodynamics最新文献

To rapidly model the gravity field near elongated asteroids, an intelligent inversion method using Hopfield neural networks (HNNs) is proposed to estimate on-orbit simplified model parameters. First, based on a rotating mass dipole model, the gravitational field of asteroids is characterized using a few parameters. To solve all the parameters of this simplified model, a stepped parameter estimation model is constructed based on different gravity field models. Second, to overcome linearization difficulties caused by the coupling of the parameters to be estimated and the system state, a dynamic parameter linearization technique is proposed such that all terms except the parameter terms are known or available. Moreover, the Lyapunov function of the HNNs is matched to the problem of minimizing parameter estimation errors. Equilibrium values of the Lyapunov function are used as estimated values. The proposed method is applied to natural elongated asteroids 216 Kleopatra, 951 Gaspra, and 433 Eros. Simulation results indicate that this method can estimate the simplified model parameters rapidly, and that the estimated simplified model provides a good approximation of the gravity field of elongated asteroids.

Stable or nearly stable orbits do not generally possess well-distinguished manifold structures that assist in designing trajectories for departing from or arriving onto a periodic orbit. For some potential missions, the orbits of interest are selected as nearly stable to reduce the possibility of rapid departure. However, the linearly stable nature of these orbits is also a drawback for their timely insertion into or departure from the orbit. Stable or nearly stable near rectilinear halo orbits (NRHOs), distant retrograde orbits (DROs), and lunar orbits offer potential long-horizon trajectories for exploration missions and demand efficient operations. The current investigation focuses on leveraging stretching directions as a tool for departure and trajectory design applications. The magnitude of the state variations along the maximum stretching direction is expected to grow rapidly and, therefore, offers information for efficient departure from the orbit. Similarly, maximum stretching in reverse time enables arrival with a minimal maneuver magnitude.

The dynamics of a probe orbiting a moon can be significantly influenced by the non-coincidence between the moon’s equatorial and orbital planes. Thus, we performed a general analysis about the effects of the angle (obliquity) between the above-mentioned planes and of the angle (nodal phasing) between the nodal lines of the mother planet’s apparent orbit and the probe orbit on the lifetime of the probe. The lifetime, strictly correlated to the variations in eccentricity of the probe orbit, was evaluated starting from low values of the semi-major axis, moderate eccentricity, and high inclination to offer high ground spatial resolution and extend latitudinal coverage of the natural satellite. This investigation, carried out through numerical simulations, may be useful for identifying the optimal initial conditions of the probe’s orbit elements, leading to an important increase in the probe lifetime in missions devoted to the exploration of natural satellites.

A robust and efficient feature matching method is necessary for visual navigation in asteroid-landing missions. Based on the visual navigation framework and motion characteristics of asteroids, a robust and efficient template feature matching method is proposed to adapt to feature distortion and scale change cases for visual navigation of asteroids. The proposed method is primarily based on a motion-constrained discriminative correlation filter (DCF). The prior information provided by the motion constraints between sequence images is used to provide a predicted search region for template feature matching. Additionally, some specific template feature samples are generated using the motion constraints for correlation filter learning, which is beneficial for training a scale and feature distortion adaptive correlation filter for accurate feature matching. Moreover, average peak-to-correlation energy (APCE) and jointly consistent measurements (JCMs) were used to eliminate false matching. Images captured by the Touch And Go Camera System (TAGCAMS) of the Bennu asteroid were used to evaluate the performance of the proposed method. In particular, both the robustness and accuracy of region matching and template center matching are evaluated. The qualitative and quantitative results illustrate the advancement of the proposed method in adapting to feature distortions and large-scale changes during spacecraft landing.

The concept of a space solar power station (SSPS) was proposed in 1968 as a potential approach for solving the energy crisis. In the past 50 years, several structural concepts have been proposed, but none have been sent into orbit. One of the main challenges of the SSPS is dynamic behavior prediction, which can supply the necessary information for control strategy design. The ultra-large size of the SSPS causes difficulties in its dynamic analysis, such as the ultra-low vibration frequency and large flexibility. In this paper, four approaches for the numerical analysis of the dynamic problems associated with the SSPS are reviewed: the finite element, absolute nodal coordinate, floating frame formulation, and structure-preserving methods. Both the merits and shortcomings of the above four approaches are introduced when they are employed in dynamic problems associated with the SSPS. Synthesizing the merits of the aforementioned four approaches, we believe that embedding the structure-preserving method into finite element software may be an effective way to perform a numerical analysis of the dynamic problems associated with the SSPS.

A group of cooperative agents can finish complicated missions that are difficult for a large machine. In the past two decades, spacecraft attitude coordination has attracted significant research attention owing to its wide potential applications. This paper presents a survey of recent research progress on the spacecraft attitude consensus problem, paying particular attention to the papers published in major aerospace, dynamics, automation, and robotics journals since 2015. Attitude consensus concepts for centralized, decentralized, and distributed cases are reviewed. This overview summarizes results on system dynamics and consensus algorithms based on frequently used attitude representations, such as Euler angles, modified Rodrigues parameters, unit quaternions, and rotation matrices. Studies conducted under complicated operating conditions are also covered. Experimental results on attitude consensus are discussed. In the final section, the main conclusions are drawn and several potential research directions are provided.

The BeiDou-3 global satellite navigation system (BDS-3) provides two radio determination satellite service (RDSS) positioning services for users, i.e., the traditional RDSS (TRDSS) positioning of the BeiDou-2 regional satellite navigation system, and the comprehensive RDSS (CRDSS) positioning, which integrates the RDSS and radio navigation satellite service. As published studies regarding the RDSS positioning service are few, we analyze and compare the performances of the two RDSS positioning modes. First, we systematically investigate the principles of the TRDSS and CRDSS positioning, and then analyze the evaluation methods in terms of their positioning accuracy, real time, and coverage range. Second, based on the BeiDou RDSS measured data, we evaluate the performances of the TRDSS and CRDSS positioning. Compared with TRDSS positioning, CRDSS positioning exhibits the following: 1) A significant increase in positioning accuracy, resulting in error improvement from 8 to 2 m and root mean square improvement from 3.13 to 0.85 m; in other words, the positioning error, constant deviation, and stability improve significantly. 2) The real time reduces slightly from 1.1 to 1.8 ns, which is within the acceptable range. 3) The coverage range expands from the areas of 62°E–145°E and 5°N–55°N to the areas of 50°E–170°E and 0°N–70°N, respectively. 4) CRDSS positioning is not restricted by the constraints of the digital elevation database or the user elevation information and can thus solve the occlusion problem effectively.

Visual navigation is imperative for successful asteroid exploration missions. In this study, an integrated visual navigation system was proposed based on angles-only measurements to robustly and accurately determine the pose of the lander during the final landing phase. The system used the lander’s global pose information provided by an orbiter, which was deployed in space in advance, and its relative motion information in adjacent images to jointly estimate its optimal state. First, the landmarks on the asteroid surface and markers on the lander were identified from the images acquired by the orbiter. Subsequently, an angles-only measurement model concerning the landmarks and markers was constructed to estimate the orbiter’s position and lander’s pose. Subsequently, a method based on the epipolar constraint was proposed to estimate the lander’s inter-frame motion. Then, the absolute pose and relative motion of the lander were fused using an extended Kalman filter. Additionally, the observability criterion and covariance of the state error were provided. Finally, synthetic image sequences were generated to validate the proposed navigation system, and numerical results demonstrated its advance in terms of robustness and accuracy.