Astrodynamics最新文献

This study made use of a shape-based method to analyze the orbital dynamics of a spacecraft subject to a continuous propulsive acceleration acting along the circumferential direction. Under the assumption of a logarithmic spiral trajectory, an exact solution to the equations of motion exists, which allows the spacecraft state variables and flight time to be expressed as a function of the angular coordinate. There is also a case characterized by specific initial conditions in which the time evolution of the state variables may be analytically determined. In this context, the presented solution is used to analyze circle-to-circle trajectories, where the combination of two impulsive maneuvers and a logarithmic spiral path are used to accomplish the transfer. The determined results are then applied to the achievement of the Earth—Mars and the Earth—Venus transfers using actual data from a recent thruster developed by NASA.

The significant characteristics of space non-cooperative targets include the uncertainties of dynamic parameters and behaviors. Herein, a hybrid proximity control strategy adapted to the behavior uncertainty of a non-cooperative target is presented. First, the relative motion dynamics between the chaser and target is established in the geocentric inertial coordinate system and transcribed based on the chaser spacecraft body coordinate system. Subsequently, to facilitate proximity control under uncertain conditions, an extended state observer is designed to estimate and compensate for the total uncertainty in the relative motion dynamics. Finally, an event-triggered sliding mode control law is designed to track the target with behavior uncertainty and realize synchronization. Numerical simulations demonstrate the effectiveness of the proposed proximity control strategy for both tumbling and maneuvering targets.

Asteroid 469219 Kamo’oalewa, also named 2016 HO3, is a small-size fast-rotating near-Earth asteroid, which is a potential target for future explorations. Owing to its weak gravity and fast spin rate, the dynamics on the surface or in the vicinity of 2016 HO3 are significantly different from those of planets or other small bodies explored in previous missions. In this study, the geophysical and orbital environments of 2016 HO3 were investigated to facilitate a potential mission design. First, the geometric and geopotential topographies of 2016 HO3 were examined using different shape models. The lift-off and escape conditions on its fast-rotating surface were investigated. Then, the periodic orbits around 2016 HO3 were studied in the asteroid-fixed frame and the Sun—asteroid frame considering the solar radiation pressure. The stable regions of the terminator orbits were discussed using different parameters. Finally, the influence of the nonspherical shape on the terminator orbits was examined. The precise terminator orbits around a real shape model of 2016 HO3 were obtained and verified in the high-fidelity model. This study shows that the polar region of 2016 HO3 is the primary region for landing or sampling, and the terminator orbits are well suited for global mapping and measurements of 2016 HO3. The analysis and methods can also serve as references for the exploration of other small fast-rotating bodies.

In this study, a supervised machine learning approach called Gaussian process regression (GPR) was applied to approximate optimal bi-impulse rendezvous maneuvers in the cis-lunar space. We demonstrate the use of the GPR approximation of the optimal bi-impulse transfer to patch points associated with various invariant manifolds in the cis-lunar space. The proposed method advances preliminary mission design operations by avoiding the computational costs associated with repeated solutions of the optimal bi-impulsive Lambert transfer because the learned map is computationally efficient. This approach promises to be useful for aiding in preliminary mission design. The use of invariant manifolds as part of the transfer trajectory design offers unique features for reducing propellant consumption while facilitating the solution of trajectory optimization problems. Long ballistic capture coasts are also very attractive for mission guidance, navigation, and control robustness. A multi-input single-output GPR model is presented to represent the fuel costs (in terms of the ΔV magnitude) associated with the class of orbital transfers of interest efficiently. The developed model is also proven to provide efficient approximations. The multi-resolution use of local GPRs over smaller sub-domains and their use for constructing a global GPR model are also demonstrated. One of the unique features of GPRs is that they provide an estimate of the quality of approximations in the form of covariance, which is proven to provide statistical consistency with the optimal trajectories generated through the approximation process. The numerical results demonstrate our basis for optimism for the utility of the proposed method.

In this study, a novel approach based on the U-Net deep neural network for image segmentation is leveraged for real-time extraction of tracklets from optical acquisitions. As in all machine learning (ML) applications, a series of steps is required for a working pipeline: dataset creation, preprocessing, training, testing, and post-processing to refine the trained network output. Online websites usually lack ready-to-use datasets; thus, an in-house application artificially generates 360 labeled images. Particularly, this software tool produces synthetic night-sky shots of transiting objects over a specified location and the corresponding labels: dual-tone pictures with black backgrounds and white tracklets. Second, both images and labels are downscaled in resolution and normalized to accelerate the training phase. To assess the network performance, a set of both synthetic and real images was inputted. After the preprocessing phase, real images were fine-tuned for vignette reduction and background brightness uniformity. Additionally, they are down-converted to eight bits. Once the network outputs labels, post-processing identifies the centroid right ascension and declination of the object. The average processing time per real image is less than 1.2 s; bright tracklets are easily detected with a mean centroid angular error of 0.25 deg in 75% of test cases with a 2 deg field-of-view telescope. These results prove that an ML-based method can be considered a valid choice when dealing with trail reconstruction, leading to acceptable accuracy for a fast image processing pipeline.

The collision probability computation of space objects plays an important role in space situational awareness, particularly for conjunction assessment and collision avoidance. Early works mainly relied on Monte Carlo simulations to predict collision probabilities. Although such simulations are accurate when a large number of samples are used, these methods are perceived as computationally intensive, which limits their application in practice. To overcome this limitation, many approximation methods have been developed over the past three decades. This paper presents a comprehensive review of existing space-object collision probability computation methods. The advantages and limitations of different methods are analyzed and a systematic comparison is presented. Advice regarding how to select a suitable method for different short-term encounter scenarios is then provided. Additionally, potential future research avenues are discussed.

Small bodies in the solar system are known to be covered by a layer of loose unconsolidated soil composed of grains ranging from dusty sands to rugged boulders. Various geophysical processes have modified these regolith layers since their origin. Therefore, the landforms on regolith-blanketed surfaces hold vital clues for reconstructing the geological processes occurring on small bodies. However, the mechanical strength of small body regolith remains unclear, which is an important parameter for understanding its dynamic evolution. Furthermore, regolith mechanical properties are key factors for the design and operation of space missions that interact with small body surfaces. The granular penetrometer, which is an instrument that facilitates in situ mechanical characterization of surface/subsurface materials, has attracted significant attention. However, we still do not fully understand the penetration dynamics related to granular regolith, partially because of the experimental difficulties in measuring grain-scale responses under microgravity, particularly on the longer timescales of small body dynamics. In this study, we analyzed the slow intrusion of a locomotor into granular matter through large-scale numerical simulations based on a soft sphere discrete element model. We demonstrated that the resistance force of cohesionless regolith increases abruptly with penetration depth after contact and then transitions to a linear regime. The scale factor of the steady-state component is roughly proportional to the internal friction of the granular materials, which allows us to deduce the shear strength of planetary soils by measuring their force-depth relationships. When cohesion is included, due to the brittle behavior of cohesive materials, the resistance profile is characterized by a stationary state at a large penetration depth. The saturation resistance, which represents the failure threshold of granular materials, increases with the cohesion strength of the regolith. This positive correlation provides a reliable tool for measuring the tensile strength of granular regolith in small body touchdown missions.

Periodic orbits are crucial in facilitating the understanding of the dynamical behavior of elongated asteroids. As a specific type of periodic orbit, resonant orbits can enrich the orbit design method of deep-space exploration missions. Herein, a dipole segment model for investigating the orbital dynamics of elongated asteroids is briefly introduced. A new numerical algorithm named the modified path searching method for identifying spin-orbit resonant orbits is proposed. Using the modified path searching and pseudo-arclength continuation methods, four spin-orbit resonant families for asteroid 2063 Bacchus are obtained. The distribution of eigenvalues and stability curves for the four resonant families are presented. In particular, some critical points corresponding to period-doubling and tangent bifurcations appear in the stability curves.

Satellite encounters during close operations, such as rendezvous, formation, and cluster flights, are typical long-term encounters. The collision probability in such an encounter is a primary safety concern. In this study, a parametric method is proposed to compute the long-term collision probability for close satellite operations with initial state uncertainty. Random relative state errors resulting from system uncertainty lead to possible deviated trajectories with respect to the nominal one. To describe such a random event meaningfully, each deviated trajectory sample should be mapped to a unique and time-independent element in a random variable (RV) space. In this study, the RV space was identified as the transformed state space at a fixed initial time. The physical dimensions of both satellites were characterized by a combined hard-body sphere. Transforming the combined hard-body sphere into the RV space yielded a derived ellipsoid, which evolved over time and swept out a derived collision volume. The derived collision volume was solved using the reachable domain method. Finally, the collision probability was computed by integrating a probability density function over the derived collision volume. The results of the proposed method were compared with those of a nonparametric computation-intensive Monte Carlo method. The relative difference between the two results was found to be < 0.6%, verifying the accuracy of the proposed method.

In this paper, we investigate the orbital behavior of the transition between the quasisatellite (QS) and horseshoe (HS) motions of 2016 HO₃. Based on the phase space structure in the Sun–Earth circular restricted three-body problem, we find that the surface of 2016 HO₃ in the torus space is a compound surface formed by QS and HS portions. Its co-orbital motion is therefore a QS–HS transition. 2016 HO₃ is currently located in a QS state, and its locus clings to the QS portion in the isosurface in agreement with the semi-analytical results. We provide a criterion to separate the QS and HS stages in the transition and obtain accurate incoming and outgoing epochs of the QS motion. We then propose an approximate curve to describe the locus of 2016 HO₃ in the ω − e projection. Virtual asteroids (VAs) near 2016 HO₃ in the isosurface were created to study the influence of the initial state of the QS–HS transition. We find that the duration of the QS state is mainly influenced by the loci in the ω − e projection. The VAs with large QS durations usually have longer loci across the QS region than those with shorter durations. In addition, although some VAs are close to 2016 HO₃ in the ω − e projection, their co-orbital behaviors are significantly different from that of the latter. This indicates that the QS–HS transition of 2016 HO₃ is sensitive to the (ω, e) position.