Astrodynamics最新文献

This paper proposes new quasi-periodic orbits around Earth–Moon collinear libration points using solar sails. By including the time-varying sail orientation in the linearized equations of motion for the circular restricted three-body problem (CR3BP), four types of quasi-periodic orbits (two types around L1 and two types around L2) were formulated. Among them, one type of orbit around L2 realizes a considerably small geometry variation while ensuring visibility from the Earth if (and only if) the sail acceleration due to solar radiation pressure is approximately of a certain magnitude, which is much smaller than that assumed in several previous studies. This means that only small solar sails can remain in the vicinity of L2 for a long time without propellant consumption. The orbits designed in the linearized CR3BP can be translated into nonlinear CR3BP and high-fidelity ephemeris models without losing geometrical characteristics. In this study, new quasi-periodic orbits are formulated, and their characteristics are discussed. Furthermore, their extendibility to higher-fidelity dynamic models was verified using numerical examples.

The current methods for designing periodic orbits in the elliptic restricted three-body problem (ERTBP) have the disadvantages of targeting limited orbits and ergodic searches and considering only symmetric orbits. A universal method for designing periodic orbits is proposed in this paper. First, the homotopy classes of orbits are structured based on their topological structures. Second, a dynamic model based on homotopy classes, ranging from the circular restricted three-body problem (CRTBP) to the ERTBP, can be built using the homotopy method. Third, a multi- and a single-period orbit were selected based on the resonance ratios. Finally, the corresponding orbit in the ERTBP was computed by modifying the initial condition of the orbit in the CRTBP. This method, without an ergodic search, can extend to any orbit, including an asymmetric orbit in the CRTBP, to the ERTBP model, and the two orbits are of the same homotopy class. Examples of the Earth–Moon ERTBP are presented to verify the efficiency of this method.

This paper answers how multiple satellites are seen from the ground. This question is inspired by space-advertising, a public exhibition in the night sky using a dot matrix of satellites that are bright enough to be seen by the naked eye. Thus, it is important for space advertisement that the specific dot matrix is seen. Moreover, the stability of the dot matrix during a visible span is very valuable. To stabilize the dot matrix, this study formulates an apparent position of a dot from a representative dot seen from the ground. The formulation, linear functions of a set of relative orbital elements, reveals the appearance of the dot matrix. The proposed relative variable in the formulation drives the instability of the dot matrix, thereby revealing an initial stable configuration of deputies from a chief. The arbitrary dot matrix designed using the configuration is stable even at low elevations without orbital control during the visible span.

The primary technique used for air traffic surveillance is radar. However, nowadays, its role in surveillance is gradually being replaced by the recently adopted Automatic Dependent Surveillance-Broadcast (ADS-B). ADS-B offers a higher accuracy, lower power consumption, and longer range than radar, thus providing more safety to aircraft. The coverage of terrestrial radar and ADS-B is confined to continental parts of the globe, leaving oceans and poles uncovered by real-time surveillance measures. This study presents an optimized Low-Earth Orbit (LEO)-based ADS-B constellation for global air traffic surveillance over intercontinental trans-oceanic flight routes. The optimization algorithm is based on performance evaluation parameters, i.e., coverage time, satellite availability, and orbit stability (precession and perigee rotation), and communication analysis. The results indicate that the constellation provides ample coverage in the simulated global oceanic regions. The constellation is a feasible and cost-effective solution for global air supervision, which can supplement terrestrial ADS-B and radar systems.

This study proposes a parametric formation control method for the cooperative observation of the China Space Station (CSS) using multiple nanosatellites. First, a simplified geometrical model of the CSS is constructed using fundamental solids, such as the capsule body and cuboid. Second, the spacecraft formation configuration for the observation mission is characterized by a three-dimensional (3D) Lissajous curve using related design parameters under the full-coverage observation requirements of specific parts, such as the CSS connecting section and collision avoidance constraints. Third, a double-layer control law is designed for each nanosatellite, in which the upper layer is a distributed observer for recognizing the target formation configuration parameters, and the lower layer is a trajectory-tracking controller to make the nanosatellite converge to its temporary target position calculated from the upper layer’s outputs. The closed-loop control stability is proven under the condition that the communication network topology of the nanosatellite cluster contains a directed spanning tree. Finally, the control method is verified by numerical simulation, where the CSS connecting section is selected as the observation target, and ten small nanosatellites are assumed to perform the cooperative observation mission. The simulation results demonstrate that the double-layer control law is robust to single-point communication failures and suitable for the accompanying missions of large space objects with multiple nanosatellites.

The regularization theory has successfully enabled the removal of gravitational singularities associated with celestial bodies. In this study, regularizing techniques are merged into a multi-impulse trajectory design framework that requires delicate computations, particularly for a fuel minimization problem. Regularized variables based on the Levi–Civita or Kustaanheimo–Stiefel transformations express instantaneous velocity changes in a gradient-based direct optimization method. The formulation removes the adverse singularities associated with the null thrust impulses from the derivatives of an objective function in the fuel minimization problem. The favorite singularity-free property enables the accurate reduction of unnecessary impulses and the generation of necessary impulses for local optimal solutions in an automatic manner. Examples of fuel-optimal multi-impulse trajectories are presented, including novel transfer solutions between a near-rectilinear halo orbit and a distant retrograde orbit.

Spinning electrodynamic tether systems (SEDTs) have promising potential for the active removal of space debris, the construction of observation platforms, and the formation of artificial gravity. However, owing to the survivability problem of long tethers, designing collision-avoidance strategies for SEDTs with space debris is an urgent issue. This study focuses on the design of collision-avoidance strategies for SEDTs with an electrodynamic force (Ampere force). The relative distance between the debris and the SEDT is first derived, and then two collision-avoidance strategies are proposed according to the two different cases. When debris collides closer to a lighter subsatellite, a stationary avoidance strategy is proposed to change the spatial position of the subsatellite by adjusting only the angular motion of the tether, which maintains the original orbit of the SEDT. When debris collides closer to a heavier main spacecraft, a comprehensive avoidance strategy is proposed to change the spatial position of the SEDT by slightly modifying the orbital height and changing the tether angular motion simultaneously. The numerical results illustrate that the proposed strategies promptly avoid potential collisions of an SEDT with space debris without significant changes in the orbital parameters of the SEDT.

This study focuses on stabilizing the libration dynamics of an electrodynamic tether system (EDTS) using generalized torques induced by the Lorentz force. In contrast to existing numerical optimization methods, a novel analytical feedback control law is developed to stabilize the in-plane and out-of-plane motions of a tether by modulating the electric current only. The saturation constraint on the current is accounted for by adding an auxiliary dynamic system to the EDTS. To enhance the robustness of the proposed controller, multiple perturbations of the orbital dynamics, modeling uncertainties, and external disturbances are approximated using a neural network in which the weighting matrix and approximation error are estimated simultaneously, such that these perturbations are well compensated for during the control design of the EDTS. Furthermore, a dynamically scaled generalized inverse is utilized to address the singular matrix in the control law. The closed-loop system is proven to be ultimately bounded based on Lyapunov stability theory. Finally, numerical simulations are performed to demonstrate the effectiveness of the proposed analytical control law.

This study proposes a novel adaptive neural dynamic-based hybrid control strategy for stable subsatellite retrieval of two-body tethered satellite systems. The retrieval speed is given analytically, ensuring a libration-free steady state. To mitigate the potential libration motion, a general control input signal is generated by an adaptive neural-dynamic (AND) algorithm and executed by adjusting the retrieval speed and thruster on the subsatellite. To address the limited retrieval speed and improve the control performance, the thruster controller is manipulated according to a novel advanced state fuzzy control law based on higher-order libration states, whereas the remaining control input is allocated to the speed controller. The Lyapunov stability of the control strategy is demonstrated analytically. Numerical simulations validate the proposed control strategy, demonstrating well-allocated control inputs for both controllers and good control performance.

An algorithm for robust initial orbit determination (IOD) under perturbed orbital dynamics is presented. By leveraging map inversion techniques defined in the algebra of Taylor polynomials, this tool returns a highly accurate solution to the IOD problem and estimates a range centered on the aforementioned solution in which the true orbit should lie. To meet the specified accuracy requirements, automatic domain splitting is used to wrap the IOD routines and ensure that the local truncation error, introduced by a polynomial representation of the state estimate, remains below a predefined threshold. The algorithm is presented for three types of ground-based sensors, namely range radars, Doppler-only radars, and optical telescopes, by considering their different constraints in terms of available measurements and sensor noise. Finally, the improvement in performance with respect to a Keplerian-based IOD solution is demonstrated using large-scale numerical simulations over a subset of tracked objects in low Earth orbit.