Astrodynamics最新文献

Future missions to the Moon and beyond are likely to involve low-thrust propulsion technologies due to their propellant efficiency. However, these still present a difficult trajectory design problem, owing to the near continuous thrust, lack of control authority and chaotic dynamics. Lyapunov control laws can generate sub-optimal trajectories for such missions with minimal computational cost and are suitable for feasibility studies and as initial guesses for optimisation methods. In this work a Reinforced Lyapunov Controller is used to design optimal low-thrust transfers from geostationary transfer orbit towards lunar polar orbit. Within the reinforcement learning (RL) framework, a dual-actor network setup is used, one in each of the Earth- and Moon-centred inertial frames respectively. A key contribution of this paper is the demonstration of a forwards propagated trajectory, removing the need to define a patch point a priori. This is enabled by an adaptive patch distance and extensive initial geometry exploration during the RL training. Results for both time- and fuel-optimal transfers are presented, along with a Monte Carlo analysis of the robustness to disturbances for such transfers. Phasing is introduced where necessary to aid rendezvous with the Moon. The results demonstrate the potential for such techniques to provide a basis for the design and guidance of low-thrust lunar transfers.

Scientific interest in asteroids and their physical characteristics is growing. These bodies provide insights into the primordial solar system and represent a valuable source of metals, silicates, and water. Several missions over the past few years have aimed to improve and better identify the main properties of these poorly known celestial bodies. However, these missions relied on touchdown(s) on the target asteroid to gather samples, which is complicated owing to the difficulty of accurately reaching and rendezvousing with the body. This study aims to assess the feasibility of an in-orbit asteroid sample collection mission. Such a strategy could prevent complex operations related to landing and touchdown maneuvers and avoid the dead times present in a mission requiring several landings. The presented collection scenario, which focuses on the asteroid Ryugu, proposes gathering samples using a spacecraft injected into a halo orbit around the second libration point, L₂. For this purpose, the orbits in the neck region of the zero velocity curves are analyzed. A novel methodology to characterize bouncing behavior is introduced. An interpolation-based approach was used to recover the appropriate restitution coefficients for each collision occurring at a specific impact angle. This was applied to both the rigid body model and the point mass approximation studied for two different sites on the asteroid. Furthermore, the study enlarged the region of interest from only L₂ to its neighboring zones to return a more global and realistic point of view. Considering the solar radiation pressure and asteroid aspherical potential, particles of different sizes ejected from different longitudes and with different ejection angles were classified according to their trajectories to finally build a database. Based on this analysis, an aerogel-based collection strategy inspired by that used in the Stardust-NExT (NASA) mission was investigated to assess its possible applicability to the analyzed scenario.

This paper investigates the heliocentric time-optimal rendezvous performance of Sun-facing diffractive solar sails with various deflection angles and acceleration capabilities. Diffractive solar sails, which generate tangential radiation pressure force, are proposed and schematically designed to achieve diverse radiation pressure distributions. The radiation pressure force model and the time-optimal control problem for these innovative Sun-facing diffractive solar sails are established. Utilizing an indirect method and the optimal control law, we explore typical heliocentric rendezvous scenarios to assess the variational trends of transfer time in relation to different deflection angles and acceleration capabilities. The results for Sun-facing diffractive sails in specific rendezvous missions are compared to reflective sails with the same area-to-mass ratio, focusing on transfer trajectory and attitude control. Our findings reveal that diffractive sails exhibit significant advantages over reflective sails, particularly in the context of normal acceleration, paving the way for more efficient space exploration.

Asteroids may contain valuable minerals. A method to exploit asteroid mines is to transfer them closer to the Earth for further mining processes. In this work, we optimally mount a set of fixed-angle spacecraft thrusters on the surface of an asteroid to conduct concurrent detumbling and redirecting to the desired orbit. The optimization objective reconciles the minimum duration of the mission with the minimum required fuel as well as the maximum uniformity of the fuel distribution required for all thrusters. Each thruster can respond to redirection and detumbling commands simultaneously. Redirection and detumbling are performed via the directional adaptive guidance method and PID controllers, respectively, and the weight factors for each orbital element and the gains of the rotational control channels are also optimized in the process. We use the particle swarm optimization algorithm to evaluate the objective function by simulating the entire mission to find the optimal design. The rotational control damps the tumbling of the asteroid without interfering with the simultaneous redirection process and eventually fixes the asteroid in the optimally selected orientation in the inertial reference frame. The rotational velocity and attitude of the asteroid are controlled via separate PID controllers, which are set robustly. We can effectively optimize the mission by collectively tuning both the system’s rotational and redirection behaviors as well as the thrusters’ configuration and optimally selecting the final attitude of the asteroid.

In this work, we attempt to investigate a luring cooperative guidance strategy for three-player inducer–defender–attacker engagement with field-of-view (FOV) and overload constraints against an attacker with speed advantages under incomplete information. We formulate the three-player inducer–defender–attacker engagement problem as the pursuit–evasion (defender–attacker) game problem. On this basis, an analytical luring cooperative guidance strategy based on backstepping control is proposed to facilitate the defender with zero overloads intercepting the attacker. Additionally, under incomplete information, we offer a parameter delay design approach to delay the unknown parameters and state design. Afterward, an improved adaptive update law is devised to address the incomplete information. The proposed luring cooperative guidance, which incorporates backstepping control and an improved adaptive update law, can guarantee that the defender captures the attacker with zero overloads under luring by the inducer. Additionally, the proposed design adopts the directed communication topology network structure. Finally, we also execute simulations that demonstrate the effectiveness of the designed luring cooperative guidance strategy and reveal that it can be extended to double-hierarchical interception and four-on-two engagement interception.

This technical note presents a practical approach to low-energy Earth–Moon transfer autonomous guidance considering high-fidelity orbital dynamics. Initially, autonomous guidance, delineated as a trajectory-tracking problem, is addressed within the framework of a predesigned reference trajectory solution, accompanied by empirical trajectory correction maneuver allocation. A series of two-point boundary value problems is subsequently formulated to incorporate guidance velocity increments. An algorithm employing quasilinearization, discretization, and recursion is proposed to address these boundary value problems, which results in enhanced convergence performance compared with traditional differential-correction-based guidance methods. Finally, a Monte Carlo analysis demonstrates the efficacy of the proposed autonomous guidance approach, indicating its potential for onboard applications.

To match the trans-lunar injection with high accuracy, a near-optimal orbit control method for phasing loops is proposed. Sensitivity analysis was performed based on Gauss’s variational equations, and a near-optimal orbit control strategy was developed. A sequential shooting method was proposed to reduce the dimensions of each shooting problem and improve convergence. To satisfy the accessibility requirements of ground facilities, a maneuvering location adjustment strategy is proposed. The advantage of the delta-V saving of the near-optimal method was verified by comparing with the differential correction method. The robustness of the practical method was verified using Monte Carlo simulations with high-fidelity dynamics. The results of this study can be applied to midcourse correction of phasing loops before the trans-lunar injection of a lunar probe.

The mapping phase is a key stage of the Tianwen-1 orbiter. It has the longest exploration time and gathers abundant radio tracking data via the Chinese deep space network. Thus, it also provides opportunities for radio science research topics such as the Mars gravity field model, ephemeris, and radio occultation experiments. At this stage, the need for imaging takes the highest priority, leading to frequent attitude adjustments for the spacecraft, which presents challenges for Precise Orbit Determination (POD). To improve the accuracy of the spacecraft’s orbit, this study analyzes the effects of arc length, the empirical acceleration, and the solar radiation pressure parameters on POD, considering the limited number of radio tracking observations. For one-day arcs, the POD is not able to adequately account for wheel off-loading and a few unknown forces with limited observations, but reasonable fitting is performed for the wheel off-loading occurring during tracking periods or the gap between two tracking periods. When extending the POD arc to three days, the estimated empirical acceleration can be well-fitted and reflects the aggregation feature, but the solar radiation pressure parameter has little impact on POD results. The root mean square of two-way range-rate residuals after POD is about 0.18–0.35 mm/s; the orbital position accuracy of 60% of the arcs is better than 100 m.

Ground- and space-based optical observation is an efficient way to catalog objects in the cislunar space. Initial orbit determination based on optical data is still an open problem for cislunar objects. The motion of these objects usually follows the law of three bodies instead of the two-body one, so current algorithms based on the two-body relation should be revised. Moreover, due to the long duration of most cislunar objects, optical observations of even hours can cover only a small fraction of one orbit, making the initial orbit determination of these objects a typical too-short-arc problem, which is difficult. A way to address this problem is to use the admissible region. In this study, an efficient algorithm constrained by the admissible region is proposed. It is easy to implement because it uses only simple iterations. Its efficiency is proven by comparing it with that of one traditional initial orbit determination algorithm.