Optimization of Interplanetary Rendezvous Trajectories for Solar Sailcraft Using a Neurocontroller

As for all low-thrust spacecraft, finding optimal solar sailcraft trajectories is a difficult and time-consuming task that involves a lot of experience and expert knowledge, since the convergence behavior of optimizers that are based on numerical optimal control methods depends strongly on an adequate initial guess, which is often hard to find. Even if the op-timizer converges to an ”optimal trajectory”, this trajectory is typically close to the initial guess that is rarely close to the global optimum. This paper demonstrates, that artificial neural networks in combination with evolutionary algorithms can be applied successfully for optimal solar sailcraft steering. Since these evolutionary neurocontrollers explore the trajectory search space more exhaustively than a human expert can do by using tradi-tional optimal control methods, they are able to find steering strategies that generate better trajectories, which are closer to the global optimum. Results are presented for a Near Earth Asteroid rendezvous mission and for a Mercury rendezvous mission

Analysis of interplanetary solar sail trajectories with attitude dynamics

We present a new approach to the problem of optimal control of solar sails for low-thrust trajectory optimization. The objective was to find the required control torque magnitudes in order to steer a solar sail in interplanetary space. A new steering strategy, controlling the solar sail with generic torques applied about the spacecraft body axes, is integrated into the existing low-thrust trajectory optimization software InTrance. This software combines artificial neural networks and evolutionary algorithms to find steering strategies close to the global optimum without an initial guess. Furthermore, we implement a three rotational degree-of-freedom rigid-body attitude dynamics model to represent the solar sail in space. Two interplanetary transfers to Mars and Neptune are chosen to represent typical future solar sail mission scenarios. The results found with the new steering strategy are compared to the existing reference trajectories without attitude dynamics. The resulting control torques required to accomplish the missions are investigated, as they pose the primary requirements to a real on-board attitude control system

Potential effects of optical solar sail degredation on trajectory design

The optical properties of the thin metalized polymer films that are projected for solar sails are assumed to be affected by the erosive effects of the space environment. Their degradation behavior in the real space environment, however, is to a considerable degree indefinite, because initial ground test results are controversial and relevant inspace tests have not been made so far. The standard optical solar sail models that are currently used for trajectory design do not take optical degradation into account, hence its potential effects on trajectory design have not been investigated so far. Nevertheless, optical degradation is important for high-fidelity solar sail mission design, because it decreases both the magnitude of the solar radiation pressure force acting on the sail and also the sail control authority. Therefore, we propose a simple parametric optical solar sail degradation model that describes the variation of the sail film's optical coefficients with time, depending on the sail film's environmental history, i.e., the radiation dose. The primary intention of our model is not to describe the exact behavior of specific film-coating combinations in the real space environment, but to provide a more general parametric framework for describing the general optical degradation behavior of solar sails. Using our model, the effects of different optical degradation behaviors on trajectory design are investigated for various exemplary missions

Evolutionary neurocontrol: A novel method for low-thrust gravity-assist trajectory optimization

This article discusses evolutionary neurocontrol, a novel method for low-thrust gravity-assist trajectory optimization

AN OPTIMIZATION OF A SOLAR SAILCRAFT TRAJECTORY IN AN EARTH-MARS TRANSFER CONSIDERING THE ATTITUDE DYNAMICS

The goal of this work was to optimize the trajectory of a solar sailcraft in an Earth-Mars transfer. Solar sailcraft is propulsion system with great interest in space engineering, since it uses solar radiation to propulsion. So there is no need for propellant to be used, thus it can remains active throughout the entire transfer maneuver. This type of propulsion system opens the possibility to reduce the cost of exploration missions in the solar system. In its simplest configuration, a Flat Solar Sail (FSS) consists of a large and thin structure generally composed by a film fixed to flexible rods. The performance of these vehicles depends largely on the sails attitude relative to the Sun. Using a FSS as propulsion, an Earth-Mars transfer optimization problem was tackled by the GEO real algorithm (Generalized Extremal Optimization with real codification). This algorithm is an Evolutionary Algorithm (AE) based on the theory of Self-Organized Criticality. The FSS was able to perform up to 10 maneuversuntil reach Mars. Two angles values are necessary to characterize the FSS film normal vector. Therefore, the GEO real algorithm had to optimize up to 20 design variables in order to minimize the transfer time from Earth to Mars. Once the optimized control law and the FSS trajectory were obtained, the attitude equations of motion were considered. Finally, the impact of this consideration in the FSS control law performance was evaluated. Keywords: Solar sailcraft, Trajectory optimization, Evolutionary algorithm, Attitude dynamics, Generalized Extremal Optimization

Real-time optimal control for attitude-constrained solar sailcrafts via neural networks

This work is devoted to generating optimal guidance commands in real time for attitude-constrained solar sailcrafts in coplanar circular-to-circular interplanetary transfers. Firstly, a nonlinear optimal control problem is established, and necessary conditions for optimality are derived by the Pontryagin's Minimum Principle. Under some assumptions, the attitude constraints are rewritten as control constraints, which are replaced by a saturation function so that a parameterized system is formulated to generate an optimal trajectory via solving an initial value problem. This approach allows for the efficient generation of a dataset containing optimal samples, which are essential for training Neural Networks (NNs) to achieve real-time implementation. However, the optimal guidance command may suddenly change from one extreme to another, resulting in discontinuous jumps that generally impair the NN's approximation performance. To address this issue, we use two co-states that the optimal guidance command depends on, to detect discontinuous jumps. A procedure for preprocessing these jumps is then established, thereby ensuring that the preprocessed guidance command remains smooth. Meanwhile, the sign of one co-state is found to be sufficient to revert the preprocessed guidance command back into the original optimal guidance command. Furthermore, three NNs are built and trained offline, and they cooperate together to precisely generate the optimal guidance command in real time. Finally, numerical simulations are presented to demonstrate the developments of the paper

Automated Trajectory Optimizer for Solar Sailing (ATOSS)

The problem of finding an optimal solar-sail trajectory must be solved by means of numerical methods, since no analytical, closed-form solutions exist. A new tool named ATOSS (Automated Trajectory Optimizer for Solar Sailing) has been developed for optimizing multi-phase solar-sail trajectories. A shape-based method for solar sailing and a two-stage approach for the optimization are the keys to the success of ATOSS, which operates with minimum inputs required to the user. Once the initial guess is generated by means of the shape-based method, the above mentioned two-stage approach works as follows. First, a solution to the optimal control problem at hand is sought; subsequently, the boundaries on the times are modified so that a better solution, in terms of total mission duration, is searched. Several numerical test cases are presented to demonstrate ATOSS' ability to automatically find optimal solar-sail trajectories for single- and multi-phase optimization problems. Moreover, the shape-based method for solar sailing has been validated as a viable method to produce initial guess solutions for a direct optimization algorithm

Solar Sail Simplified Optimal Control Law for Reaching High Heliocentric Distances

The aim of this paper is to analyze optimal trajectories of a solar sail-based spacecraft in missions towards the outer Solar System region. The paper proposes a simplified approach able to estimate the minimum flight time required to reach a given (sufficiently high) heliocentric distance. In particular, the effect of a set of solar photonic assists on the overall mission performance is analyzed with a simplified numerical approach. A comparison with results taken from the existing literature show the soundness of the proposed approach

Analysis of NEO Deflection Using Planetary Sunshade Sailcraft for Planetary Defence

In response to the urgent climate crisis, the Planetary Sunshade Foundation envisions deploying a high number sunshade sailcraft, ranging from hundreds of millions to 1.5 billion units, near Sun-Earth Lagrange point 1. Assuming these sunshade sailcraft are already deployed in interplanetary space, this space-based geoengineering initiative, holds potential not only for addressing climate concerns but also for deflecting potentially hazardous asteroids by applying the kinetic impactor energy technique. This study focuses on designing deflection mission scenarios for these sailcraft arrangements. The primary objective is to determine the required sailcraft mass and quantity within a specific time frame to achieve a deflection distance of two Earth radii. Target body for the analysis is the asteroid 2023 PDC, a fictitious asteroid which is designed for the scenario within the 8th Planetary Defence Conference 2023. A hybrid approach is employed to find the best sailcraft trajectories among the analysed scenarios. Initial deflection simulations using Poliastro, a Python library for astrodynamics, while InTrance, integrating neural networks, drives the optimisation process. This methodology is applied to two distinct sunshade sailcraft configurations introduced by Fuglesang et al. in [32]. The findings demonstrate a deflection efficiency of 10 metres per kilogram impacting sail mass for the first sailcraft arrangement and 5 metres per kilogram for the second. In contrast the analytically approximated case achieves an efficiency of 1.5 metres per kilogram. This investigation underscores the substantial impact of the applied launch window analysis beyond extended deflection time on enhancing efficiency. Therefore the significant mass in interplanetary space, a result of the planetary sunshade deployment, provides a strategic edge for the kinetic energy impactor technique

Solar sail science mission applications and advancement : solar sailing: concepts, technology, missions

Solar sailing has long been envisaged as an enabling or disruptive technology. The promise of open-ended missions allows consideration of radically new trajectories and the delivery of spacecraft to previously unreachable or unsustainable observation outposts. A mission catalogue is presented of an extensive range of potential solar sail applications, allowing identification of the key features of missions which are enabled, or significantly enhance, through solar sail propulsion. Through these considerations a solar sail application-pull technology development roadmap is established, using each mission as a technology stepping-stone to the next. Having identified and developed a solar sail application-pull technology development roadmap, this is incorporated into a new vision for solar sailing. The development of new technologies, especially for space applications, is high-risk. The advancement difficulty of low technology readiness level research is typically underestimated due to a lack of recognition of the advancement degree of difficulty scale. Recognising the currently low technology readiness level of traditional solar sailing concepts, along with their high advancement degree of difficulty and a lack of near-term applications a new vision for solar sailing is presented which increases the technology readiness level and reduces the advancement degree of difficulty of solar sailing. Just as the basic principles of solar sailing are not new, they have also been long proven and utilised in spacecraft as a low-risk, high-return limited-capability propulsion system. It is therefore proposed that this significant heritage be used to enable rapid, near-term solar sail future advancement through coupling currently mature solar sail, and other, technologies with current solar sail technology developments. As such the near-term technology readiness level of traditional solar sailing is increased, while simultaneously reducing the advancement degree of difficulty along the solar sail application-pull technology development roadmap