Solar Sail Research Articles

Orbital analysis in generalised solar sail problem with Stokes drag effect

Orbital analysis in generalised solar sail problem with Stokes drag effect

Template-guided Silicon Micromotor Assembly for Enhanced Cell Manipulation.

Light-driven micro/nanorobots (LMNRs) are tiny, untethered machines with great potential in fields like precision medicine, nano manufacturing, and various other domains. However, their practicality hinges on developing light-manipulation strategies that combine versatile functionalities, flexible design options, and precise controllability. Our study introduces an innovative approach to construct micro/nanorobots (MNRs) by utilizing micro/nanomotors as fundamental building blocks. Inspired by silicon Metal-Insulator-Semiconductor solar cell principles, we design a new type of optomagnetic hybrid micromotors (OHMs). These OHMs have been skillfully optimized with integrated magnetic constituent, resulting in efficient light propulsion, precise magnetic navigation, and the potential for controlled assembly. One of the key features of the OHMs is their ability to exhibit diverse motion modes influenced by fracture surfaces and interactions with the environment, streamlining cargo conveyance along "micro expressway" - the predesigned microchannels. Further enhancing their versatility, a template-guided assembly strategy facilitates the assembly of these micromotors into functional microrobots, encompassing various configurations such as "V-shaped", "N-shaped", and 3D structured microrobots. The heightened capabilities of these microrobots, underscore the innovative potential inherent in hybrid micromotor design and assembly, which provides a foundational platform for the realization of multi-component microrobots. Our work moves a step toward forthcoming microrobotic entities boasting advanced functionalities.

Template‐guided Silicon Micromotor Assembly for Enhanced Cell Manipulation

Light‐driven micro/nanorobots (LMNRs) are tiny, untethered machines with great potential in fields like precision medicine, nano manufacturing, and various other domains. However, their practicality hinges on developing light‐manipulation strategies that combine versatile functionalities, flexible design options, and precise controllability. Our study introduces an innovative approach to construct micro/nanorobots (MNRs) by utilizing micro/nanomotors as fundamental building blocks. Inspired by silicon Metal‐Insulator‐Semiconductor solar cell principles, we design a new type of optomagnetic hybrid micromotors (OHMs). These OHMs have been skillfully optimized with integrated magnetic constituent, resulting in efficient light propulsion, precise magnetic navigation, and the potential for controlled assembly. One of the key features of the OHMs is their ability to exhibit diverse motion modes influenced by fracture surfaces and interactions with the environment, streamlining cargo conveyance along "micro expressway" ‐ the predesigned microchannels. Further enhancing their versatility, a template‐guided assembly strategy facilitates the assembly of these micromotors into functional microrobots, encompassing various configurations such as "V‐shaped", "N‐shaped", and 3D structured microrobots. The heightened capabilities of these microrobots, underscore the innovative potential inherent in hybrid micromotor design and assembly, which provides a foundational platform for the realization of multi‐component microrobots. Our work moves a step toward forthcoming microrobotic entities boasting advanced functionalities.

Improving Spacecraft Reliability Through Digital Transformation

This paper demonstrates the reliability engineering benefit achievable by spacecraft digital transformation. The space industry has evolved in the past decade to increasingly incorporate new computing practices into the sector’s ground service and backoffice operations, hailed as a “digital transformation” of their information technology (IT) infrastructure. Parallel sectors that heavily engage control systems, such as utilities and manufacturing, have not only embraced an IT digital transformation but also incorporated new computing architectures, chipsets, and data processing techniques into their operational technology (OT) systems. The space sector has lagged to adopt such digital technologies for their OT, such as spacecraft, and has not realized many of the associated benefits. Through a reliability engineering analysis of small satellites and a comparative case study of a digitally transformed solar sail, we demonstrate the reliability impacts of digital transformation for spacecraft.

Design, analysis, and ground deployment test of space deployable mast based on double-layer deployable unit

The space deployable mast has been successfully applied to space equipment such as solar sails and space telescopes. At present, the deployable units of the space deployable mast mostly adopt the configurations of deployable units of FAST (Folding Articulated Square Truss), HIMAT, and ADAM (Able Deployable Articulated Mast). The configuration of the deployable unit is relatively few. Besides, there is a lack of ground micro-gravity environment simulation test devices for space deployable masts. This paper proposes the space deployable mast based on the double-layer deployable unit. Firstly, the configuration design method of the double-layer deployable unit based on the screw theory has been carried out. Three double-layer hybrid mechanisms serving as the basic units of the deployable mast have been obtained. Then, the kinematic and dynamic models of deployment of the space deployable mast have been established. And the deployment simulation based on MATLAB and Simscape has been performed. Furthermore, modal and static simulations have been performed to obtain the fundamental frequencies and maximum deformation displacements of the deployable masts consisting of 1, 2, 4, 8, and 12 units with and without cables. Finally, the ground test device has been developed to carry out the ground deployment test of the space deployable mast in the ground micro-gravity environment. It has been found that the ground test device could achieve the micro-gravity simulation level of 90.5%.

Optimal Trajectories of Diffractive Sail to Highly Inclined Heliocentric Orbits

Recent literature indicates that the diffractive sail concept is an interesting alternative to the more conventional reflective solar sail, which converts solar radiation pressure into a (deep space) thrust using a thin, lightweight highly reflective membrane, usually metalized. In particular, a diffractive sail, which uses a metamaterial-based membrane to diffract incoming solar rays, is able to generate a steerable thrust vector even when the sail nominal plane is perpendicular to the Sun–spacecraft line. This paper analyzes the optimal transfer performance of a diffractive-sail-based spacecraft in a challenging heliocentric scenario that is consistent with the proposed Solar Polar Imager mission concept. In this case, the spacecraft must reach a near-circular (heliocentric) orbit with a high orbital inclination with respect to the Ecliptic in order to observe and monitor the Sun’s polar regions. Such a specific heliocentric scenario, because of the high velocity change it requires, is a mission application particularly suited for a propellantless propulsion system such as the classical solar sail. However, as shown in this work, the same transfer can be accomplished using a diffractive sail as the primary propulsion system. The main contribution of this paper is the analysis of the spacecraft transfer trajectory using a near-optimal strategy by dividing the entire flight into an approach phase to a circular orbit of the same radius as the desired final orbit but with a smaller inclination, and a subsequent cranking phase until the desired (orbital) inclination is reached. The numerical simulations show that the proposed strategy is sufficiently simple to implement and can provide solutions that differ by only a few percentage points from the optimal results obtainable with a classical indirect approach.

Adaptive Finite-time Attitude Tracking Control for Solar Sail with State-dependent Torque Saturation

Adaptive Finite-time Attitude Tracking Control for Solar Sail with State-dependent Torque Saturation

Electric Sail Test Cube–Lunar Nanospacecraft, ESTCube-LuNa: Solar Wind Propulsion Demonstration Mission Concept

The electric solar wind sail, or E-sail, is a propellantless interplanetary propulsion system concept. By deflecting solar wind particles off their original course, it can generate a propulsive effect with nothing more than an electric charge. The high-voltage charge is applied to one or multiple centrifugally deployed hair-thin tethers, around which an electrostatic sheath is created. Electron emitters are required to compensate for the electron current gathered by the tether. The electric sail can also be utilised in low Earth orbit, or LEO, when passing through the ionosphere, where it serves as a plasma brake for deorbiting—several missions have been dedicated to LEO demonstration. In this article, we propose the ESTCube-LuNa mission concept and the preliminary cubesat design to be launched into the Moon’s orbit, where the solar wind is uninterrupted, except for the lunar wake and when the Moon is in the Earth’s magnetosphere. This article introduces E-sail demonstration experiments and the preliminary payload design, along with E-sail thrust validation and environment characterisation methods, a cis-lunar cubesat platform solution and an early concept of operations. The proposed lunar nanospacecraft concept is designed without a deep space network, typically used for lunar and deep space operations. Instead, radio telescopes are being repurposed for communications and radio frequency ranging, and celestial optical navigation is developed for on-board orbit determination.

Fast initialization of the indirect optimization problem in the solar sail circle-to-circle orbit transfer

This Short Communication presents a procedure to approximate, in an analytical form, the solution of the optimization problem that gives the minimum-time trajectory of a low-performance solar sail, in a classical circle-to-circle heliocentric transfer. More precisely, the proposed procedure gives an accurate approximation of the solution of the two-point boundary value problem associated to the optimization process, when an indirect approach is exploited to obtain the optimal transfer trajectory and an ideal force model is used to describe the solar sail thrust vector. In particular, the analytical results illustrated in this work extend the model discussed in the recent literature, obtained with an ideal electric thruster, to the case of a flat, perfectly reflecting, solar sail-based scenario.

Ultrafast transfer of low-mass payloads to Mars and beyond using aerographite solar sails

With interstellar mission concepts now being under study by various space agencies and institutions, a feasible and worthy interstellar precursor mission concept will be key to the success of the long shot. Here we investigate interstellar-bound trajectories of solar sails made of the ultra lightweight material aerographite. Due to its extremely low density (0.18kg m−3) and high absorptivity (A∼1), a thin shell can pick up an enormous acceleration from the solar irradiation. Payloads of up to 1kg can be transported rapidly throughout the solar system, e.g., to Mars and beyond. Our simulations consider various launch scenarios from a polar orbit around Earth including directly outbound launches as well as Sun-diver launches towards the Sun with subsequent outward acceleration. We use the poliastro Python library for astrodynamic calculations. For a spacecraft with a total mass of 1kg (including 720g aerographite) and a cross-sectional area of 104m2, corresponding to a shell with a radius of 56m, we calculate the positions, velocities, and accelerations based on the combination of gravitational and radiation forces on the sail. We find that the direct outward transfer to Mars near opposition to Earth results in a relative velocity of 65km s−1 with a minimum required transfer time of 26d. Using an inward transfer with solar sail deployment at 0.6AU from the Sun, the sail’s velocity relative to Mars is 118km s−1 with a transfer time of 126d, where Mars is required to be in one of the nodes of the two orbital planes upon sail arrival. Transfer times and relative velocities can vary substantially depending on the constellation between Earth and Mars and the requirements on the injection trajectory to the Sun diving orbit. The direct interstellar trajectory has a final velocity of 109km s−1. Assuming a distance to the heliopause of 120AU, the spacecraft reaches interstellar space after 5.3yr. When using an initial Sun dive to 0.6AU instead, the solar sail obtains an escape velocity of 148km s−1 from the solar system with a transfer time of 4.2yr to the heliopause. Values may differ depending on the rapidity of the Sun dive and the minimum distance to the Sun. The mission concepts presented in this paper are extensions of the 0.5kg tip mass and 196m2 design of the successful IKAROS mission to Venus towards an interstellar solar sail mission. They allow fast flybys at Mars and into the deep solar system. For delivery (rather than fly-by) missions of a sub-kg payload, for example medical supply or replenishment of essential materials, the biggest obstacle remains in the deceleration upon arrival.

A light sail astrobiology precursor mission to Enceladus and Europa

Icy moons with subsurface oceans of liquid water rank among the most promising astrobiological targets in our Solar System. In this work, we assess the feasibility of deploying laser sail technology in precursor life-detection missions. We investigate such laser sail missions to Enceladus and Europa, as these two moons emit plumes that seem accessible to in situ sampling. Our study suggests that GigaWatt laser technology could accelerate a 100 kg probe to a speed of ∼30kms−1, thereupon reaching Europa on timescales of 1–4 years and Enceladus with flight times of 3–6 years. Although the ideal latitudes for the laser array vary, placing the requisite infrastructure close to either the Antarctic or Arctic Circles might represent technically viable options for an Enceladus mission. Crucially, we determine that the minimum encounter velocities with these moons (about 6kms−1) may be near-optimal for detecting biomolecular building blocks (e.g., amino acids) in the plumes by means of a mass spectrometer akin to the Surface Dust Analyzer onboard the Europa Clipper mission. In summary, icy moons in the Solar System are potentially well-suited for exploration via the laser sail architecture approach, especially where low encounter speeds and/or multiple missions are desirable.

Analysis of Using the Light Pressure Effect to Drive Spacecraft under Complex Conditions

Light pressure driving has attracted widespread attention due to its unique physical properties and potential in various scientific and technological fields. Due to the limitations of current technology and material levels, achieving a macro-level light pressure-driven approach in the short term is unrealistic. A wide range of research areas for light-pressure driving are focused on the micro level and suitable light-pressure materials. Under the current theoretical framework, a light pressure-driven spacecraft with suitable light sail materials is a highly competitive alternative for interstellar navigation. This article mainly simulates the process of light pressure-driven spacecraft accelerating to sub-light speed through laser irradiation on the Earth’s surface and decelerating the returning spacecraft. The article comprehensively considered factors such as laser frequency, sail size, and spacecraft mass during the simulation process and provided simulation results under appropriate conditions. Due to the significant relativistic effect of this process, this paper also considered the red shift and blue shift effects of relativistic light in the simulation process.

Image Segmentation Solutions for Improved Non-Cooperative Target Recognition

The number of failed satellites in space is increasing, and they need to be fueled through space docking to extend their life or clean them out of orbit. Visual measurement is widely used in the docking session because of its real-time performance and economy, but the collected images will have background interference, which directly leads to the degradation of the accuracy of visual measurement. Reduce the difficulty of subsequent image processing by solving these problems. For the non-cooperative target of the star-arrow docking ring and the solar sail panel, which are two significant targets, this paper is based on target detection, according to the image difference, binarization, morphological operations and other methods to complete the accurate segmentation of the two targets, which can be more accurately complete the target detection, and the image segmentation effect is obvious. The target image obtained by image segmentation does not contain background interference, which is convenient for feature extraction and matching of the image.

Design concepts and control algorithm to minimize the control effort for earth-orbit-raising solar sails

This paper presents novel design concepts and a robust sliding mode control (RSMC) algorithm for a solar sail optimized for an Earth-orbit-raising demonstration mission. The design of the solar sail is focused on minimizing mission difficulty and control effort during the Earth-orbit-rising mission. To this end, a gravity-stabilized long boom and one-sided black-coating film are introduced in the solar sail system, and a reaction wheel is used as a control torque actuator. The strategic combination of these components modifies the attitude control task from 90° back-and-forth pitch motion control for maintaining the proper attitude for receiving solar radiation pressure (SRP) to that of stabilizing the sail attitude perturbed from gravity-stabilized equilibrium. This simplification of the control task can minimize the mission difficulty and control input energy because attitude control is required only for small deviations from the attitude equilibrium, while the one-sided black-coated film with a reflective surface on the opposite side ensures that SRP propulsion effectively pushes the sail toward the orbit-rising direction. Thus, the control torque of the reaction wheel size can be reduced. To validate the Earth-orbit-raising mission performance, a quaternion-based RSMC approach is established for the six degree-of-freedom dynamic model. The simulation results confirm that the proposed solar sail system can stabilize its attitude with minimal control torque energy of the reaction wheels during Earth-orbit-raising missions.

Characterization of a Solar Sail Membrane for Abaqus-Based Simulations

Photonic solar sails are a class of advanced propellantless propulsion systems that use thin, large, lightweight membranes to convert the momentum of light from the Sun into thrust for space navigation. The conceptually simple nature of such a fascinating propulsion system requires, however, advances in materials, packaging, deployment, and control of a very large space structure. In this context, the finite element method (FEM), implemented in a robust and flexible software such as the commercial software Abaqus, represents a fundamental instrument to progress with the practical study of this promising propulsion system concept. In particular, in a typical (medium-size) square solar sail design process, the FEM-based analyses are used to better understand fundamental aspects of structural design, such as, for example, membrane pre-tensioning, deformations induced by Solar Radiation Pressure (SRP), and the buckling of reinforcing booms. The aim of this study is to describe an effective procedure to model a classical square solar sail structure into a typical commercial software for finite element analysis, such as the well-known suite Abaqus. In particular, we compare various membrane pre-tensioning techniques (useful for increasing the membrane’s bending stiffness) and describe possible approaches to applying the SRP-induced load in a realistic way. Additionally, the flexibility of the structure under the solar sail loads and the criticality of section shape and boom size are taken into account, with particular regard to the problem of structural instability. In this context, performance and critical issues of different structural solutions are discussed and compared, allowing an improvement in the preliminary design phase of solar sails to be obtained.

Enhanced transfer performance of sun-facing diffractive sails in solar polar imager missions

A diffractive sail represents an advancement in solar sailing technology, capable of generating tangential radiation pressure force when oriented towards the sun. This unique property allows for varied radiation pressure distributions, making it a potential candidate for complex space missions. This paper delves into the transfer performance of the sun-facing diffractive solar sail in a solar polar imager mission.We establish both the radiation pressure force model and the time-optimal control problem specific to the sun-facing diffractive solar sail in interplanetary transfers. Applying an indirect method and a combined approach of parameter optimization with the direct method, we explore how different diffractive angles and acceleration capacities affect transfer times. This research offers insights to the design and fabrication of thin novel optical metamaterial films that efficiently diffract light at appropriate angles for potential solar sails in the solar polar imager mission. Compared with reflective sails, the diffractive sail demonstrates remarkable transfer efficiency and simplicity in attitude control, making it a more suitable choice in the solar polar imager mission.

Quasi-periodic orbits of small solar sails with time-varying attitude around Earth–Moon libration points

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.

Theoretical approach to circular solar sail deployment

A solar sail presents a flat low areal density membrane and is an example of propellant-less propulsion system for the future space exploration. To date, the study of sail membrane deployment strategies is of considerable importance. In this work we present a general theoretical approach to deployment of solar sail of circular shape. We consider a system of a circular membrane attached to a toroidal rim under a force uniformly distributed along the rim’s circumference. The stress and strain of the system required for the successful deployment and mechanical stability of the sail are considered in deployed static configuration. Three examples of the deployment force of different nature are presented: magnetic, electric, and the pressurized gas. We give limitations for the solar sail radius for each considered force.

Reinforcement learning-based attitude control for a barbell electric sail

The electric solar wind sail (E-sail) is a new propellant-free propulsion concept. The under-actuated and highly nonlinear features of E-sail systems pose a great challenge to their attitude controller design. Conventional control schemes may not be capable of dealing with this tough problem. To this end, a reinforcement learning (RL)-based control scheme, which can explore and obtain optimal policies in the absence of training datasets, is proposed for the attitude control of a barbell E-sail system. The barbell E-sail comprises two end satellites linked to an insulated confluence point through long and conductive tethers. The voltages of the two tethers can be individually modulated for attitude control. The system attitude dynamics is described using a nonsingular formulation. The control scheme has a two-stage design. In the first stage, an RL controller based on the Proximal Policy Optimization (PPO) algorithm is used to obtain an RL control strategy, which is emulated and updated by neural networks. In the second stage, the attitude feedback control is accomplished with low computation and energy consumption and fast convergence speed by performing a real-time mapping from the system state to the control output using the updated control strategy. Finally, the simulation results demonstrate that the proposed RL-based control scheme can effectively adjust the E-sail to the design attitude by regulating the tether voltage difference. The comparisons with the NMPC scheme also indicate that the developed control scheme can significantly reduce the computation time with control accuracy maintained.

Assessment of combined passive cooling strategies for improving outdoor thermal comfort in a school courtyard

Both artificial shading and evaporative cooling have proven to be effective strategies for improve outdoor thermal comfort. However, their combined effect on microclimates or thermal sensations has rarely been investigated, hindering our understanding of the interactions among cooling strategies. In this study, we tested the performance of sun sails with different coverage ratios, mist-spray systems with different nozzle arrangements, and a combination of these two strategies for cooling a kindergarten courtyard using validated ENVI-met models. Among the strategies, we found that the shade + mist strategy is the most effective and can reduce the physiological equivalent temperature (PET) by up to 14.43 °C and heat stress levels by 2–3 categories in originally exposed areas. This was followed by the sun sail shading strategy. The mist-spray system had a relatively weak cooling effect. The cooling effects of sun sails increased with coverage ratios and mounting heights, whereas the spatial cooling distribution of mist spraying was mainly determined by wind rather than by nozzle arrangements. In addition, we found that shading can enhance the cooling effect of mist spraying in terms of air temperature, but reducing its cooling effect in terms of the mean radiant temperature. Our results highlight a great potential of comprehensively using multiple strategies to improve outdoor thermal comfort, and provide a design basis for enhancing thermal comfort in similar school courtyards in Hunan Province in China.