Solar Sail Research Articles

Influence of curved thin-film device on deformation of a solar sail

A spinning solar sail IKAROS’s membrane is estimated to unexpectedly deform into an inverted pyramid shape due to thin-film devices with curvature, such as thin-film solar cells and steering devices on the membrane. It is important to investigate the deformation caused by the curved thin-film devices and predict the sail shape because the out-of-plane deformation greatly affects solar radiation pressure (SRP) and SRP torque. The purpose of this paper is to clarify the relationship between the global shape and orientation and position of curved thin-film devices and to evaluate SRP torque on the global shape using finite element analysis. The global shape is evaluated based on the out-of-plane displacement and the SRP torque. When the curved thin-film devices make the membrane shrink in the circumferential, diagonal, and radial direction, the sail deforms into a pyramid shape, an inverted pyramid one, and a saddle one, respectively. The saddle shape is more desirable for solar sails than the inverted pyramid shape and the pyramid one from the viewpoint of shape stability to SRP and control of SRP torque in the normal direction of the sail (windmill torque). The position of the thin-film device tends to increase the absolute value of windmill torque when it is biased circumferentially from the petal central axis. The suggested design principles for the arrangement of thin-film devices is that the curved thin-film devices should be directed so that the sail shrinks in the radial direction in order to deform the sail into a saddle shape with high shape stability, and the position of the thin-film devices should be biased in the circumferential direction paying attention to the absolute value of windmill torque to determine the direction of windmill torque.

Structural dynamic responses of a stripped solar sail subjected to solar radiation pressure

The stripped solar sail whose membrane is divided into separate narrow membrane strips is believed to have the best structural efficiency. In this paper, the stripped solar sail structure is regarded as an assembly made by connecting a number of boom-strip components in sequence. Considering the coupling effects between booms and membrane strips, an exact and semi-analytical method to calculate structural dynamic responses of the stripped solar sail subjected to solar radiation pressure is established. The case study of a 100 m stripped solar sail shows that the stripped architecture helps to reduce the static deflections and amplitudes of the steady-state dynamic response. Larger prestress of the membrane strips will decrease stiffness of the sail and increase amplitudes of the steady-state dynamic response. Increasing thickness of the boom will benefit to stability of the sail and reduce the resonant amplitudes. This proposed semi-analytical method provides an efficient analysis tool for structure design and attitude control of the stripped solar sail.

Electric sail static structural analysis with finite element approach

The propulsive characteristics of an Electric Solar Wind Sail are usually evaluated using a simplified model in which all the sail tethers are coplanar and form a sort of rigid disk. However, the three-dimensional arrangement of the tethers is fundamental information in the study of the spacecraft performance, and must be accounted for in refined mission analyses. In this paper, a Finite Element approach is chosen to estimate the deflected shape of the tethers, thus allowing important information on the structural response of the sail to be obtained. A parametric code is developed to perform a static analysis of an Electric Solar Wind Sail, whose requirements are given in terms of payload mass and spacecraft characteristic acceleration. In particular, the tether structural response is investigated using three different beam models, which are compared in terms of accuracy and computational efficiency. The analysis is specialized to the noteworthy case of a Sun-facing sail that is placed at a distance of one astronomical unit from the Sun. The numerical results, which concern a set of possible sail configurations, are compared with those taken from analytical models.

Solar sail optimal control with solar irradiance fluctuations

The optimization of a solar sail-based orbital transfer amounts to searching for the control law that minimizes the flight time. In this context, the optimal trajectory is usually determined assuming constant solar properties. However, the total solar irradiance undergoes both long-term (solar cycles) and short-term variations, and recent analyses have shown that this may have an impact on solar sailing for missions requiring an accurate thrust modulation. In this regard, the paper discusses a strategy to overcome such an issue by suitably adjusting the thrust vector in order to track a reference, optimal, transfer trajectory. In particular, the sail propulsive acceleration magnitude is modified by means of a set of electrochromic material panels, which change their optical properties on application of a suitable electric voltage. The proposed control law is validated with a set of numerical simulations that involve a classical Earth-Mars, orbit-to-orbit, heliocentric transfer.

Innovative Solar Sail Earth-Trailing Trajectories Enabling Sustainable Heliophysics Missions

The presented trajectory design study demonstrates that near-future solar sails can reach and maintain innovative science orbits about non-traditional Earth-trailing equilibrium points. The proposed configurations can enable long duration stereoscopic solar imaging while potentially alleviating telemetry requirements constraining current solar sail studies. Initial guesses for controlled periodic orbits about equilibrium points that trail the Sun-Earth line by 1.5∘-15∘ are constructed from a linearized solar sail circular restricted three body problem equations of motion. Orbits are then converged in the full nonlinear model using a high order direct collocation method. Transfers to Earth-trailing orbits are then constructed under the assumption that the solar sail is a secondary payload on a larger spacecraft en-route to the Sun-Earth L1 Lagrange point. Naturally occurring gravitational manifolds flowing towards the Lagrange point, as well as navigation data from previous Lagrange point missions, are used to generate a set of baseline trajectories for the primary spacecraft. End-to-end trajectory design and optimization is then carried out to construct time optimal solar sail transfers to each target science orbit from initial conditions constrained to lie on the carrier spacecraft’s Lagrange point trajectory. Additionally, trade studies are performed to assess how sail performance and Earth-trailing orbit selection affect transfer time of flight and instrument pointing accuracy. Results indicate that, based on current technological developments, near future solar sails are capable of station keeping about periodic Earth-trailing orbits while maintaining near-constant solar observation. Moreover, time of flights on the order of 1 year are observed for most combinations of sail performance and feasible initial conditions.

Improved Modal Damping Characterization for Small-Scale Heliogyro Blades

The heliogyro solar sail maneuvers by actuating high-aspect-ratio blades at their root with sinusoidal pitch profiles, producing spin-averaged forces and moments. The lightweight blade material has little inherent damping, requiring active control to attenuate blade vibration caused by maneuvering. Paradoxically, some amount of inherent damping at the blade’s higher-frequency modes is needed to add damping to the larger-magnitude low-frequency modes, and so the control design’s robustness depends on the accuracy of the blade damping model. Therefore, characterization of blade damping is critical for increasing the Technology Readiness Level for the heliogyro. This paper describes damping characterization tests performed on small-scale heliogyro blades hanging in a high-vacuum chamber, the closest analog possible for centrifugally loaded blades in space. Improvements to the measurements and a new modal damping algorithm, which the authors call the incremental and reduced frequency response function method, allowed separate flap and twist damping ratios to be calculated for the first three modes of these lightly damped blades to within ±2% error. This unprecedented precision enables definitive conclusions that the residual air damping is insignificant and that an assumption of a linear viscous torsional blade damping model is insufficient for the design of a robust proximal blade twist feedback controller.

Analysis of the solar sail deformation based on the point cloud method

The deformation of the solar-sail membrane is an important factor for causing inaccuracies in the solar-sail missions. This paper describes the solar sail under deformation by using a new modelling technique based on point cloud and triangular mesh generation. Two types of deformation, stemming from wrinkling and billowing, are modelled. The changes in the solar radiation pressure force and the moment caused by deformation are calculated and compared to the ideal non-deformed case. The heliocentric spiral trajectory and the orbital angular momentum reversal trajectory are taken as examples to quantify the influence of the deformation from an orbit point of view. Additionally, point cloud simplification, based on the normal vector and bounding box, is utilized to simplify the original deformed-sail model. It involves a reasonable reduction and renewal of the points in the model considering the variation of surface curvature. The simplification and its modelling accuracy are numerically investigated as well as computational efficiency.

Hybrid removal of end-of-life geosynchronous satellites using solar radiation pressure and impulsive thrusts

This paper proposes an analytical solution of removing end-of-life GEO satellites to the GEO graveyard region using solar radiation pressure (SRP) and impulsive thrusts. The dynamic model of a GEO satellite equipped with a solar sail is first built upon the magnitude comparisons of different accelerations exerted on the satellite. Then the dynamic system is constructed based on the Gauss’s Variation of Parameter (VOP) equations, and linearized along a nominal trajectory. Control angles of the sail and impulsive thrust vectors are generated using the proposed optimal hybrid disturbance-accommodation tracking maneuvers. Simulations indicate that, to remove a satellite in 360 days using only SRP with the proposed method, a minimal area-to-mass (A/M) ratio of 0.13 m2/kg is required. When the A/M ratio of spacecraft is smaller than the minimal value, impulsive thrusts are applied to assist the removal process. For a satellite with an A/M ratio of 0.1 m2/kg, a total impulse of 10.5 m/s is required.

Design considerations for relativistic laser sails*

Physics based methods have been developed to obtain accurate design estimates for the performance of relativistic interstellar laser sails and to identify technologies to mitigate losses inherent in the physics. The physical principles that are applied include those of the Special Relativity and Quantum Mechanics. Special Relativity is especially difficult to apply consistently. A method is summarized which makes the application of the Special Relativity straightforward, reducing the possibility of errors generated by neglecting important effects and by reducing mathematical difficulties. Once launched, the spacecraft design must remain fixed, and this dictates a design for the sail that must be able to respond to a broad range of possible events. Although physics-based losses cannot be eliminated, or even reduced, technologies can be applied at the source to help reduce their effect at the sail. These losses include: 1) the decrease in frequency, and hence energy, due to Doppler effects and 2) decreases in the intensity due to delays in the arrival of the photons. Including relativistic effects amplifies these losses at the velocities necessary for interstellar flight. When the sail reaches one fifth of the speed of light the losses become significant. Some losses can be mitigated while others cannot. For example, free electron lasers can be used to keep the frequency (and hence the energy of the photons) constant at the sail and a phased array can be expanded in area to narrow the beam width. Both can be used keep the momentum transferred constant at the sail. A phased array will also allow the beam direction to be controlled. Mathematical models and results will be presented for Doppler and intensity losses, beam width and direction control. A straightforward method to include effects of relativity has been applied to aid in performance estimates for relativistic interstellar laser sails. Although losses based on the physics remain the same their effects at the sail can be reduced significantly. Phased arrays will help with direction control, beam spreading, and intensity adjustments while free electron lasers can help mitigate Doppler effects. Sail structural dynamics, an important consideration not previously discussed, is introduced and methods to lessen the effects are discussed.

A simple control law for reducing the effective characteristic acceleration of a solar sail

The direction and magnitude of a solar sail acceleration are strongly related. For this reason, once the characteristic acceleration has been fixed, it is not possible to modulate the acceleration in a particular direction. In this work, a semi-analytical switching control law is derived, enabling a solar sail to emulate a smaller effective characteristic acceleration (without changes in geometry or optical properties); by periodically changing the pitch (cone) angle of the sail, in average over time, the acceleration produced by the sail matches exactly (in both direction and magnitude) that of a “smaller” sail. The range in which this is possible is determined, and the limitations on this range due to the size difference is computed. The method is validated on optimal Earth-Mars trajectories.

Coastal navigation by a solar sail

In this paper, we study relative motions of a light spacecraft equipped with a solar sail and tethered somehow to a heavy heliocentric orbital space station. One can say that such spacecraft realizes a kind of a coastal navigation. Formulating a model problem of the spacecraft motion, we state that if the sail can be oriented arbitrary then motions along a rectilinear tether are possible in both directions. Also, we present algorithm of the spacecraft relocation if it is joined with the station by a tether. This algorithm is based on the motion equations solutions that can be interpreted as perturbed motions of a simple pendulum.

Propulsion of Spacecraft to Relativistic Speeds Using Natural Astrophysical Sources

Abstract In this paper, we explore from a conceptual standpoint the possibility of using natural astrophysical sources to accelerate spacecraft to relativistic speeds. We focus on light sails and electric sails, which are reliant on momentum transfer from photons and protons, respectively, because these two classes of spacecraft are not required to carry fuel on board. The payload is assumed to be stationed near the astrophysical source, and the sail is subsequently unfolded and activated when the source is functional. By considering a number of astrophysical objects such as massive stars, microquasars, supernovae, pulsar wind nebulae, and active galactic nuclei, we show that terminal speeds approaching the speed of light might be realizable under idealized circumstances provided that sufficiently advanced sail materials and control techniques exist. We also investigate the constraints arising from the sail’s material properties, the voyage through the ambient source environment, and the passage through the interstellar medium. While all of these considerations pose significant challenges to spacecraft, our analysis indicates that they are not insurmountable in optimal conditions. Finally, we sketch the implications for carrying out future technosignature searches.

A family of linear stable equilibria in the Sun-Earth-Sail problem

The collinear libration point of the Sun-Earth Circular Restricted Three-Body Problem (CR3BP), $L_{3}$ is located opposite to the Earth with respect to the Sun. Whereas several space missions have been launched to the other two collinear equilibrium points, i.e., $L_{1}$ and $L_{2}$, the region around $L_{3}$ is so far unexploited essentially because of the severe communication limitations caused by Sun’s blocking location. By using an adequate size, location and attitude of a solar sail, the equilibrium point can be displaced from its original location to allow direct communication between the satellite and Earth. This paper presents several families of artificial equilibria located on the semi-space which is permanently opposite to Earth in relation to the Sun, but which allows direct communication with Earth. We present a family of such equilibria which are linearly stable and therefore very useful for space missions.

Artificial Collinear Lagrangian Point Maintenance With Electric Solar Wind Sail

This article discusses the maintenance of an $L_1$ -type artificial equilibrium point in the Sun–[Earth+Moon] circular restricted three-body problem by means of an electric solar wind sail. The reference configuration instability is compensated for with a feedback control law that adjusts the grid voltage as a function of the distance from the natural $L_1$ point. Two different control strategies are analyzed assuming the solar wind fluctuations to be modeled through a statistical approach.

Shape Memory Alloys for Aerospace, Recent Developments, and New Applications: A Short Review.

Shape memory alloys (SMAs) show a particular behavior that is the ability to recuperate the original shape while heating above specific critical temperatures (shape memory effect) or to withstand high deformations recoverable while unloading (pseudoelasticity). In many cases the SMAs play the actuator’s role. Starting from the origin of the shape memory effect, the mechanical properties of these alloys are illustrated. This paper presents a review of SMAs applications in the aerospace field with particular emphasis on morphing wings (experimental and modeling), tailoring of the orientation and inlet geometry of many propulsion system, variable geometry chevron for thrust and noise optimization, and more in general reduction of power consumption. Space applications are described too: to isolate the micro-vibrations, for low-shock release devices and self-deployable solar sails. Novel configurations and devices are highlighted too.

Solar sail deployment dynamics

The deployment dynamics of a solar sail consisting of four flexible booms and four membrane quadrants are studied. First, previous work on modelling only one membrane quadrant attached to two axially moving beams using time-varying quasi-modal expansion is extended to be applicable to the complete four-quadrant system. This is achieved via “lifting” the quadrant-level matrices into system-level forms by mapping the former’s constituent blocks to the correct partitions in the latter. After the quadrant-to-system conversion of the matrices, the equations of motion from the authors’ previous work readily apply to the complete system. Modal analysis is performed on a constant-length sail to validate the model’s basic foundations against the results obtained by finite element methods in the past literature. Deployment simulation results are presented, numerical parameter studies that show possibility of instability are performed using the system’s eigenvalues, and the stability results are discussed.

Enhancing Debris Tracking Missions in Geostationary Orbit with Advanced Solar Photon Thrusters

The advanced solar photon thruster (ASPT) concept was first proposed, developed, and analyzed by Dachwald and Wurm. Since its debut as an alternative to the flat solar sail (FSS) for interplanetary missions, it has been deemed inferior for its technical complexity, poor scalability, and time-optimal transfer trajectory performance. A novel application of the ASPT to the space object tracking and detection mission has revealed several key performance benefits illuminating small debris in geostationary orbit (GEO). A numerical procedure to optimize the ASPT average solar reflected intensity was developed, and the optimized performance results were compared with those of an FSS with an equal total mass. Results demonstrate that although the FSS offers slightly better acceleration performance, in agreement with previously published literature, the ASPT can provide larger reflected solar intensities over a wider range of applicable phase angles, resulting in a 200% detection improvement when tracking a 10-cm-diam object. In addition, the vehicle slewing requirements for the ASPT are reduced to just one revolution per day as the surface directing the sun light onto small objects is decoupled from the large solar collector pointing at the sun. More specifically, a ground observer could continually detect small debris when illuminated by the ASPT, whereas the FSS design allowed for its detection when solar phase angles were 60 deg or larger. The ASPT offers substantial performance benefits to the GEO small debris tracking mission when considering flight safety, anomaly characterization, local area clearing around high-value assets, and space object catalog maintenance activities.

An Interplanetary Mission Design of a Solar Sailing CubeSat to Mars

While solar sailing missions have been developed in the past, orbital solar sailing missions are limited in number. Increasing access to the solar system can be achieved by leveraging the potential of solar sailing spacecraft. A feasibility study is performed to analyse a controlled solar sailing mission to Mars using a CubeSat platform. The proposal to send a solar sailing CubeSat to Mars would be revolutionary in delivering small payloads to the red planet by harnessing the solar radiation pressure emitted from the Sun. By utilising solar sailing and aerocapture techniques in the mission design, the need for chemical propulsion for transfer and capture is greatly reduced, minimising launch mass and maximizing payload mass efficiency.In this study, investigations were carried out as mission analyses in the area of trajectory architecture and subsystem overview for systems available today and in the future. The influence and evolution of trajectories under gravitational and environmental conditions on Mars and the interplanetary transfer were scrutinised individually as relevant restricted dynamic systems. For a chosen insertion orbit, several feasible trajectories to Mars based on different solar sail systems were investigated, including optimised ballistic trajectories and the Sundiver transfer for solar sails. For the interplanetary trajectories, the planetary capture manoeuvre of the spacecraft to a serviceable orbit using aerobraking capture is evaluated. The final trajectory design features minimum-time optimisation for the interplanetary transfer of a solar sailing spacecraft from Earth to Mars. As the selected spacecraft platform is limited to low-thrust solar sailing propulsion, severe performance limitations apply to this mission. This work aims to highlight possible interplanetary trajectories for present and future small satellite platforms despite these limitations by using dynamical orbital simulation models.

Characteristics of ion beams generated in the interaction of ultra-short laser pulses with ultra-thin foils

Experiments investigating ion acceleration from laser-irradiated ultra-thin foils on the GEMINI laser facility at the Rutherford appleton laboratory indicate a transition to ‘light sail’ radiation pressure acceleration when using circularly polarised, high contrast laser pulses. This paper complements previously published results with additional data and modelling which provide information on the multispecies dynamics taking place during the acceleration, and provides an indication on expected scaling of these processes at higher laser intensities.

Simulation of evaporation and propulsion of small particles in a laser beam

The technique of numerical simulation of laser surface evaporation of small particles ranging in size from tens to several millimeters falling into the field of laser radiation is developed. The interaction of a laser beam with solid or liquid particles freely flying in a gas-dispersed stream is accompanied by heating and evaporation of the material, which occurs only from the irradiated part of the particle surface. The result is a reactive force created by the laser, which depends on the characteristics of the radiation and the physical properties of the particle material. The technique allows describing the pre-threshold, near-threshold and super-threshold modes of evaporation and is designed to calculate the light propulsion force due to the vapor recoil pressure arising from the irradiated part of the particle surface in the range of Mach numbers to unity. The Meshcherskii equation is used to simulate the reactive acceleration of particles. It is shown that, in the case of a pulsed laser effect, the theory is in good agreement with experimental data on reactive acceleration of aluminum, corundum, and graphite particles. A distinctive feature of the technique is the ability to calculate the gas dynamic parameters of steam and recoil pressure in a wide range of the power density of the absorbed laser radiation from 10 to 10,000 $$\hbox {GW}/\hbox {m}^{{2}}$$.