Solar sailing enables Earth-bound missions such as Active Debris Removal and satellite servicing. Yet, Low Earth Orbit orbital rendezvous remains unaddressed for solar sails. This maneuver presents significant challenges due to the sail's asymmetric control envelope, eclipse periods, and Earth's oblateness. To bridge this gap, this paper proposes a three-stage control architecture to achieve end-to-end orbital rendezvous by merging two Lyapunov feedback control laws: the Solar Sail Q-Law and the Ion-Engine Rendezvous Q-Law. To prevent algorithmic stagnation due to J₂-induced oscillations, averaged orbital elements are used to match the target's orbit shape and orientation in stage 1 (orbit matching) and achieve phase synchronization in stage 2 (phase matching). Precise rendezvous is handled using osculating elements in stage 3. While the complete architecture is developed, the performance of stage 2 is evaluated in Sun-Synchronous Orbits ranging from sunlight perpendicular to the orbit (Dawn-Dusk) to in-plane illumination (Noon-Midnight). Results demonstrate that Time-of-Flight bifurcates based on initial geometry. When natural orbital drift assists phase matching (favorable geometries), the sail achieves transfer times comparable to ion engines with equivalent thrust. When the sail opposes natural drift (unfavorable regimes), asymmetric control induces Time-of-Flight  penalties. Ultimately, phase matching is highly dependent on the solar geometry and initial phase offset. ... Read more

Solar sails navigate the cosmos pushed by sunlight, like sailboats driven by the wind. Close to our planet, however, additional sources of acceleration affect sailcraft dynamics.
This dissertation investigates these dynamics, their modeling, and impact on solar-sail maneuverability, revealing the limits and potential of Earth-bound solar sailing. ... Read more

Solar sailing is a propellant-free propulsion method, leveraging the momentum of Sun-emitted photons to generate thrust. In Earth orbit, the small and constrained magnitude of the solar-sail thrust with respect to the planetary gravity
implies the need for many revolutions to accomplish an orbital transfer. Solving the resulting optimization problem requires algorithms capable of handling very large sets of decision variables. This thesis focuses on the development of a Differential Dynamic
Programming (DDP) optimization algorithm, introducing adaptive parameter tuning and novel methodologies to tackle constrained and variable-duration problems. The DDP solver is characterized (in terms of hyper-parameter sensitivity and convergence properties)
and validated against a state-of-the-art direct optimization method. The devised algorithm is applied to time-optimal Earth-centered solar-sail transfers at GEO and LEO altitudes, successfully optimizing transfer durations of up to 1000 revolutions: solutions
display distinct acceleration and drift phases, apogee reversals to optimize orbit circularization, and altitude-dependent requirements on attitude control. A variable-duration transfer problem is solved by initializing DDP using a regression performed on
the previously optimized solutions. ... Read more

Given the potential of solar sails for applications around Earth, this paper investigates their performance in executing collision avoidance maneuvers. An extensive set of conjunctions (e.g., varying orbital regimes, sail control authorities, and collision geometries) is built. An "ideal" and a "real" case are examined, with the latter accounting for greater uncertainties (modeled via a covariance-mapping algorithm) and stricter collision probability requirements. The optimal control problem is derived and solved through direct collocation, seeking time optimality while constraining the probability. For all scenarios, maneuvers are completed within the one-day threshold, proving solar sails fit the current operational framework. Key findings are: 1) Better debris state knowledge (and later warnings) reduce maneuver time; 2) Higher altitudes increase the maneuver time, while greater sail control authority decreases it; 3) Eclipses influence results; 4) The Earth-Sun configuration only weakly affects the maneuver time; and 5) In-plane control is always non-zero. The locally optimal steering laws to change the semi-major axis and eccentricity best approximate the optimized maneuvers: especially for longer maneuver times, these straightforward laws comply with collision probability requirements. ... Read more

This paper develops an indirect optimization framework for planetocentric circular-to-circular solar-sail transfers using Pontryagin’s Maximum Principle. The formulation is general and applicable to any planet, with numerical results presented for Earth-centered transfers. The optimal control problem is reduced to a two-point boundary value problem solved via single-shooting. Assuming an ideal sail, planar motion, and point-mass gravity (neglecting eclipses and third-body effects), the study yields three main findings. First, transfer performance, measured as final-radius gain for a given transfer duration, strongly depends on the “start-phase” (timing of departure relative to the Sun’s apparent motion). Optimal performance occurs when the Sun-line is parallel to the projection of the orbital angular momentum onto the ecliptic at transfer midpoint, whereas worst performance arises when it is perpendicular. This phasing effect dominates high-inclination transfers and becomes negligible at $\boldsymbol{0^\circ}$ inclination due to constant illumination. Second, dimensional analysis collapses the parameter space into three independent dimensionless groups. Numerical exploration reveals robust power-law scaling of transfer performance with these groups, enabling accurate extrapolation of results across sail designs and initial altitudes from a single benchmark optimization. Third, detailed investigation of the single-shooting solver shows wide convergence basins and smooth solution dependence on orbital parameters, sail characteristics, and transfer duration. Convergence is notably easier for longer transfers and higher ecliptic inclinations, whereas low-inclination, short-duration cases remain the most challenging. The proposed indirect optimization method is therefore demonstrated to be robust, efficient, and suitable for systematic performance mapping of planetocentric solar-sail orbit raising. ... Read more

Planet-centred solar sailing offers a propellantless way of sustaining non-Keplerian motion for Earth-centred missions. For preliminary mission design and broad trade-space exploration, rapid yet accurate trajectory propagation tools are required. This work evaluates the performance of the Stark model, an analytical formulation that represents the dynamics as two-body motion subject to a uniform perturbing acceleration, applied to controlled solar-sail trajectories and benchmarked against classical numerical integration. Two control strategies for the sail are considered: (i) constant cone-angle laws, for which the Stark solution enables direct state evaluation, and (ii) time-varying locally optimal steering laws designed to target individual Keplerian elements. Performance is assessed in terms of positional accuracy and computational cost over representative one-day propagations. For constant control laws, accuracy is shown to improve with increasing perturbation magnitude, corresponding to larger sail lightness numbers and smaller cone angles. Sensitivity analyses reveal that smaller semi-major axes and larger eccentricities lead to faster dynamical regimes, resulting in increased position error and higher computational cost. For time-varying control laws, the Stark model’s performance depends strongly on the smoothness of the control law: smooth profiles (semi-major axis-, eccentricity-, and argument of periapsis-raising) yield broader regions of superiority in the accuracy-cost trade space compared to numerical integration, whereas abrupt profiles (inclination- and right ascension of the ascending node-raising) significantly reduce these regions. Furthermore, larger lightness numbers diminish the model’s ability to capture rapid dynamics, owing to the restriction of fixed step sizes. Overall, the results demonstrate that the Stark model provides a computationally efficient alternative for preliminary planet-centred solar-sail trajectory design, with advantages over classical numerical integration methods in specific regions of the accuracy-cost trade-off space, particularly for smooth control regimes. ... Read more

The rapid growth in the population of objects orbiting the Earth has led to increased congestion and collision risk. Solar-sail missions have been proposed as a means of debris removal by harnessing the perpetual force from sunlight to perform maneuvers; however, their capability to avoid collisions under the combined effects of solar radiation pressure and atmospheric drag remains to be investigated.

To address this gap, a framework was developed to simulate conjunctions between a sail and debris using representative uncertainties to compute collision risk. Analytical and numerical locally-optimal control laws were applied to steer the sail away from conjunctions and minimize maneuver durations while safely reducing the collision risk. The results revealed patterns in the applicability of specific control laws, with maneuver durations ranging from minutes to hours and showing strong dependence on orbital, physical, and conjunction parameters. ... Read more

Solar-sailing is a promising propellant-free propulsion method leveraging the momentum of photons to generate a thrust force, making them attractive for long-term missions both in Earth-bound and interplanetary space. In Earth orbit, solar-sails have been envisioned for space debris removal missions aiming to de-orbit multiple defunct satellites. However, their large sail area make them vulnerable to hypervelocity impacts with debris, potentially causing loss of attitude control. Therefore, this thesis presents a study of the long-term effects of tumbling on a sail's orbit and of the capability of a modern vane attitude control system to time-optimally stabilise the attitude motion. The tumbling dynamics result in an orbital eccentricity growth which is independent of the tumbling rate, potentially leading to a re-entry of the sail. The vane system is capable of detumbling rotational velocities up to 26 deg/s. For rotational velocities up to 8 deg/s, this system is capable of detumbling the sailcraft at a linear rate of 2 deg/s per day. For larger rotational velocities, the duration of the detumbling manoeuvre grows non-linearly. These results are considered for the specific case study of hypervelocity impacts and the sensitivity of the results to the sail reflectance model, the orbital regime, and the number of degrees of freedom of the vanes is assessed. ... Read more

The escalating problem of space debris necessitates effective solutions, such as active debris removal, to ensure sustainable orbital environments. Solar sails, with their nearly unlimited ΔV budget, present a promising, propellant-free method for targeting and potentially removing debris. However, the unique dynamics of solar sails prevent them from maintaining fixed positions relative to a target. This research explores the use of hold trajectories as alternatives to static hold points during far-range rendezvous operations. Using InTrance, a trajectory optimisation tool based on neuroevolution, the study assesses how operational constraints impact hold trajectories and the viability of preliminary homing trajectories. Results indicate that hold trajectories allow safe, extended solar sail operations close to debris, supporting sustained observation and monitoring efforts for debris management. ... Read more

Solar sailing is a promising propellantless propulsion method that employs large reflective surfaces to harness solar radiation pressure for spacecraft propulsion. Despite the fact that several solar-sail near-Earth missions will launch in the coming years, there is notable lack of published studies on the uncertainties associated with missions of this kind. This thesis addresses this gap in knowledge by quantifying uncertainties related to the solar sail's optical coefficients, structural deformations, and attitude profiles. Through two uncertainty propagation methods, namely Monte Carlo simulations and the Gauss von Mises method, the study reveals the significant impact of the optical coefficient uncertainties on mission performance. The results indicate a worst-case 3-sigma uncertainty of 8.1% in altitude gain and 16.5% uncertainty in inclination gain for the NEA Scout solar sail model. Specularity coefficient uncertainty emerges as the primary driver of performance uncertainty among the analyzed optical coefficients. Structural deformation, on the other hand, exerts minimal impact. Uncertainty in the attitude profile is modelled through Ornstein-Uhlenbeck processes and is found to impact mean mission performance as well as introduce performance uncertainty. Overall, this work demonstrates the critical importance of characterizing uncertainties and provides insights crucial for mission planning and decision-making. ... Read more

The first mission proposals to visit the Alpha Centauri system use photon-sail acceleration as a mode of propulsion to reach this stellar system closest to our own Solar System. To prepare for a future mission, the photon-sail dynamics in the system is investigated. Planar Lyapunov orbits around the colinear classical Lagrange points are designed to explore the Alpha Centauri system. This has been done before in other systems like the Earth-moon and Sun-Earth systems, but not yet in an elliptical binary star system. Starting with an initial guess in the circular restricted three-body problem without photon-sail acceleration, a Multiple Shooting Differential Correction (MSDC) algorithm changes the trajectory to a periodic orbit. A continuation method increases the eccentricity to match e = 0.5208, which is the eccentricity of the inner binary system of Alpha Centauri. The lightness number of the photon sail is increased to add photon-sail acceleration to the model up to a defined maximum of ?ZNe = 2. A set of five constant steering laws is chosen to investigate its effect. Next to that, the moment at which the periodic orbit starts in terms of the true anomaly is varied as well. This results in a set of 40 families of periodic orbits with increasing lightness numbers. Depending on the orientation, the augmented Lyapunov orbit either shrinks into smaller orbits or expands into larger orbits when increasing the lightness number. If the orbit shrinks, it can either converge into an artificial equilibrium point or the photon-radiation pressure on the sail can become minimal. In that case, the Lyapunov orbit becomes (almost) independent on the lightness number and reaches ?ZNe = 2. If the orbit expands, the maximum velocity will eventually go to infinity. At this vertical asymptote, the maximum lightness number is found. The initial true anomaly of Alpha Centauri 0 has a great effect on the Lyapunov orbits around L2 and L3 in the classical ER3BP. For 0 = 0, the orbit either converges to an AEP or the maximum velocity goes to infinity. For 0 = , a few orientations can reach ?ZNe = 2. To further explore Alpha Centauri, an adaptive differential evolution algorithm is used to design trajectories between the Lyapunov orbits. The performance of the algorithm is expressed as the Euclidean difference between the states at the end of the departure leg and the beginning of the arrival leg. Three different lightness number of ? = 0.1, 0.5 and 2 are used for these trajectories. With a lightness number of 0.1, the dimensionless Euclidean error is in the range of 1E-1 to 1E-3, depending on the Lyapunov orbits. With this lightness number, the stars are also used as a gravity assist. For larger lightness numbers, the Euclidean error becomes negligible in the range 1E-7. With a lightness number of 2, the time of flight during the trajectory is significantly lower. In future research, this can be further decreased using an MSDC algorithm. ... Read more

This work investigates the possibility of setting up an Earth-asteroid cycler to asteroid 2001AE2 using solar sail technology. An ideal solar sail model with near-future technology levels (𝛽 = 0.05) is implemented alongside the circular restricted three-body problem, two-body problem and the elliptic Hill problem. The spacecraft cycles between the Sun-Earth 𝐿2 point (SE − L2) and the Sun-asteroid 𝐿1 point (Sa − L1). From these equilibrium points, the spacecraft state vector is propagated forwards and backwards with a constant sail attitude to generate solar-sail assisted invariant manifolds. Initial guess trajectories for the outbound and inbound sections of the cycle are generated with a genetic algorithm by searching for optimal sail attitudes for the different dynamical models and departure, connection and arrival times. These initial guess trajectoryies are used to seed the optimization software PSOPT. This pseudospectral collocation method using Legendre-Chebyshev polynomials transforms the infinite dimensional control problem into a finite dimensional non-linear programming problem. This way a continuous control profile can be found that justifies the dynamical models and results in a time-optimal trajectory. The resulting cycler is designed to have a cycle time of 11.04 years, with an outbound trajectory departing from SE − L2 on 01 − 03 − 2036 and arriving at Sa − L1 on 02 − 04 − 2039 and an inbound trajectory departing from Sa − L1 on 04 − 08 − 2043 and arriving back at SE − L2 on 31 − 03 − 2046. This results in dwelling times at SE − L2 of 351 days (0.95y) and at Sa − L1 of 1585 days (4.34y). The trajectories are assumed time-optimal given the assumptions made in the work, but require further refining for non-ideal properties of the solar sail and other higher fidelity models. ... Read more

Now that a rocky planet is confirmed to orbit in the habitable zone of our closest stellar neighbor Proxima Centauri, the interest in visiting that system is growing; especially since Breakthrough Starshot proposed a fly-through mission of the Alpha Centauri system by sending a swarm of laser-driven photon sails. While many engineering problems still need to be solved for such a mission to succeed, research has shown that futuristic, theoretical photon-sail configurations can reach the Alpha Centauri system within 75-80 years while also getting captured in a bound orbit about one of the binary stars. This paper investigates trajectories from the binary star system towards planet Proxima b. A mission to Proxima b is scientifically grounded since measurements or pictures could help us better comprehend the evolution of rocky planets and potential life-formation in our Universe. The classical Lagrange points in the binary system (AC-A/AC-B) and the system Proxima Centauri-Proxima b (AC-C/Proxima b) are used to find possible trajectories towards Proxima b. The transfer is divided into a departure phase from AC-A/AC-B and an arrival phase to AC-C/Proxima b. Heteroclinic connections are then exploited using a patched restricted three-body problem method to connect the two phases. A grid search is applied on the optimization parameters to explore the design space, after which a genetic algorithm is applied to further optimize the link, focusing on minimization of the position, velocity, and time error at linkage. Futuristic sail configurations are used, including double-sided reflective sails and lightness numbers up to ß = 1779. The design space exploration shows that a double-sided sail provides little improvement over a one-sided sail, mainly due to the constant sail attitude along the trajectories. Results from the genetic algorithm show that a transfer from the L2-point in the AC-A/AC-B system to the L1-point in the AC-C/Proxima b can be accomplished with a transfer time of 235 years for the one-sided graphene-based sail with a surface of 315x315 m^2 carrying a payload of 10 grams. A transfer from the L2-point in the AC-A/AC-B system to the L3-point in the AC-C/Proxima b, with a smaller one-sided graphene-based sail (75x75 m^2, carrying a payload of 10 grams), results in a transfer time of 1025 years. For both sail configurations, the position error at linkage is kept below 1% of the total travel distance, the velocity error below 1% of the velocity at linkage, and the time error below 1% of the total transfer time. ... Read more

Recent studies have shown the feasibility of differential dynamic programming (DDP) in optimizing Earth-centered solar-sail trajectories. In order to further demonstrate the ability of DDP in the optimization of solar-sail trajectories, this work investigates the performance of DDP for optimizing interplanetary solar-sail trajectories. The selected dynamical framework is based on the two-body problem, augmented with an ideal solar-sail force model. A superior numerical performance is obtained for the optimization algorithm by propagating the state in modified equinoctial elements and applying a Sundman transformation to change the independent variable from time to the true anomaly. The developed algorithm finds similar or more optimal solutions than locally optimal steering laws for the maximization of different orbital elements. In addition, constrained time-optimal Earth-Mars orbital transfers are investigated for different sail performance levels. The DDP algorithm is proven to be efficient and robust for different optimization settings and initial guesses for solar-sail trajectory optimization in the interplanetary regime. ... Read more

Solar sailing is a flight-proven low-thrust propulsion technology with strong potential for innovative scientific missions. The heliogyro is promising sailcraft design that utilizes a set of long slender blades which are deployed and flattened by spin-induced tension and whose orientations can be individually controlled. The main advantages of such a design are the easier stowage and deployment, and potentially lower structural mass. The heliogyro’s translational and rotational motions are strongly coupled, with non-trivial relationships between the control inputs and the forces and moments produced by the sail. The purpose of this research is to investigate, for the first time, the coupled roto-translational motion of the heliogyro. Two dynamical models of the heliogyro motion are developed and applied to design Earth-to-Mars stopover cycler trajectories. The resulting heliogyro trajectories are then compared to those of a traditional fixed-area and flat sail-system design demonstrating potential advantages of the heliogyro. ... Read more

This paper investigates the use of solar sailing propulsion to visit as many co-orbital near-Earth asteroids (NEAs) as possible, within a fixed time-frame. This research builds on previous publications, which have shown solar sailing to be a suitable propulsion method to visit NEAs. The dynamics of this problem are modelled within the Solar Sail Augmented Circular Restricted Three-Body Problem (CR3BPS), and assume a near-term solar sailing technology level. A sequence generation algorithm is developed which generates trajectories to visit multiple co-orbital NEAs beginning at either the artificial co-linear equilibrium point SL1 or SL2. This algorithm develops trajectories with fixed controls to transfer between target asteroids, using Monte Carlo simulations to propagate a wide range of random combinations of settings before selecting those that perform the best. It is shown that the tuning performed within this research can generate a trajectory that enables 18 asteroid fly-bys within the selected nominal mission lifetime of ten years. Following this sequence generation, the first fly-by of the trajectory is optimised as proof of concept that each leg of the trajectory can be optimised for fly-by distance and velocity. An optimal control problem is developed, which is then implemented and solved using direct pseudospectral methods. The solution to this optimal control problem reduces the fly-by distance by 99.95 %, down to 158.73 km, while reducing the fly-by velocity by 9.68 % to 4.33 km/s. ... Read more

Operating spacecraft in a perturbed environment of a binary asteroid system is a challenging task. In light of the near-future exploration of the 65803 Didymos system by the Hera probe and the lack of study of orbital evolution of naturally-levitated regolith particles in this system, a method is here proposed to identify regions of high risk of collision with the levitated regolith grains. Regions of regolith levitation are identified, periodic orbits and regions of stable motion are computed through a grid search method, and the distance between trajectories leading from the off-surface levitation of the grains from the primary body and the trajectories of bounded motion is then assessed to determine the occurrence of temporary capture. A qualitative evaluation of the expected patterns of motion of regolith particles is presented together with a discussion of the key conclusions in the context of in situ operations planning for the Hera probe. ... Read more

Thousands of space debris objects remain in space after decades of spaceflight without sustainability regulations. Some of these objects de-orbit naturally, but not objects in the geostationary region for which active debris removal is needed. This thesis presents the case of geostationary debris removal using solar sailing, a propulsion method where no propellant is consumed, which allows for repeatable debris removal. A focus is given to find minimum-time trajectories between the geostationary region and a so-called ‘graveyard orbit’ and back. Optimisation using numerical methods is time-consuming, as these trajectories include hundreds of orbit revolutions. This work utilises analytical control methods instead to determine solar-sail control, specifically the ’Accessibility-and-deficit blending method’ based on locally optimal steering laws. Resulting mission times are compared with literature for validation, and a catalogue of mission time is found for a wide range of mission parameters, including additional thrust from a solar-electric propulsion engine. ... Read more

A planetary sunshade is a large, reflecting disk built to shield the Earth from a small fraction of solar irradiance, partly compensating global warming caused by greenhouse gas emissions. As a specific form of solar geoengineering, the sunshade is an emergency solution that would be implemented to prevent catastrophic climate change, while working towards the net-zero emission goal. In this paper, a dynamic sunshade is proposed. Such a system is capable of not only reducing the global mean surface temperature anomaly, but also minimizing regional climate changes by tailoring the sunshade's motion according to climate requirements. A sunshade orbiting in the vicinity of the Sun-Earth L1 point is able to reduce the global mean surface temperature from 16.39°C (scenario with 680 ppm of atmospheric CO2) to 14.13°C until equilibrium is reached. It also reduces the polar mean surface temperature by more than 2°C with respect to a scenario without sunshade. ... Read more

This paper investigates the use of solar-sail technology to increase the warning time for Coronal Mass Ejections (CMEs) heading towards Earth. In addition, this research will build upon the current understanding of using solar-sail dynamics with regards to CME detection by providing insights into the problem characteristics. The warning time is proportional to the distance from the Earth to the spacecraft detecting the CME: a current warning time of 30 to 60 minutes is achieved by satellites at or near the Sun-Earth L1 point. By considering the actual shape of a CME, the continuous solar-sail acceleration from the solar sail can be used to find a periodic trajectory that travels further upstream of the CME-axis, thereby increasing the warning time with respect to current missions. Finding a periodic solar-sail trajectory can be regarded as an optimal control problem, which requires a near-feasible initial guess trajectory. the latter is found by generating heteroclinic connections between artificial equilibrium points in the vicinity of the sub-L1 and sub-L5 point through the use of a grid search and a genetic algorithm. The optimal control problem is solved with a direct pseudospectral method, resulting in four representative trajectories, each having specific (dis)advantages. The performance impact due to (the uncertainty of) non-ideal sail properties, change in lightness number, and variation in CME size are investigated. Ultimately, the most optimal trajectory increases the average and maximum warning time by a factor 20 and 30 with respect to current missions at L1, respectively, with a 90\% probability that the spacecraft detects the CME. ... Read more