The aim of this paper is to evaluate the minimum flight time of a solar sail-based spacecraft towards Earth-synchronous (heliocentric) circular displaced orbits. These are special displaced non-Keplerian orbits characterized by a period of one year, which makes them suitable for the observation of Earth’s polar regions. The solar sail is modeled as a flat and purely reflective film with medium-low performance, that is, with a characteristic acceleration less than one millimeter per second squared. Starting from a circular parking orbit of radius equal to one astronomical unit, the optimal steering law is sought by considering the characteristic acceleration that is required for the maintenance of the target Earth-synchronous displaced orbit. The indirect approach used for the calculation of the optimal transfer trajectory allows the minimum flight time to be correlated with several Earth-synchronous displaced orbits, each one being characterized by given values of Earth- spacecraft distance and displacement over the ecliptic. The proposed mathematical model is validated by comparison with results available in the literature, in which a piecewise-constant steering law is used to find the optimal flight time for a transfer towards a one-year Type I non-Keplerian orbit.

This paper describes attitude dynamics properties of spinning, momentum-biased and zero-momentum solar sail spacecraft. The model called “Generalized Sail Dynamics Model” (GSDM) is introduced, which can deal with general and practical sail configurations, such as arbitrary optical property distribution, shape and surface wrinkles. Attitude stability criteria and other key dynamical characteristics are derived and compared by compact analytical equations induced from the GSDM. The newly derived zero-momentum sail dynamics is compared with that of spinning and momentum-biased sails. It is shown that the spinning and momentum sails have an advantage in terms of dynamical stability whereas zero-momentum sails are only statically stable. With this special property, angular momentum-stabilized sails can realize a sun-pointing stable attitude with almost zero-fuel, which are discussed with actual space flight experience of the JAXA’s two interplanetary missions, IKAROS and Hayabusa2.

To deal with the vibration problem of the solar power satellite (SPS), the distributed vibration control approach is investigated in this paper. Taking the Multi-Rotary joints SPS as the research objective, the control unit (CU) and the location relationship matrix are firstly defined for distributed controller design according to the configuration of SPS. The dynamic model of each CU is therefore established based on the finite element method. The dynamic model of the whole SPS structure is then developed using the CU models, and is updated along with on-orbit assembly. The distributed cooperative controller, using proportional and differential feedback and the interaction feedback among adjacent CUs, is proposed to suppress vibration. The close-loop distributed cooperative control system is then achieved by integrating all distributed controllers, and the asymptotic stability is proofed by the Lyapunov’s stability theorem. To verify the feasibility of the proposed control system, three numerical cases are finally presented. The results demonstrate that the distributed cooperative controllers can effectively suppress vibration during on-orbit assembly and operation after assembly, and the closed-loop system has good fault tolerance.

This paper investigates a problem of determining the optimal terminal-time or time-to-go of the ZEM/ZEV (Zero-Effort-Miss/Zero-Effort-Velocity) feedback guidance law for a variety of orbital intercept or rendezvous maneuvers. A generalized ZEM/ZEV guidance problem, whose objective is to minimize a combination of the control energy and terminal time, is examined. Algebraic equations whose solution provides the optimal terminal-time of the orbital intercept/rendezvous problems are derived based on the optimal control theory. The effectiveness of the proposed approach is demonstrated for various orbital maneuver problems.

Laser Interferometer Space Antenna (LISA) is a project to detect and measure gravitational waves. The project has three spacecraft flying in a formation of near equilateral triangle in a heliocentric orbit trailing Earth. Many sources of perturbations cause the configuration to deviate from the nominal. This paper studies the formation design problem for a LISA-like mission by considering ephemeris-based dynamics. This type of mission is well-known for addressing several strict mission requirements under the realistic dynamics. The problem is formulated as optimizing multiple mission performance indices. It is observed that some indices are correlated with each other, whereas some indices have different sensitivities with respect to the semi-major axis. Therefore, the problem is transformed into a two-step cascade single-objective optimization, in which the optimal solution of the first optimization problem is fed to the second optimization as initial value. In addition, the major perturbing celestial bodies are picked up to make a simplified but accurate enough dynamics to speed up the optimization. Numerical examples verify the analysis and show the effectiveness of the optimization procedure. The influences of mission lifetime and spatial scales on the optimal solutions are also presented.

In this paper, the performance of two distinct classes of feedback guidance algorithms is evaluated for a spacecraft rendezvous problem utilizing a continuous low-thrust propulsion system. They are the DG (Differential Geometric) and ZEM/ZEV (Zero-Effort-Miss/Zero- Effort-Velocity) feedback guidance algorithms. Even though these two guidance algorithms do not attempt to minimize the onboard fuel consumption or ΔV directly, the ΔV requirement is used as a measure of their orbital rendezvous performance for various initial conditions and a wide range of the rendezvous time (within less than one orbital period of the target vehicle). For the DG guidance, the effects of its guidance parameter and terminal time on the closed-loop performance are evaluated by numerical simulations. For the ZEM/ZEV guidance, its nearfuel- optimality is further demonstrated for a rapid, short-range orbital rendezvous, in comparison with the corresponding open-loop optimal solutions. Furthermore, the poor ΔV performance of the ZEM/ZEV guidance for a slow, long-range orbital rendezvous is remedied by simply adding an initial drift phase. The ZEM/ZEV feedback guidance algorithm and its appropriate variants are then shown to be a simple practical solution to a non-impulsive rendezvous problem, in comparison with the DG guidance as well as the open-loop optimal guidance.

The number of operational satellites and debris objects in the valuable geosynchronous ring has increased steadily over time such that active debris removal missions are necessary to ensure long-term stability. These objects are very large and tumbling, making any mission scenarios requiring physical contact very challenging. In the last 10 years, the concept of using an electrostatic tractor has been investigated extensively. With the electrostatic tractor concept, active charge emission is employed to simultaneously charge the tug or services vehicle, while aiming the charge exhaust onto the passive space debris object to charge it as well. The resulting electrostatic force has been explored to actuate this debris object to a disposal orbit or to detumble the object, all without physical contact. This paper provides a survey of the related research and reviews the charging concepts, the associated electrostatic force and torque modeling, and the feedback control developments, as well as the charge sensing research.

We investigate the equilibrium points and orbits around asteroid 1333 Cevenola by considering the full gravitational potential caused by the 3D irregular shape. The gravitational potential and effective potential of asteroid 1333 Cevenola are calculated. The zero-velocity curves for a massless particle orbiting in the gravitational environment have been discussed. The linearized dynamic equation, the characteristic equation, and the conserved quantity of the equilibria for the large-size-ratio binary asteroid system have been derived. It is found that there are totally five equilibrium points close to 1333 Cevenola. The topological cases of the outside equilibrium points have a staggered distribution. The simulation of orbits in the full gravitational potential caused by the 3D irregular shape of 1333 Cevenola shows that the moonlet’s orbit is more likely to be stable if the orbit inclination is small.

This paper describes a rapid method for validation and visualization of agile Earth-observation satellites scheduling. Benefited from the previous work, various algorithms are proposed for scheduling the observations of agile satellites. However, the satellite maneuvers are three- dimensional, this characteristic makes it difficult for the operation engineers to validate and interpret the scheduled solutions. They have to plot these attitude data to analyze different situations such as an observing phase or a slew maneuver. Finally, one tries to imagine the three-dimensional situations from many one-dimensional plots, which is time-consuming and susceptible to errors. Moreover, now it is low-efficiency to deal with the data about ephemeris, targets, etc., because different software platforms are required. In this research, a validation and visualization method is suggested to overcome this barrier. It is successful to integrate the Satellite Tool Kit ActiveX and the C# programming language. Based on the embedded scheme, all the interaction and assessment can be visualized. Practical techniques for modelling satellite objects, sensor objects, target objects and satellite attitudes are presented. Such a method has been applied for Chinese agile satellites project, and a software interface has been developed. The simulation results indicate that the proposed method is intuitive and efficient. Note that this method is general, and thus it can be applied to other Earth observation missions. Enough details are provided for interested readers to develop the software interface.

Conventional reachable domain (RD) problem with an admissible velocity increment, Δv, in an isotropic distribution, was extended to the general case with Δv in an anisotropic ellipsoidal distribution. Such an extension enables RD to describe the effect of initial velocity uncertainty because a Gaussian form of velocity uncertainty can be regarded as possible velocity deviations that are confined within an error ellipsoid. To specify RD in space, the boundary surface of RD, also known as the envelope, should be determined. In this study, the envelope is divided into two parts: inner and outer envelopes. Thus, the problem of solving the RD envelope is formulated into an optimization problem. The inner and outer reachable boundaries that are closest to and farthest away from the center of the Earth, respectively, were found in each direction. An optimal control policy is then formulated by using the necessary condition for an optimum; that is, the first-order derivative of the performance function with respect to the control variable becomes zero. Mathematical properties regarding the optimal control policy is discussed. Finally, an algorithm to solve the RD envelope is proposed. In general, the proposed algorithm does not require any iteration, and therefore benefits from quick computation. Numerical examples, including two coplanar cases and two 3D cases, are provided, which demonstrate that the proposed algorithm works efficiently.