Relative Orbital Elements Research Articles

An orbital design method for satellite formation flying

An orbital design method of the formation initialization based on the relative orbital element method is presented. It firstly constructed the relative motion equation of the satellite formation flying in terms of the leader and followers’ orbital elements. Then the equation was simplified when the orbit eccentricity of the leader satellite was small. And according to the satellites’ mission, a general design method for the relative trajectory was proposed. The advantage of this method is that one can get a very simple analytical formula of each follower satellite’s orbital elements when the orbital eccentricity of the leader satellite is zero. The simulation results show that the method is effective.

Useful relative motion description method for Perturbations analysis in satellite Formation flying

A set of parameters called relative orbital elements were defined to describe the relative motion of the satellites in the formation flying. With the help of these parameters, the effect of the perturbations on the relative orbit trajectory and geometric properties of satellite formation can be easily analyzed. First,the relative orbital elements are derived, and pointed out: if the eccentricity of the leading satellite is a small value, the relative orbit trajectory is determined by the intersection between an elliptic cylinder and a plane in the leading satellite orbit frame reference; and the parameters that describe the elliptic cylinder and the plane can be used to obtain the relative orbit trajectory and the relative orbital elements. Second, by analyzing the effects of gravitational perturbations on the relative orbit using the relative orbital elements,it is found that the propagation of a relative orbit consists of two parts: one is the drift of the elliptic cylinder; and the other is the rotation of the plane resulted from the rotation of the normal of the plane. Meanwhile, the analytic formulae for the drift and rotation rates of a relative trajectory under gravitational perturbations are presented. Finally, the relative orbit trajectory and the corresponding changes were analyzed with respect to the J2 perturbation.

Study on relative orbital configuration in satellite formation flying

In this paper, the relative orbital configurations of satellites in formation flying with non-perturbation and J2 perturbation are studied, and an orbital elements method is proposed to obtain the relative orbital configurations of satellites in formation. Firstly, under the condition of non-perturbation, we obtain many shapes of relative orbital configurations when the semi-major axes of satellites are equal. These shapes can be lines, ellipses or distorted closed curves. Secondly, on the basis of the analysis of J2 effect on relative orbital configurations, we find out that J2 effect can induce two kinds of changes of relative orbital configurations. They are distortion and drifting, respectively. In addition, when J2 perturbation is concerned, we also find that the semi-major axes of the leading and following satellites should not be the same exactly in order to decrease the J2 effect. The relationship of relative orbital elements and J2 effect is obtained through simulations. Finally, the minimum relation perturbation conditions are established in order to reduce the influence of the J2 effect. The results show that the minimum relation perturbation conditions can reduce the J2 effect significantly when the orbital element differences are small enough, and they can become rules for the design of satellite formation flying.

State Transition Matrix of Relative Motion for the Perturbed Noncircular Reference Orbit

A precise analytic solution that includes the effects of the reference orbit eccentricity and differential perturbations is needed for the relative motion of formation-flying satellites. As a result of the spherical Earthand circular reference orbit assumptions, Hill's equations, which have often been used for describing relative motion, are insufficient for the long-term prediction of the relative motion. A new approach, called the geometric method, is developed to obtain the state transition matrix for the relative motion that includes the effects caused by the reference orbit eccentricity and the differential gravitational perturbations. The geometric method uses the relationship between the relative states and differential orbital elements to obtain the state transition matrix instead of directly solving the complex relative motion differential equations. The state transition matrices are derived for both mean and osculating elements with the primary gravitational perturbation that results from the equatorial bulge term J 2 . Although the results are based on the J 2 effects, the approach can be extended easily to include other perturbing forces.

Comparison of two methods in satellite formation flying

Recently, the research of dynamics and control of the satellite formation flying has been attracting a great deal of attentions of the researchers. The theory of the research was mainly based on Clohessy-Wiltshire's (C-W's) equations, which describe the relative motion between two satellites. But according to some special examples and qualitative analysis, neither the initial parameters nor the period of the solution of C-W's equations accord with the actual situation, and the conservation of energy is no longer held. A new method developed from orbital element description of single satellite, named relative orbital element method (ROEM), was introduced. This new method, with clear physics conception and wide application range, overcomes the limitation of C-W's equation, and the periodic solution is a natural conclusion. The simplified equation of the relative motion is obtained when the eccentricity of the main satellite is small. Finally, the results of the two methods (C-W's equation and ROEM) are compared and the limitations of C-W's equations are pointed out and explained.

Dynamical behaviors and relative trajectories of the spacecraft formation flying

To describe the relative motion of spacecraft formation flying, this paper presents a method based on relative orbital elements, which is suitable to elliptical orbit with arbitrary eccentricity. The long time formation flying conditions are theoretically derived taken into account the relationship between relative motion and relative orbital elements. These conditions include that both the orbital periods of all participating spacecrafts should be the same and other relative orbital elements should be small enough. The expected relative distance of the spacecrafts would determine the magnitudes of such relative orbital elements. Theoretical analysis and numerical simulation results show that the spacecrafts with sufficient small relative orbital elements can keep long time formation flying without any active control when the orbital perturbations are not considered. The results also show that Hill's equation is only suitable for describing a short time formation flying.

Differential angle tracking for close geostationary satellites

For the determination of relative motion of two satellites located in close proximity in the geostationary orbit, a method of differential angle observation from a ground station is proposed. Observability of the relative orbital elements is proved, and the determination accuracy is analyzed on the basis of a linearized two-body orbital model. Experimental pseudodifferential angle observation indicates an accuracy of a few hundred meters for the determination of relative satellite position.