Feasible region and stability analysis for hovering around elongated asteroids with low thrust

This paper investigates properties of low-thrust hovering, including the feasible region and stability, in terms of the dynamical parameters for elongated asteroids. An approximate rotating mass dipole model, by which the description of the rotational gravitational field is reduced to two independent parameters, is employed to construct normalized dynamical equations. The boundaries of the feasible region are determined by contours representing the magnitude of the active control. The effects of a rotating gravitational field and maximal magnitude of the low thrust on the feasible hovering regions are analyzed with numerical results. The stability conditions are derived according to the forms of the eigenvalues of the linearized equation near the hovering position. The stable regions are then determined by a grid search and the effects of the relevant parameters are analyzed in a parametric way. The results show that a close hovering can be easier to realize near the middle of the asteroid than near the two ends in the sense of both required control magnitude and stability.

New applications of the H-reversal trajectory using solar sails

Advanced solar sailing has been an increasingly attractive propulsion system for highly non-Keplerian orbits.Three new applications of the orbital angular momentum reversal（H-reversal） trajectories using solar sails are presented：space observation,heliocentric orbit transfer and collision orbits with asteroids.A theoretical proof for the existence of double H-reversal trajectories（referred to as‘H2RTs’） is given,and the characteristics of the H2RTs are introduced before a discussion of the mission applications.A new family of H2RTs was obtained using a 3D dynamic model of the two-body frame.In a time-optimal control model,the minimum period H2RTs both inside and outside the ecliptic plane were examined using an ideal solar sail.Due to the quasi-heliostationary property at its two symmetrical aphelia,the H2RTs were deemed suitable for space observation.For the second application,the heliocentric transfer orbit was able to function as the time-optimal H-reversal trajectory,since its perihelion velocity is a circular or elliptic velocity.Such a transfer orbit can place the sailcraft into a clockwise orbit in the ecliptic plane,with a high inclination or displacement above or below the Sun.The third application of the H-reversal trajectory was simulated impacting an asteroid passing near Earth in a head-on collision.The collision point can be designed through selecting different perihelia or different launch windows.Sample orbits of each application were presented through numerical simulation.The results can serve as a reference for theoretical research and engineering design.

Asteroid body-fixed hovering using nonideal solar sails

The problem of body-fixed hovering over an asteroid using a compact form of nonideal solar sails with a controllable area is investigated. Nonlinear dynamic equations describing the hovering problem are constructed for a spherically symmet- ric asteroid. Numerical solutions of the feasible region for body-fixed hovering are obtained. Different sail models, including the cases of ideal, optical, parametric and solar photon thrust, on the feasible region is studied through numerical simulations. The influence of the asteroid spinning rate and the sail area-to-mass ratio on the feasi- ble region is discussed. The required orientations for the sail and their corresponding variable lightness numbers are given for different hovering radii to identify the feasible region of the body-fixed hovering. An attractive scenario for a mission is introduced to take advantage of solar sail hovering.