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With the rapid increase in the number of spacecraft in outer space, the unknown maneuvers of a spacecraft significantly increase the probability of a collision between neighborhoods. In order to guarantee the safety of an operational spacecraft, we need to estimate and predict the relative trajectories of a non-cooperative target in real time. Traditional filter routines are ineffective when the target spacecraft performs unknown continuous maneuvers. In this work, we focus on the development of relative estimators with enhanced robustness against unknown maneuvers. First, a variable state dimension estimator based on filter switching and covariance inflation is proposed to adaptively cope with a constant unknown maneuver. To strengthen the robustness in response to the time-varying maneuvers, a novel observer-enhanced Kalman filter is subsequently proposed by incorporating an observer into the filtering routines. Finally, the performance of the proposed estimators is evaluated with a series of numerical simulations, both the advantages and the disadvantages are analyzed using the simulation results.

This paper addresses issues relevant to thruster-aided deployment of spin-stabilized tethered formations in a circular orbit. The dynamics of the tethered formation are first established by treating the parent satellite as a finite-sized body with respect to its spinning motion. To achieve the minimum-power trajectories for formation deployment, the optimal deployment problem is analytically formulated using Pontryagin’s minimum principle. Physical constraints on tether tension, thrust amplitude, and libration angle are also considered. To handle nonlinearities, the problem is solved numerically using a direct method based on the Gauss pseudospectral approach, in which the optimal deployment profiles are obtained and all of the solutions are proven to be within a feasible range. Finally, based on a variety of simulations, the optimal solution’s sensitivity to certain parameters is also analyzed.

A spacecraft performing unknown maneuvers significantly increases the probability of a collision between spacecraft with neighboring orbits. Traditional orbit determination filters cannot robustly cope with unknown maneuvers. To track non-cooperative, unknowingly maneuvering spacecraft, a novel variable structure estimator is proposed based on the input compensation to a normal filter. We develop an observer to estimate the unknown maneuver and then analyze the estimated maneuver performance based on error propagation. Once the maneuver detector declares the occurrence of an unknown maneuver, the estimated maneuver is fed to an extended Kalman filter as compensation, which enables the estimator to work adaptively. Finally, a series of numerical simulations are carried out to demonstrate the effectiveness of the proposed variable structure estimator, and the estimation performances in the cases of constant and time-varying maneuvers are analyzed based on the simulation results.

On-orbit refueling technologies provide a new way to extend the lifespan of satellites that run out of propellant. During propellant transfer, the equivalent mass redistribution between the service...

This paper presents a novel constrained Kalman filter framework for autonomous orbit determination. By using Lagrangian multiplier techniques, the conserved terms of orbit motion are incorporated into the estimation routines to reconstruct the Kalman filter, and then the orthogonal and multipartial-norm-constrained Kalman filters are developed for the satellite in circular orbit and eccentric ones, respectively. Finally, scenarios of both circular and eccentric orbits with unknown measurement bias are simulated by using the proposed constrained Kalman filter; the simulation results show that the estimation accuracy is significantly improved after introducing the conservative terms as constraint.

This paper presents the deployment strategies for planar multi-tethered satellite formation that spins in orbit plane. By using Lagrange principles, the deployment dynamics, which treat the parent satellite as a finite sized rigid body, are established under gravity gradient perturbation. Comparing with the simplified dynamics that take the parent satellite as mass point, the model in this work enables the investigation on dynamical coupling between parent satellite and tethers. To achieve successful deployment, typical strategies are developed firstly with active gravity gradient compensation, both the tether deployment rate and parent satellite spinning profile are derived under specific motion constraints, after that, the deployment strategy capable of compensating the gravity gradient perturbation is also developed. For the fully deployed system, the minimum spinning rate that ensures the configuration stabilization is mathematically analyzed by employing Jacobi Integrator. Finally, series numerical simulations are performed to validate the proposed deployment strategies.