Damiana Losa

A Spherical Coordinate Parametrization for an In-Orbit Bearings-Only Navigation Filter

In-orbit rendezvous is a key enabling technology for many space missions. Implementing it employing only bearing measurements would simplify the relative navigation hardware currently required, increasing robustness and reliability by reducing complexity, launch mass and cost. The problem of bearings-only navigation has been studied intensively by the Naval and Military communities. Several authors have proposed that a polar or spherical coordinate parametrization of the underlying dynamics produces a more robust navigation filter due to the inherent de-coupling of the observable and un-observable states. Nevertheless, the complexity of this problem increases significantly when the underlying dynamics follow those of relative orbital motion. This paper develops a spherical coordinate parametrization of the linearized relative orbital motion equations for elliptical orbits and uses an approximation of these equations for circular orbits to develop an Extended Kalman Filter (EKF) for bearings-only navigation. The resulting filter is compared to its equivalent based on the well known Hill Equations in cartesian coordinates via a Monte Carlo analysis for a given reference trajectory. Simulations show that a spherical coordinate based EKF can perform better than its cartesian coordinate counterpart in terms of long-term stability tracking of the reference trajectory, with little additional computational effort.

Bearings-Only Rendezvous with Enhanced Performance

Employing only bearing/angular measurements for navigation during the far to medium range rendezvous with a non-cooperative target has several advantages with respect to directly measuring the range using active sensors such as RADAR or LIDAR. Angular measurements can be acquired using simple sensors such as a single optical camera, significantly reducing the mass and power requirements. Nevertheless, several challenges arise form the lack of a direct range measurement, which renders the problem instantaneously unobservable. The execution of known maneuvers is thus necessary to introduce observability in the estimation problem, which results in the navigation performance being directly dependent on the trajectory followed. A few single-maneuver schemes have been proposed to enhance bearings-only navigation performance. Nonetheless, little research has been published on the use of on-line trajectory optimization methods accounting for observability on the complete rendezvous trajectory. This paper presents the non-linear simulation results of a Model Predictive Control architecture for rendezvous that simultaneously enhances bearings-only observability in order to improve navigation performance. A detailed simulation environment provided by Thales Alenia Space France is used to show that the proposed scheme based on linearized equations displays satisfactory performance in a higher fidelity non-linear environment, when observability is considered in the trajectory optimization.

Control of a Magnetic Capture Device for Autonomous In-orbit Rendezvous

Abstract Mission concepts proposed to return Mars soil samples to Earth involve a critical rendezvous phase with a passive sample container placed in Mars orbit by an ascent vehicle. An innovative magnetic capture device was recently proposed to increase the reliability and simplify capture operations. The present paper presents control aspects of this device. More specifically, the magnetic capture devices allows to damp rotation rates and to enforce a specific relative orientation of the sample container at a range of about 4 meters. The final contact is secured thanks to a additional, small, passive magnet. The linear stability and performance of the controller is analyzed, and non-linear simulations are presented.

Smart architecture for highly available, robust and autonomous satellite

Abstract European leader for satellite systems and at the forefront of orbital infrastructures, Thales Alenia Space is a joint venture between Thales (67%) and Finmeccanica (33%) and forms with Telespazio a Space Alliance. Thales Alenia Space is a worldwide reference in telecoms, radar and optical Earth observation, defense and security, navigation and science. Thales Alenia Space has 11 industrial sites in 4 European countries (France, Italy, Spain and Belgium) with over 7,200 employees worldwide. Satellite evolution and wish to design more autonomous mission imply an enhancement of satellite architecture to enable the smart control of spacecraft. New system architecture needs to be defined to permit the decision-taking, and special attention has to be paid to FDIR (Fault Detection, Isolation and Recovery) and the way action can be engaged. Nevertheless the constraints on architecture and related technique composing it, stay still invariant: robustness, high availability, industrially viable and cost efficient. This paper gives first some elements about a decisional architecture defined in joined work by Thales Alenia Space and CNES, then the current context of FDIR is briefly described and then a new FIDR strategy permitting smart decision is introduced, finally the way decision can be engaged on-board for the next generation of autonomous satellites is presented.