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We present the current design of the E-ELT M4 deformable mirror consolidated at the conclusion of the Preliminary Design activity. The most prominent features of this system are the SiC Reference Body now mounted to the positioner by a whiffle-tree and cell structure, actuators bricks, capacitive sensors layout and new cooling concept. All this allowed achieving the challenging stability requirements demanded to the M4U, as proved by analysis and test results measured on the Demonstration Prototype, which has been updated to implement the current design. The final design and construction contract is now on-going: Final Design Review is planned on mid 2017 and delivery to site by late 2022.

In this paper the problem of designing a robust controller with given structure for a plant describing a drag-free satellite is addressed. From recent experiences in drag-free control design we first derive an uncertain plant set representative of many drag-free missions with nonspherical test masses. The design plant is uncertain and a performance requirement is imposed on the absolute acceleration of the test mass along a measurement axis. The ν-gap metric is first used to derive a simplified uncertain design plant. Then the main performance requirement is broken down into requirements on the uncertain closed loop behavior of the simplified system. The fulfillment of this new set of requirements guarantees robust achievement of the overall system goal. Then optimal single-input-single- output controllers are designed that robustly achieve the desired level of performance. The method proposed allows one to properly account for the uncertainties in the system retaining the decentralized structure of the controller suggested by the peculiar features of the design plant. [ABSTRACT FROM AUTHOR]

We present a satellite path-planning technique able to make a set of identical spacecraft acquire a given configuration. The technique exploits a behavior-based approach to achieve an autonomous and distributed control over the relative geometry, making use of limited sensorial information. A desired velocity is defined for each satellite as a sum of different contributions coming from generic high-level behaviors. The behaviors are further defined by an inverse-dynamic calculation dubbed equilibrium shaping. We show that by considering only three different kinds of behavior it is possible to acquire a number of interesting formations, and we describe the theoretical framework needed to find the entire set. We find that by allowing a limited amount of communication the technique may be used also to form complex lattice structures. Several control feedbacks able to track the desired velocities are introduced and discussed. Our results suggest that sliding-mode control is particularly appropriate in connection with the developed technique. [ABSTRACT FROM AUTHOR]