ESA's Darwin mission is devoted to direct detection and spectroscopic characterisation of Earth-like planets in the
thermal infrared domain by nulling interferometry in space. This technique requires deep and stable starlight rejection to
an efficiency around 106 over the whole spectral band. Darwin is a major target for Thales Alenia Space, and is
considered as a strategic part of its programme roadmap.
In this paper we present the main outcomes of the Darwin mission study conducted by Thales Alenia Space from Oct.
2005 to Jul. 2007. Studying this mission in depth, our proposed most promising configuration features spacecraft in non
planar arrangement (called Emma). It offers the best science return in terms of number of stars detected and sky
accessibility while staying compliant with mass and volume constraints of a single Ariane 5 launch. Our solution
dramatically alleviates engineering constraints thanks to a fully non deployable concept. As compared to the more
conventional planar arrangement (called Charles), Emma suppresses Single Point Failures and spurious flexible modes,
thus maximising both the system reliability and the stability of the dynamical environment. Emma is fully compatible
with either 3 or 4 collectors.
This paper describes a concept of a formation flyer for ASPICS (Association de Satellites Pour l'Imagerie et la Coronagraphie Solaire), a giant 100 m based, externally occulted coronagraph aimed at observing the inner corona (and the solar disk) in the visible and ultra-violet. The two-satellite formation approach, based on existing space systems, is composed of a Myriade micro-satellite supporting the occulter and a Proteus platform as the main system carrying the coronagraph and imager scientific instruments. Both spacecrafts are launched as a single composite and deployed once on orbit, preferably a 3-day orbit or at the L1 Lagrange point. The coronagraph satellite acts as the "master" and provides the main functions of the mission (data handling, communication, propulsion, Guidance Navigation and control) while the Myriade acts as the "slave". The control of the formation is performed in two steps: i) RF metrology for deployment and preliminary pointing, ii) classical optical attitude sensors and metrology based on diverging laser beams. This will insure the nominal requirement of a lateral positioning with an accuracy of 1 mm and a longitudinal positioning with an accuracy of 500 mm.
The 3-meter stroke `LAROCA' Delay Line (DL) was designed, built and tested in France in 1993, with full success in terms of performance and of length and loading scalability. The highly stringent stability requirements in delay line motion led to devise an original guiding and motorizing concept that affords outstanding displacement accuracy, minimizing lateral and, more importantly, longitudinal vibrations. LAROCA's architecture hinges on a two-stage concept: a high-precision upper carriage, for precision positioning, controlled for longitudinal vibration compensation by a high-bandwidth, hybrid analog/digital controller, and a less accurate lower carriage for global DL translation on a two-cylindrical-rail track using a classical position control system. Excellent interstage decoupling, using a contactless suspension, yields long-stroke capability together with the required stability of the high- precision stage. After a presentation of the LAROCA project requirements and an overview of the general architecture, this paper describes the overall servo-control subsystem. Finally some important results are presented.
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