Understanding the nature of Dark Matter and Dark Energy is one of the most pressing issues in cosmology
and fundamental physics. The purpose of the DUNE (Dark UNiverse Explorer) mission is to study these two
cosmological components with high precision, using a space-based weak lensing survey as its primary science
driver. Weak lensing provides a measure of the distribution of dark matter in the universe and of the impact
of dark energy on the growth of structures. DUNE will also include a complementary supernovae survey to
measure the expansion history of the universe, thus giving independent additional constraints on dark energy.
The baseline concept consists of a 1.2m telescope with a 0.5 square degree optical CCD camera. It is designed
to be fast with reduced risks and costs, and to take advantage of the synergy between ground-based and space
observations. Stringent requirements for weak lensing systematics were shown to be achievable with the baseline
concept. This will allow DUNE to place strong constraints on cosmological parameters, including the equation
of state parameter of the dark energy and its evolution from redshift 0 to 1. DUNE is the subject of an ongoing
study led by the French Space Agency (CNES), and is being proposed for ESA's Cosmic Vision programme.
ESA's DARWIN mission is to accomplish the unprecedented challenge of finding Earth-like planets orbiting nearby stars. To tell apart the planet from its blinding 'sun', the system relies upon nulling interferometry: the light collected by six free-flying telescopes is recombined inside a central 'hub', in a way that the beams from the star are 'nulled', while those from the planet interfere constructively. The diameter (50 to 500m) of the free-flying interferometer is determined by the need for angular resolution. In contrast, the differences in optical pathlength between the incoming beams must be kept below 5 nm.
It is the purpose of the ongoing "Interferometer Constellation Control" Research & Development study for the European Space Agency (ESA) to propose a design and validate the performances for the GNC system adapted to such a high-precision formation-flying application. The requirements & detailed design of this GNC system are addressed first, including the close connection with the parallel ESA study called "High Precision Optical Metrology" used to verify the feasibility of the critical DARWIN optical metrology system. Then, the modelling & performance assessment of the GNC system is presented, together with the way forward to build a high precision coupled optical/GNC simulator.