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The NEAT (Nearby Earth Astrometric Telescope) mission is a proposition submitted to ESA for its 2010 call for M-size mission within the Cosmic Vision 2015-2025 plan [1]. The main scientific goal of the NEAT mission is to detect and characterize planetary systems in an exhaustive way down to 1 Earth mass in the habitable zone and further away, around nearby stars for F, G, and K spectral types. This survey would provide the actual planetary masses, the full characterization of the orbits including their inclination, for all the components of the planetary system down to that mass limit. Only extremelyhigh-precision astrometry, in space, can detect the dynamical effect due to even low mass orbiting planets on their central star, reaching those scientific goals. NEAT will continue the work performed by Hipparcos (1mas precision) and Gaia (7µas aimed) by reaching a precision that is improved by two orders of magnitude (0.05µas, 1σ accuracy). The NEAT mission profile is driven by the fact that the two main modules of the payload, the telescope and the focal plane, must be placed 40m away leading to a formation flying option that has been studied as the reference mission. The NEAT satellites are foreseen to operate at L2 for 5 years, the telescope satellite moving around the focal plane one to point different targets and allowing whole sky coverage in less than 20 days. The payload is made of 3 subsystems: primary mirror and its dynamic support, the focal plane with the detectors, and the metrology. The principle is to measure the angles between the target star, usually bright (R ≤ 6), and fainter reference stars (R ≤ 11) using a metrology system that projects dynamical Young's fringes onto the focal plane. The proposed mission architecture relies on the use of two satellites of about 700 kg each in formation flying, offering a capability of more than 20,000 reconfigurations. The two satellites are launched in a stacked configuration using a Soyuz ST launch, and are deployed after launch in order to individually perform cruise to their operational Lissajous orbit.

Several experiments have been performed by CNES during the extended PRISMA mission which started in August 2011. A first session in October 2011 addressed two objectives: (1) demonstrate angles-only navigation to rendezvous with a non cooperative object, (2) exercise transitions between RF based and vision based control during final formation acquisition. A complementary experiment in September 2012 mimicked some future astrometry mission and implemented the manoeuvres required to point the two satellite axis to a celestial target and maintain it fixed during some observation period. In its first section, the paper presents the experiment motivations, describes its main design features including the guidance and control algorithms evolutions and provides a synthesis of the most significant results along with a discussion of the lessons learned. In the last part, the paper evokes the applicability of these experiment results to some active debris removal mission concept that is currently being studied. The analysis focuses on the re-use of demonstrated functionalities and collected metrology data to maximize ground simulation representativeness and help to extrapolate the level of achievable performances in a different mission context.

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