A complete census of planetary systems around a volume-limited sample of solar-type stars ( FGK dwarfs ) in the Solar neighborhood ( d \leq 15 pc ) with uniform sensitivity down to Earth-mass planets within their Habitable Zones out to several AUs would be a major milestone in extrasolar planets astrophysics .
This fundamental goal can be achieved with a mission concept such as NEAT — the Nearby Earth Astrometric Telescope .

NEAT is designed to carry out space-borne extremely-high-precision astrometric measurements at the 0.05 \mu as ( 1 \sigma ) accuracy level , sufficient to detect dynamical effects due to orbiting planets of mass even lower than Earth ’ s around the nearest stars .
Such a survey mission would provide the actual planetary masses and the full orbital geometry for all the components of the detected planetary systems down to the Earth-mass limit .
The NEAT performance limits can be achieved by carrying out differential astrometry between the targets and a set of suitable reference stars in the field .
The NEAT instrument design consists of an off-axis parabola single-mirror telescope ( D = 1m ) , a detector with a large field of view located 40 m away from the telescope and made of 8 small movable CCDs located around a fixed central CCD , and an interferometric calibration system monitoring dynamical Young ’ s fringes originating from metrology fibers located at the primary mirror .
The mission profile is driven by the fact that the two main modules of the payload , the telescope and the focal plane , must be located 40 m away leading to the choice of a formation flying option as the reference mission , and of a deployable boom option as an alternative choice .
The proposed mission architecture relies on the use of two satellites , of about 700 kg each , operating at L2 for 5 years , flying in formation and offering a capability of more than 20,000 reconfigurations .
The two satellites will be launched in a stacked configuration using a Soyuz ST launch vehicle .

The NEAT primary science program will encompass an astrometric survey of our 200 closest F- , G- and K-type stellar neighbors , with an average of 50 visits each distributed over the nominal mission duration .
The main survey operation will use approximately 70 % of the mission lifetime .
The remaining 30 % of NEAT observing time might be allocated , for example , to improve the characterization of the architecture of selected planetary systems around nearby targets of specific interest ( low-mass stars , young stars , etc . )
discovered by Gaia , ground-based high-precision radial-velocity surveys , and other programs .
With its exquisite , surgical astrometric precision , NEAT holds the promise to provide the first thorough census for Earth-mass planets around stars in the immediate vicinity of our Sun .