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Gridless Narrow-Angle Astrometry (GNAA) is an astrometry technique developed at the California Institute of Technology Jet Propulsion Laboratory under contract to NASA. GNAA allows star positions to be measured without first setting up a grid of reference stars; instead, it sets up a reference frame using several reference stars and a target star observed from different locations, and star positions are calculated using delay measurements from the separate observations.
GNAA was developed to give an accuracy of 1 micro-arcsecond to the early stages of the Space Interferometry Mission.