  Accurate astrometry is crucial for determining orbits of near-Earth-asteroids
(NEAs) and therefore better tracking them. This paper reports on a
demonstration of 10 milliarcsecond-level astrometric precision on a dozen NEAs
using the Pomona College 40 inch telescope, at the JPL's Table Mountain
Facility. We used the technique of synthetic tracking, in which many short
exposure (1 second) images are acquired and then combined in post-processing to
track both target asteroid and reference stars across the field of view. This
technique avoids the trailing loss and keeps the jitter effects from atmosphere
and telescope pointing common between the asteroid and reference stars,
resulting in higher astrometric precision than the 100 mas level astrometry
from traditional approach of using long exposure images. Treating our synthetic
tracking of near-Earth asteroids as a proxy for observations of future
spacecraft while they are downlinking data via their high rate optical
communication laser beams, our approach shows precision plane-of-sky
measurements can be obtained by the optical ground terminals for navigation. We
also discuss how future data releases from the Gaia mission can improve our
results.
