  There are more than 750,000 asteroids identified in the main belt. These
asteroids are diverse in composition and size. Some of these asteroids can be
traced back to the early solar system and can provide insight into the origins
of the so-lar system, origins of Earth and origins of life. Apart from being
important tar-gets for science exploration, asteroids are strategically placed
due to their low-gravity well, making it low-cost to transport material onto
and way from them. They hold valuable resources such as water, carbon, metals
including iron, nickel and platinum to name a few. These resources maybe used
in refueling depots for interplanetary spacecraft and construction material for
future space colonies, communication relays and space telescopes. The costs of
getting to the main asteroid belt, combined with large numbers of objects to be
explored encourage the application of small spacecraft swarms. The size and
capability of the result-ing nano-spacecraft can make detection from Earth
difficult. This paper dis-cusses a method by which a spacecraft can establish
ephemeris autonomously using line of sight measurements to nearby asteroids
with Extended Kalman Filtering techniques, without knowing accurate ephemeris
of either the asteroids or the spacecraft initially. A description of the
filter implementation is followed by examples of resultant performance.
