An autonomous passive navigation method for nanosatellite exploration of the asteroid belt

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 solar system, origins of Earth and origins of life. Apart from being important targets for science exploration, asteroids are strategically placed due to their lowgravity 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 resulting nano-spacecraft can make detection from Earth difficult. This paper discusses 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.