Complex sentence: SIM Lite would have operated in an Earth-trailing heliocentric orbit, drifting away from Earth at the rate of 0.1 AU per year ultimately reaching a distance of 82 million km from Earth.
Split into simpler sentences: SIM Lite would have operated in an Earth-trailing heliocentric orbit. At the end of the planned mission, it would have reached a distance of 82 million km from Earth.