  This paper discusses the physics, engineering and mission architecture
relating to a gram-sized interstellar probe propelled by a laser beam. The
objectives are to design a fly-by mission to Alpha Centauri with a total
mission duration of 50 years travelling at a cruise speed of 0.1c. Furthermore,
optical data from the target star system is to be obtained and sent back to the
Solar system. The main challenges of such a mission are presented and possible
solutions proposed. The results show that by extrapolating from currently
existing technology, such a mission would be feasible. The total mass of the
proposed spacecraft is 23g and the space-based laser infrastructure has a beam
power output of 15GW. Rurther exploration of the laser - spacecraft tradespace
and associated technologies are necessary.
