ACES: a time and frequency mission for the International Space Station

ACES (Atomic Clock Ensemble in Space) was selected by ESA as a candidate express pallet adapter payload. Part of the early utilisation phase of the International Space Station, Express Pallet Adapters are specific external locations dedicated to the accommodation of small instruments and experiments. ACES tests a new generation of micro-gravity clocks with frequency stability in the range 10/sup -16/ to 10/sup -17/. The ACES mission is outlined with emphasis placed on payload engineering.