SAGE III (Stratospheric Aerosol and Gas Experiment), an Earth-observation instrument developed by NASA's Langley Research Center (LaRC), was one of the first scientific external payloads selected for the International Space Station. It was conceived to fly on a spacecraft able to provide +/- 1 degree pointing accuracy. Since the ISS's attitude can vary by several degrees over a long period, it was therefore necessary to provide a dedicated nadir-pointing system. For this task, NASA selected the hexapod-based pointing system ("Hexapod" for short) included by ESA in the list of proposed European contributions to the ISS early utilisation phase. Launch is currently scheduled with assembly flight UF-3, although this could be modified by revisions in the ISS assembly sequence.