Telescience and interferometric metrology on the international space station

Scientific experiments performed in space require real-time control by the scientists on earth, i.e. Telescience/Teleoperation. In fluid science research, non-invasive optical diagnostic tools help to gain a better understanding of phenomena within transparent media. During the last years, electronic cameras started to take over the role of quantitative imaging from photographic imaging. For that purpose cameras must offer at least 1k×1k spatial resolution, 8 bit pixel depth and 33 ms (30 fps) time resolution. This results in data rates (240 Mbps) far beyond the downlink capacities of typical carriers for scientific payloads. A double rack on the International Space Station (ISS), e.g. gets only 2 Mbps continuously. This paper concentrates on the compressibility of interferometric image data for Telescience. In particular, a solution is presented for Electronic Speckle Pattern Interferometry (ESPI), one of the interferometers, e.g. planned for the Fluid Science Laboratory (FSL) on ISS. Pre-tests had shown that ESPI raw images could hardly be compressed, i.e. by a factor 1-1.5 only. But a factor of 60 is at least required to allow Telescience with an image sequence of 15 fps (120 Mbps), still providing a good qualitative impression about the spatial and temporal behaviour of an experiment. This paper provides answers concerning qualitative imaging with ESPI in addition to Shearing Interferometry and Holographic Interferometry.