Abstract

The ESO telescopes in Chile are operated in a geographically distributed scheme, in which some of the essential steps in the end-to-end observing chain take place in Europe. Most notably, the health status of the instruments as derived from the data themselves is monitored in Europe and the results fed back to the observatory within the hour. The flexibility of this scheme strongly depends on the speed with which the data stream produced by the telescopes can be sent to Europe for analysis and storage. The main challenge to achieve a fast intercontinental data transfer is the data volume itself, which currently reaches an average 25 GB/night (compressed) for the four VLT Unit Telescopes. Since late 2008, this stream has been entirely transferred through the internet via a 4.56 Mbit/s bandwidth assured via a Quality of Service policy, which sufficed to transfer an average night of data within a few hours. A very recent enlargement of this capacity to 9.12 Mbit/s will soon allow the addition of the calibration data for VISTA, the new infrared survey telescope on Paranal, to the data stream transferred through the internet. Ultimately, the average data volume produced on Paranal once the visible VLT Survey Telescope (VST) and the full complement of second-generation VLT instruments becomes available is expected to exceed 200 GB/night. Transferring it over the internet will require a new fiber-based infrastructure currently under construction, as well as the use of additional high bandwidth channels. This infrastructure, provided by the European Union co-funded project EVALSO, should provide a data transfer capacity exceeding 1 Gbit/s that will allow the transfer to Europe of the entire Paranal data stream, as well as that of the nearby Observatory of Cerro Armazones and of the future European Extremely Large Telescope, with a delay of minutes at most since the data were taken. © 2010 Copyright SPIE - The International Society for Optical Engineering.