VLT telescope control software- status, development and lessons learned

The four 8m VLT telescopes on Paranal are now in full science operation, and they all deliver good results with very small technical downtimes. Of course, many factors are contributing to these results, and also the telescope control software has its share. It has demonstrated to be robust and reliable and also flexible and expandable. In the four years since First Light of the first VLT telescope, this software has been continuously maintained and developed, for improvements on the 8m telescopes but also for use on other telescopes. In addition to the 8m ones, another three telescopes, using applicable parts of the same software, are in operation on Paranal: the 350-mm seeing monitor and two 400-mm siderostats. And the process continues: in the beginning of 2003 the first of three 1.8m Auxiliary Telescopes for the VLT Interferometer will be installed; the control software to 80% being the same as for the 8m telescopes, but with additional devices and control functionality. Another three ESO telescopes on La Silla are also using the same software, as well as two wide field telescopes for Paranal that are now in the design and manufacturing phase. In this development process, and in particular after first installation, we have learned lessons in many areas of software project work. System design and engineering, standardization, tools, testing: these are example areas where there is always room for improvement. Another lesson learned is the importance of the concept of Commissioning, i.e. the work to take the telescope from "integrated" to "working"! What the future of telescope control software will be, that we don't know, but we are working on it! And we try to keep an evolutionary approach, taking advantage of the lessons learned.