Young, PeterKiekebusch, Mario JChiozzi, Gianluca2015-12-13June 27-309780819482303http://hdl.handle.net/1885/83764Engineers in several observatories are now designing the next generation of optical telescopes, the Extremely Large Telescopes (ELT). These are very complex machines that will host sophisticated astronomical instruments to be used for a wide range of scientific studies. In order to carry out scientific observations, a software infrastructure is required to orchestrate the control of the multiple subsystems and functions. This paper will focus on describing the considerations, strategies and main issues related to the definition and analysis of the software requirements for the ELT's Instrument Control System using modern development processes and modelling tools like SysML.Keywords: Astronomical instrument; Complex machines; ELT; Extremely Large Telescopes; framework; Instrument control; Instrument control softwares; instrument control system; Modelling tools; Modern development; Multiple subsystems; Scientific observations; Scientif ELT; framework; instrument control system; software requirements201010.1117/12.8572412016-02-24