Main stellar spectrograph of the 6-meter telescope. Analysis,reconstruction, and operation

The Main Stellar Spectrograph (MSS) of the 6-m telescope of the Special Astrophysical Observatory was developed in the early 1970s and has been in permanent operation since 1975. This instrument has been successfully kept operational for a long time by equipping it with modern detectors and significantly upgrading its optical layout. In this paper we present the main parameters of the optomechanical layout of the MSS, the design features of auxiliary devices, operational experience and statistics of the use of the instrument with various detectors, and the characteristics of the corresponding observational techniques.