The new JCMT telescope control system

As part of the upgrades to our observatory control software, we have developed a replacement for the astrometric kernel and the servoing system at the James Clerk Maxwell Telescope. The new PTCS (Portable Telescope Control System) astrometric kernel operates within the DRAMA (Distributed RealTime AAO Monitor for Astronomy) tasking system. An EPICS (Experimental Physics and Industrial Control System) servo controls the antenna drives. The THI (Telescope Hardware Interface), a DRAMA task, translates demands from the kernel and sends them to the servo, and then feeds back to the kernel the current drive encoder positions and the expected time of arrival at source position. The TEL DRAMA task at the top level interfaces between the existing observation control software and the telescope-independent PTCS task. This new system is replacing components of an existing observatory facility, and as such is compatible with the existing software. The previous telescope astrometric kernel operated on a Var platform and sent demands via GPIB (General Purpose Interface Bus) to a servo on a VME platform. The new PTCS and the THI software run on a Unix machine and communicate via the DRAMA message system to the upper layer observatory system and via Channel Access (TCP/IP) to the EPICS servo running VxWorks on the VME platform. In this paper we will review the main features of the new telescope control system, and report on progress with implementation.