The 50cm robotic telescope: control system upgrade and automation

Abstract

We describe the details into the design and development of a low-cost yet efficient telescope control system (TCS) and observatory control software (OCS) for the 50cm telescope at the Indian Astronomical Observatory. The TCS and OCS facilitate precise pointing and tracking of the main axes, handle peripheral sub systems such as the secondary focuser and the filter wheel, conduct observation, monitor weather and incorporate safety interlocks, aimed to run the telescope in a robotic manner. The TCS comprises a computer, control hardware components and an efficient programmable system on chip (PSoC) based motion controller. A distributed control architecture on the controller area network (CAN) bus allows for controlling many subsystems in a modular fashion. The control algorithm comprises the close loop proportional integral derivative (PID) controller and the motion profiler, which ensure very precise pointing and tracking performances. After optimum tuning of the PID gains, we could achieve performance that otherwise one can expect only in large telescopes. The control level pointing accuracy is 3 arc-seconds and unguided sidereal tracking accuracy of 2 arc-seconds over 10 minutes is achieved. The TCS related high-level calculations such as topo-centric and geocentric corrections and the pointing model etc. are carried out in a dedicated computer system, whereas the low-level control program runs in the PSoC. The pointing model software developed is automated and computes the coefficients by image processing using the plate solve method. The OCS which is the top most layer in the control architecture, handles the filter wheel, the detector, the enclosure, the weather station as well as many safety mechanisms. The OCS combined with the scheduler tool and client-server architecture facilitates the un-manned operation of the telescope.