Simulation strategies employed in the development and maintenance of the Hobby-Eberly Telescope control system

The recently reinvented Hobby-Eberly Telescope (HET) has undergone a multi-year upgrade replacing the wide-field corrector, tracker, and metrology systems. The timelines for the production and delivery of the various upgrade components, combined with the desired turn around on deployment and integration, required that a majority of the core control system software functionality be implemented, and notionally tested, without access to the related hardware. We present the approaches to simulating the HET hardware systems, their evolution, the successes and shortcomings of the current level of capabilities, and ideas for improvements to simulation and integration testing.