Many large scientific facilities operate their systems over long time-scales, sometimes 30 years or more. During that period, requirements can change, the facility is upgraded and new technologies emerge. And software bugs can sometimes take years to emerge. The control systems will evolve to reflect these changes.
Observatory Sciences is providing long-term software support for several major scientific facilities, including the European Southern Observatory and Diamond Light Source (UK). Sometimes we provide on-site personnel, alternatively we might do most of the work remotely with occasional on-site visits for testing and commissioning.