The Tail Wags the Dog: Managing Large Telescope Construction Projects with Lagging Requirements and Creeping Scope

摘要

In a perfect world, large telescopes would be developed and built in logical, sequential order. First, scientific requirements would be agreed upon, vetted, and fully developed. From these, instrument designers would define their own subsystem requirements and specifications, and then flesh out preliminary designs. This in turn would then allow optic designers to specify lens and mirror requirements, which would permit telescope mounts and drives to be designed. Finally, software and safety systems, enclosures and domes, buildings, foundations, and infrastructures would be specified and developed. Unfortunately, the order of most large telescope projects is the opposite of this sequence. We don't live in a perfect world. Scientists usually don't want to commit to operational requirements until late in the design process, instrument designers frequently change and update their designs due to improving filter and camera technologies, and mount and optics engineers seem to live by the words 'more' and 'better' throughout their own design processes. Amplifying this is the fact that site construction of buildings and domes are usually the earliest critical path items on the schedule, and are often subject to lengthy permitting and environmental processes. These facility and support items therefore must quickly get underway, often before operational requirements are fully considered. Mirrors and mounts also have very long lead times for fabrication, which in turn necessitates that they are specified and purchased early. All of these factors can result in expensive and time-consuming change orders when requirements are finalized and/or shift late in the process. This paper discusses some of these issues encountered on large, multi-year construction projects. It also presents some techniques and ideas to minimize these effects on schedule and cost. Included is a discussion on the role of Interface Control Documents (ICDs), the importance (and danger) of making big-picture decisions early, and designing flexibility and adaptability into subsystems. In a perfect world, science would be the big dog in the room, wagging the engineering tail. In our non-perfect world, however, it's often the tail that ends up wagging the dog instead.