When an original equipment manufacturer no longer supplies and/or supports a product then the product is considered to be obsolete. Obsolescence is a significant problem for systems whose operational and support life is much longer than the procurement lifetimes of their constituent components. Unlike high-volume, commercial products, which are quickly evolved, long field life, low-volume systems, such as aircraft may require updates of their components and technology called design refreshes to simply remain manufacturable and supportable. However these systems can't perform design refreshes all the time due to the high nonrecurring and re-qualification costs. One approach to optimally managing this problem is to use DRP (Design Refresh Planning), which is a strategic method for scheduling design refreshes such that the life cycle cost impact of obsolescence is minimized. The planning of these design refreshes is restricted by various constraints, which need to be implemented into the DRP process. These constraints can reflect technology roadmap requirements, obsolescence management realities, logistical restrictions, budget ceilings and management policy. In this paper, constraints imposed on the DRP process are explored, classified within a taxonomy, and implemented in the planning process. A communications system design example is included.