Contents 1. Introduction
Although definitions of digital twins vary from implementer to implementer, they share some common themes. A digital twin has been described as a virtual representation of real-world entities [1], or even more abstractly as “a set of information constructs that mimics the structure, context and behavior of an individual physical asset” [2]. Had these definitions stopped here they would simply be describing digital models, so most go on to include how these special models interact with physical twin counterparts. Digital twins not only model physical systems, but they are digitally connected with them. They are dynamically updated with data from their physical twins [2] and may be synchronized with them at a specified frequency and fidelity [1]. For spacecraft, this could be realized by using telemetry data from on-orbit systems to update the digital model to improve its representation of the real system in its operational environment. A primary purpose of a digital twin (DT) is to inform decisions about the physical entity of interest to realize value [2], [3], and [4]. A DT enables a digital thread [5] which creates a closed loop between digital and physical worlds to optimize products or performance [6]. For spacecraft, this could mean uplinking data or commands informed by the DT that improve performance. There is digital feedback between the twins, where the physical twin provides telemetry data relating reality to the digital twin which can refine its model of reality and return “tuning” data back to its physical counterpart to optimize its performance (right side of Figure 1). One other common attribute of DTs is their applicability across the entire lifecycle of the physical system [2], [3] from concept development through design, integration, test, deployment, operation, and disposal. As it has been described so far, a DT only serves a role in optimizing performance of an operational system. But what is its role during earlier lifecycle phases? A full-lifecycle DT should not only support operations, but it should also help optimize the design during design phases [7]. A DT supporting design may initially serve as a method of verifying concepts ensuring requirements will be met through simulation or other forms of analysis. In this manner, the DT helps link V & V data to system requirements providing digital traceability, a digital thread connecting system attributes with verification activities (left side of Figure 1). To demonstrate the application of DTs to concept development, The Aerospace Corporation is developing an integrated spacecraft digital twin flight simulator for its Concept Design Center (CDC). This paper presents some of the findings, lessons learned, and other observations collected to date.
Digital twinning throughout the lifecycle. Early in the lifecycle, a digital twin is synchronized with system concepts. Later it synchronizes with its physical twin.
