Timeline as Unifying Concept for Spacecraft Operations

摘要

The notion of Timeline has been used informally in spacecraft operations software for some time, but it has not heretofore been formalized and unified either syntactically or semantically. We have formalized and unified the Timeline so that the commonality can be exploited to reduce the cost of developing and using spacecraft operations software. The Timeline can then be used as the common data structure for storage and communications between spacecraft planning and operations software elements. We have formalized linear timelines (both instantaneous events and functions continuous in time) and activities (potentially overlapping set of activities). Most spacecraft planning and operations processes are naturally expressed in terms of software tools that read timelines from databases as input and generate results as new or modified timelines that are written to the databases. Timelines are rigorously versioned, and each version is immutable, thus a versioned timeline name forever represents exactly the same contents. The name is therefore as good as the contents, and the need for keeping files of contents for communicating between programs, or for associating several timelines or even values on those timelines, or for keeping a record of past values, is eliminated. Timelines thus form the syntactic and semantic method of integration of software elements, leading to decreased adaptation cost. Operations efficiency is increased because historically segregated elements are easily integrated so that there are fewer gaps in the operations process that must currently be closed, if they are closed at all, by expensive or inefficient means.