Evolving the Ulysses Mission Control System - A Long Term Support Case Study

Abstract

The Ulysses mission is a collaborative effort of the European Space Agency (ESA) and the National Aeronautics and Space Administration (NASA) to study the Sun's environment, the heliosphere, especially over its polar regions. Mission operations are carried out by a joint multi-national ESA/NASA team located at NASA's Jet Propulsion Laboratory. At the time of writing, the nominal date for the end of science mission operations is the end of March 2008, a total mission duration of 17½ years from the launch date of 6th October 1990. Supporting such a long duration mission using the original mission control system is clearly undesirable for a number of reasons: hardware failures, hardware and operating system obsolescence and requirements imposed due to reasons external to the mission or user requests. This paper presents the real-life experiences of the Ulysses flight control team in evolving the Ulysses mission control system (UMCS) to support on-going mission operations. The UMCS is into its third generation and the lessons learned in migrating from the first to the second generation and carried over into the recently completed migration will be discussed in this paper. One example of such a lesson is the need to understand fully the requirements driving the migration and assigning priorities to such requirements. Another is the need to identify the migration paths available and trade them off in terms of risks and costs. One of the major contributors to both successful migrations was the decision to stay with the same operating system family, HP OpenVMS, for the UMCS. Another was that the need for minimal changes to the application code base, modify code to support hardware only, was clearly understood by the user community. A crucial element in migration success was the live comparison testing of the new and old UMCS carried out by the UMCS users, which generated an auditable trail for system validation. This exercise also produced strong confidence among all stakeholders that the new UMCS is even better than the old.