Mission and system analyses for satellites with unified bi-propellant propulsion systems

Unified or combined liquid bi-propellant systems are being used increasingly for all propulsion needs for the new generation of communication satellites such as Intelsat VI, Olympus and Eurostar. Their characteristics have a large influence on spacecraft design, and on mission design. This paper attempts to summarize the system-level impacts of these systems, and describes in particular detail the mission design impacts. Although the discussion draws heavily upon the detailed mission analyses performed for the Olympus and Eurostar spacecraft, it attempts to retain a broader perspective in order to highlight areas that will be of common interest to a whole range of spacecraft designs. A statement of the overall advantages and disadvantages of bi-propellant systems is followed by a discussion of the spacecraft stability aspects unique to such systems. This is followed by a detailed discussion of apogee manoeuver design and related mission and operational aspects. It is shown that, though the system impacts of bi-propellant systems are many and complex, these are generally well understood, and this enables the spacecraft designer confidently to exploit the benefits that such systems can yield.