SUN DIRECTION DETERMINATION FOR THE SOLAR PROBE PLUS SPACECRAFT

The Solar Probe Plus (SPP) mission plans to launch a spacecraft to explore the Sun in 2018. This paper presents the process applied in the attitude control flight software for the spacecraft to determine the best Sun direction from Sun sensor data or a vector derived from on-board ephemeris models and the estimated attitude. Self-consistency checks applied to determine validity of these different knowledge sources are explained, with emphasis on processing of solar limb sensor data. Consistency checks between the available data sources are described. The paper concludes with a presentation of the logical hierarchy that determines which source to select from among the available and valid sources and results of the consistency checks between them.