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For most Earth observation spacecrafts (EOS), repeating sun-synchronous orbit is a preferred working orbit for the Earth observation spacecraft. Repeating ground trace can provide an ideal observation geometry for space-crafts devoted to Earth observation missions. Sun-synchronous orbit can provide an ideal supply of solar power for the space-crafts. Payloads for EOS usually need demanding pointing stability. One of the main factors which may lead to the variation of payload pointing is the solar radio flux. In different year, the solar radio flux varies. This paper focuses on the characteristics of payload pointing stability due to the variation of the solar radio flux. As historic dataset, solar radio flux shows periodic change of 11 years. In 11 years, solar radio flux experiences the maximal and the minimal solar flux units (sfu). In the case of the payload beam boresight, the simulation results indicate that during the year of severe solar activity with 230sfu, 4 months of orbit drifting without any orbit maneuver will result in payload pointing change less than ±2 deg, and that during the year of severe solar activity with 230 sfu, 2 months of orbit drifting without any orbit maneuver will result in payload pointing change less than ±0.5 deg. And the simulations also indicate that during the year of average solar activity with 150sfu, 4 months of orbit drifting without any orbit maneuver will result in payload pointing change less than ±0.5 deg, and that during the year of average solar activity with 150sfu, 2 months of orbit drifting without any orbit maneuver will result in payload pointing change less than ±0.1 deg; In the case of the payload beam edge, the simulation results indicate that during the year of severe solar activity with 230sfu, 4 months of orbit drifting without any orbit maneuver will result in payload pointing change less than ±5 deg, and that during the year of severe solar activity with 230 sfu, 2 months of orbit drifting without any orbit maneuver will result in payload pointing change less than ± deg. And the simulations also indicate that during the year of average solar activity with 150sfu, 4 months of orbit drifting without any orbit maneuver will result in payload pointing change less than ±2 deg, and that during the year of average solar activity with 150sfu, 2 months of orbit drifting without any orbit maneuver will result in payload pointing change less than ±0.5 deg; The simulations provide an effective constraint of orbit maneuver scenario planning, and further boost the feasibility of space-crafts engineering.
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