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As I understand, Solar Sail runs on dual energy: light pressure and solar wind. While the former is quite deterministic and rigidly following calculations, solar flares create huge bursts of solar wind - at unpredictable points in time, of unpredictable intensity.

How would they affect solar sail propulsion?

  • solar sail needs to be huge and light - that means quite fragile. Would it be possible they could damage (tear) it?
  • even if it withstands them physically, wouldn't they throw the craft off painstakingly calculated trajectory?
  • anything else I missed?

(and generally, what is the proportion between "propulsive power" between the two accelerating factors of solar sail?)

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This response addresses the last part of the question: "what is the proportion between "propulsive power" between the two accelerating factors of solar sail?"

  • Solar Wind is between 1-6x10-9 N/m2

    "The wind exerts a pressure at 1 AU typically in the range of 1–6 nPa (1–6×10−9 N/m2), although it can readily vary outside that range."

  • Solar Radiation Pressure is about 9x10-6 N/m2

    9.08 µPa (µN/m2) at 1AU.

Thus the latter is "typically" a thousand times larger.

This at least seems consistent with operational experience on conventional geostationary satellites. In this scenario solar radiation pressure is an orbit disturbance. Solar wind on the other hand, or rather the flares and CMEs that modulate it, is the bringer of ESD, SEUs and long anomaly management meetings. I'm unable to offer guidance as to the magnitude of the solar wind under flare/CME conditions.

Its not beyond belief that there could by a dynamic effect from the solar wind on a very large area to mass object, particularly if its approach vector to the object isn't radial from the Sun (don't count on CMEs being radially directed). However this is speculation placed here as a straw-man for someone else to pick up!

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  • $\begingroup$ Even in the case of the strongest observed CMEs (i.e., $n_{o} \sim 100 \ cm^{-3}$ and $V \sim 2000 \ km/s$), the dynamic pressure is still ~$0.7 \mu Pa$, so I think @Puffin is correct. $\endgroup$ – honeste_vivere Jan 13 '16 at 14:22

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