Hi I am Steve Hurley. I work in the IT industry. I studied for a PhD in astronomy in the 1980s. Outside work my real passion is explaining scientific concepts to a non-scientific audience. My blog (explainingscience.org) covers various scientific topics, but primarily astronomy. It is written in a style that it is easily understandable to the non scientist.
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9 thoughts on “Solar Sails”
So a solar sail can’t move towards a solar source unless it is powering some sort of motor or engine? I’m wondering what a solar space craft needs to do to come back or return? Or is it best considered a one way trip?
Well, I learned something today! I hadn’t thought about the light that gets absorbed by the sail. But of course, as you say, no mirror is 100% efficient. No anything is 100% efficient. So absorbed light would have to be a factor in how solar sailing works.
In practice of course the Sun emits more than photons: also a variety of fast-moving particles, though their “luminosity” is variable & less predictable. This would be good news – though there’d be absorption or penetration rather than reflection & there might be a need for the occasional mid-course correction. It also means that in a spacecraft totalling only 10kg, the electronics would have to be shielded well enough to survive without damage!
In your example you assumed a sail thickness of 10 µm – this is slightly thinner than ‘clingfilm’ & most particles would have the energy to go through it. I’ve no data on the IKAROS sail but I’d guess that, unlike the circuitry, any impairment of the sail in a 2-year voyage wouldn’t be significant.
I plan to write a post about IKAROS in the near future, which will give more details on its mission, but according to the specification document https://global.jaxa.jp/activity/pr/brochure/files/sat28.pdf
its solar sail was square having a diagonal length of 20-m (which equates to an area of roughly 200 square metres)
and the thickness of the sail was only 7.5 µm !!!
Explaining Science 
So a solar sail can’t move towards a solar source unless it is powering some sort of motor or engine? I’m wondering what a solar space craft needs to do to come back or return? Or is it best considered a one way trip?
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It is definitely NOT a one way trip !
A solar sail can be orientated so that the spacecraft moves in towards the Sun, This is shown in example 2
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Well, I learned something today! I hadn’t thought about the light that gets absorbed by the sail. But of course, as you say, no mirror is 100% efficient. No anything is 100% efficient. So absorbed light would have to be a factor in how solar sailing works.
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Yes definitely !!
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In practice of course the Sun emits more than photons: also a variety of fast-moving particles, though their “luminosity” is variable & less predictable. This would be good news – though there’d be absorption or penetration rather than reflection & there might be a need for the occasional mid-course correction. It also means that in a spacecraft totalling only 10kg, the electronics would have to be shielded well enough to survive without damage!
In your example you assumed a sail thickness of 10 µm – this is slightly thinner than ‘clingfilm’ & most particles would have the energy to go through it. I’ve no data on the IKAROS sail but I’d guess that, unlike the circuitry, any impairment of the sail in a 2-year voyage wouldn’t be significant.
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Hi David,
Thanks for your comments.
I plan to write a post about IKAROS in the near future, which will give more details on its mission, but according to the specification document https://global.jaxa.jp/activity/pr/brochure/files/sat28.pdf
its solar sail was square having a diagonal length of 20-m (which equates to an area of roughly 200 square metres)
and the thickness of the sail was only 7.5 µm !!!
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Nice image.. Inverse square rule?
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Thank you
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😊
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