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Post by Anonymous on Dec 8, 2018 2:23:08 GMT
I hear a lot about Shkadov Thurster type stellar engine. Nobody explains how come the statites do not fly away from photon pressure. How does the star stay its connection to the statites to make coherent engine? Gravity is not enough, right?
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Post by bigbombr on Dec 8, 2018 7:25:01 GMT
No, they do maintain the same distance thanks to the interplay of solar wind pressure and gravity. Both are quadratic, they become 4 times weaker at twice the distance. By varying the surface area of the individual statites you can regulate the distance (whether they move away or towards the star depends on surface area/mass). It's one of his older videos, but Isaac Arthur still explains it pretty well. |
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Post by Anonymous on Dec 9, 2018 7:27:58 GMT
Hi. I watched the video. But I still do not know how come the star is not left behind. How does thrust transfer from the statites to star? It is too small target to reflect most photon momentum back to the star, correct? How come the statite shell and the star move together like solid? I want to find a force diagram, maybe.
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Post by bigbombr on Dec 9, 2018 8:52:36 GMT
Hi. I watched the video. But I still do not know how come the star is not left behind. How does thrust transfer from the statites to star? It is too small target to reflect most photon momentum back to the star, correct? How come the statite shell and the star move together like solid? I want to find a force diagram, maybe. The star emits light and solar wind in all directions (no netto thrust). Statites on one side of the star reflect this, this is a force that pushes the statites away from the star. Gravity is a force that pulls the statites towards the star. By varying your surface area facing the star relative to the mass of the statite (expressed in m²/kg) you can balance these forces to keep the statites at a fixed distance (or draw them closer or push them further out as desired), this means the thrust from the reflection balances the gravitational pull. So the statites can maintain a constant distance from the star. But as the star pulls on the statites with gravity, the statites pull the star, moving the star (which doesn't produce thrust, as it emits approximately equally as much in all directions). You could also look at it from the perspective of conservation of momentum: the statites mean your star+statite cloud emits solar wind and light in only one direction, and conservation of momentum dictates that this impulse has to be balanced out somehow. So as the light and solar wind mostly moves in one direction, the star and statite cloud move in the opposite direction. |
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