re: 3 Body Problem - Netflix

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The nano-fiber sail ship. It needed a thousand nuclear detonations to reach 1% light speed correct?

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I thought the number was 30. But yes, even just getting those 30 magically in place that quickly and precisely requires quite a stretch of the imagination.

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So the wallfacer stuff. They have to come up individually with a way to fight the aliens but never talk about or act on it until it’s time to put it in action? How does that work? What if something needs to be constructed? Someone explain this to me.

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They give the orders on what to build but don't have to explain how to use it or what it does or anything else. It's not exactly practical, but it serves the point of finding ways to deal with every word being recorded by the SanTi.

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1. The nano-fiber sail ship. It needed a thousand nuclear detonations to reach 1% light speed correct? How would they have placed let’s say the last 200 or so warheads so far out so quick? At that point where the sail ship would be and how fast it was moving would have taken normal propulsion well over a decade to get there to put the warheads in place. Didn’t make sense to me.

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They wound up only getting 300 warheads, which is why they had to reduce the mass of the capsule so much. That said, it’s an interesting question. Using some pretty big assumptions:
- Assuming ~17 km/s capsule velocity at the end of the conventional burn
- Assuming linear acceleration with each successive detonation
- Assuming the warheads are evenly spaced
- Assuming ~10 seconds between the first and second detonation

.. then the capsule’s velocity would increase at roughly 10 km/s with each detonation, putting it just over 1% speed of light after 300 detonations. After the first detonation it would be traveling at roughly 27 km/s, and would travel 270 km total between the first and second warhead. 270 km/warhead * 300 warheads = 81,000 km total travel distance.

That’s actually… not that far. Earth is 150 million km from the Sun. Using the same 17 km/s post-burn velocity for the warheads, it would only take about 80 minutes for one of them to travel 81,000 km. Of course, there are other considerations:
- The warheads have to decelerate, which will increase their travel time.
- The acceleration after each detonation probably isn’t linear. So the capsule velocity probably increases by more than 10 km/s after the first detonation.
- I didn’t rewatch the scene to check the time between the first two detonations.

I actually think the bigger technical issue would be the precision required to position each warhead in the exact location required to pass through the hole on the sail. I think a more realistic failure mechanism would have been a warhead that barely missed the hole and collapsed the sail rather than a failed cable connection.

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Also the name of the show. Is that just a reference to 3 Suns in the system the aliens reside in?

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It’s a reference to the classical physics problem that the San-Ti face as a civilization. There is no known mathematical solution for the movements of objects in a 3-body system, due to the chaotic way in which the gravitational fields interact. Here’s an image from Wikipedia that sort of illustrates the issue: