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Comment by sebringj | Hacker News Reader

Interesting caveat about traveling close to the speed of light...if you run into hydrogen atoms, which is near 100% likely, your ship violently explodes because at very high speeds, there is a huge reaction on tiny matter collisions. I just learned this and it was like learning that sound doesn't travel in space when I was young and ruined many a starwars movie effects. I keep learning how ignorant and dumb I am the more I follow SpaceX and become curious about space.

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Star Trek in particular did put energy into handwaving/explaining away how their ships avoid this issue:

https://memory-alpha.fandom.com/wiki/Navigational_deflector

I always thought it was a nice touch and hopefully a teaching moment when they talk about it in the show.

At least Star Trek tries to answer this in some way even though bs but still cool for the effort, mainstream space is definitely dumbed down compared to that.

Interstellar ships will be shaped like pencils to deflect rather than impact gasses. They will also have to have consumable nose cone sections with old ones in the front being removed and new ones installed at that back. Like a mechanical pencil.

What happens when the ship has to turn around to decelerate, with its engines facing the front?

Turn on the drives as soon as you can for the deceleration burn and pray.

The only realistic option is another set of engines on the other end.

Zubrin, in Entering Space, introduced me to the idea of using a solar or much larger magnetic sail to drag against the outcoming solar wind of the destination star. So that's one way to spend no energy slowing down for interstellar travel.

The turn-around takes place at the half-way point of the journey. This means that for the entire second half of the journey, the engine is pointed at the oncoming dust.

Engines used in such long journeys will likely emit a thin stream of particles at extreme velocities. This stream is not wide enough or thick enough to stop space dust from hitting the engine. An unshielded forward-facing engine will get destroyed. So we must shield the engine.

Instead of having two shields and turning the ship around, just turn the engine around. Make the engine emit streams forward from the sides of the ship.

Or like a funnel: https://en.wikipedia.org/wiki/Bussard_ramjet

Arthur C Clarke posits a consumable shield made of ice in The Songs of Distant Earth [1]

[1] https://en.wikipedia.org/wiki/The_Songs_of_Distant_Earth

Isn't it vanishingly unlikely to ever encounter one particle in interstellar space?

Interstellar space is full of particles flying around. There's plenty of hydrogen in the galaxy. Between galaxies not so much but we're not talking inter-galactic space.

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