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Relativistic Spaceship

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Re: Relativistic Spaceship

#191

Post by Eddy_Viscosity2 »

MilStdJunkie wrote: post #165
knodi123 wrote: post #51

Earlier quoted context omitted.

In the book series The Expanse, that was pretty much the only unrealistic technology that the humans had, which allowed them to colonize the solar system. Sure, there was some might-as-well-be-magic alien stuff later in the book, but by page 1, humans have colonized the solar system, purely with a hand-wavy engine that can generate sustained thrust without needing tons of reaction mass and without turning your exhaus…

I'm going to embarrass myself horribly here, but I've only seen the series, so I'm not a hundred percent clear on how much acceleration they're pulling in cruise[1]. If it's something like .3 g then they're fairly close[2] to the limits of something like a fusion pulse drive (tiny nodules of deuterium or whatever, ejected out the back of the ship, then lasered into fusing, then the reaction pushes on the whatever - m…

The ships cruise anywhere from 0.3 to 1G, the lower end mainly for comfort of people who grew up in space. But, the fictional drive is so efficient it could sustain 10s of G for extended periods (weeks, months).

Re: Relativistic Spaceship

#193

Post by GuB-42 »

MilStdJunkie wrote: post #26
AlexAndScripts wrote: post #15

Earlier quoted context omitted.

I suppose you would also have to worry about surviving the trip - every atom in the interstellar medium would damage your ship, likely penetrating the entire way through, and electromagnetic repulsion would only work with charged particles.

Every proton would have the energy of a baseball. It's bananas. Granted, space is really empty, but it's not that empty, somewhere around a hundred atoms per cubic meter. Your ship might look like a very, very long shooting star. Probably dialing the speed down a touch would be worth it for whatever your shielding material is, but who knows? We're talking miracle engines here. I think in the "Valkyrie" ship-on-a-stri…

Even if you managed to avoid matter, at some point, photons will start to become a problem. As you continue to accelerate, eventually, the cosmic microwave background itself will become deadly X-rays.

Re: Relativistic Spaceship

#194

Post by EA-3167 »

lostmsu wrote: post #178
ryandrake wrote: post #12

Great visualization of the unintuitive nature of special relativity. It's kind of mind blowing to realize that if we could accelerate our spaceship at a mere 1G continuously, we could visit the center of the Milky Way in under 20 years (spaceship time), totally do-able in a human lifespan. Of course 27900 years would have passed on Earth, so you wouldn't be able to tell anyone about your vacation.

It does not take much more years to the edge of the visible universe.

Iirc to get to Proxima Centauri at a constant 1g would require a fairly impressive mass of antimatter, to continue to the edge of the observable universe would be so many more orders of magnitude more energy than that it's barely worth discussing. Even though we can't reach c, as we start to approach it the energy requirements rise catastrophically, along with the risk of colliding with some random mote of Hydrogen and remembering that your relative velocity is .99999c, in the moment before you and your ship are atomized.

Re: Relativistic Spaceship

#195

Post by knodi123 »

moron4hire wrote: post #112
knodi123 wrote: post #51

Earlier quoted context omitted.

In the book series The Expanse, that was pretty much the only unrealistic technology that the humans had, which allowed them to colonize the solar system. Sure, there was some might-as-well-be-magic alien stuff later in the book, but by page 1, humans have colonized the solar system, purely with a hand-wavy engine that can generate sustained thrust without needing tons of reaction mass and without turning your exhaus…

No, the exhaust port definitely was an unimaginable hell cannon. The characters spoke several times about slagging a ship or a surface base in their drive plume.

Oh, I missed that! Seems like those drives ought to have been more carefully regulated then.

Re: Relativistic Spaceship

#196

Post by senectus1 »

timschmidt wrote: post #106
notfed wrote: post #92

Earlier quoted context omitted.

At which point shielding gets even more complicated.

Less complicated. The rocket exhaust literally forms a plasma shield in front of the decelerating rocket.

what about for the period of time that you're travelling sideways with a largely unshielded broadside facing not exactly empty space?

Re: Relativistic Spaceship

#197

Post by antihipocrat »

GuB-42 wrote: post #193
MilStdJunkie wrote: post #26

Earlier quoted context omitted.

Every proton would have the energy of a baseball. It's bananas. Granted, space is really empty, but it's not that empty, somewhere around a hundred atoms per cubic meter. Your ship might look like a very, very long shooting star. Probably dialing the speed down a touch would be worth it for whatever your shielding material is, but who knows? We're talking miracle engines here. I think in the "Valkyrie" ship-on-a-stri…

Even if you managed to avoid matter, at some point, photons will start to become a problem. As you continue to accelerate, eventually, the cosmic microwave background itself will become deadly X-rays.

Would a layer of water in the forward hull positions mitigate this?

Re: Relativistic Spaceship

#198

Post by eru »

dfee wrote: post #147
MilStdJunkie wrote: post #26

Earlier quoted context omitted.

Every proton would have the energy of a baseball. It's bananas. Granted, space is really empty, but it's not that empty, somewhere around a hundred atoms per cubic meter. Your ship might look like a very, very long shooting star. Probably dialing the speed down a touch would be worth it for whatever your shielding material is, but who knows? We're talking miracle engines here. I think in the "Valkyrie" ship-on-a-stri…

I’d like to see a map of the known universe visualizing atomic density on a log scale. I’d never seen “a hundred atoms per cubic meter”, but it’s always been my intuition that, without some quite interesting shielding, you couldn’t make it anywhere near the speed of light. And on the other hand, I’ve seen claims that “space is really big” as you mentioned; but that claim has always seemed dubious.

> I’d never seen “a hundred atoms per cubic meter”, but it’s always been my intuition that, without some quite interesting shielding, you couldn’t make it anywhere near the speed of light.

It's not that bad. With currently known science, your fuel would most likely be hydrogen so you can run a fusion reactor.

The rocket equation tells you that most of your starship by mass would be fuel, if you want to go fast.

Of all the stuff on your ship that's not fuel, you'd probably need quite a bit of water for survival needs.

So you would make your spaceship relatively long and thin (to maximize internal volume for a given frontal area), and you would store your fuel (and water) in front of you to serve as exactly that shield.

Re: Relativistic Spaceship

#199

Post by eru »

actionfromafar wrote: post #137
perardi wrote: post #104

Earlier quoted context omitted.

[pushes up glasses] They implied they avoided that because warping into a gravity well would cause some vague catastrophe. Of course, the real reason was far more sinister: it’s way more dramatic to slowly creep up on the planet while listening to the captain’s log monologue to start the episode.

If nothing else, if you miss just a little dropping out of warp inside a planet, must be a Very Bad Thing in-universe. The ramifications would be seen even out-of-universe. ;-)

Planets are tiny compared to the vastness of space.

So you would never accidentally warp inside a planet.

Re: Relativistic Spaceship

#200

Post by eru »

api wrote: post #123
perardi wrote: post #28

Earlier quoted context omitted.

Unless you could somehow make an Alcubierre warp drive. Of course…even if that was possible, it’s conjectured that the colonists already at your destination won’t appreciate you boiling the atmosphere when you hit them with blue shifted radiation. https://www.universetoday.com/93882/warp-drives-may-come-wit...

> it’s conjectured that the colonists already at your destination won’t appreciate you boiling the atmosphere when you hit them with blue shifted radiation. There's a general principle known as Jon's Law (not sure where the name comes from) that any powerful space drive is by definition a weapon of mass destruction. You see this in The Expanse when incredibly powerful fusion torchship rockets (a major part of the Exp…

> Even present-day chemical rockets could be pretty destructive. Get something massive that won't burn up (like a rod of tungsten) up to interplanetary velocities and you can approach the yield of a small tactical nuke from just kinetic energy.

Of course, that energy didn't come for free: if the rod came from earth, your rockets have to provide the energy.

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