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Highly relativistic spaceflight would be fatal for passengers and instruments

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Re: Highly relativistic spaceflight would be fatal for passengers and instruments

#11

Post by gliese1337 »

wging wrote: post #6
jonathanyc wrote: post #3

Earlier quoted context omitted.

Because, if I am reading the article correctly, some hydrogen (which has become radiation) will go through you anyway. This kills you. Somehow gathering up all of the radiation and trying to use it to fuel a ramjet is the same thing as trying to make some sort of shield, which the article says would be very difficult.

I think the idea is that it doesn't ever touch your ship--you just funnel it into your reactor directly. (You have to ionize it somehow...) So it's not equivalent to shielding--it's designed to avoid shielding.

> So it's not equivalent to shielding--it's designed to avoid shielding.

Not quite. Electromagnetic shielding is a potentially viable thing, and can be much less massive than material shielding; a Bussard Ramjet doesn't avoid shielding so much as repurposes the electromagnetic shielding you already needed anyway.

Ionizing is not that big of a problem. If you're going fast enough, hydrogen atoms will be ionized by the interaction with your electromagnetic field. If you're not going fast enough, you can shine a maser ahead of you to ionize things in your path (which cuts in to the efficiency of the ramjet).

Re: Highly relativistic spaceflight would be fatal for passengers and instruments

#12

Post by noonespecial »

There's one thing I never quite got about these speculations. When you consider a ship leaving a solar system and accelerating, and the speed gained turning the "ambient hydrogen" into deadly radiation, why does it always seem to assume that hydrogen atoms are just kind of hanging out at low velocities relative to the home solar system and only turn into a problem when the bald captain says "engage"?

Its a big universe, might the hydrogen atoms already be traveling at these deadly speeds relative to the ship once it leaves Sol? Might there be a "galactic current" so that the ship can go with the flow?

I know its just for fun but its still silly to think that anyone who could propel a canned ape at .8c wouldn't be able fend off a few rouge hydrogen atoms.

Re: Highly relativistic spaceflight would be fatal for passengers and instruments

#15

Post by gliese1337 »

mbq wrote: post #8

Another point for using warp drive (=

Not necessarily. There are some interesting potential radiation issues with "warp drives" as well. For example, at the boundary of a warp bubble of the generally-Alcubierre-like variety, space is shearing / expanding such that virtual particle pairs are incapable of recombining, just like at an event horizon. That could potentially create a great deal of radiation draining energy from the warp field. Additionally, what happens to particles that are intercepted by the travelling bubble? They don't just disappear!

Re: Highly relativistic spaceflight would be fatal for passengers and instruments

#16

Post by gliese1337 »

superkuh wrote: post #13

That's okay, there's time to work on the shielding. 0.03 c is the most that can be feasibly achieved using top-end near future technology like dusty plasma fission fragment rockets. https://en.wikipedia.org/wiki/Fission-fragment_rocket

Thermonuclear pulse propulsion (a la Project Orion) can do better than that- up to 0.1c. And that requires no unproven technology; just a lot of money and a lot of politics (and a lot of fission fuel to buy with that money; I dunno if it's more than you could actually get on the market or not, but it would definitely cost A Lot).

Re: Highly relativistic spaceflight would be fatal for passengers and instruments

#17

Post by gliese1337 »

noonespecial wrote: post #12

There's one thing I never quite got about these speculations. When you consider a ship leaving a solar system and accelerating, and the speed gained turning the "ambient hydrogen" into deadly radiation, why does it always seem to assume that hydrogen atoms are just kind of hanging out at low velocities relative to the home solar system and only turn into a problem when the bald captain says "engage"? Its a big univer…

Because the hydrogen atoms we care about are bound in galactic orbit, and that means they have a relatively low maximum relative velocity to us. If they weren't, they would all fly out into the intergalactic void in geologically short timescales, star formation would cease, and we'd have no such radiation problems after all.

Re: Highly relativistic spaceflight would be fatal for passengers and instruments

#18

Post by [deleted] »

noonespecial wrote: post #12

There's one thing I never quite got about these speculations. When you consider a ship leaving a solar system and accelerating, and the speed gained turning the "ambient hydrogen" into deadly radiation, why does it always seem to assume that hydrogen atoms are just kind of hanging out at low velocities relative to the home solar system and only turn into a problem when the bald captain says "engage"? Its a big univer…

[deleted]

Re: Highly relativistic spaceflight would be fatal for passengers and instruments

#19

Post by gliese1337 »

salimmadjd wrote: post #7

I think once we are advanced enough to figure out how to propel anything that fast or able to pack the needed energy, this part might be easy to solve. Remember per special relativity mass increases as we approach C. Also I think there will be other physiological problems while accelerating to C. It would take like 34 days at 10g acceleration to get to C. I wonder how our bodies would handle 34 days at that kind of g…

> Lastly, we don't really have a good physical understanding of matter at near C speed limits. With mass increasing as we approach C, I don't know we can assume the same physical properties of any material in classical models.

Yes, we do, and yes, we can. Matter travelling at near c relative to us behaves exactly the same as any other matter. That's what frame invariance means. From our perspective, yes, the ship would seem to have more mass, which is a direct result of the equivalence of mass and energy and the fact that it has a crap-tonne of kinetic energy. But from the ship's own perspective, its mass does not change at all- rather, the entire surrounding universe seems to become more massive.

Re: Highly relativistic spaceflight would be fatal for passengers and instruments

#20

Post by celerity »

You know what else is an obstacle to relativistic spaceflight? Being able to do relativistic space flight.

Fun fact: people realized this a long time ago, and proposed different "shields" in front of the ship (it turns out that the most effective shape is a smoothed-out cone [of ice, say] -- see Asimov's Song of a Distant Earth).

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