7 ms·

Some Emerging Possibilities For Space Propulsion

53 points by mike_esspe 12y ago

thearn4 12y ago
NASA used to have a small program to evaluate concepts for breakthrough propulsion, which ended around 2002. http://www.grc.nasa.gov/WWW/bpp/ http://www.grc.nasa.gov/WWW/bpp/
- chroem 12y ago
  Why not a fission fragment rocket? We could send a probe to the centauri system with current technology. https://en.wikipedia.org/wiki/Fission-fragment_rocket https://en.wikipedia.org/wiki/Fission-fragment_rocket
Steuard 12y ago
Speaking as a professional physicist, this page feels awfully light on actual information. And as far as I can tell, that's merited: there's not a lot of solid science discussed on this page, or even especially tantalizing ideas for what might come next. They spend a lot of time discussing quantum vacuum energy, but the one short note about its "propulsion implications" includes the comment that "Those particular gravity theories are still up for debate." That's perhaps generous: quantum gravity isn't far from my field, and I've never heard of this take on the origin of gravity and inertia. I'm also rather puzzled by the quote "Although gravity’s effects on electromagnetism and spacetime have been observed, the reverse possibility, of using electromagnetism to affect gravity, inertia, or spacetime is unknown." That's really not at all true. Our models of gravity all include very well-defined effects of electromagnetism on spacetime: the energy density in those fields causes space to curve, just like any other form of mass or energy. Hypothesizing anything else would require fundamental changes to the theory. That's entirely possible! But it's misleading to characterize the current state of affairs as having an unfilled gap like this. So yeah. I'd love a good spacedrive as much as the next guy. But this article doesn't do much to make me optimistic about it.
- mrfusion 12y ago
  How do these "legitimate" ideas for FTL deal with causality? I've always wondered that. People always use causality to argue against FTL, but then readily acknowledge that wormholes or Albicurie might allow it. I'm not getting that disconnect?
  - TheLoneWolfling 12y ago
    http://arxiv.org/abs/1005.1614 http://arxiv.org/abs/1005.1614
    - jordan0day 12y ago
      That was an interesting paper, but I'm having trouble with the concluding paragraphs. Is the argument against the grandfather paradox essentially "You can set up the mechanism to create the grandfather paradox, but it won't actually work the way you think it will?"
      - TheLoneWolfling 12y ago
        Pretty much.
      - Steuard 12y ago
        Bob's argument is (more or less) that it's easy to set up a thought experiment in which you imagine setting up closed causal curves, but that the devil is in the details. Earlier in the paper, he argued that the new physics will still have its own causal structure, in a well-defined sense involving initial conditions and differential equations. If you start with complete and well-behaved initial data, his argument is essentially that the state of the system will always evolve forward in time in a consistent way (and in particular, there's no way for closed causal curves to arise out of nowhere). So those last paragraphs that you're asking about attempt to interpret that conclusion in the context of a thought experiment aimed at creating a grandfather paradox. Geroch's answer is to say "the details will depend on your precise model, but the math makes it unavoidable that something about the model will make your plan impossible". Maybe the experimenter's normal-matter hands just can't ever move fast enough to push the special fluid past light speed. Maybe FTL-fluid is explosive when it comes in contact with normal matter. But the ultimate mathematical conclusion must hold. (I won't swear to have worked through every step of these arguments in detail myself, but Bob Geroch is a world-class expert on this sort of thing. The one caveat that I'd add is that I think his arguments here are classical, and that bringing quantum mechanics into the mix might change things. It's possible that it would only change things in topologically disjoint sectors within a general-relativistic spacetime, but something like that might conceivably escape his premises.)
eudox 12y ago
I honestly can't imagine why NASA even acknowledges the idea of FTL travel - Is there some kind of propeller beanie PAC forcing their hand? They should just have a page that says: "FTL is impossible, but that's fine, once you get used to the way things are."
- ceejayoz 12y ago
  Scientists, rightly so, are a little leery of stating "we know everything". There's no guarantees our current theories are perfect - in fact, it's extraordinarily unlikely that they are. Also of note: https://en.wikipedia.org/wiki/Alcubierre_drive https://en.wikipedia.org/wiki/Alcubierre_drive
  - jp555 12y ago
    I consider how we understand that at the speed of light, all distances are zero. So even if you can somehow travel at C, there would be nowhere to go, because you're already everywhere. Given this, travelling faster than C can be seen as travelling a distance of less than zero... which makes no sense.
    - ceejayoz 12y ago
      Humans have always had a big gap between "how we understand" and knowing everything. Plenty of stuff in physics doesn't make intuitive sense, and there are things like https://en.wikipedia.org/wiki/Alcubierre_drive https://en.wikipedia.org/wiki/Alcubierre_drive theorized that wouldn't require brute force exceeding C.
      - jp555 12y ago
        That drive has a bit of an issue that even if it worked, it would probably destroy it's destination in a annihilating blast of gamma radiation on arrival.
- TheCraiggers 12y ago
  >They should just have a page that says: "FTL is impossible, but that's fine, once you get used to the way things are." No offense intended to you, but I feel this is a disastrously negative attitude to have. Except where morals dictate otherwise (which are outside the scope of science anyway) nothing is banned from exploration. Suggesting otherwise implies that we know all there is to know about a subject; to me, this is analogous to willful ignorance. Science is dedicated to removing ignorance, not enforcing it.
sdegutis 12y ago
"Theory for a faster-than-light "warp drive" consistent with general relativity." For real?
- madaxe_again 12y ago
  http://en.wikipedia.org/wiki/Alcubierre_drive http://en.wikipedia.org/wiki/Alcubierre_drive
  - crusso 12y ago
    The only bright spot in that article is that the math doesn't contradict general relativity. Everything else points to its being a curiosity that would disappear if GR were more integral with Quantum Mechanics.
sehugg 12y ago
For something a bit more realistic, we are still studying nuclear propulsion in fits and starts since we halted its development in the 60s: http://www.nasa.gov/topics/technology/features/ntrees.html#.U5cQ6i8ikUs http://www.nasa.gov/topics/technology/features/ntrees.html#....
deleted 12y ago
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deleted 12y ago
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- venomsnake 12y ago
  And you will need earth sized spaceship to survive crashes even with hydrogen atoms. Unless there is something that I don't understand. You just cannot travel with that kind of speeds in normal space IMO.
madaxe_again 12y ago
Here's an interesting Wired interview with Podkletnov on his anti-gravity work from '97 : http://archive.wired.com/wired/archive/6.03/antigravity.html?pg=1&topic=&topic_set= http://archive.wired.com/wired/archive/6.03/antigravity.html...
jcfrei 12y ago
I would be much more excited if NASA resumed the research on NERVA (http://en.wikipedia.org/wiki/NERVA http://en.wikipedia.org/wiki/NERVA). 50 years later a nuclear propulsion drive still seems like the most promising and cost-efficient way to explore our solar system.
misterfusion 12y ago
A real-life warp drive can be practically possible by employing phased standing waves. http://www.youtube.com/watch?v=6zh9abFF3ZE http://www.youtube.com/watch?v=6zh9abFF3ZE
throwwit 12y ago
The submitter should have tacked on (2007).

53 points by mike_esspe 12y ago

NASA used to have a small program to evaluate concepts for breakthrough propulsion, which ended around 2002. http://www.grc.nasa.gov/WWW/bpp/ http://www.grc.nasa.gov/WWW/bpp/

chroem 12y ago
Why not a fission fragment rocket? We could send a probe to the centauri system with current technology. https://en.wikipedia.org/wiki/Fission-fragment_rocket https://en.wikipedia.org/wiki/Fission-fragment_rocket

Steuard 12y ago

Speaking as a professional physicist, this page feels awfully light on actual information. And as far as I can tell, that's merited: there's not a lot of solid science discussed on this page, or even especially tantalizing ideas for what might come next. They spend a lot of time discussing quantum vacuum energy, but the one short note about its "propulsion implications" includes the comment that "Those particular gravity theories are still up for debate." That's perhaps generous: quantum gravity isn't far from my field, and I've never heard of this take on the origin of gravity and inertia. I'm also rather puzzled by the quote "Although gravity’s effects on electromagnetism and spacetime have been observed, the reverse possibility, of using electromagnetism to affect gravity, inertia, or spacetime is unknown." That's really not at all true. Our models of gravity all include very well-defined effects of electromagnetism on spacetime: the energy density in those fields causes space to curve, just like any other form of mass or energy. Hypothesizing anything else would require fundamental changes to the theory. That's entirely possible! But it's misleading to characterize the current state of affairs as having an unfilled gap like this. So yeah. I'd love a good spacedrive as much as the next guy. But this article doesn't do much to make me optimistic about it.

mrfusion 12y ago
How do these "legitimate" ideas for FTL deal with causality? I've always wondered that. People always use causality to argue against FTL, but then readily acknowledge that wormholes or Albicurie might allow it. I'm not getting that disconnect?
- TheLoneWolfling 12y ago
  http://arxiv.org/abs/1005.1614 http://arxiv.org/abs/1005.1614
  - jordan0day 12y ago
    That was an interesting paper, but I'm having trouble with the concluding paragraphs. Is the argument against the grandfather paradox essentially "You can set up the mechanism to create the grandfather paradox, but it won't actually work the way you think it will?"
    - TheLoneWolfling 12y ago
      Pretty much.
    - Steuard 12y ago
      Bob's argument is (more or less) that it's easy to set up a thought experiment in which you imagine setting up closed causal curves, but that the devil is in the details. Earlier in the paper, he argued that the new physics will still have its own causal structure, in a well-defined sense involving initial conditions and differential equations. If you start with complete and well-behaved initial data, his argument is essentially that the state of the system will always evolve forward in time in a consistent way (and in particular, there's no way for closed causal curves to arise out of nowhere). So those last paragraphs that you're asking about attempt to interpret that conclusion in the context of a thought experiment aimed at creating a grandfather paradox. Geroch's answer is to say "the details will depend on your precise model, but the math makes it unavoidable that something about the model will make your plan impossible". Maybe the experimenter's normal-matter hands just can't ever move fast enough to push the special fluid past light speed. Maybe FTL-fluid is explosive when it comes in contact with normal matter. But the ultimate mathematical conclusion must hold. (I won't swear to have worked through every step of these arguments in detail myself, but Bob Geroch is a world-class expert on this sort of thing. The one caveat that I'd add is that I think his arguments here are classical, and that bringing quantum mechanics into the mix might change things. It's possible that it would only change things in topologically disjoint sectors within a general-relativistic spacetime, but something like that might conceivably escape his premises.)

eudox 12y ago

I honestly can't imagine why NASA even acknowledges the idea of FTL travel - Is there some kind of propeller beanie PAC forcing their hand? They should just have a page that says: "FTL is impossible, but that's fine, once you get used to the way things are."

ceejayoz 12y ago
Scientists, rightly so, are a little leery of stating "we know everything". There's no guarantees our current theories are perfect - in fact, it's extraordinarily unlikely that they are. Also of note: https://en.wikipedia.org/wiki/Alcubierre_drive https://en.wikipedia.org/wiki/Alcubierre_drive
- jp555 12y ago
  I consider how we understand that at the speed of light, all distances are zero. So even if you can somehow travel at C, there would be nowhere to go, because you're already everywhere. Given this, travelling faster than C can be seen as travelling a distance of less than zero... which makes no sense.
  - ceejayoz 12y ago
    Humans have always had a big gap between "how we understand" and knowing everything. Plenty of stuff in physics doesn't make intuitive sense, and there are things like https://en.wikipedia.org/wiki/Alcubierre_drive https://en.wikipedia.org/wiki/Alcubierre_drive theorized that wouldn't require brute force exceeding C.
    - jp555 12y ago
      That drive has a bit of an issue that even if it worked, it would probably destroy it's destination in a annihilating blast of gamma radiation on arrival.
TheCraiggers 12y ago
>They should just have a page that says: "FTL is impossible, but that's fine, once you get used to the way things are." No offense intended to you, but I feel this is a disastrously negative attitude to have. Except where morals dictate otherwise (which are outside the scope of science anyway) nothing is banned from exploration. Suggesting otherwise implies that we know all there is to know about a subject; to me, this is analogous to willful ignorance. Science is dedicated to removing ignorance, not enforcing it.

sdegutis 12y ago

"Theory for a faster-than-light "warp drive" consistent with general relativity." For real?

madaxe_again 12y ago
http://en.wikipedia.org/wiki/Alcubierre_drive http://en.wikipedia.org/wiki/Alcubierre_drive
- crusso 12y ago
  The only bright spot in that article is that the math doesn't contradict general relativity. Everything else points to its being a curiosity that would disappear if GR were more integral with Quantum Mechanics.

sehugg 12y ago

For something a bit more realistic, we are still studying nuclear propulsion in fits and starts since we halted its development in the 60s: http://www.nasa.gov/topics/technology/features/ntrees.html#.U5cQ6i8ikUs http://www.nasa.gov/topics/technology/features/ntrees.html#....

deleted 12y ago

[deleted]

deleted 12y ago

[deleted]

venomsnake 12y ago
And you will need earth sized spaceship to survive crashes even with hydrogen atoms. Unless there is something that I don't understand. You just cannot travel with that kind of speeds in normal space IMO.

madaxe_again 12y ago

Here's an interesting Wired interview with Podkletnov on his anti-gravity work from '97 : http://archive.wired.com/wired/archive/6.03/antigravity.html?pg=1&topic=&topic_set= http://archive.wired.com/wired/archive/6.03/antigravity.html...

jcfrei 12y ago

I would be much more excited if NASA resumed the research on NERVA (http://en.wikipedia.org/wiki/NERVA http://en.wikipedia.org/wiki/NERVA). 50 years later a nuclear propulsion drive still seems like the most promising and cost-efficient way to explore our solar system.

misterfusion 12y ago

A real-life warp drive can be practically possible by employing phased standing waves. http://www.youtube.com/watch?v=6zh9abFF3ZE http://www.youtube.com/watch?v=6zh9abFF3ZE

throwwit 12y ago

The submitter should have tacked on (2007).