NASASpaceFlight.com Forum
General Discussion => New Physics for Space Technology => Topic started by: officialBillyMays on 02/27/2016 09:45 pm
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From everything I've seen about the emDrive, this forum seems to be the place where people are closest to the action happening in the experiments, and which are dominated neither by offhand dismissals nor total cheerleading of the technology.
Even without combing through hundreds of pages of the main threads, from what I've gleaned from elsewhere it seems obvious that no one really knows how the hell this is supposed to work, if it really can at all. Given that the following questions probably don't make any sense - but if there's anyone up for trying them, then what I want to know is the following.
Based on what we know (or think we know) now, what are the likely capabilities and limits of this device?
The thing about the emDrive is that to me (with my layman's, basic-high-school-level knowledge of physics), this seems to be one of those technologies that could bring to life classic, 2001 and Jetsons-style SF to life (cultural and economic factors notwithstanding). Is there any possibility that this thing could really scale up to the 1 N/W or sustained 1 g acceleration figure I've seen quoted in some places? How much of that is just hype?
And if we can reach that 1 g figure, then that does truly give us flying cars (and helicarriers, and landspeeders, and jetpacks, etc.), right? Or space launch as easy as modern air freight? And how would latter even work? If 1 g acceleration upwards cancels out the Earth's gravity, doesn't that only enable a static hover? Wouldn't you still need to accelerate upward and laterally to some degree in order to reach orbit? Or could you reach a high enough point that the steady weakening of Earth's gravity field would enable you to just slowly float upwards??
Moreover - when out of the Earth's gravity well, is there anything stopping us from eventually accelerating to within minute fractions of c, Bussard Ramjet style?? From my limited understanding of conservation of momentum, it's that as the craft goes faster the kinetic energy of its momentum becomes greater than what the engine is putting into acceleration and is being created out of nothing. So does that build in a hard efficiency limit to any possible reactionless or quasi-reactionless engine, such that we'd eventually a hit a maximum speed lower than c?? TL;DR assuming it works and works this well, does physics as we know it allow an engine such as the emDrive to give us rapid interstellar travel within a (subjective) human lifetime? The closest to Star Trek we'll likely ever get??*
I understand that if it never scales up that well there's still some things it could do really well in the vein of faster and more efficient interplanetary travel (much better than modern ion drives or VASIMR). I just want to know if current research leaves any optimism that it'll ever get that far, and what physics will and will not allow us to do assuming it does. So if someone up to date with this could try their hand at answering this it'd be highly appreciated!! :D
*I'm not banking on the Alcubierre drive just yet - perhaps partly on the Fermi Paradox implications.
PS: I understand that these sorts of applications require an amazing, lightweight energy source better than anything we have at the moment. I've been following LENR for a few years now and I think there's enough positives to say that it's a real phenomenon, so I'm hopeful that we'll eventually figure that out. And if that doesn't work, perhaps compact classical fusion could also fill those shoes.
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This probably belongs in the Feature Article thread (http://forum.nasaspaceflight.com/index.php?topic=37438.0), which is closer to a "the EM Drive effort for newbies" thread than anything else on site, but I'll answer none the less. :)
The answer to all of the above is "we don't know." It's proving to be a struggle to get a strong signal to noise ratio in the experiments that have been publicly discussed and produced by hobby engineers and third parties, and cannot yet draw firm conclusions about what the source or potential of the apparent, anomalous forces might be. Between more thoroughly documented experiments, more power, and better EM drive engineering, we're all looking for a way to get the signal out of the noise floor to prove (or disprove) the existence of propellantless thrust.
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Page 1, post 1 of the main EM Drive thread gives links to the relevant wiki.
Beyond that, as stated, there are no few unknowns. Severe problems abound with the theoretical work, the experiments, and the various models - but there is just enough in the way of positive info from all those sources to make one wonder.
I have been following the various EM Drive threads for over a year and a half now, and my 'belief-o-meter' remains stuck on 'maybe.'
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If you can't go through all the threads and the wiki then you can't understand the research process so far. The topic is too complex and multifaceted to be condensed down to one post or even one paper, though some have tried. For any newcomer, even with a relevant degree mind you, it is best to start with the wiki and read the theory sections. Then see the experimental data since 2015 (least error prone). Then see the sims and engineering talk throughout the threads.
There is no shortcut to understanding why relatively sane people devote so much time and money to this other than setting out a good 30 or so hours to fully absorb the threads so far. Consider it a university course.
If you value intellectual integrity, don't fall into the mental trap of blindly accepting or dismissing the effect without familiarizing yourself with the detailed debate and observations so far. Of course I say this having followed since the third thread so I appreciate how big of an ask reading all the threads is, but it is well worth it.
Happy reading to all :)