If I'm reading this at all correctly (as ever, not a given), then one of these Hyperion Power Modules ought to be sufficient for virtually any reasonable SSTO application short of a Pournelle/Niven novel. If that truly proves to be the case (and we ought to have a fairly definitive answer by next spring per Prof Yang), then a robotic mission to capture and deliver an asteroidal body to Earth orbit oughtn't not be too much further into the near-term future I should think. Something small to start, on the order of a cubic mile say.
The above is my comment in initial reaction to this Brian Wang post regarding a potential EMDrive module to be tested in China later this year.
While reference is made to solar power being the energizing force, I suggest that an enclosed and stable power supply as part of any vehicle's structure (whether space or atmospheric) is much more versatile and reliable (within design parameters, of course). Getting a mission to Mars in 41 days via solar power is all well and good, but powering any subsequent surface activity post orbital insertion is going to require something a bit more substantial and less subject to external debilitation, I would think.
I've forwarded this to Rand Simberg and Jerry Pournelle for their thoughts.
Update 8/25: Not a direct response to my e-mail, but on topic nonetheless, from Jerry Pournelle's Current View for Thursday, Sept 25 entry:
For some reason there are a lot of recent reports of reactionless drives. I pay little attention to them, because if someone can build a working model, it is easy enough to demonstrate. After all it doesn't need to work very well; just a tiny bit of hanging off center in a swing is all that's needed to generate enormous excitement. If there's any thrust at all, it is easy to prove. We have had many theories of reactionless drives, the best worked out being that of Col. Wm. Davis, Ph.D.; none of these have resulted in a working model. I have neither the time nor the competence to evaluate theories, and so far no one has offered me the chance to inspect an actual working model. I'd still love to see a working spacedrive. I doubt that I ever will.
Shaw drive - not workable
Regarding the reactionless drive the Chinese are wasting their money on: ShawyerFraud.
The short version: Shaw's diagrams leave out the axial vector component of the force exerted on the slanting sides of the cone, which, added to the lesser force on the smaller end, precisely balances out the force on the larger end. There is no change in overall motion.
I have other notes claiming that the Chinese are working on reactionless drives. I doubt much will come of it, but I certainly wouldn't stop watching them just in case...
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Blissfully displaying my ignorance, I wonder if the Shawyer drive force is at all equivalent to the electromagnetic force? If a magnet is placed within the field of a larger magnet the smaller of the two moves without any measurable change of force on the part of the smaller magnet. If you substitute a variable current to an electro-magnet for the smaller magnet, wouldn't the subsequent action be equivalent to that proposed by Shawyer? I don't know obviously, but given the limits of analogy (magnetism for gravity) this seems to fit the description of what's theoretically happening.