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25 September 2008

Chinese Claim Em Drive Works


The EM Drive is a reactionless drive originally developed by a man named Roger Shawyer.  He to use a magnetron to create and bounce microwaves around a chamber.  The thrust comes from an imbalance in the resultant forces coming from the reflections due to relativistic effects.  The EmDrive has been panned by the scientific community and there has been no independent peer review.

With that said, after the original British and then American interest fell through, the Chinese picked it up.  They now claim to have developed an experimental simulation that confirms the validity of Shawyer's drive.  The thrust produced is comparable to ion drives but the main differences are that there is no reaction mass and weight.  The Em Drive weighs 7 kilos and produces 85 mN (milli-Newtons) of thrust.  NASA's NSTAR ion thruster weighs upwards of 30 kilos, uses four times more power, consumes 10 grams of fuels per hour and produces 92 mN of thrust.  I have not been able to confirm the weight of the NSTAR but according to, NSTAR uses just over 4 grams of fuel per hour.  A bit of an overstatement.

The EmDrive is something that I would need to see to believe until then, its a perpetual motion machine.


kert said...

Well, it can really reliably be confirmed to "work" in space as deep space propulsion is about the only useful application for it, so seeing it at work could be a challenge ...

Alexander DeClama said...

Thrust is thrust, whether in orbit or on the ground. We knew ion drives worked before we sent them out to space. It stands to reason that I can expect the same out of the EmDrive.

kert said...

Couple of caveats. If thrust was shown on the ground, you still dont know if it will actually work in space. Asymmetric capacitor thrusters ( the "lifters" ) were speculated to be able to work in space as well for a long time. Obviously they actually dont work in vacuum.
And then there are couple of concepts for space propulsion that can really only be proven in space, like magnetic momentum exchange tethers.

IMHO even if you get the demonstration on ground for EmDrive producing thrust, this will be no guarantee that it will perform its only useful function, deep space propulsion.

Its like with cold fusion. One can experiment and claim all he wants, but until you can power a light bulb without putting extra energy in its still useless. I guess its an engineers, not scientist POW :)

Anonymous said...

Sounds interesting--and it reminds me of Battlestar Galactica. ;-)

That aside, if the Chinese are able to get this working (and that is a big if) then they may have a head start towards Alpha Centauri.


Alexander DeClama said...

Yes we do know. Just like with the lifters, legitimate science knew that the lift was provided by airflow, not magic em fields. The problem is that there is no legit reason for the EmDrive to produce thrust. It violates the very principle that makes conventional rockets work. You are partially correct about the tethers, they cannot be demonstrated on the ground. But we have a working model that shows it will work. We dont for the EmDrive. If whether it works in deep space is your concern, put it in a vacuum chamber and hook it up to a force gauge. My point is that if no one else can get it to work, it's probably bunk.

Alexander DeClama said...

Colonyworlds - how so? I thought they used regular old school thrusters

Anonymous said...

Hey Alexander,

Your right! A quick Google search revealed that fairly quick to me!

Either way, I am not sure how China will be able to make this work.

If (against all odds) they do succeed, then I guess I'll have to pick up Chinese as another language to learn.


Alexander DeClama said...

If the Chinese do get it working, in the short run it's probably a VBT. In the long run, it'll spur development in it domestically, just like Sputnik did for NASA.