What’s an emDrive?

A means of producing thrust in a vacuum without using a reaction mass. Possibly a reactionless drive.  If it really works, then this is a game changer for spaceflight. The chances that it’s real? Don’t hold your breath. 

Wikipedia has a pretty good article looking at how it works, along with the controversy surrounding the apparently positive independent tests. For now, as long as the method is not disproven, this is a usable means of providing a reactionless drive in Science Fiction. It overcomes one of the major issues in space travel, namely the incredible mass requirements to travel anywhere within a solar system in timeframes reasonable for a interplanetary commerce to make sense. 

Taking the value in the Wikipedia article of 0.1 N/kW, we can compute the mass that could be accelerated at one gravity. Since F=ma, and F=0.1 N and a=9.8 m/sec squared, 0.1=9.8m. Solving for m, we get more=0.1/9.8=.98 kilograms/kW. 

At this point you’ll need to determine the mass necessary to generate that kilowatt of power. I don’t think you can get reasonable results with solar. Possibly 0.1 g in the inner solar system, where the solar flux is higher. I’m not sure nuclear fission will work, either. Haven’t done the math, but the shielding is generally heavy. Nuclear fusion ought to work well. 

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