31 thoughts on “The Reactionless Drive”

  1. What I don’t understand is why they don’t just build a car?

    Different tests have shown 30 mN per 100 watts.

    So you’d only need about 15kW (200 hp) to lift 1000 lbs.

    Crank ‘er up.

      1. Never do google math after a three day ‘The Invaders’ marathon. So obviously it’s Paul’s fault. 😉 The 1985 movie is so much funnier after seeing the series which I somehow missed as a child.

    2. That’s in milliNewtons, not Newtons. 200 HP would lift about a pound.

      To generate 200 HP of microwave radiation the spacecraft is going to need about 60 square meters of solar cells, which should have about 0.36 milliNewtons of solar radiation pressure.

  2. They are supposedly testing the Cannae drive not the EmDrive. NASA tested both on a vacuum chamber and the Cannae drive produced no thrust IIRC.

    Still it would be interesting if these reactionless drives work. You wouldn’t need to carry any mass on the vehicle.

  4. Suppose there was some “there”, there, that the experiment recorded some measurable thrust?

    How do you know the effect is not some kind of “force field” or “tractor beam”, neither of which violates F=ma.

    To know if something is truly reactionless, you would need to test it far from any bodies it could push against?

    1. Well it has to be pushing against something. Even assuming it does work like they say it works.

      It’s basically the difference between a rocket and a propeller craft. The rocket ejects mass to provide thrust while the propeller pushes against the medium (air, water, etc) to provide propulsion forward. In practice we cannot do this in space because there is little matter there to push against. The way these “reactionless drives” are supposed to work is by pushing against something that is there in space. Call it quantum vacuum foam or whatever.

      So not it does not break physics. You do need to put energy in to get thrust out. Assuming it works anyway.

      1. Pushing against mass outside the device resolves most of the stronger physics difficulties, but leaves the question of what previously unknown force is doing the pushing. Pushing against “quantum vacuum foam”, which is not observed to have a particular motion frame, still leaves the conservation of momentum problem unresolved.

        1. The Earth and near-Earth environment is filled with all manners of electric and magnetic fields. The device is coupling through such fields to push against the Earth. The forces are small enough that this very well could be the case.

          I am “hand waving” in not proposing a precise mechanism, but I am proposing that if the thing “works”, there has to be a mechanism, and it is more likely something not involving strange Physics but instead strange engineering calculations.

          I am also saying that if you are really going to test this thing, you may need to place it in interplanetary or even interstellar space?

          1. Yes, I would agree with that. However, even if it is an expensive EM compass, it might find application in LEO or any orbit that experiences a significant flux of Earth’s geomagnetic field. How much is enough to be considered “significant”? A perfect question for a cube sat to answer!

      2. They both provide thrust. They both work by exchanging momentum, boosting some mass one way, which propels the other mass the other.

        Here, there is nothing carrying away a reaction momentum, except for the very small momentum of radiation that flees. The most force you could get from that would be the power divided by c, so for 100 W, you could get 100/3e8 = about 0.3 micro-N.

        For this thing to work, you’d basically have to have something in the universe absorb the reaction momentum. I see nothing here that can couple to any matter or energy field to do that. I think it’s just a bunch of measurement error.

    2. How far is far enough? According to Mach’s Principle, every body in the universe is ganging up to produce a force proportional to your acceleration relative to their collective mass center, which is the m*a bit from f = m*a.

      It’s an interesting thought experiment – if there were no matter in the universe but you, how could you establish an inertial frame? How would you know if you are accelerating? Accelerating toward what?

      1. That is equivalent to stating that the universe itself is moving. With nothing to compare to, there would be no way to measure distance or elapsed time. There would be no way to differentiate between a million years and a millisecond.

        Or, imagine there are only two objects in the universe. Are they spiraling inwards or are they moving directly towards each other?

  5. This is the best way to answer all of the questions, and is made possible by the advent of the cubesat. Though I have some inside information on the EmDrive that suggests it works, I don’t believe it yet. This is a great experiment.

    If it works, then when it comes to space propulsion, Fetta will be the Big Cheese.

  6. The physics of these make my head hurt. And that’s after graduate studies specifically in physical chemistry/optics.

    Both “It is reactionless” and “It is -not- reactionless” are interesting results at this point, IMNSHO. Because even if it isn’t reactionless, there’s something unexpected going on.

  7. I’m not sure just getting a cubesat with a test article drive module into orbit will necessarily settle anything beyond reasonable doubt. You’d eliminate most terrestrial influences, to be sure, but you’d hardly eliminate Earth’s magnetic field. If the thrust seemingly detected in Earthside experimental lash-ups is actually due to some obscure interaction with Earth’s magnetic field, the thing would work about as well in LEO as it, at least sometimes, seems to work down here.

    For a definitive answer about whether, and, if so, how well, the thing will work in deep space, I suspect there’s no substitute for doing the test in deep space. Just to also eliminate Earth’s gravity field as the source of an even more obscure interaction, the nearest suitable place to do as fair a test as possible would seem to be L1.

    If we see measurable net thrust at L1, I’m prepared to say the thing works even if we can’t explain how. What the heck, we’ve been using electricity and magnetism for a couple centuries now and there is plenty we still don’t seem to know about both of them.

    1. Well, if it works in LEO and then thrusts its way up to a certain altitude but then can go no further I guess we’ll know it has something to do with being in Earth’s vicinity.

    2. But even the Professor couldn’t figure out how to turn Gilligan’s radio into an interplanetary propulsion system.

  8. Unless there is a current flowing into the cubesat on one side and out the other side, the earth’s magnetic field couldn’t possibly change the velocity of the satellite. A magnetic field acting on a body having only internal current loops (or no current loops) can only impose a torque, not a linear force.

    I guess there is one other “unless,” and that would be: unless the cubesat contains a magnetic monopole. Now that would be exciting!

    1. Yes, this is the idea behind current carrying tethers in LEO – the circuit is completed through the plasma surrounding the tethered vehicles, so it is possible to get net force on the tether because you only get half of the torque couple acting on it.

  9. Ridiculous discussion. Give them a patent and make a thousand of them, pass them around to physics departments around the world and let them play with them. I imagine within a month or two we would know all about it, one way or the other.
    Not rocket science.

    1. In the case of the EmDrive it was all classified until recently. He has a deal with UK government to declassify information after 10 years have passed. So he has shown some the data and the design he obtained for his initial tests but his later work is still classified.

    2. IIRC, there already are several physics departments that have duplicated the experiments and had the same results that still can’t be explained.

      1. I watched a show on it. Some university in Germany got positive results. Then, they turned the thing upside down, and got the same result. It was just a measurement bias.

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