The Current Status of the “Anomalous Thrust” Results

There is a recent paper from the NASA / JSC “Eagle Works” that discusses “anomalous thrust” from various sorts of drives that (to be blunt) violate at least the conservation of linear momentum. These have gotten some breathless reports in the press (Nasa validates ‘impossible’ space drive
) and also the inevitable push back (How to fool the world with bad science)

I thought that the “bad science” take was pretty appropriate when all we had to go on was the conference abstract. Now, however, the full paper, Anomalous Thrust Production… (still not peer reviewed), is out, and it is much better. I still think it is wrong, but I do not think it is bad science, and it will, in my opinion, have to be refuted experimentally.


The “null thruster” in the abstract (which showed about the same effect as the test thruster) is something of a red herring. Reading the paper, they have a true “null load,” which shows no thrust, while the “null thruster” was a modification of a Cannae drive that was not supposed to produce thrust in the Cannae drive theory, and so this was more of a test of drive theory than the experimental setup. In any event, they tested several types of drives, and so weren’t dependent on the Cannae theory overall.

They did pretty much all of the things you would like to see as experimental checks, at least on a first read (such as reversing the direction and making sure the thrust reverses).

They seem to have done a thoughtful and careful job, including testing in vacuum and documenting what they were doing.

So, I still think they are likely wrong, but this ups the ante. In my opinion, you can’t just say “this is obviously wrong.” I bet there will be a bunch of attempts to replicate it in labs all over the place.

I find the theories here (and I have now read several in some depth) to be bad, either wrong, or handwavy, or both*. I would discount them entirely. In the unlikely event that this effect is real (and I mean, some non-standard physics effect), then the theory is likely to be something different than any of the proposals, The experiment’s the thing, and the game now has to be disproving the Eagleworks results. Only once a bunch of people have failed to do that (or one person has done it) is there much else to say.

* On pushing on virtual particles or quantum spacetime or whatever. These are 1 GHz photons, more or less. Such pushing would cause a _vacuum_ dispersion. Vacuum dispersion limits are set by timing of high energy photons from Gamma Ray Bursts across cosmic distances. These tests use ~ 100 MeV photons over ~10^10 light years, and so are many orders of magnitude tighter than the NASA Eagle Works results. This in my opinion rules out any photon – vacuum interaction as the cause of these anomalous thrusts.


5 thoughts on “The Current Status of the “Anomalous Thrust” Results

  1. I would, by the way, entertain a $200 bet on this being overturned. (In other words, I would bet that the standard model would be upheld, why the other side would bet that this anomalous thrust is real. In case there is no agreement, the bet would be resolved by the presence or absence of an operational (and successful) use of anomalous thrust in a space mission up until 10 years to the day after the bet is made (in other words, if in 10 years it is being used to move spacecraft around, I lose).

  2. The Pioneer 10 and 11 spacecraft had ~ 5 watt radios that were always on, yielding a force of ~ 1.7 x 10^-8 Newtons, directed away from the Sun. With a mass ~ 250 kg, that’s an acceleration of 7 x 10^-11 m/sec^2, directed away from the Sun. As it happens, thanks to the so-called “Pioneer anomaly” we can model the acceleration of Pioneer 10 and 11 to order 9 x 10^-10 m/sec^2 (or a little better), so we can say, with great confidence, that the radio system force is ~ 10^-7 Newtons or less.

    Now, this radio system does not have a large Q, but this about a factor of 400 smaller than the 40 microNewtons observed in the NAS Eagle Works paper. Note that radio is at prime focus, so photons do travel from there and reflect off the dish, so there is a Q of order 1. I would curious to see the predictions from the various theories for this case.

  3. If you read the NASA paper very carefully it appears that they were not actually able to test their thrusters in a vacuum. (Frankly, I find this point very confusing; the paper needs a better description of just what was done.) They talk about the vacuum chamber, how it was pumped out, etc., but then say

    ” Vacuum compatible RF amplifiers with power ranges of up to 125 watts will allow testing at vacuum conditions which was not possible using our current RF amplifiers due to the presence of electrolytic capacitors.”

    So, from that, I assume that they did not test in vacuum. That makes a big, big difference (and is not a good sign for those who are in favor of new physics here), as it raises the prospect of air currents causing their 40 microNewtons of thrust;

  4. I feel like living dangerously, so I am going to post this here.

    Assume for a moment that the various experimental claims of EM thrust are true (which I think is decreasingly likely). How might they be explained? I think that there are two possibilities – one is that there is a failure of a conservation law, the other is that momentum is being carried off by some (presumably) new particle. My strong inclinations would lean towards the latter case, and I have been thinking about ways things might be made right. Consider the axion, which is well grounded in QCD, but which is not in the standard standard model (although it easily could be, should the blasted things ever be detected.) Axions would interact with photons in the Primakoff effect, where one axion interacts with two photons – see for an overview.

    Basically, in the Primakoff effect, 2 photons could collide and create a photon, say inside the Sun, and then out here the axions could convert back to 2 photons in a magnetic field. This has led to attempts to look for axions using solar telescopes located underground – the so called “Light shinning through the wall” experiments. (There are no positive results to date.)

    So, as a theory to explain EM thrust, imagine an axion-like particle, massive but very light and non-interacting with ordinary matter, but one that can interact with photons and has a sharp resonance in particle-photon interactions for photons around 1 GHz. You set up a suitable waveguide, 1 GHz photons get converted into these particles, and momentum (and energy) is thus leaked out through the wall. Photons at other wavelengths would (hypothetically) have a negligible interaction (in this model), and so (waving my hands furiously) various other experimental constraints are not a problem.

    You can even use the relation between energy and thrust to estimate the velocity of the produced particles. The NASA paper claims 40 micronewtons produced by 28 watts, or a ratio of 1.4 x 10^-6. Now, for photons momentum, p, = E / c (where E is the energy), so the thrust to power ratio is 3.3 x 10^-9, or a factor of 427 smaller. Since for ordinary (non-relativistic) matter p / E = m v / (1/2 m v^2) = 2 / v, the ratio of ratios (thrust / power for ordinary matter divided by thrust / power for light) is = 2 c / v, so the claimed ratio implies v ~ 5 x 10^-3 c or 1400 km / sec. The photons of 1 GHz light have an energy of 6.6 x 10^-25 joules, so if 2 photons give rise to one new particle at a velocity of v = 1400 km/sec, it has a mass of 2 E = 1/2 m v^2, or m = 10^-36 kg, or a rest mass energy of 0.75 electron volts (which, as it happens, it just on the dicey upper edge of the allowed axion mass range).

    Now,as it happens, people have looked for axions using a similar technique and with much greater sensitivity (see ). So, the big problem with this sort of explanation is why don’t the axion searches see this effect? What’s different between the two types of microwave resonant cavities ? Or did they just happen not to look at exactly the right frequency (which I doubt).

    Also, these sorts of explanations have a “just so story” aspect to them, which is, to me, unconvincing. However, in the unlikely eventuality that these results are upheld, I would expect to see a plethora of theoretical speculation along these lines, and a serious reanalysis of a lot of the microwave axion searches.

  5. A 6 U cubesat is going to be stretched to generate 20 watts of power at peak. I don’t see any reason why you couldn’t shrink the thruster by a factor of 4, to 7 watts and maybe 10 microN. Say the mass came in at 10 kg – that’s a thrust of 10^-6 m/sec^2. Using the info here
    I get that the drag on a 10 x 10 cm cubesat released from the ISS would be 4 x 10^-7 m/sec^2. (That should be regarded as very approximate.) So, there is just a chance that a cubesat with a EM thruster would be able to raise its orbital altitude. Now, while I frankly am extremely skeptical about these drives actually working, I do have to admit that this test, if passed, would be pretty conclusive.

    All it would take is someone cutting a check for a sufficient amount…

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