You’re supposed to talk out your cool idea before you embarrass yourself publicly

So that’s how unicorns fly through space — by pooping out rainbow-colored slinkies. I’ve always wondered.

The brain-twisting image comes from a review of NASA’s “helical drive” proposal, the idea that you could get massless thrust by accelerating particles to the speed of light as they traveled forward, gaining mass, and then slowing them down as they bounce back so they’d lose mass. Presto! Net acceleration forward. Only it won’t work, because:

The problem is that, even though the author does a very nice simulation, he has left out the fields that do the accelerating. When we accelerate ions using a magnetic or electric field, the ions push back on the field. There is an equal and opposite force exerted on the electrodes and coils that produce the fields, and those just happen to be in the spaceship, too.

The concept is trivially dismissed. What’s odd about it all is that the guy who proposed it to NASA is at NASA, and even admitted in his proposal that there are a few weaknesses.

  • Basic concept is unproven
  • Has not been reviewed by subject-matter experts
  • Math errors may exist!

His proposal is full of charts and calculations, and is obviously carefully thought out and represents a substantial investment of work, yet he never rolled his office chair out into the hallway and asked an engineer in one of the cubicles nearby for a quick reality check, before going public with a crazy idea that was going to get shot down in a few seconds by some smart guy on the internet? Is this what NASA managers do all day?

This is a good example of how communication is an essential component of science. Individual minds can get led down the garden path by a tantalizing notion, but a group of minds can ferret out the problems before you make a big splashy investment of your reputation in something with a fatal flaw.


  1. slithey tove (twas brillig (stevem)) says

    Incomplete analysis of the system. Like saying a sphere has the same volume as a cube because they both are based on R^3

  2. slithey tove (twas brillig (stevem)) says

    You know the famous: power your sailboat with on onboard fan blowing the sails

  3. Akira MacKenzie says

    I have a good friend who used to adamantly believe in ghosts, bigfoot, UFOs and other supernatural phenomenon (he’s become a lot more skeptical since then) for the mere reason that “They’re just too cool NOT to exist.”

    I think we’re dealing with something similar here.

  4. Andrew G. says

    There are rare cases, though, when an idea that looks obviously stupid turns out to actually work; one of the better examples is described here.

  5. PaulBC says

    It’d be interesting to know how he made it to NASA without (apparently) ever hearing of conservation of momentum. I say that not because I know for certain whether there is some very esoteric and speculative physics that could potentially violate it, but that I would expect anyone proposing a propulsionless drive like this to include “appears to violate conservation of momentum” among the bullet points, and explain upfront why this should not be an obstacle to reading further.

  6. nomadiq says


    Agreed. I would think the title of the paper should be along the lines of ‘Violation of Conservation of Momentum In New Propulsion Scheme’ – any other title is burying the lead.

  7. cvoinescu says

    PaulBC @ #7:

    […] I would expect anyone proposing a propulsionless drive like this to include “appears to violate conservation of momentum” among the bullet points, and explain upfront why this should not be an obstacle to reading further.

    He does say that upfront, only perhaps too obliquely:

    • “Conservation of Momentum” for concept is not well understood
    • Several paths exist for momentum conservation

    The second statement is mere wishful thinking, but the first one is an understatement, if anything. Not well understood indeed.

  8. a_ray_in_dilbert_space says

    To day “conservation of momentum” is not well understood is utter complete horseshit. It is one of the most fundamental conservation laws in physics. That said, no less physicists than Werner Heisenberg and Niels Bohr seemed willing to give up on it in an absolute sense (they still demanded it be true “on average”) to explain the apparent violations of conservation of momentum and energy that were observed in nuclear beta decay.

    Wolfgang Pauli took a different approach–positing the existence of the neutrino in 1930. Pauli, himself, wasn’t really sure whether to take the idea seriously, considering that either such a particle ought to have already been observed or that it would be “impossible” to observe, and so a “great sin”. Fermi was the one who worked out the theory and coined the term “neutrino”. Neutrinos were first observed in 1956 (for which the discoverers received the Nobel prize in 1995) and now are one of the frontiers of astronomical research.

    The putative existence of dark matter and dark energy are similar ideas–an attempt to save energy and momentum conservation in the midst of observations that seem to contradict them on large, intergalactic scales.

  9. pilgham says

    The Daily Mirror takes one step further with “NASA engineer proposes fuelless engine to propel spacecraft ‘almost at speed of light'” which I’m sure even the original author would agree is wrong.

  10. chrislawson says


    In special relativity everything with mass is moving at almost the speed of light in some reference frame :-)

  11. chrislawson says


    Actually, the hard part for us primitive mass-encrusted creatures is NOT bending spacetime…

  12. cvoinescu says

    a_ray_in_dilbert_space @ #10:

    To day “conservation of momentum” is not well understood is utter complete horseshit.

    No no no. He says “Conservation of Momentum” for concept is not well understood. Surely he means it’s not well understood by him — particularly in his description of this concept!

  13. chrislawson says


    I didn’t read that as Burns saying conservation of momentum was a poorly understood concept, I took it as Burns saying his attempt to address conservation of momentum in his space drive was something he was struggling with. Not that it makes his proposal any more grounded.

    Here’s the abstract: “A new concept for in-space propulsion is proposed in which propellant is not ejected from the engine, but instead is captured to create a nearly infinite specific impulse. The engine accelerates ions confined in a loop to moderate relativistic speeds, and then varies their velocity to make slight changes to their mass. The engine then moves ions back and forth along the direction of travel to produce thrust. This in-space engine could be used for long-term satellite station-keeping without refueling. It could also propel spacecraft across interstellar distances, reaching close to the speed of light. The engine has no moving parts other than ions traveling in a vacuum line, trapped inside electric and magnetic fields.”

    What he’s proposing is a circular particle accelerator that keeps ions in constant looping motion, accelerating and decelerating them to increase or decrease their relativistic mass and thus produce propellant-less acceleration. Apart from not understanding that the acceleration and decleration of ions will produce its own, completely negating thrust, he also seems to be befuddled by the concept of relativistic mass (some physicists have argued that relativistic mass is so confusing to students that it should not be taught in undergrad textbooks).

    I suspect Burns is very adept at crunching numbers and pushing equations around algebraicly, but I also suspect he has not had a solid foundation in the fundamental principles of physics. Simply proposing a drive with “nearly infinite specific impulse” shows a lack of understanding because specific impulse is defined as thrust per unit of propellant, and if his drive is propellant-free then its specific impulse would by definition be actually infinite. (And I don’t think a good engineer should be using terms like “nearly infinite”; there’s not really such a thing; it’s either infinite or finite, and even if it’s a mindbogglingly large finite number like a Graham’s number is still infinitely smaller in magnitude than actual infinity.)

    Even if the drive could do what he says, it still needs a power source, and that power source (engine + fuel) would add to the inertia of the drive. Even if the drive could accelerate indefinitely, there is any power source would either run out of fuel way before it reached any significant proportion of c or it would be so massive that the drive itself would barely dent its momentum. It takes an awful lot of ions to budge a nuclear reactor.

    Of course, ion drives are real and have been used in space travel. But they work by accelerating ions out the back of the craft and are thus propellant rockets. To give some numbers from a real ion drive space probe, Deep Space 1 has a dry mass of 373 kg using 2.1 kW of power to drive its NSTAR ion thruster with 82kg of xenon as propellant. The only reason Deep Space 1 could achieve its mission was because it didn’t have to carry its power source as well: it used solar panels for energy, which is fine given its mission orbit was only slightly beyind Earth’s, but it wouldn’t work for interstellar travel where sunlight is weak (by the time we reach Neptune’s orbit, solar irradiance is 1000th the strength at Earth orbit — and that’s just the start…we’d have to travel another 9000x the distance of Neptune before we reach Alpha Centauri).

  14. PaulBC says

    I think someone with an idea that violates conservation of momentum might propose, as an initial step forward, some experimental setup to demonstrate a small but measurable amount of non-conservation instead of jumping right into the plans for a starship. But maybe I am just a big fuddy-duddy.

  15. DLC says

    Ha! everyone knows electro-drive is really powered by Unicorn Farts!
    Really though, NASA needs to get on to discovering the Bergenholm inertia neutralizer. After all, Einstien’s work is Only a Theory.

  16. garysturgess says

    DLC@17: Unfortunately we’ve already invented transistors and integrated circuits, so we can be assured that we are not in a galaxy that contains Arisians (who would have stopped us, since it might eventually lead to becoming cyborgs). We might still manage a Rhodebush/Cleveland drive though, we’ll just have to remember to remind them to try uranium instead of allotropic iron.

  17. says

    The guy at NASA didn’t know, or didn’t pay attention to, what Feynman called The First Principle: “You must not fool yourself, and you are the easiest person to fool.”

    BTW, #10: Bohr was chiefly willing to give up conservation of energy. See e.g. Niels Bohr Collected Works, vol. 9, pp. 4-14, and his unpublished 1929 manuscript included in the same volume, pp. 87-89. It is striking that Bohr had even earlier thought to give up conservation of energy in the famous Bohr-Kramers-Slater papers of 1924 – which Slater strenuously protested, but he had no control over the paper. Slater was of course right to do so, and BKS was experimentally disproved within a few months by Bothe and Geiger.

  18. wzrd1 says

    I looked at a story on it, then jumped to the paper, did a bit of calculating and realized, he thinks he has found a free lunch, but entirely failed to capture every force vector, such as the impact on magnetic fields.

    What was proven, yet again, TANSTAAFL.
    Something every child learned early trying to jump start a swing.

  19. alkisvonidas says

    Even if a violation of momentum conservation is finally discovered, it won’t be discovered within already established physics. (This is something that most cranks never get; there is no “going back and checking again” on already performed experiments. Unless the original experimenters screwed up, it’s done and decided; Nature is not going to change her mind). And all the guy has shown is some plain old special relativity: no exotic particles, no space-time warping, no nothing, just ordinary matter operated on by ordinary E/M fields. It’s not going to work, period.