Paddy Neumann’s Bounce Per Ounce Is Better Than NASA’s

[Paddy Neumann] is an Australian physicist and founder of Neumann Space, a space start-up with a record-breaking ion drive.

The team at Neumann Space built an ion engine that broke the previous specific impulse (bounce per ounce) record. NASA’s HIPEP thruster previously held this record with a specific impulse of ~9600 seconds (+/- 200 seconds). The Neumann Drive’s specific impulse as recorded by the University of Sydney was ~14,690 seconds (+/- 2,000 seconds). This all equates to better efficiency by the Neumann Drive, however its acceleration does not match that of the HIPEP.

CathodeGraphic
Simplified ion engine diagram courtesy of Neumann Space

The Neumann Drive has another unique advantage in its range of usable fuels. In comparison to the HIPEP which uses Xenon gas as fuel the Neumann Drive accepts a variety of metals including: Molybdenum, Magnesium, Aluminum, Carbon, Titanium, Vanadium, Tin, last and also least according to Neumann Space is Bismuth.

Interestingly, Neumann offered his intellectual property (IP) to the University of Sydney, since the research was done at the University but they passed on the offer. This allowed the IP to be returned to Paddy and he subsequently applied for a patent and began the search for funding for continued research.

Here at Hackaday we like space, in fact we’ve offered to send you to space more than once with the Hackaday Prize. We also enjoy amateur rocketry and young rocket scientists.

51 thoughts on “Paddy Neumann’s Bounce Per Ounce Is Better Than NASA’s

  1. Specific impulse is just one of many parameters in a rocket design. If you wanted maximum Isp, you could use a ground based laser, solar sail or magnetic tether propulsion. But none of those will get you off the planet. I think theoerotically a flashlight has a specific impulse of the speed of light, but it’s not useful because the thrust is insignificant (and I think the battery mass ruins it too?).

    Having said that, it’s great to hear of independent hackers breaking space technology records! Best of luck to him.

    1. Yeah, bounce per ounce is not a thing for electric propulsion. It’s only meaningful for chemical propulsion where the energy is intrinsic to the mass of the fuel. If you use a larger acceleration voltage, the ions and electrons come out faster, so you get more impulse per unit mass.

      The problem is that while momentum scales with v, energy scales with v squared. So doubling the impulse of the engine per unit mass quadruples the energy requirement, or for a system with limited power reduces the thrust by a factor of 4.

      This is an old old trade off.

      1. For long-term missions, especially probes, minimal fuel usage is often what they’re looking for, since lower launch weight etc. Indeed carrying less fuel makes the probe lighter, so better acceleration there, not that it makes up for it entirely.

        1. I think that is simplistic. No one sending anything to space wants to waste mass. I’m not saying that a ‘high Isp’ electric engine has no use, just that it isn’t really a figure of merit for an electric engine. It certainly isn’t any way to gauge if that engine has been designed well.

          1. Ion engines like this are used because of their high isp. Chem engines are for thrust. The trade off is that for a given fuel mass one gets you moving much faster, it may take longer but thats not a problem. And energy isnt really a problem either, especially if you are going inwards from Earth. Fuel mass is the only real limiting factor.

    2. “Specific impulse is just one of many parameters in a rocket design. If you wanted maximum Isp, you could use a ground based laser, solar sail or magnetic tether propulsion.”

      None of those are rockets, and they all impose huge additional constraints on the payload: you’re gaining thrust from something external to the payload, so you can’t easily redirect that thrust (well, not as easily as a rocket, anyway). Ion thrusters are pure rockets, so they work anywhere and can be pointed in any direction.

      “I think theoretically a flashlight has a specific impulse of the speed of light, but it’s not useful because the thrust is insignificant (and I think the battery mass ruins it too?).”

      That’s not really true. The specific impulse of a photon rocket is a lot of times quoted as the speed of light, but that’s only for a really, really specific kind of photon rocket – one that magically turns matter directly into photons. The specific impulse of a flashlight is ungodly terrible, because it needs batteries. Batteries have an energy density (joules/kg), which means the total momentum change you get out of them, assuming perfect light conversion, would be the energy from the batteries, divided by the speed of light. There’s no way to store energy without matter, and the best battery you can build is matter itself ( around 10^17 J/kg).

      So, for instance, a lithium-ion flashlight (again, perfect light conversion), with around ~150 Wh/kg, would have a specific impulse of something like 0.002 Ns/kg (order of magnitude-ish, could be factors of 2 lying around). Or you could throw the flashlight out the back of the probe and get several orders of magnitude larger specific impulse. :)

      1. “The specific impulse of a flashlight is ungodly terrible, because it needs batteries.”

        Except if it’s run off a solar cell. I agree it’s a poor practical example, but it’s an excellent theoretical point and I’d hazard most ion drives in space will be running off sealed nuclear sources or solar cells.

        1. Yeah, this actually is a big problem with comparing chemical propellants and electric propellants using specific impulse: if you ignore the power consumption entirely, the electric propellants look like they have an awesome specific impulse. For small thrust, it isn’t a big deal, because you can just throw on solar cells.

          But with the very, very high power ion drives that people are talking about, generating the power tends to dominate the weight. I know people criticize Ad Astra’s “Mars in 39 days” press release because it requires a lightweight power generation that doesn’t exist (and isn’t really planned).

  2. Why is it you keep offering to send your readers into space? Is it a question of the greater good for those that remain? Or are you just trying to get rid of us or something?

    Is the bounce per ounce the same for each of the different fuels?

    1. Different fuel, difference bounce: “…specific impulse over 14,000s in the case of magnesium, and around 5,000s with the case of molybdenum…”

      But while Mg is the most efficient, Mo produces the fastest acceleration. Aluminum, while it excels at nothing, could be readily obtained from space junk. And carbon could be obtained from “astronaut waste products”.

      One other neat feature which wasn’t mentioned in the write-up. The accelerated ions reputedly don’t come in contact with any part of the drive, like some others that direct them through a grid. So no erosion of anything but the intended material, the fuel rods.

  3. Biggest advantages here are more than just the high Isp. The fuel here is solid so you get better mass fraction and storability isn’t an issue. Also the hot ions don’t touch the engine so you don’t have problems like grid erosion. Finally, Al and C and Mg are way easier to pick up from whatever rock you run across than Xe.

      1. For asteroid mining, if you have a huge supply of metal, maybe a simple mass driver would be better, more energy efficient, and much higher acceleration. Just magnetically wang a load of metal dust out the back end, or even metal pellets. Ion engines are generally for long-term, gentle acceleration, that adds up to something fast given enough time.

        I wonder, do any Earth satellites use ion engines to maintain their orbit? Might be a bugger, all those ions and fields near sensitive electronics, but that’s just a question of doing it properly.

        1. “I wonder, do any Earth satellites use ion engines to maintain their orbit?”

          Yup. The Boeing 702SP series is the first one I know of that’s completely ion-engine based. I think some earlier ones had ion engines onboard for stationkeeping only.

  4. Interesting that despite being non-usa-ian, they still use the non-SI (“metric”) form of specific impulse, which uses the archaic “pound-seconds per pound”, shorthanded to “seconds”. Not only is this not SI, it confuses the issue by calling a pound of mass and a pound of force the same thing, which is only true on earth.

    Despite the more rational definitions of specific impulse (like Newton-seconds per kilogram) being dimensionally identical to “exhaust velocity”, and far easier to use, I’m going to hazard a guess that this unit is going to be one of the last vestiges of imperial units used in aerospace, purely due to convention and corporate inertia.

    1. https://en.wikipedia.org/wiki/Specific_impulse#Units

      [quote]By far the most common unit used for specific impulse today is the second, and this is used both in the SI world as well as where Imperial units are used. Its chief advantages are that its units and numerical value are identical everywhere, and essentially everyone understands it. Nearly all manufacturers quote their engine performance in seconds, and it is also useful for specifying aircraft engine performance.[/quote]

      1. kgf is also not a SI unit, and is just as moronic a unit of force as the pound…

        A pound(mass) yields a pound(force) to high precision only on a tiny fraction of earths surface. lbf is a lousy, imprecise, poorly thought-out unit, and promotes sloppy thinking in the engineers who persist in using it. kgf has the same properties.

      1. Ha ha. Good workaround. But not correct. It’s defined as the momentum change per unit propellant *mass* consumed, not weight. What happens when the fuel gets into a ballistic trajectory (like after engine cutoff)? Its weight is zero. Does that mean its Isp is now infinity? That lousy unit promotes this kind of sloppy thinking.

        1. “It’s defined as the momentum change per unit propellant *mass* ”

          Well, the only ‘definition’ I’ve ever seen is thrust/(Earth’s gravitational acceleration*mass consumed per unit time). You might be trying to say that it makes more sense to be defined “per mass” instead of “per weight,” although defining it as “per weight” has the nice benefit of only depending on one unit of measure rather than 2.

          “What happens when the fuel gets into a ballistic trajectory (like after engine cutoff)? Its weight is zero. Does that mean its Isp is now infinity?”

          Reread what I said. It’s momentum change (impulse) per *launch weight*. A rocket doesn’t care what the weight of the fuel is after launch. Only at launch. That’s what costs money.

          And yeah, obviously, that doesn’t make sense when you build, fuel, and launch a rocket from Mars. When that happens, I’ll be happy to yield to your definition.

        2. According to wikipedia page on Specific Impulse, it is “the impulse delivered per *unit* of propellant consumed” (2nd sentence). It doesn’t say per unit of mass; just “unit”. Wikipedia then follows up with:

          “If mass (kilogram or slug) is used as the unit of propellant, then specific impulse has units of velocity. If weight (newton or pound) is used instead, then specific impulse has units of time (seconds). The conversion constant between these two versions is the standard gravitational acceleration constant (g0).”

        1. Again, sloppy thinking promoted by a lousy unit. Weight (or force) is not mass. Just because the two units are called ‘pounds’ doesn’t mean they measure the same quantity. They don’t cancel out unless you’re lazy and sloppy and don’t really understand what you’re doing. It’s a convenience that on most locations on earth a pound of mass exerts very close to a pound of force on the earth, but that’s a shortcut that causes errors in understanding.

    1. Quite well, apparently, if measured by speculative funding and woo. But Isp? No-one has reproducible results or credible theory yet, so no comparison possible…

      Neumann, fortunately, has well-understood physics on his side.

  5. I am glad, as most of you should be too, that I don’t work for NASA. It would take all my will power not to do pelvic thrusts while talking about their new HIPEP thruster.

    1. A while back (1 year? 2?) There was on HaD someone with a very small thruster suitable for Cubesats. A sort of sponge with liquid and a porous surface with nano-points and electric field and all that. It looked very cool for Cubesats. Inquiries from a couple of University teams got no response.

  6. aren’t all those metals used as fuel close to rarity as what is currently used and actually heavier? Also since we can’t preserve living humans speed is the name of the game for long space travel..

    1. We’ve still got nothing anywhere near capable of sending humans to the nearest star without them dying, possibly as the spaceship falls to bits or they run out of selenium in their diet, or some other trace nutrient.

      The Alcubierre drive is getting more research done, although since there’s a lack of negative energy (PP3 battery connected the wrong way round?), it’s mostly mathematical in nature.

      1. Or the human body falls apart from less gravity which is the problem waiting after we accomplish speed; diet is naturally taken care of for most places because division of time.

        I know a little physics and some decent math and chemistry. From what little I know I’d be looking to use photons or dark matter as fuel for something. Somthing there is practically infinite abundance of that you are actually always in so no mining, refining, depletion etc..

        Using any form of earth mined material for long space travel even if un-manned seems like running in place..

        1. Long space missions are only long for the people left behind, as the ship continues to gain velocity it experiences greater levels of time dilation. Using a magnetic scoop would let you collect fuel from a large area of space along your path and funnel it into an engine to be accelerated and used as reaction mass. The logical power option is to have reactors that are periodically brought online then dumped as they are worn out. That would give you many decades, ship time, of travel. All this was worked out years ago.

          1. If your ship is unable to maintain average acceleration greater than 1G then you age faster than the earther’s. But it’s worse than that, time dilation only gets you back what you lose due to the limited speed of light, so without human unfriendly conditions you never get useful amounts over a normal lifespan. A big magnetic field would probably be a better brake than collector but a bigger problem is that the interstellar vacuum has very little in it, above our atmosphere the stars are not fuzzy from scattering, so it’s reasonable to assume that the amount of available gas on the trip is much less than in the same cross section of our atmosphere.

            So yes, this was all worked out years ago, and it fails for reasons you don’t need maths to understand.

          2. Something weird happened when I hit reply, and then I hit report by mistake.

            If your ship is unable to maintain average acceleration greater than 1G then you age faster than the earther’s. But it’s worse than that, time dilation only gets you back what you lose due to the limited speed of light, so without human unfriendly conditions you never get useful amounts over a normal lifespan. A big magnetic field would probably be a better brake than collector but a bigger problem is that the interstellar vacuum has very little in it, above our atmosphere the stars are not fuzzy from scattering, so it’s reasonable to assume that the amount of available gas on the trip is much less than in the same cross section of our atmosphere.

            So yes, this was all worked out years ago, and it fails for reasons you don’t need maths to understand.

        2. Dark matter as fuel.. You’ll never run out and there is no known negative effect on space, galaxy, distant mass, or universe at the rate you’d use it even after quintillenniums. Photons would be next but would need some secondary which would require materials unless we can properly master synthesis and radiation..

          1. If you can find a bucket of dark matter to put in it, go ahead. Using photons as fuel, isn’t that the same as solar panels? There’s just not much of anything in space to use.

            Getting to the sort of speeds where time dilation takes effect is unimaginable with anything we actually have or know how to make, even in principle. Assuming you don’t have forever to accelerate.

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