That looks awesome! The photo of the plasma discharge from the solid molybdenum fuel rod in the datasheet is worth looking at [1], perfectly illustrating the "Centre-Triggered Pulsed Cathodic Arc" that is the basis for this thruster.
The ion and hall effect thrusters that this drive would replace require a propellant tank to hold xenon, krypton, iodine, etc. so integrating them is a bit of a pain in the ass. Anyone know how the mass stacks up though? Hall effect thrusters from Busek have a (much) higher power/mass ratio but that doesn't include the propellant tank.
I haven't been able to find that yet, but even if significantly worse this may still have an important big upcoming space. In the upcoming Starship era, economics is going to play a historically huge new role in space, just as it does in Starship itself where many of the design and material decisions are optimized around cost and simplicity, even at some performance penalty, vs the old space total focus on perf. A drive that performs worse, but is much easier and cheap, could be useful alongside the others in some roles when you can throw 100+ tons at a problem at <$200/kg to LEO, or even <$100/kg.
The weight on this one looks really good, not even counting the lack of propellant. I'm going to guess that has a downside, that the total impulse is limited by how small the fuel rod is.
The molybdenum rod IS the propellant. It eventually ends up out in space.
I'm only aware of one propellantless thruster, and I'm waiting to see if it works aboard Barry-1[1] It uses electric power in an entirely closed drive, generating 1 milli-newton of thrust. It should be switched on in a month or two.
I am aware of zero propellant less drives. My Prescence on the internet and news sites is not what it used to be but I'm sure I wouldn't have missed Newtons laws being upended.
Very cool. I love seeing development in commercial non-chemical-propellant technologies.
Question about the total impulse. For ND-500+, they claim up to 250kNs of total impulse and a wet mass of 10-20kg. Assuming a spacecraft mass of about 100kg, and a fuel payload of 10kg, that's only about 2000m/s dV. Not enough to go to Mars, but enough to extend an LEO mission or to send a tug to deorbit space junk.
> For ND-500+, they claim up to 250kNs of total impulse and a wet mass of 10-20kg
Wouldn't bet on it.
The same PDF on their website[0] claims an Isp of 2500 seconds. If you do the math (I=mv), the propellant mass works out to 10.2 kg. So at the low end of their "10-20 kg" estimate, 102% of the total thruster mass would need to be the eroded solid propellant, leaving a -2% mass budget left over to cover the power supply, capacitors, control electronics, and all non-eroded structures.
That seems... optimistic.
The technology seems cool, but putting trivially impossible numbers on your launch website is a big red flag.
>up to 250kNs of total impulse and a wet mass of 10-20kg
The specific impulse here is 3-6 times better than the one of chemical. Considering the existing tech the solar+ionic seems to be the best option for going to Mars. With some very feasible development of existing tech the nuclear+ionic seems to be the best for farther into Solar and beyond (if I didn't make large mistakes https://news.ycombinator.com/item?id=38445404)
I would note that delta v from LEO to mars orbit is 7500m/s, which would only need ~40kg of fuel from your calculations (didn’t recalculate with additional fuel mass, ymmv). That doesn’t seem outrageous.
I'm a little out of touch with the space-related investment right now in Adelaide, so I hadn't heard of these guys, but as soon as I saw that airport photo on the main page I knew where they were based! :)
Can someone with an electrical or physics background help translate what this means "Our propulsion system uses a cathodic arc discharge powered by a capacitor bank"?
I take it it uses capacitors to release larges amounts of electricity on a given period, thus producing plasma which creates propulsion?
4. Now that the atom is charged, shoot it out the back of the engine really fast using electrical repulsion.
5. Shoot the electron out the back (using a different pipe) so that the exhaust doesn't come back at you due to electrostatic attraction.
6. Now you have the rod, with one less atom. Repeat. A whole ton of times.
Steps 2&3 might happen simultaneously, not entirely sure the mechanism but generally an electrical arc is violent, it will spallate and ionize a few atoms here and there.
Not having a tank is huge, and the first ionization energy of many metal ions is far far lower than noble gases, which are what is commonly used in normal ion drives
That looks like it, I take it the "solid state" aspect of using a metal rod as the source of material to ionize is the main claim to fame here. It does mean 'refueling' is easy, just pop another rod in (easy if you happen to in orbit nearby, that is). The suggestion that you could make new rods from asteroids etc. is cool, but there's quite a gap between theory and practice still...
The Etc includes dead hardware in Earth orbit: that's a smaller gap than mining asteroids. Maybe not molybdenum but probably lots of magnesium, titanium and aluminum.
Yeah they'll use a capacitor to charge up and then dump high current quickly (that's what they're good at, as opposed to batteries which are better suited for a longer, steadier, lower current output).
> We have found that refractory metals such as molybdenum make excellent propellants, and recycled aluminium alloys can also be used. Exceptions include mercury and gallium, tin, bismuth and lithium (due to their low melting points), cadmium and technetium.
Oh darn, I was hoping they'd found a use for all my spare technetium.
"How long would it take to throw one of these between two ISS ships spaced one AU apart"
Here is the conversation - I started by asking it to define terms based on the spec sheet from Neumann, so I could fully understand how to read it. Then I wanted to figure out how these little guys would fly in space.
I learned a ton about Specific Impulse, the Rocket Equation, and it lead to GPT breaking, but we came up with the formula - but before I could arrive at specific numbers - GPT race-conditioned and hallucinated on the responses. [0], [1]...
It messed up and didn’t give you an answer and you have no way of knowing if the information you ‘learned’ is true if you don’t already understand ISP etc.
I mean wolfram alpha would give you the answer immediately without all the bullshit conversation.
It’s so weird to me how this glorified ELIZA has people so keen to tell us what GPT said in every single thread.
I didnt want the answer immediately. I wanted to learn how to read the spec sheet, and be then able to infer information from future spec sheets now that I know how to read them and what the physical implications of the values mean. (thats why you'll notice I started with asking it to teach me something.
What I enjoyed was this Neumann article lead me down a rabbit whole and I learned things I didnt know - it was fun and I didnt expect it.
Its not cool that gpt failed - which is why I had it summarize the formula to I can try it in another session and then with gpt 4. Plus my kids love it.
There is an amazing researcher from MIT that is talking about autonomously self-assembling structures in space. She was on Lex Fridman [0]
Simply one of the most articulate people I have listened to on such an interesting subject.
These appear as if they may be able to be to core thruster for nodes which can be launched like starlink and then, well... star-link-up using the same orchestration software that terrestrial drones use for big displays.
What would the thrust capabilities be for arrays of these. If the fuel needs replacing - create little bots that can give in vacuum re fueling?
I wonder why they're using Molybdenum instead of just lead. All of the thrust comes from throwing atoms out of the thruster, so, throwing something denser makes sense in my mind... surely there's a reason?
Density doesn’t mean anything at the ion level. Yes, lead has a higher atomic mass, but at the end of the day it’s about momentum and energy. If they can shoot a Mo2+ out twice as fast as Pb2+, it’s about them same.
> If they can shoot a Mo2+ out twice as fast as Pb2+, it’s about them same.
Is it? Twice the velocity (v) but ~half the mass (m) might give you the same momentum, but it requires twice the energy: E = ½(m/2) * (2v)² = 2 × ½mv².
Maybe it's worth spending energy to save mass, because energy is delivered by the sun, whereas mass has to be launched. There's probably a thrust vs. delta-v tradeoff for different elements.
Nice to see some Adelaide representation! I’ve had the pleasure of working with these guys— we have a Neumann thruster on one of our satellites. Very cool technology and great team.
Mitigating factor is that the outbound craft exhaust functions as an AM radio. Admittedly modulation is slow, around 6Hz according to one data-sheet, but also quite energetic and directed.
I love that we’re doing space stuff with sci-fi sounding names.
Looking forward to the time when we’ll do online comparisons to decide if the family is buying a Neumann drive or a Cherenkov Drive spaceship minivan.
I'm sure they spent loads of time thinking about their website, but I find these webpages that reveal information only when you scroll to them really annoying. I find it such a distraction from trying to digest the content I generally give up, like I just did.
The ion and hall effect thrusters that this drive would replace require a propellant tank to hold xenon, krypton, iodine, etc. so integrating them is a bit of a pain in the ass. Anyone know how the mass stacks up though? Hall effect thrusters from Busek have a (much) higher power/mass ratio but that doesn't include the propellant tank.
[1] https://neumannspace.com/wp-content/uploads/2023/09/Neumann-...