Electric Propulsion Magnets Ready for Space Tests
39 comments
·February 24, 2025nkoren
DarkmSparks
its not been tested yet, so they probably have no idea.
They for sure expect better than the ones currently in use/testing (e.g. the nstar ion thruster)
squeedles
Rocket equation applies to more than just chemical fuel. The article quoted 1T for about a watt of input, which is ludicrously efficient. So the higher field means more thrust. Less input power means less power generation hardware mass and less cooling hardware mass, which will compound with the higher thrust for a very favorable specific impulse. Very exciting, and I wish them well!
SecretDreams
Totally agreed. The same logic applies to really all forms of transportation. Mass begets mass.
Ancalagon
Mass baguettes mass!
null
ChrisMarshallNY
> very stringent stray magnetic field requirements of the ISS.
I'm sure that others, here are far more conversant with the tech, but it's my understanding that one of the attributes of superconducting magnets, is that the very strong field is extremely localized. It doesn't extend too far from the magnet.
kamaal
I thought the strength of most(all?) fields is inversely proportional to the square of the distance from the center/source? I think this is called inverse square law.
Its also for these reasons making a very large nuke is pointless, after some distance the effects are almost 0.
gus_massa
If we ever find a monopole, the field will be inversely proportional to the square of the distance.
Bug normal magnets and superconductor magnets have canceling magnetic charge, the same amount of S and N, so after a few math tricks [1] the field will be inversely proportional to the cube of the distance.
[1] The filed from N decays as 1/r^2 and the field form S as -1/r^2 but they are indifferent places (the r is not the same on both), so the difference is almost like 1/r^3 more details in https://en.wikipedia.org/wiki/Multipole_expansion
kamaal
Thanks for the link.
Sometimes I wish Xanadu had actually happened. The moment I opened the article I saw something like |R^3. Honestly speaking I don't really know what |R means. And R keeps showing up all over the article.
I will dig more into this using ChatGPT with time.
But I could understand very little from reading the article.
closewith
Magnetic fields produced by dipoles have an inverse cube dependence, so dissipate much faster than gravity or other fields.
ChrisMarshallNY
Yes, that's what I would think, but I remember reading that, and thought it sounded strange. The article made it seem as if the rules were different for superconducting magnets.
Might just be a manifestation of the Inverse Square Law. Like I said, not my area of expertise.
hollerith
Very large nuclear bombs are inefficient because most of the energy goes into heating up air, so not relevant to the current thread.
naasking
There are many efficiency metrics. For instance, how much energy went into constructing and deploying the bomb vs. how much destruction it caused. I think large nuclear bombs would look quite ok on this metric.
taneq
They're only inefficient if you want them to do something other than heat up a lot of air by a very large amount very fast. :)
kamaal
Agreed that I know very little about this subject.
But heat itself can be imagined as a kind of field. For eg: A candle, the closer you move to the flame, every point closer to flame, the temperature is higher. The farther you move apart the temperature reduces. Same with the Sun.
Take for eg- Sound. The closer you move to the source of it, the louder it sounds, the farther you move from it, the fainter it gets.
Now you could call this a wave. Like the wavelength stretches with distance, also decreasing frequency and amplitude. Another way of looking at this a field. Imagine 3D space with points, like a lattice. Each point has a value, and the values get denser to the center, and move farther apart as move away from center.
If Im not wrong a lot of physical phenomenon exhibit this behaviour. Including thing like light, sound, temperature, gravitation etc.
While you can make a beam of light, I doubt you can make a beam of magnetic field(ray?) or gravity for that matter?
rich_sasha
Surely a n00b question, but: why superconducting electromagnets?
I get that means zero electrical resistance and stronger magnetic field at rest, but ultimately the engine is doing work accelerating ions, which will be "felt" as resistance in the electrical system. The total energy must be conserved. I would imagine (?) that work done accelerating the ions is far greater than the losses to heat in the magnetic coils.
Or maybe that's not right?
credit_guy
Here's a link to the actual paper [1]. According to the paper, the magnetic part of the thruster consumes between 10 and 100 kW if it uses regular magnets, and only 0.2 kW with these superconducting magnets. Most spacecraft use solar panels, and they claim the largest satellites produce 30 kW of power. It follows that 10 kW is an unacceptable level of power consumption, while 0.2 kW is ok. They admit that nuclear powered spacecraft don't necessarily need this new technology, because 10 kW might be negligible for them.
[1] https://www.sciencedirect.com/science/article/pii/S277283072...
IanCal
Power consumption may not be the only concern but also dissipating the heat. You don't have air or water around you to dump the heat into so you're limited by what you can radiate (is my understanding). Trying to radiate out 200W of heat vs 10-100kW is a dramatically different challenge.
vlovich123
Fill a surrounding container with a volumetric shit ton of nitrogen gas (perhaps with stepped pressure gradients) and you might be able to radiate a significantly larger amount by increasing your surface area without drastically increasing your weight (or use nuclear power to mitigate the weight concerns).
But yes, today’s design space generally prefers as low a power envelope as possible to not have to worry about dissipation.
VladVladikoff
Wouldn’t it still be better to use more efficient engines? could they not just have more of them?
bluGill
That is an economic question. What does efficiency costs vs what does providing more power cost?
wiredfool
You’d get more thrust, but lower delta-v for the same total mass, because you’re replacing propellant mass with fixed mass.
alwayslikethis
Generating a strong field requires a lot of current. If you have any resistance at all, that's a lot of heat dissipation, which will require cooling.
mapt
VASIMR is one of the few test articles with flight hours of this category (or maybe a sibling category), and when you factor into account the thruster and the power supply, its thrust to weight ratio for the VX-200 prototype was unworkably low. Not "too low for launch", I mean "too low for a steady burn of months to attain meaningful progress towards interplanetary or orbital objectives".
You have to simultaneously solve for power to weight ratio issues on solar panels, power supply, and the actual thruster. The best solutions right now for most purposes are relatively low Isp (low propellant efficiency) Hall thrusters.
In space, heat dissipation is remarkably harder than it is on Earth, so getting to, for example, 97% thermal efficiency rather than 94% would be a big deal in terms of the mass of the heat dissipation system, and I think this and reducing the mass of the actual electromagnet is the advance here, if there is any.
api
One of the biggest things that always bothers me in sci-fi, even harder sci-fi like The Expanse, is the missing heat sinks. All those ships would need massive radiators or they’d melt.
The starship in Avatar got that right. Rest of the film is comic book level and derivative but the ship is good.
pfdietz
Less energy use, lower mass? I know superconducting magnets are a goal for both aircraft propulsion systems and use in wind turbine generators, just for the mass reduction.
Would sure be nice to have some numbers on expected thrust, weight, and ISP, in order to have some kind of context in which to understand this!