Ion thrusters are an amazing spacecraft propulsion technology, providing very high efficiency with relatively little fuel. Yet getting one to produce more thrust than that required to lift a sheet of A4 paper requires a lot of electricity. This is why they have been only used for applications where sustained thrust and extremely low fuel usage are important, such as the attitude management of satellites and other spacecraft. Now researchers in New Zealand have created a prototype magnetoplasmadynamic (MPD) thruster with a superconducting electromagnet that is claimed to reduce the required input power by 99% while generating a three times as strong a magnetic field.
Although MPD thrusters have been researched since the 1970s – much like their electrostatic cousins, Hall-effect thrusters – the power limitations on the average spacecraft have limited mission profiles. Through the use of a high-temperature superconducting electromagnet with an integrated cryocooler, the MPD thruster should be able to generate a very strong field, while only sipping power. Whether this works and is as reliable as hoped will be tested this year when the prototype thruster is installed on the ISS for experiments.
I wonder why all the bother with a superconductor. They say the magnet coil draws 1 watt to generate a 0.5 Tesla magnetic field, “a 99 percent reduction in input power compared to a copper electromagnet”.
I didn’t see the model of cryocooler they are using, but that size typically draws about 100 watts, so it’s not like they are really saving on their power budget.
The AMS experiment flying on the ISS uses a 1.2 tonne permanent magnet, producing 0.14 T over a huge internal volume, so getting powerfula magnets into space is not an issue. Smaller, lighter ones making 1 T fields are commercially available, so the field strength is not the issue.
So, why the hassle of a superconductor when a permanent magnet looks like it could do the job?
Wouldn’t a cryocooler be significantly more efficient in the shade in space at around 100 K?
Absolutely. James Webb’s cryocooler, sitting behind that giant sunshade, sips just 33 watts to make 0.25 watts of cooling at 14 K.
Because it’s bigger and heavier, so you lose on fuel for having to accelerate that extra mass.
And copper coils are very inefficient, so I would be that 99% reduction is counted with the pump in operation, and it doesn’t need to run all the time because space is pretty cold as it is. For a quick search, a small electromagnet could operate at some hundreds of watts to generate 0.5 Tesla, but a bigger one might need kilowatts to extend the field over a larger volume.
A “bagel size” (their words) 0.5 T permanent magnet would weigh (much) less than the HTS magnet, cryocooler, its cooling system, and the additional required solar panels and power systems.
i haven’t thought any of this through but
can you get a permanent magnet of the required geometry?
One thing we did for a different job used a permanent magnet of ALMOST the right shape, plus three little solenoids to shape the magnetic field when the device was on. It worked pretty good overall, and it looked a tiny bit like the arc reactor from the first Iron Man movie, so that’s what we ended up calling it in the shop.
I should do more writeups about this stuff. I used to pre-covid but I lost my self confidence since then.
What is the growing factor here? If you want a 10T field, do you need 10W with a super conductor (but the same cryocooler, since a super conductor is, well, O ohm conductor, so no joule effect here) ?
With permanent magnet, you’d need 10x the mass right (or even more?) ?
Yeah, scaling changes things. It’s easy to get a 1 T permanent magnet the size of your fist or your head — no need for a heavy, power-hungry cryocooler. By the time you get up to car-size, the mass favours superconductors to get the desired field, provided you have the multi-kilowatt power budget.
Early permanent-magnet MRI systems weighed 100 tons. The supercons that replaced them came in under 20 tons, even with the cryocooler and extra power systems.
1 Tesla at 1 Watt?! That’s wild. Imagine leveraging this tech for lightweight low power MRI machines.
Any modern medical MRI system generates 3 Tesla while requiring zero power to maintain the field, and less than one watt of cooling.
Unfortunately producing 0.5 watts of cooling at the 5-10 Kelvin required takes 10 kilowatts of electrical input power for the cryocooler…
Hence why high temperature superconductors that operate above 77 K. Recent ones work at 133 K (−140 °C) and some even higher under high pressures.
They are getting better and better, for sure.
But they are still subject to the same stubborn problem that you don’t get high field and high temperature at the same time: Safe, reliable operation of a big magnet at 3 T still needs 20 K temperature.
It looks like they’ve figured out the worst of how to handle the material and produce tapes you can use like wire. Once they get a handle on the cost of making the stuff it will replace the niobium-based wire, but you still need roughly a ton of the material for a clinical MRI magnet, so cost is important for that application. Saving $20k of annual running cost will never pay off an additional $500k capital cost.
Late to the conversation, but how much of an improvement would it be to replace the traditional niobium-tin superconducting wire with YBCO or BSCCO wire or tape? They can operate at around 100K and remain superconducting. Or can they not generate the high field required at that temperature?
Wait till they fire that puppy up with a 5kW excited path….
I keep hearing “magnetohydrodynamic drive”, and wanting to say “Maybe it’s a problem with the liquid helium, or the superconductors” in a bad fake Russian accent.
I’m waiting for the new improved model that has the turboencabulator-power-boost.
Those are the ones with the enhanced geometry Dingle arms and articulated framis, right?
Yes, but you need a mk42 Interocitor to run the Dingle arms
I would say you can borrow my Interocitor, but I use every day to make hot chocolate…
Here, hold this. No, like this. I wish to see if my interocitor can withstand 50,000 volts.
We used to watch that movie and eat Twinkies in hot dogs. Shudder.
Did he ever even try a Russian accent?
problem with plasma thrusters isnt the thrusters. its the power requirements and the fact that we have few power options beyond solar (big and heavy) and rtgs (weak). we (us but mostly russia) have flow nuclear reactors proper in space back during the cold war, but these were not high performance reactors, ultimately limited by radiator area (big and heavy again). fusion might work, and come before power reactors, since fusion for propulsion need not be break even, but then you still need a power supply and probibly a cap bank.
That sounds like some Geordi LaForge level technobabble.