5 ms·

Electric Propulsion Magnets Ready for Space Tests

106 points by sohkamyung 2y ago

rich_sasha 2y ago
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?
- pfdietz 2y ago
  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.
- alwayslikethis 2y ago
  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.
- credit_guy 2y ago
  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/S2772830724000504 https://www.sciencedirect.com/science/article/pii/S277283072...
  - VladVladikoff 2y ago
    Wouldn’t it still be better to use more efficient engines? could they not just have more of them?
    - wiredfool 2y ago
      You’d get more thrust, but lower delta-v for the same total mass, because you’re replacing propellant mass with fixed mass.
    - bluGill 2y ago
      That is an economic question. What does efficiency costs vs what does providing more power cost?
    - credit_guy 2y ago
      There are several ways a spacecraft engine can be efficient. The fundamental thing is the tyranny of the rocket equation: in order to get faster you need fuel, and then you need fuel to push that fuel, into a compounding way. The best way to address this tyranny of the rocket equation is to have an engine that expels something at a very high speed. The best chemical rockets push hot gas at about 4.5 km/s. The engines discussed here are "magnetoplasmadynamic thrusters" [1]. They push plasma with a velocity in excess of 15 km/s. Some studies suggest even 100 km/s. They are basically the most efficient rocket engines our current technology can build. The next type of efficiency is how much of the source energy is converted into the energy of the plasma jet. Is it 50%, 90%, 99%. That I don't know, and obviously you want as much as possible. But this project is addressing a different problem. In order to create this plasma jet, you need a very strong magnetic field to contain the plasma while it is being accelerated. The field itself does not provide the propulsion, it is there only for containment. You don't want to expend a lot of energy maintaining this field. Superconducting magnets are much better than regular electromagnets, so it's no surprise that containing this plasma with superconducting magnets requires a fraction of the power of regular magnets. But someone still needed to do the actual research. What works on paper doesn't translate always in things that work in real life. These guys did just that, and now are ready to send a technology demonstrator in space. [1] https://en.wikipedia.org/wiki/Magnetoplasmadynamic_thruster https://en.wikipedia.org/wiki/Magnetoplasmadynamic_thruster
- mapt 2y ago
  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 2y ago
    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.
    - DennisP 2y ago
      It's worse than you think. Here's a really interesting article on what it would take to get Epstein drive performance: https://toughsf.blogspot.com/2019/10/the-expanses-epstein-drive.html https://toughsf.blogspot.com/2019/10/the-expanses-epstein-dr... This thing would produce more power than all of civilization does today. No radiator could handle it. They use laser fusion, exploding D-He3 fuel pellets well behind the ship, with a giant magnetic nozzle. A tungsten heat shield protects the ship, and reaches an equilibrium temperature without active cooling.
    - XorNot 2y ago
      In the Expanse though The Drive is always on, which means the ship is tossing propellant mass (efficiently) out the back of it - which means it can dissipate most of it's heat that way.
- chris_va 2y ago
  The magnetic field here is acting as a nozzle. The circuit driving the field is not doing work on the ions, and any power loss is just parasitic. It's generally not worth it for small thrusters, because the extra efficiency gained by having a magnetic nozzle is offset by the parasitic mass and power cost (here they eliminate the power cost).
squeedles 2y ago
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!
- squeedles 2y ago
  Also, when did the Standard Breakfast Equivalent for torus become a bagel instead of the established donut :-)
  - wat10000 2y ago
    Woke is ruining everything!
    - Smoosh 2y ago
      Your comment has just made me realise that when people say “woke” to mean “anything I don’t like” the subtext is “I don’t want to face up to the responsibility and effort required to participate in a decent society. I just want to do whatever I like without consequences.” Thanks for providing the trigger for my insight.
      - wat10000 2y ago
        I’m glad my stupid joke served some purpose.
  - rsynnott 2y ago
    Sugar tax.
    - jolt42 2y ago
      But not a calorie tax.
ChrisMarshallNY 2y ago
> 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 2y ago
  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.
  - ChrisMarshallNY 2y ago
    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 2y ago
    Very large nuclear bombs are inefficient because most of the energy goes into heating up air, so not relevant to the current thread.
    - taneq 2y ago
      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. :)
      - hollerith 2y ago
        OK: they're inefficient at killing people and destroying buildings and other structures relative to bombs with yields like 500 kilotons.
deleted 2y ago
[deleted]
nkoren 2y ago
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!
- DarkmSparks 2y ago
  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)
westurner 2y ago
How long will it be before this new space propulsion capability can be scaled in order to put the ISS on the moon instead of in the ocean?
- jfengel 2y ago
  Long after it already is. The ISS is aging, and there was every intention of retiring it even before its principal sponsors started a proxy war. There's certainly zero chance that it could be on the moon. It wasn't designed to survive on a surface. It would not be able to support itself. If we want something in orbit around the moon, it will still be far cheaper to build a new thing designed for that purpose.
  - BobaFloutist 2y ago
    It does seem a shame that it can't be recovered and donated to museums or preserved in some way. I assume that it would be prohibitively expensive/complicated to try to do so, but it's a huge part of the history of space research, and it's a bit of a bummer to just throw it away.
    - rpmisms 2y ago
      I mean, if Starship works well, it could theoretically retrieve the ISS in a piecemeal fashion.
      - westurner 2y ago
        Orbital refuelling of non-satellite spacecraft at greater than IDK a few km has not been demonstrated. Rendezvouzing and pushing or pulling a 900K lb (350K kg) object in orbit has never been demonstrated. In-orbit outer hull repair on a vessel with occupants has also never been demonstrated? Are there NEO avoidance plans that do not involve fracturing the object into orbital debris on approach?

106 points by sohkamyung 2y ago

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?

pfdietz 2y ago
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.
alwayslikethis 2y ago
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.
credit_guy 2y ago
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/S2772830724000504 https://www.sciencedirect.com/science/article/pii/S277283072...
- VladVladikoff 2y ago
  Wouldn’t it still be better to use more efficient engines? could they not just have more of them?
  - wiredfool 2y ago
    You’d get more thrust, but lower delta-v for the same total mass, because you’re replacing propellant mass with fixed mass.
  - bluGill 2y ago
    That is an economic question. What does efficiency costs vs what does providing more power cost?
  - credit_guy 2y ago
    There are several ways a spacecraft engine can be efficient. The fundamental thing is the tyranny of the rocket equation: in order to get faster you need fuel, and then you need fuel to push that fuel, into a compounding way. The best way to address this tyranny of the rocket equation is to have an engine that expels something at a very high speed. The best chemical rockets push hot gas at about 4.5 km/s. The engines discussed here are "magnetoplasmadynamic thrusters" [1]. They push plasma with a velocity in excess of 15 km/s. Some studies suggest even 100 km/s. They are basically the most efficient rocket engines our current technology can build. The next type of efficiency is how much of the source energy is converted into the energy of the plasma jet. Is it 50%, 90%, 99%. That I don't know, and obviously you want as much as possible. But this project is addressing a different problem. In order to create this plasma jet, you need a very strong magnetic field to contain the plasma while it is being accelerated. The field itself does not provide the propulsion, it is there only for containment. You don't want to expend a lot of energy maintaining this field. Superconducting magnets are much better than regular electromagnets, so it's no surprise that containing this plasma with superconducting magnets requires a fraction of the power of regular magnets. But someone still needed to do the actual research. What works on paper doesn't translate always in things that work in real life. These guys did just that, and now are ready to send a technology demonstrator in space. [1] https://en.wikipedia.org/wiki/Magnetoplasmadynamic_thruster https://en.wikipedia.org/wiki/Magnetoplasmadynamic_thruster
mapt 2y ago
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 2y ago
  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.
  - DennisP 2y ago
    It's worse than you think. Here's a really interesting article on what it would take to get Epstein drive performance: https://toughsf.blogspot.com/2019/10/the-expanses-epstein-drive.html https://toughsf.blogspot.com/2019/10/the-expanses-epstein-dr... This thing would produce more power than all of civilization does today. No radiator could handle it. They use laser fusion, exploding D-He3 fuel pellets well behind the ship, with a giant magnetic nozzle. A tungsten heat shield protects the ship, and reaches an equilibrium temperature without active cooling.
  - XorNot 2y ago
    In the Expanse though The Drive is always on, which means the ship is tossing propellant mass (efficiently) out the back of it - which means it can dissipate most of it's heat that way.
chris_va 2y ago
The magnetic field here is acting as a nozzle. The circuit driving the field is not doing work on the ions, and any power loss is just parasitic. It's generally not worth it for small thrusters, because the extra efficiency gained by having a magnetic nozzle is offset by the parasitic mass and power cost (here they eliminate the power cost).

squeedles 2y ago

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!

squeedles 2y ago
Also, when did the Standard Breakfast Equivalent for torus become a bagel instead of the established donut :-)
- wat10000 2y ago
  Woke is ruining everything!
  - Smoosh 2y ago
    Your comment has just made me realise that when people say “woke” to mean “anything I don’t like” the subtext is “I don’t want to face up to the responsibility and effort required to participate in a decent society. I just want to do whatever I like without consequences.” Thanks for providing the trigger for my insight.
    - wat10000 2y ago
      I’m glad my stupid joke served some purpose.
- rsynnott 2y ago
  Sugar tax.
  - jolt42 2y ago
    But not a calorie tax.

ChrisMarshallNY 2y ago

> 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 2y ago
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.
- ChrisMarshallNY 2y ago
  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 2y ago
  Very large nuclear bombs are inefficient because most of the energy goes into heating up air, so not relevant to the current thread.
  - taneq 2y ago
    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. :)
    - hollerith 2y ago
      OK: they're inefficient at killing people and destroying buildings and other structures relative to bombs with yields like 500 kilotons.

deleted 2y ago

[deleted]

nkoren 2y ago

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!

DarkmSparks 2y ago
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)

westurner 2y ago

How long will it be before this new space propulsion capability can be scaled in order to put the ISS on the moon instead of in the ocean?

jfengel 2y ago
Long after it already is. The ISS is aging, and there was every intention of retiring it even before its principal sponsors started a proxy war. There's certainly zero chance that it could be on the moon. It wasn't designed to survive on a surface. It would not be able to support itself. If we want something in orbit around the moon, it will still be far cheaper to build a new thing designed for that purpose.
- BobaFloutist 2y ago
  It does seem a shame that it can't be recovered and donated to museums or preserved in some way. I assume that it would be prohibitively expensive/complicated to try to do so, but it's a huge part of the history of space research, and it's a bit of a bummer to just throw it away.
  - rpmisms 2y ago
    I mean, if Starship works well, it could theoretically retrieve the ISS in a piecemeal fashion.
    - westurner 2y ago
      Orbital refuelling of non-satellite spacecraft at greater than IDK a few km has not been demonstrated. Rendezvouzing and pushing or pulling a 900K lb (350K kg) object in orbit has never been demonstrated. In-orbit outer hull repair on a vessel with occupants has also never been demonstrated? Are there NEO avoidance plans that do not involve fracturing the object into orbital debris on approach?