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The Dipole Drive: A New Concept in Space Propulsion

84 points by cl42 7y ago

ThomasBarb 7y ago
Should be an interesting read. Can't reach the site. Is it up or down? Tried loading it several times but it didn't load for me.
deleted 7y ago
[deleted]
samcheng 7y ago
I found a non-paywalled discussion here: https://www.centauri-dreams.org/2018/06/29/the-dipole-drive-a-new-concept-for-space-propulsion/ https://www.centauri-dreams.org/2018/06/29/the-dipole-drive-...
jcims 7y ago
Isn’t this basically electrohydrodynamics?
osamagirl69 7y ago
The fact that the abstract does not mention laser driven sails, the currently most viable approach to relativistic propulsion (ie, the current breakthrough starshot plan), does not give me much hope in this researchers credibility in the rest of the paper. Furthermore, the performance of this engine is abismal. To put it into perspective,a modest ion engine would produce about a million times more thrust per power. While the ion engine of course requires carrying fuel, and is thus governed by the tyranny of the rocket equation and not directly comparable in performance, this engine still requires a power source and thus effectively requires fuel anyway. Also worth mentioning is that the least efficient possible massless thruster, a simple blackbody radiator with reflector to aim all of the photons behind you, is only about 1000x worse than this unit in terms of propulsion force per power, and essentially infinitely better than the unit in terms of propulsion force per mass, since this structure is incredibly massive where as you can usually generate blackbody radiation directly from you power source.
- deleted 7y ago
  [deleted]
- vidarh 7y ago
  The author is Robert M. Zubrin. To write it off because the abstract doesn't mention a specific technique seems a bit silly, especially given that Zubrin personally knows a lot of the people involved in Breakthrough Starshot and surely is aware of it, including its massive caveats. It's worth noting that the paper specifically discusses the need for methods that are not limited in travel direction, and in that respect Breakthrough Starshot has the same caveats as a solar sail and so treating laser driven propulsion separately is pointless. Another major difference that is so obvious as to not require a mention of every specific alternative is that it is talking about a propulsion method that avoids the need for us to provide a source of thrust. Laser driven systems doesn't require the ship to carry propellant, but we're still paying the cost to provide thrust, while this design is basically 'just' relying on there being a source of protons and electrons with a speed differential relative to the current speed and direction of travel of the ship that it can 'scoop up'. That makes for fundamentally different tradeoffs relative to classical sail based propulsion.
  - deleted 7y ago
    [deleted]
- choeger 7y ago
  > Furthermore, the performance of this engine is abismal. To put it into perspective,a modest ion engine would produce about a million times more thrust per power. Would it, though? The proposal mentions 14mN/kW. What ion engine produces 14N/W ? I think that such an engine would be a massive improvement of current designs. VASIMIR, for instance, is designed with 1N/14kW.
ScottBurson 7y ago
Previously discussed: https://news.ycombinator.com/item?id=17428751 https://news.ycombinator.com/item?id=17428751 I chewed on this idea for several days, eventually coming to the same conclusion others had: it won't work. This poster came up with a correct explanation much faster than I did: https://news.ycombinator.com/item?id=17432975 https://news.ycombinator.com/item?id=17432975 Zubrin has taken a familiar approximation -- that the field near a flat charged plate is uniform -- and forgotten that it's only an approximation, and that the keyword is "near". As particles leave the vicinity of the drive, they will be attracted back toward it, reversing the momentum transfer.
- starpilot 7y ago
  So the particles follow the path of a doublet?
- stareatgoats 7y ago
  That stance received some knowledgeable opposition in the quoted thread if I'm not mistaken. I'm in no position to assess the soundness of the arguments, but I noticed that the poster admitted to some flaws in his own reasoning at the tail end of it.
  - Steuard 7y ago
    None of that second commenter's objections even began to address the core of the original poster's point: whatever the exact details of the field configuration might be, it's inescapably true that the electric potential is zero at infinity, rises to a positive maximum at the + plate, falls quickly to a negative minimum at the - plate, and then returns gradually to zero at infinity again. That means that if an ion's initial speed is "v0" well before it encounters the device, it may speed up and slow down while interacting, but its final speed will be "v0" again once the device has passed by. If its direction is unchanged (which is the intended case for the thrust-producing protons, as illustrated in Fig. 1 of https://www.centauri-dreams.org/2018/06/29/the-dipole-drive-a-new-concept-for-space-propulsion/ https://www.centauri-dreams.org/2018/06/29/the-dipole-drive-...), that means that the ion will experience zero net change in momentum due to the device. By conservation of momentum (and/or Newton's 3rd law), the device won't have any net change in momentum either. (And if an ion reflects back, as the electrons are intended to in that illustration, the device is equivalent to a single charged plate.) The debate in that earlier comment thread was all about how to correctly model the non-zero fields outside of the parallel plates: how quickly do they fall off to zero? But in the end, that doesn't matter. However small the fields outside may be, it is mathematically guaranteed that they will also extend over a large enough distance so their integrated effect from infinity to the nearer plate is exactly opposite to their integrated effect from that plate to the center of the gap between the plates. [Background: I'm a physics professor. I teach basic E&M every year and upper-level undergraduate E&M occasionally.]
fxj 7y ago
The dipole drive uses the protons and electrons of the solar wind for propulsion. They are reflected in an electric field and the paper claims that velocities higher than the solar wind speed can be achieved. But take the proposal with a grain of salt, because the whole mechanism highly depends on the plasma density of the solar wind which is rather small in the interplanetary space. It really works well only close to planets or stars where the plasma density is high.
stareatgoats 7y ago
> the dipole drive can be used to accelerate a spacecraft at velocities greater than that of the solar wind [0] and > [the Dipole drive] therefore offers potential as a means of achieving ultra-high velocities necessary for interstellar flight. Sorry, but I couldn't come up with anything else than: warp-drive!! (if it can deliver on that promise that is). I have long hoped/expected we would crack the challenge of propellant-less acceleration through space, not sure if this is it though. [0] https://news.ycombinator.com/item?id=20666722 https://news.ycombinator.com/item?id=20666722
- Dylan16807 7y ago
  Nothing that accelerates at a tiny fraction of a percent of 1g is within miles of a "warp drive", no matter how high the max speed is.
  - taneq 7y ago
    The point of a warp drive is to bypass the speed of light limit by warping space. Acceleration is kind of irrelevant.
    - peter_d_sherman 7y ago
      Theoretically, in addition to the warp drive, you also need some kind of secondary propulsion, no matter how slow, to move the ship through the warp bubble/vortex/portal/curved space, etc. Later versions of warp will be able to move the bubble/vortex/portal of curved space itself -- around the ship and from front to back, thus obviating the need for motion relative to the warp field. Technology-wise think of the steps like this: 1) Figure out how to create a warp bubble 2) Figure out how to move it, relative to what's projecting it Without #2, secondary propulsion is required. #1 is the first technological achievement, #2 would follow upon that. Until #2 is achieved, secondary propulsion is required... #2 is a little bit wierd to do, because once you've changed your location in space, you've changed the location of what's projecting the warp field -- you need to include that in your warp field projection calculations for #2... and that's IF it could be done... In fact, the initial version of warp might look something like this: Ship A, stationary in space, projects the warp bubble, Ship B goes through it. Why? Because otherwise you've got all kinds of relative motion that would need to be compensated for... Of course, all of this is theoretical...
peter_d_sherman 7y ago
6 milli-Newtons per kW is not a lot of force relative to the electricity consumed... but this is sort of the early alpha version of this technology. I expect future versions of this to be greatly improved. So, all in all, a brilliant set of ideas with a lot of future potential!
amingilani 7y ago
I feel as though this is one of those points where a picture is worth a thousand words.
amluto 7y ago
Better link: https://www.centauri-dreams.org/2018/06/29/the-dipole-drive-a-new-concept-for-space-propulsion/ https://www.centauri-dreams.org/2018/06/29/the-dipole-drive-...
T-A 7y ago
General note to naysayers: before you present yet another "obvious" argument why Zubrin's proposal can't possibly work, you may want to check how it applies to this: http://news.mit.edu/2018/first-ionic-wind-plane-no-moving-parts-1121 http://news.mit.edu/2018/first-ionic-wind-plane-no-moving-pa... https://www.nature.com/articles/s41586-018-0707-9 https://www.nature.com/articles/s41586-018-0707-9 It's essentially the same thing, except it has to ionize the medium (air) on its own rather than just pick up the ions from its surroundings. (Yes, it does so in front of the vehicle, so on average stripped-off electrons get less work done on them by the electric field than positive ions, but the electrons would carry less momentum than the more massive ions even at kinetic energy parity, with the difference going to the vehicle, as Zubrin correctly says - please let's not beat that dead horse again.)

84 points by cl42 7y ago

Should be an interesting read. Can't reach the site. Is it up or down? Tried loading it several times but it didn't load for me.

deleted 7y ago

[deleted]

samcheng 7y ago

I found a non-paywalled discussion here: https://www.centauri-dreams.org/2018/06/29/the-dipole-drive-a-new-concept-for-space-propulsion/ https://www.centauri-dreams.org/2018/06/29/the-dipole-drive-...

jcims 7y ago

Isn’t this basically electrohydrodynamics?

osamagirl69 7y ago

The fact that the abstract does not mention laser driven sails, the currently most viable approach to relativistic propulsion (ie, the current breakthrough starshot plan), does not give me much hope in this researchers credibility in the rest of the paper. Furthermore, the performance of this engine is abismal. To put it into perspective,a modest ion engine would produce about a million times more thrust per power. While the ion engine of course requires carrying fuel, and is thus governed by the tyranny of the rocket equation and not directly comparable in performance, this engine still requires a power source and thus effectively requires fuel anyway. Also worth mentioning is that the least efficient possible massless thruster, a simple blackbody radiator with reflector to aim all of the photons behind you, is only about 1000x worse than this unit in terms of propulsion force per power, and essentially infinitely better than the unit in terms of propulsion force per mass, since this structure is incredibly massive where as you can usually generate blackbody radiation directly from you power source.

deleted 7y ago
[deleted]
vidarh 7y ago
The author is Robert M. Zubrin. To write it off because the abstract doesn't mention a specific technique seems a bit silly, especially given that Zubrin personally knows a lot of the people involved in Breakthrough Starshot and surely is aware of it, including its massive caveats. It's worth noting that the paper specifically discusses the need for methods that are not limited in travel direction, and in that respect Breakthrough Starshot has the same caveats as a solar sail and so treating laser driven propulsion separately is pointless. Another major difference that is so obvious as to not require a mention of every specific alternative is that it is talking about a propulsion method that avoids the need for us to provide a source of thrust. Laser driven systems doesn't require the ship to carry propellant, but we're still paying the cost to provide thrust, while this design is basically 'just' relying on there being a source of protons and electrons with a speed differential relative to the current speed and direction of travel of the ship that it can 'scoop up'. That makes for fundamentally different tradeoffs relative to classical sail based propulsion.
- deleted 7y ago
  [deleted]
choeger 7y ago
> Furthermore, the performance of this engine is abismal. To put it into perspective,a modest ion engine would produce about a million times more thrust per power. Would it, though? The proposal mentions 14mN/kW. What ion engine produces 14N/W ? I think that such an engine would be a massive improvement of current designs. VASIMIR, for instance, is designed with 1N/14kW.

ScottBurson 7y ago

Previously discussed: https://news.ycombinator.com/item?id=17428751 https://news.ycombinator.com/item?id=17428751 I chewed on this idea for several days, eventually coming to the same conclusion others had: it won't work. This poster came up with a correct explanation much faster than I did: https://news.ycombinator.com/item?id=17432975 https://news.ycombinator.com/item?id=17432975 Zubrin has taken a familiar approximation -- that the field near a flat charged plate is uniform -- and forgotten that it's only an approximation, and that the keyword is "near". As particles leave the vicinity of the drive, they will be attracted back toward it, reversing the momentum transfer.

starpilot 7y ago
So the particles follow the path of a doublet?
stareatgoats 7y ago
That stance received some knowledgeable opposition in the quoted thread if I'm not mistaken. I'm in no position to assess the soundness of the arguments, but I noticed that the poster admitted to some flaws in his own reasoning at the tail end of it.
- Steuard 7y ago
  None of that second commenter's objections even began to address the core of the original poster's point: whatever the exact details of the field configuration might be, it's inescapably true that the electric potential is zero at infinity, rises to a positive maximum at the + plate, falls quickly to a negative minimum at the - plate, and then returns gradually to zero at infinity again. That means that if an ion's initial speed is "v0" well before it encounters the device, it may speed up and slow down while interacting, but its final speed will be "v0" again once the device has passed by. If its direction is unchanged (which is the intended case for the thrust-producing protons, as illustrated in Fig. 1 of https://www.centauri-dreams.org/2018/06/29/the-dipole-drive-a-new-concept-for-space-propulsion/ https://www.centauri-dreams.org/2018/06/29/the-dipole-drive-...), that means that the ion will experience zero net change in momentum due to the device. By conservation of momentum (and/or Newton's 3rd law), the device won't have any net change in momentum either. (And if an ion reflects back, as the electrons are intended to in that illustration, the device is equivalent to a single charged plate.) The debate in that earlier comment thread was all about how to correctly model the non-zero fields outside of the parallel plates: how quickly do they fall off to zero? But in the end, that doesn't matter. However small the fields outside may be, it is mathematically guaranteed that they will also extend over a large enough distance so their integrated effect from infinity to the nearer plate is exactly opposite to their integrated effect from that plate to the center of the gap between the plates. [Background: I'm a physics professor. I teach basic E&M every year and upper-level undergraduate E&M occasionally.]

fxj 7y ago

The dipole drive uses the protons and electrons of the solar wind for propulsion. They are reflected in an electric field and the paper claims that velocities higher than the solar wind speed can be achieved. But take the proposal with a grain of salt, because the whole mechanism highly depends on the plasma density of the solar wind which is rather small in the interplanetary space. It really works well only close to planets or stars where the plasma density is high.

stareatgoats 7y ago

> the dipole drive can be used to accelerate a spacecraft at velocities greater than that of the solar wind [0] and > [the Dipole drive] therefore offers potential as a means of achieving ultra-high velocities necessary for interstellar flight. Sorry, but I couldn't come up with anything else than: warp-drive!! (if it can deliver on that promise that is). I have long hoped/expected we would crack the challenge of propellant-less acceleration through space, not sure if this is it though. [0] https://news.ycombinator.com/item?id=20666722 https://news.ycombinator.com/item?id=20666722

Dylan16807 7y ago
Nothing that accelerates at a tiny fraction of a percent of 1g is within miles of a "warp drive", no matter how high the max speed is.
- taneq 7y ago
  The point of a warp drive is to bypass the speed of light limit by warping space. Acceleration is kind of irrelevant.
  - peter_d_sherman 7y ago
    Theoretically, in addition to the warp drive, you also need some kind of secondary propulsion, no matter how slow, to move the ship through the warp bubble/vortex/portal/curved space, etc. Later versions of warp will be able to move the bubble/vortex/portal of curved space itself -- around the ship and from front to back, thus obviating the need for motion relative to the warp field. Technology-wise think of the steps like this: 1) Figure out how to create a warp bubble 2) Figure out how to move it, relative to what's projecting it Without #2, secondary propulsion is required. #1 is the first technological achievement, #2 would follow upon that. Until #2 is achieved, secondary propulsion is required... #2 is a little bit wierd to do, because once you've changed your location in space, you've changed the location of what's projecting the warp field -- you need to include that in your warp field projection calculations for #2... and that's IF it could be done... In fact, the initial version of warp might look something like this: Ship A, stationary in space, projects the warp bubble, Ship B goes through it. Why? Because otherwise you've got all kinds of relative motion that would need to be compensated for... Of course, all of this is theoretical...

peter_d_sherman 7y ago

6 milli-Newtons per kW is not a lot of force relative to the electricity consumed... but this is sort of the early alpha version of this technology. I expect future versions of this to be greatly improved. So, all in all, a brilliant set of ideas with a lot of future potential!

amingilani 7y ago

I feel as though this is one of those points where a picture is worth a thousand words.

amluto 7y ago

Better link: https://www.centauri-dreams.org/2018/06/29/the-dipole-drive-a-new-concept-for-space-propulsion/ https://www.centauri-dreams.org/2018/06/29/the-dipole-drive-...

T-A 7y ago

General note to naysayers: before you present yet another "obvious" argument why Zubrin's proposal can't possibly work, you may want to check how it applies to this: http://news.mit.edu/2018/first-ionic-wind-plane-no-moving-parts-1121 http://news.mit.edu/2018/first-ionic-wind-plane-no-moving-pa... https://www.nature.com/articles/s41586-018-0707-9 https://www.nature.com/articles/s41586-018-0707-9 It's essentially the same thing, except it has to ionize the medium (air) on its own rather than just pick up the ions from its surroundings. (Yes, it does so in front of the vehicle, so on average stripped-off electrons get less work done on them by the electric field than positive ions, but the electrons would carry less momentum than the more massive ions even at kinetic energy parity, with the difference going to the vehicle, as Zubrin correctly says - please let's not beat that dead horse again.)