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Space Science

Could Spacecraft Catch the Solar Winds With 'Electric Sails'? (arxiv.org) 62

Posted by EditorDavid from the touching-the-sun dept.
RockDoctor (Slashdot reader #15,477) writes: For over a century, the "solar sail" has been a concept in theoretical spaceflight, in science fiction, and in the last few years, actual spaceflight. Recently, the Breakthrough Starshot project has been prompting and funding a lot of work to optimise and explore the operational possibilities of flying spacecraft to nearby stars, and this has produced another (relatively) novel idea for efficient spacecraft propulsion — an electric sail.

It is well known that stars produce both radiation (light) and material outflows ("solar wind"). It is less well known that the momentum transferred by the solar wind can be considerably higher that that transferred by light. Recent calculations by the paper's authors, Loeb and Lingam, with not-unreasonable premises, show that for many classes of star (including the most common star types) the solar wind is considerably stronger than the radiation pressure. They propose that a mesh of wires, positively charged, can drive a spacecraft more efficiently than reflecting radiation. Moreover, by using the radiation to generate electrical power, the wire grid can be kept charged and incident electrons discharged in a beam to keep the spacecraft electrically neutral. Thirdly, maintaining a charge on the grid in interstellar space can act to brake the spacecraft, or even steer it, depending on the "space weather" it encounters.

Clearly, applying these mechanisms to optimising "Breakthrough" spacecraft could considerably widen the range of trajectories and mission profiles possible.
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Could Spacecraft Catch the Solar Winds With 'Electric Sails'? More

Could Spacecraft Catch the Solar Winds With 'Electric Sails'?

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  • "Could" it? (Score:1)

    by Anonymous Coward

    Could it? yes.

    Will it? How about you tell us, you're supposed to be the reporter...

    • That's the editor's headline, not mine. I take it you've never made a submission to the Slashdot system.

      The physics should work. That people are working on designing how to optimally use that physics suggests that someone is putting together a design for an actual demonstration device, but that's not a question that the paper addresses directly.

      Breakthrough Starshot contributors are pricing up facilities for testing (and incrementally improving) hardware. See, for example, this paper [arxiv.org], discussing a (FTFAbs

  • As long as it's not made by Boeing.

  • And that's final.

  • could the technology be adapted to propel a surfboard through the galaxy ?
    • The mechanism has an intrinsic speed limit - that of the incoming particles and/ or radiation which transfers momentum to the sail (electric, magnetic, or light-reflecting). So, no you're not going to get anywhere faster than the Speed Limit [wikipedia.org].
    • answer: 42

  • If an interstellar space craft is powered with a solar wind sail, then it will be stopped as it approaches another star by that star's stellar wind. The space craft will begin decelerating when it reaches the point where the stellar wind from the other star is as strong as the solar wind propelling it.

    • As an AC says, that's not a flaw, it's a design feature. Unless you want to do a flyby, you do want to slow down to orbital speeds when you reach your target system. Compare the Voyager missions to Cassini, Juno and ... oh, we haven't looked closely at anything further out than Saturn's orbit.

      Previous work in this vein has shown a variety of trajectories whereby solar sails launched by laser from the Solar system could indeed be slowed down or stopped at their destination, or perform slingshot manouvers. T

  • Sailing (Score:3)

    by rossdee ( 243626 ) on Sunday December 22, 2019 @08:16PM (#59548600)

    Can you use the solar wind for propulsion? Yes.

    To nearby stars? Not in a reasonable amount of time.
    The solar wind only goes so far. I believe some of the probes we have sent out have already reached that limit.

    You'd be better off using a light sai , which you can boost by using sokar powered laser.
    (But thats still a crazy Eddie idea.)

    See Sunjammer (A C Clarke)
    Flight of the Dragonfly (Robert L Forward)
    and of course The Mote in Gods Eye (Niven % Pournelle
     

    • Re: (Score:1)

      by Thing 1 ( 178996 )

      Wow. Robert L. Forward wrote "The Dragon's Egg" which I referred to at voat recently. This world is smaller than we imagine!

    • Re: (Score:2)

      by quenda ( 644621 )

      The solar wind only goes so far.

      Any method "only goes so far". Including lasers and nuclear rockets.
      The real reason you don't use solar wind for interstellar travel is that it is so slow!
      Even if you could build a light-enough sail for the sub-nanopascal pressure.

      However, you could consider the solar wind for slowing down at the other end.
      No "laser the size of the moon" needed.
      Could be combined with nuclear pulse propulsion, halving your transit time (double speed) compared to if you had to save half your delta-V for braking.

      An i

      • However, you could consider the solar wind for slowing down at the other end.

        The (probably) humanoid has caught the point. You can launch from the Solar system to [target star] using the accelerating power of ground-based (or asteroid-based) "launching masers", spend most of the time in a coasting phase, then turn on the electric sail when the target star's light is strong enough to power the electrostatic generators.

        The numbers you're proposing are not the Breakthrough Starshot base design, but that is pu

  • The answer is yes [space.com]. But not interstellar ones, if you want them to get there on a human time scale.

    • if you want them to get there on a human time scale.

      There is no physically plausible technology capable of doing that (unless you've got an idea which you've published somewhere). But why be so limiting as to restrict oneself to working within a human timescale. I know (in the only way that it is possible to know) that no descendant of mine will sunbathe under an alien star, but I see no reason to claim that descendants of yours will never do so.

      Didn't the Founding Mothers of America leave Plymouth harbour

  • that electricity is the dominant force in space.
    • Electricity (well, the electro-weak force) can be either attractive or repulsive. Which is why the attractive-only force of gravity is dominant on large scales in the universe. On small scales (say, under a petametre), the electro-weak and strong forces dominate, but on the larger scales, it's gravity that matters.

      • Re: (Score:1)

        by danda ( 11343 )
        nice job parroting the party line. gold star for you.

        Let's do a little thought experiment... If you, RockDoctor, lived during copernicus's time, do you think you would be seeking out new ideas that challenge the status quo and would support the notion that the sun is at the center of the solar system even when your peers think that is crazy, or would you be "informing" such people of what you have been taught all your life, that everything revolves around the earth?

        I have a pretty good guess whi

        • Re: (Score:2)

          by cusco ( 717999 )

          I think most of the people on this site would be looking at the evidence and trying to figure out which alternative explanation makes most sense. Since at this point all of the evidence point at gravity being the most important force at large distance or in large quantities of mass, and there is absolutely no evidence at all for the 'Electric Universe' hypothesis, that is what is mostly discussed.

          • Re: (Score:1)

            by danda ( 11343 )
            ask yourself.  Is it that there is "no evidence for electric universe" or that you personally have not taken the time and effort to research the matter for yourself.

            • Re: (Score:2)

              by cusco ( 717999 )

              I've read the links that other EU believers have sent me in the past, and have found mostly speculation, some phenomena that can be better explained by conventional physics, a lot of misunderstanding of how electrical and magnetic fields work, and some outright fraud. There also seems to be a lot of whining about how the great worldwide conspiracy of physicists and engineers are hiding "the truth" from the world for some undefined nefarious reason.

              It has all the hallmarks of a cult and nothing of science.

              • Re: (Score:1)

                by danda ( 11343 )
                the information is out there. In actual books and papers. Not only about EU but many many alternatives to the "standard model". I'm not going to repeat or point it out here because anyone with an inquiring mind who actually wonders "how do things work" will have already sought out and evaluated for themselves. And anyone else wouldn't care enough to bother even if spoon-fed the info.

                I find reading slashdot so tiring anymore because it seems most everyone here just blindly accep
                • I find reading slashdot so tiring anymore

                  Don;t let the door hit you on the arse as you leave. It might damage the door.

            • The last time I was carrying out experiments on the electric force - you know, with springs to measure the forces, and rulers to measure the distances and displacements - my feet remained firmly pinned to the floor by gravity, while the planet providing that gravity orbited contentedly about the sun under the influence of it's gravity. When I went swimming, I'd see the sea rise and fall twice-daily in response to the interplay of gravitational forces from the Sun, Earth and Moon, but no measurable influence

  • The paper shows that solar wind propulsion would work better that photon propulsion around M-type stars. Nice to know. It would even be useful to us if the Sun was an M-type star. It isn't, it is a G-type star and solar wind propulsion is not better for our star.

    So, no, this "breakthrough" offers no promise for any space mission for humans.

    • Most potential targets for extra-solar exploration (indeed, most stars) are M-stars. So for putting research probes into orbit in those systems (rather than doing a high-speed flyby), incorporating an electric sail into a solar sail becomes very potentially useful.
    • I think you've misunderstood the effects discussed in the paper. Though the total forces generated by electric sails versus light sails switch over at around a half a solar mass (down in the K-class of stars), the initial acceleration from a "habitable zone" planet are considerably higher for an electric sail than a light sail, and habitable zones are much closer in for low mass stars than high mass stars, which combine (figure 3 FTFPaper) to produce higher terminal velocities for electric sails, up to abou

  • M2P2 (Score:2)

    by OoSync ( 444928 )

    Sounds like a variant of Mini-Magnetosphere Plasma Propulsion (M2P2), reported here about 20 years ago.

    • I've never heard of that, and I was here 20 years ago. I didn't read every thread though. [Searches, not Googles] A very quick summary [washington.edu]. It's very definitely not the same concept, but the M2P2 does have some relationships to the "magnetic sail" prospect mentioned at points in the paper I cite. The paper on that topic is "in work".

  • Some facts about e-sails (Score:4, Interesting)

    by Ignatius ( 6850 ) on Monday December 23, 2019 @06:05AM (#59549442)

    Solar wind pressure is orders of magnitudes lower than light pressure. But:

    - e-sails can be made of thin charged wires.
    - the effective size of a sparse e-sail is inversely proportional to the density of the solar wind flow due to shielding effects
    - b/c of the above, there are operating regimes (sparse sail, high flow) where the total force on an e-sail decreases with 1/r instead of a light-sail's 1/r^2
    - solar wind is slow (most of it below solar escape velocity), so attainable speeds are limited, but
    - solar wind in great for breaking from high velocities

    So you cannot go interstellar with an e-sail alone but you can use it for deceleration from interstellar (i.e. >> than 3rd cosmic) velocities, which improves the necessary (non relativistic) mass ratio by a square root or allows for reactionless "acceleration-only" proulsion concepts (beam, particle stream). So it can be a game changer but no silver bullet for interstellar travel.

    [in good slashdot tradition, all of the above is from memory and w/o reading TFA, so caveat emptor]

    ignatius

    • So you cannot go interstellar with an e-sail alone

      You can, but your time-of-flight is large. Chemical propulsion with gravity assists has sent two Voyagers and several (?) Pioneers on interstellar trajectories, but with time-of-flight comparable to a stone tool design "culture" lifetime.

      but you can use it for deceleration from interstellar (i.e. >> than 3rd cosmic) velocities

      Since there's nothing inherent to prevent an electric sail from being incorporated into a solar sail, that's going to be a ver

    • BTW, what did you mean by this?

      interstellar (i.e. >> than 3rd cosmic) velocities

      • Re: (Score:2)

        by Ignatius ( 6850 )

        I define a velocity to be interstellar when it is considerably greater than the solar escape velocity. For a ballistic trajectory, this means that you are far into hyperbolic territory and your kinetic energy is far greater than the gravitational binding (i.e negative potential) energy to your star.

        • So, in your terminology, the "first interstellar velocity" would be greater than Earth (planet of origin) escape velocity ;
          - "second interstellar velocity" would be greater than inner Solar system escape velocity ;
          - "third interstellar velocity" greater than whole-Solar system escape velocity (escape velocity varies continuously with position in the system under consideration, of course, even if you have included al of the mass in the system within the radius for which you're calculating the escape veloci

  • The best result so far has been to deploy a sail. That's kind of it. No actual sailing or anything which is seemingly a resounding refutation of the feasibility of the concepts. So why does it persist? Is it the yearning for the fantasy of the swashbuckling space sailor traveling under simple technology from one planet to another; a life of carefree adventuring?

    • It takes time to develop technologies. This hasn't exactly been a priority technology for development, until now. It's not exactly overbrimming with potential for killing foreigners or for making huge amounts of money, which are the main drivers of technology.

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