We've seen a lot lately about light sails, but this article talks about an "e-sail" that gets pushed along by radio waves. The article says that the idea is for a "sail" that is an electric field generated by the spacecraft itself. Author Michael Flynn talked about his concept in The Wreck of the River of Stars.

How would such a spacecraft keep its sails "aloft"? Does it need to constantly generate power, or can it pick up enough power from the radiation it's sailing on to keep the sail going?


1 Answer 1



  1. http://www.nasa.gov/centers/marshall/news/news/releases/2016/nasa-begins-testing-of-revolutionary-e-sail-technology.html
  2. http://spectrum.ieee.org/tech-talk/aerospace/space-flight/electrostatic-glider-can-maneuver-around-asteroids-without-expending-fuel

Specific answer first: The "power" or actually the propulsive momentum comes from the protons in the solar wind itself. The spacecraft uses some electrical power to charge up, and maintain a positive bias, but then is passively pushed by the electrostatic fields from the larger number of protons piled up behind the craft (sunward) compared to the lower number of protons expected in the wake at the front of the craft (forward).

The article in your link (Gizmag) actually talks about electostatic repulsion, not radio waves. If you look at the bottom of the article you can get out of Gizmag's self-referencing environment and to something more reliable.

Source NASA

That takes you to NASA Begins Testing of Revolutionary E-Sail Technology, where they do NOT claim that a 20km long, 1mm metal wire "weighs only a few grams" the way Gizmag does.

Extending outward from the center of the spacecraft, 10 to 20 electrically charged, bare aluminum wires would produce a large, circular E-Sail that would electrostatically repel the fast moving protons of the solar wind. The momentum exchange produced as the protons are repelled by the positively charged wires would create the spacecraft’s thrust. Each tether is extremely thin, only 1 millimeter -- the width of a standard paperclip -- and very long, nearly 12 and a half miles -- almost 219 football fields. As the spacecraft slowly rotates at one revolution per hour, centrifugal forces will stretch the tethers into position.

The testing, which is taking place in the High Intensity Solar Environment Test system, is designed to examine the rate of proton and electron collisions with a positively charged wire. Within a controlled plasma chamber simulating plasma in a space, the team is using a stainless steel wire as an analog for the lightweight aluminum wire. Though denser than aluminum, stainless steel’s non-corrosive properties will mimic that of aluminum in space and allow more testing with no degradation.

The spacecraft uses an electron gun to loose electrons - thereby charging itself positive. The mutual repulsion moves all the excess charge to the wires.

I get 42 kilograms per wire for Aluminum 1mm diameter, 20km long. They may be using solid metal wire for testing, and planning to use something more clever and light weight later on.

What is necessary is

  1. A modest{1} amount of conductivity - doesn't have to be metal, seems current should be low
  2. Good tensile strength to weight ratio - doesn't break under own centrifugal force
  3. Deployability = flexible and stowable
  4. Durability in space environment - ergo the High Intensity Solar Environment Test system

{1} if the space plasma has a lot of high frequency noise, then you do need low resistitivity (short RC time constant).

I think the radio wave-driven sail you are thinking of must be another technology. See if you can find it, and ask a separate question.

By the way, in the Michael Flynn story, the propulsion seems to involve magnetic fields and superconductors not electric fields, and the Farnsworth-Hirsch Fusor which is a real thing and still actively discussed - see Section 1.1. The magnetic drive use in that story would be a good question for scifi.stackexchange.com if it's not there already.

Philo T. Farnsworth is sometimes called "inventor of the television" although it was more of a collective effort. His likeness can be seen in the Letterman Digital Arts Center as well as the Futurama Wiki. Now you know why the name sounds familliar!

Philo T. Farnsworth CROPPED from Wikipedia

Philo T. Farnsworth (Right): Philo T. Farnsworth - on the right

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    $\begingroup$ Thanks for all the exposition. Just so you know, this question was originally asked on worldbuilding.stackexchange.com where writers discuss aspects of fictional settings. I'm definitely interested in the science, but unlike the real world, we have the capability to use "literary license" to slightly adjust reality. $\endgroup$
    – J.D. Ray
    Apr 14, 2016 at 3:35
  • $\begingroup$ Absolutely! Science fiction and actual space science and exploration have always been linked. I think it's great to see the cross-overs and connections, as long as we don't mix them up (much). $\endgroup$
    – uhoh
    Apr 14, 2016 at 3:41

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