Electric Sails: Leave the Propellant at Home

by Paul Gilster on April 24, 2008

A Finnish design making the news recently is hardly the only concept for near-term space sailing, but the possibility of testing it in space for a relatively small sum of money is attractive. This is especially true at a time when strapped budgets like NASA’s are focused on ratcheting up conventional propulsion techniques to get us back to the Moon and on to Mars. Yes, let’s keep pushing outward into nearby space with what we’ve got, but we need next-generation thinking, too, and the Finnish sail, the work of Pekka Janhunen and Arto Sandroos, points in that direction.

Unlike magnetic sails that create an artificial magnetosphere around the spacecraft, the Finnish concept is to use long, thin conductive wires that are kept at a positive potential through the use of an onboard electron gun. The two researchers considered how the charged particles of the solar wind would interact with a single charged wire in a 2007 paper that we looked at in this Centauri Dreams article just over a year ago. A full-scale mission would use fifty to one hundred 20-kilometer long charged tethers. Supercomputer simulations come up with potential speeds of 100 kilometers per second, which is about five times what New Horizons is doing on its way to Pluto/Charon.

That’s also a speed that gets you into the nearby interstellar medium in about fifteen years, a time frame that should quicken the heart of many a deep space scientist. When he looked at some of the potential mission concepts in Next Big Future, Brian Wang mentioned the possibility of transporting raw materials from the asteroids for use in making fuel at high Earth orbit. I see that Janhunen noted the asteroid idea in a recent interview, tying it to a broader human future: “Starting the long-awaited asteroid resource utilization could be significant for the longer-term well-being and survival of our civilization on this planet.”

That article, published in Space.com (and thanks to John Hunt for the link), notes the nature of the sail’s first prototype, seen as a smaller sail using 8-kilometer long tethers in an elliptical Earth orbit, a scenario that would allow tests on the force of the solar wind on the spacecraft. The team would also investigate using radio waves to excite solar wind particles in an attempt to boost the possible thrust.

So many good concepts, so many budgetary constraints. Long an admirer of Robert Winglee’s Mini-Magnetospheric Plasma Propulsion concept, I watched with growing enthusiasm as it sailed through Phase I and Phase II rounds at NASA’s Institute for Advanced Concepts and went on to further scrutiny, but getting some kind of solar, magsail or electric sail concept into actual space testing now seems a remote possibility. The Finnish team’s sail awaits the resolution of its own funding issues, a quick fix being the infusion of somewhere around 5 million Euros.

One thing is for sure: Propulsion concepts that let us leave the fuel on Earth have a huge future in opening up the outer planets and the interesting places beyond. Solar sails can do this by using the momentum provided by photons from the Sun, but these effects drop dramatically as we move beyond Jupiter. The solar wind, streaming outward from the Sun at speeds approaching 1.5 million kilometers per hour, may offer a way to boost sail performance through magsail and electric concepts, but we have much to learn about how sails might interact with it. In both cases, we need sail deployment in space to take the necessary next steps.

A good way to keep up with the Finnish sail studies is to track the latest papers and press releases here. You’ll also find the latest paper I know about, which is Mengali et al., “Electric sail performance analysis,” Journal of Spacecraft and Rockets Volume 45, Issue 1 (Jan-Feb, 2008), pp. 122-129, available as an abstract with included figures on the site. It’s interesting as well to see that a workshop on electric sailing will be held at the European Space Research and Technology Centre in the Netherlands on Monday, May 19.

Enzo April 24, 2008 at 18:15

Pardon my ignorance on the subject, but can any of these methods be used to brake ? I mean, at 100 Km/s it’s nice to be able to get to Pluto in 2 years, but, once there, traversing 100,000Km in 15 minutes might not be very good for science.
Maybe aereocapture for a fast mission to Uranus/Neptune ?

It should be good to study the interstellar medium though but a still a bit slow to reach 1000 AU…….

James M. Essig April 24, 2008 at 20:47

Hi Folks;

A really cool idea would envolve a very high mass specific area magnetic sail that would use the magnetic field gradients within the interstellar medium and perhaps within the intergalactic medium for propulsion. The idea here is simillar to the idea of a magnet being pulled to the end of a cylindrical arrangment of multiple identical magnets.

Perhaps the magnetic sail could be of a porous net like configuration to increase magnetic flux capture per unit of sail mass if such a porous net would actually catch more flux per unit of magnetic material surface area subtention relative to a continuous monolithic magnetic sheet.

The sheet might optionally include a grid of nano scale or micron-scale superconducting magnets that have a continuous loop of current perpetually circulating thru the loops wherein the magnetic energy would only be depleted upon reaction with the interstellar medium to increase or decrease the kinetic energy of the ship. The magnetic coils could be restocked with electrical energy from insitu ambient mattergy collection or from beamed energy collection mechanisms.

Another really bazaar idea would be to utilize magnetic fields in higher dimensional space that are oriented in terms of force of attraction or repulsion along a direction that is orthogonal to all three spatial directions in which the space ship exists. The electrodynamics of the magnetic field of a magnet somehow located in hyperspace that might possibly be used to pull the space craft into hyperspace and thus into a frontier beyond the final frontier of 4-D ordinary Einstienian spacetime. Perhaps the hyperspace-based magnetic field could be oriented orthogonally to only a limited subset of the three spatial dimensions perhaps even only to one such dimension wherein the magnetic flux gradient extends orthogonally into hyperspace from the one or two axial dimensions under consideration.

Thanks;

Jim

John Hunt April 25, 2008 at 1:22

Enzo,

I think that a lot of us interstellar mission advocates are counting on the concept of our craft traveling at .1c or so deploying a superconducting loop to ionize the interstellar medium and decelerating so that we can do much more than just a flyby in a neighboring solar system.

So your hope that an outer solar system mission would use the magnetic sails to decelerate might be able to provide a practical laboratory for developing and testing such a concept. So, although an aerocapture could provide a practical solution, for outer solar system mission purposes, learning how to use charged thin wires for deceleration would provide us an important step towards an interstellar mission. I just can’t imagine an aerocapture as the deceleration solution for an interstellar mission.

This post triggers a question in my mind. I don’t believe that we have room temperature superconducing material yet. At 1 AU, the sun side of a superconducting loop is going to be well above room temperature. Yet, if the first interstellar mission turns out to use particle beams against a craft using magnetic fields then we might want to launch such a mission with particle beams deployed within the solar system (e.g. on various asteroids). Hopefully in the foreseeable future we’ll have high temperature superconducting material. But does anyone know of a simple solution to this problem?

John Hunt

John Hunt April 25, 2008 at 2:36

For further reading on this subject I would suggest the following link:

http://www.thehindu.com/fline/fl2408/stories/20070504006312300.htm

Also, below is a video clip illustrating the concept:

http://video.google.com/videoplay?docid=1120563232158554193&q=Pekka+Janhunen&ei=iYkRSNL9B4mSrwLF4MCeAg&hl=en

John Hunt

Adam April 25, 2008 at 4:39

Hi Enzo

Flights to the near interstellar medium don’t necessarily have to slow down to be useful. A flight to Pluto via this mechanism would need to carry a decceleration stage to provide sufficient braking, meaning the transit velocity will be a lot less than 100 km/s. I have seen designs for a fast aerobraked lander mission
Galileo proved that a small hardy probe can be deccelerated from 48 km/s in an atmosphere of H2/He. Perhaps a feasible approach for Uranus/Neptune missions will be aerobraking at ~ 48 km/s down to ~ 25 km/s for transfer out to the moons. Alternatively the particles trapped in the planetary magnetospheres might provide some electrostatic braking, though the decceleration required will be several gees.

dad2059 April 25, 2008 at 5:56

I can’t elucidate my thoughts like Jim above did, but my opinions are the same as Enzo’s, a mite slow for interstellar travel just yet.

But hey, I’ll take it! I’ve been following this story myself for two weeks now and I’m keeping my fingers crossed in the hope the Finns get this experiment aloft and prove the theory out.

Outer solar system in under a year and Pluto in two? Great leap forward I’d say!

And I’m confident we’ll solve the deceleration problem too.

george scaglione April 25, 2008 at 8:59

everybody: yes we do tendto think about acceleration to get spacecraft to where it is we wish to go to the virtual exclusion of all else.but i have found some decent ideas for deceleration above,thank you. john what you just said on the subject above sounds as if it could be promisiing but most certainly will call for alot of investigation and study! and jim! good idea for acceleration also!!!!! thank you one and all for sharing your interesting concepts and ideas with the group. sincerely your friend george

george scaglione April 25, 2008 at 9:07

jim i was just about to leave this site but then i had to come back to read something you had said again…to use the magnetic field gradients within the interstellar medium for propulsion!!! what an ELEGANT idea that is!!!! more and more we think up ways to derive propulsion from space itself ! completely neat!wow. thank you your friend george

Jim Baerg April 25, 2008 at 9:21

Re: braking at the end of the trip
IIRC Winglee’s M2P2 idea includes the ability to use the magnetosphere of the destination planet for braking.

Another possibility if you don’t accelerate to too high a speed is to make your 1st pass by the planet so that its gravity bends your path around so you then are going directly toward the sun relative to the planet. Then you can turn on the current in your electromagnetic sail to brake against the solar wind.

None of these would be usable in all circumstances so interplanetary spacecraft will likely have both an ion drive & some sort of ‘sail’. IINM the M2P2 device & an ion drive would have several major components in common.

george scaglione April 25, 2008 at 12:58

jim baerg above…yes good idea! why could not the home star of theworld you wish to visit in each case not be used as lol “the brakes”?! another good idea. you know i get so excited about trying to find ways to move faster and faster so as to reach the stars that sometimes i loose track of brakes! you know lol no matter how fast your car will go sooner or later your going to badly want brakes! …..and, dad,you bet we will solve the deceleration problem too ! looks to me like mr baerg above has just begun to take a good stab at that already.but one more thing he is talking about space sails.how about a ship like kirks enterprise? lol can anybody tell me please how that used to slow down! heck,they too used to move pretty faaaaast!!!! but hell let me venture an answer right now – no matter how much energy you kick out the rear still it will only just be so much.say enough to take you from point a to point b : so- with really good computers and i mean really good computers you could have already figured it out as to how far this burst of energy will take you before you more or less have to stop anyway! i’d really like to know what everybody thinks. your friend george

Adam April 26, 2008 at 2:56

Hi John

A cylindrical cross-section to the ring superconductor or wire means the effective temperature of a blackbody is reduced to 295 K at 1 AU. Make it 90% reflective and the temperature is below the 185 K superconduction record that Brian Wang has reported recently at “Next Big Future”. Make it a double layer with a vacuum between and the temperature is lower and now has a Whipple shield against micrometeorites.

James M. Essig May 20, 2008 at 3:44

Hi Folks;

I could imagine a space craft in the form of a huge ring with a very very small thickness aspect ratio, almost like a loop made of super fine thread that would have a means to sail or react against the magnetic flux passing through the inner region bounded by such a ring.

The ring might be set slowly rotating and might perhaps be anywhere from several kilometers to, in the extreme limits, billions of kilometers in diameter wherein the rotation would provide the artificial gravity to simulate one Earth G. The caveat for the large end limiting size of such space ship rings is obviously the need for moderate or normal matter density materials (or other materials) with unheard of or extreme tensile strength properties. Perhaps the materials science folks could cook something up for such a purpose.

Perhaps some sort of super fine magnetic superconducting mesh bridging the interior of the ring could be used to collect magnetic flux energy and/or CMBR energy. If such a ring could accelerate to extreme relativistic velocities and thus very high gamma factors, then perhaps the mesh or grid could be composed of some type of negative index of refraction material in order to be pulled in the direction of incident highly relativistically blue shifted CMBR. Perhaps the grid could be mostly empty space to reduce drag from incident electrons, atoms, and ions, and also be self repairing with nanotech means. If such a grid could be made out of atomic nucleus density materials, much shorter blue shifted CMBR could possibly be used to propel the craft forward and pico-technology or femto-technology self assembly repair means could be used to repair the grid damaged by the incident interstellar medium particles and fields.

The ship might optionally take the form of a long aspect ratio cylinder with a very thin aspect ratio cylinder wall in order to increase the mass of the ship with respect to its drag inducing forward oriented surface area.

I will have more to say about this concept in the coming days.

Thanks;

Jim

James M. Essig May 21, 2008 at 3:34

Hi Folks;

I can’t seem to stay away from this thread. Electrodynamic space craft propulsion system concepts have always intrigued me.

I can imagine a ring-like space craft as described above with the same range of size for the diameter for the examples given above, in fact even space craft as such with much larger diameters perhaps as great in scale as light-years. These craft would be set rotating very slowly, so slowly that the centripetal acceleration of a diametric portion of the ring would be a miniscule fraction of a G yet fast enough to keep the space craft in circular configuration.

The craft I am imagining would consist of a huge diameter toriodal ring with magnetic energy and/or CMBR energy capturing mechanisms such as the ones mentioned in my previous posting above wherein living quarters in the form of minor torus diameter circumferentially disposed rings would wrap and rotate around the minor diameter of the larger toriod in a manner similar to that of a person wrapping his hands around one side of a donut with his fingers passing through the central hole of the donut.

The living quarters units could number in the millions if not billions or even trillions for a primary toriod with a diameter on the order of light years. The living quarters elements could be mounted on low friction bearing surfaces or by frictionless magnetic bearing systems.

This huge craft could accelerate slowly, but I would like to think that such a craft could accelerate somehow forever always approaching C ever more closely. However, with today’s current understanding of the interstellar medium and even the intergalactic medium, currents paradigms in basic kinematics would dictate that at some point, drag induced by the interstellar medium and the blue shifted CMBR and star light would become intolerable. Our on-site colleague Adam has offered me good advice on some of the limiting factors involving such drag. If only we could figure out how to make such a space craft pass through the portion of the incident mattergy that it would not harvest for propulsion, that would be a great thing.

Thanks;

Jim

ljk May 30, 2008 at 15:21

POLAR Investigation of the Sun – POLARIS

Authors: T. Appourchaux, P. Liewer, M. Watt, D. Alexander, V. Andretta, F. Auchere, P. D’Arrigo, J. Ayon, T. Corbard, S. Fineschi, W. Finsterle, L. Floyd, G. Garbe, L. Gizon, D. Hassler, L. Harra, A. Kosovichev, J. Leibacher, M. Leipold, N. Murphy, M. Maksimovic, V. Martinez-Pillet, B.S.A. Matthews, R. Mewaldt, D. Moses, J. Newmark, S. Regnier, W. Schmutz, D. Socker, D. Spadaro, M. Stuttard, C. Trosseille, R. Ulrich, M. Velli, A. Vourlidas, C. R. Wimmer-Schweingruber, T. Zurbuchen

(Submitted on 28 May 2008)

Abstract: The POLAR Investigation of the Sun (POLARIS) mission uses a combination of a gravity assist and solar sail propulsion to place a spacecraft in a 0.48 AU circular orbit around the Sun with an inclination of 75 degrees with respect to solar equator.

This challenging orbit is made possible by the challenging development of solar sail propulsion. This first extended view of the high-latitude regions of the Sun will enable crucial observations not possible from the ecliptic viewpoint or from Solar Orbiter.

While Solar Orbiter would give the first glimpse of the high latitude magnetic field and flows to probe the solar dynamo, it does not have sufficient viewing of the polar regions to achieve POLARIS’ primary objective : determining the relation between the magnetism and dynamics of the Sun’s polar regions and the solar cycle.

Comments: 23 pages, 14 figures, 4 tables, Accepted by Experimental Astronomy

Subjects: Astrophysics (astro-ph)

Cite as: arXiv:0805.4389v1 [astro-ph]

Submission history

From: Thierry Appourchaux [view email]

[v1] Wed, 28 May 2008 17:10:41 GMT (1092kb)

http://arxiv.org/abs/0805.4389

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