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The Winds of Deep Space

If we can use solar photons to drive a sail, and perhaps use their momentum to stabilize a threatened observatory like Kepler, what about that other great push from the Sun, the solar wind? Unlike the stream of massless photons that exert a minute but cumulative push on a surface like a sail, the solar wind is a stream of charged particles moving at speeds of 500 kilometers per second and more, a flow that has captured the interest of those hoping to create a magnetic sail to ride it. A ‘magsail’ interacts with the solar wind’s plasma. The sailing metaphor remains, but solar sails and magsails get their push from fundamentally different processes.

Create a magnetic field around your spacecraft and interesting things begin to happen. Those electrons and positively charged ions flowing from the Sun experience a force as they move through the field, one that varies depending on the direction the particles are moving with respect to the field. The magsail is then subjected to an opposing force, producing acceleration. The magsail concept envisions large superconducting wire loops that produce a strong magnetic field when current flows through them, taking advantage of the solar wind’s ‘push.’

A magsail sounds like a natural way to get to the outer Solar System or beyond, but the solar wind introduces problems that compromise it. One is that it’s a variable wind indeed, weakening and regaining strength, and although I cited 500 kilometers per second in the introductory paragraph, the solar wind can vary anywhere from 350 to 800 kilometers per second. An inconstant wind raises questions of spacecraft control, an issue Gregory Matloff, Les Johnson and Giovanni Vulpetti are careful to note in their 2008 title Solar Sails: A Novel Approach to Interplanetary Travel (Copernicus, 2008). Here’s the relevant passage:

While technically interesting and somewhat elegant, magsails have significant disadvantages when compared to solar sails. First of all, we don’t (yet) have the materials required to build them. Second, the solar wind is neither constant nor uniform. Combining the spurious nature of the solar wind flux with the fact that controlled reflection of solar wind ions is a technique we have not yet mastered, the notion of sailing in this manner becomes akin to tossing a bottle into the surf at high tide, hoping the currents will carry the bottle to where you want it to go.

Interstellar Tradewinds and the Local Cloud

We have much to learn about the solar wind, but missions like Ulysses and the Advanced Composition Explorer have helped us understand its weakenings and strengthenings and their effect upon the boundaries of the heliosphere, that vast bubble whose size depends upon the strength of the solar wind and the pressures exerted by interstellar space. For we’re not just talking about a wind from the Sun. Particles are also streaming into the Solar System from outside, and data from four decades and eleven different spacecraft have given us a better idea of how these interactions work.

A paper from Priscilla Frisch (University of Chicago) and colleagues notes that the heliosphere itself is located near the inside edge of an interstellar cloud, with the two in motion past each other at some 22 kilometers per second. The result is an interstellar ‘wind,’ says Frisch:

“Because the sun is moving through this cloud, interstellar atoms penetrate into the solar system. The charged particles in the interstellar wind don’t do a good job of reaching the inner solar system, but many of the atoms in the wind are neutral. These can penetrate close to Earth and can be measured.”


Image: The solar system moves through a local galactic cloud at a speed of 50,000 miles per hour, creating an interstellar wind of particles, some of which can travel all the way toward Earth to provide information about our neighborhood. Credit: NASA/Adler/U. Chicago/Wesleyan.

We’re learning that the interstellar wind has been changing direction over the years. Data on the matter go back to the 1970s, and this NASA news release mentions the U.S. Department of Defense’s Space Test Program 72-1 and SOLRAD 11B, NASA’s Mariner, and the Soviet Prognoz 6 as sources of information. We also have datasets from Ulysses, IBEX (Interstellar Boundary Explorer), STEREO (Solar Terrestrial Relations Observatory), Japan’s Nuzomi observatory and others including the MESSENGER mission now in orbit around Mercury.

Usefully, we’re looking at data gathered using different methods, but the flow of neutral helium atoms is apparent with each, and the cumulative picture is clear: The direction of the interstellar wind has changed by some 4 to 9 degrees over the past forty years. The idea of the interstellar medium as a constant gives way to a dynamic, interactive area that varies as the heliosphere moves through it. What we don’t know yet is why these changes occur when they do, but our local interstellar cloud may experience a turbulence of its own that affects our neighborhood.

The interstellar winds show us a kind of galactic turbulence that can inform us not only about the local interstellar medium but the lesser known features of our own heliosphere. Ultimately we may learn how to harness stellar winds, perhaps using advanced forms of magnetic sails to act as brakes when future probes enter a destination planetary system. As with solar sails, magsails give us the possibility of accelerating or decelerating without carrying huge stores of propellant, an enticing prospect indeed as we sort through how these winds blow.

The paper is Frisch et al., “Decades-Long Changes of the Interstellar Wind Through Our Solar System,” Science Vol. 341, No. 6150 (2013), pp. 1080-1082 (abstract)


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  • ljk December 5, 2013, 11:32

    Going Interstellar

    When it comes to star travel, some people won’t take no for an answer.

    By Damond Benningfield

    Air & Space magazine, January 2014

    Like many boys growing up in 1950s England, Gerald Webb dreamed of the stars. He followed the exploits of the British Buck Rogers—Dan Dare, “pilot of the future”—and was thrilled by the launch of Sputnik in October 1957. Unlike most boys, Webb followed his dream. He joined the British Interplanetary Society at age 16, earned a degree in physics, and was helping to build payloads for sounding rockets when the society asked for volunteers for a new project: designing an interstellar probe. The team met every few weeks at a pub, The Rising Sun, and in 1978 produced the world’s first detailed plan for a starship: Daedalus, a 60,000-ton agglomeration of spheres, disks, and cones with an engine nozzle big enough to cover Trafalgar Square.

    After that, Webb lost touch with the stars for a while. He stayed in the space business, becoming an aerospace consultant and helping to start a company that brokered satellite launches on Russian boosters, but the scope of his work was limited to Earth orbit.

    On an unusually mild afternoon last August in Dallas, though, the stars once again feel within his grasp. Webb has joined about 200 other attendees at Starship Congress, a conference dedicated to promoting interstellar travel. The discussions range from solar sails to distributed databases, warp bubbles to game theory, exoplanets to international monetary policy. Session chairs periodically call on Webb, a sort of minor rock star among the interstellar crowd, for comments or to lead off the questioning.

    While the speakers in the hotel meeting room talk about future searches for extraterrestrial intelligence, Webb, taking a break from the presentations, sits just outside, fidgeting with piles of brochures on a display table. Starship posters line the wall behind him, while another table offers colorful postcards promoting “Sunny Gliese 581e: Only 22 Light Years.”

    “There hasn’t been a lot of progress in the field—all the problems we talked about are still being discussed,” Webb says. “I’m not disappointed in the lack of progress though. Things have started to get better—the necessary conditions for a starship are being laid. It’s reached the point where I think it’s inevitable. It will happen.”

    Full article:


  • David Cummings December 6, 2013, 8:21

    Another exciting discussion on the many possibilities of intra-solar-system and inter-stellar travel. Thanks for posting this. And thanks for your link, ljk.

    At the same time we read pieces like this on Centauri Dreams, however, it seems like we are entering a dark ages in the rest of the country:


    An already emasculated NASA budget is now working out schemes for further cuts. Very depressing.

  • Frank Smith December 6, 2013, 9:32

    Estonian students built ESTCube-1 satellite to test electric solar sail technology. It was launched in May 2013.

    The August issue of CQ Magazine has a three page article about the satellite and electric solar wind propulsion.

    Electric solar wind sail propulsion website.

    Hams and SWL’s can listen for Cubesat’s signals on 437.250 MHz (CW beacon and Callsign) and 437.505 MHZ for telemetry and callsign. Both frequencies are within the 70cm Ham band.

    Frank Smith WS1MH

  • ljk December 6, 2013, 10:11

    David Cummings said on December 6, 2013 at 8:21:

    “At the same time we read pieces like this on Centauri Dreams, however, it seems like we are entering a dark ages in the rest of the country:


    “An already emasculated NASA budget is now working out schemes for further cuts. Very depressing.”

    This is why space science, engineers, and supporters need to do more than just worry about the nuts and bolts of deep space missions. We need to educate and excite the general public and our political representatives about exploring the galaxy and more. As has been stated throughout Centauri Dreams in recent posts, we need to be more inclusive, too.

    Otherwise we can expect more such cuts to space science and future decades of starship conferences where the recipients continue to lament about the fact that we are no nearer to reaching Alpha Centauri than we are now. Or manned bases on Luna and Mars, for that matter.

    President Obama may be making great strides with various social programs, but he and Congress leave much to be desired when it comes to space science and technology support. See here:


    Contacting your representatives in Washington, D.C. is one place to start. Offering to do public lectures at local museums and schools is another idea. Writing about space science in your local papers or a blog is a third plan.

  • Alex Tolley December 6, 2013, 12:18

    This is why space science, engineers, and supporters need to do more than just worry about the nuts and bolts of deep space missions.

    I think we need to show the benefits and payback to the those paying the bills. We may be enthused by the science, but most people couldn’t care less about the universe. And even if they do, they want to know what they [personally] get back from their “investment”. We are even seeing this from Congress with demands that the NSF(?) can only fund research with direct economic or military returns.

    I think early space advocates had the same problem, but satellite technology for communication and weather forecasting showed the direct value.

    We’ve talked about having a solar system wide economy, but this is mostly hand waving. Resource extraction and mass market space tourism are still unproven economically. Without it, we won’t have the ability to build and propel star ships anywhere, unless they are the size of post cards.
    If it is a case of “build it and they will come”, then the heavy lifting will have to be done by private enterprise. The public purse should just support research and competitive contracts for path finding missions and proto commercial services.

    Just out of interest, does anyone have examples of commercial products that emerged from micro-g research on the ISS? All that excitement about foamed metals and pharmaceuticals was vaporware. Did other products emerge?

  • Michael December 6, 2013, 15:45

    It is possible to integrate the two techniques, mag sail and solar sail concepts into one craft. The nice thing about the mag sail technology is that it can be switched on/off, perhaps this interplay between photons and ions will allow better control of the craft. There is also the possibility of using mag sail technologies to move asteroids by wrapping them around the rock to form a coil and perhaps using any iron content as a aid to increase the magnetic field size for free.

  • Eniac December 7, 2013, 0:41

    Paul, great article, as usual, but I feel compelled to point out an important fact you seem to have omitted: The solar wind is orders of magnitude (four, I believe?) weaker than photon pressure, making is correspondingly more difficult to use for propulsion.

  • David Cummings December 7, 2013, 11:30
  • Paul Gilster December 7, 2013, 11:56

    Eniac writes:

    The solar wind is orders of magnitude (four, I believe?) weaker than photon pressure, making is correspondingly more difficult to use for propulsion.

    I didn’t realize the difference was this large! Thanks — I want to track down more on this.

  • David Hoskins December 8, 2013, 19:35

    It may be time to allow NASA to seek corporate sponsorships like the Russians have been doing for decades.

    I know many cringe with the thought of a space shuttle painted up like a NASCAR coming to mind. But isn’t that better than what we have now, which is nothing?

    I’d wager that getting the swoosh on every spacesuit for the next 5 years would be worth a minimum of $250 mil to Nike. Probably much more if Reebok, Converse were allowed to bid as well. There so many ways that so much money could be raised this way and their is really no downside! I can deal with astronauts saying that the “Lowes science module was great today” or “Look at the latest images from the Clearvue Hubble space telescope.” If it means we get Mars or the outer solar system then being a whore to corporate America is a small price to pay.

  • Tom December 9, 2013, 6:33

    From propulsion ideas to space policy; lots of diverse commentary on this article. People are trying to figure this out. NASA doesn’t have an appropriate flagship; however, this isn’t 1960s America, worrying about Soviet domination of Outer Space.

    We live in a completely different era politically, technologically, financially & economically. Globally, we are advancing to a point that former developing countries are ‘home-growing’ space travel… even South Korea & Iran! Most of these nations aren’t competitive with what the Russians do with a Soyuz or what the U.S. is capable with its robots on Mars or Titan, so breathe.

    Leadership, both in industry & government, has an ear on this.

    There are so many holes in how we compete, we will feel it. It’s good because this changes consensus… falling behind France or India in launch services spurred COTS more than the Augustine Report.

    The return issue of ‘Nation Space Investment’ is actually concrete; the giggle factor on that died after EADS was competitive with Boeing.
    Reality check… the US has 6-10 years left before proprietary customer launches will be obsolete (except NRO & DOD).

    Aerospace electronics and telemetry support may be an ‘App’ on the model year 2020 cell phone. These are the consequences in living in 2013-14.
    Hell, you could grow a space agency on what 1 single major city in the US spends on keeping its convention centers and stadiums current.
    Costs are working down to a point where the US (and every country) that can get into space will be on a level playing field, as far as labor & services are concerned. Not my concern, we live within our means, not what we dream on spending.

    NASA is no more the center of the Universe than Earth. I’m no more anti-NASA than I am anti-Radioshack; more accurately, with E-mail and a half dozen package carriers, the post office is feeling competition.
    And so is NASA. The agency has excellent networks of labs and assets of partnered Universities and can put a board together for its needs.
    Charlie Bolden & everybody coming after him are dealing with politicians who are more concerned about jobs in their respective districts and they have voters who feedback every election cycle.

    Pedagogical & ideals of ‘man in the Universe’ isn’t very practical when 2500 to 100,000 voters lose their homes or have a cancelled program on their resumes. Enough said; money/politics/society are very Spacey as well as Earthly concerns.

    STEM (science,technology,engineering & math) is the new word on national & international development. Getting a bunch of kids into the next spaceship generation has been our current catch phrase. Reality check, the kids read more ‘Harry Potter’ than Isaac Newton or Robert Goddard.
    Ironically, we have expertise; the scientist & engineers already exist.
    We aren’t working the established people now? How exactly will the new employed scientists & engineers and the 10,000+ specialists of the future render the 10 million man-hours and result into ‘magical spacecrafts’?
    It is very contorted, anything in technology falls back relative to what capabilities and limitation on everything listed above.
    I have no formal training in any of the subjects necessary for advanced spaceflight fields; however, we are competent enough to know that all this stuff has to be organized at least on 2 levels!
    Better systems matched with effective management of all this coming together within cost & schedule.
    We lost the SCC (Superconducting Collider) not on technical or scientific research merits, it went through 80% of it scheduled budget correctly.
    It died and failed implementation over things like government purchase contracts for houseplants and such.
    Now LHC is filling that void, when the US could have ‘thrown the switch’ 10 years before the Europeans broke ground on their program?
    And nuclear physics of any ilk is difficult to stock the field. It literally was ‘build it & they will come’ planning.

    I see the potential, the hurdles of future space activities being crossed; not that it is inevitable. Even if it cost 1 penny a taxpayer once a month, and we could build from drawing board to flight ready in 2-5 years. Remember how successful the Moon program was? It was cancelled, but with a promise we’d be up and running routinely with better ships by 1978! That each launch would be $5 million each, ready to go every 2 weeks! 25-100 moon missions a year capability(relative to number of shuttle & support craft in this future fleet?)!
    The reality didn’t live up to the potential.
    This needs to change more than the laws of physic. It’s going to have to be done, regardless of the factors. The space workshop will have to exceed existing both cost & capability if it is going to be funded.
    And the money has to come on schedule.
    We still have a long way, stay safe and take care.

  • Eniac December 10, 2013, 0:15

    Paul: I was off by one order of magnitude, but the priciple remains. See here: http://en.wikipedia.org/wiki/Solar_sail#Solar_radiation_pressure

    Solar wind, the flux of charged particles blown out from the sun, exerts a nominal dynamic pressure of about 3 to 4 nPa, three orders of magnitude less than solar radiation pressure on a reflective sail.[16]

  • Paul Gilster December 10, 2013, 10:20

    Excellent. Thanks for tracking this down, Eniac. That’s quite an interesting figure!