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The Flight of the Solar Sail

Posted by CowboyNeal on Sat Jun 04, 2005 11:42 AM
from the kon-tiki-in-space dept.
Space Science
N3wsByt3 writes "After months of uncertainty, the final verdict has fallen: The Planetary Society has reveiled that it will launch its Cosmos 1 on June 21. Cosmos 1 will be the first non-governmental spaceship that makes use of solar sails as main propulsion mechanism - it is pushed along by light particles from the Sun, instead of bringing its fuel along for the ride - which makes this a unique experiment in more then one way." This was supposed to have happened already, so here's hoping things get off the ground this time.
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[+] Finnish Electric Solar Sail Nears Implementation 66 comments
eldavojohn writes "A recent meeting held by the Finnish Meteorological Institute has resulted in plans to build an electric solar sail that will circle the Earth, gaining speed to test its acceleration. The purpose? 'A flight out of the solar system to measure the gas, dust, plasma and magnetic field in the undisturbed interstellar space would perhaps be the "flagship" thing to do,' said Pekka Janhunen, a researcher developing the sail at the FMI. The details and papers of this project (over two years in the making) are also available. I certainly hope it will show more success than the launch of the similar U.S.-Russian venture and its subsequent complete failure."
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The Flight of the Solar Sail 25 Comments More /

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  • Uhm (Score:5, Funny)

    by Mr_Icon (124425) on Saturday June 04 2005, @11:48AM (#12724000) Homepage
    "reveiled:" is that like the opposite of "unveiled?" So, are you saying that they have tried to cover up the news? And if so, then how are we finding out? Or is it from the French "reveil:" the awakening. Did they wake up to the news? Is that why they tried to cover it up?

    So confused.
  • all the governmental solar sail spacecraft? WTF?
    • The principles of solar sails have been perfectly well understood for decades, and used in varying degrees for the entire time. Note the sails at the ends of the solar array tips on Mariner 4 (little blue squares) :

      http://www.jpl.nasa.gov/missions/past/mariner3-4. h tml [nasa.gov]

      That was in 1964.

      The only unique thing about this flight is that it's the only purpose of the mission.

      Brett

      • Re:As opposed to... (Score:4, Informative)

        by BlackStar (106064) on Saturday June 04 2005, @12:20PM (#12724193) Homepage
        Perhaps if you actually looked into it rather than knee-jerk looking to prove it wrong, you'd find that Cosmos-1 is ONLY powered by the solar sails after orbit insertion. No hydrazine corrective thrusters, no other propellant capabilities. The tips on the Mariner series aided in studying the solar wind environment, but they did not assist in propulsion or stabilization to any measurable extent.

        This is the first spacecraft propelled completely by solar wind.

  • This seems silly (Score:3, Insightful)

    by Albinofrenchy (844079) on Saturday June 04 2005, @12:03PM (#12724075)
    Honestly the idea that because it doesn't carry fuel makes it easy to 'travel to the stars' is kinda stupid. For one thing, almost by definition you can't travel towards a star on this thing because as you approach it, it will start to slow down, and eventually stop.

    The idea of using the suns energy is good, but maybe they should find a way to harness that energy so one could move the direction one pleases.

    • Re:This seems silly (Score:5, Informative)

      by spune (715782) on Saturday June 04 2005, @12:11PM (#12724128) Homepage
      The sail ideally will reach 0.1c exiting the solar system. After that point, the sail does ditttysquat and can be removed from the craft the sail is bearing. Combining solar sails with conventional space manuvering systems isn't all that difficult; this would allow all the steering one would like.

      As the sail would approach another star, the sail would slow if both sides of the sail were mirrored. This would merely mean that were we traveling to another star, we could actually stop rather than keep on going. Doesn't that kinda sound handy at all?
    • Well, isnt slowing down and stopping exactly the thing you WANT when approaching the destination star? :)

      But yes, its not that easy. And yeah, at least in earth orbit, solar wind dominates over photon pressure. Also, the interstellar medium would be a much too big drag factor.

    • Re:This seems silly (Score:4, Insightful)

      by rsynnott (886713) <synnottr@tcd.ie> on Saturday June 04 2005, @12:13PM (#12724139) Homepage
      Actually, that's one of the nice things about it. Assuming the other star has the same solar wind as the original (which it probably won't) your spacecraft may actually come to a complete halt at the other star, which is what you want. A classic problem with interstellar travel is that not only do you need to carry fuel to accellerate you towards the objective, but to slow you once you get there as well.
      • I'd say the most classic problem is interstellar travel itself; since our most far-out space craft are just now breaching what we know to be the end of our solar system, we have no idea about any of the dangers of interstellar travel. And my guess is that we won't for another two hundred or so years, once everything in our solar system has been "decently" explored and the technology exists to cheaply put things into space.

        Besides, slowing down isn't as difficult as speeding up; use the slingshot effect i

    • Tacking (Score:5, Informative)

      by Beryllium Sphere(tm) (193358) on Saturday June 04 2005, @12:22PM (#12724201) Homepage Journal
      You could use a solar sail to go from Earth to Mercury if you wanted.

      Angle it so that thrust is opposite the orbital motion of the earth. You slow down relative to the sun. You fall to a lower orbit. Nifty, huh?

      If you're really in a hurry to slow down you detach a reflector, let it fly in front of you, and have a planet-based launching laser fire at the reflector, bounce back to you and slow you down.
    • "as you approach it, it will start to slow down, and eventually stop"

      It may seem counterintuitive, but sailboats here on Earth can actually sail against the wind. Not directly -- most sailboats can point about 45 degrees into the wind (i.e., if the wind is blowing from north to south, a sailboat can travel northeast or northwest as well as anything more southerly than that). When sailing against the wind, the sails (which are allowed to curve) become airfoils and "pull" the boat upwind in exactly the same
      • I don't think this approach would work with space sails for one single reason: you are neglecting the effect of a sailboat's keel or daggerboard in the mechanics of upwind sailing. Without a keel, you will slide sideways because there is nothing in the stationary medium of water to resist the pressure differential produced by the sails acting as airfoils.

    • Re:This seems silly (Score:4, Informative)

      by RichardX (457979) on Saturday June 04 2005, @03:39PM (#12725196) Homepage
      For one thing, almost by definition you can't travel towards a star on this thing because as you approach it, it will start to slow down, and eventually stop.

      From the Planetary.org solar sail FAQ [planetary.org]

      9 . Can a solar sail only provide thrust away from the sun?

      No, thrust can be generated inward or outward with respect to the sun. By turning the sail at different angles, we can add or subtract velocity to the spacecraft. When we add velocity, the sail flies away from the Sun. When we subtract velocity, its orbit spirals inward.
      • Yeah, replying to my own post, but there's another misconception a lot of people here seem to have that needs addressed.

        Also from the Planetary.org Solar Sail FAQ [planetary.org]

        5. Does a solar sail fly on the solar wind?

        No! The solar wind is made up of ionized particles ejected by the Sun. These particles move much slower than light. A solar sail does not stop or reflect them, although they also may impart some of their momentum to the solar sail. However, the force from the solar wind is less than one percent of th
  • so apparantly we have the technology to propel objects via sunlight... but we still cant make our cars to utilize a resource besides gasoline ( with a little hydrogen somestimes)?

    • Re:So umm.. (Score:2, Informative)

      by spune (715782)
      As the solar sail travels the solar system, it would slowly accellerate, reaching approximately 0.1c exiting the system, according to Carl Sagan's wife, who is funding the project.
    • This particular sail is not expected to escape from earth. From the article: " It is possible that by this time the spacecraft will have risen to a high enough orbit that it will remain there, forever orbiting the Earth. It is more likely, however, that the orbit will slowly decay, and Cosmos 1 will end its days as a fireball in the Earth's atmosphere."

      That's because the material of the sails is not very resistant and will break after about a month. I suppose that a stronger sail could eventually reach the

    • Short answer: a few days (Score:5, Informative)

      by mangu (126918) on Saturday June 04 2005, @01:08PM (#12724466)
      how long would it take the solar sails to reach the edge


      A solar sail could, theoretically, pass the Voyagers in less than a week. That's the advantage of having continuous thrust along the way, rather than one impulse at the start and then coasting as the Voyagers did.


      The Voyagers are now at a distance of about 13 light-hours from the sun. A thin and lightweight solar sail would quickly accelerate to almost the speed of light, so it's possible to cover that distance in a few days at most.

      • "quickly" is a highly subjective term :) Assuming no relativistic effects, a one earth-gravity acceleration would take almost a year to reach 1.0c. The solar sail is nowhere near 1 earth-gravity acceleration

        Relativistic effects means that once you start to approach 1.0c, time dialation reduces the 'real' effectiveness of such acceleration.

        As your speeds become higher and higher, interstellar gas, sparse as it is, gives you a SIGNIFICANT friction force, again reducing the effectiveness of acceleration, and
        • what would be REALLY effective is Ramjets

          Alas, ramjets don't work in Sol's part of the galaxy --- the interstellar medium's not right. (I don't know the details, but I believe that you can't get enough thrust from a certain collector area to overcome the drag needed by your collector.)

          And you're quite right, it takes about a year's worth of 1g acceleration to reach relativistic velocities. Which is why Starwisp [wikipedia.org], the closest thing we've got to a decent design for an interstellar probe, will accelerate at 115g.

          The entire probe only weighs 16 grams. It is, in effect, a microwave-frequency light sail, a kilometre across, powered by a 10 gigawatt maser based in Earth orbit; the maser provides both propulsion and power for the probe to return data once it reaches its target.

          Starwisps should be mass producable, and only require a few days of thrust to launch, so you could use one maser to power practically any number of them. Since they cruise at 0.2c, we might also end up getting data back within our lifetimes...

      • Long answer: a few years. (Score:4, Interesting)

        by ciroknight (601098) on Saturday June 04 2005, @01:29PM (#12724587)
        The problem with the parent's post is the sail itself. Our solar system is a rocky and dangerous space, and so far, we have no idea what the area outside of it is like either.

        The sail would quickly break apart as it gets struck by all kinds of space debris, some left by us, others by more natural occurances. Thus, for an effective craft, multiple sails would be kept on board, being deployed stratigically when the previous sails are no longer providing maximal thrust, and when the coast is clear.

        Next, between those times when the sails are not up, the ship will probably want to keep thrust, so it will have to carry onboard some propellant to keep its thrust up during the times it is without sails. Thus, the ship will lose a significant portion of weight during its travel.

        Lastly, unless we align everything like we did with the Voyager launches, gravity will not be so forth coming for this space craft. This will probably mean multiple near-sun passes to build up the speed nessicary to exit the solar system and continue on to the next star. This means some clever routing by computer simulations, along with a computer figuring when to discard and open new sails along the way.

        Not only will all of this cost a lot, it will likely make it take much longer to get out of the solar system. Lucky for us, as we can pile on the goodies like cameras, radio antenna, and do some exploration as it passes through the planets building up gravitational accelleration.
    • first of all, there's no such thing as a perfect reflector, so there's always going to be be some loss. but there's a grand tradition of frictionless planes and other such things in these though experiments, so we'll give you that.

      second, unless you have perfectly coherent light (super laser), you'll have dissipation of the beam. we'll spot that, too (see above).

      once those have been taken care of, the dealbreaker is going to be that the reflected photons are red-shifted when they bounce off each sail.

      t

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