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Space Science Technology

Japanese Deploy Solar Sail 433

Posted by timothy
from the ix-as-an-archipeligo dept.
Chuck1318 writes "The Japanese ISAS (Institute of Space and Astronautical Science) announced the launch and deployment of the first ever large-scale solar sail. In the news release they state "Because it carries no fuel and keeps accelerating over almost unlimited distances, it is the only technology now in existence that can one day take us to the stars.""
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Japanese Deploy Solar Sail

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  • Stellar Pong? (Score:4, Insightful)

    by infonick (679715) * on Tuesday August 10, 2004 @12:57AM (#9926832) Homepage
    "...it is the only technology now in existence that can one day take us to the stars." Well, unless the Japanese can automate retraction of the sails, it wont reach any stars. While it's powered by solar wind, it will slow down and reverse as it gets farther from the original star and closer to the destination star.
    • Re:Stellar Pong? (Score:4, Interesting)

      by mrchaotica (681592) on Tuesday August 10, 2004 @01:02AM (#9926850)
      What if it's only reflective on one side?
      • Re:Stellar Pong? (Score:5, Informative)

        by pclminion (145572) on Tuesday August 10, 2004 @01:24AM (#9926941)
        What if it's only reflective on one side?

        A perfectly non-reflective surface (i.e. a black surface) would experience half the force that a perfectly reflective surface would. In other words, a black sail will work, but only half as well as a mirrored sail would work.

        This is due to conservation of momentum. If a photon is reflected, its momentum p is reversed to be -p. Thus the sail must acquire a momentum 2p to conserve momentum. Whereas if the photon is absorbed, its momentum changes from p to 0, thus the momentum of the sail must increase by p, again to preserve momentum.

        The difference in kinetic energy is converted into heat. A black sail heats up. An ideal, perfectly reflective mirrored sail does not heat up at all.

        • Re:Stellar Pong? (Score:3, Insightful)

          by Rick.C (626083)
          The difference in kinetic energy is converted into heat. A black sail heats up. An ideal, perfectly reflective mirrored sail does not heat up at all.

          If you could somehow cause the energy absorbed by the leading black surface of the sail to be emitted out the rear surface as photons, then you would have something practical.

          The parent's point was that as the sail gets farther away from Sol, the energy from other, nearer stars (the destination) would "push" on the leading surface and this force would eventua

    • While it's powered by solar wind, it will slow down and reverse as it gets farther from the original star and closer to the destination star.

      No, see, that's where Jeff Bridges comes in.
    • Re:Stellar Pong? (Score:5, Insightful)

      by Anonymous Coward on Tuesday August 10, 2004 @01:04AM (#9926862)
      I call baloney. Doesn't a solar sail work because of it's high reflectivity? Isn't that high reflectivity only on one side of the sail?

      And what's so difficult about retracting the sail? The force on the sail at any given time is so miniscule it's trivial to retract them (as opposed to, say, when you have intense winds blowing on your sailboat's sail).
    • by rf0 (159958) <rghf@fsck.me.uk> on Tuesday August 10, 2004 @01:06AM (#9926872) Homepage
      Solar Anchor :)

      Rus
    • Re:Stellar Pong? (Score:2, Insightful)

      by Anonymous Coward
      Well, unless the Japanese can automate retraction of the sails, it wont reach any stars
      Why retract? Just release. It's not like it's going to be used again.
    • Re:Stellar Pong? (Score:5, Informative)

      by Anonymous Coward on Tuesday August 10, 2004 @01:10AM (#9926885)
      Actually you want to slow down when you reach the other star. Or else you miss your stop. Once there, you jettison the sale, or use it to fly around the star system.

      Read "Flight of the Dragonfy"/"Rocheworld" (they are the same book) by Doctor Robert L. Forward for an informative and entertaining novel using (laser pumped) solar sails.

      • Re:Stellar Pong? (Score:5, Informative)

        by halowolf (692775) on Tuesday August 10, 2004 @01:39AM (#9926994)
        Also the The Mote in God's Eye [amazon.com] is a good read that has a solar sail powered craft, however a huge assortment of lasers were used to propel it up to speed, far beyond what solar energy would of provided. And its also not the focus of the book. But hey read it and find out!

        There is also a sequel but I will leave that up to you as a project to find out what it is.

        • Re:Stellar Pong? (Score:3, Informative)

          by Anonymous Coward
          far beyond what solar energy would of provided

          It's would have, you blithering idiot.
      • Read "Flight of the Dragonfy"/"Rocheworld" (they are the same book) by Doctor Robert L. Forward for an informative and entertaining novel using (laser pumped) solar sails.

        That was new!

        Now, I'll agree with informative -- but entertaining??

        I usually describe Forward as the absolutely worst author whose books I buy in hardcover.

        You must be a nerd and talking about the physics and engineering as "entertaining" -- and not any literary qualities!

        (-: Reminds me of when I recommended a Farmer book to

      • Re:Stellar Pong? (Score:4, Insightful)

        by Famatra (669740) on Tuesday August 10, 2004 @02:15AM (#9927124) Journal

        "Once there, you jettison the sale, or use it to fly around the star system."

        Perhaps you'd like to explain how jettisoning a solar sail has enough force to slow down the craft.

        That sail would have to be pretty massive, like the mass of a planet, in order to counteract years of acceleration so you could push it away from yourself to slow down ;).

        That is the problem with getting somewhere in space. To get there the fastest you have to accelerate continually there till the 1/2 way point, turn the ship around around and use an equal force / fuel to decelerate. Reminds me of a scene in Battle Star Galatica Crew Member: "Sir we've ran out of fuel", Admiral "Come to a complete stop", The right reply: "But Sir, I said we ran out of fuel".

    • by Marsala (4168) on Tuesday August 10, 2004 @01:13AM (#9926898) Homepage
      That's why one crew member will be trained extensively in the use of tin snips in zero-gee environments.

      Although that'd be a great way to freak out an alien race... Kind of like pulling a Rama on 'em.
    • by eric76 (679787)
      An interstellar yoyo?
    • Re:Stellar Pong? (Score:3, Interesting)

      by Igmuth (146229)
      And alot sooner than you would think... Once you cross the heliopause [wikipedia.org], the solar wind is basically moot.
    • Re:Stellar Pong? (Score:2, Informative)

      by mark-t (151149)
      No. Once you have reached whatever your desired cruising velocity is, you discard the sail completely (or somehow retract it, if that is possible). The gravitational pull of the star at your destination will give you even more accelleration later on.

      You use on board rockets to help steer as you draw close to your destination.

      • Re:Stellar Pong? (Score:5, Informative)

        by Phanatic1a (413374) on Tuesday August 10, 2004 @02:32AM (#9927173)
        Using onboard rockets to steer doesn't help you slow down. As you point out, the gravitational pull of the destination star will cause you to accelerate even more. You'll end up heading towards your destination at greater than the escape velocity for that system.

        This doesn't help you stop. To do that, you flip yourself around so that the sail is pointing towards the destination, and you use the radiation pressure from that star to kill your velocity. Can't do this if you're already jettisoned it.

        And, no, chemical rockets won't work to shed that much velocity. If you get get that much delta-v from chemical rockets, you'd just use chemical rockets to get on your way as well. But that's precisely why you're using a solar sail instead: chemical rockets suck in terms of specific impulse.
  • Ironically (Score:3, Funny)

    by chancycat (104884) on Tuesday August 10, 2004 @01:00AM (#9926844) Journal
    Ironically, this technology can take us to 'the stars' but not toward our own. Better not change your mind and want to turn around less than half-way to Alpha Proxima...
    • by StarHeart (27290) *
      There is probably some engineering trick to work around this. It might be possible to use mirrors to shine on the opposite side of the sail. Almost surely wouldn't be as fast, but seems like it would be doable.
      • And why don't we just use a fan to move a sailboat?
        (Hint: think conservation of energy.)
        • Re:Ironically (Score:2, Interesting)

          by Anonymous Coward
          And why don't we just use a fan to move a sailboat? (Hint: think conservation of energy.)
          You might be joking, but my dad used to do this all the time when he'd take us sailing if the wind would die down and we were all still out on the lake. He had a big gasoline generator and a 36-inch fan. Worked fine; moved us right along. (True, by "gasoline generator" I mean "all of us kids" and by "36-inch fan" I mean "enough oars for all of us," but, still, it worked just fine.)
      • Re:Ironically (Score:4, Interesting)

        by FireFury03 (653718) <`slashdot' `at' `nexusuk.org'> on Tuesday August 10, 2004 @02:31AM (#9927171) Homepage
        There is probably some engineering trick to work around this. It might be possible to use mirrors to shine on the opposite side of the sail. Almost surely wouldn't be as fast, but seems like it would be doable.

        Interesting idea... you wouldn't be able to carry the mirror with you once you turned around (since the mirror would be producing exactly the opposite force of your solar sail), but you could probably drop it in space pointing in the right direction - the mirror would accellerate backwards because of the light pressure but it would still reflect the light forwards which I guess you could use.
    • Going to Sol (Score:3, Informative)

      by anactofgod (68756)
      You just have to tack into the solar wind. *grynn*

      You heard it hear first -- America's Cup 2200.

      ---anactofgod---
    • Actually, to be a bit serious, I seem to recall through clouded memory from college days long gone by that flipping the sail around was one method to decelerate the rocket on approach to the target star. In this scenario, the rocket would have maximum velocity somewhere around the mid-point between the source and destination stars.

      So, unless one had other means of propulsion to facilitate a return to Sol, one would have to change one's mind a whole heck of a lot sooner than ~half-way to Alpha Proxima, oth
    • Turn the mirror sideways so that thrust is lateral instead of radial.

      Use the lateral thrust to kill your orbital velocity.

      Furl the sail.

      This would work great for a trip to Mercury, actually. If you want to reverse course in between stars you need to use one of the ideas the late Bob Forward played with, e.g. a disposable mirror in front of you reflecting a launch laser to force you backwards.
      • late Bob Forward
        Helvete. Google confirmed. The world is a poorer place.

        So that was why he stopped writing. :-(

        You miss important stuff when you're too busy.

    • Re:Ironically (Score:5, Informative)

      by gibodean (224873) on Tuesday August 10, 2004 @01:49AM (#9927030)
      I'm surprised that no-one else has mentioned this.

      The truth is that a solar sail doesn't get you away from the sun by just having the sail aimed straight at the sun. It does it much more trickily than that :).

      What happens is that you orientate the sail at 45% (or something like that) to the sun. That way, a large amount of the force from the sun actually goes to changing your orbital speed, and not just pushing you away from the sun. By orienting the sail so that it increases your orbital speed, you end up making greater size orbits around the sun, until you are far enough away from the sun and you can do some other tricky stuff to leave the solar system.

      But, it works the opposite way too. Orient your sail so that you are decreasing your orbital speed. You go slower, and therefore your orbit size decreases, and you start approaching the sun.

      Of course another poster queried why you would want to travel to the sun. Good question. But how about Mercury or Venus ?
    • Re:Ironically (Score:5, Insightful)

      by mcrbids (148650) on Tuesday August 10, 2004 @01:55AM (#9927055) Journal
      Ironically, this technology can take us to 'the stars' but not toward our own.

      And, why not?

      Sailing ships have sailed "upwind" for many centuries.

      In outer space, you are either in orbit, or falling directly towards the nearest large body. A solar sail can be used to slow down or accellerate lateral speed simply by rotating it 45 degrees.

      A simple google search turned up this [nasa.gov] in case you are curious.

      Although they are right, in that solar sails do accelerate the entire trip and carry no fuel, I don't think that sails are "the way to go" unless we're talking about a ten thousand year multi-generational ship.

      I consider the Bussard RamJet the "only way to fly". It carries no fuel, but is powered by carving a planet-sized swath out of the ambient hydrogen atoms out of interstellar space and fusing them.

      With interstellar distances, the real issue is: how quickly can you get to relativistic speeds? Because, at .5 C, it'd take thousands to millions of years to get anywhere. But, at relativistic speeds, it'd still take thousands of years, but to the crew on board, it'd be like mere hundreds or even tens of years.

      You need power to get you there in less than hundreds of years - thus the RamJet.
      • Solar vs. wind sail (Score:2, Informative)

        by anno1602 (320047)
        If I understand solar sails right, they are actually pretty different from the way wind sails work. Contrary to what your NASA links is telling us, most of the force from the sail does *not* come from the wind trapped in the sail pushing it along. Rather, under the pressure of the wind, the sail takes the form of a wing, and Bernoulli forces propel the boat along. This also enables sailing (up to a degree depending on the craft and the rigging) against the wind. I do not see how Bernoulli forces would appea
        • by CrowScape (659629) on Tuesday August 10, 2004 @02:50AM (#9927214)
          Where wind sails have Bernoulli to work off of to go against the wind, solar sails have Newton. What the gp is saying is you start off in orbit around a star. If you want to get away from that star, you angle your sail +45 degrees, which reflects the light back along your orbit. Thanks to conservation of momentum you gain tangental velocity which propells you in a spiral outwards as you slowly break the sun's gravitational pull. If you want to go towards that star, you angle your sail -45 degrees, reflecting the light forward along your orbit. You lose tangental velocity and the sun's gravitational pull reels you in. You're right, completely different principles are at work, but you get a similar result.
      • Re:Ironically (Score:5, Informative)

        by stevelinton (4044) <sal@dcs.st-and.ac.uk> on Tuesday August 10, 2004 @02:25AM (#9927153) Homepage
        Unfortunately, it turns out that the interstellar medium is much thinner, in most places and in particular around the Sun, than Bussard thought. Even if you could somehow persuade protons to fuse in the few nanoseconds while they are passing through your ship at nearly the speed of light (and on average it takes about 15 billion years for any given proton to fuse in the core of the Sun), there just aren't many of them around here.

        A beamrider of some kind (leave the engines at home and ship momentum up to the spacecraft in some convenient form) or an antimatter rocket are looking like the best ideas at present.

        Steve
        • I ran across this novel form of propulsion [astrobio.net] the other day that looks promising if it pans out.

          The idea is to entangle two cesium atoms, then send one up into space. Back on earth, excite the one that remains and the one in space will do the same. In theory that could be used as an ion drive while keeping the bulk of your engine back on the ground.
      • Re:Ironically (Score:4, Informative)

        by atcurtis (191512) on Tuesday August 10, 2004 @02:38AM (#9927190) Homepage Journal

        You're forgetting the biggest drawback of the Bussard Ramjet... That is the gas collection.

        The gas collection mechanism will create such resistance at high velocities that it would jam up and slow the device down a lot.

        I believe that there has been some research done which suggest that it would never be able to obtain velocities exceeding 0.1c let alone 'relativistic velocities'.

        I think we are more or less stuck on this island Earth, until we can think of something better than Newtonian physics to traverse the gap between the stars... Some revolution akin to Gene Roddenberry's Warp drive or Iain Banks's Exotic Matter drive - something which doesn't require a reaction mass.

        OT: Early STTOS was fun - somehow the warp drive sound effects always sound like the London Underground trains...

  • Solar sail (Score:4, Interesting)

    by Uplore (706578) on Tuesday August 10, 2004 @01:04AM (#9926863)

    What I dont understand is how they intend to protect these massive sails from being shot full of holes by meteorites and space dust as it propels its way through space.

    Also, seing as how it is powered by solar wind, what happens when the craft is between 2 or more stars which are all exerting equal force on the sails. With no fuel it is doomed to slow down and be 'blown' around in space.

    • Re:Solar sail (Score:2, Informative)

      by Anonymous Coward
      please read this [howstuffworks.com]. The work because of the reflectivity. It's not really a 'sail' in the Earthly sense, it's a giant mirror that's only reflective on one side.
    • who cares if it gets knocked full of holes? as long as the dust doesnt hit whatever the sail is pulling, i dont see it mattering as long as the damage isnt total and is roughly uniform in distribution.
    • What I dont understand is how they intend to protect these massive sails from being shot full of holes by meteorites and space dust as it propels its way through space.

      Maybe you don't. Just make the sail big enough that to generate adequate "thrust" with a few holes in it. Solar sails are very big and very thin. Any debries that hits is just going to create hole and keep on going.

      Also, seing as how it is powered by solar wind, what happens when the craft is between 2 or more stars which are all exert
    • What I dont understand is how they intend to protect these massive sails from being shot full of holes by meteorites and space dust as it propels its way through space.

      They don't have to. The force imparted by the solar radiation is probably not strong enough to cause any holes to expand on their own. They could further prevent tearing using a cross-hatch "rip-stop" pattern of slightly greater thickness.

    • what happens when the craft is between 2 or more stars which are all exerting equal force on the sails.

      It is directional. It can only be pushed by solar wind from one direction, so unless they turn-around, the star they are approaching will not affect the solar sail much at all.
    • Also, seing as how it is powered by solar wind, what happens when the craft is between 2 or more stars which are all exerting equal force on the sails. With no fuel it is doomed to slow down and be 'blown' around in space.
      As others have pointed out, they are directional. But aside from that, when you are halfway from one star to the next you'll want to start slowing down anyway.
    • Re:Solar sail (Score:5, Informative)

      by serutan (259622) <(moc.nozakeeg) (ta) (guodpoons)> on Tuesday August 10, 2004 @02:05AM (#9927090) Homepage
      The article was short on technical details. A lot more info can be found easily on the net, such as here [solarsails.info].

      To clear up one point, solar sails are not powered by the solar wind, which is a stream of particles. They are powered by light, which exerts several thousand times more force than the solar wind.

      The sail is not direction. It is affected by light coming from all directions, but it "blows" in the direction of the prevailing light, which would come from the brightest/closest star. To change direction a solar sail ship must change the angle of the sail in relation to the nearest star.

      At the start of a journey the sail would be ahead of the ship, towing the ship behind it. Sometime between stars the ship could use small maneuvering jets or something to flip itself around and put the sail behind it. The increasingly strong light from the destination star would gradually slow it down.

      More likely though, the sail would be retracted or jettisoned in mid-journey, when the light from the destination star equalled the light from the original star. This is when the ship would be at its maximum velocity. It would then coast at that speed for the rest of the trip and use the gravity of the destination star or planets to decelerate much more quickly.
      • Re:Solar sail (Score:4, Informative)

        by JohnPM (163131) on Tuesday August 10, 2004 @04:02AM (#9927388) Homepage
        Nice post, but one detail has to be wrong. If you could use the destination system for gravity braking then you would be able to equally use our own system for gravity acceleration. The only way the destination is more effective is if you actually slam into it (or perform aerobraking).

        The speeds involved in inter-stellar are so high that gravity assisted decelleration is probably out of the question. Aero-braking in an atmosphere is certainly not an option. There have been some proposals for braking on interstellar hydrogen I believe (ramjet concept).
  • What Solar Sails Are (Score:5, Interesting)

    by SlashChick (544252) <ericaNO@SPAMerica.biz> on Tuesday August 10, 2004 @01:04AM (#9926866) Homepage Journal
    In case you, like me, didn't know that much about solar sails, there's a great article at How Stuff Works about them: How Solar Sails Will Work. [howstuffworks.com] Looks like a pretty interesting technology!
    • by Cecil (37810)
      Wow, that surprised me. I thought they actually used the solar wind to power them, not light. But that is not so. The article says the light produces 9 newtons per square mile (3.5 newtons per km^2) whereas by my calculations, an average strength solar wind stream of 1 proton per cm^3 at 500km/s would only produce about 0.0004 newtons per km^2.

      Kind of counterintuitive. I thought the unbelievably small mass of a proton would still outweigh the nearly infinitesimal mass of a photon. But I guess our star puts
  • Physics (Score:4, Interesting)

    by caitsith01 (606117) on Tuesday August 10, 2004 @01:05AM (#9926869) Journal
    Anyone care to fill us in on the rate at which the energy received by a surface decreases with distance? I imagine that, given the incredibly weak force applied by light, it would take one HUGE sail to get anything like meaningful acceleration for space travel. Surely be the time you are a few million kilometres from the Sun the amount of force being applied will have dropped off by a huge amount?

    Anyway, we should get to Mars and back a few times before we try to get to the stars... baby steps.
    • Re:Physics (Score:5, Informative)

      by CrankyFool (680025) on Tuesday August 10, 2004 @01:13AM (#9926897)
      The amount of force exerted on the sail decreases as a square of the distance (since the amount of light reaching the sail decreases by a square of the distance). We're not talking about 'meaningful acceleration' in anything like our current thinking of space travel -- this isn't "get on this space yacht and a few months down the road you'll get to the other star," but rather "put something on this vessel and several hundred/thousand years from now it'll get to where you wanted it to get."

      This isn't about travel.

      Either way, the Japanese are trying to make this look cool by saying it's star-faring technology. Probably true, but only because we're not likely to put humans on this thing -- so it's possible we'll do this before we get to Mars, because the expense and risk could be vastly lower.
      • The acceleration is very low but it operates continuously. Given a choice between a few minutes of using a rocket before it's out of fuel, versus months of gradual acceleration on a solar sail, you can actually get more speed from the sail.

        For the foreseeable future the real applications would be inside the solar system.
    • Re:Physics (Score:3, Insightful)

      by Jetson (176002)
      Anyone care to fill us in on the rate at which the energy received by a surface decreases with distance?

      I'm no scientist, but wouldn't the thrust follow the same inverse-square law as radiant light?

      To make best use of a solar sail, it would probably make sense to use a conventional rocket to establish a highly eccentric (parabolic) orbit around the sun and then pop the sail open after perihelion where the sail would contribute the most energy to the orbit.

      I think aiming the spacecraft (on the outbound

    • Re:Physics (Score:2, Insightful)

      by rippleone (601783)
      We need to remember to always ask the question do we really need to go to another planet when we can't seem to get along with each other here. We don't even use our natural resources with the level of accountability that we should given that for right now this is it for us. We have yet to even mine an asteroid. We really need to work out just a few issues before we start littering the solar system with McDonalds wrappers.
  • Wrong (Score:5, Informative)

    by HeghmoH (13204) on Tuesday August 10, 2004 @01:05AM (#9926870) Homepage Journal
    ...it is the only technology now in existence that can one day take us to the stars.

    Orion [islandone.org] can take us to the stars, and it can be done with today's technology, not something that's just starting to enter the very earliest test phases. But it's nuk-yu-ler, so it doesn't count.
    • Re:Wrong (Score:5, Insightful)

      by gilroy (155262) on Tuesday August 10, 2004 @01:48AM (#9927024) Homepage Journal
      Blockquoth the poster:

      Orion can take us to the stars, and it can be done with today's technology, not something that's just starting to enter the very earliest test phases.

      Because Orion needs to carry its fuel, its period of acceleration is necessarily limited. If you count Orion as a star-faring technology, then you need to count chemical rockets, too... Just ask Pioneer 10.
  • We'll sail to the stars.

    Please. One poster has already pointed out that this only works within the limit of a star's solar wind. It's also a very slow mode of transport. If you want to send your decayed remanants (even the bones will have disintegrated) HALF way to the stars this is definitely the way to go!

    For travel within the inner solar system however, as a secondary form of propulsion it may have its uses.
  • by bigsteve@dstc (140392) on Tuesday August 10, 2004 @01:26AM (#9926950)
    Quote from article:
    ISAS succeeded in deploying a big thin film for solar sail in space for the first time in the world. ISAS launched a small rocket S-310-34 from Uchinoura Space Center in Kagoshima, Japan, at 15:15, August 9, 2004 (Japan Standard Time). The launch was the culmination of a historic new technology, the world-first successful full-fledged deployment of big films for solar sail.
    My interpretation of this and the rest of the article is that they were testing deployment mechanisms for sail material, rather than deploying a working solar sail.

    The pictures in the article which show the test sail deployed immediately behind the launch vehicle imply the same thing. The following text says that the launch vehicle reentered and splashed down 400 seconds after liftoff. This can only mean that both the LV and the sail experiment were in ballistic flight when the latter was deployed. For a solar sail to work, it would need to be deployed after orbital insertion (or after escaping the magnetosphere.) The article does not mention orbital insertion, nor was there time for this to occur.

    • At the SPS 04 [congrex.nl] meeting we heard about a planned launch in a couple of years of something very similar - a suborbital rocket with 20 minutes or so in space at zero gravity, which will deploy a large triangular mesh intended to resemble a possible structure for a solar power satellite. Then two or three teams of robots will be competing to maneuver about this mesh under vacuum/zero-g conditions, and see how far/fast they can go, and what they can do. One of the teams involved spoke - they seem to have previous
  • Good to see (Score:4, Interesting)

    by T.Hobbes (101603) on Tuesday August 10, 2004 @01:32AM (#9926967)
    It's very good to see this branch of space technology getting funding. I'd rather travel in a starship with warp drive, but until then we need some feasable way to get to other stars. There's no reason, in my mind, why we shouldn't send a few of these off to nearby stars with the sole purpose of taking some close-in measurements and somehow getting the data back here (getting the data back would probably be harder than getting the spacecraft there in the first place). The very fact that it would take hundreds or thousands of years for them to get there is the best reason to start sending them now.

    Let's all raise a glass of Sake to the engineers behind this project!

  • by xoboots (683791)
    Is just me or do those press photos look like they are CG? Circa Doom II.
  • by Alsee (515537) on Tuesday August 10, 2004 @01:44AM (#9927009) Homepage
    They deployed a sail less than two minutes after launch, had it in place less than two minutes, threw it away, deployed a second sail, then less than three minutes later it crashed into the ocean.

    Total trip, liftoff to crash-down, less than 7 minutes.

    -
  • Not wind! (Score:3, Informative)

    by Anonymous Coward on Tuesday August 10, 2004 @01:47AM (#9927019)
    Just to clarify what people seem to be mistaking, the sail is *not* powered by Solar Wind, it is powered by the light of from the sun. The idea is that each photon of light that reflects off of the surface of the sail transfers a little bit of it's momentum to the sail.
  • by antikarma (804155) on Tuesday August 10, 2004 @01:47AM (#9927022)
    It won't be a viable method of transportation between solar systems until it has an anti-pirate defense system. Giant solar sails just scream "come and get me space pirates."
  • by MMHere (145618) on Tuesday August 10, 2004 @01:50AM (#9927038)
    1. Did they get high enough above Earth to enter the inter-planetary "void," and thus avoid the significant effects of Earth's atmosphere? 100, 230, and 400 seconds after liftoff hardly seem "high enough."

    2. What happens to such sails when they cross the heliosphere of a regionally prominent star such as Sol? Is it all chaotic photons and miscellanous radiation in the interstellar "void?" Or are conditions regulated by the nearest stellar bodies?

    -- In other words, how would one navigate effectively once the prominent wind from Sol fades and is replaced by other forces? Are you doomed to follow your trajectory mainly established by Sol once you leave its heliosphere, possibly modifed by various minor (uncontrollable) forces from other winds in the void? Can you take advantage of such extra-Solar winds to go where you want?
  • Just a question... (Score:3, Interesting)

    by ScottZ (14863) * on Tuesday August 10, 2004 @01:52AM (#9927047)
    How do you run against the solar wind? What are the appropriate forces to run your 'keel' against when you want to track across a solar system (say, to somewhere useful)?

    Anyone got any pointers?
  • by Lifix (791281)
    First of, I am not a trained professional. I am a high school senior but I believe that I understand the principals behind this technology. The term solar sail is a modern misnomer. Solar sails are only capable of accelerating away from a star. This is because the sail is powered by reflecting solar radiation/solar wind. (I'm not sure, but I believe that this is limited by the inverse square law, which means that every time you double the distance between you and the source of the radiation, you decrease i
    • Solar sails can be used to move towards or away from a star. The trick is that the sail is not generally perpendicular to the star but at a 45 degree angle, so that light is reflected behind the vehicle (to accelerate), in front of it (to slow down) or at some sideways angle (for a sideways vector).

      If you accelerate, you move into a higher orbit (and move away from the star). If you decelerate you move into a lower orbit (towards the star). Sideways vectors are used to change the plane of your orbit.

      All

  • Ortw (Score:3, Informative)

    by Keith McClary (14340) on Tuesday August 10, 2004 @02:07AM (#9927095)
    A clover type deployment was started at 100 seconds after liftoff at 122 km altitude, and a fan type deployment was started at 169 km altitude at 230 seconds after liftoff
  • Didn't Count Dooku - aka Darth Tyrannus - have one of these? Probably not the fastest vehicle for escaping Yoda's army of clones, but maybe it leaves no heat signature or something ;-)
  • by gentoo4ever (804205) on Tuesday August 10, 2004 @02:28AM (#9927165)
    These solar sails are pretty useless. Here http://solarsails.jpl.nasa.gov/introduction/design -construction.html [nasa.gov] are calculations from NASA guys. It looks like this Japanese sail has acceleration of few mm/s^2 and is not able to get out of sun gravitational field (and, of course, the Earth's one). It would take solar sail 100 years to get to alpha centauri if it had acceleration 10 m/s^2 (table 3 in the above link, there is "-" in the table for 5 m/s^2 and less , that is it will never get away from sun ). There was a good idea though to build a huge mirror to focus sunlight on such sail. This would effectivly increase surface area of a sail and pressure would not drop as square of the distanse from the sun.
    • These solar sails are pretty useless. Here http://solarsails.jpl.nasa.gov/introduction/desig n -construction.html are calculations from NASA guys. It looks like this Japanese sail has acceleration of few mm/s^2

      And a few millimeters per second per second is useless, why?

      3 millimeters per second squared, and after a week you're moving at 1.8 kilometers per second. After a month, 7.2 kilometers per second. After 2 months, you've already exceeded Earth's escape velocity from the surface, let alone from or
      • by Johnny Vector (93021) on Tuesday August 10, 2004 @07:57AM (#9928218) Homepage
        3 millimeters per second squared, and after a week you're moving at 1.8 kilometers per second. After a month, 7.2 kilometers per second. After 2 months, you've already exceeded Earth's escape velocity from the surface, let alone from orbit. Solar escape velocity at 1 AU is about 48 kilometers per second, so it would take you half a year to get fast enough to escape the solar system altogether. Actually, less than that, because as you're accelerate you're moving outward and so the solar escape velocity from your present position is continuously decreasing, but I'm in no mood for calculus right now.

        Except you're losing thrust faster than the escape velocity decreases. Escape velocity goes as 1/sqrt(r), whereas the light intensity (hence thrust) goes as 1/r^2. Solar sails probably aren't the best way to go interstellar. But then, neither is anything else we can imagine at the moment. sigh

        And now, safely buried in the comments because I have limited bandwidth...

        Photos of the Uchinoura Space Center [kevland.com], from back when they called it Kagoshima Space Center. (Kagoshima is the prefecture, Uchinoura is the town. Nobody in Japan has heard of Uchinoura, so they called it Kagoshima Space Center until with the increased level of joint projects with a certain American space agency they decided 'KSC' was too easy to confuse with Kennedy Space Center.)

  • Bullshit! (Score:3, Interesting)

    by logicnazi (169418) <logicnazi@gmailEULER.com minus math_god> on Tuesday August 10, 2004 @03:04AM (#9927246) Homepage
    Yes, it keeps accelerating over long distances....but I can make a rocket do the same thing by asymptotically slowing down the rate of fuel burn. A solar sail is doing nothing differnt, while the sail will keep accelerating the accelaration will fall off with the radiation pressure (about 1/r^2).

    Personally, I tend to believe things like ion drive are actually much more efficent and likely to work well with stare exploration (ion drive is just a fancy way of saying you shoot very small amounts of mass out the back going very fast. This is important because it means you can get more thrust from the same amount of fuel weight if you have something like a nuclear power source to accelerate the ions).
  • Yikes! (Score:3, Funny)

    by payndz (589033) on Tuesday August 10, 2004 @03:18AM (#9927279)
    Those pictures make it look like Vejur, coming to cleanse the carbon-unit infestation from the Creator's planet...
  • by O0o0Oblubb!O0o0O (526718) on Tuesday August 10, 2004 @03:44AM (#9927333) Homepage
    For those of you who are - like me - not experts in physics, this technology was featured in the BBC documentary "Space" presented by Sam Neill.

    http://www.imdb.com/title/tt0273608/

    http://www.bbcshop.com/invt/bbcdvd1090&bklist=ic at ,5,,11,science,831

    One of the chapters discusses how travel to other stars would be possible. As far as I remember there is another technical solution in discussion which would involve nuclear detonations as part of a propulsion system. (I might have confused something there, though)
  • solar wind (Score:5, Interesting)

    by N3wsByt3 (758224) <Newsbyte&freenethelp,org> on Tuesday August 10, 2004 @04:14AM (#9927424) Homepage Journal
    Solar sails do not use (or not primarely, exept maybe when close to the star, in the beginning) solar wind to propel itself. It uses the reflection of the sunlight; thus, photons, rather then ions.

    It's also not correct that solarsails can't be used to reach other suns, because the sun there gives an oposite force. It's quite trivial, when using adaptive (rotating) solarsails, which have only one higly reflective side, to slow down or accelerate when nearing a solarsystem. And even withing a solarsystem; for an interesting project in that regard, see the planetary society [planetary.org] where they plan to launch the first non-gov solarsail-powered probe.

  • by Insipid Trunculance (526362) on Tuesday August 10, 2004 @06:53AM (#9927874) Homepage
    Hasnt anybody read this story by Arthur C. Clarke about an Earth to Moon race in solar sail powered space ships.

    A beautiful story with an excellent description of some problems which may exist.Read the story,i will spare the spoilers.

  • by Edward Faulkner (664260) <(ude.tim.mula) (ta) (fe)> on Tuesday August 10, 2004 @07:51AM (#9928177)
    There is another existing technology that could travel interstellar distances. NASA's Orion project designed a starship propelled by nuclear weapons and a big pusher plate. And yes, the crew can be properly shielded.

    Of course what we really should be working on is actual nuclear rockets - controlled nuclear burn instead of explosives. Nuclear gas core rockets [nuclearspace.com] are really not beyond present technology, their exhaust is cleaner than the space shuttle's, and they're so powerful you can build big, heavy, safe vehicles.
  • Limited directions? (Score:3, Interesting)

    by wikdwarlock (570969) on Tuesday August 10, 2004 @08:34AM (#9928496) Homepage
    Can someone in the know answer me this:

    Since a solar sail needs light pressure to accelerate, can it only accelerate in a direct line away from a star?

    also

    Isn't there a problem, once the sail gets far enough from its original star, that pressure from other stars will interfere w/ the path?

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