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Space Science

Solar Sails And Space Propulsion 134

Posted by Zonk from the to-infinity dept.
Doomie writes "The Economist has an interesting article about solar sails. It talks about the Russian ICBM that will launch Cosmos 1 (mentioned previously on /.) 'The first craft powered by solar-sail technology to orbit the Earth', and the link between this technology and interplanetary travel. Cosmos 1 will orbit Earth starting on June 21st and could, in theory, reach '200,000kph after three years of acceleration' due to the fact that 'particles of light, or photons, that strike a surface give it a tiny push'. The official homepage of the project has more details." Update: 06/18 18:57 GMT by Z : While space trains would be cool, that wasn't the intent of the story. Changed rails to sails.
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Solar Sails And Space Propulsion More

Solar Sails And Space Propulsion

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  • Wow (Score:1)

    by wlowe84 ( 614517 )
    Solar rails???

    • Re:Wow (Score:2, Funny)

      by Darvin ( 878219 )
      Looks like the spelling was derailed.

    • Re:Wow (Score:3, Informative)

      by Rei ( 128717 )
      Yeah, I noticed that, too. Also incorrectly stated:

      Cosmos 1 will orbit Earth starting on June 21st and could, in theory, reach '200,000kph after three years of acceleration' due to the fact that 'particles of light, or photons,

      Actually, "in theory", the thing will fall apart in months because the mylar is not designed to withstand long-term solar exposure. A spacecraft designed for lasting longer could, in theory, reach those speeds.

    • Re:Wow (Score:2, Funny)

      by mahmud ( 254877 )
      Am I the only one who thought of Interstella 999?
    • it probably flew under the radar because it'd only be the 39th article about something "On Rails"
  • New web development venture?

    Space trains?

    L. Ron Hubbard was right [google.com]?

  • Spelling errors (Score:4, Funny)

    by xwizbt ( 513040 ) on Saturday June 18, 2005 @02:43PM (#12852038)

    Isn't this supposed to be a professional website? I'm not the first poster, I realise, which means I'm certainly not the first person to notice the spelling error. But... hasn't this gone past an editor? I mean... what is going on here. Every post has an error of some kind... spelling, grammar... anything...



    I'd offer my services as a proofreader but I don't think I want to be associated with something so consistently shoddy...

  • So let me guess (Score:4, Funny)

    by Rosco P. Coltrane ( 209368 ) on Saturday June 18, 2005 @02:45PM (#12852041)
    Union Pacific is to build the ship?

  • the article (non-free) (Score:5, Informative)

    by Anonymous Coward on Saturday June 18, 2005 @02:45PM (#12852042)
    Sail of the century
    Jun 16th 2005
    From The Economist print edition

    One small step into orbit may be one giant leap for interplanetary travel

    Rick Sternbach, The Planetary Society

    ON JUNE 21st, a Russian nuclear submarine is due to launch an intercontinental ballistic missile (ICBM) from beneath the surface of the Barents Sea in the Arctic Ocean. Fortunately, this will not be the opening volley in a global thermonuclear war. Rather, it is intended to open up a new age of space exploration.

    The ICBM's payload is Cosmos 1, an experimental spacecraft being launched by the Planetary Society (a space-advocacy group founded in 1980), in conjunction with NPO Lavochkin (a Russian firm which built the craft) and the Makeev Rocket Design Bureau (which modified the ICBM). If the mission, which will cost $4m and has been paid for entirely by private subscription, is successful, Cosmos 1 will become the first craft powered by solar-sail technology to orbit the Earth.

    Solar sails rely on the fact that particles of light, or photons, that strike a surface give it a tiny push. Ideally, such sails should be as big as possible, to maximise the amount of sunlight collected, and as reflective as possible, because a photon bouncing off a perfectly reflective sail produces twice as much thrust as one absorbed by a non-reflective sail. Even so, the thrust generated is tiny: a sail with an area of one square kilometre would feel the same force that a kilogram weight exerts on a table on Earth. But there is no air resistance in the vacuum of space, and the sun shines continuously. Slowly but surely, the light-propelled tortoise outruns the rocket-driven hare, reaching 200,000kph after three years of acceleration.

    The Planetary Society has details of the forthcoming launch of Cosmos 1. The Makeev Rocket Design Bureau modified the ICBM which will carry the craft.

    Solar sails would thus be especially useful for journeys to distant planets or vastly more distant stars, as they do not need to carry any fuel with them. But while they have lived in the imaginations of scientists and science-fiction writers for over a century, their track record in real life has been limited. The Japanese Aerospace Exploration Agency has tested the unfurling of solar sails on sub-orbital rockets, but no one has put solar sails into orbit. Cosmos 1 should change that and, if it works, it will prove the feasibility of the technology for future missions.

    Eight triangular sails arranged like the petals of a flower will propel the craft. Each of the sails is 15 metres long, and in total they span 600 square metres--roughly the size of the penalty area on a football pitch. During launch, the sails will be rolled up like so many sleeping bags. Once the ground crew has decided that the craft is in a stable orbit, though, a series of tubular "masts" will be inflated that will unfurl the sails as they expand.

    Solar sails require special materials if they are to reflect sunlight efficiently while weighing as little as possible. They must also be able to fold up easily into a small space. Cosmos 1's sails are made from plastic sheets just five microns (millionths of a metre) thick. That is about a quarter of the thickness of a plastic dustbin liner. The plastic in question, Mylar, is coated with aluminium to make it reflective. Mylar is perhaps more familiar from its use in helium-filled party balloons.

    If all goes as planned, the spacecraft will go into an orbit that flies over the Earth's poles. Four days later, the sails will be deployed. Once this has happened, the team will monitor Cosmos 1's altitude. The sails are able to swivel slightly, and the ground crew can tilt them individually in order to catch the most sunlight. The resulting increase in the altitude of the orbit will indicate that the sails are indeed feeling the sun's push.

    Provided all this works well, the team will then try one last experiment. In order to use solar sails to travel to the outer planets, where the sun's l

    • Metric conversion (Score:2, Funny)

      by Anonymous Coward
      200,000kph = 200,000 km/h

    • Ideally, such sails should be as big as possible, to maximise the amount of sunlight collected, and as reflective as possible, because a photon bouncing off a perfectly reflective sail produces twice as much thrust as one absorbed by a non-reflective sail.

      So, the photon hits the sail with the speed of light. And leaves the sail again at the speed of light. The energy transfered to the sail from this action comes from ..... where???

      • Re:the article (non-free) (Score:2, Informative)

        by Anonymous Coward
        from... the photon. Its energy is proportional to its wavelength, which will decrease (get redder) as the energy is transfered to the sail.
      • No extra energy is needed. Before the momentum was for a stationary sail:

        momentum_of_particle + 0

        and after its:

        -momentum_of_particle + 2*momentum_of_particle

        Where 2*momentum_of_particle is now in the sail.

        Both before and after have the same momentum.

  • WFT? (Score:1, Insightful)

    by Anonymous Coward
    Whoever posted the link to the Article failed to comprehend the fact that I have to pay and register to view it - so please why don't you also publish your username and password so others can also see it.

    Not all of us /.ers are rich enough to afford to pay for the thousands of rip-off subscriptions.

    • Re:WFT? (Score:3, Funny)

      by Anonymous Coward
      You tried to read the article?? You must be new here.

  • Rails and Sails (Score:1, Informative)

    by antiaktiv ( 848995 )
    The similarities are striking, in that with both solar rails and solar sails, you don't have much option what direction you want to go.

    • Re:Rails and Sails (Score:5, Informative)

      by MyLongNickName ( 822545 ) on Saturday June 18, 2005 @02:59PM (#12852109) Journal
      Untrue. By changing the angle of the surfaces reflecting the sunlight, one can change direction. Admittedly, this is like turning the Titantic with a spatula. But given enough time, you can change direction.
      • Informative was definitely not the modding i was going for there.
      • I am curious. On a sailboat, you have either side boards, a centerboard, or a hull design (some of the catermarins) that prevent sideways slippage for when you are beating or reaching to the wind. How will this work? What will prevent the craft doing more of a run?
        • Orbital mechanics will do a lot of the work: to go to a higher orbit, aim the reflected light behind you; to go to a lower orbit, aim the reflected light in front off you. You can't really tack, but you can maneuver pretty well, given enough time.
          • I would think that if orbiting earth, the craft must be capable of doing a tack (and a jib). Basically this craft is expected to be used in orbiting the earth. As such, I would think that it would require a tack (and a jib, but that is easy).

            Otherwise, about the only way that I can imagine this working, is if you use the sail for propulsion during a run, possibly a reach, and expect that at best, you use the sail for slight control during a beat(perhaps as a rudder would).
        • I am far from an expert. However, I think you will have a lot of "run" when you use a simple mirror model. Like the spatula turning the titantic analogy.

          More complex mirror configuration (light reflecting off more than one mirror) could be used to mitigate this effect. However, solar pressure is still very small compared to the enormous kinetic energy such a sail would build over a period of months or years. Don't expect these things to spot an asteroid, veer out of the path of danger, and then get right b
        • If you want to fly toward the sun, you rotate the sail at such an angle that the arriving light gets reflected forward along the direction of the orbital motion. That reduces the orbital speed, which causes the opposite side of the orbit to pass closer to the sun -- in other words, you've done what amounts to a very small retro burn.

          If you rolled up the sail at this point, you would pass through the same point one rev later...but if you keep it positioned, you will gradually spiral inward.

          rj
          • Yes, that is called a beat in sailing. But to prevent sideways slipage, you need a sideboard, centerboard, or something similar to that. Otherwise, you get no forward motion.
            • Yes, you get the "slippage" in solar sailing, but you don't care. The small amount of outward velocity addition is more than overcome by the orbital effect of the decrease in forward velocity. (And remember: half a rev later, the outward force will be acting in the opposite direction. It takes many revs to get anywhere.)

              Yes, it sounds weird, but it works. And it gets weirder: the longer you apply a retarding force backward along the flight path, the faster you go forward. Practically everything about orbi

      • Interplanetary travelers using solar sails will
        be able to "tack" in space, providing that their
        "keel (or daggerboard)" can "dig into" the dark
        matter of space.

        I can almost picture a swarm of robotic "sailors"
        keeping the sail in proper "trim".

        Of course, with a top speed of 0.1c, any trip
        will be a rather long one. Once they have reached
        their destination, hopefully their "sea anchor"
        will function properly.
    • Actually, you can fly anywhere you want, including towards the sun.
    • Not true.

      The acceleration produced by a sail is always (ignoring sail imperfections) normal to the sail surface. As a result, solar sails are able to maneuver by varying the angle of between the sail plane and the incident sunlight. Since a solar sail has the ability to produce an acceleration component in the direction of its orbit velocity vector, it can manipulate its orbit.

      There's a very nice Java applet that simulates solar sail orbit dynamics available here [ec-lille.fr], if you want to play around with maneuveri

      • Hey, that's a great applet! I set the sail so I spiralled on a crash course towards the sun. I cam close, and then slipped right by and made a tight slingshot maneuver, careening straight out into deep space at 0,01c. Insane speeds! We gotta build these! If only we could make the sail disregard the intense heat, just like in the simulation run!

    • Re:Rails and Sails (Score:3, Interesting)

      by 0WaitState ( 231806 )
      Two things: the sails are maneuverable, so you can get different thrust vectors within a certain rangle of angle.

      More importantly, you have solar gravity pulling you in the exact opposite direction of the photon pressure. So, to go towards the sun, just use the solar sail to kill some of your orbital momentum. This also works around smaller bodies such as the earth, assuming you already are in orbit (which is a given for the Cosmos I satellite).
    • With (wind) sailing, modern sails can allow a sailboat to travel anywhere from close-hauled (typically 45 degrees into the wind) to a run (dead away from the wind).
  • Now all they need to do is hit a tachyon eddy and we can reach Cardasia
  • So..this sail will orbit earth?

    What about all the space debris that will rip the hell out of the sail?

    I don't think that the sail will last anymore than someone throwing a paper airplane in the air and have a firing squad shoot at it until their is no more. Lets see that plane fly for 4 years
    • This mission is tested on Earth polar orbit; there are less space debris in there.

      Besides this is a validation and verification mission. If it gets punctured by debris, that's a new lesson learned.
    • If debris hits the sails, the debris will merely rip a hole. The mylar is not polymerized such that the enitre sail will be torn apart; only the area receiving direct impact will be affected. Given the minute dimensions of debris likely to be encountered, there should be no problem on this mission.
  • I have always been facsinated by the idea of solar sails. Something about them seems so elegant and simple. The idea of branching from sailing ships to sailing starships just seems so right to me.
    • I have always been facsinated by the idea of solar sails. Something about them seems so elegant and simple. The idea of branching from sailing ships to sailing starships just seems so right to me.

      Indeed. And as far as I'm concerned the only thing needed is a good life support plan. (Yeah, I know, Duh! ;-) If we were to think on a large enough scale I"m sure it would be doable.

      The problem I see now is that $BIG_CORPS don't really see space as profitable yet. If they did we'd almost certainly have a wa
      • I'm sure future ship-modders will be creating wild ships in ye olde style. As well as neon rims, water-cooled sail retractors, large led-fans with no effect, air tubes to guide the highly efficient space ether to cool the right spots, transparent hulls, chrome plated sails, and paint jobs that'll make the moon cry.
        • I'm sure future ship-modders will be creating wild ships in ye olde style. As well as neon rims, water-cooled sail retractors, large led-fans with no effect, air tubes to guide the highly efficient space ether to cool the right spots, transparent hulls, chrome plated sails, and paint jobs that'll make the moon cry.

          [Future TV Show]
          "Welcome to Pimp My Starship! Today we're going to take a guy with and old model 3623827 ship and make it so it's 'All that!'"
          [/Future TV Show]

          :-)

          *watches karma go up in flam

    • Jack Vance: "Sail 25" (Score:2, Interesting)

      by anubi ( 640541 )
      You would probably immensely enjoy the science fiction short-story "Sail 25" by Jack Vance. Its a good hour read at the library.

      Its about a training voyage with six cadets and a instructor who thorougly trains his cadets by making the voyage a living nightmare of failures, as well as making sure they make it on their own ( as he's already seen to it the radio does not work, and he's let it be known very clear to the cadets he expects to die in space - the ship is theirs to navigate using the forces of nat

  • More info on Cosmos 1 (Score:5, Informative)

    by FleaPlus ( 6935 ) on Saturday June 18, 2005 @03:14PM (#12852162) Journal
    Darn, I was in the middle of preparing a submission on Cosmos 1 when I saw this. Anyways, I have a little more info which people might find interesting, so I'll go ahead and paste it below:

    Countdown to First Solar Sail Spacecraft

    The Planetary Society's Cosmos 1 [planetary.org], the first spacecraft to be propelled by a solar sail [wikipedia.org], has just been loaded onto a converted ICBM in preparation for its launch [wired.com] from a Russian submarine this Tuesday, June 21. This is the first mission by a non-profit space advocacy group and is being funded by private donations. Project Operations Assistant Emily Lakdawalla is posting a running description of events on the official blog [planetary.org]. Videos and animations [planetary.org] describing the mission are available, including commentary from the Planetary Society's Vice President, Bill Nye the Science Guy. Downloadable print-out model kits [spacecraftkits.com] are also available.

    One of the many neat things about this project is that if the first phase of regular solar sailing is successful, they'll run a later experiment with focusing a microwave beam on the sail to see how well it propels the craft. I wish the Planetary Society the best in this high-risk endeavour.
  • What about using a giant rail-gun to launch a space vehicle from the moon?

    Once spaceborn, the vehicle could deploy its deep-space propulsion, such as solar sails or ion drive.
    • But then the Loonies could revolt and use the rail gun to bomb the Earth!
      I read a scientific article about it [amazon.com] once.
    • I posted a question about using a giant rail-gun to ASSIST the use of SOLAR SAILS, the subject of the story.

      How is that off-topic?

      Yeesh.

    • Re:Rails? Hmmm, interesting. (Score:4, Informative)

      by mikael ( 484 ) on Saturday June 18, 2005 @07:17PM (#12853321)
      The idea of rail-guns for launching vehicles came about because on other planets there wasn't enough atmosphere for aerodynamics to work or for jet engines to work. The relative vacuum and low gravity was an advantage for anything that didn't need to carry its own fuel. The rail gun would use electromagnetic fields to accelerate the vehicle to beyond escape velocity.

      However, for Earth, you need a take off velocity of at least 7 miles/second (or 25,000 miles/hour). And that doesn't take into air friction. Assuming you could build such an aerodynamic capsule, you would need a considerable acceleration for a period of the launch phase.

      To minimize the amount of energy you need to use, you'd want to travel straight up, and to generate enough energy you would probably have to burn gallons of hydrocarbons or run a whole chain of nuclear reactors. Since energy is most efficient when you use the least number of conversion stages, you really end up with a vertical rocket launch with solid or liquid fuel.
      • But I asked about doing it from the Moon. Not much air friction there :-).
        • You've still got to get your launch rail transported and built, along with your power supply (nuclear reactor/solar panels). The launch rail would have to be anchored to the ground rock (if there is any) to make sure nothing works loose. And it would still have to project the vehicle up to at least 3600 miles/hour, which means it would have to be a few miles long. Using rockets is still the most efficient method.

  • Quirks and Quarks (Score:5, Interesting)

    by astrosmash ( 3561 ) on Saturday June 18, 2005 @03:54PM (#12852412) Journal

    Check out this week's Quirks and Quarks podcast [www.cbc.ca], which covers the same topic. They interview the Planitary Society project manager about the upcoming solar sail launch.

    While I'm at it, they've also got a segment on quantum cryptography this week which is kind of interesting.

  • I'm unclear as to how energy is conserved in this case.

    Clearly the energy of the reflected photon must be less than the incident photon.

    Since the energy of the photon is inversely proportional to the frequency, does the frequency of the light change after it is reflected ?

    • I was discussing this with my physics lecturer about a year ago. As some solar sail's are supposedly 100% reflective so they dont heat up. Which made me ask about how can any useful work being obtained if no heat is exchanged (a heat engine seeing that virtually everying is one that moves).

      Anyway yes the frequency does change after the satellite gets push along slightly the reflected photon will have a slightly longer wavelength and therefore energy transfer.
    • Since the energy of the photon is inversely proportional to the frequency, does the frequency of the light change after it is reflected ?

      Well where do you THINK the energy comes from, the magical Alterverse? Yes, the frequency of the photon changes. And the energy is directly proportional to the frequency, not inversely.

  • 1. Patent soalr sails. 2. Wait for Technology to develope. 3. Lawsuite. 4. Profit.
  • "Solar sails would thus be especially useful for journeys to distant planets or vastly more distant stars" But, as the distance from Sun increases, light intensity DECREASES as SQUARE of distance. When the sail reaches half way to another star, Sun will push it almost as much as that star (ok, a bit less because of difference in reflection).
    • Great, so you can begin decelerating!

    • Orbiting? (Score:2, Interesting)

      by Tisha_AH ( 600987 )
      If this is to "orbit" the earth it faces alot of challenges. Out atmosphere extends quite a distance to the moon. Sure it is atoms per cubic meter but it's appreceable . I suspect there will some frictional losses that will constrain the top end velocity. If it orbits that means that it has to go back around the other side, while the front surface is facing to the sun. Sure you can play tricks where maybe one side is reflective and the other approaches an ideal black body object and just absorbs. Or maybe
    • For journeys in the outer solar system, or further, you need to supply your own light. You shine some kind of beam (laser light most likely) at the sail from back home.

      Of course stopping at another star is still a bit tricky. Robert Forward proposed detaching part of the sail and using it to reflect the beam back onto the rest, Larry Niven & Jerry Pournelle just had the probe diving in very close to the star. I've also seen the suggestion of using the galactic magnetic field to take you around the back
  • Just make some long rails between few large bodies in our solar system. The rails would transfer the electricity to points right behind the train with electro magnetics and superconductors on the train would repulse it from the magnetic field. So there wouldn't be any mass for propulsion to move. As a superconductors inside rails would move the propulsion power to the ship.

    Sure, sure I definitely read the article ;)
  • Did a little back of the spreadsheet calculation. If you take thr trhrust numbers fomr the article, you get a kilogram of thrust from every square kilometer. That's a millionth of a Kg from every square meter. Or a thousandth of a gram. If you assume the sail weighs .1 gram per square meter, that's an acceleration of 1/100th of a G. Not terribly impressive. Certainly not enough to push anything out of earth orbit. And a very slow way to tour the solar system. And what do you do at night? :)
    • ....like thinking a kilogram is a unit of thrust?

      Their website says the acceleration is ~ .0005 m/s/s, which is 5/100,000 of a g (not a G), and the 'g' referred to here is not a gram, but the acceleration due to gravity at the Earth's surface, 9.8 m/s/s. That's very impressive, considering that acceleration could continue for as long as the sun keeps shining, which is more than enough time to lift something out of Earth orbit. Assuming the craft doesn't trade any kinetic for gravitational potential energ

      • >Assuming the craft doesn't trade any kinetic for gravitational potential energy. I don't think it has any choice. >, it could speed up by 1600 m/s in a year But escape veliocity is about 1.4 times orbital velocity, so it's going to take let's see-- 7500 m/s * 1.4 - 7500, wow only about 2 years! Of course this is just the acceleration of the sail, if the satellite package has any mass, you're going to have to add more sail to help drag that along.

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