Slashdot is powered by your submissions, so send in your scoop

 



Forgot your password?
typodupeerror
Space Transportation Science Technology

Ikaros Spacecraft Successfully Propelled In Space 229

Posted by timothy
from the best-place-for-it-really dept.
An anonymous reader writes "Japan's IKAROS spacecraft has already successfully deployed the first solar sail in space, but today it made the only first that really matters: it successfully captured the sun's rays with its 3,000-square-foot sail and used the energy to speed its way through space. Each photon of light exerts 0.0002 pounds of pressure on the 3,000-square-foot sail, and the steady stream of solar exposure has succeeded in propelling the nearly 700-pound drone."
This discussion has been archived. No new comments can be posted.

Ikaros Spacecraft Successfully Propelled In Space

Comments Filter:
  • by waives (1257650) on Friday July 16, 2010 @06:41PM (#32933726)
    stupid writers reported the total force on the sail (1.12mN) = 0.0002 lbf as the per-photon pressure.
  • Top Speed ? (Score:5, Insightful)

    by meerling (1487879) on Friday July 16, 2010 @06:43PM (#32933738)
    Great, now they can see if it's acceleration is anywhere near what proponents and sci-fi writers have been saying for decades.
    Also, maneuverability, as I just don't see most of those sailing techniques working in a vacuum.
    Can't wait for final results :)
    • Re: (Score:3, Interesting)

      by mcrbids (148650)

      It appears to be operating well within expectations, looking at the linked website from the Japanese space administration, it's looking to be well within expectations.

      But even so, we're talking about a very, very small acceleration effect - if you were on board, you basically wouldn't notice it at all. It's what, 2/10,000 of a pound of thrust, with a 700 pound payload? Since it takes 1 pound of thrust acting on 1 pound of material to equal 1 G [howstuffworks.com], the amount of accelleration on this is something like 2/(10,000

    • Re: (Score:2, Interesting)

      by BitZtream (692029)

      I just don't see most of those sailing techniques working in a vacuum.

      Nope, tried and true sailing techniques won't work in a vacuum. Neither do solar sails either, so thats not really relevant.

      Space is not a vacuum, its just not very dense.

    • Re: (Score:3, Informative)

      by GileadGreene (539584)

      Also, maneuverability, as I just don't see most of those sailing techniques working in a vacuum.

      Solar sails don't, and have never been intended to, use "sailing techniques". In that sense "solar sail" is an unfortunate misnomer. Solar sail maneuvers typically take advantage of the fact that changing the sail orientation enable you to direct the resultant force from the solar radiation pressure either along or counter to the orbital velocity vector. Depending on which way you point the sail you either increa

  • by jonabbey (2498) * <jonabbey@ganymeta.org> on Friday July 16, 2010 @06:43PM (#32933740) Homepage

    The figure of 0.0002 pounds of pressure per photon is off by a vast degree. The Wikipedia article on Solar Sails [wikipedia.org] cites a figure of 4.57x106 N/m2, or .00000457 Newtons of force ( 0.000001027 pound-feet) against a square meter of sail material given the full flux of the Sun at Earth's orbit. A single photon would provide less than a trillionth of that amount.

    • The figure of 0.0002 pounds of pressure per photon is off by a vast degree. The Wikipedia article on Solar Sails [wikipedia.org] cites a figure of 4.57x106 N/m2, or .00000457 Newtons of force ( 0.000001027 pound-feet) against a square meter of sail material given the full flux of the Sun at Earth's orbit. A single photon would provide less than a trillionth of that amount.

      And your use of "pound-feet" is amusingly incorrect. That would be torque. Did you mean pounds-force?
      -Taylor

      • by jonabbey (2498) *

        And your use of "pound-feet" is amusingly incorrect. That would be torque. Did you mean pounds-force? -Taylor

        Ups, of course I did, thanks.

    • Re: (Score:3, Informative)

      They reported the total pressure on the sail as the pressure of one photon.
    • by jonabbey (2498) *

      And while I'm confirming my hand-waving stupidity, I'd like to cite http://cubesat.wikidot.com/opticalflux [wikidot.com], which has a quick calculation showing on the order of 2.55453 x 1020 photons.s-1.m-2, so when I cleverly said 'less than a trillionth of that amount', you should read 'less than 1^1020th' of that amount instead.

      Fortunately for me, 1^1020 is more than a trillionth, so dividing it out would result in 1/1^1020, which is less than a trillionth. So it kind of works out.

      • by jonabbey (2498) *

        Point the first: 1^1020 = 1.

        Point the second: 1/1 = 1, which is greater than a trillionth.

        Point the third: The cited article calculates 2.55453 X 10^20, and a trillion is 10^12, so the trillionth guess was only off by 8 orders of magnitude, not 1,020 orders, as I thought when I wrote that.

        Point the main: I should not try to show off my math on the Internet.

    • Sigh. (Score:3, Insightful)

      by robbak (775424)

      It's all part of the 'Knots per hour' and 'Watts per day' malaise that all journalists are infected with.

      None of them* can use units correctly, leaving us to try to interpret what the scientist, who wrote the notes that were mismassaged into a press release which was misinterpreted by the journalist, was trying to say.

      *unjustified absolute. YHBT

      • by Timmmm (636430)

        Watts per day really pisses me off. You even get it on technical blobs like Engadget, who should know better. Then again, they are also stupid enough to think a "$100" phone is much better value than a "$200" phone...

  • Also. (Score:3, Insightful)

    by Facegarden (967477) on Friday July 16, 2010 @06:54PM (#32933824)

    Aside from the article being wrong about the forces exerted, I hate that last sentence.

    "...the steady stream of solar exposure has succeeded in propelling the nearly 700-pound drone."

    Well... how fast has it gotten to so far? That's what it sounds like the sentence is going to say, and then it just ends. It bothers me.
    -Taylor

    • Re: (Score:3, Insightful)

      by PitaBred (632671)

      Just the fact that it has been propelled, at all, is the achievement. It doesn't matter how fast or how far. Kinda like the satellite... didn't really matter that it just beeped. The achievement was that it was up there.

  • by Anonymous Coward on Friday July 16, 2010 @07:00PM (#32933856)
    Use SI-units for crying out loud. This is a scientific context. Not a grocery list. Also so the rest of the 90% of the world population can understand it.
  • by Co0Ps (1539395) on Friday July 16, 2010 @07:02PM (#32933862)
    Use SI-units for crying out loud. This is a scientific context. Not a grocery list. Also so the rest of the 90% of the world population can understand it..
    • Re: (Score:3, Funny)

      by MollyB (162595)

      "Japan's IKAROS spacecraft has already successfully deployed the first solar sail in space, but today it made the only first that really matters: it successfully captured the sun's rays with its 278.709 square meter-sail and used the energy to speed its way through space. Each photon of light exerts 0.090718474 grams of pressure on the 278.709 square meter-sail, and the steady stream of solar exposure has succeeded in propelling the nearly 317.514659 kilogram-drone."

      Better?

      • by jonabbey (2498) *
        Heh.
      • by Anonymous Coward on Friday July 16, 2010 @08:02PM (#32934212)

        Or you can get the more precise values from the original at http://www.jaxa.jp/projects/sat/ikaros/index_e.html
        JAXA uses metric units. The conversion to American units in the article is rounded.

        Another fun fact about imperial units that you are probably not aware of, almost all contries have them, just that they differ. The rest of the world changed to metric units partly to get rid of the problem that the length of an inch were different depending on what country you were in.

        • by Thing 1 (178996)

          The rest of the world changed to metric units partly to get rid of the problem that the length of an inch were different depending on what country you were in.

          LOL "In Brazil, I'm 9 inches!"

    • by Bigjeff5 (1143585)

      No.

  • Epic unit fail (Score:5, Insightful)

    by johndoe42 (179131) on Friday July 16, 2010 @07:04PM (#32933890)

    > Each photon of light exerts 0.0002 pounds of pressure on the 3,000-square-foot sail

    C'mon people, can't you even check if what you're saying makes the slightest sense before posting it? There are two impressive errors in that sentence. First, each photon [1] applies some impulse to the sail. Impulse is what you feel pushing you back when someone punches you. It's a one-time effect and is neither a force (impulse per unit time) nor a pressure. Second, a pound might be a unit of force or of mass, depending who you ask, what you're talking about, and how pedantic you are, but it is never a unit of pressure. (If it were, you might say that the Earth's atmosphere weights 14 pounds, a statement that makes no sense at all.)

    [1] For the physically inclined, there's a more subtle error, too. The impulse supplied by a photon is related to its momentum, which is a function of wavelength. So, unless something weird's happening in the sail, blue photons supply a larger impulse than red photons.

    • by AikonMGB (1013995)

      [1] For the physically inclined, there's a more subtle error, too. The impulse supplied by a photon is related to its momentum, which is a function of wavelength. So, unless something weird's happening in the sail, blue photons supply a larger impulse than red photons.

      This is, in fact, the case -- not all photons exert the same impulse on the sail. However, there are other factors as well -- for one, the sail reflectivity is not uniform across all wavelengths, and so will have different absorption rates throughout the spectrum; for another, the solar spectrum is not uniform either, and emits many more photons at certain wavelengths than at others. This means that, on average, you may get more thrust out of a lower-energy portion of the spectrum than from a higher energy

    • by epp_b (944299)

      Second, a pound might be a unit of force or of mass, depending who you ask, what you're talking about, and how pedantic you are, but it is never a unit of pressure.

      I am pedantic, you insensitive clod, and a pound is unit of weight!

    • by Dahamma (304068)

      And you even missed the MOST impressive error in that sentence... if each photon exerted that impulse then the sun would have pretty much instantly obliterated the satellite (and all life on earth). That number should be the TOTAL, not PER PHOTON. All in all, an absolutely horrible article and summary.

  • Wow! (Score:5, Funny)

    by Zevensoft (1784070) on Friday July 16, 2010 @07:21PM (#32933998)
    "Each photon of light exerts 0.0002 pounds of pressure" I was knocked over when I read that!
    • Re: (Score:2, Redundant)

      by MichaelSmith (789609)

      "Each photon of light exerts 0.0002 pounds of pressure"

      I was knocked over when I read that!

      You should turn down the intensity on your monitor and read /. in the dark.

  • Last time I checked a pound was not a unit of pressure. On that note, I wish pounds weren't used to measure anything.

    • Re: (Score:2, Funny)

      by NEDHead (1651195)
      Euros are soooooo much more useful
    • It is correct grammar to refer to pounds of pressure as pounds are units of force. A narrower definition of pressure is, of course, force/area. Anyway, I much prefer the usage of pounds for units of force than grams or kilograms.
  • Its a good start (Score:5, Interesting)

    by MichaelSmith (789609) on Friday July 16, 2010 @07:40PM (#32934128) Homepage Journal

    A 3000 square foot sail is about 16 metres across. Imagine what you could do with a sail one kilometre across. To get to Titan: kill your orbit around the sun with your sail. Gravitational slingshot off the sun with a single burn, possibly combining the sail with a solar thermal rocket, then aero-brake in the atmosphere of Saturn, then repeat at Titan. How's that for a fast trip?

    • by sl3xd (111641) *

      The problem there is that solar sails (supposedly) aren't that efficient past Mars. They're great for the inner solar system (theoretically, you can tack them like a normal sail, so you can get closer to the sun with one), but the outer solar system? Not a prime candidate for a solar sail. Great for trips to Venus or Mars, though.

      • Thats why I suggested using the sun for a gravity slingshot.

        • Re:Its a good start (Score:5, Informative)

          by GileadGreene (539584) on Saturday July 17, 2010 @06:15AM (#32935984) Homepage
          The problem is that bleeding off energy with a solar sail isn't like just jumping onto a sunward elliptical orbit. You're likely to spiral in towards the sun, rather than zip around it. More importantly, a "slingshot" [wikipedia.org] takes advantage of planetary motion relative to the sun to achieve a large trajectory change: a "slingshot" around the sun won't do anything except get you onto the outbound leg of the trajectory you're already on (i.e. it won't help you get further out from the sun than you were already going anyway). You'd probably be better off conserving the energy you already have, and using the sail to spiral out into a higher orbit.
  • by exp(pi*sqrt(163)) (613870) on Friday July 16, 2010 @07:56PM (#32934176) Journal
    > Each photon of light exerts 0.0002 pounds of pressure

    That's why I stay indoors.

  • Wait a minute... if photons exert that much force and there are millions or billions of them hitting me in full daylight, shouldn't I feel lighter at night??? Granted I'm a Slashdotter who lives in Mom's basement and plays WoW nonstop and doesn't see the light of day much, but still. I should feel so much lighter that I can fly like a vampire.

  • Sunjammer (Score:3, Interesting)

    by Nom du Keyboard (633989) on Friday July 16, 2010 @10:06PM (#32934692)
    Once upon a time (about 1962) Arthur C. Clarke wrote a story called Sunjammer. I was fortunate enough to read it in its original publication. I hunted for it for years afterwards to read again, but he had changed the name because it duplicated the name of another unrelated SF story that year. Imaginary points to anyone who can name:

    1: The original magazine of publication.
    2: The new story name.

    I've been in love with the idea of solar sailing, and in fear of the sun's stormy season, ever since.
  • Ok, we get it (Score:5, Insightful)

    by FleaPlus (6935) on Friday July 16, 2010 @11:17PM (#32934944) Journal

    Ok folks, we get it -- almost every single comment so far has been about the unit error in the article. You noticed how silly it is, and are therefore smart. Can we get past that now and talk about how ridiculously awesome it is that the first-ever solar sail has been successful, and is propelling through the inner solar system by riding photons from the Sun?

What this country needs is a dime that will buy a good five-cent bagel.

Working...