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Ikaros Spacecraft Successfully Propelled In Space

Posted by timothy on 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."

25 of 229 comments (clear)

  1. Sad writing (and summary) by waives · · Score: 5, Insightful

    stupid writers reported the total force on the sail (1.12mN) = 0.0002 lbf as the per-photon pressure.

    1. Re:Sad writing (and summary) by RichMan · · Score: 5, Funny

      Someone should ask the writers why they can stand outside on a summer's day and no be pounded into the pavement.

    2. Re:Sad writing (and summary) by Martin+Blank · · Score: 4, Informative

      I did some math and came up with something like 2.1E20 pounds of thrust. It would either far away or (more likely) shattered to pieces with that much thrust. Doing some other math, I come up with about 1.9E-28 pounds of thrust per photon. That seems more realistic to me.

      Based on total force of 1.12mN and assuming a static photon count, that looks like an acceleration of 4E-6 m/s^2, so each day it will pick up a velocity of about 0.3 m/s.

      Am I getting this correct?

      --
      You can never go home again... but I guess you can shop there.
    3. Re:Sad writing (and summary) by Jarik+C-Bol · · Score: 5, Informative

      http://www.jaxa.jp/press/2010/07/20100709_ikaros_e.html

      the actual press release from the people that *made* the thing. It has better math, as well as a couple fancy graphs. Perhaps this is what should have been posted to /. instead of a 3rd party report?

      --
      I've decided to Diversify my Holdings. I've divided my cash between my left and right pockets, instead of all in one.
    4. Re:Sad writing (and summary) by abigor · · Score: 4, Informative

      Dale Colombo. Here it is: http://books.google.com/books?id=s3fIzLrLOq0C&pg=PA77&lpg=PA77&dq=%22the+amplified+boy%22+boy's+life&source=bl&ots=nxBO5ccMW5&sig=QWULOXqhu9lM90w8X37bNDoR2Ks&hl=en&ei=gPhATP2MC4zksQPKjtiJDQ&sa=X&oi=book_result&ct=result&resnum=1&ved=0CBIQ6AEwAA#v=onepage&q&f=false

      Story starts on page 25.

    5. Re:Sad writing (and summary) by JohnFluxx · · Score: 4, Interesting

      > Based on total force of 1.12mN and assuming a static photon count, that looks like an acceleration of 4E-6 m/s^2, so each day it will pick up a velocity of about 0.3 m/s.

      Yep. ( ((1.12 millinewton) / (700 pounds)) * (1 day) = 0.304767031 m / s )

    6. Re:Sad writing (and summary) by abigor · · Score: 4, Funny

      No...thank the Holy Google. I am merely an Earthly conduit.

    7. Re:Sad writing (and summary) by neo8750 · · Score: 4, Funny

      Perhaps this is what should have been posted to /. instead of a 3rd party report?

      You must be new here...

    8. Re:Sad writing (and summary) by Bruce+Perens · · Score: 4, Interesting

      This means they have a most precise frequency standard behind their doppler measurements.

      --
      Bruce Perens.
    9. Re:Sad writing (and summary) by boxo1 · · Score: 5, Funny

      Someone should ask the writers why they can stand outside on a summer's day and no be pounded into the pavement.

      They are not pounded into the ground because reflected light from the pavement pounds back with an upward force.

    10. Re:Sad writing (and summary) by mangu · · Score: 4, Informative

      how is this thing going to slow down once it gets to where it wants to go?

      The same way sailboats go against the wind.

      Set the sail at an angle different from 90 degrees towards the sun. The resulting force can be divided in two components, one pointing outwards to the sun, which is cancelled by the sun's gravitation, and another component perpendicular to the first, which will increase or decrease the spacecraft's orbital velocity.
       

  2. Top Speed ? by meerling · · Score: 5, Insightful

    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 :)

    1. Re:Top Speed ? by jpmorgan · · Score: 4, Insightful

      No, not really. Photons carry several orders of magnitude more momentum than solar wind. The only "practical" way to capture momentum from solar wind is with a magnetic sail, since the surface area required (hundreds of square km) would be unfeasible with any physical material.

    2. Re:Top Speed ? by DesertNomad · · Score: 5, Informative

      Barely distinguishable? Jupiter is only 5 times Earth's distance from the Sun. Outside Earth's atmosphere, solar insolation averages around 1370 watts per square meter. At Jupiter's orbital distance, it's about 50 watts per sq meter. That's a huge amount of power. At Jupiter's distance, the Sun is well over a million times brighter than Sirius, the brightest star in the Terran sky. Barely distinguishable? Bah.

  3. Photon pressure wildly, ludicrously off by jonabbey · · Score: 4, Informative

    The figure of 0.0002 pounds of pressure per photon is off by a vast degree. The Wikipedia article on Solar Sails 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.

    --
    - jon

    Ganymede, a GPL'ed metadirectory for UNIX
  4. Use scientific units... by Anonymous Coward · · Score: 4, Insightful

    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.

    1. Re: Use scientific units... by Anonymous Coward · · Score: 4, Informative

      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.

  5. Use scientific units... by Co0Ps · · Score: 5, Insightful

    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..

  6. Epic unit fail by johndoe42 · · Score: 4, Insightful

    > 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.

  7. Wow! by Zevensoft · · Score: 5, Funny

    "Each photon of light exerts 0.0002 pounds of pressure" I was knocked over when I read that!

  8. Its a good start by MichaelSmith · · Score: 5, Interesting

    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?

    --
    http://michaelsmith.id.au
    1. Re:Its a good start by GileadGreene · · Score: 4, Informative

      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" 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.

  9. Troglodyte? Who? Me? by exp(pi*sqrt(163)) · · Score: 5, Funny
    > Each photon of light exerts 0.0002 pounds of pressure

    That's why I stay indoors.

    --
    Doesn't it make you feel good to know that our freedoms are protected by politicans, lawyers and journalists.
  10. Ok, we get it by FleaPlus · · Score: 4, Insightful

    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?

    1. Re:Ok, we get it by Cesa · · Score: 4, Funny

      We'll just save that for the dupe.