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Ikaros Spacecraft Successfully Propelled In Space

timothy posted about 4 years ago | from the best-place-for-it-really dept.

Space 229

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."

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229 comments

Well that's good (0)

Anonymous Coward | about 4 years ago | (#32933706)

But when they tried to go to the moon they had to have Ed Belbruno save their butts.

Sad writing (and summary) (5, Insightful)

waives (1257650) | about 4 years ago | (#32933726)

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

Re:Sad writing (and summary) (5, Funny)

RichMan (8097) | about 4 years ago | (#32933754)

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

Re:Sad writing (and summary) (1, Troll)

IvyKing (732111) | about 4 years ago | (#32933782)

What do you expect with the linked article from a technically ignorant greenie publication?

Arthur C Clarke did a much better job of explaining the concept with his "Sunjammer" story that appeared in Boy's Life ca 1964.

Re:Sad writing (and summary) (1, Flamebait)

Chris Burke (6130) | about 4 years ago | (#32933902)

Arthur C Clarke did a much better job of explaining the concept with his "Sunjammer" story that appeared in Boy's Life ca 1964.

What?! Clarke was writing for Boy's Life in 1964? When and why did that lame-ass publication become so lame-ass when I was reading it in the 80s?!

Re:Sad writing (and summary) (0)

Anonymous Coward | about 4 years ago | (#32934670)

When the Mormons took over BSA, and didn't want boys thinking they could fly to their private planets early using solar sails?

Re:Sad writing (and summary) (1, Interesting)

$RANDOMLUSER (804576) | about 4 years ago | (#32933932)

Totally OT, but also from Boy's Life, same era, do you (or anyone else) know who wrote a story called The Amplified Boy? I've been looking for it for a long time. It had power suits similar to Starship Troopers.

Re:Sad writing (and summary) (4, Informative)

abigor (540274) | about 4 years ago | (#32934052)

Re:Sad writing (and summary) (2)

$RANDOMLUSER (804576) | about 4 years ago | (#32934106)

Holy crap!! Thank you SO MUCH!!

Re:Sad writing (and summary) (4, Funny)

abigor (540274) | about 4 years ago | (#32934148)

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

Re:Sad writing (and summary) (1)

hitmark (640295) | about 4 years ago | (#32934470)

hmm, scouts. There is something odd about that story...

Re:Sad writing (and summary) (1)

Thing 1 (178996) | about 4 years ago | (#32934474)

I absolutely LOVE that there's an "ad" for the ZIP code in there! Took a while to catch on; I wasn't born until a few years later, and I still remember having to learn "the new system" in school -- they must have been pushing that idea for over a decade!

Re:Sad writing (and summary) (4, Informative)

Martin Blank (154261) | about 4 years ago | (#32933852)

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?

Re:Sad writing (and summary) (4, Interesting)

JohnFluxx (413620) | about 4 years ago | (#32934136)

> 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 )

Re:Sad writing (and summary) (1)

LBArrettAnderson (655246) | about 4 years ago | (#32933884)

Haha, thanks for clarifying. When I read that I thought "man, that thing must be going pretty dang fast by now!"

Re:Sad writing (and summary) (5, Informative)

Jarik C-Bol (894741) | about 4 years ago | (#32933938)

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

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?

Re:Sad writing (and summary) (4, Funny)

neo8750 (566137) | about 4 years ago | (#32934374)

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

You must be new here...

Re:Sad writing (and summary) (1)

Jarik C-Bol (894741) | about 4 years ago | (#32934596)

not really, I'm just going for that whole 'optimism' thing. Of course, this is /. where over engineering (and decent articles) would have been a virtue, if laziness hadn't won out.

Re:Sad writing (and summary) (1)

sfm (195458) | about 4 years ago | (#32934618)

So, if the velocity graph has no units, is it safe to
assume the measurement is in "Furlongs Per Fortnight" ??

Anybody have a metric equivalent ?

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

> 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?

Re:Sad writing (and summary) (1)

Jarik C-Bol (894741) | about 4 years ago | (#32934730)

well, not per fortnight, the time scale is unitized. the press release is still far more informative than the linked article in the /. story.

Re:Sad writing (and summary) (0)

Anonymous Coward | about 4 years ago | (#32934698)

Yea why the hell isn't the actual press release linked, instead of the shallow 3rd party blurb that filters out everything interesting and introduces its own egregious errors?

If the press release had been linked, maybe we would have been discussing the graphs instead of heretofore unknown super photons.

From the JAXA press release:

The thrust by solar light pressure is 1.12 mili-Newton (*2,) which is the expected value.

and

1.12 mN is equivalent to about 0.114 g

For some interesting perspective on this acceleration courtesy of Wolfram Alpha:

0.114g is:

* 1.118 m/s^2
* 4.025 km/hr/s
* 2.501 mi/hr/s

So every hour the velocity of Ikaros will increase by about 9,000 mi/h ( 14,490 km/h ). After a day it's speed will have increased by about 216,086 mi/h ( 347,760 km/h ).

This is assuming the acceleration continues linearly for a day. I have no idea if that's a reasonable assumption.

There are a few other interesting calculations on Wolfram: Wolfram Alpha [wolframalpha.com]

Re:Sad writing (and summary) (1, Informative)

Anonymous Coward | about 4 years ago | (#32934038)

Not to mention that a pressure is a time average but photons are discrete. An impulse per photon would be the correct quantity to use if you wanted to put it in the article. That impulse is (h/c)*f; h being Planck's constant, c is the speed of light in a vacuum and f is the frequency of the photon.

Re:Sad writing (and summary) (1)

Gibbs-Duhem (1058152) | about 4 years ago | (#32934642)

What makes the pendantic side of me even more pissed is that they use pounds to measure the force on the sail, and then attempt to use pounds to indicate the mass of the spacecraft. I actually looked at this first and said to myself (just for a second)... 0.0002 pounds isn't nearly enough force to counteract 700 pounds... and in what direction?

I wouldn't call it IKAROS (0, Offtopic)

prefec2 (875483) | about 4 years ago | (#32933728)

As we all know that I Ikaros (engl. Icarus) flew too close to the sun. This is a bad name for a space craft or any other flying device to call it after an pilot who messed up.

Re:I wouldn't call it IKAROS (1)

Michael Kristopeit (1751814) | about 4 years ago | (#32933744)

the only way a solar sail would ever work is to fly "close" to the sun.

Re:I wouldn't call it IKAROS (3, Insightful)

Anonymous Coward | about 4 years ago | (#32933748)

Also, it's going the wrong direction.

Re:I wouldn't call it IKAROS (2, Interesting)

Anonymous Coward | about 4 years ago | (#32933962)

Not necessarily:

"The craft will spend six months traveling to Venus, and then it will begin a three-year journey to the far side of the Sun." from wikipedia [wikimedia.org]

and

https://secure.wikimedia.org/wikipedia/en/wiki/Solar_sail#H-reversal_sun_flyby_trajectory [wikimedia.org]

Re:I wouldn't call it IKAROS (1, Funny)

Anonymous Coward | about 4 years ago | (#32934490)

Huh.

So you CAN tack in space...!

Re:I wouldn't call it IKAROS (1)

jpmorgan (517966) | about 4 years ago | (#32934118)

Amusing, yes, but incorrect, since we're talking about an object orbiting the sun. You go further away from the sun by reflecting the light behind you, and get closer by reflecting the light in front of you. In fact, I can't think of any orbital maneuver where you'd want to reflect sunlight back to the sun.

Crazy Eddie (1)

rossdee (243626) | about 4 years ago | (#32934192)

Perhaps if you were coming from another star, after beimg accelerated to a few percent of c by giant lasers.

Re:Crazy Eddie (1)

Penguinshit (591885) | about 4 years ago | (#32934506)

You should remove the beam from your own eye before seeking to remove The Mote in God's Eye. [wikipedia.org]

Re:I wouldn't call it IKAROS (1)

Kepesk (1093871) | about 4 years ago | (#32934246)

Hah, at least it's doing better than the last attempt at a solar sail spacecraft. Who the heck chose a submarine launch for that one anyway?

Re:I wouldn't call it IKAROS (0)

Anonymous Coward | about 4 years ago | (#32934250)

Its official new name is, SORAKI.

Top Speed ? (5, Insightful)

meerling (1487879) | about 4 years ago | (#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:Top Speed ? (0, Redundant)

jd (1658) | about 4 years ago | (#32933784)

Arthur C Clarke's writings on solar sails usually (not always, but usually) didn't involve photonic pressure but rather involved the charged particles of the solar wind. Much more energy is involved and you can operate further from the sun. (Almost no photonic energy by the time you reach Jupiter - the sun is barely distinguishable from any other star at that distance - but the solar wind remains significant until you reach the heliopause.)

Re:Top Speed ? (4, Insightful)

jpmorgan (517966) | about 4 years ago | (#32933964)

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 [wikipedia.org] , since the surface area required (hundreds of square km) would be unfeasible with any physical material.

Re:Top Speed ? (1)

BiggerIsBetter (682164) | about 4 years ago | (#32934532)

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.

Hmm. We can make bigger sails, or we can make the space the photons they're capturing smaller. We really need to figure out how to manipulate space-time and/or gravity.

Re:Top Speed ? (1, Interesting)

Anonymous Coward | about 4 years ago | (#32933982)

Solar wind is just too slow. 400km/s is nothing.

Re:Top Speed ? (5, Informative)

DesertNomad (885798) | about 4 years ago | (#32934056)

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.

Re:Top Speed ? (2, Interesting)

mcrbids (148650) | about 4 years ago | (#32934294)

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 * 700) or 1/3,500,000 of 1 G.

Unless I missed something basic, this satellite is going to be accelerating for a *long* time...

Re:Top Speed ? (0)

Anonymous Coward | about 4 years ago | (#32934338)

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

IKAROS is just a proof-of-concept. The next craft in the series, DEDALUS, will be able to maneuver by virtue of its keel...

Photon pressure wildly, ludicrously off (4, Informative)

jonabbey (2498) | about 4 years ago | (#32933740)

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.

Re:Photon pressure wildly, ludicrously off (1)

Facegarden (967477) | about 4 years ago | (#32933770)

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

Re:Photon pressure wildly, ludicrously off (1)

jonabbey (2498) | about 4 years ago | (#32933786)

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:Photon pressure wildly, ludicrously off (2, Informative)

NonUniqueNickname (1459477) | about 4 years ago | (#32933790)

They reported the total pressure on the sail as the pressure of one photon.

Re:Photon pressure wildly, ludicrously off (1)

jonabbey (2498) | about 4 years ago | (#32933872)

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.

Further idiotic errors (2, Insightful)

jonabbey (2498) | about 4 years ago | (#32934040)

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. (2, Insightful)

robbak (775424) | about 4 years ago | (#32934028)

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

Re:Sigh. (1)

emt377 (610337) | about 4 years ago | (#32934086)

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

They should just stick to "high rate of speed". The reader gets to guess all the same, anyway.

Google thinks it can hit light speed in 7 years (0)

Anonymous Coward | about 4 years ago | (#32933822)

the speed of light / (((.0002 psi) * (3000 (sq ft))) / (700 pounds)) = 7.8485537 years

Re:Google thinks it can hit light speed in 7 years (1)

Chris Burke (6130) | about 4 years ago | (#32933952)

Uh... more like you incorrectly thought that equation was valid for calculating acceleration to speeds approaching c, and Google faithfully did the math you told it to.

Not trying to be mean, but Newton need not apply for such a calculation and Google can't exactly be expected to know what you're trying to do. Also, TFS said 0.0002 pounds (not psi) of pressure (so uh, it should be psi but they gave force) per photon (which is just plain wrong, photon momentum = Plank's constant / wavelength, i.e. way smaller than that), so sadly your math was kinda screwed from the get go.

Re:Google thinks it can hit light speed in 7 years (2, Interesting)

grantek (979387) | about 4 years ago | (#32934308)

It's an interesting example of relativity though, because you're using the speed of light to try to accelerate you to the speed of light - once you understand that the speed of light is always constant, you arrive at the fact that the faster you're going, the less energy the light has. The light "shifts" to the red side of the spectrum.

Re:Google thinks it can hit light speed in 7 years (1)

Chris Burke (6130) | about 4 years ago | (#32934366)

once you understand that the speed of light is always constant, you arrive at the fact that the faster you're going, the less energy the light has. The light "shifts" to the red side of the spectrum.

Heh, yep. c stays constant, and instead the wavelength changes. What a bizarre and amazing universe we live in! :)

Re:Google thinks it can hit light speed in 7 years (2, Funny)

Thing 1 (178996) | about 4 years ago | (#32934512)

Also, TFS said [...]

We've begun implementing Microsoft's latest "developer stack" at work. Now every time someone refers to "TFS", I think "what, Slashdot is on Team Foundation Server too?" Great. Thanks Microsoft.

Re:Google thinks it can hit light speed in 7 years (0)

Anonymous Coward | about 4 years ago | (#32934154)

It's not exerting 0.0002 pounds per square inch, but a force of 0.0002 pounds (*9.8m/s^2) for the entire 3000 sq ft.

So ignoring relativity:

c / ((1.12 millinewton) / (700 pounds)) = 2 693 219.62 years

2.5 million years.

Also. (2, Insightful)

Facegarden (967477) | about 4 years ago | (#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

Use scientific units... (4, Insightful)

Anonymous Coward | about 4 years ago | (#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.

Hope it doesn't fly too close to the sun...! (0)

Anonymous Coward | about 4 years ago | (#32933858)

But I guess it *shouldn't*, since it's using the sun's light to propel itself *away* from it.

Perhaps they should've called it Anti-Ikaros, Not-Ikaros, !Ikaros, etc. :)

Use scientific units... (5, Insightful)

Co0Ps (1539395) | about 4 years ago | (#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: Use scientific units... (0)

Anonymous Coward | about 4 years ago | (#32933906)

Agreed.

Re: Use scientific units... (3, Funny)

MollyB (162595) | about 4 years ago | (#32934058)

"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?

Re: Use scientific units... (1)

jonabbey (2498) | about 4 years ago | (#32934102)

Heh.

Re: Use scientific units... (0)

arth1 (260657) | about 4 years ago | (#32934200)

Um, no. Pressure isn't measured in gram -- that's a thousandth of the unit for measuring mass. Unless Ikaros resides on Earth at sea level, the two are not interchangeable even in practical terms. (And that would be rather heavy photons. Higgs boson, move over, there's a photon that wants to kick your ass!)

Pressure is measured in Newton per square meter.

Re: Use scientific units... (0)

Anonymous Coward | about 4 years ago | (#32934302)

Most people don't understand what N/m^2 is, so a technique called "popular science" was invented so the common mortal could understand concepts they've forgotten since high school. Using grams is just a more intuitive representation and is still perfectly valid as long as it is assumed to use the standard g constant.

Re: Use scientific units... (4, Informative)

Anonymous Coward | about 4 years ago | (#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.

Re: Use scientific units... (1)

Thing 1 (178996) | about 4 years ago | (#32934498)

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!"

Re: Use scientific units... (1)

noidentity (188756) | about 4 years ago | (#32934370)

And to talk of pounds in space is rather silly. Most things weigh neirly nothing.

Re: Use scientific units... (1, Informative)

epp_b (944299) | about 4 years ago | (#32934404)

I was waiting for this comment. The correct usage here is a unit of mass (318.18 kilograms), not weight. Mass is constant, weight is dependent on gravity.

Re: Use scientific units... (1)

noidentity (188756) | about 4 years ago | (#32934534)

I either have some slow degenerative neural disease, or have just been slowly losing my attention for spelling. I've seen it go downhill over the past several years. It's kind of worrying.

Re: Use scientific units... (0)

Anonymous Coward | about 4 years ago | (#32934598)

Pound is the only commonly used unit of mass in this system. Far fewer people know what a slug is than a kilogram. It's usually clear from context whether you mean pound-force or pound-mass.

Re: Use scientific units... (0)

Anonymous Coward | about 4 years ago | (#32934576)

The rest of the world population doesn't know how to convert between pounds and newtons? You're right though .0002 pounds is too small for people to imagine anyway, might as well give the numbers in scientific units just note "that's really really small", for people who think a newton is a fig cookie.

Before you know it... (0, Offtopic)

TheRedDuke (1734262) | about 4 years ago | (#32933876)

...giant fighting robots with swords will be propelled by solar sails throughout the solar system!

Epic unit fail (4, Insightful)

johndoe42 (179131) | about 4 years ago | (#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.

Re:Epic unit fail (1)

AikonMGB (1013995) | about 4 years ago | (#32934168)

[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 portion.

Aikon-

Re:Epic unit fail (1)

epp_b (944299) | about 4 years ago | (#32934418)

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!

Re:Epic unit fail (0)

Anonymous Coward | about 4 years ago | (#32934518)

ummm hey johndoe42 you say pounds is never a unit of pressure but what about psi? it is pounds per square inch and denotes pressure and the way I see it the article makes sense even if not technically accurate.. you say "It's a one-time effect..." but it does make a kind of sense. each photon is a one time effect, but considering that you are subject to an "infinite" photons in a row it could be seen as a constant effect. now I'll be the first to admit I'm a dunce when it comes to crap like this so I'm sure I'm missing something, but what the writer says does make the "slightest" sense.

Wow! (5, Funny)

Zevensoft (1784070) | about 4 years ago | (#32933998)

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

Re:Wow! (1, Redundant)

MichaelSmith (789609) | about 4 years ago | (#32934076)

"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.

Pound of pressure? (2, Insightful)

ubergeek65536 (862868) | about 4 years ago | (#32934104)

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:Pound of pressure? (3, Funny)

NEDHead (1651195) | about 4 years ago | (#32934162)

Euros are soooooo much more useful

Re:Pound of pressure? (-1, Flamebait)

Anonymous Coward | about 4 years ago | (#32934734)

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

Excepting of course the British monetary unit.

Re: £ of pressure? (1)

Namlak (850746) | about 4 years ago | (#32934804)

On that note, I wish pounds weren't used to measure anything.

If I had a pound for every time someone misused pound as a unit, I'd be rich!

Its a good start (5, Interesting)

MichaelSmith (789609) | about 4 years ago | (#32934128)

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?

Re:Its a good start (0)

evilviper (135110) | about 4 years ago | (#32934310)

A 3000 square foot sail is about 16 metres across.

Am I missing some attempted nuance here?

3000 feet is 914 meters.

On the off chance you're talking about the length of one edge, the sqrt of 914 is 30 meters. So, still, nothing matches 16.

Re:Its a good start (1, Insightful)

Anonymous Coward | about 4 years ago | (#32934382)

And 10 Square feet is approximately 1 Square meter.

You can convert linear feet to linear meters, and you can convert square feet to square meters. You can even convert cubic feet to cubic meters. But you can't convert linear feet to square meters (directly), and while you can tune a piano, you can't tuna fish.

Re:Its a good start (1)

elfprince13 (1521333) | about 4 years ago | (#32934396)

from math import sqrt sqrt(3000)/3.28 = 16.7

Re:Its a good start (0)

Anonymous Coward | about 4 years ago | (#32934406)

Actually, 3000 SQUARE feet is about 279 SQUARE meters, and the square root of that is 16.7 meters...

Re:Its a good start (1)

waives (1257650) | about 4 years ago | (#32934428)

Yes, you're missing something:
sail (note shape)
O


o
-|-
^ - you

Re:Its a good start (0)

Anonymous Coward | about 4 years ago | (#32934466)

Check your units again. 3000 feet is 914 meters, but 3000 square feet is only about 279 square meters.

Re:Its a good start (0)

Anonymous Coward | about 4 years ago | (#32934472)

3000 ft^2 != (3000ft)^2

3000 ft^2 = 55ft on a side, which is roughly 17m.

Re:Its a good start (1)

MichaelSmith (789609) | about 4 years ago | (#32934594)

A 3000 square foot sail is about 16 metres across.

Am I missing some attempted nuance here?

3000 feet is 914 meters.

On the off chance you're talking about the length of one edge, the sqrt of 914 is 30 meters. So, still, nothing matches 16.

3000 square feet [wolframalpha.com]

Engrish (1, Interesting)

Anonymous Coward | about 4 years ago | (#32934150)

I think the per photon thing has to do with the original Japanese release (i.e. Engrish). Japanese science writers without a great command of English sometimes use "photon" for "photons." Hamamatsu, a Japanese video company, for example, used to have the following slogan: "Photon is our business."

Congratulations (1)

bloobamator (939353) | about 4 years ago | (#32934170)

Kampei! Congratulations to the Japanese. This is a very cool accomplishment, and something all of us geeks have been waiting for for a long time.

Re:Congratulations (1)

snooo53 (663796) | about 4 years ago | (#32934640)

No kidding, an amazing accomplishment, and yet 95% of the comments in this thread are bitching about the units in the summary.

Troglodyte? Who? Me? (5, Funny)

exp(pi*sqrt(163)) (613870) | about 4 years ago | (#32934176)

> Each photon of light exerts 0.0002 pounds of pressure

That's why I stay indoors.

Ikaros? (0)

Anonymous Coward | about 4 years ago | (#32934210)

OMG, do we need to jump start the sun??? I thought that was just a movie, not a documentary...

Losing weight at night (1)

macraig (621737) | about 4 years ago | (#32934602)

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 (2, Interesting)

Nom du Keyboard (633989) | about 4 years ago | (#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.

Ahhh good source... (1)

HelperMunkee (1852366) | about 4 years ago | (#32934700)

I see this Slashdot article cites a Slashdot article. Holy recursive Batman!
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