Ikaros Spacecraft Successfully Propelled In 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."
Sad writing (and summary) (Score:5, Insightful)
Top Speed ? (Score:5, Insightful)
Also, maneuverability, as I just don't see most of those sailing techniques working in a vacuum.
Can't wait for final results
Re:I wouldn't call it IKAROS (Score:3, Insightful)
Also, it's going the wrong direction.
Also. (Score:3, Insightful)
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... (Score:4, Insightful)
Use scientific units... (Score:5, Insightful)
Epic unit fail (Score:5, 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.
Re:Top Speed ? (Score:5, 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 [wikipedia.org], since the surface area required (hundreds of square km) would be unfeasible with any physical material.
Sigh. (Score:3, Insightful)
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
Further idiotic errors (Score:3, Insightful)
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.
Pound of pressure? (Score:2, Insightful)
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:Its a good start (Score:1, Insightful)
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.
Ok, we get it (Score:5, 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?
Re:Sad writing (and summary) (Score:2, Insightful)
Re:Also. (Score:3, Insightful)
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.
Re: Use scientific units... (Score:3, Insightful)
Um, no. Pressure isn't measured in gram
[...]
Pressure is measured in Newton per square meter.
This is almost tragic. So much discussion of the correct unit for pressure, yet nobody seems to realize that the "pressure" described in the article is not a pressure. It is the total force acting on the sail.
So the correct unit is neither pounds, gram nor N/m. It is N.
Re:Top Speed ? (Score:3, Insightful)
You cannot adjust the keel vector in a sailboat either, the force is always perpendicular to the direction you are moving. But that's not important, you only need to adjust one of the two vectors to get a resultant vector in any direction you need.
The main difference between ocean sailing and solar sailing is the rudder. Considering it's used for small corrections to compensate for waves and currents, which do not exist in space, solar sailing can be done without it.