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."
Re:Sad writing (and summary) (Score:2, Interesting)
Re:I wouldn't call it IKAROS (Score:2, Interesting)
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:Top Speed ? (Score:1, Interesting)
Solar wind is just too slow. 400km/s is nothing.
Its a good start (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?
Re:Sad writing (and summary) (Score:5, 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 )
Engrish (Score:1, Interesting)
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."
Re:Top Speed ? (Score:3, Interesting)
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:Google thinks it can hit light speed in 7 years (Score:3, Interesting)
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.
Sunjammer (Score:3, Interesting)
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.
Re:Top Speed ? (Score:2, Interesting)
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: Use scientific units... (Score:4, Interesting)
Most people don't know what a N/m^2 is, sure, but a N/m^2 also has the name Pascal (Pa), which a lot of people do know. Even U.S. high schools are pushing students to use Pa for pressure units instead of atmospheres or Torr or the dreaded inches of Hg. In any case, grams times the standard "g" constant still isn't pressure, it's force, and gram is never an SI unit of pressure or force, nor is gram times g.
Re:Sad writing (and summary) (Score:5, Interesting)
Re:Venus is closer to the Sun then Earth (Score:3, Interesting)
It might not be able to tack, but it can do something like reaching. It's been a decade since I played with the maths for this, so I'm going to be handwaving and relying on my memory for most of this post - someone doing some actual calculation, please feel free to correct me...
There are two forces acting on the craft. One is the force from the sail, the other is from the Sun's gravity. Actually, this is a massive oversimplification, it's really an n-body problem, and at the moment the Earth and Moon's gravity will also be significant factors.
The important thing to remember, however, is that it already has a considerable orbital velocity. It is not going to fall into the Sun, it is going to continue in the Earth's orbit unless some extra force acts on it. By angling the sail away from the Sun, it can make its orbit more eccentric, meaning that perihelion will be closer. As it falls into this eccentric orbit, it will gain velocity. It can then swing around Venus and head out, at which point it will be running (solar wind directly behind it).
Sailing metaphors are actually not very helpful, because inertia doesn't matter much when sailing (except when you come about), but it is incredibly important in orbital mechanics.
Re:Sad writing (and summary) (Score:2, Interesting)
Actually, after just 20 weeks, they will go at 1048 km*s^-1 (assuming your calculations are correct). Which is an amazing speed. Speed of light is 300 000 km*s^-1, which you would reach during the 29th week, if speed could continue increasing that way.
So yeah, Jupiter (5 light-hours or so) in 2 years seems about right.
Re:Sad writing (and summary) (Score:3, Interesting)
(note to Americans: please use metric for anything involving science. Stuff goes badly wrong if you need to stuff your equations full of fudge factors)
It's worse than that. If you don't know what's the difference between a slug and a poundal, use metric. If you do, you already realize why you should use metric.